The exploration and development theory and technology of marine shale gas with shallow burial depth of 3500 m in South China has become mature after more than 10 years of practice.In order to continuously promote the ...The exploration and development theory and technology of marine shale gas with shallow burial depth of 3500 m in South China has become mature after more than 10 years of practice.In order to continuously promote the exploration and development of shale gas in China,based on the research results of many scholars,combined with production practice,the main characteristics of marine shale gas in China and the main theory and technology of exploration and development are further summarized.The results show that:(1)The basic characteristics of marine shale gas in southern China are marine deep-water shelf deposition,and organic-rich shale is distributed continuously in a large area;The organic matter is stored in situ after high thermal maturity gas generation,and the gas content of shale is affected by late tectonic activity;The reservoir space is dominated by nano-scale pores,and the reservoir is super-tight and ultra-low permeability,which has no natural productivity without well stimulation;Bedding and natural fracture affect the productivity of shale gas wells;The mechanical properties of shale rock determine the effect of horizontal wells.In the early stage of well production,the production rate is high and the decline is fast,while in the middle and late stage,the rate is low but the production cycle is long.(2)Based on the above characteristics,the theory of“sweet spot”and“sweet interval”of shale gas and the theory of effective development of artificial gas reservoir are established,that is,the sedimentary and tectonic interaction forms the“sweet area”or“sweet spot”of marine shale gas.Gas productivity is determined by geological and engineering factors,so the“sweet spot”must be found to develop.By constructing artificial gas reservoir through“making an artificial high permeability area,and reconstructing a seepage field”,the effective development of ultra-tight and low permeability shale gas reservoirs can be realized.It is the most effective technique for shale gas development to accurately create“transparent geological body”of reservoirs based on geologyengineering integrated evaluation technology and establish artificial gas reservoir through multi-stage fracturing technology.(3)The overpressure area in the southern Sichuan Basin is the“sweet area”for shale gas development.The“sweet interval”of the lower Silurian Longmaxi Formation with a thickness of 3e5 m and high brittle-rich organic matter is the optimal“golden target”for horizontal wells.(4)The development leapfrog from the first generation to the second generation has been realized by the key technology of multi-stage fracturing of horizontal wells.The EUR per well of Upper Ordovician Wufeng Formation and Longmaxi Formation in southern Sichuan has increased from 0.5108 m3 in the initial stage to 1.0108 e1.2108 m3 at present with a buried depth of shallower than 3500 m.(5)The effective area favorable for shale gas development in southern Sichuan is 2.0104 km2,and it is estimated that the proven geological reserves of shale gas can reach 101012 m3.It is preliminarily predicted that the shale gas production in China will exceed 300108 m3 in 2025 and reach 400108 m3 in 2035.展开更多
Complex tectonic movements and high thermal maturity of marine shale dominate South China,where preservation conditions are critical for shale gas enrichment and productivity.Based on the exploration practices of the ...Complex tectonic movements and high thermal maturity of marine shale dominate South China,where preservation conditions are critical for shale gas enrichment and productivity.Based on the exploration practices of the Silurian shale gas at the southeastern margin of the Sichuan Basin in recent years,conventional gas and shale gas were compared in terms of their preservation conditions.The results revealed that superior roof and floor conditions are indispensable to shale gas preservation.Moreover,the self-sealing ability and the huge gap of up to 2–8 times between vertical and lateral permeability of shale gas reservoirs determine the lateral diffusion as the basic pattern of shale gas migration.The unconformity at the bottom of Lower Cambrian leads to worse preservation conditions in the system,and cutting by faults may accelerate the diffusion of shale gas.Major controlling factors for shale gas preservation and their criteria of discrimination were also investigated.It is suggested that:(1)the strength of tectonic modification is the major factor controlling shale gas preservation.Broad and gentle structures with continuous seals and an anticlinal setting are more favorable for the enrichment of shale gas,and a closed evolutionary environment with late uplifting is more favorable for the preservation of shale gas;(2)shale gas can be preserved well in downdip areas without faults or effectively closed or shielded by faults and areas far away from outcrops or zones with stratigraphic hiatus;(3)pressure coefficient is a comprehensive indicator for discriminating preservation conditions.In the study area,the pressure coefficient is in positive correlation with shale gas production and the high or super-high pressure of reservoir is a signal of good preservation condition for shale gas;and(4)in the areas within the southeastern Sichuan Basin,other than those close to erosion zones or hiatus,the Wufeng Fm.of Upper Ordovician and the Longmaxi Fm.of Lower Silurian present high pressure coefficient(up to 2.25)generally,demonstrating good preservation conditions for shale gas,while the pressure coefficient reduces progressively toward or outside the margin of the basin,corresponding to downgrading preservation conditions.展开更多
There are abundant natural gas resources in the marine shale gas reservoir of Middle Ordovician Wulalike Formation in the Ordos Basin,which is an important resource base for PetroChina Changqing Oilfield Company to in...There are abundant natural gas resources in the marine shale gas reservoir of Middle Ordovician Wulalike Formation in the Ordos Basin,which is an important resource base for PetroChina Changqing Oilfield Company to increase the reserves and production of oil and gas.Compared with the other shale gas reservoirs at home and aboard,however,the marine shale gas reservoir of Middle Ordovician Wulalike Formation in the Ordos Basin has a lower formation pressure coefficient and poorer reservoir physical properties and gas-bearing property,so its production increase difficulty is higher.In this paper,horizontal-well volume fracturing was studied and tested based on the earlier vertical well tests.According to the technical idea of the staged multi-cluster massive fracturing of long horizontal section,the propagation mechanisms and morphological characteristics of fractures were studied and analyzed based on the fracturing geological characteristics of the shale gas reservoir in the Ordos Basin.On this basis,a full three-dimensional fracture model was optimally established for parameter optimization.The fracturing of the test well ZP1 was carried out with 15 stages and 103 clusters.After the fracturing,a more complex fracture network was formed with a fracture complexity index of 0.4-0.6.The microseismic monitoring zone is 579 m long and 266 m wide and the fracture is 146 m high.To address the drainage difficulty after large-volume fracturing of low-pressure shale gas in the Ordos Basin,this paper carries out a gas energized fracturing test.Considering the characteristics of reservoir physical properties,gas-bearing property and segmented fractures,805 m3 liquid nitrogen was injected in stages during the fracturing of the test horizontal well.The formation pressure coefficient measured from pressure buildup data is increased from 0.7 to 0.8 to 1.88.The wellbore gaseliquid flow model was established and the parameters of long-period controlpressure drainage were optimized.The critical surface equipment was upgraded to achieve accurate measurement,safety and environmental protection.And the following research and practice results were obtained.First,based on the technological innovation and optimization,continuous gaseliquid two-phase flow is realized in the test well ZP1 and its production rate and pressure during the test are stable with the tested daily shale gas production at the wellhead of 6.42×10^(4)m^(3).Second,after fracturing,the absolute open flow of the test well reaches 26.4×10^(4)m^(3)/d,which is more than 10 times higher than the production rate of the vertical well in the same block during the test.Thus,a significant breakthrough is realized in the exploration of marine shale gas in North China.展开更多
The exploration and development of marine shale gas reservoirs in South China is challenged by complex geological and geographical conditions,such as strong transformation,post maturity,complex mountains and humanity....The exploration and development of marine shale gas reservoirs in South China is challenged by complex geological and geographical conditions,such as strong transformation,post maturity,complex mountains and humanity.In this paper,the evaluations on shale gas sweet spots conducted in Zhaotong demonstration zone in the past six years and the construction of 500 million m 3 shale gas productivity in Huangjinba region were discussed,and the results of shale gas reservoir evaluations in China and abroad were investigated.Accordingly,it is proposed that another two key indicators be taken into consideration in the evaluation on shale gas sweet spots in marine mountains in South China,i.e.shale gas preservation conditions and pore pressure,and the research on ground stress and natural microfracture systems should be strengthened.Then,systematic analysis was conducted by integrating shale gas multidisciplinary data and geological and engineering integration study was carried out.Finally,a 3D model,which was composed of“geophysics,reservoir geology,fracture system and rock geomechanics”,was established for shale gas reservoirs.Application practice shows that the geological engineering integration and the 3D reservoir modeling are effective methods for evaluating the shale gas sweet spots in complex marine mountains in South China.Besides,based on shale gas sweet spot evaluation,3D spatial congruency and superposition effects of multiple attributes and multiple evaluation parameters are presented.Moreover,the short-plate principle is the factor controlling the distribution patterns and evaluation results of shale gas sweet spots.It is concluded that this comprehensive evaluation method is innovative and effective in avoiding complex geological and engineering risks,so it is of guiding significance in exploration and development of marine shale gas in South China.展开更多
The identification of high-quality marine shale gas reservoirs has always been a key task in the exploration and development stage.However,due to the serious nonlinear relationship between the logging curve response a...The identification of high-quality marine shale gas reservoirs has always been a key task in the exploration and development stage.However,due to the serious nonlinear relationship between the logging curve response and high-quality reservoirs,the rapid identification of high-quality reservoirs has always been a problem of low accuracy.This study proposes a combination of the oversampling method and random forest algorithm to improve the identification accuracy of high-quality reservoirs based on logging data.The oversampling method is used to balance the number of samples of different types and the random forest algorithm is used to establish a highprecision and high-quality reservoir identification model.From the perspective of the prediction effect,the reservoir identification method that combines the oversampling method and the random forest algorithm has increased the accuracy of reservoir identification from the 44%seen in other machine learning algorithms to 78%,and the effect is significant.This research can improve the identifiability of high-quality marine shale gas reservoirs,guide the drilling of horizontal wells,and provide tangible help for the precise formulation of marine shale gas development plans.展开更多
The first fractured shale gas well of China was constructed in 2010.After 10 years of development,China has become the second country that possesses the core technology of shale gas development around the world,realiz...The first fractured shale gas well of China was constructed in 2010.After 10 years of development,China has become the second country that possesses the core technology of shale gas development around the world,realized the shale gas fracturing techniques from zero to one and from lagging to partially leading,and constructed the fracturing theory and technology system suitable for middle-shallow marine shale gas exploitation.In order to provide beneficial guidance for the efficient exploitation of shale gas in China in the future,this paper comprehensively reviews development history and status of domestic fundamental theories,optimized design methods,fluid systems,tools and technologies of shale gas fracturing and summarizes the research results in fundamental theories and optimized design methods,such as fracturing sweet-spot cognition,fracture network propagation simulation and control,rock hydration and flowback control,and SRV(stimulated reservoir volume)evaluation and characterization.The development and application of slick-water fracturing fluid system and new fracturing fluid with little or no water is discussed.The development and independent research&development level of multi-stage fracturing tools are evaluated,including drillable composite plug,soluble plug,large-diameter plug and casing cementing sleeve.The implementation situations of field technologies and processes are illustrated,including the early conventional multi-stage multi-cluster fracturing and the current“dense cluster”fracturing and temporary plugging fracturing.Based on this,the current challenges to domestic shale gas fracturing technologies are analyzed systematically,and the development direction of related technologies is forecast.In conclusion,it is necessary for China to continuously research the fracturing theories,technologies and methods suitable for domestic deep and ultra-deep marine shale gas,terrestrial shale gas and transitional shale gas to facilitate the future efficient development of shale gas in China.展开更多
In this paper,shale gas cores from the Lower Silurian Longmaxi Formation in the Zhaotong National Shale Gas Demonstration Area were selected to study the hydration effect of differentfluids on the fracture morphology ...In this paper,shale gas cores from the Lower Silurian Longmaxi Formation in the Zhaotong National Shale Gas Demonstration Area were selected to study the hydration effect of differentfluids on the fracture morphology inside the shale,the rock tensile strength and the Brazilian tensile failure mode.Fresh water and slick water were adopted for hydration pretreatments and the CT technique was used to compare the changes of the fabric in the shale.Then,Brazilian tensile tests were carried out to study the tensile strength and tensile failure modes of the shale specimen after hydration pretreatment.Finally,two horizontal wells in the study area were selected to perform pilot tests of hydration pre-treatment in their fracturing operation sites.And the following research results were obtained.First,in the process of spontaneous imbibition,the hydration effect of fresh water is superior to that of slick water in promoting the fracture complexity of marine shale in the same hydration duration.Second,fresh water has greater surface tension and lower viscosity and its hydration effect can not only promote the propagation of original fractures but induce new micro-fractures or branches,while the hydration effect of slick water mainly promotes the propagation of original fractures.Third,due to hydration effect,marine shale is damaged and its tensile strength is reduced.After the hydration pretreatment by fresh water and slick water,the tensile strength of the shale specimens are reduced by 35.6%and 18.1%,respectively.Fourth,according to the propagation paths of main fractures,the Brazilian tensile failure modes of hydrated shale can be divided into four types(i.e.,step shaped,dog-leg shaped,branching shaped and arc shaped)or their combinations,while the tensile failure mode of unhydrated shale is only a straight line.Fifth,hydration effect can effectively increase the complexity of the hydraulic fractures in marine shale,so if the conditions permit,it is recommended to inject a certain amount of fresh water at a high pumping rate within the limited pressure after perforation and to shut in the well until the hydraulic fracturing operation.And in order to reduce the difficulties of pumping the proppant during the hydraulic fracturing operation,a pumping strategy of“low proppant concentration,large volume of slurries”can be adopted to reach the expected proppant 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
基金Project supported by the Prospective Basic Research Project of CNPC“Exploration and development technologies for marine shale gas”(No.2021DJ19).
文摘The exploration and development theory and technology of marine shale gas with shallow burial depth of 3500 m in South China has become mature after more than 10 years of practice.In order to continuously promote the exploration and development of shale gas in China,based on the research results of many scholars,combined with production practice,the main characteristics of marine shale gas in China and the main theory and technology of exploration and development are further summarized.The results show that:(1)The basic characteristics of marine shale gas in southern China are marine deep-water shelf deposition,and organic-rich shale is distributed continuously in a large area;The organic matter is stored in situ after high thermal maturity gas generation,and the gas content of shale is affected by late tectonic activity;The reservoir space is dominated by nano-scale pores,and the reservoir is super-tight and ultra-low permeability,which has no natural productivity without well stimulation;Bedding and natural fracture affect the productivity of shale gas wells;The mechanical properties of shale rock determine the effect of horizontal wells.In the early stage of well production,the production rate is high and the decline is fast,while in the middle and late stage,the rate is low but the production cycle is long.(2)Based on the above characteristics,the theory of“sweet spot”and“sweet interval”of shale gas and the theory of effective development of artificial gas reservoir are established,that is,the sedimentary and tectonic interaction forms the“sweet area”or“sweet spot”of marine shale gas.Gas productivity is determined by geological and engineering factors,so the“sweet spot”must be found to develop.By constructing artificial gas reservoir through“making an artificial high permeability area,and reconstructing a seepage field”,the effective development of ultra-tight and low permeability shale gas reservoirs can be realized.It is the most effective technique for shale gas development to accurately create“transparent geological body”of reservoirs based on geologyengineering integrated evaluation technology and establish artificial gas reservoir through multi-stage fracturing technology.(3)The overpressure area in the southern Sichuan Basin is the“sweet area”for shale gas development.The“sweet interval”of the lower Silurian Longmaxi Formation with a thickness of 3e5 m and high brittle-rich organic matter is the optimal“golden target”for horizontal wells.(4)The development leapfrog from the first generation to the second generation has been realized by the key technology of multi-stage fracturing of horizontal wells.The EUR per well of Upper Ordovician Wufeng Formation and Longmaxi Formation in southern Sichuan has increased from 0.5108 m3 in the initial stage to 1.0108 e1.2108 m3 at present with a buried depth of shallower than 3500 m.(5)The effective area favorable for shale gas development in southern Sichuan is 2.0104 km2,and it is estimated that the proven geological reserves of shale gas can reach 101012 m3.It is preliminarily predicted that the shale gas production in China will exceed 300108 m3 in 2025 and reach 400108 m3 in 2035.
基金Sinopec special and significant project“Formative conditions of shale gas in lower strata association in the periphery of Sichuan Basin and play evaluation”(No.P13129).
文摘Complex tectonic movements and high thermal maturity of marine shale dominate South China,where preservation conditions are critical for shale gas enrichment and productivity.Based on the exploration practices of the Silurian shale gas at the southeastern margin of the Sichuan Basin in recent years,conventional gas and shale gas were compared in terms of their preservation conditions.The results revealed that superior roof and floor conditions are indispensable to shale gas preservation.Moreover,the self-sealing ability and the huge gap of up to 2–8 times between vertical and lateral permeability of shale gas reservoirs determine the lateral diffusion as the basic pattern of shale gas migration.The unconformity at the bottom of Lower Cambrian leads to worse preservation conditions in the system,and cutting by faults may accelerate the diffusion of shale gas.Major controlling factors for shale gas preservation and their criteria of discrimination were also investigated.It is suggested that:(1)the strength of tectonic modification is the major factor controlling shale gas preservation.Broad and gentle structures with continuous seals and an anticlinal setting are more favorable for the enrichment of shale gas,and a closed evolutionary environment with late uplifting is more favorable for the preservation of shale gas;(2)shale gas can be preserved well in downdip areas without faults or effectively closed or shielded by faults and areas far away from outcrops or zones with stratigraphic hiatus;(3)pressure coefficient is a comprehensive indicator for discriminating preservation conditions.In the study area,the pressure coefficient is in positive correlation with shale gas production and the high or super-high pressure of reservoir is a signal of good preservation condition for shale gas;and(4)in the areas within the southeastern Sichuan Basin,other than those close to erosion zones or hiatus,the Wufeng Fm.of Upper Ordovician and the Longmaxi Fm.of Lower Silurian present high pressure coefficient(up to 2.25)generally,demonstrating good preservation conditions for shale gas,while the pressure coefficient reduces progressively toward or outside the margin of the basin,corresponding to downgrading preservation conditions.
基金Project supported by the National Major Science and Technology Project“Development Demonstration Project of Large-scale Low-permeability Lithologic-Stratigraphic Reservoirs in the Ordos Basin”(No.2016ZX05050)。
文摘There are abundant natural gas resources in the marine shale gas reservoir of Middle Ordovician Wulalike Formation in the Ordos Basin,which is an important resource base for PetroChina Changqing Oilfield Company to increase the reserves and production of oil and gas.Compared with the other shale gas reservoirs at home and aboard,however,the marine shale gas reservoir of Middle Ordovician Wulalike Formation in the Ordos Basin has a lower formation pressure coefficient and poorer reservoir physical properties and gas-bearing property,so its production increase difficulty is higher.In this paper,horizontal-well volume fracturing was studied and tested based on the earlier vertical well tests.According to the technical idea of the staged multi-cluster massive fracturing of long horizontal section,the propagation mechanisms and morphological characteristics of fractures were studied and analyzed based on the fracturing geological characteristics of the shale gas reservoir in the Ordos Basin.On this basis,a full three-dimensional fracture model was optimally established for parameter optimization.The fracturing of the test well ZP1 was carried out with 15 stages and 103 clusters.After the fracturing,a more complex fracture network was formed with a fracture complexity index of 0.4-0.6.The microseismic monitoring zone is 579 m long and 266 m wide and the fracture is 146 m high.To address the drainage difficulty after large-volume fracturing of low-pressure shale gas in the Ordos Basin,this paper carries out a gas energized fracturing test.Considering the characteristics of reservoir physical properties,gas-bearing property and segmented fractures,805 m3 liquid nitrogen was injected in stages during the fracturing of the test horizontal well.The formation pressure coefficient measured from pressure buildup data is increased from 0.7 to 0.8 to 1.88.The wellbore gaseliquid flow model was established and the parameters of long-period controlpressure drainage were optimized.The critical surface equipment was upgraded to achieve accurate measurement,safety and environmental protection.And the following research and practice results were obtained.First,based on the technological innovation and optimization,continuous gaseliquid two-phase flow is realized in the test well ZP1 and its production rate and pressure during the test are stable with the tested daily shale gas production at the wellhead of 6.42×10^(4)m^(3).Second,after fracturing,the absolute open flow of the test well reaches 26.4×10^(4)m^(3)/d,which is more than 10 times higher than the production rate of the vertical well in the same block during the test.Thus,a significant breakthrough is realized in the exploration of marine shale gas in North China.
文摘The exploration and development of marine shale gas reservoirs in South China is challenged by complex geological and geographical conditions,such as strong transformation,post maturity,complex mountains and humanity.In this paper,the evaluations on shale gas sweet spots conducted in Zhaotong demonstration zone in the past six years and the construction of 500 million m 3 shale gas productivity in Huangjinba region were discussed,and the results of shale gas reservoir evaluations in China and abroad were investigated.Accordingly,it is proposed that another two key indicators be taken into consideration in the evaluation on shale gas sweet spots in marine mountains in South China,i.e.shale gas preservation conditions and pore pressure,and the research on ground stress and natural microfracture systems should be strengthened.Then,systematic analysis was conducted by integrating shale gas multidisciplinary data and geological and engineering integration study was carried out.Finally,a 3D model,which was composed of“geophysics,reservoir geology,fracture system and rock geomechanics”,was established for shale gas reservoirs.Application practice shows that the geological engineering integration and the 3D reservoir modeling are effective methods for evaluating the shale gas sweet spots in complex marine mountains in South China.Besides,based on shale gas sweet spot evaluation,3D spatial congruency and superposition effects of multiple attributes and multiple evaluation parameters are presented.Moreover,the short-plate principle is the factor controlling the distribution patterns and evaluation results of shale gas sweet spots.It is concluded that this comprehensive evaluation method is innovative and effective in avoiding complex geological and engineering risks,so it is of guiding significance in exploration and development of marine shale gas in South China.
基金This project was funded by the Laboratory for Marine Geology,Qingdao National Laboratory for Marine Science and Technology,(MGQNLM-KF202004)China Postdoctoral Science Foundation(2021M690161,2021T140691)+2 种基金Postdoctoral Funded Project in Hainan Province(General Program)Chinese Academy of Sciences-Special Research Assistant Projectthe Open Fund of Key Laboratory of Exploration Technologies for Oil and Gas Resources(Yangtze University),Ministry of Education(No.K2021–03,K2021-08)。
文摘The identification of high-quality marine shale gas reservoirs has always been a key task in the exploration and development stage.However,due to the serious nonlinear relationship between the logging curve response and high-quality reservoirs,the rapid identification of high-quality reservoirs has always been a problem of low accuracy.This study proposes a combination of the oversampling method and random forest algorithm to improve the identification accuracy of high-quality reservoirs based on logging data.The oversampling method is used to balance the number of samples of different types and the random forest algorithm is used to establish a highprecision and high-quality reservoir identification model.From the perspective of the prediction effect,the reservoir identification method that combines the oversampling method and the random forest algorithm has increased the accuracy of reservoir identification from the 44%seen in other machine learning algorithms to 78%,and the effect is significant.This research can improve the identifiability of high-quality marine shale gas reservoirs,guide the drilling of horizontal wells,and provide tangible help for the precise formulation of marine shale gas development plans.
文摘The first fractured shale gas well of China was constructed in 2010.After 10 years of development,China has become the second country that possesses the core technology of shale gas development around the world,realized the shale gas fracturing techniques from zero to one and from lagging to partially leading,and constructed the fracturing theory and technology system suitable for middle-shallow marine shale gas exploitation.In order to provide beneficial guidance for the efficient exploitation of shale gas in China in the future,this paper comprehensively reviews development history and status of domestic fundamental theories,optimized design methods,fluid systems,tools and technologies of shale gas fracturing and summarizes the research results in fundamental theories and optimized design methods,such as fracturing sweet-spot cognition,fracture network propagation simulation and control,rock hydration and flowback control,and SRV(stimulated reservoir volume)evaluation and characterization.The development and application of slick-water fracturing fluid system and new fracturing fluid with little or no water is discussed.The development and independent research&development level of multi-stage fracturing tools are evaluated,including drillable composite plug,soluble plug,large-diameter plug and casing cementing sleeve.The implementation situations of field technologies and processes are illustrated,including the early conventional multi-stage multi-cluster fracturing and the current“dense cluster”fracturing and temporary plugging fracturing.Based on this,the current challenges to domestic shale gas fracturing technologies are analyzed systematically,and the development direction of related technologies is forecast.In conclusion,it is necessary for China to continuously research the fracturing theories,technologies and methods suitable for domestic deep and ultra-deep marine shale gas,terrestrial shale gas and transitional shale gas to facilitate the future efficient development of shale gas in China.
基金Project supported by the National Major Science and Technology Project“Zhaotong Shale Gas Exploration and Development Demonstration Project”(No.2017ZX05063)the Science and Technology Project of CNPC Chuanqing Drilling Engineering Company Limited“Study and Application of Hydration Mechanism of Shale Reservoir”(No.CQ2018B-23-1-4).
文摘In this paper,shale gas cores from the Lower Silurian Longmaxi Formation in the Zhaotong National Shale Gas Demonstration Area were selected to study the hydration effect of differentfluids on the fracture morphology inside the shale,the rock tensile strength and the Brazilian tensile failure mode.Fresh water and slick water were adopted for hydration pretreatments and the CT technique was used to compare the changes of the fabric in the shale.Then,Brazilian tensile tests were carried out to study the tensile strength and tensile failure modes of the shale specimen after hydration pretreatment.Finally,two horizontal wells in the study area were selected to perform pilot tests of hydration pre-treatment in their fracturing operation sites.And the following research results were obtained.First,in the process of spontaneous imbibition,the hydration effect of fresh water is superior to that of slick water in promoting the fracture complexity of marine shale in the same hydration duration.Second,fresh water has greater surface tension and lower viscosity and its hydration effect can not only promote the propagation of original fractures but induce new micro-fractures or branches,while the hydration effect of slick water mainly promotes the propagation of original fractures.Third,due to hydration effect,marine shale is damaged and its tensile strength is reduced.After the hydration pretreatment by fresh water and slick water,the tensile strength of the shale specimens are reduced by 35.6%and 18.1%,respectively.Fourth,according to the propagation paths of main fractures,the Brazilian tensile failure modes of hydrated shale can be divided into four types(i.e.,step shaped,dog-leg shaped,branching shaped and arc shaped)or their combinations,while the tensile failure mode of unhydrated shale is only a straight line.Fifth,hydration effect can effectively increase the complexity of the hydraulic fractures in marine shale,so if the conditions permit,it is recommended to inject a certain amount of fresh water at a high pumping rate within the limited pressure after perforation and to shut in the well until the hydraulic fracturing operation.And in order to reduce the difficulties of pumping the proppant during the hydraulic fracturing operation,a pumping strategy of“low proppant concentration,large volume of slurries”can be adopted to reach the expected proppant 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.
