As shale gas technology has advanced,the horizontal well fracturing model has seen widespread use,leading to substantial improvements in industrial gas output from shale gas wells.Nevertheless,a swift decline in the p...As shale gas technology has advanced,the horizontal well fracturing model has seen widespread use,leading to substantial improvements in industrial gas output from shale gas wells.Nevertheless,a swift decline in the productivity of individual wells remains a challenge that must be addressed throughout the development process.In this study,gas wells with two different wellbore trajectory structures are considered,and the OLGA software is exploited to perform transient calculations on various tubing depth models.The results can be articulated as follows.In terms of flow patterns:for the deep well A1(upward-buckled),slug flow occurs in the Kick-off Point position and above;for the deep well B1(downward-inclined),slug flow only occurs in the horizontal section.Wells with downward-inclined horizontal sections are more prone to liquid accumulation issues.In terms of comparison to conventional wells,it is shown that deep shale gas wells have longer normal production durations and experience liquid accumulation later than conventional wells.With regard to optimal tubing placement:for well A1(upward-buckled),it is recommended to place tubing at the Kick-off Point position;for well B1(downward-inclined),it is recommended to place tubing at the lower heel of the horizontal section.Finally,in terms of production performance:well A1(upward-buckled)outperforms well B1(downward-inclined)in terms of production and fluid accumulation.In particular,the deep well A1 is 1.94 times more productive and 1.3 times longer to produce than conventional wells.Deep well B1 is 1.87 times more productive and 1.34 times longer than conventional wells.展开更多
Pressure control in deep shale gas horizontal wells can reduce the stress sensitivity of hydraulic fractures and improve the estimated ultimate recovery(EUR).In this study,a hydraulic fracture stress sensitivity model...Pressure control in deep shale gas horizontal wells can reduce the stress sensitivity of hydraulic fractures and improve the estimated ultimate recovery(EUR).In this study,a hydraulic fracture stress sensitivity model is proposed to characterize the effect of pressure drop rate on fracture permeability.Furthermore,a production prediction model is introduced accounting for a non-uniform hydraulic fracture conductivity distribution.The results reveal that increasing the fracture conductivity leads to a rapid daily production increase in the early stages.However,above 0.50 D·cm,a further increase in the fracture conductivity has a limited effect on shale gas production growth.The initial production is lower under pressure-controlled conditions than that under pressure-release.For extended pressure control durations,the cumulative production initially increases and then decreases.For a fracture conductivity of 0.10 D·cm,the increase in production output under controlled-pressure conditions is~35%.For representative deep shale gas wells(Southern Sichuan,China),if the pressure drop rate under controlled-pressure conditions is reduced from 0.19 to 0.04 MPa/d,the EUR increase for 5 years of pressure-controlled production is 41.0 million,with an increase percentage of~29%.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
The pivotal areas for the extensive and effective exploitation of shale gas in the Southern Sichuan Basin have recently transitioned from mid-deep layers to deep layers.Given challenges such as intricate data analysis...The pivotal areas for the extensive and effective exploitation of shale gas in the Southern Sichuan Basin have recently transitioned from mid-deep layers to deep layers.Given challenges such as intricate data analysis,absence of effective assessment methodologies,real-time control strategies,and scarce knowledge of the factors influencing deep gas wells in the so-called flowback stage,a comprehensive study was undertaken on over 160 deep gas wells in Luzhou block utilizing linear flow models and advanced big data analytics techniques.The research results show that:(1)The flowback stage of a deep gas well presents the characteristics of late gas channeling,high flowback rate after gas channeling,low 30-day flowback rate,and high flowback rate corresponding to peak production;(2)The comprehensive parameter AcmKm1/2 in the flowback stage exhibits a strong correlation with the Estimated Ultimate Recovery(EUR),allowing for the establishment of a standardized chart to evaluate EUR classification in typical shale gas wells during this stage.This enables quantitative assessment of gas well EUR,providing valuable insights into production potential and performance;(3)The spacing range and the initial productivity of gas wells have a significant impact on the overall effectiveness of gas wells.Therefore,it is crucial to further explore rational well patterns and spacing,as well as optimize initial drainage and production technical strategies in order to improve their performance.展开更多
Casing deformation and frac-hit pose significant challenges to the development of deep shale gas in southern Sichuan Basin.By analyzing the mechanism and main control factors of casing deformation and frac-hit,two kin...Casing deformation and frac-hit pose significant challenges to the development of deep shale gas in southern Sichuan Basin.By analyzing the mechanism and main control factors of casing deformation and frac-hit,two kinds of risk assessment methods were defined,and the overall prevention and control concept and practice were formulated.The results show that initial stress,pore pressure,fault development and large scale fracturing in local block are the main factors leading to the deformation.The development of fracture through well group and uncontrolled fracturing fluid volume are the main factors leading to pressure channeling.Based on this,the risk classification technology of casing deformation and frac-hit is established,and the dual-optimal,dual-control concept and technology are formed.In terms of the prevention and control of casing deformation,the formation of small-diameter bridge plug fracturing,large section combined fracturing,glass beads cementing,singlewell staggered and platform straddle fracturing mode,dual-dimension controlled and lift fracturing,hyperbolic diagnosis,etc.Frac-hit prevention and control formed pump sequence optimization mode,physical and chemical temporary plugging and other methods.The above technology achieved casing deformation rate decreased from 50.4%to 25.4%,frac-hit rate decreased from 58.6%to 33.9%,and the average well kilometer EUR reached 0.52e0.7 million square meters,an increase of 7.7%compared with the previous research,with remarkable results.展开更多
The enrichment characteristics of deep shale gas in the Ordovician Wufeng-Silurian Longmaxi formations in the Sichuan Basin and its surrounding areas are investigated through experiments under high temperature and hig...The enrichment characteristics of deep shale gas in the Ordovician Wufeng-Silurian Longmaxi formations in the Sichuan Basin and its surrounding areas are investigated through experiments under high temperature and high pressure,including petrophysical properties analyses,triaxial stress test and isothermal adsorption of methane experiment.(1)The deep shale reservoirs drop significantly in porosity and permeability compared with shallower shale reservoirs,and contain mainly free gas.(2)With higher deviatoric stress and axial strain,the deep shale reservoirs have higher difficulty fracturing.(3)Affected by structural location and morphology,fracture characteristics,geofluid activity stages and intensity,deep shale gas reservoirs have more complicated preservation conditions.(4)To achieve the commercial development of deep shale gas reservoirs,deepening geological understanding is the basis,and exploring reservoir simulation technology befitting the geological features is the key.(5)The siliceous shale and limestone-bearing siliceous shale in the Metabolograptus persculptus-Parakidograptus acuminatus zones(LM1-LM3 graptolite zones)are the high-production intervals for deep shale gas and the most favorable landing targets for horizontal drilling.Deeps water areas such as Jiaoshiba,Wulong,Luzhou and Changning with deep shale reservoirs over 10 m thickness are the most favorable areas for deep shale gas enrichment.It is recommended to carry out exploration and development practice in deep-water shale gas areas deposited deep with burial depth no more than 5000 m where the geological structure is simple and the shale thickness in the LM1-LM3 graptolite zone is greater than 10 m.It is better to increase the lateral length of horizontal wells,and apply techniques including high intensity of perforations,large volume of proppant,far-field and near-wellbore diversions to maximize the stimulated deep reservoir volume.展开更多
To efficiently develop deep shale gas in southern Sichuan Basin,under the guidance of“extreme utilization”theory,a basic idea and solutions for deep shale gas development are put forward and applied in practice.In v...To efficiently develop deep shale gas in southern Sichuan Basin,under the guidance of“extreme utilization”theory,a basic idea and solutions for deep shale gas development are put forward and applied in practice.In view of multiple influencing factors of shale gas development,low single-well production and marginal profit of wells in this region,the basic idea is to establish“transparent geological body”of the block in concern,evaluate the factors affecting shale gas development through integrated geological-engineering research and optimize the shale gas development of wells in their whole life cycle to balance the relationship between production objectives and development costs.The solutions are as follows:(1)calculate the gold target index and pinpoint the location of horizontal well drilling target,and shale reservoirs are depicted accurately by geophysical and other means to build underground transparent geological body;(2)optimize the drilling and completion process,improve the adaptability of key tools by cooling,reducing density and optimizing the performance of drilling fluid,the“man-made gas reservoir”is built by comprehensively considering the characteristics of in-situ stress and fractures after the development well is drilled;(3)through efficient management,establishment of learning curve and optimization of drainage and production regime,the development quality and efficiency of the well are improved across its whole life cycle,to fulfil“extreme utilization”development of shale gas.The practice shows that the estimated ultimate recovery of single wells in southern Sichuan Basin increase by 10%-20%than last year.展开更多
There are abundant marine shale gas resources in the Sichuan Basin.After almost one decade of exploration and development,three national shale gas demonstration areas have been built in the Sichuan Basin and its perip...There are abundant marine shale gas resources in the Sichuan Basin.After almost one decade of exploration and development,three national shale gas demonstration areas have been built in the Sichuan Basin and its periphery,and large-scale commercial development of middle and deep(above 3500 m in depth)shale gas has been successfully achieved.The volume of deep shale gas resources(3500e4500 m deep)of the upper Ordovician Wufeng Formation-lower Silurian Longmaxi Formation in the southern Sichuan Basin is 6.61012 m3,with huge exploration and exploitation potential,so it is an important area for large-scale shale gas production increase in China during the 14th Five-year Plan.Deep shale gas in the southern Sichuan Basin is influenced by complex geological engineering conditions,such as great burial depth,high temperature and pressure,and large stress and stress difference,and its high-quality development faces many challenges.After systematically summarizing the new progresses and achievements in deep shale gas exploration and development in the southern Sichuan Basin,this paper analyzes the difficulties and challenges in deep shale gas exploration and development and puts forward the next research directions.And the following research results are obtained.First,based on early practical exploration and independent innovation,key shale gas exploration and development technologies with good area selection,good well deployment,good well drilling,good well fracturing and good well management as the core are formed,and the cultivation mode of high production well is established,which supports the large-scale benefit development of deep shale gas in the southern Sichuan Basin.Second,systematical analysis indicates that the exploration and development of deep shale gas still faces a series of challenges in such three major fields as basic theory,key technology and management mode.Third,in the face of challenges,it is necessary to deepen basic theory research related to exploration and development,continuously improve key main technologies and constantly innovate mechanisms,systems and management modes.In conclusion,after years of continuous researches and pilot tests,a series of main exploration and development technologies suitable for the working conditions of deep shale gas in the southern Sichuan Basin have been basically formed,the first deep shale gas reserves of trillion cubic meters has been submitted,and the first deep shale gas production increase block of ten billion cubic meters has been selected.Thus,great progresses have been made in the exploration and development of deep shale gas,which confirms the confidence and determination in exploring and developing deep shale gas and is of great guiding significance to the rapid development of shale gas industry in China.展开更多
Stimulation of hydraulic fracturing of horizontal shale gas wells in Weirong Block has always been facing many difficulties due to many factors such as complicated geological conditions,small differences between the h...Stimulation of hydraulic fracturing of horizontal shale gas wells in Weirong Block has always been facing many difficulties due to many factors such as complicated geological conditions,small differences between the horizontal principal stress and the vertical principal stress,high working pump pressures,and low sensitive sand ratios.In view of this,by combing the geological structure,engineering geological characteristics and the difficulties of fracturing of deep shale gas wells in Weirong Block,learning from the general idea of volumetric fracturing for shale gas reservoirs at home and abroad,we determined the main ideas and technical countermeasures for fracturing in the area and applied them to the subsequent fracturing practices of shale gas wells.And the following achievements were obtained.First,the conventional fracturing technology applied to the shale gas wells in Weirong Block resulted in low fracture complexity,small stimulated reservoir volume(SRV),difficulties in guaranteeing the effectiveness of perforation clusters,low strength of proppant adding,difficulties in obtaining higher conductivity,poor stable production capacity after stimulation,and difficulties in meeting the need of well fracturing with casing deformation.Second,in view of the difficulties of fracturing stimulation in deep shale gas wells of Weirong Block,super high pressure,huge displacement,large fluid volume,temporary plugging and diverting in fracturing,and variable displacement technology can effectively increase SRV and the complexity of fractures in distant wells.The effectiveness of multi-cluster perforation can be guaranteed by comprehensive utilization of multi-cluster perforation optimization technology,big displacement technology and temporary plugging and diverting&fracturing technology at slots.The continuous proppant-adding technology with huge displacement,high viscosity,low sand ratio,low density and small particle size can improve sand adding strength and fracture conductivity.Besides,the stimulation technology for casing deformed wells using coiled tubing fast processing+small diameter bridge plug and separate pumping technology of perforating gun have been formed.Third,after the above fracturing technologies have been applied in five shale gas horizontal wells in Weirong Block,the average absolute open flow(QAOF)reached 26.11×10^(4)m^(3)/d,indicating a good stimulation effect.In conclusion,this paper can provide meaningful reference for the development of deep shale gas wells of the similar type.展开更多
Deep shale gas reservoirs being developed by SINOPEC are characterized by significant buried depths, high rock strengths, high temperatures and pressures, multiple layers, low ROPs, prolonged drilling time and prohibi...Deep shale gas reservoirs being developed by SINOPEC are characterized by significant buried depths, high rock strengths, high temperatures and pressures, multiple layers, low ROPs, prolonged drilling time and prohibitoryhigh costs. All of these factors may negatively affect the economic and effective development of shale gas. Under such circumstances, existing drilling techniques for deep shale gas around the world have been reviewed to highlight technical challenges in deep shale gas drilling in China. With consideration to the previous drilling operations of SINOPEC for deep shale gas, technical solutions for deep shale gas drilling have been proposed with regard to the optimization of casing programs, enhanced drilling, trajectory control, high-density oil-based drilling fluid, cementation for deep shale gas development and other aspects. Some of these research findings have been deployed with great successes in Pingqiao, Jiangdong Block in the 2nd Phase of Fuling Project, Dingshan Block and other blocks with deep shale gas development. Among them, Well JY-74-2HF has had a drilling time of only 54.25d, whereas Well JY-187-2HF has a TVD up to 4024.14m. Relevant research results may provide valuable guidance and references for the optimization of drilling programs andthe enhancement ofdrilling ef^ciency for deep shale gas development.展开更多
In recent years,exploration and development of deep shale gas(at a burial depth of 3,500-4,500 m)has become a hotspot in the industry.However,the state of gas storage and transporting mechanism for deep shale gas unde...In recent years,exploration and development of deep shale gas(at a burial depth of 3,500-4,500 m)has become a hotspot in the industry.However,the state of gas storage and transporting mechanism for deep shale gas under high pressure and temperature have not been thoroughly explored,compared with its shallower counterpart.A numerical model for deep shale gas recovery considering multi-site nonisothermal excess adsorption has been established and applied using Finite Element Method.Results from the simulation reveal the following.(1)Excess desorption significantly impacts early-stage performance of deep shale gas well;the conventional way for shallower shale gas development,in which the density of adsorbed gas is not distinguished from that of free gas,overestimates the gas in place(GIP).(2)Although thermal stimulation can speed up the desorption and transporting of deep shale gas,the incremental volume of produced gas,which is impacted not only by seepage velocity but also density of gas,is insignificant,far from expectation.Only an additional 2.03%of cumulative gas would be produced under treatment temperature of 190C and initial reservoir temperature of 90C in a period of 5 years.(3)Matrix porosity,which can be measured on cores in laboratory and/or estimated by using well logging and geophysical data,is the most favorable parameter for deep shale gas recovery.With 60%increase in matrix porosity,an extra 67.25%shale gas on a daily base would be recovered even after 5-year depletion production;(4)Production rate for gas wells in shale reservoirs at 3,500 m and 4,500 m deep would be raised by 5.4%in a 5-year period if the depth of target interval would increase by 340 m without thermal treatment according to the numerical model proposed in the study.展开更多
Deep shale gas resources in the Sichuan Basin have great potential,and this is a major area for future shale gas exploration and development.Deep shale gas wells face problems with liquid loading throughout the produc...Deep shale gas resources in the Sichuan Basin have great potential,and this is a major area for future shale gas exploration and development.Deep shale gas wells face problems with liquid loading throughout the production cycle.Regarding deliquification techniques,it is necessary to consider the requirements of gas wells over the full life cycle,as well as the main form of artificial lift used at different stages,to achieve economically efficient development.This paper divides the life cycle of a deep shale gas well into two stages:early production and middle/late production.Pressure-control production is conducted in the early stage of production,whereas investigations on critical liquid-carrying models,the flow distribution in the wellbore,and the main form of artificial lift are conducted in the middle and late stages of production.A recommended scheme of deliquification techniques over the full life cycle has been developed to guide the development and enhancement of artificial lift methods in deep shale gas reservoirs.As of March 2022,in the PetroChina Southwest Oil&Gasfield Company managed-pressure production has been implemented in 14 wells in the early stage of deep shale gas production.In eight wells,plunger gas lift has been implemented in the middle and late stages of production.In seven wells,foam lift has been implemented.The abovementioned techniques are effective in increasing and stabilizing production and achieving deliquification in deep shale gas reservoirs.展开更多
Aiming at the problems of deep shale gas wells in Baima Block of Fuling Shale Gas Field, such as deep burial, complicated geological structure, frequent leakage, low penetration rate and low cementing quality rate, th...Aiming at the problems of deep shale gas wells in Baima Block of Fuling Shale Gas Field, such as deep burial, complicated geological structure, frequent leakage, low penetration rate and low cementing quality rate, the difficulties in drilling and completion of deep shale gas in Baima Block are summarized based on the analysis of the geological characteristics of the block and the previous drilling and completion data. Through the technical research of differential wellbore structure optimization, sectional wellbore trajectory control, personalized PDC bit design, anti-high temperature leak-proof and plugging drilling fluid technology and narrow safety window cementing technology, A set of fast drilling and completion technology suitable for deep shale gas in Baima Block has been formed and applied in this block for 15 wells, with the average penetration rate increased by 41.95% year on year, the drilling cycle shortened by 30.40%, and the cementing quality rate increased by 10%. The application effect is good. The technology can be popularized and applied as fast drilling and completion technology for deep shale gas in Baima Block.展开更多
The deep shale gas reservoirs of Upper Ordovician WufengeLower Silurian Longmaxi Formation in the Dingshan area of the southeastern Sichuan Basin have a great burial depth and complicated geologic features,so the frac...The deep shale gas reservoirs of Upper Ordovician WufengeLower Silurian Longmaxi Formation in the Dingshan area of the southeastern Sichuan Basin have a great burial depth and complicated geologic features,so the fracturing technologies that are used for mediumeshallow shale gas reservoirs are not suitable for their stimulation.In this paper,"double sweet spot"zones of shale gas were selected by combining engineering and geological research.The horizontal well fracturing technology suitable for deep shale gas reservoir was developed.And the fracturing mode suitable for mediumeshallow shale gas reservoirs was improved.In addition,the improved fracturing mode and technology were applied in 3 deep shale gas wells in the Dingshan area.And the following research results were obtained.First,the deep shale gas reservoirs in the northwest of the Dingshan area have the characteristics of"double sweet spot"of geology and fracturing,and the development of natural fractures and bedding fractures provides a favorable condition for the formation of complex fracture networks after fracturing.Second,a combined fracturing mode of"pre acid+gel+slickwater+gel"was developed for the"double sweet spot"zones.In this mode,high-viscosity slickwater is adopted to increase the proppant-transport ability of liquid and enhance the fracture-creating effect,the fracturing technology of"controlling the near and extending the far"can increase the effective stimulated reservoir volume far from the well,and the ultra-high pressure facility can increase the fracturing displacement and the net pressure in fractures.Third,after reservoir stimulation,3 deep shale gas wells present remarkable stimulation results,and their shale gas production rate during the testing is in the range of 10.50×10^(4)-20.56×10^(4)m^(3)/d.In conclusion,the improved fracturing mode and technology can provide a technical method for the stimulation of deep shale gas reservoirs in the Dingshan area,as well as a support for the breakthrough of exploration and development of deep shale gas reservoirs.展开更多
Clarifying the flow laws of shale gas under high temperature and high pressure is the prerequisite to accurately predicting the productivity of deep shale gas wells.In this paper,a self-diffusion flow model of flow fi...Clarifying the flow laws of shale gas under high temperature and high pressure is the prerequisite to accurately predicting the productivity of deep shale gas wells.In this paper,a self-diffusion flow model of flow field and temperature field coupling(referred to as self-diffusion flow and heat coupling model)was established based on the previously proposed self-diffusion flow model,while considering the influence of the temperature field change.Then,its calculation result was compared with that of the flow model based on Darcy's law and Knudsen diffusion(referred to as modified Darcy flow model).Based on the self-diffusion flow and heat coupling model,the self-diffusion flow behaviors of deep shale gas under the influence of temperature field change were analyzed,and the influence of bottomhole temperature on the degree of reserve recovery of deep shale gas was discussed.Finally,the self-diffusion flow and heat coupling model was applied to simulate the production of one shale-gas horizontal well in the Upper Ordovician Wufeng FormationeLower Silurian Longmaxi Formation in the Changning Block of the Sichuan Basin.And the following research results were obtained.First,at the same parameters,the shale gas production calculated by the selfdiffusion flow and heat coupling model is higher than the result calculated by the modified Darcy flow model.Second,when temperature field change is taken into consideration,the selfedviffusion coefficient profile presents a peak,the gas density profile presents a valley and the data points corresponding to the peak/valley move synchronously to the internal formation,which indicates that the selfediffusion coefficient influences the gas mass transfer rate,and the influence range of near well low temperature on gas self-diffusion increases continuously as the production continues.Third,when the bottomhole temperature is lower than the formation temperature,the selfediffusion coefficient of the gas near the well decreases and the gas is blocked near the well,which reduces the gas well production.Fourth,the production simulation result of the case well shows that the self-diffusion flow and heat coupling model can predict the production of deep shale gas more accurately if temperature field change is taken into consideration.In conclusion,the self-diffusion flow and heat coupling model established in this paper is of higher reliability and accuracy and can be used for productivity simulation and prediction of deep shale gas wells.The conclusion of this paper has certain guiding significance for deep shale gas production and gas well productivity prediction.展开更多
To explore and evaluate the longitudinal utilization degree of marine shale gas horizontal wells in southern Sichuan Basin(hereinafter referred to as“southern Sichuan”),focusing on the shale of Wufeng formation-Long...To explore and evaluate the longitudinal utilization degree of marine shale gas horizontal wells in southern Sichuan Basin(hereinafter referred to as“southern Sichuan”),focusing on the shale of Wufeng formation-Longyi1 sub-member in the deep Z block.By using the data from core experiments,well logging,and fracture height detection,a systematic analysis from the perspectives of reservoir distribution,longitudinal utilization height of hydraulic fractures,and longitudinal utilization degree of horizontal wells was conducted.The research results show that:(1)The overall reservoir conditions of theWufeng formation-Longyi1 sub-member in the study area are relatively favorable,although the quality of Type I reservoir varies significantly among different well blocks;(2)The proppant tracer fracture height detection results show that fractures tend to extend upwards,the average total fracture height of fracture extend is 12.7 m,with the average upward extension height is 2.5 times the downward extension height;(3)The combination of fracture height and gas well productivity analysis suggests that targeting sub-layer 1 as the horizontal well target can achieve full production of the continuous thickness of Type I reservoir in Z2 well block,whereas in Z1 well block,due to the significant proportion of the Wufeng formation in the continuous thickness of Type I reservoir,in the areas where the continuous thickness of Type I reservoir in Wufeng formation to middle sub-layer 1 is greater than 4 m,horizontal wells cannot achieve full longitudinal utilization of the continuous thickness in top-quality Type I reservoir.The conclusion is that due to the limitations of longitudinal utilization height by artificial fracture networks and the variability in the distribution of continuous thickness of Type I reservoir,Z1 well block can continue to conduct horizontal well target tests and differentiated fracturing designs to further enhance the longitudinal utilization degree of the top-quality Type I reservoir.展开更多
To investigate the porosity, permeability and rock mechanics of deep shale under temperature-pressure coupling, we selected the core samples of deep shale from the Lower Silurian Longmaxi Formation in the Weirong and ...To investigate the porosity, permeability and rock mechanics of deep shale under temperature-pressure coupling, we selected the core samples of deep shale from the Lower Silurian Longmaxi Formation in the Weirong and Yongchuan areas of the Sichuan Basin for porosity and permeability experiments and a triaxial compression and sound wave integration experiment at the maximum temperature and pressure of 120 ℃ and 70 MPa. The results show that the microscopic porosity and permeability change and the macroscopic rock deformation are mutually constrained, both showing the trend of steep and then gentle variation. At the maximum temperature and pressure, the porosity reduces by 34%–71%, and the permeability decreases by 85%–97%. With the rising temperature and pressure, deep shale undergoes plastic deformation in which organic pores and clay mineral pores are compressed and microfractures are closed, and elastic deformation in which brittle mineral pores and rock skeleton particles are compacted. Compared with previous experiments under high confining pressure and normal temperature,the experiment under high temperature and high pressure coupling reveals the effect of high temperature on stress sensitivity of porosity and permeability. High temperature can increase the plasticity of the rock, intensify the compression of pores due to high confining pressure, and induce thermal stress between the rock skeleton particles, allowing the reopening of shale bedding or the creation of new fractures along weak planes such as bedding, which inhibits the decrease of permeability with the increase of temperature and confining pressure. Compared with the triaxial mechanical experiment at normal temperature, the triaxial compression experiment at high temperature and high pressure demonstrates that the compressive strength and peak strain of deep shale increase significantly due to the coupling of temperature and pressure. The compressive strength is up to 435 MPa and the peak strain exceeds 2%, indicating that high temperature is not conducive to fracture initiation and expansion by increasing rock plasticity. Lithofacies and mineral composition have great impacts on the porosity, permeability and rock mechanics of deep shale. Shales with different lithologies are different in the difficulty and extent of brittle failure. The stress-strain characteristics of rocks under actual geological conditions are key support to the optimization of reservoir stimulation program.展开更多
Deep shale gas has become an important frontier for future shale gas exploration and development.The Wufeng-Longmaxi formations in southern China have undergone complex tectonic and transformation through multi-stage ...Deep shale gas has become an important frontier for future shale gas exploration and development.The Wufeng-Longmaxi formations in southern China have undergone complex tectonic and transformation through multi-stage tectonic movements.Deep shale gas enrichment conditions are complex,which greatly restricts the exploration and development of deep shale gas.In this study,based on systematic analysis of basic geological characteristics and gas reservoir characteristics of deep shales,the main factors controlling deep shale gas enrichment in southern China were investigated,and enrichment modes were established.The results show that high-quality shales were developed in the deep-water continental shelf facies,characterized by moderate thermal maturity,high silica content,and abundant organic matter.These characteristics provide a good basis for the formation and enrichment of shale gas.The deep shale gas reservoir is featured by overpressure,high porosity and high gas content.The development and maintenance of high porosity,favorable roof and floor sealing conditions,and weak tectonic activity during uplift stage are the main factors to control deep shale gas enrichment.Based on a comprehensive analysis,the enrichment modes of deep shale gas under three different tectonic patterns were established,namely overpressure enrichment within the basin,overpressure enrichment in the faulted nose or slope of the margin,and overpressure enrichment in the remnant syncline outside the basin.This study provides a reference for exploration and development of deep shale gas in Sichuan Basin and other areas.展开更多
There is a huge amount of marine shale gas resources in the southern Sichuan Basin in China, and most of the resources are at the buried depth of 3500</span><span style="font-family:""> <...There is a huge amount of marine shale gas resources in the southern Sichuan Basin in China, and most of the resources are at the buried depth of 3500</span><span style="font-family:""> </span><span style="font-family:Verdana;">-</span><span style="font-family:""> </span><span style="font-family:Verdana;">4500 meters. At present, deep shale gas is in the early stage of exploration and development. In order to achieve large-scale efficient development, in addition to optimizing favorable blocks, it is also to identify the optimal target in the vertical direction combine geology, drilling, and fracturing. Therefore, Taking the Longmaxi formation shale in the Luzhou block as the research object, based on drilling, logging, and core experiment data, through single well and 3D geomechanical modeling methods, analyze the characteristics of organic matter abundance, porosity, pore pressure, collapse pressure, mineral composition and in-situ stress of different layers of shale in Longmaxi formation. Systematically summarized the main controlling factors of the “sweet spot” of deep shale gas and establish the comprehensive evaluation system of deep shale gas “sweet spots”, to clarify the optimal “sweet spots” of geology, drilling, and fracturing in the Longmaxi reservoir. Results show that the total organic carbon content, porosity, and gas saturation of the long111 layer are higher than other layers. The Long111 layer has a low collapse pressure and a high compressive strength, the risk of wellbore instability is relatively low. The stress difference coefficient of All layers is less than 0.3, and the brittleness index of the Long111 layer is 62.35%. A complex fracture network is easier to form after fracturing. The conclusion shows that the Long111 layer is the optimal reservoir section of the Longmaxi Formation. Ensure the drilled rate of the Long111 layer and maximize the length of the horizontal section can obtain higher production.展开更多
This paper introduces a deep learning workflow to predict phase distributions within complex geometries during two-phase capillary-dominated drainage.We utilize subsamples from Computerized Tomography(CT)images of roc...This paper introduces a deep learning workflow to predict phase distributions within complex geometries during two-phase capillary-dominated drainage.We utilize subsamples from Computerized Tomography(CT)images of rocks and incorporate pixel size,interfacial tension,contact angle,and pressure as inputs.First,an efficient morphology-based simulator creates a diverse dataset of phase distributions.Then,two commonly used convolutional and recurrent neural networks are explored and their deficiencies are highlighted,particularly in capturing phase connectivity.Subsequently,we develop a Higher-Dimensional Vision Transformer(HD-ViT)that drains pores solely based on their size,with phase connectivity enforced as a post-processing step.This enables inference for images of varying sizes,resolutions,and inlet-outlet setup.After training on a massive dataset of over 9.5 million instances,HD-ViT achieves excellent performance.We demonstrate the accuracy and speed advantage of the model on new and larger sandstone and carbonate images.We further evaluate HD-ViT against experimental fluid distribution images and the corresponding Lattice-Boltzmann simulations,producing similar outcomes in a matter of seconds.In the end,we train and validate a 3D version of the model.展开更多
文摘As shale gas technology has advanced,the horizontal well fracturing model has seen widespread use,leading to substantial improvements in industrial gas output from shale gas wells.Nevertheless,a swift decline in the productivity of individual wells remains a challenge that must be addressed throughout the development process.In this study,gas wells with two different wellbore trajectory structures are considered,and the OLGA software is exploited to perform transient calculations on various tubing depth models.The results can be articulated as follows.In terms of flow patterns:for the deep well A1(upward-buckled),slug flow occurs in the Kick-off Point position and above;for the deep well B1(downward-inclined),slug flow only occurs in the horizontal section.Wells with downward-inclined horizontal sections are more prone to liquid accumulation issues.In terms of comparison to conventional wells,it is shown that deep shale gas wells have longer normal production durations and experience liquid accumulation later than conventional wells.With regard to optimal tubing placement:for well A1(upward-buckled),it is recommended to place tubing at the Kick-off Point position;for well B1(downward-inclined),it is recommended to place tubing at the lower heel of the horizontal section.Finally,in terms of production performance:well A1(upward-buckled)outperforms well B1(downward-inclined)in terms of production and fluid accumulation.In particular,the deep well A1 is 1.94 times more productive and 1.3 times longer to produce than conventional wells.Deep well B1 is 1.87 times more productive and 1.34 times longer than conventional wells.
基金supported by the Chongqing Natural Science Foundation Innovation and Development Joint Fund(CSTB2023NSCQ-LZX0078)the Science and Technology Research Program of Chongqing Municipal Education Commission(KJQN202201519),which are gratefully acknowledged.
文摘Pressure control in deep shale gas horizontal wells can reduce the stress sensitivity of hydraulic fractures and improve the estimated ultimate recovery(EUR).In this study,a hydraulic fracture stress sensitivity model is proposed to characterize the effect of pressure drop rate on fracture permeability.Furthermore,a production prediction model is introduced accounting for a non-uniform hydraulic fracture conductivity distribution.The results reveal that increasing the fracture conductivity leads to a rapid daily production increase in the early stages.However,above 0.50 D·cm,a further increase in the fracture conductivity has a limited effect on shale gas production growth.The initial production is lower under pressure-controlled conditions than that under pressure-release.For extended pressure control durations,the cumulative production initially increases and then decreases.For a fracture conductivity of 0.10 D·cm,the increase in production output under controlled-pressure conditions is~35%.For representative deep shale gas wells(Southern Sichuan,China),if the pressure drop rate under controlled-pressure conditions is reduced from 0.19 to 0.04 MPa/d,the EUR increase for 5 years of pressure-controlled production is 41.0 million,with an increase percentage of~29%.
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.
文摘The pivotal areas for the extensive and effective exploitation of shale gas in the Southern Sichuan Basin have recently transitioned from mid-deep layers to deep layers.Given challenges such as intricate data analysis,absence of effective assessment methodologies,real-time control strategies,and scarce knowledge of the factors influencing deep gas wells in the so-called flowback stage,a comprehensive study was undertaken on over 160 deep gas wells in Luzhou block utilizing linear flow models and advanced big data analytics techniques.The research results show that:(1)The flowback stage of a deep gas well presents the characteristics of late gas channeling,high flowback rate after gas channeling,low 30-day flowback rate,and high flowback rate corresponding to peak production;(2)The comprehensive parameter AcmKm1/2 in the flowback stage exhibits a strong correlation with the Estimated Ultimate Recovery(EUR),allowing for the establishment of a standardized chart to evaluate EUR classification in typical shale gas wells during this stage.This enables quantitative assessment of gas well EUR,providing valuable insights into production potential and performance;(3)The spacing range and the initial productivity of gas wells have a significant impact on the overall effectiveness of gas wells.Therefore,it is crucial to further explore rational well patterns and spacing,as well as optimize initial drainage and production technical strategies in order to improve their performance.
文摘Casing deformation and frac-hit pose significant challenges to the development of deep shale gas in southern Sichuan Basin.By analyzing the mechanism and main control factors of casing deformation and frac-hit,two kinds of risk assessment methods were defined,and the overall prevention and control concept and practice were formulated.The results show that initial stress,pore pressure,fault development and large scale fracturing in local block are the main factors leading to the deformation.The development of fracture through well group and uncontrolled fracturing fluid volume are the main factors leading to pressure channeling.Based on this,the risk classification technology of casing deformation and frac-hit is established,and the dual-optimal,dual-control concept and technology are formed.In terms of the prevention and control of casing deformation,the formation of small-diameter bridge plug fracturing,large section combined fracturing,glass beads cementing,singlewell staggered and platform straddle fracturing mode,dual-dimension controlled and lift fracturing,hyperbolic diagnosis,etc.Frac-hit prevention and control formed pump sequence optimization mode,physical and chemical temporary plugging and other methods.The above technology achieved casing deformation rate decreased from 50.4%to 25.4%,frac-hit rate decreased from 58.6%to 33.9%,and the average well kilometer EUR reached 0.52e0.7 million square meters,an increase of 7.7%compared with the previous research,with remarkable results.
基金Supported by the National Natural Science Foundation of China(41872124,42130803)Sinopec Key Scientific and Technological Project(P20046)。
文摘The enrichment characteristics of deep shale gas in the Ordovician Wufeng-Silurian Longmaxi formations in the Sichuan Basin and its surrounding areas are investigated through experiments under high temperature and high pressure,including petrophysical properties analyses,triaxial stress test and isothermal adsorption of methane experiment.(1)The deep shale reservoirs drop significantly in porosity and permeability compared with shallower shale reservoirs,and contain mainly free gas.(2)With higher deviatoric stress and axial strain,the deep shale reservoirs have higher difficulty fracturing.(3)Affected by structural location and morphology,fracture characteristics,geofluid activity stages and intensity,deep shale gas reservoirs have more complicated preservation conditions.(4)To achieve the commercial development of deep shale gas reservoirs,deepening geological understanding is the basis,and exploring reservoir simulation technology befitting the geological features is the key.(5)The siliceous shale and limestone-bearing siliceous shale in the Metabolograptus persculptus-Parakidograptus acuminatus zones(LM1-LM3 graptolite zones)are the high-production intervals for deep shale gas and the most favorable landing targets for horizontal drilling.Deeps water areas such as Jiaoshiba,Wulong,Luzhou and Changning with deep shale reservoirs over 10 m thickness are the most favorable areas for deep shale gas enrichment.It is recommended to carry out exploration and development practice in deep-water shale gas areas deposited deep with burial depth no more than 5000 m where the geological structure is simple and the shale thickness in the LM1-LM3 graptolite zone is greater than 10 m.It is better to increase the lateral length of horizontal wells,and apply techniques including high intensity of perforations,large volume of proppant,far-field and near-wellbore diversions to maximize the stimulated deep reservoir volume.
基金Suppoted by the Forward-Looking Basic Project of China National Petroleum Corporation(2021DJ19).
文摘To efficiently develop deep shale gas in southern Sichuan Basin,under the guidance of“extreme utilization”theory,a basic idea and solutions for deep shale gas development are put forward and applied in practice.In view of multiple influencing factors of shale gas development,low single-well production and marginal profit of wells in this region,the basic idea is to establish“transparent geological body”of the block in concern,evaluate the factors affecting shale gas development through integrated geological-engineering research and optimize the shale gas development of wells in their whole life cycle to balance the relationship between production objectives and development costs.The solutions are as follows:(1)calculate the gold target index and pinpoint the location of horizontal well drilling target,and shale reservoirs are depicted accurately by geophysical and other means to build underground transparent geological body;(2)optimize the drilling and completion process,improve the adaptability of key tools by cooling,reducing density and optimizing the performance of drilling fluid,the“man-made gas reservoir”is built by comprehensively considering the characteristics of in-situ stress and fractures after the development well is drilled;(3)through efficient management,establishment of learning curve and optimization of drainage and production regime,the development quality and efficiency of the well are improved across its whole life cycle,to fulfil“extreme utilization”development of shale gas.The practice shows that the estimated ultimate recovery of single wells in southern Sichuan Basin increase by 10%-20%than last year.
基金Project supported by the Scientific Research and Technology Development Project of Petro China Company Limited“Research and test on key technologies for effective exploitation of deep shale gas”(No.2019F-31).
文摘There are abundant marine shale gas resources in the Sichuan Basin.After almost one decade of exploration and development,three national shale gas demonstration areas have been built in the Sichuan Basin and its periphery,and large-scale commercial development of middle and deep(above 3500 m in depth)shale gas has been successfully achieved.The volume of deep shale gas resources(3500e4500 m deep)of the upper Ordovician Wufeng Formation-lower Silurian Longmaxi Formation in the southern Sichuan Basin is 6.61012 m3,with huge exploration and exploitation potential,so it is an important area for large-scale shale gas production increase in China during the 14th Five-year Plan.Deep shale gas in the southern Sichuan Basin is influenced by complex geological engineering conditions,such as great burial depth,high temperature and pressure,and large stress and stress difference,and its high-quality development faces many challenges.After systematically summarizing the new progresses and achievements in deep shale gas exploration and development in the southern Sichuan Basin,this paper analyzes the difficulties and challenges in deep shale gas exploration and development and puts forward the next research directions.And the following research results are obtained.First,based on early practical exploration and independent innovation,key shale gas exploration and development technologies with good area selection,good well deployment,good well drilling,good well fracturing and good well management as the core are formed,and the cultivation mode of high production well is established,which supports the large-scale benefit development of deep shale gas in the southern Sichuan Basin.Second,systematical analysis indicates that the exploration and development of deep shale gas still faces a series of challenges in such three major fields as basic theory,key technology and management mode.Third,in the face of challenges,it is necessary to deepen basic theory research related to exploration and development,continuously improve key main technologies and constantly innovate mechanisms,systems and management modes.In conclusion,after years of continuous researches and pilot tests,a series of main exploration and development technologies suitable for the working conditions of deep shale gas in the southern Sichuan Basin have been basically formed,the first deep shale gas reserves of trillion cubic meters has been submitted,and the first deep shale gas production increase block of ten billion cubic meters has been selected.Thus,great progresses have been made in the exploration and development of deep shale gas,which confirms the confidence and determination in exploring and developing deep shale gas and is of great guiding significance to the rapid development of shale gas industry in China.
基金supported by the Scientific Research Project of Sinopec Oilfield Service Corporation“Key technologies for deep shale gas fracturing and gas testing in Weiyuan-Yongchuan”(No.:SG1704-02K).
文摘Stimulation of hydraulic fracturing of horizontal shale gas wells in Weirong Block has always been facing many difficulties due to many factors such as complicated geological conditions,small differences between the horizontal principal stress and the vertical principal stress,high working pump pressures,and low sensitive sand ratios.In view of this,by combing the geological structure,engineering geological characteristics and the difficulties of fracturing of deep shale gas wells in Weirong Block,learning from the general idea of volumetric fracturing for shale gas reservoirs at home and abroad,we determined the main ideas and technical countermeasures for fracturing in the area and applied them to the subsequent fracturing practices of shale gas wells.And the following achievements were obtained.First,the conventional fracturing technology applied to the shale gas wells in Weirong Block resulted in low fracture complexity,small stimulated reservoir volume(SRV),difficulties in guaranteeing the effectiveness of perforation clusters,low strength of proppant adding,difficulties in obtaining higher conductivity,poor stable production capacity after stimulation,and difficulties in meeting the need of well fracturing with casing deformation.Second,in view of the difficulties of fracturing stimulation in deep shale gas wells of Weirong Block,super high pressure,huge displacement,large fluid volume,temporary plugging and diverting in fracturing,and variable displacement technology can effectively increase SRV and the complexity of fractures in distant wells.The effectiveness of multi-cluster perforation can be guaranteed by comprehensive utilization of multi-cluster perforation optimization technology,big displacement technology and temporary plugging and diverting&fracturing technology at slots.The continuous proppant-adding technology with huge displacement,high viscosity,low sand ratio,low density and small particle size can improve sand adding strength and fracture conductivity.Besides,the stimulation technology for casing deformed wells using coiled tubing fast processing+small diameter bridge plug and separate pumping technology of perforating gun have been formed.Third,after the above fracturing technologies have been applied in five shale gas horizontal wells in Weirong Block,the average absolute open flow(QAOF)reached 26.11×10^(4)m^(3)/d,indicating a good stimulation effect.In conclusion,this paper can provide meaningful reference for the development of deep shale gas wells of the similar type.
文摘Deep shale gas reservoirs being developed by SINOPEC are characterized by significant buried depths, high rock strengths, high temperatures and pressures, multiple layers, low ROPs, prolonged drilling time and prohibitoryhigh costs. All of these factors may negatively affect the economic and effective development of shale gas. Under such circumstances, existing drilling techniques for deep shale gas around the world have been reviewed to highlight technical challenges in deep shale gas drilling in China. With consideration to the previous drilling operations of SINOPEC for deep shale gas, technical solutions for deep shale gas drilling have been proposed with regard to the optimization of casing programs, enhanced drilling, trajectory control, high-density oil-based drilling fluid, cementation for deep shale gas development and other aspects. Some of these research findings have been deployed with great successes in Pingqiao, Jiangdong Block in the 2nd Phase of Fuling Project, Dingshan Block and other blocks with deep shale gas development. Among them, Well JY-74-2HF has had a drilling time of only 54.25d, whereas Well JY-187-2HF has a TVD up to 4024.14m. Relevant research results may provide valuable guidance and references for the optimization of drilling programs andthe enhancement ofdrilling ef^ciency for deep shale gas development.
基金support by the program of National Science and Technology Major Project under Grant No.2016ZX05061Sinopec Ministry of Science and Technology Projects(Grant No.P21042-4,P20059-6,P19017-3).
文摘In recent years,exploration and development of deep shale gas(at a burial depth of 3,500-4,500 m)has become a hotspot in the industry.However,the state of gas storage and transporting mechanism for deep shale gas under high pressure and temperature have not been thoroughly explored,compared with its shallower counterpart.A numerical model for deep shale gas recovery considering multi-site nonisothermal excess adsorption has been established and applied using Finite Element Method.Results from the simulation reveal the following.(1)Excess desorption significantly impacts early-stage performance of deep shale gas well;the conventional way for shallower shale gas development,in which the density of adsorbed gas is not distinguished from that of free gas,overestimates the gas in place(GIP).(2)Although thermal stimulation can speed up the desorption and transporting of deep shale gas,the incremental volume of produced gas,which is impacted not only by seepage velocity but also density of gas,is insignificant,far from expectation.Only an additional 2.03%of cumulative gas would be produced under treatment temperature of 190C and initial reservoir temperature of 90C in a period of 5 years.(3)Matrix porosity,which can be measured on cores in laboratory and/or estimated by using well logging and geophysical data,is the most favorable parameter for deep shale gas recovery.With 60%increase in matrix porosity,an extra 67.25%shale gas on a daily base would be recovered even after 5-year depletion production;(4)Production rate for gas wells in shale reservoirs at 3,500 m and 4,500 m deep would be raised by 5.4%in a 5-year period if the depth of target interval would increase by 340 m without thermal treatment according to the numerical model proposed in the study.
文摘Deep shale gas resources in the Sichuan Basin have great potential,and this is a major area for future shale gas exploration and development.Deep shale gas wells face problems with liquid loading throughout the production cycle.Regarding deliquification techniques,it is necessary to consider the requirements of gas wells over the full life cycle,as well as the main form of artificial lift used at different stages,to achieve economically efficient development.This paper divides the life cycle of a deep shale gas well into two stages:early production and middle/late production.Pressure-control production is conducted in the early stage of production,whereas investigations on critical liquid-carrying models,the flow distribution in the wellbore,and the main form of artificial lift are conducted in the middle and late stages of production.A recommended scheme of deliquification techniques over the full life cycle has been developed to guide the development and enhancement of artificial lift methods in deep shale gas reservoirs.As of March 2022,in the PetroChina Southwest Oil&Gasfield Company managed-pressure production has been implemented in 14 wells in the early stage of deep shale gas production.In eight wells,plunger gas lift has been implemented in the middle and late stages of production.In seven wells,foam lift has been implemented.The abovementioned techniques are effective in increasing and stabilizing production and achieving deliquification in deep shale gas reservoirs.
文摘Aiming at the problems of deep shale gas wells in Baima Block of Fuling Shale Gas Field, such as deep burial, complicated geological structure, frequent leakage, low penetration rate and low cementing quality rate, the difficulties in drilling and completion of deep shale gas in Baima Block are summarized based on the analysis of the geological characteristics of the block and the previous drilling and completion data. Through the technical research of differential wellbore structure optimization, sectional wellbore trajectory control, personalized PDC bit design, anti-high temperature leak-proof and plugging drilling fluid technology and narrow safety window cementing technology, A set of fast drilling and completion technology suitable for deep shale gas in Baima Block has been formed and applied in this block for 15 wells, with the average penetration rate increased by 41.95% year on year, the drilling cycle shortened by 30.40%, and the cementing quality rate increased by 10%. The application effect is good. The technology can be popularized and applied as fast drilling and completion technology for deep shale gas in Baima Block.
基金Project supported by the Science and Technology Research Project of China Petroleum&Chemical Corporation"Drilling,Completion and Fracturing Technology of Deep Shale Gas Exploration Well"(No.P18020).
文摘The deep shale gas reservoirs of Upper Ordovician WufengeLower Silurian Longmaxi Formation in the Dingshan area of the southeastern Sichuan Basin have a great burial depth and complicated geologic features,so the fracturing technologies that are used for mediumeshallow shale gas reservoirs are not suitable for their stimulation.In this paper,"double sweet spot"zones of shale gas were selected by combining engineering and geological research.The horizontal well fracturing technology suitable for deep shale gas reservoir was developed.And the fracturing mode suitable for mediumeshallow shale gas reservoirs was improved.In addition,the improved fracturing mode and technology were applied in 3 deep shale gas wells in the Dingshan area.And the following research results were obtained.First,the deep shale gas reservoirs in the northwest of the Dingshan area have the characteristics of"double sweet spot"of geology and fracturing,and the development of natural fractures and bedding fractures provides a favorable condition for the formation of complex fracture networks after fracturing.Second,a combined fracturing mode of"pre acid+gel+slickwater+gel"was developed for the"double sweet spot"zones.In this mode,high-viscosity slickwater is adopted to increase the proppant-transport ability of liquid and enhance the fracture-creating effect,the fracturing technology of"controlling the near and extending the far"can increase the effective stimulated reservoir volume far from the well,and the ultra-high pressure facility can increase the fracturing displacement and the net pressure in fractures.Third,after reservoir stimulation,3 deep shale gas wells present remarkable stimulation results,and their shale gas production rate during the testing is in the range of 10.50×10^(4)-20.56×10^(4)m^(3)/d.In conclusion,the improved fracturing mode and technology can provide a technical method for the stimulation of deep shale gas reservoirs in the Dingshan area,as well as a support for the breakthrough of exploration and development of deep shale gas reservoirs.
基金Project supported by the Youth Science Foundation Project of National Natural Science Foundation of China“Dynamic Evolution Mechanism of Shale Reservoir Stress Field under Multi-well Interference”(No.5190040058)the General Project of National Natural Science Foundation of China“Research on Hydrodynamic Mechanism of Multi-scale Channels in Tight Reservoir”,(No.51874321)the Scientific Research Foundation of China University of Petroleum(Beijing)for Young Top Talent“Multi-scale Characteristics of Fluid Flow in Complex Fracture Network of Shale Gas Reservoirs”(No.2462018YJRC014).
文摘Clarifying the flow laws of shale gas under high temperature and high pressure is the prerequisite to accurately predicting the productivity of deep shale gas wells.In this paper,a self-diffusion flow model of flow field and temperature field coupling(referred to as self-diffusion flow and heat coupling model)was established based on the previously proposed self-diffusion flow model,while considering the influence of the temperature field change.Then,its calculation result was compared with that of the flow model based on Darcy's law and Knudsen diffusion(referred to as modified Darcy flow model).Based on the self-diffusion flow and heat coupling model,the self-diffusion flow behaviors of deep shale gas under the influence of temperature field change were analyzed,and the influence of bottomhole temperature on the degree of reserve recovery of deep shale gas was discussed.Finally,the self-diffusion flow and heat coupling model was applied to simulate the production of one shale-gas horizontal well in the Upper Ordovician Wufeng FormationeLower Silurian Longmaxi Formation in the Changning Block of the Sichuan Basin.And the following research results were obtained.First,at the same parameters,the shale gas production calculated by the selfdiffusion flow and heat coupling model is higher than the result calculated by the modified Darcy flow model.Second,when temperature field change is taken into consideration,the selfedviffusion coefficient profile presents a peak,the gas density profile presents a valley and the data points corresponding to the peak/valley move synchronously to the internal formation,which indicates that the selfediffusion coefficient influences the gas mass transfer rate,and the influence range of near well low temperature on gas self-diffusion increases continuously as the production continues.Third,when the bottomhole temperature is lower than the formation temperature,the selfediffusion coefficient of the gas near the well decreases and the gas is blocked near the well,which reduces the gas well production.Fourth,the production simulation result of the case well shows that the self-diffusion flow and heat coupling model can predict the production of deep shale gas more accurately if temperature field change is taken into consideration.In conclusion,the self-diffusion flow and heat coupling model established in this paper is of higher reliability and accuracy and can be used for productivity simulation and prediction of deep shale gas wells.The conclusion of this paper has certain guiding significance for deep shale gas production and gas well productivity prediction.
文摘To explore and evaluate the longitudinal utilization degree of marine shale gas horizontal wells in southern Sichuan Basin(hereinafter referred to as“southern Sichuan”),focusing on the shale of Wufeng formation-Longyi1 sub-member in the deep Z block.By using the data from core experiments,well logging,and fracture height detection,a systematic analysis from the perspectives of reservoir distribution,longitudinal utilization height of hydraulic fractures,and longitudinal utilization degree of horizontal wells was conducted.The research results show that:(1)The overall reservoir conditions of theWufeng formation-Longyi1 sub-member in the study area are relatively favorable,although the quality of Type I reservoir varies significantly among different well blocks;(2)The proppant tracer fracture height detection results show that fractures tend to extend upwards,the average total fracture height of fracture extend is 12.7 m,with the average upward extension height is 2.5 times the downward extension height;(3)The combination of fracture height and gas well productivity analysis suggests that targeting sub-layer 1 as the horizontal well target can achieve full production of the continuous thickness of Type I reservoir in Z2 well block,whereas in Z1 well block,due to the significant proportion of the Wufeng formation in the continuous thickness of Type I reservoir,in the areas where the continuous thickness of Type I reservoir in Wufeng formation to middle sub-layer 1 is greater than 4 m,horizontal wells cannot achieve full longitudinal utilization of the continuous thickness in top-quality Type I reservoir.The conclusion is that due to the limitations of longitudinal utilization height by artificial fracture networks and the variability in the distribution of continuous thickness of Type I reservoir,Z1 well block can continue to conduct horizontal well target tests and differentiated fracturing designs to further enhance the longitudinal utilization degree of the top-quality Type I reservoir.
基金Supported by the National Natural Science Foundation of China(41872124,42130803)Sinopec Key Science and Technology Project(P20046).
文摘To investigate the porosity, permeability and rock mechanics of deep shale under temperature-pressure coupling, we selected the core samples of deep shale from the Lower Silurian Longmaxi Formation in the Weirong and Yongchuan areas of the Sichuan Basin for porosity and permeability experiments and a triaxial compression and sound wave integration experiment at the maximum temperature and pressure of 120 ℃ and 70 MPa. The results show that the microscopic porosity and permeability change and the macroscopic rock deformation are mutually constrained, both showing the trend of steep and then gentle variation. At the maximum temperature and pressure, the porosity reduces by 34%–71%, and the permeability decreases by 85%–97%. With the rising temperature and pressure, deep shale undergoes plastic deformation in which organic pores and clay mineral pores are compressed and microfractures are closed, and elastic deformation in which brittle mineral pores and rock skeleton particles are compacted. Compared with previous experiments under high confining pressure and normal temperature,the experiment under high temperature and high pressure coupling reveals the effect of high temperature on stress sensitivity of porosity and permeability. High temperature can increase the plasticity of the rock, intensify the compression of pores due to high confining pressure, and induce thermal stress between the rock skeleton particles, allowing the reopening of shale bedding or the creation of new fractures along weak planes such as bedding, which inhibits the decrease of permeability with the increase of temperature and confining pressure. Compared with the triaxial mechanical experiment at normal temperature, the triaxial compression experiment at high temperature and high pressure demonstrates that the compressive strength and peak strain of deep shale increase significantly due to the coupling of temperature and pressure. The compressive strength is up to 435 MPa and the peak strain exceeds 2%, indicating that high temperature is not conducive to fracture initiation and expansion by increasing rock plasticity. Lithofacies and mineral composition have great impacts on the porosity, permeability and rock mechanics of deep shale. Shales with different lithologies are different in the difficulty and extent of brittle failure. The stress-strain characteristics of rocks under actual geological conditions are key support to the optimization of reservoir stimulation program.
基金support from a project of the Basic Research Program on Deep Petroleum Resource Accumulation and Key Engineering Technologies(U19B6003).
文摘Deep shale gas has become an important frontier for future shale gas exploration and development.The Wufeng-Longmaxi formations in southern China have undergone complex tectonic and transformation through multi-stage tectonic movements.Deep shale gas enrichment conditions are complex,which greatly restricts the exploration and development of deep shale gas.In this study,based on systematic analysis of basic geological characteristics and gas reservoir characteristics of deep shales,the main factors controlling deep shale gas enrichment in southern China were investigated,and enrichment modes were established.The results show that high-quality shales were developed in the deep-water continental shelf facies,characterized by moderate thermal maturity,high silica content,and abundant organic matter.These characteristics provide a good basis for the formation and enrichment of shale gas.The deep shale gas reservoir is featured by overpressure,high porosity and high gas content.The development and maintenance of high porosity,favorable roof and floor sealing conditions,and weak tectonic activity during uplift stage are the main factors to control deep shale gas enrichment.Based on a comprehensive analysis,the enrichment modes of deep shale gas under three different tectonic patterns were established,namely overpressure enrichment within the basin,overpressure enrichment in the faulted nose or slope of the margin,and overpressure enrichment in the remnant syncline outside the basin.This study provides a reference for exploration and development of deep shale gas in Sichuan Basin and other areas.
文摘There is a huge amount of marine shale gas resources in the southern Sichuan Basin in China, and most of the resources are at the buried depth of 3500</span><span style="font-family:""> </span><span style="font-family:Verdana;">-</span><span style="font-family:""> </span><span style="font-family:Verdana;">4500 meters. At present, deep shale gas is in the early stage of exploration and development. In order to achieve large-scale efficient development, in addition to optimizing favorable blocks, it is also to identify the optimal target in the vertical direction combine geology, drilling, and fracturing. Therefore, Taking the Longmaxi formation shale in the Luzhou block as the research object, based on drilling, logging, and core experiment data, through single well and 3D geomechanical modeling methods, analyze the characteristics of organic matter abundance, porosity, pore pressure, collapse pressure, mineral composition and in-situ stress of different layers of shale in Longmaxi formation. Systematically summarized the main controlling factors of the “sweet spot” of deep shale gas and establish the comprehensive evaluation system of deep shale gas “sweet spots”, to clarify the optimal “sweet spots” of geology, drilling, and fracturing in the Longmaxi reservoir. Results show that the total organic carbon content, porosity, and gas saturation of the long111 layer are higher than other layers. The Long111 layer has a low collapse pressure and a high compressive strength, the risk of wellbore instability is relatively low. The stress difference coefficient of All layers is less than 0.3, and the brittleness index of the Long111 layer is 62.35%. A complex fracture network is easier to form after fracturing. The conclusion shows that the Long111 layer is the optimal reservoir section of the Longmaxi Formation. Ensure the drilled rate of the Long111 layer and maximize the length of the horizontal section can obtain higher production.
基金supported by the International Cooperation Programme of Chengdu City(No.2020-GH02-00023-HZ)。
文摘This paper introduces a deep learning workflow to predict phase distributions within complex geometries during two-phase capillary-dominated drainage.We utilize subsamples from Computerized Tomography(CT)images of rocks and incorporate pixel size,interfacial tension,contact angle,and pressure as inputs.First,an efficient morphology-based simulator creates a diverse dataset of phase distributions.Then,two commonly used convolutional and recurrent neural networks are explored and their deficiencies are highlighted,particularly in capturing phase connectivity.Subsequently,we develop a Higher-Dimensional Vision Transformer(HD-ViT)that drains pores solely based on their size,with phase connectivity enforced as a post-processing step.This enables inference for images of varying sizes,resolutions,and inlet-outlet setup.After training on a massive dataset of over 9.5 million instances,HD-ViT achieves excellent performance.We demonstrate the accuracy and speed advantage of the model on new and larger sandstone and carbonate images.We further evaluate HD-ViT against experimental fluid distribution images and the corresponding Lattice-Boltzmann simulations,producing similar outcomes in a matter of seconds.In the end,we train and validate a 3D version of the model.
