Deep and ultra-deep reservoirs have gradually become the primary focus of hydrocarbon exploration as a result of a series of significant discoveries in deep hydrocarbon exploration worldwide.These reservoirs present u...Deep and ultra-deep reservoirs have gradually become the primary focus of hydrocarbon exploration as a result of a series of significant discoveries in deep hydrocarbon exploration worldwide.These reservoirs present unique challenges due to their deep burial depth(4500-8882 m),low matrix permeability,complex crustal stress conditions,high temperature and pressure(HTHP,150-200℃,105-155 MPa),coupled with high salinity of formation water.Consequently,the costs associated with their exploitation and development are exceptionally high.In deep and ultra-deep reservoirs,hydraulic fracturing is commonly used to achieve high and stable production.During hydraulic fracturing,a substantial volume of fluid is injected into the reservoir.However,statistical analysis reveals that the flowback rate is typically less than 30%,leaving the majority of the fluid trapped within the reservoir.Therefore,hydraulic fracturing in deep reservoirs not only enhances the reservoir permeability by creating artificial fractures but also damages reservoirs due to the fracturing fluids involved.The challenging“three-high”environment of a deep reservoir,characterized by high temperature,high pressure,and high salinity,exacerbates conventional forms of damage,including water sensitivity,retention of fracturing fluids,rock creep,and proppant breakage.In addition,specific damage mechanisms come into play,such as fracturing fluid decomposition at elevated temperatures and proppant diagenetic reactions at HTHP conditions.Presently,the foremost concern in deep oil and gas development lies in effectively assessing the damage inflicted on these reservoirs by hydraulic fracturing,comprehending the underlying mechanisms,and selecting appropriate solutions.It's noteworthy that the majority of existing studies on reservoir damage primarily focus on conventional reservoirs,with limited attention given to deep reservoirs and a lack of systematic summaries.In light of this,our approach entails initially summarizing the current knowledge pertaining to the types of fracturing fluids employed in deep and ultra-deep reservoirs.Subsequently,we delve into a systematic examination of the damage processes and mechanisms caused by fracturing fluids within the context of hydraulic fracturing in deep reservoirs,taking into account the unique reservoir characteristics of high temperature,high pressure,and high in-situ stress.In addition,we provide an overview of research progress related to high-temperature deep reservoir fracturing fluid and the damage of aqueous fracturing fluids to rock matrix,both artificial and natural fractures,and sand-packed fractures.We conclude by offering a summary of current research advancements and future directions,which hold significant potential for facilitating the efficient development of deep oil and gas reservoirs while effectively mitigating reservoir damage.展开更多
Deep shale gas reserves that have been fractured typically have many relatively close perforation holes. Due to theproximity of each fracture during the formation of the fracture network, there is significant stress i...Deep shale gas reserves that have been fractured typically have many relatively close perforation holes. Due to theproximity of each fracture during the formation of the fracture network, there is significant stress interference,which results in uneven fracture propagation. It is common practice to use “balls” to temporarily plug fractureopenings in order to lessen liquid intake and achieve uniform propagation in each cluster. In this study, a diameteroptimization model is introduced for these plugging balls based on a multi-cluster fracture propagationmodel and a perforation dynamic abrasion model. This approach relies on proper consideration of the multiphasenature of the considered problem and the interaction force between the involved fluid and solid phases. Accordingly,it can take into account the behavior of the gradually changing hole diameter due to proppant continuousperforation erosion. Moreover, it can provide useful information about the fluid-dynamic behavior of the consideredsystem before and after plugging. It is shown that when the diameter of the temporary plugging ball is1.2 times that of the perforation hole, the perforation holes of each cluster can be effectively blocked.展开更多
In order to improve the effectiveness of shale gas stimulated reservoir volume(SRV),it is necessary to evaluate and study the permeability of different types of induced fractures in shale and its influential factors.I...In order to improve the effectiveness of shale gas stimulated reservoir volume(SRV),it is necessary to evaluate and study the permeability of different types of induced fractures in shale and its influential factors.In this paper,the mineral composition characteristics,reservoir pore and fracture characteristics of shale were investigated,and the permeability of three types of induced fractures in shale(i.e.,in-situ closed type,shear self-propped type and single-layer propped type)was tested.Besides,the effects of fracture type,fracture surface roughness,carbonate content,shale bedding and confining pressure on the permeability of induced fractures in shale reservoirs were studied systematically.The following research results were obtained.First,the permeabilityepressure relationship of in-situ closed fracture is in accordance with the Walsh theory.The permeability decreases with the increase of confining pressure and it is in the range of 0.13e16.75 mD.In-situ closed fracture plays the same role in increasing the productivity of shale gas reservoirs with or without proppant filling or dislocation.Second,compared with in-situ closed fracture permeability,the shear self-propped fracture permeability is 1e2 orders of magnitude(7.53e88.48 mD)higher,and single-layer propped fracture permeability is 2e3 orders of magnitude(9.98e771.82 mD)higher.Third,the larger the fracture surface roughness,the higher the fracture permeability.And there is a better positive correlation between the fractal dimension and the fracture permeability.Fourth,the permeabilityepressure relationship of shear self-propped fracture and single-layer propped fracture is,to some extent,deviated from the Walsh theory,which reflects the influence of self-propped point crushing,proppant embedding and crushing.In conclusion,the experimental results can be used as the reference for the selection of shale fracturing technologies and the optimization of parameters.展开更多
The precise managed pressure drilling(MPD)technology is mainly used to deal with the difficulties encountered when oil and gas open hole sections with multiple pressure systems and the strata with narrow safety densit...The precise managed pressure drilling(MPD)technology is mainly used to deal with the difficulties encountered when oil and gas open hole sections with multiple pressure systems and the strata with narrow safety density window are drilled through.If its liner cementing is carried out according to the conventional method,lost circulation is inevitable in the process of cementing while the displacement efficiency of smallclearance liner cementing is satisfied.If the positive and inverse injection technology is adopted,the cementing quality cannot meet the requirements of later well test engineering of ultradeep wells.In this paper,the cementing operation ofØ114.3 mm liner in Well Longgang 70 which was drilled in the Jiange structure of the Sichuan Basin was taken as an example to explore the application of the cementing technology based on the precise MPD and pressure balancing method to the cementing of long open-hole sections(as long as 859 m)with both high and low pressures running through multiple reservoirs.On the one hand,the technical measures were taken specifically to ensure the annulus filling efficiency of slurry and the pressure balance in the whole process of cementing.And on the other hand,the annulus pressure balance was precisely controlled by virtue of precise MPD devices and by injecting heavy weight drilling fluids through central pipes,and thus the wellbore pressure was kept steady in the whole process of cementing in the strata with narrow safety density window.It is indicated thatØ114.3 mm liner cementing in this well is good with qualified pressure tests and no channeling emerges at a funnel during the staged density reduction.It is concluded that this method can enhance the liner cementing quality of complex ultradeep gas wells and improve the wellbore conditions for the later safe well tests of high-pressure gas wells.展开更多
The development of shale gas is faced with low reservoir porosity,low reservoir permeability and high formation fracture pressure.In order to deal with these problems,this paper selected shale samples from the bottom ...The development of shale gas is faced with low reservoir porosity,low reservoir permeability and high formation fracture pressure.In order to deal with these problems,this paper selected shale samples from the bottom of the Lower Silurian LongmaxieWufeng Formation of Upper Ordovician in the Weiyuan Block of the southern Sichuan Basin as the research objects.After acid dissolution experiments were carried out,the microstructures and the mechanical parameters of shale after acidizing treatment were investigated by means of X-ray diffraction,scanning electron microscopy and triaxial mechanical test.Then,the effect of acidizing treatment on the microstructures and the mechanical properties of shale were analyzed.And the following research results were obtained.First,after acidizing treatment,the carbonate mineral content of shale decreases and the number and size of pores increase.In the process of dissolution,micro-fractures occur,leading to the increase of shale porosity and permeability.Second,after acidizing treatment,the mechanical properties of shale change.Its deformation mode transforms gradually from elasticebrittle deformation to elasticeplastic deformation,and its fracture mode transits from brittle to semi-brittle and semi-ductile.Third,after shale is treated with the acid with the concentration of 15%for 240 min,its permeability is increased by 3.09 times.After 3 days,its porosity is increased by 1.65 times.And after 7 days,its compressive strength,Young's modulus and brittleness index are decreased by 50.1%,58.1%and 32.8%,respectively.Fourth,the mechanical parameters of shale of the LongmaxieWufeng Formation in the Weiyuan Block is in a quadratic relationship with an average pore size and permeability and in a quadratic or linear relationship with porosity,and their correlation is strong.In conclusion,the research results provide technical support for the prediction of the mechanical parameters of shale in this block after acidizing treatment and for the design of acid fracturing scheme.展开更多
Fracture propagation in shale under in situ conditions is a critical but poorly understood mechanical process in hydraulic fracturing for deep shale gas reservoirs. To address this, hydraulic fracturing experiments we...Fracture propagation in shale under in situ conditions is a critical but poorly understood mechanical process in hydraulic fracturing for deep shale gas reservoirs. To address this, hydraulic fracturing experiments were conducted on hollow double-wing crack specimens of the Longmaxi shale under conditions simulating the ground surface(confining pressure σ_(cp)=0, room temperature(Tr)) and at depths of 1600 m(σ_(cp)=40 MPa, Ti=70 ℃) and 3300 m(σ_(cp)=80 MPa, high temperature Ti=110 ℃) in the study area.High in situ stress was found to significantly increase fracture toughness through constrained microcracking and particle frictional bridging mechanisms. Increasing the temperature enhances rather than weakens the fracture resistance because it increases the grain debonding length, which dissipates more plastic energy and enlarges grains to close microdefects and generate compressive stress to inhibit microcracking. Interestingly, the fracture toughness anisotropy in the shale was found to be nearly constant across burial depths, despite reported variations with increasing confining pressure. Heated water was not found to be as important as the in situ environment in influencing shale fracture. These findings emphasize the need to test the fracture toughness of deep shales under coupled in situ stress and temperature conditions rather than focusing on either in situ stress or temperature alone.展开更多
No shale-rock physical model has been established in the observation coordinate system.To this end,this paper carried out anisotropic wave velocity tests on shale rock and compared the Thomsen,Daley,and Berryman solut...No shale-rock physical model has been established in the observation coordinate system.To this end,this paper carried out anisotropic wave velocity tests on shale rock and compared the Thomsen,Daley,and Berryman solutions to characterize anisotropic acoustic wave velocity.Finally,the Daley solution was selected.Based on basic rock physical models,such as SCA and DEM methods,and combined with the Daley solution,an anisotropic shale-rock physical model was established in the observation coordinate system and applied in Well B1 in the Luzhou area,Sichuan Basin.Our research conclusions were as follows:1.for the samples from the same core,the P-wave velocities in three directions were in the order VP11>VP45>VP33,shear wave velocity VS11 was the largest,but VS33 and VS45 did not follow the law of Vs33>Vs45 for some samples;2.the Daley solution,which not only considers the accuracy requirements but also has a complete expression of P-,SV-,and SH-waves,is most suitable for characterization of anisotropic wave velocity in this study area;3.the rock physical model constructed in the observation coordinate system has high accuracy,in which the absolute value of the relative error of the P-wave slowness was between 0%and 5.05%(0.55%on average),and that of shear-wave slowness was between 0%and 6.05%(0.59%on average);4.the acoustic waves recorded in Well B1 in the observation coordinate system were very different from those in the constitutive coordinate system.The relative difference of the P-wave was between 6.76%and 30.84%(14.68%on average),and that of the S-wave was between 7.00%and 23.44%(13.99%on average).The acoustic slowness measured in the observation coordinate system,such as in a deviated well or a horizontal well section,must be converted to the constitutive coordinate system before it can be used in subsequent engineering applications;5.the anisotropic shale-rock physical model built in the observation coordinate system proposed in this paper can provide basic data and guidance for subsequent pore pressure prediction,geomechanical modeling,and fracturing stimulation design for deviated and horizontal wells.展开更多
In oilfield fracturing construction, to solve the technical problems such as poor dissolution effect and long dissolution time of polymer drag reducer powder, the rheological regulator, phase transfer agent, organic s...In oilfield fracturing construction, to solve the technical problems such as poor dissolution effect and long dissolution time of polymer drag reducer powder, the rheological regulator, phase transfer agent, organic solvent, and drag reducer powder were compounded to prepare a drag reducer emulsion that was soluble in water. The stability of the drag reducer emulsion was observed at room temperature for 90 days. The effects of the rheological regulator, phase transfer agent, and organic solvent on the stability and solubility of the drag reducer emulsion were studied. The dissolution time, dissolution effect, viscosity of the aqueous solution, and drag reduction performance of the drag reducer emulsion were evaluated. The results show the stability rate of the drag reducer emulsion prepared by MOST-1 rheological regulator, BHJ-8 and BHJ-6 compound phase inversion agent, ethylene glycol ether and 120 - 140 mesh powder can reach 97% at room temperature for 90 days. Compared with the drag reducer powder, when the aqueous solution concentration is 0.1%, the dissolution time is only 28 s, the viscosity can be increased by 30%, and the drag reduction rate can be increased by up to 8%.展开更多
For mitigating the hazards of slurry flowing back into the casing after liner cementing,the deficiency of slurry backflow prevention structure of current liner hangers at home and aboard was analyzed in this paper.The...For mitigating the hazards of slurry flowing back into the casing after liner cementing,the deficiency of slurry backflow prevention structure of current liner hangers at home and aboard was analyzed in this paper.Then,a structurally new casing plug,i.e.,a semi-hollow casing plug was designed and developed.And it,combined with the hanger,was tested on site.And the following research results were obtained.First,the deficiency of the slurry backflow prevention structure of liner hanger,is that the locking mechanism on the drill pipe plug is damaged before it reaches the casing plug and matches with each other.Second,the inner bore of the semi-hollow casing plug is designed as a bend hole,which has a hollow round hole in its upper part and a solid column in its lower part.Third,during the cementing operation,the drill pipe plug enters into the semi-hollow casing plug once it gets to the position of hanger.And it is stuck at the bend and cannot go down anymore.Consequently it is integrated with the casing plug as a whole part.Fourth,when the shear pin goes down to the setting seat through the casing string under the force of drilling fluid,the solid column at the lower part of the semi-hollow casing plug is squeezed into the inner hole of the seat.In this situation,the backflow of cement slurry can be prevented only by using sealing elements and locking device on the casing plug instead of by using drill pipe plug.Fifth,field tests show that the cement top of test wells is only 24 m higher than the designed value while that of offset wells is 59 m higher.Obviously,the former is 50%less than the latter.In conclusion,this newly developed semi-hollow casing plug matches well with hangers,having no negative effects on cementing operation,so the cement top after cementing can be well controlled.展开更多
Large-scale hydraulic fracturing combined with horizontal well drilling is the key technology in shale gas development.But poor cementing quality is a crucial bottleneck restricting well completion and reservoir stimu...Large-scale hydraulic fracturing combined with horizontal well drilling is the key technology in shale gas development.But poor cementing quality is a crucial bottleneck restricting well completion and reservoir stimulation.In this paper,the shale gas development blocks in the Sichuan Basin were taken as the examples to explore the process and support measures that can be used to keep the mechanical integrity of cement sheath under the effect of hydraulic fracturing.It is indicated that the near-bit three-centralizer drifting BHA used for casing stiffness simulation can decrease the casing running difficulty in the long horizontal section of a shale gas well and increase the time efficiency and safety of casing running;that the flushing efficiency of high-efficiency oil flushing spacer fluid system is higher than 90%from room temperature to 120℃,so it can guarantee the displacement efficiency of cement slurry to the oil-based drilling fluid and the effective cementing of borehole wall;that the performance of anti-channeling ductile cement slurry used in the cementing of long horizontal sections in this area after it is set is confirmed,with the elastic modulus of set cement being lower than 7 GPa and triaxial strength being higher than 40 MPa,so as to alleviate or avoid the damage to cement sheath in the process of fracturing;and that cementing quality is improved by applying the support technologies,e.g.drilling fluid adjustment,pre-stress cementing and ground high-pressure pumping.During 2015e2016,these cementing technologies were applied in 85 wells in the Sichuan Basin.The average well depth of these wells is 4832 m,the average length of horizontal sections is 1560 m and the quality rate of well cementing is 89.58%.During the waiting-on-cement(WOC)time after well cementing,there is no sustained casing pressure.And gas channeling in the annulus during well drilling,completion and test is improved remarkably.It is concluded that this suite of technologies can guarantee and improve the cementing quality of long horizontal sections in shale gas wells and provides good cementing conditions for shale gas development.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 recent years,shale oil and gas development has been thriving in China.However,the shale oil and gas production always suffers a rapid decline.Based on the analysis of a large amount of former theories and experienc...In recent years,shale oil and gas development has been thriving in China.However,the shale oil and gas production always suffers a rapid decline.Based on the analysis of a large amount of former theories and experiences,a summary of acid treatment stimulation methods in shale oil and gas is presented,and the acid stimulation mechanism is analyzed.The mainstream technique in acid treatments includes:acid wash,matrix acidizing,prop fracturing with acid preflush,and multi-stage alternate-inject acid fracturing.The main stimulation mechanism of acid treatment can be summarized into 3 categories:a)the influence on shale matrix,namely the acid-induced increase of porosity and permeability,and reduce of wetting property of shale;b)the influence on rock mechanical properties,namely shale brittleness and toughness,and even Young Modulus to some degree;c)the influence on fractures'conductivity,caused by the fact that acid dissolves calcite-enrichment area in priority,and then increases roughness on fracture surface.In room temperature and atmospheric pressure,acid reduces fractures'conductivity,while in pressurized condition,the acid-soaked fractures'conductivity is higher than the conductivity of non-acid-soaked fractures.These knowledges would provide useful reference for furthering stimulation techniques and processes in shale oil and gas development.展开更多
In this work,numerical models were developed to investigate the critical inclination of a pipeline to eliminate the water accumulation at the floor of the pipe carrying oil-water fluid.Computational fluid dynamics sof...In this work,numerical models were developed to investigate the critical inclination of a pipeline to eliminate the water accumulation at the floor of the pipe carrying oil-water fluid.Computational fluid dynamics software was used to establish a geometric model of the pipe with various inclination angles,and a grid-independent verification was conducted to determine a reasonable meshing method.Quantitative relationships were determined between the pipe inclination angle and the affecting factors including the flow velocity,viscosity and the pipe diameter,where the water accumulation would not be able to occur.Generally,the critical inclination angle increases with the fluid flow velocity.The refluxing of water is the key mechanism causing the water accumulation at the bottom of the pipe.In addition to the fluid flow velocity,an increase in fluid viscosity and a decrease in the pipe diameter cause an increase of the critical inclination angle that the water phase can be carried away by oil.The model can be used to determine the critical inclination of pipelines carrying oil-water fluid to cause the water accumulation and the operating conditions that can eliminate the accumulation of water phase at the pipe floor.展开更多
A new quantitative risk assessment method for hot work is proposed based on the analytic hierarchy process(AHP)and fuzzy comprehensive evaluation(FCE).It can help pipeline companies realize the risk management of hot ...A new quantitative risk assessment method for hot work is proposed based on the analytic hierarchy process(AHP)and fuzzy comprehensive evaluation(FCE).It can help pipeline companies realize the risk management of hot work and further ensure the safe operation of oil and gas pipelines.Taking one natural gas pipeline in China as an example,this paper evaluates the risk of a single hot work in the spring of one natural gas pipeline in a high consequence region.First of all,the risk factors are determined with reference to the job safety analysis(JSA),and then experts were invited to fill out a questionnaire to collect their opinions.According to the results of the questionnaire,AHP is used to calculate the weight coefficients of the evaluation indicators,and FCE is used to evaluate the risk level of hot work.After calculation,the comprehensive risk score of hot work is 40.888.It belongs to a"general risk".This method can not only quantitatively evaluate the risk levels of hot work,but also reasonably sort the importance of various risk factors.It is helpful for the effective management of hot work and provides suggestions for implementing control measures.展开更多
基金Dao-Bing Wang was supported by the Beijing Natural Science Foundation Project(No.3222030)the National Natural Science Foundation of China(No.52274002)+1 种基金the PetroChina Science and Technology Innovation Foundation Project(No.2021DQ02-0201)Fu-Jian Zhou was supported by the National Natural Science Foundation of China(No.52174045).
文摘Deep and ultra-deep reservoirs have gradually become the primary focus of hydrocarbon exploration as a result of a series of significant discoveries in deep hydrocarbon exploration worldwide.These reservoirs present unique challenges due to their deep burial depth(4500-8882 m),low matrix permeability,complex crustal stress conditions,high temperature and pressure(HTHP,150-200℃,105-155 MPa),coupled with high salinity of formation water.Consequently,the costs associated with their exploitation and development are exceptionally high.In deep and ultra-deep reservoirs,hydraulic fracturing is commonly used to achieve high and stable production.During hydraulic fracturing,a substantial volume of fluid is injected into the reservoir.However,statistical analysis reveals that the flowback rate is typically less than 30%,leaving the majority of the fluid trapped within the reservoir.Therefore,hydraulic fracturing in deep reservoirs not only enhances the reservoir permeability by creating artificial fractures but also damages reservoirs due to the fracturing fluids involved.The challenging“three-high”environment of a deep reservoir,characterized by high temperature,high pressure,and high salinity,exacerbates conventional forms of damage,including water sensitivity,retention of fracturing fluids,rock creep,and proppant breakage.In addition,specific damage mechanisms come into play,such as fracturing fluid decomposition at elevated temperatures and proppant diagenetic reactions at HTHP conditions.Presently,the foremost concern in deep oil and gas development lies in effectively assessing the damage inflicted on these reservoirs by hydraulic fracturing,comprehending the underlying mechanisms,and selecting appropriate solutions.It's noteworthy that the majority of existing studies on reservoir damage primarily focus on conventional reservoirs,with limited attention given to deep reservoirs and a lack of systematic summaries.In light of this,our approach entails initially summarizing the current knowledge pertaining to the types of fracturing fluids employed in deep and ultra-deep reservoirs.Subsequently,we delve into a systematic examination of the damage processes and mechanisms caused by fracturing fluids within the context of hydraulic fracturing in deep reservoirs,taking into account the unique reservoir characteristics of high temperature,high pressure,and high in-situ stress.In addition,we provide an overview of research progress related to high-temperature deep reservoir fracturing fluid and the damage of aqueous fracturing fluids to rock matrix,both artificial and natural fractures,and sand-packed fractures.We conclude by offering a summary of current research advancements and future directions,which hold significant potential for facilitating the efficient development of deep oil and gas reservoirs while effectively mitigating reservoir damage.
基金supported by the National Natural Science Foundation of China (No.U21B2071).
文摘Deep shale gas reserves that have been fractured typically have many relatively close perforation holes. Due to theproximity of each fracture during the formation of the fracture network, there is significant stress interference,which results in uneven fracture propagation. It is common practice to use “balls” to temporarily plug fractureopenings in order to lessen liquid intake and achieve uniform propagation in each cluster. In this study, a diameteroptimization model is introduced for these plugging balls based on a multi-cluster fracture propagationmodel and a perforation dynamic abrasion model. This approach relies on proper consideration of the multiphasenature of the considered problem and the interaction force between the involved fluid and solid phases. Accordingly,it can take into account the behavior of the gradually changing hole diameter due to proppant continuousperforation erosion. Moreover, it can provide useful information about the fluid-dynamic behavior of the consideredsystem before and after plugging. It is shown that when the diameter of the temporary plugging ball is1.2 times that of the perforation hole, the perforation holes of each cluster can be effectively blocked.
基金supported by National Major Science and Technology Project“Horizontal well fracturing design optimization system”(No.2016ZX05023-001).
文摘In order to improve the effectiveness of shale gas stimulated reservoir volume(SRV),it is necessary to evaluate and study the permeability of different types of induced fractures in shale and its influential factors.In this paper,the mineral composition characteristics,reservoir pore and fracture characteristics of shale were investigated,and the permeability of three types of induced fractures in shale(i.e.,in-situ closed type,shear self-propped type and single-layer propped type)was tested.Besides,the effects of fracture type,fracture surface roughness,carbonate content,shale bedding and confining pressure on the permeability of induced fractures in shale reservoirs were studied systematically.The following research results were obtained.First,the permeabilityepressure relationship of in-situ closed fracture is in accordance with the Walsh theory.The permeability decreases with the increase of confining pressure and it is in the range of 0.13e16.75 mD.In-situ closed fracture plays the same role in increasing the productivity of shale gas reservoirs with or without proppant filling or dislocation.Second,compared with in-situ closed fracture permeability,the shear self-propped fracture permeability is 1e2 orders of magnitude(7.53e88.48 mD)higher,and single-layer propped fracture permeability is 2e3 orders of magnitude(9.98e771.82 mD)higher.Third,the larger the fracture surface roughness,the higher the fracture permeability.And there is a better positive correlation between the fractal dimension and the fracture permeability.Fourth,the permeabilityepressure relationship of shear self-propped fracture and single-layer propped fracture is,to some extent,deviated from the Walsh theory,which reflects the influence of self-propped point crushing,proppant embedding and crushing.In conclusion,the experimental results can be used as the reference for the selection of shale fracturing technologies and the optimization of parameters.
文摘The precise managed pressure drilling(MPD)technology is mainly used to deal with the difficulties encountered when oil and gas open hole sections with multiple pressure systems and the strata with narrow safety density window are drilled through.If its liner cementing is carried out according to the conventional method,lost circulation is inevitable in the process of cementing while the displacement efficiency of smallclearance liner cementing is satisfied.If the positive and inverse injection technology is adopted,the cementing quality cannot meet the requirements of later well test engineering of ultradeep wells.In this paper,the cementing operation ofØ114.3 mm liner in Well Longgang 70 which was drilled in the Jiange structure of the Sichuan Basin was taken as an example to explore the application of the cementing technology based on the precise MPD and pressure balancing method to the cementing of long open-hole sections(as long as 859 m)with both high and low pressures running through multiple reservoirs.On the one hand,the technical measures were taken specifically to ensure the annulus filling efficiency of slurry and the pressure balance in the whole process of cementing.And on the other hand,the annulus pressure balance was precisely controlled by virtue of precise MPD devices and by injecting heavy weight drilling fluids through central pipes,and thus the wellbore pressure was kept steady in the whole process of cementing in the strata with narrow safety density window.It is indicated thatØ114.3 mm liner cementing in this well is good with qualified pressure tests and no channeling emerges at a funnel during the staged density reduction.It is concluded that this method can enhance the liner cementing quality of complex ultradeep gas wells and improve the wellbore conditions for the later safe well tests of high-pressure gas wells.
基金supported by the National Natural Science Foundation of China"Flow mechanism of induced fractures and conductivity prediction model of shale fracture network in deep strata under high pressure"(No.:51704251)"Fracturing and acidizing of low-permeability and tight reservoirs"(No.:51525404).
文摘The development of shale gas is faced with low reservoir porosity,low reservoir permeability and high formation fracture pressure.In order to deal with these problems,this paper selected shale samples from the bottom of the Lower Silurian LongmaxieWufeng Formation of Upper Ordovician in the Weiyuan Block of the southern Sichuan Basin as the research objects.After acid dissolution experiments were carried out,the microstructures and the mechanical parameters of shale after acidizing treatment were investigated by means of X-ray diffraction,scanning electron microscopy and triaxial mechanical test.Then,the effect of acidizing treatment on the microstructures and the mechanical properties of shale were analyzed.And the following research results were obtained.First,after acidizing treatment,the carbonate mineral content of shale decreases and the number and size of pores increase.In the process of dissolution,micro-fractures occur,leading to the increase of shale porosity and permeability.Second,after acidizing treatment,the mechanical properties of shale change.Its deformation mode transforms gradually from elasticebrittle deformation to elasticeplastic deformation,and its fracture mode transits from brittle to semi-brittle and semi-ductile.Third,after shale is treated with the acid with the concentration of 15%for 240 min,its permeability is increased by 3.09 times.After 3 days,its porosity is increased by 1.65 times.And after 7 days,its compressive strength,Young's modulus and brittleness index are decreased by 50.1%,58.1%and 32.8%,respectively.Fourth,the mechanical parameters of shale of the LongmaxieWufeng Formation in the Weiyuan Block is in a quadratic relationship with an average pore size and permeability and in a quadratic or linear relationship with porosity,and their correlation is strong.In conclusion,the research results provide technical support for the prediction of the mechanical parameters of shale in this block after acidizing treatment and for the design of acid fracturing scheme.
基金supported by the National Natural Science Foundation of China(No.12172240).
文摘Fracture propagation in shale under in situ conditions is a critical but poorly understood mechanical process in hydraulic fracturing for deep shale gas reservoirs. To address this, hydraulic fracturing experiments were conducted on hollow double-wing crack specimens of the Longmaxi shale under conditions simulating the ground surface(confining pressure σ_(cp)=0, room temperature(Tr)) and at depths of 1600 m(σ_(cp)=40 MPa, Ti=70 ℃) and 3300 m(σ_(cp)=80 MPa, high temperature Ti=110 ℃) in the study area.High in situ stress was found to significantly increase fracture toughness through constrained microcracking and particle frictional bridging mechanisms. Increasing the temperature enhances rather than weakens the fracture resistance because it increases the grain debonding length, which dissipates more plastic energy and enlarges grains to close microdefects and generate compressive stress to inhibit microcracking. Interestingly, the fracture toughness anisotropy in the shale was found to be nearly constant across burial depths, despite reported variations with increasing confining pressure. Heated water was not found to be as important as the in situ environment in influencing shale fracture. These findings emphasize the need to test the fracture toughness of deep shales under coupled in situ stress and temperature conditions rather than focusing on either in situ stress or temperature alone.
基金supported by the Post Doctoral Project of Southwest Oil and Gas Field Research on Geomechanics and Effective Fracturing Factors of Deep Shale” (No. 20210302-31)the Scientific Research Project of Southwest Oil and Gas Field Branch “Geological Engineering Integration of Well Block Yang101”。
文摘No shale-rock physical model has been established in the observation coordinate system.To this end,this paper carried out anisotropic wave velocity tests on shale rock and compared the Thomsen,Daley,and Berryman solutions to characterize anisotropic acoustic wave velocity.Finally,the Daley solution was selected.Based on basic rock physical models,such as SCA and DEM methods,and combined with the Daley solution,an anisotropic shale-rock physical model was established in the observation coordinate system and applied in Well B1 in the Luzhou area,Sichuan Basin.Our research conclusions were as follows:1.for the samples from the same core,the P-wave velocities in three directions were in the order VP11>VP45>VP33,shear wave velocity VS11 was the largest,but VS33 and VS45 did not follow the law of Vs33>Vs45 for some samples;2.the Daley solution,which not only considers the accuracy requirements but also has a complete expression of P-,SV-,and SH-waves,is most suitable for characterization of anisotropic wave velocity in this study area;3.the rock physical model constructed in the observation coordinate system has high accuracy,in which the absolute value of the relative error of the P-wave slowness was between 0%and 5.05%(0.55%on average),and that of shear-wave slowness was between 0%and 6.05%(0.59%on average);4.the acoustic waves recorded in Well B1 in the observation coordinate system were very different from those in the constitutive coordinate system.The relative difference of the P-wave was between 6.76%and 30.84%(14.68%on average),and that of the S-wave was between 7.00%and 23.44%(13.99%on average).The acoustic slowness measured in the observation coordinate system,such as in a deviated well or a horizontal well section,must be converted to the constitutive coordinate system before it can be used in subsequent engineering applications;5.the anisotropic shale-rock physical model built in the observation coordinate system proposed in this paper can provide basic data and guidance for subsequent pore pressure prediction,geomechanical modeling,and fracturing stimulation design for deviated and horizontal wells.
文摘In oilfield fracturing construction, to solve the technical problems such as poor dissolution effect and long dissolution time of polymer drag reducer powder, the rheological regulator, phase transfer agent, organic solvent, and drag reducer powder were compounded to prepare a drag reducer emulsion that was soluble in water. The stability of the drag reducer emulsion was observed at room temperature for 90 days. The effects of the rheological regulator, phase transfer agent, and organic solvent on the stability and solubility of the drag reducer emulsion were studied. The dissolution time, dissolution effect, viscosity of the aqueous solution, and drag reduction performance of the drag reducer emulsion were evaluated. The results show the stability rate of the drag reducer emulsion prepared by MOST-1 rheological regulator, BHJ-8 and BHJ-6 compound phase inversion agent, ethylene glycol ether and 120 - 140 mesh powder can reach 97% at room temperature for 90 days. Compared with the drag reducer powder, when the aqueous solution concentration is 0.1%, the dissolution time is only 28 s, the viscosity can be increased by 30%, and the drag reduction rate can be increased by up to 8%.
文摘For mitigating the hazards of slurry flowing back into the casing after liner cementing,the deficiency of slurry backflow prevention structure of current liner hangers at home and aboard was analyzed in this paper.Then,a structurally new casing plug,i.e.,a semi-hollow casing plug was designed and developed.And it,combined with the hanger,was tested on site.And the following research results were obtained.First,the deficiency of the slurry backflow prevention structure of liner hanger,is that the locking mechanism on the drill pipe plug is damaged before it reaches the casing plug and matches with each other.Second,the inner bore of the semi-hollow casing plug is designed as a bend hole,which has a hollow round hole in its upper part and a solid column in its lower part.Third,during the cementing operation,the drill pipe plug enters into the semi-hollow casing plug once it gets to the position of hanger.And it is stuck at the bend and cannot go down anymore.Consequently it is integrated with the casing plug as a whole part.Fourth,when the shear pin goes down to the setting seat through the casing string under the force of drilling fluid,the solid column at the lower part of the semi-hollow casing plug is squeezed into the inner hole of the seat.In this situation,the backflow of cement slurry can be prevented only by using sealing elements and locking device on the casing plug instead of by using drill pipe plug.Fifth,field tests show that the cement top of test wells is only 24 m higher than the designed value while that of offset wells is 59 m higher.Obviously,the former is 50%less than the latter.In conclusion,this newly developed semi-hollow casing plug matches well with hangers,having no negative effects on cementing operation,so the cement top after cementing can be well controlled.
基金Project supported by the National Major Science and Technology Project“Development of large-scale oil/gas fields and CBM”0“New technologies for improving the cementing quality and wellbore integrity under the condition of large-scale volume fracturing”(No.2016ZX05022-005).
文摘Large-scale hydraulic fracturing combined with horizontal well drilling is the key technology in shale gas development.But poor cementing quality is a crucial bottleneck restricting well completion and reservoir stimulation.In this paper,the shale gas development blocks in the Sichuan Basin were taken as the examples to explore the process and support measures that can be used to keep the mechanical integrity of cement sheath under the effect of hydraulic fracturing.It is indicated that the near-bit three-centralizer drifting BHA used for casing stiffness simulation can decrease the casing running difficulty in the long horizontal section of a shale gas well and increase the time efficiency and safety of casing running;that the flushing efficiency of high-efficiency oil flushing spacer fluid system is higher than 90%from room temperature to 120℃,so it can guarantee the displacement efficiency of cement slurry to the oil-based drilling fluid and the effective cementing of borehole wall;that the performance of anti-channeling ductile cement slurry used in the cementing of long horizontal sections in this area after it is set is confirmed,with the elastic modulus of set cement being lower than 7 GPa and triaxial strength being higher than 40 MPa,so as to alleviate or avoid the damage to cement sheath in the process of fracturing;and that cementing quality is improved by applying the support technologies,e.g.drilling fluid adjustment,pre-stress cementing and ground high-pressure pumping.During 2015e2016,these cementing technologies were applied in 85 wells in the Sichuan Basin.The average well depth of these wells is 4832 m,the average length of horizontal sections is 1560 m and the quality rate of well cementing is 89.58%.During the waiting-on-cement(WOC)time after well cementing,there is no sustained casing pressure.And gas channeling in the annulus during well drilling,completion and test is improved remarkably.It is concluded that this suite of technologies can guarantee and improve the cementing quality of long horizontal sections in shale gas wells and provides good cementing conditions for shale gas development.
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).
基金supported jointly by the National Natural Science Foundation of China(No.51574197)Educational Commission of Sichuan Province of China(No.16ZA0071).
文摘In recent years,shale oil and gas development has been thriving in China.However,the shale oil and gas production always suffers a rapid decline.Based on the analysis of a large amount of former theories and experiences,a summary of acid treatment stimulation methods in shale oil and gas is presented,and the acid stimulation mechanism is analyzed.The mainstream technique in acid treatments includes:acid wash,matrix acidizing,prop fracturing with acid preflush,and multi-stage alternate-inject acid fracturing.The main stimulation mechanism of acid treatment can be summarized into 3 categories:a)the influence on shale matrix,namely the acid-induced increase of porosity and permeability,and reduce of wetting property of shale;b)the influence on rock mechanical properties,namely shale brittleness and toughness,and even Young Modulus to some degree;c)the influence on fractures'conductivity,caused by the fact that acid dissolves calcite-enrichment area in priority,and then increases roughness on fracture surface.In room temperature and atmospheric pressure,acid reduces fractures'conductivity,while in pressurized condition,the acid-soaked fractures'conductivity is higher than the conductivity of non-acid-soaked fractures.These knowledges would provide useful reference for furthering stimulation techniques and processes in shale oil and gas development.
文摘In this work,numerical models were developed to investigate the critical inclination of a pipeline to eliminate the water accumulation at the floor of the pipe carrying oil-water fluid.Computational fluid dynamics software was used to establish a geometric model of the pipe with various inclination angles,and a grid-independent verification was conducted to determine a reasonable meshing method.Quantitative relationships were determined between the pipe inclination angle and the affecting factors including the flow velocity,viscosity and the pipe diameter,where the water accumulation would not be able to occur.Generally,the critical inclination angle increases with the fluid flow velocity.The refluxing of water is the key mechanism causing the water accumulation at the bottom of the pipe.In addition to the fluid flow velocity,an increase in fluid viscosity and a decrease in the pipe diameter cause an increase of the critical inclination angle that the water phase can be carried away by oil.The model can be used to determine the critical inclination of pipelines carrying oil-water fluid to cause the water accumulation and the operating conditions that can eliminate the accumulation of water phase at the pipe floor.
文摘A new quantitative risk assessment method for hot work is proposed based on the analytic hierarchy process(AHP)and fuzzy comprehensive evaluation(FCE).It can help pipeline companies realize the risk management of hot work and further ensure the safe operation of oil and gas pipelines.Taking one natural gas pipeline in China as an example,this paper evaluates the risk of a single hot work in the spring of one natural gas pipeline in a high consequence region.First of all,the risk factors are determined with reference to the job safety analysis(JSA),and then experts were invited to fill out a questionnaire to collect their opinions.According to the results of the questionnaire,AHP is used to calculate the weight coefficients of the evaluation indicators,and FCE is used to evaluate the risk level of hot work.After calculation,the comprehensive risk score of hot work is 40.888.It belongs to a"general risk".This method can not only quantitatively evaluate the risk levels of hot work,but also reasonably sort the importance of various risk factors.It is helpful for the effective management of hot work and provides suggestions for implementing control measures.
