Heterogeneity in carbonate formations due to discontinuities(e.g.,fractures and cavities)will bring about distinctive acid stimulation effects.However,the differences in fracturing behavior between homogeneous and het...Heterogeneity in carbonate formations due to discontinuities(e.g.,fractures and cavities)will bring about distinctive acid stimulation effects.However,the differences in fracturing behavior between homogeneous and heterogeneous carbonate formations remain unclear,complicating the optimization of acid fracturing strategies.In this paper,full-diameter carbonate rock samples with different degrees of discontinuity development are selected to investigate the fracturing behavior under different fluid types and injection schemes.Advanced techniques,including 3D CT scanning and 3D laser scanning,are employed to analyze fracture morphology and etching characteristics,respectively.Experimental results show that the coupled hydraulic-chemical effects play different roles in fracture induction between fracture-cavity developed and undeveloped carbonate rocks.Acid-fracturing stimulation consistently induces multiple types of complex fractures in fracture-cavity carbonate rocks,whereas it results in a single artificial fracture in less fracture-cavity carbonate rocks.Furthermore,localized etching patterns are prevalent in most fracture-cavity carbonate rocks,whereas homogeneous carbonate rocks exhibit regional or global etching characteristics.In both carbonate rocks,the stimulation effect of guar fluid is inferior to that of gelled acid but comparable to self-generating acid.Further findings are that alternating fracturing with guar and acid fluids in fracture-cavity carbonate rocks can sustain or even increase the injection pressure,facilitating the formation of new or depth-penetrating fractures.This phenomenon,however,is not observed in fracture-cavity undeveloped carbonate rocks.Potential interaction modes between induced fracture and natural fractures/cavities under different injection conditions are also identified.Finally,preferred fracturing schemes applicable to different carbonate formations are recommended based on the area,number and roughness of the induced fractures.展开更多
The combination of ultrasonic and acid fracturing fluid can strengthen the modification effect on the micropore structure of the coal matrix,thereby enhancing the efficiency of the acid fracturing process.In this rese...The combination of ultrasonic and acid fracturing fluid can strengthen the modification effect on the micropore structure of the coal matrix,thereby enhancing the efficiency of the acid fracturing process.In this research,acetic acid was utilized to formulate acid fracturing fluids with varying concentrations,and the evolutionary traits of both the acid fracturing fluids and ultrasonic waves in relation to coal samples were investigated.The functional group structure,mineral composition,micropore structure and surface morphology of coal samples were characterized by FTIR,XRD,N_(2)adsorption at low temperature and SEM-EDS.The results showed that aromatics(I)and branching parameters(CH_(2)/CH_(3))were reduced by 81.58%and 88.67%,respectively,after 9%acetic acid treatment.Acetic acid can dissolve carbonates and clay minerals in coal,create new pores,and increase porosity,pore volume and pore fractal dimension.After modification by 7%acetic acid,the pore volume increased by 5.7 times.SEM observation shows that the diameter of coal surface holes increases,EDS scanning shows that the content of mineral elements in coal decreases,the connectivity of coal holes increases,and the holes expand.The findings of this research offer theoretical direction for optimizing ultrasonic-enhanced acid fracturing fluid modification.展开更多
For the purpose of improving the accuracy and effectiveness of acid fracturing design for carbonate reservoirs with developed natural fractures,an acidizingfluidflow and reaction model taking the multiple leak-off effec...For the purpose of improving the accuracy and effectiveness of acid fracturing design for carbonate reservoirs with developed natural fractures,an acidizingfluidflow and reaction model taking the multiple leak-off effect of natural fracture,wormhole and matrix into account was established according to the liquid phase reaction equilibrium principle and the local reaction equilibrium principle after the dynamic change of fracture geometry in the process of fracture created by prepadfluid was simulated in the classical pseudo-three dimensional mathematical model of fracture propagation.Then,the acid fracturing stimulation of a case well on site was taken as an example.The newly developed model was used to simulate thefiltration process of acidizingfluid in fractures and the dynamic etching morphology of acidic rocks during the acidizingfluid injection of prepad acid fracturing.The effective length of etched fractures was determined by analyzing the concentration change of acidizingfluid along the direction of hydraulic fracture length and the threshold concentration of residual acidizingfluid comprehensively,and then it was compared with the interpretation result of pressure buildup test.And the following research results were obtained.First,in the process of acid fracturing in fracturedeporous reservoirs,the acidizingfluidfiltration velocity along the direction of fracture length is not constant and thefiltration velocity curvefluctuates in a serrated shape.And the acidizingfluidfiltration velocity where etched wormholes meet natural fractures is commonly higher than that in matrix.Second,acidizingfluid is lost seriously and the effective distance of acidizingfluid gets short significantly during the acid fracturing of fracturedeporous reservoirs.Third,acid fracturing in the verification well is remarkable in blockage removing and stimulation,and its well test interpretation results are consistent with the simulation interpretation results provided by the newly developed mathematical model.It is indicated that this newly developed model is reliable.In conclusion,the mathematical model of prepad acid fracturing which considers multiple leak-off effect is more suitable for acid fracturing simulation of fracturedeporous reservoirs.展开更多
Carbonate outcrops were taken from Ma 51 sub-member in the Lower Paleozoic in the Yan’an gas field to conduct true tri-axial hydraulic fracturing experiments with water, liquid CO_(2) and supercritical CO_(2). CT sca...Carbonate outcrops were taken from Ma 51 sub-member in the Lower Paleozoic in the Yan’an gas field to conduct true tri-axial hydraulic fracturing experiments with water, liquid CO_(2) and supercritical CO_(2). CT scan was applied to analyze initiation and propagation laws of hydraulic fractures in carbonate rocks. The experiments show that supercritical CO_(2) has low viscosity, strong diffusivity and large filtration during fracturing, which is more liable to increase pore pressure of rocks around wellbore and decrease breakdown pressure of carbonate rocks. However, it would cost much more volume of supercritical CO_(2) than water to fracture rocks since the former increases the wellbore pressure more slowly during fracturing. For carbonate rocks with few natural fractures, tensional fractures are generated by fracturing with water and liquid CO_(2), and these fractures propagate along the maximum horizontal principal stress direction;while fracturing with supercritical CO_(2) can form shear fractures, whose morphology is rarely influenced by horizontal stress difference. Besides, the angle between propagation direction of these shear fractures near the wellbore and the maximum horizontal principal stress is 45°, and the fractures would gradually turn to propagate along the maximum horizontal principal stress when they extend to a certain distance from the wellbore, leading to an increase of fracture tortuosity compared with the former. For carbonate rocks with well-developed natural fractures, fracturing with fresh water is conducive to connect natural fractures with low approaching angle and form stepped fractures with simple morphology. The key to forming complex fractures after fracturing carbonate rocks is to connect the natural fractures with high approaching angle. It is easier for liquid CO_(2) with low viscosity to realize such connection. Multi-directional fractures with relatively complex morphology would be formed after fracturing with liquid CO_(2).展开更多
Acid fracturing is an important means of reservoir stimulation,whose purpose is to form an incompletely closed acid-etched fracture as the flow channel for oil and gas during production.The length and conductivity of ...Acid fracturing is an important means of reservoir stimulation,whose purpose is to form an incompletely closed acid-etched fracture as the flow channel for oil and gas during production.The length and conductivity of acid-etched fractures can be used to evaluate acid fracturing and directly impact production.To study their influence on the stimulation effect and final production,an acid fracturing coupling model including a fracture propagation model coupled with reservoir flow and temperature field models is established for the first time in this study based on an embedded discrete fracture model(EDFM),which can realize the coupling of fracture propagation and reservoir flow and simplify the solution of fracture and reservoir temperatures.The simulation results of the acid fracturing coupling model are introduced into the productivity model,which is also based on the EDFM to analyze and evaluate well productivity.The results show that:(1)the EDFM can easily couple fracture propagation and reservoir flow and can be used to rapidly solve the temperature fields in the fracture and reservoir successfully for the first time.(2)Reservoir flow impacts the propagation of fractures by increasing or decreasing the leak-off velocity of the working fluid.(3)Temperature diffusion is much weaker than pressure diffusion during acid fracturing and is limited near the acid fracture.The reaction between the acid and rock increases the local temperature around the acid fracture,and may even exceed the initial formation temperature.(4)Raising the injection rate reasonably enhances H^(+) diffusion,increases the effective length of acid-etched fractures,enlarges the drainage area of oil and gas,and benefits long-term well production.展开更多
The carbonate gas reservoir of the fourth Member of Upper Sinian Dengying Formation(hereinafter referred as“Deng 4 Member”)is characterized by deep burial,high temperature,low porosity,low permeability and strong he...The carbonate gas reservoir of the fourth Member of Upper Sinian Dengying Formation(hereinafter referred as“Deng 4 Member”)is characterized by deep burial,high temperature,low porosity,low permeability and strong heterogeneity in the Gaoshiti-Moxi area of the central Sichuan Basin.In order to effectively enhance the well productivity and gas reservoir development benefits,this paper defines the reservoir stimulation factor by comprehensively considering the drilling,logging and well type characteristic parameters,to carry out quantitative reservoir evaluation.Then,the refined segmentation method was developed by fully considering the reservoir stimulation factor,in-situ stress and borehole condition.In addition,the differential acid fracturing technology was prepared for different types of reservoirs.On this basis,the specified staged acid fracturing technology of horizontal well for strong-heterogeneity carbonate reservoirs was developed and then applied in the field.And the following research results were obtained.First,the reservoir stimulation factor(y)can be used to accurately evaluate the reservoir characteristics.The high quality reservoir has y≥1.0,the moderate reservoir has 0.5≤y<1.0,and the low quality reservoir has y˂0.5.Second,the specified staged acid fracturing technology considering the influence of reservoir stimulation factor,in-situ stresses and borehole condition comprehensively is formed.Stimulation measures are applied specifically in different types of reservoir intervals to give full play to the resource potential in each stimulation segment of a long horizontal section,so as to improve the production rate of natural gas reserves in strong-heterogeneity reservoirs.Third,the acid fracturing technology suitable for different types of reservoirs is also different.It is recommended to adopt acid fracturing with gelled acid or diverting acid in high quality reservoirs,acid fracturing with self-generating acid prepad in moderate reservoirs,and acid fracturing with 2–3 stages alternate injection of self-generating acid prepad and gelled acid in low quality reservoirs.Fourth,69 wells in the production area of the platform margin of Deng 4 Member gas reservoir in Gaoshiti-Moxi area are stimulated with specified staged acid fracturing.The average absolute open flow is 127.6×10^(4)m^(3)/d,which is 46.5%higher than that in the early stage of gas reservoir development.In conclusion,the research results provide remarkable stimulation effects,increase the single well gas production greatly and effectively support the efficient development of Deng 4 Member gas reservoir in the Gaoshiti-Moxi area.展开更多
Acid fracturing is an indispensable technology in the efficient development of carbonate oil and gas rosarvoirs.As for deep and ultra-deep marine carbonate oil and gas reservoirs,however,existing acid fracturing techn...Acid fracturing is an indispensable technology in the efficient development of carbonate oil and gas rosarvoirs.As for deep and ultra-deep marine carbonate oil and gas reservoirs,however,existing acid fracturing technologies can hardly create complex fracture networks because of their particular engineering and geological characteristics.In order to realize the efficient three-dimensional development of deep and ultra-deep marine carbonate oil and gas reservoirs,this paper revealed the acid fracturing difficulties of this kind of reservoirs based on the engineering and geological characteristics of deep marine carbonate oil and gas reservoirs in China.Then,by taking the efficient three-dimensional development of deep and ultra-deep marine carbonate oiland gas reservoirs as the target,the technical conceptof three-dimensional acid fracturing(3D-AF)was putforward based on the techniques of volume acid fracturing and deep acid fracturing.In addition,its technical connotation was il lustrated,and its key technologies were described in detail.Finally,its development direction in the next step was pointed out.And the following research results were obtained.First,the 3D-AF technology contains three basic connotations:(1)selecting the corresponding acid penetration technology according to reservoir types so as to realize sufficient resarvoir stimulation on the plane;(2)creating complex acid-fracture volume with higher flow conductivity under high closed pressure;(3)deploying acid-fracture volume rationally along the long hole section so as to realize sufficient reservoir stimulation in the wellbore direction.Second,there are three key technologies of 3D-AF,i.e.,the technology for predicting the effective acid-penetrate distance under the coupling action of multi-feld,multi-scale and multi-fluid,the technology for optimizing the flow conductivity of complex acid-fracture volume,and the technology for precisely deploying acid in the long section of horizontal well or highly deviated well.Third,in order to promote the further development of 3D-AFtechnology,it is necessary to carry out researches on three technologies,i.e.,the technology for predicting and reducing the fracturing pressure of ultra-deep reservoir,the tech-nology for predicting the geometry of acid-fracture body ina strongly heterogeneous reservoir,and the staged reservoir production technology and new fluid technology with high temperature resistance,low reaction rate and low friction resistance coefficient for long hole sections(over 7000 m).展开更多
In this study,acid fracturing treatments were simulated for a tight limestone reservoir within a shale formation using FRACPRO software.The purpose was to investigate the optimum acid fracturing design that leads to a...In this study,acid fracturing treatments were simulated for a tight limestone reservoir within a shale formation using FRACPRO software.The purpose was to investigate the optimum acid fracturing design that leads to a higher fracture etched length and width,and higher fracture conductivity.Moreover,the impact of the rock-acid contact time and whether to consider a post-flush or fluids flowback,on the acid fracturing outcomes were also investigated.A simple geological model was constructed which consists of different lithological layers.Different acid fracturing design scenarios were considered starting from a single stage of acid injection to multi-stage treatment.In multi-stage acid treatment,alternate acid-slickwater injection was considered.Plain HCl acids with different concentrations and other acids that are already included in FRACPRO database were used.The results showed that the acid loss during post-flush is among the main problems of the acid fracturing in tight carbonate shale reservoir.For the single stage of acid injection,it is recommended to flow back the acid after well shut-in instead of considering a post-flush stage.The multi-stage alternate acid slickwater injection reduces or even eliminated the acid loss.However,it is recommended to inject a slickwater before well shut-in to reduce the rock-acid contact time,thus reducing the formation damage.The results also showed that the created fracture etched width decreases and the fracture etched length increases as the fracturing stages increase.In this study,because of the low carbonate layer permeability and compressive strength,a two-stage alternate 28%HCl and slickwater injection with a post-flush stage is recommended.展开更多
Multipole array sonic logging tools have widely been employed in Chinese oilfields in recent years. We have developed a software package for rock mechanical analysis with multipole array sonic logs. This advanced data...Multipole array sonic logging tools have widely been employed in Chinese oilfields in recent years. We have developed a software package for rock mechanical analysis with multipole array sonic logs. This advanced data processing method and software have been applied to the Tahe oilfield in Northern West China to provide guidance to acid hydraulic fracturing design and evaluation. In this paper, we present the field examples of such data processing and applications to demonstrate the validity and advantages of our method and software package.展开更多
How to effectively develop tight-gas carbonate reservoir and achieve high recovery is always a problem for the oil and gas industry.To solve this problem,domestic petroleum engineers use the combination of the success...How to effectively develop tight-gas carbonate reservoir and achieve high recovery is always a problem for the oil and gas industry.To solve this problem,domestic petroleum engineers use the combination of the successful experiences of North American shale gas pools development by stimulated reservoir volume(SRV)fracturing with the research achievements of Chinese tight gas development by acid fracturing to propose volume acid fracturing technology for fractured tightgas carbonate reservoir,which has achieved a good stimulation effect in the pilot tests.To determine what reservoir conditions are suitable to carry out volume acid fracturing,this paper firstly introduces volume acid fracturing technology by giving the stimulation mechanism and technical ideas,and initially analyzes the feasibility by the comparison of reservoir characteristics of shale gas with tight-gas carbonate.Then,this paper analyzes the validity and limitation of the volume acid fracturing technology via the analyses of control conditions for volume acid fracturing in reservoir fracturing performance,natural fracture,horizontal principal stress difference,orientation of insitu stress and natural fracture,and gives the solution for the limitation.The study results show that the volume acid fracturing process can be used to greatly improve the flow environment of tight-gas carbonate reservoir and increase production;the incremental or stimulation response is closely related with reservoir fracturing performance,the degree of development of natural fracture,the small intersection angle between hydraulic fracture and natural fracture,the large horizontal principal stress difference is easy to form a narrow fracture zone,and it is disadvantageous to create fracture network,but the degradable fiber diversion technology may largely weaken the disadvantage.The practices indicate that the application of volume acid fracturing process to the tight-gas carbonate reservoir development is feasible in the Ordovician Majiagou Formation of lower Paleozoic,which is of great significance and practical value for domestic tight-gas carbonate reservoir development and studies in the future.展开更多
To explore the damage behavior of O-ring in acid environment,a high-temperature and high-pressure(HTHP)autoclave was used to simulate the service environment of O-ring,and then 168h corrosion test of hydrogenated nitr...To explore the damage behavior of O-ring in acid environment,a high-temperature and high-pressure(HTHP)autoclave was used to simulate the service environment of O-ring,and then 168h corrosion test of hydrogenated nitrile butadiene rubber(HNBR)and fluororubber(FM)O-rings were carried out.The corrosion damage behaviors of two kinds of rubber O-rings in the acidizing fluid were studied through determining their tensile strength,elongation at break,hardness,permanent compressive deformation,tensile fracture morphology and sealing property.The results showed that the crosssectional area and the compression permanent deformation increased,the tensile strength and hardness decreased when the HNBR and FM O-rings under the free state were subjected to acid corrosion.The elongation at break of HNBR decreased,and that of FM rubber increased greatly.Similar with free state,the HNBR and FM O-rings under sealed state also presented the same variation trend.The decrease in the reliability of the O-rings under the sealed state was less significant than that in the free state.In the test,tensile fractures were mostly brittle fractures,HNBR and FM O-rings had obvious corrosion damages such as deformation and swelling.The results could provide a technical basis for the selection of sealing materials,tool optimization design,and construction work in oil and gas fields.展开更多
The microscopic characteristics and mechanical properties of rocks change after the action of acid on deep shale,which affects the fracturing effect.Accordingly,we designed and conducted indoor experiments related to ...The microscopic characteristics and mechanical properties of rocks change after the action of acid on deep shale,which affects the fracturing effect.Accordingly,we designed and conducted indoor experiments related to the changes in macro and microscopic characteristics after the interaction of acid with the shale of Wujiaping Formation,based on which the characteristic law of fracture volume modification after acid fracturing was studied using numerical simulation.The results demonstrate that the pores and fractures are enlarged and the structure is significantly loosened after the acid immersion.And a 15%concentration of hydrochloric acid can effectively dissolve shale.Furthermore,the degree of acid-etching reaction is highly variable because of the different carbonate content,which reveals the strong inhomogeneity of the shale system in the Wujiaping Group reservoir section.After the acid interacted with the shale rock samples,the triaxial compressive strength,elastic modulus,and Poisson’s ratio of shale decreased.Moreover,the evaluation of the effect after acid fracturing simulated by fracturing software revealed that the smaller the value of elastic modulus in shale-based reservoirs,the more favorable the fracture volume modification.This discovery not only provides a theoretical basis for the expansion and extension patterns of acid-fracturing in carbonaceous shale formations but also offers research methods and theoretical insights for the fundamental exploration of other deep-seated oil and gas resources.展开更多
Acid fracturing treatment is the key technique for stimulation and stable production in carbonate reservoirs.In order to improve the carbonate reservoirs acid fracturing effect,in this paper,with a large number of exp...Acid fracturing treatment is the key technique for stimulation and stable production in carbonate reservoirs.In order to improve the carbonate reservoirs acid fracturing effect,in this paper,with a large number of experiments as the main research methods,study on influencing factors of acidfracturing effect for carbonate reservoirs from increase the effective distance of living acid,increase acid corrosion eched fracture conductivity,reduce the acid fluid loss,etc.The effective distances of live acid calculated with reacted acid limitations measured in different acid systems are quite different from those calculated according to previous standard.Fracture conductivity is one of the key parameters that affects acid fracturing effects,but it's difficult to be predicted accurately due to the strong randomness of acid-rock reaction as well as various influence factors.Analyses of the impacts on fracture conductivity resulted from the rock embedment intensity,closure stress,acid dosage,rock-acid contact time,acid fluid loss,acid pumping rate through self-developed small-core fracture capacity test instrument.Fluid loss during acid fracture can be well controlled by thickened liquid as well as solid particles,but formation damage occurs inevitably.Foamed acid is a specific fluid with high viscosity,low fluid loss,small friction resistance,good retarding property,strong fracture making ability,easy flowback and low damage,which is an ideal acid system for low pressure and low permeability carbonate reservoirs.In this paper,the theoretical study on percolation mechanism and fluid-loss control mechanism of foam(acid)in porous medium are presented with the help of visual microscopic model fluid drive unit.展开更多
The Sinian Dengying Formation gas reservoir in the Anyue gas field of the Sichuan Basin is an ultra-deep ancient dolomite karst gas reservoir,whose development is of high difficulty,for the reservoir is thin and scatt...The Sinian Dengying Formation gas reservoir in the Anyue gas field of the Sichuan Basin is an ultra-deep ancient dolomite karst gas reservoir,whose development is of high difficulty,for the reservoir is thin and scattered with strong heterogeneity and is overall characterized by low porosity and low permeability.In order to provide support for the large-scale productivity construction of the gas reservoir of the fourth member of Dengying Formation(Deng 4 Member)in the marginal platform belt of the Anyue gas field,this paper carries out multi-discipline comprehensive researches on the technical bottlenecks based on the geological characteristics of the gas reservoir.In addition,the targeted key technologies for the efficient development of gas reservoirs were developed in the mode of“simultaneous research,application and improvement”.And the following research results are obtained.First,based on the modeling technology of fracturedevuggy dolomite karst reservoirs,accurate modeling of karst reservoirs is realized.Late actual drilling results show that the model's coincidence rate is increased from 63.0% to 90.7% and the“transparency”of gas reservoirs is achieved.Second,based on the reserve mobility evaluation technology of lowporosity and highly-heterogeneous karst reservoirs,the recovery factors of different reservoirs are determined.And consequently,the lower limit of well-controlled reserves and radius for the efficient development of different reservoirs are obtained and type Ⅰ and Ⅱ reservoirs are selected as the main development targets.Third,based on the development optimization design technology of highly-heterogeneous karst gas reservoirs,it is recommended to apply highly-deviated wells(the maximum deviation angle of 75°-84°)in the situations with multiple reservoirs crossed and superimposed.If type Ⅰ and Ⅱ reservoirs are developed intensively,it is recommended to adopt horizontal well drilling with a horizontal section of 800-1100 m.What's more,the reasonable well spacing in type Ⅰ and Ⅱ reservoirs shall be 1.6-3.3 km and 0.9-1.4 km,respectively.Fourth,based on the distinguished drilling technology of highly-deviated wells/horizontal wells in deep carbonate rocks,the fault complexity ratio is decreased from 20.7% to 4.9%,so safe and fast drilling and completion of highly-deviated wells/horizontal wells is realized and well control risks are diminished.What's more,the drilling rates of type Ⅰ and Ⅱ reservoirs are increased from 24.2% to 87.3%,indicating an effective improvement of reservoir drilling rates.Fifth,based on the open-hole segmented accurate acid fracturing technology of highly-deviated and horizontal wells,the difficulty in the highly-heterogeneous reservoir stimulation by horizontal well drilling is solved by conducting the differentiated acid fracturing process of“one segment,one strategy”.Based on the application of these innovative development technologies in the Deng 4 Member gas reservoir in the marginal platform belt of the Anyue gas field,the annual natural gas production capacity and cumulative natural gas production by the end of December 2020 are 60×10^(8) m^(3) and 103×10^(8) m^(3),respectively.In this way,the Sinian Dengying Formation gas reservoir of the Anyue gas field,the economic benefit of which is close to the marginal benefit,becomes the main force of conventional natural gas production increase.展开更多
The Yuanba Gasfield is another large gasfield with reserves of a hundred billion cubic meters that was discovered by Sinopec after the Puguang Gasfield in the Sichuan Basin.At present,it is the deepest marine carbonat...The Yuanba Gasfield is another large gasfield with reserves of a hundred billion cubic meters that was discovered by Sinopec after the Puguang Gasfield in the Sichuan Basin.At present,it is the deepest marine carbonate sour gasfield in China.Its principal reservoir,the Upper Permian Changxing Fm,is characterized by ultra depth,high temperature,high sulfur content,high CO_(2)content,and complex gasewater relationship.Therefore,well completion is faced with complicated engineering geological conditions,diverse well types and well completion modes and high-difficulty operation.In view of this,Sinopec Southwest Petroleum Engineering Co.,Ltd.carried out technical research and practice.As a result,a series of key well completion and commissioning technologies were developed,including well completion testing and ground control,in-depth acid fracturing stimulation,ultra-deep slim-hole wellbore processing,micro-tooth mark make-up and air tightness detection,and safety control.Based on these technologies,the worldwide technical difficulties of well completion and commissioning in the process of gasfield development are settled,such as string corrosion prevention,in-depth acid fracturing,high-yield testing,and safety control.These technologies have been applied successfully in nearly 40 wells,providing an important technical support for the realization of 34×10^(8)m^(3)annual gas production capacity construction in the Yuanba Gasfield.展开更多
The main zone of production of Sinian gas reservoirs in the Sichuan Basin(China)is the Deng 4 member of the Gaoshiti–Moxi structure.In the Deng 4 member,the rock type is mostly dolomite,and the main types of storage ...The main zone of production of Sinian gas reservoirs in the Sichuan Basin(China)is the Deng 4 member of the Gaoshiti–Moxi structure.In the Deng 4 member,the rock type is mostly dolomite,and the main types of storage space are brecciated interporosity and large-scale interporosity characterized by low porosity and low permeability(average porosity:3.21%,average permeability:2.19 mD).In the Gaoshiti structure of the Deng 4 member gas reservoir,annual gas production of 60 billion cubic meters has been realized using differential segmented acid fracturing stimulation technology.However,with development of the Moxi structure,such technology is unable to adapt the reservoir because it requires continuous optimization according to reservoir characteristics.To provide effective support for optimization of reservoir stimulation technology,this study performed experiments using a large-scale true triaxialacid fracturing model.On the basis of the simulation of the reservoir reconstruction process,optimization of the process was investigated,an optimization scheme was proposed,and a field test was performed.The results,which indicated that gelling acid fracturing technology can effectively improve the stimulation effect of the Deng 4 member of the Moxi gas reservoir and substantially increase single-well production,could provide technical support for enhanced production of the Gaoshiti–Moxi gas reservoir.展开更多
During the life of a well,treatments are carried out to boost productivity by stimulating initially unproduced zones.These treatments include hydraulic fracturing,matrix acidization,and acid fracturing,among others.Hy...During the life of a well,treatments are carried out to boost productivity by stimulating initially unproduced zones.These treatments include hydraulic fracturing,matrix acidization,and acid fracturing,among others.Hydraulic fracturing treatment is generally applied to deeper reservoirs of oil or natural gas for enhanced recovery.By infusing proppant,water,and chemicals under extreme pressure during the fracturing procedure,fissures in and beneath the reservoir layer can be accessed and expanded.Another stimulating procedure,matrix acidization,involves injecting acid down the drilling hole to permeate the rock fissures at stresses lower than the fracture stress.In addition,carbonate reservoir acid fracturing stimulation is commonly used as an acid treatment technique whereby a pressure greater than the formation disintegration pressure or spontaneous fracture closure pressure is used to compress acid into the reservoir.These treatments allow existing wells to sustain hydrocarbon production without new wells being drilled.Diverters,when employed efficiently,can prevent the need to use a rig to provide momentary physical barriers,thus lowering the cost of the workover.Recent improvements in diversion technology make use of a variety of degradable particles that act as momentary bridges,either at the perforation entries or inside the existing fractures.The aim of this study is to introduce different types of mechanical and chemical diverters used to enhance the productivity of wells.This study explains the concepts of different types of diverters and their applications in several formations,it will also help readers to understand the selection procedures based on the suitability and requirements of diverter use by case studies from around the world.展开更多
The propagation of wormhole is vital important for matrix acidizing and acid fracturing in carbonate reservoirs.While the formation of acid dissolved wormhole is derived from heterogeneous physical and chemical transp...The propagation of wormhole is vital important for matrix acidizing and acid fracturing in carbonate reservoirs.While the formation of acid dissolved wormhole is derived from heterogeneous physical and chemical transportations and reactions.Alveolate dissolved pores,krast caves,and natural fissures are the major reservoir spaces for the Sinian dolomite formation in the Anyue gas field of the Sichuan Basin.There were four categories of formation,which are matrix dominated,inter-breccia dissolved pore dominated,dissolved pore and cave dominated,and fissure and cave dominated,based on the development intensity and connectedness of caves and fissures.The caves and fissures make the wormhole formation and propagation particularly complicated.Firstly,the 3-D topological structure of dissolved pores,vugs,fissures and throats inside cores is quantitatively scanned by CT imaging technology for its feature of vivid and damage-free.Secondly,3-D patterns of wormhole are obtained with CT scanning after core flooding by acid.Additionally,the porethroat network model is reconstructed with digital cores technology.Then,the size and ratio of pore and throat before and after core flooding by acid is analyzed and the absolute permeability of pore scale flow is numerically simulated to understand the fundamental influence of pores and vugs distribution and connectedness on wormhole propagation.Lastly,the wormhole pattern gained by CT scanning and simulating with two-scale model is compared.Meanwhile,the corrected two-scale model is utilized to simulate the wormhole propagation for matrix acidizing and acid fracturing of Sinian fractured-vuggy dolomite in Anyue gas field,Sichuan Basin.The optimized injection rate and volume were in agreement with the characteristic matrix acidizing operating curve,which indicates that the two-scale model was suitable for matrix acidizing optimization design of such formations.In addition,the simulated acid etched fracture length with considering the dynamic wormhole leakoff was consistent with the well testing interpreted result.展开更多
Conventional stimulation methods such as matrix acidizing,acid fracturing,or proppant fracturing have resulted in products that perform poorly and/or fail within months.Other options,such as water fracs with light san...Conventional stimulation methods such as matrix acidizing,acid fracturing,or proppant fracturing have resulted in products that perform poorly and/or fail within months.Other options,such as water fracs with light sand,give better results but are prohibitively expensive.Mineral composition,brittleness index,stress regime,and petrophysical properties,which are favorable for creating complex fracture networks,can be obtained by geochemical and geomechanical analysis.The extended Reshaw and Pollard criterion shows that hydraulic fractures tend to be arrested by pre-existing natural fractures,and complex fracture networks would be created during fracturing.Additionally,the critical stressed faults theory indicates that the pre-existing natural fractures tend to slip with the shear mode as the pore fluid pressure increases.Rotating disk experiments and conductivity tests with artificial sheared plates have shown that flow channels can be etched at the location of scratches on fracture surfaces.Meanwhile,the carbonate cement in natural fractures can be chelated to form wormhole likely flow channels.Complex fracture networks with sufficient acid etched conductivity can be generated by water fracs with acid.A novel and economical volume stimulation strategy known as network acid fracturing has provided Tarim Oil Company the means to develope ultra-deep,ultra-high pressure,high temperature,and ultralow permeability but fractured gas reservoirs.Post-stimulation production performances of numerous wells with network acid fracturing are comparable to those with stimulated reservoir volumes.展开更多
Tight multi-medium oil reservoirs are the main source of hydrocarbon resources around the world.Acid fracturing is the most effective technology to improve productivity in such reservoirs.As carbonates are primarily c...Tight multi-medium oil reservoirs are the main source of hydrocarbon resources around the world.Acid fracturing is the most effective technology to improve productivity in such reservoirs.As carbonates are primarily composed of dolomite and calcite,which are easily dissolved by hydrochloric acid,high-permeability region will be formed near the well along with the main artificial fracture when acid fracturing is implemented in tight multi-medium oil reservoirs.In this study,a comprehensive composite linear flow model was developed to simulate the transient pressure behavior of an acid fracturing vertical well in a naturally fractured vuggy carbonate reservoir.By utilizing Pedrosa's substitution,perturbation,Laplace transformation and Stehfest numerical inversion technol-ogy,the pressure behavior results were obtained in real time domain.Furthermore,the result of this model was validated by comparing with those of previous literature.Additionally,the influences of some prevailing parameters on the type curves were analyzed.Moreover,the proposed model was applied to an acid fracturing well to evaluate the effectiveness of acid fracturing measures,to demonstrate the practicability of the proposed model.展开更多
基金supported by the National Natural Science Foundation of China(Grant No.52404020 and Grant No.U1762216).
文摘Heterogeneity in carbonate formations due to discontinuities(e.g.,fractures and cavities)will bring about distinctive acid stimulation effects.However,the differences in fracturing behavior between homogeneous and heterogeneous carbonate formations remain unclear,complicating the optimization of acid fracturing strategies.In this paper,full-diameter carbonate rock samples with different degrees of discontinuity development are selected to investigate the fracturing behavior under different fluid types and injection schemes.Advanced techniques,including 3D CT scanning and 3D laser scanning,are employed to analyze fracture morphology and etching characteristics,respectively.Experimental results show that the coupled hydraulic-chemical effects play different roles in fracture induction between fracture-cavity developed and undeveloped carbonate rocks.Acid-fracturing stimulation consistently induces multiple types of complex fractures in fracture-cavity carbonate rocks,whereas it results in a single artificial fracture in less fracture-cavity carbonate rocks.Furthermore,localized etching patterns are prevalent in most fracture-cavity carbonate rocks,whereas homogeneous carbonate rocks exhibit regional or global etching characteristics.In both carbonate rocks,the stimulation effect of guar fluid is inferior to that of gelled acid but comparable to self-generating acid.Further findings are that alternating fracturing with guar and acid fluids in fracture-cavity carbonate rocks can sustain or even increase the injection pressure,facilitating the formation of new or depth-penetrating fractures.This phenomenon,however,is not observed in fracture-cavity undeveloped carbonate rocks.Potential interaction modes between induced fracture and natural fractures/cavities under different injection conditions are also identified.Finally,preferred fracturing schemes applicable to different carbonate formations are recommended based on the area,number and roughness of the induced fractures.
基金financially supported by the National Natural Science Foundation of China(Nos.52304129 and 52274130)Natural Science Foundation of Sichuan Province(No.2024NSFSC0971)+1 种基金Guizhou Provincial Basic Research Program(Natural Science)(No.ZK[2023]general 070)Shandong Key Laboratory of Mining Disaster Prevention and Control,Shandong University of Science and Technology(No.SMDPC202403)。
文摘The combination of ultrasonic and acid fracturing fluid can strengthen the modification effect on the micropore structure of the coal matrix,thereby enhancing the efficiency of the acid fracturing process.In this research,acetic acid was utilized to formulate acid fracturing fluids with varying concentrations,and the evolutionary traits of both the acid fracturing fluids and ultrasonic waves in relation to coal samples were investigated.The functional group structure,mineral composition,micropore structure and surface morphology of coal samples were characterized by FTIR,XRD,N_(2)adsorption at low temperature and SEM-EDS.The results showed that aromatics(I)and branching parameters(CH_(2)/CH_(3))were reduced by 81.58%and 88.67%,respectively,after 9%acetic acid treatment.Acetic acid can dissolve carbonates and clay minerals in coal,create new pores,and increase porosity,pore volume and pore fractal dimension.After modification by 7%acetic acid,the pore volume increased by 5.7 times.SEM observation shows that the diameter of coal surface holes increases,EDS scanning shows that the content of mineral elements in coal decreases,the connectivity of coal holes increases,and the holes expand.The findings of this research offer theoretical direction for optimizing ultrasonic-enhanced acid fracturing fluid modification.
基金supported by the National Major Science and Technology Project“Demonstrative development project of large carbonate gas field in Sichuan Basin”(No.:2016ZX05052).
文摘For the purpose of improving the accuracy and effectiveness of acid fracturing design for carbonate reservoirs with developed natural fractures,an acidizingfluidflow and reaction model taking the multiple leak-off effect of natural fracture,wormhole and matrix into account was established according to the liquid phase reaction equilibrium principle and the local reaction equilibrium principle after the dynamic change of fracture geometry in the process of fracture created by prepadfluid was simulated in the classical pseudo-three dimensional mathematical model of fracture propagation.Then,the acid fracturing stimulation of a case well on site was taken as an example.The newly developed model was used to simulate thefiltration process of acidizingfluid in fractures and the dynamic etching morphology of acidic rocks during the acidizingfluid injection of prepad acid fracturing.The effective length of etched fractures was determined by analyzing the concentration change of acidizingfluid along the direction of hydraulic fracture length and the threshold concentration of residual acidizingfluid comprehensively,and then it was compared with the interpretation result of pressure buildup test.And the following research results were obtained.First,in the process of acid fracturing in fracturedeporous reservoirs,the acidizingfluidfiltration velocity along the direction of fracture length is not constant and thefiltration velocity curvefluctuates in a serrated shape.And the acidizingfluidfiltration velocity where etched wormholes meet natural fractures is commonly higher than that in matrix.Second,acidizingfluid is lost seriously and the effective distance of acidizingfluid gets short significantly during the acid fracturing of fracturedeporous reservoirs.Third,acid fracturing in the verification well is remarkable in blockage removing and stimulation,and its well test interpretation results are consistent with the simulation interpretation results provided by the newly developed mathematical model.It is indicated that this newly developed model is reliable.In conclusion,the mathematical model of prepad acid fracturing which considers multiple leak-off effect is more suitable for acid fracturing simulation of fracturedeporous reservoirs.
基金Supported by National Natural Science Foundation of China Project(51704249)The Open Fund Project of the State Key Laboratory Oil and Gas Reservoir Geology and Exploitation(PLN2020-1)。
文摘Carbonate outcrops were taken from Ma 51 sub-member in the Lower Paleozoic in the Yan’an gas field to conduct true tri-axial hydraulic fracturing experiments with water, liquid CO_(2) and supercritical CO_(2). CT scan was applied to analyze initiation and propagation laws of hydraulic fractures in carbonate rocks. The experiments show that supercritical CO_(2) has low viscosity, strong diffusivity and large filtration during fracturing, which is more liable to increase pore pressure of rocks around wellbore and decrease breakdown pressure of carbonate rocks. However, it would cost much more volume of supercritical CO_(2) than water to fracture rocks since the former increases the wellbore pressure more slowly during fracturing. For carbonate rocks with few natural fractures, tensional fractures are generated by fracturing with water and liquid CO_(2), and these fractures propagate along the maximum horizontal principal stress direction;while fracturing with supercritical CO_(2) can form shear fractures, whose morphology is rarely influenced by horizontal stress difference. Besides, the angle between propagation direction of these shear fractures near the wellbore and the maximum horizontal principal stress is 45°, and the fractures would gradually turn to propagate along the maximum horizontal principal stress when they extend to a certain distance from the wellbore, leading to an increase of fracture tortuosity compared with the former. For carbonate rocks with well-developed natural fractures, fracturing with fresh water is conducive to connect natural fractures with low approaching angle and form stepped fractures with simple morphology. The key to forming complex fractures after fracturing carbonate rocks is to connect the natural fractures with high approaching angle. It is easier for liquid CO_(2) with low viscosity to realize such connection. Multi-directional fractures with relatively complex morphology would be formed after fracturing with liquid CO_(2).
基金supported by the China Postdoctoral Sci-ence Foundation(2020M683360)National Natural Science Foundation of China(U19A2043).
文摘Acid fracturing is an important means of reservoir stimulation,whose purpose is to form an incompletely closed acid-etched fracture as the flow channel for oil and gas during production.The length and conductivity of acid-etched fractures can be used to evaluate acid fracturing and directly impact production.To study their influence on the stimulation effect and final production,an acid fracturing coupling model including a fracture propagation model coupled with reservoir flow and temperature field models is established for the first time in this study based on an embedded discrete fracture model(EDFM),which can realize the coupling of fracture propagation and reservoir flow and simplify the solution of fracture and reservoir temperatures.The simulation results of the acid fracturing coupling model are introduced into the productivity model,which is also based on the EDFM to analyze and evaluate well productivity.The results show that:(1)the EDFM can easily couple fracture propagation and reservoir flow and can be used to rapidly solve the temperature fields in the fracture and reservoir successfully for the first time.(2)Reservoir flow impacts the propagation of fractures by increasing or decreasing the leak-off velocity of the working fluid.(3)Temperature diffusion is much weaker than pressure diffusion during acid fracturing and is limited near the acid fracture.The reaction between the acid and rock increases the local temperature around the acid fracture,and may even exceed the initial formation temperature.(4)Raising the injection rate reasonably enhances H^(+) diffusion,increases the effective length of acid-etched fractures,enlarges the drainage area of oil and gas,and benefits long-term well production.
基金supported by China National Petroleum Corporation's major scientific and technological project“Research and Application of Reservoir Stimulation Technology for Deep HPHT Sour Gas Reservoirs in the Sichuan Basin”(No.:2016E-0609).
文摘The carbonate gas reservoir of the fourth Member of Upper Sinian Dengying Formation(hereinafter referred as“Deng 4 Member”)is characterized by deep burial,high temperature,low porosity,low permeability and strong heterogeneity in the Gaoshiti-Moxi area of the central Sichuan Basin.In order to effectively enhance the well productivity and gas reservoir development benefits,this paper defines the reservoir stimulation factor by comprehensively considering the drilling,logging and well type characteristic parameters,to carry out quantitative reservoir evaluation.Then,the refined segmentation method was developed by fully considering the reservoir stimulation factor,in-situ stress and borehole condition.In addition,the differential acid fracturing technology was prepared for different types of reservoirs.On this basis,the specified staged acid fracturing technology of horizontal well for strong-heterogeneity carbonate reservoirs was developed and then applied in the field.And the following research results were obtained.First,the reservoir stimulation factor(y)can be used to accurately evaluate the reservoir characteristics.The high quality reservoir has y≥1.0,the moderate reservoir has 0.5≤y<1.0,and the low quality reservoir has y˂0.5.Second,the specified staged acid fracturing technology considering the influence of reservoir stimulation factor,in-situ stresses and borehole condition comprehensively is formed.Stimulation measures are applied specifically in different types of reservoir intervals to give full play to the resource potential in each stimulation segment of a long horizontal section,so as to improve the production rate of natural gas reserves in strong-heterogeneity reservoirs.Third,the acid fracturing technology suitable for different types of reservoirs is also different.It is recommended to adopt acid fracturing with gelled acid or diverting acid in high quality reservoirs,acid fracturing with self-generating acid prepad in moderate reservoirs,and acid fracturing with 2–3 stages alternate injection of self-generating acid prepad and gelled acid in low quality reservoirs.Fourth,69 wells in the production area of the platform margin of Deng 4 Member gas reservoir in Gaoshiti-Moxi area are stimulated with specified staged acid fracturing.The average absolute open flow is 127.6×10^(4)m^(3)/d,which is 46.5%higher than that in the early stage of gas reservoir development.In conclusion,the research results provide remarkable stimulation effects,increase the single well gas production greatly and effectively support the efficient development of Deng 4 Member gas reservoir in the Gaoshiti-Moxi area.
基金supported by the National Natural Science Foundation of China"Research on acidizing mechanism under the coupling of temperature,fracture flow,acid-rock reaction,and stress damage for fractured carbonate rocks"(No.51704249)National Natural Science Foundation of China"Acid fracturing of low-permeability and tight oil and gas reservoirs"(No.51525404)the China Postdoctoral Science Foundation-General Program Research on acidizing mechanism of fracture network in deep,high-temperature,fractured carbonat rocks"(No.2017M623063).
文摘Acid fracturing is an indispensable technology in the efficient development of carbonate oil and gas rosarvoirs.As for deep and ultra-deep marine carbonate oil and gas reservoirs,however,existing acid fracturing technologies can hardly create complex fracture networks because of their particular engineering and geological characteristics.In order to realize the efficient three-dimensional development of deep and ultra-deep marine carbonate oil and gas reservoirs,this paper revealed the acid fracturing difficulties of this kind of reservoirs based on the engineering and geological characteristics of deep marine carbonate oil and gas reservoirs in China.Then,by taking the efficient three-dimensional development of deep and ultra-deep marine carbonate oiland gas reservoirs as the target,the technical conceptof three-dimensional acid fracturing(3D-AF)was putforward based on the techniques of volume acid fracturing and deep acid fracturing.In addition,its technical connotation was il lustrated,and its key technologies were described in detail.Finally,its development direction in the next step was pointed out.And the following research results were obtained.First,the 3D-AF technology contains three basic connotations:(1)selecting the corresponding acid penetration technology according to reservoir types so as to realize sufficient resarvoir stimulation on the plane;(2)creating complex acid-fracture volume with higher flow conductivity under high closed pressure;(3)deploying acid-fracture volume rationally along the long hole section so as to realize sufficient reservoir stimulation in the wellbore direction.Second,there are three key technologies of 3D-AF,i.e.,the technology for predicting the effective acid-penetrate distance under the coupling action of multi-feld,multi-scale and multi-fluid,the technology for optimizing the flow conductivity of complex acid-fracture volume,and the technology for precisely deploying acid in the long section of horizontal well or highly deviated well.Third,in order to promote the further development of 3D-AFtechnology,it is necessary to carry out researches on three technologies,i.e.,the technology for predicting and reducing the fracturing pressure of ultra-deep reservoir,the tech-nology for predicting the geometry of acid-fracture body ina strongly heterogeneous reservoir,and the staged reservoir production technology and new fluid technology with high temperature resistance,low reaction rate and low friction resistance coefficient for long hole sections(over 7000 m).
文摘In this study,acid fracturing treatments were simulated for a tight limestone reservoir within a shale formation using FRACPRO software.The purpose was to investigate the optimum acid fracturing design that leads to a higher fracture etched length and width,and higher fracture conductivity.Moreover,the impact of the rock-acid contact time and whether to consider a post-flush or fluids flowback,on the acid fracturing outcomes were also investigated.A simple geological model was constructed which consists of different lithological layers.Different acid fracturing design scenarios were considered starting from a single stage of acid injection to multi-stage treatment.In multi-stage acid treatment,alternate acid-slickwater injection was considered.Plain HCl acids with different concentrations and other acids that are already included in FRACPRO database were used.The results showed that the acid loss during post-flush is among the main problems of the acid fracturing in tight carbonate shale reservoir.For the single stage of acid injection,it is recommended to flow back the acid after well shut-in instead of considering a post-flush stage.The multi-stage alternate acid slickwater injection reduces or even eliminated the acid loss.However,it is recommended to inject a slickwater before well shut-in to reduce the rock-acid contact time,thus reducing the formation damage.The results also showed that the created fracture etched width decreases and the fracture etched length increases as the fracturing stages increase.In this study,because of the low carbonate layer permeability and compressive strength,a two-stage alternate 28%HCl and slickwater injection with a post-flush stage is recommended.
基金This project is sponsored by Natural Science Foundation of China supported project No. 50674098.
文摘Multipole array sonic logging tools have widely been employed in Chinese oilfields in recent years. We have developed a software package for rock mechanical analysis with multipole array sonic logs. This advanced data processing method and software have been applied to the Tahe oilfield in Northern West China to provide guidance to acid hydraulic fracturing design and evaluation. In this paper, we present the field examples of such data processing and applications to demonstrate the validity and advantages of our method and software package.
基金The project was supported jointly by National Science and Technology Major Project of China(2011ZX05044)National Natural Science Foundation of China(51474182).
文摘How to effectively develop tight-gas carbonate reservoir and achieve high recovery is always a problem for the oil and gas industry.To solve this problem,domestic petroleum engineers use the combination of the successful experiences of North American shale gas pools development by stimulated reservoir volume(SRV)fracturing with the research achievements of Chinese tight gas development by acid fracturing to propose volume acid fracturing technology for fractured tightgas carbonate reservoir,which has achieved a good stimulation effect in the pilot tests.To determine what reservoir conditions are suitable to carry out volume acid fracturing,this paper firstly introduces volume acid fracturing technology by giving the stimulation mechanism and technical ideas,and initially analyzes the feasibility by the comparison of reservoir characteristics of shale gas with tight-gas carbonate.Then,this paper analyzes the validity and limitation of the volume acid fracturing technology via the analyses of control conditions for volume acid fracturing in reservoir fracturing performance,natural fracture,horizontal principal stress difference,orientation of insitu stress and natural fracture,and gives the solution for the limitation.The study results show that the volume acid fracturing process can be used to greatly improve the flow environment of tight-gas carbonate reservoir and increase production;the incremental or stimulation response is closely related with reservoir fracturing performance,the degree of development of natural fracture,the small intersection angle between hydraulic fracture and natural fracture,the large horizontal principal stress difference is easy to form a narrow fracture zone,and it is disadvantageous to create fracture network,but the degradable fiber diversion technology may largely weaken the disadvantage.The practices indicate that the application of volume acid fracturing process to the tight-gas carbonate reservoir development is feasible in the Ordovician Majiagou Formation of lower Paleozoic,which is of great significance and practical value for domestic tight-gas carbonate reservoir development and studies in the future.
基金Project supported by the National Natural Science Foundation of China“Study on the mechanism of force-chemical damage of screw sealing surface of H_(2)S/CO_(2)gas well completion string under static load,vibration and corrosion”(No.51774249)Sichuan Science and Technology Program(No.21JCQN0066).
文摘To explore the damage behavior of O-ring in acid environment,a high-temperature and high-pressure(HTHP)autoclave was used to simulate the service environment of O-ring,and then 168h corrosion test of hydrogenated nitrile butadiene rubber(HNBR)and fluororubber(FM)O-rings were carried out.The corrosion damage behaviors of two kinds of rubber O-rings in the acidizing fluid were studied through determining their tensile strength,elongation at break,hardness,permanent compressive deformation,tensile fracture morphology and sealing property.The results showed that the crosssectional area and the compression permanent deformation increased,the tensile strength and hardness decreased when the HNBR and FM O-rings under the free state were subjected to acid corrosion.The elongation at break of HNBR decreased,and that of FM rubber increased greatly.Similar with free state,the HNBR and FM O-rings under sealed state also presented the same variation trend.The decrease in the reliability of the O-rings under the sealed state was less significant than that in the free state.In the test,tensile fractures were mostly brittle fractures,HNBR and FM O-rings had obvious corrosion damages such as deformation and swelling.The results could provide a technical basis for the selection of sealing materials,tool optimization design,and construction work in oil and gas fields.
基金This study is supported by a Scientific Research Project of Sinopec(Program No.P21087-2)the Open Fund of Key Laboratory of Marine Oil&Gas Reservoirs Production,Sinopec(Grant No.33550000-22-FW2099-0004).
文摘The microscopic characteristics and mechanical properties of rocks change after the action of acid on deep shale,which affects the fracturing effect.Accordingly,we designed and conducted indoor experiments related to the changes in macro and microscopic characteristics after the interaction of acid with the shale of Wujiaping Formation,based on which the characteristic law of fracture volume modification after acid fracturing was studied using numerical simulation.The results demonstrate that the pores and fractures are enlarged and the structure is significantly loosened after the acid immersion.And a 15%concentration of hydrochloric acid can effectively dissolve shale.Furthermore,the degree of acid-etching reaction is highly variable because of the different carbonate content,which reveals the strong inhomogeneity of the shale system in the Wujiaping Group reservoir section.After the acid interacted with the shale rock samples,the triaxial compressive strength,elastic modulus,and Poisson’s ratio of shale decreased.Moreover,the evaluation of the effect after acid fracturing simulated by fracturing software revealed that the smaller the value of elastic modulus in shale-based reservoirs,the more favorable the fracture volume modification.This discovery not only provides a theoretical basis for the expansion and extension patterns of acid-fracturing in carbonaceous shale formations but also offers research methods and theoretical insights for the fundamental exploration of other deep-seated oil and gas resources.
基金The project was supported jointly by National Science and Technology Major Project of China(2011ZX05044)National Natural Science Foundation of China(51474182).
文摘Acid fracturing treatment is the key technique for stimulation and stable production in carbonate reservoirs.In order to improve the carbonate reservoirs acid fracturing effect,in this paper,with a large number of experiments as the main research methods,study on influencing factors of acidfracturing effect for carbonate reservoirs from increase the effective distance of living acid,increase acid corrosion eched fracture conductivity,reduce the acid fluid loss,etc.The effective distances of live acid calculated with reacted acid limitations measured in different acid systems are quite different from those calculated according to previous standard.Fracture conductivity is one of the key parameters that affects acid fracturing effects,but it's difficult to be predicted accurately due to the strong randomness of acid-rock reaction as well as various influence factors.Analyses of the impacts on fracture conductivity resulted from the rock embedment intensity,closure stress,acid dosage,rock-acid contact time,acid fluid loss,acid pumping rate through self-developed small-core fracture capacity test instrument.Fluid loss during acid fracture can be well controlled by thickened liquid as well as solid particles,but formation damage occurs inevitably.Foamed acid is a specific fluid with high viscosity,low fluid loss,small friction resistance,good retarding property,strong fracture making ability,easy flowback and low damage,which is an ideal acid system for low pressure and low permeability carbonate reservoirs.In this paper,the theoretical study on percolation mechanism and fluid-loss control mechanism of foam(acid)in porous medium are presented with the help of visual microscopic model fluid drive unit.
基金Project supported by the National Science and Technology Major Project“Demonstration Project of Giant Carbonate Gas Field Development in Sichuan Basin”(No.2016ZX05052)the PetroChina Major Technology Special Project“Research and Application of Key Technology for Large-scale Efficient Development of the Fourth Member of Dengying Formation in Central Sichuan”(No.:2016E-0606).
文摘The Sinian Dengying Formation gas reservoir in the Anyue gas field of the Sichuan Basin is an ultra-deep ancient dolomite karst gas reservoir,whose development is of high difficulty,for the reservoir is thin and scattered with strong heterogeneity and is overall characterized by low porosity and low permeability.In order to provide support for the large-scale productivity construction of the gas reservoir of the fourth member of Dengying Formation(Deng 4 Member)in the marginal platform belt of the Anyue gas field,this paper carries out multi-discipline comprehensive researches on the technical bottlenecks based on the geological characteristics of the gas reservoir.In addition,the targeted key technologies for the efficient development of gas reservoirs were developed in the mode of“simultaneous research,application and improvement”.And the following research results are obtained.First,based on the modeling technology of fracturedevuggy dolomite karst reservoirs,accurate modeling of karst reservoirs is realized.Late actual drilling results show that the model's coincidence rate is increased from 63.0% to 90.7% and the“transparency”of gas reservoirs is achieved.Second,based on the reserve mobility evaluation technology of lowporosity and highly-heterogeneous karst reservoirs,the recovery factors of different reservoirs are determined.And consequently,the lower limit of well-controlled reserves and radius for the efficient development of different reservoirs are obtained and type Ⅰ and Ⅱ reservoirs are selected as the main development targets.Third,based on the development optimization design technology of highly-heterogeneous karst gas reservoirs,it is recommended to apply highly-deviated wells(the maximum deviation angle of 75°-84°)in the situations with multiple reservoirs crossed and superimposed.If type Ⅰ and Ⅱ reservoirs are developed intensively,it is recommended to adopt horizontal well drilling with a horizontal section of 800-1100 m.What's more,the reasonable well spacing in type Ⅰ and Ⅱ reservoirs shall be 1.6-3.3 km and 0.9-1.4 km,respectively.Fourth,based on the distinguished drilling technology of highly-deviated wells/horizontal wells in deep carbonate rocks,the fault complexity ratio is decreased from 20.7% to 4.9%,so safe and fast drilling and completion of highly-deviated wells/horizontal wells is realized and well control risks are diminished.What's more,the drilling rates of type Ⅰ and Ⅱ reservoirs are increased from 24.2% to 87.3%,indicating an effective improvement of reservoir drilling rates.Fifth,based on the open-hole segmented accurate acid fracturing technology of highly-deviated and horizontal wells,the difficulty in the highly-heterogeneous reservoir stimulation by horizontal well drilling is solved by conducting the differentiated acid fracturing process of“one segment,one strategy”.Based on the application of these innovative development technologies in the Deng 4 Member gas reservoir in the marginal platform belt of the Anyue gas field,the annual natural gas production capacity and cumulative natural gas production by the end of December 2020 are 60×10^(8) m^(3) and 103×10^(8) m^(3),respectively.In this way,the Sinian Dengying Formation gas reservoir of the Anyue gas field,the economic benefit of which is close to the marginal benefit,becomes the main force of conventional natural gas production increase.
基金supported by the Sinopec Technology Development Project Pilot on Acid Frcturing Technology of Ultn-deep Marine Horizontal Wells in Yuanba Gasfiel"(No.:GJ-258-1254)SinopecTechnology Application Project"Optimization Design for the Testing of High-Pressure High-Yield Acid Gas Wells in Northeast Sichuan Basin"(No.:JPO8001)Technical Pillot Experiment Project of Sinopec Petroleum Engincering Company(No.SG1314-03K).
文摘The Yuanba Gasfield is another large gasfield with reserves of a hundred billion cubic meters that was discovered by Sinopec after the Puguang Gasfield in the Sichuan Basin.At present,it is the deepest marine carbonate sour gasfield in China.Its principal reservoir,the Upper Permian Changxing Fm,is characterized by ultra depth,high temperature,high sulfur content,high CO_(2)content,and complex gasewater relationship.Therefore,well completion is faced with complicated engineering geological conditions,diverse well types and well completion modes and high-difficulty operation.In view of this,Sinopec Southwest Petroleum Engineering Co.,Ltd.carried out technical research and practice.As a result,a series of key well completion and commissioning technologies were developed,including well completion testing and ground control,in-depth acid fracturing stimulation,ultra-deep slim-hole wellbore processing,micro-tooth mark make-up and air tightness detection,and safety control.Based on these technologies,the worldwide technical difficulties of well completion and commissioning in the process of gasfield development are settled,such as string corrosion prevention,in-depth acid fracturing,high-yield testing,and safety control.These technologies have been applied successfully in nearly 40 wells,providing an important technical support for the realization of 34×10^(8)m^(3)annual gas production capacity construction in the Yuanba Gasfield.
文摘The main zone of production of Sinian gas reservoirs in the Sichuan Basin(China)is the Deng 4 member of the Gaoshiti–Moxi structure.In the Deng 4 member,the rock type is mostly dolomite,and the main types of storage space are brecciated interporosity and large-scale interporosity characterized by low porosity and low permeability(average porosity:3.21%,average permeability:2.19 mD).In the Gaoshiti structure of the Deng 4 member gas reservoir,annual gas production of 60 billion cubic meters has been realized using differential segmented acid fracturing stimulation technology.However,with development of the Moxi structure,such technology is unable to adapt the reservoir because it requires continuous optimization according to reservoir characteristics.To provide effective support for optimization of reservoir stimulation technology,this study performed experiments using a large-scale true triaxialacid fracturing model.On the basis of the simulation of the reservoir reconstruction process,optimization of the process was investigated,an optimization scheme was proposed,and a field test was performed.The results,which indicated that gelling acid fracturing technology can effectively improve the stimulation effect of the Deng 4 member of the Moxi gas reservoir and substantially increase single-well production,could provide technical support for enhanced production of the Gaoshiti–Moxi gas reservoir.
文摘During the life of a well,treatments are carried out to boost productivity by stimulating initially unproduced zones.These treatments include hydraulic fracturing,matrix acidization,and acid fracturing,among others.Hydraulic fracturing treatment is generally applied to deeper reservoirs of oil or natural gas for enhanced recovery.By infusing proppant,water,and chemicals under extreme pressure during the fracturing procedure,fissures in and beneath the reservoir layer can be accessed and expanded.Another stimulating procedure,matrix acidization,involves injecting acid down the drilling hole to permeate the rock fissures at stresses lower than the fracture stress.In addition,carbonate reservoir acid fracturing stimulation is commonly used as an acid treatment technique whereby a pressure greater than the formation disintegration pressure or spontaneous fracture closure pressure is used to compress acid into the reservoir.These treatments allow existing wells to sustain hydrocarbon production without new wells being drilled.Diverters,when employed efficiently,can prevent the need to use a rig to provide momentary physical barriers,thus lowering the cost of the workover.Recent improvements in diversion technology make use of a variety of degradable particles that act as momentary bridges,either at the perforation entries or inside the existing fractures.The aim of this study is to introduce different types of mechanical and chemical diverters used to enhance the productivity of wells.This study explains the concepts of different types of diverters and their applications in several formations,it will also help readers to understand the selection procedures based on the suitability and requirements of diverter use by case studies from around the world.
基金The authors are grateful for the research support of the Postdoctoral Program of Postdoctoral Work Centre,Southwest Oil&Gas Field Company(No.20150304-08).
文摘The propagation of wormhole is vital important for matrix acidizing and acid fracturing in carbonate reservoirs.While the formation of acid dissolved wormhole is derived from heterogeneous physical and chemical transportations and reactions.Alveolate dissolved pores,krast caves,and natural fissures are the major reservoir spaces for the Sinian dolomite formation in the Anyue gas field of the Sichuan Basin.There were four categories of formation,which are matrix dominated,inter-breccia dissolved pore dominated,dissolved pore and cave dominated,and fissure and cave dominated,based on the development intensity and connectedness of caves and fissures.The caves and fissures make the wormhole formation and propagation particularly complicated.Firstly,the 3-D topological structure of dissolved pores,vugs,fissures and throats inside cores is quantitatively scanned by CT imaging technology for its feature of vivid and damage-free.Secondly,3-D patterns of wormhole are obtained with CT scanning after core flooding by acid.Additionally,the porethroat network model is reconstructed with digital cores technology.Then,the size and ratio of pore and throat before and after core flooding by acid is analyzed and the absolute permeability of pore scale flow is numerically simulated to understand the fundamental influence of pores and vugs distribution and connectedness on wormhole propagation.Lastly,the wormhole pattern gained by CT scanning and simulating with two-scale model is compared.Meanwhile,the corrected two-scale model is utilized to simulate the wormhole propagation for matrix acidizing and acid fracturing of Sinian fractured-vuggy dolomite in Anyue gas field,Sichuan Basin.The optimized injection rate and volume were in agreement with the characteristic matrix acidizing operating curve,which indicates that the two-scale model was suitable for matrix acidizing optimization design of such formations.In addition,the simulated acid etched fracture length with considering the dynamic wormhole leakoff was consistent with the well testing interpreted result.
基金The authors thank financial support from the National Natural Science Fund(51404207)
文摘Conventional stimulation methods such as matrix acidizing,acid fracturing,or proppant fracturing have resulted in products that perform poorly and/or fail within months.Other options,such as water fracs with light sand,give better results but are prohibitively expensive.Mineral composition,brittleness index,stress regime,and petrophysical properties,which are favorable for creating complex fracture networks,can be obtained by geochemical and geomechanical analysis.The extended Reshaw and Pollard criterion shows that hydraulic fractures tend to be arrested by pre-existing natural fractures,and complex fracture networks would be created during fracturing.Additionally,the critical stressed faults theory indicates that the pre-existing natural fractures tend to slip with the shear mode as the pore fluid pressure increases.Rotating disk experiments and conductivity tests with artificial sheared plates have shown that flow channels can be etched at the location of scratches on fracture surfaces.Meanwhile,the carbonate cement in natural fractures can be chelated to form wormhole likely flow channels.Complex fracture networks with sufficient acid etched conductivity can be generated by water fracs with acid.A novel and economical volume stimulation strategy known as network acid fracturing has provided Tarim Oil Company the means to develope ultra-deep,ultra-high pressure,high temperature,and ultralow permeability but fractured gas reservoirs.Post-stimulation production performances of numerous wells with network acid fracturing are comparable to those with stimulated reservoir volumes.
文摘Tight multi-medium oil reservoirs are the main source of hydrocarbon resources around the world.Acid fracturing is the most effective technology to improve productivity in such reservoirs.As carbonates are primarily composed of dolomite and calcite,which are easily dissolved by hydrochloric acid,high-permeability region will be formed near the well along with the main artificial fracture when acid fracturing is implemented in tight multi-medium oil reservoirs.In this study,a comprehensive composite linear flow model was developed to simulate the transient pressure behavior of an acid fracturing vertical well in a naturally fractured vuggy carbonate reservoir.By utilizing Pedrosa's substitution,perturbation,Laplace transformation and Stehfest numerical inversion technol-ogy,the pressure behavior results were obtained in real time domain.Furthermore,the result of this model was validated by comparing with those of previous literature.Additionally,the influences of some prevailing parameters on the type curves were analyzed.Moreover,the proposed model was applied to an acid fracturing well to evaluate the effectiveness of acid fracturing measures,to demonstrate the practicability of the proposed model.
