Over more than a decade of development,medium to deep shale gas reservoirs have faced rapid production declines,making sustained output challenging.To harness remaining reserves effectively,advanced fracturing techniq...Over more than a decade of development,medium to deep shale gas reservoirs have faced rapid production declines,making sustained output challenging.To harness remaining reserves effectively,advanced fracturing techniques such as infill drilling are essential.This study develops a complex fracture network model for dual horizontal wells and a four-dimensional in-situ stress evolution model,grounded in elastic porous media theory.These models simulate and analyze the evolution of formation pore pressure and in-situ stress during production.The investigation focuses on the influence of infill well fracturing timing on fracture propagation patterns,individual well productivity,and the overall productivity of well clusters.The findings reveal that,at infill well locations,the maximum horizontal principal stress undergoes the most significant reduction,while changes in the minimum horizontal principal stress and vertical stress remain minimal.The horizontal stress surrounding the infill well may reorient,potentially transitioning the stress regime from strike-slip to normal faulting.Delays in infill well fracturing increase lateral fracture deflection and diminish fracture propagation between wells.Considering the stable production phase and cumulative gas output of the well group,the study identifies an optimal timing for infill fracturing.Notably,larger well spacing shifts the optimal timing to a later stage.展开更多
The viscosity of fracturing fluid and in-situ stress difference are the two important factors that affect the hydraulic fracturing pressure and propagation morphology. In this study, raw coal was used to prepare coal ...The viscosity of fracturing fluid and in-situ stress difference are the two important factors that affect the hydraulic fracturing pressure and propagation morphology. In this study, raw coal was used to prepare coal samples for experiments, and clean fracturing fluid samples were prepared using CTAB surfactant. A series of hydraulic fracturing tests were conducted with an in-house developed triaxial hydraulic fracturing simulator and the fracturing process was monitored with an acoustic emission instrument to analyze the influences of fracturing fluid viscosity and horizontal in-situ stress difference on coal fracture propagation. The results show that the number of branched fractures decreased, the fracture pattern became simpler, the fractures width increased obviously, and the distribution of AE event points was concentrated with the increase of the fracturing fluid viscosity or the horizontal in-situ stress difference. The acoustic emission energy decreases with the increase of fracturing fluid viscosity and increases with the increase of horizontal in situ stress difference. The low viscosity clean fracturing fluid has strong elasticity and is easy to be compressed into the tip of fractures, resulting in complex fractures. The high viscosity clean fracturing fluids are the opposite. Our experimental results provide a reference and scientific basis for the design and optimization of field hydraulic fracturing parameters.展开更多
The tight sandstone in the Tarim Basin has the characteristics of large burial depth and development of nature fractures due to concentrated in-situ stress. Identifying the present-day in-situ stress orientation is im...The tight sandstone in the Tarim Basin has the characteristics of large burial depth and development of nature fractures due to concentrated in-situ stress. Identifying the present-day in-situ stress orientation is important in hydrocarbon exploration and development, but also a key scientific question in understanding naturally fractured reservoirs. This paper presents a case study where we integrate various methods using wireline and image-log data, to identify present-day in-situ stress direction of ultra-deep fractured tight sandstone reservoirs, in the Kuqa depression. We discuss the formation mechanism of the elliptical borehole, compares the advantages and applicable conditions of the double caliper method,resistivity image logs and array sonic logs method. The well borehole diameter is measured orthogonally,then the ellipse is fitted, and the in-situ stress orientation is identified by the azimuth of the short-axis borehole, but it fails in the borehole expansion section, the fracture development section and the borehole collapse section. The micro-resistivity image logs method reveals the borehole breakouts azimuth, and also the strike of induced fractures, which are used to determine the orientation of in-situ stress. However, under water-based mud conditions, it’s hard to distinguish natural fractures from induced fractures by image logs. Under oil-based mud conditions, the induced fractures are difficult to identify due to the compromised image quality. As for the sonic log, shear waves will split when passing through an anisotropic formation, shear waves will split during propagation, and the azimuth of fast shear waves is consistent with the orientation of in-situ stress. However, it is usually affected by the anisotropy caused by the excessively fast rotation of the well log tools, so that the azimuth of fast shear wave cannot effectively reflect the orientation of the in-situ stress. Based on comprehensive assessment and comparison, in this paper we propose a method integrating various logging data to identify the orientation of in-situ stress. Among various types of logging data, the breakouts azimuth identified by image logs is proved to be the most credible in identifying the orientation of in-situ stress, while using the direction of induced fractures under water-based mud conditions is also viable. However, the azimuth of the fast shear wave is consistent with the orientation of maximum in-situ stress only when the rotation speed of the logging tool is low. The caliper method can be used as a reference for verifying the other two methods. Using this integrated method to study the orientation of in-situ stress in the Keshen8 trap, the results show that faults are an important factor affecting the direction of in-situ stress, while multi-level faults will produce superimposed effects that cause the current direction of in-situ stress to change.展开更多
In-situ stress measurement using the hydraulic fracturing technique was made at Wanfu Coal Mine in Shandong Province, China. To solve problems caused by great measuring depth and extra thick overburden soil layers in ...In-situ stress measurement using the hydraulic fracturing technique was made at Wanfu Coal Mine in Shandong Province, China. To solve problems caused by great measuring depth and extra thick overburden soil layers in the mine, a series of improved techniques were developed for the traditional hydraulic fracturing technique and equipment to increase their pressure-enduring ability and to ensure safe and flexible removal of the sealing packers with other experimental apparatus. Successful in-situ stress measurement at 37 points within 7 boreholes, which were mostly over 1000 m deep, was completed. Through the measurement, detailed information of in-situ stress state has been provided for mining design of the mine. The improved hydraulic fracturing technique and equipment also provide reliable tools for in-situ stress measurement at great depth of other mines.展开更多
A new method, which is based on formation fracturing test and Kaiser effect method, has been developed for confirming the oilfield in-situ stress in this paper. The new method has been used in a certain oilfield of Ch...A new method, which is based on formation fracturing test and Kaiser effect method, has been developed for confirming the oilfield in-situ stress in this paper. The new method has been used in a certain oilfield of China and the determined oilfield in-situ stresses is more accurate than that based on one single method.展开更多
Four months after the Wenchuan Ms 8 earthquake in western Sichuan, China, in situ stress measurements were carried out along the Longmenshan fault zone with the purpose of obtaining stress parameters for earthquake ha...Four months after the Wenchuan Ms 8 earthquake in western Sichuan, China, in situ stress measurements were carried out along the Longmenshan fault zone with the purpose of obtaining stress parameters for earthquake hazard assessment. In-situ stresses were measured in three new boreholes by using overcoring with the piezomagnetic stress gauges for shallow depths and hydraulic fracturing for lower depths. The maximum horizontal stress in shallow depths （-20 m） is about 4.3 MPa, oriented N19°E, in the epicenter area at Yingxiu Town, about 9.7 MPa, oriented N51°W, at Baoxing County in the southwestern Longmenshan range, and about 2.6 MPa, oriented N39°E, near Kangding in the southernmost zone of the Longmenshan range. Hydraulic fracturing at borehole depths from 100 to 400 m shows a tendency towards increasing stress with depth. A comparison with the results measured before the Wenchuan earthquake along the Longmenshan zone and in the Tibetan Plateau demonstrates that the stress level remains relatively high in the southwestern segment of the Longmenshan range, and is still moderate in the epicenter zone. These results provide a key appraisal for future assessment of earthquake hazards of the Longmenshan fault zone and the aftershock occurrences of the Wenchuan earthquake.展开更多
Geothermal energy plays an important role in urban construction of the Xiong’an New Area.Geothermal reservoir fracture distribution of the Mesoproterozoic Jixianian Wumishan Formation(Fm.)carbonate reservoir in the R...Geothermal energy plays an important role in urban construction of the Xiong’an New Area.Geothermal reservoir fracture distribution of the Mesoproterozoic Jixianian Wumishan Formation(Fm.)carbonate reservoir in the Rongcheng geothermal field are evaluated based on FMI log from Wells D19 and D21.The results show carbonate reservoir fracture density of Well D19 is 15.2/100 m,greater than that of Well D21 with a value of 9.2/100 m.Reservoir porosity and permeability of Well D19 are better than that of Well D21,and the water saturation is bimodally distributed.The movable fluid volume ratio(BVM)of Well D19 is 2%to 8%with some zones exceeding 20%,while the value of Well D21 is less than 4%.Therefore,reservoir fractures in Well D19 are more conducive to fluid flow.Reservoir fractures have a similar occurrence to normal faults,indicating that the tensile stress field controlled the formation of such fractures.Developed reservoir fractures provide a good channel for groundwater convection.The circulation of regional groundwater and the heat exchange between water and rock and the multiple heat accumulation patterns form a stable and high potential heat reservoir in the Rongcheng geothermal field.展开更多
To predict fracture height in hydraulic fracturing, we developed and solved a hydraulic fracture height mathematical model aiming at high stress and multi-layered complex formations based on studying the effect of pla...To predict fracture height in hydraulic fracturing, we developed and solved a hydraulic fracture height mathematical model aiming at high stress and multi-layered complex formations based on studying the effect of plastic region generated by stress concentration at fracture tip on the growth of fracture height. Moreover, we compared the results from this model with results from two other fracture height prediction models(MFEH, Frac Pro) to verify the accuracy of the model. Sensitivity analysis by case computation of the model shows that the hydraulic fracture growth in ladder pattern, and the larger the fracture height, the more obvious the ladder growth pattern is. Fracture height growth is mainly influenced by the in-situ stresses. Fracture toughness of rock can prohibit the growth of fracture height to some extent. Moreover, the increase of fracturing fluid density can facilitate the propagation of the lower fracture tip.展开更多
To solve the technical cruxes of the conventional system in deep rock mass, an automatic testing system for hydraulic fracturing that includes a single tube for hydraulic loop, a pressure-relief valve, central-tubeles...To solve the technical cruxes of the conventional system in deep rock mass, an automatic testing system for hydraulic fracturing that includes a single tube for hydraulic loop, a pressure-relief valve, central-tubeless packers, and a multichannel real-time data acquisition system was used for in-situ stresses measurement at great depths （over 1000 m） in a coalfield in Juye of Northern China. The values and orientations of horizontal principal stresses were determined by the new system. The virgin stress field and its distributing law were decided by the linear regression from the logged 37 points in seven boreholes. Besides, the typical boreholes arranged in both the adjacent zone and far away zone of the faults were analyzed, respectively. The results show that a stress concentration phenomenon and a deflection in the orientation of the maximal horizontal stress exist in the adjacent zone of the faults, which further provides theoretical basis for design and optimization of mining.展开更多
When deep and ultra-deep shale gas well fracturing is carried out,multi-cluster fracturing can hardly realize synchronous initiation and propagation of hydraulic fractures due to the combined effects of heterogeneity ...When deep and ultra-deep shale gas well fracturing is carried out,multi-cluster fracturing can hardly realize synchronous initiation and propagation of hydraulic fractures due to the combined effects of heterogeneity of deep in-situ stress and"dense cluster"fracture arrangement,and the strong interference between fractures aggravates the unbalanced fracture propagation degree.Field practice proves that the fracture-opening temporary plugging fracturing technology can effectively control the unbalanced propagation of multiple fractures.In addition,the application effect of temporary plugging process can be improved by developing a method for simulating fracture control during fracture-opening temporary plugging fracturing of deep/ultra-deep shale-gas horizontal wells.Based on rock mechanics,elasticity mechanics,fluid mechanics and fracture propagation theory,combined with the flow distribution equation of horizontal-well multi-cluster fracturing and the plugging equation of temporary plugging balls,this paper establishes a fracture propagation model and a fracture control simulation method for the fracture-opening temporary plugging fracturing of deep/ultra-deep shale gas horizontal wells.Then,the influences of the number of temporary plugging balls and the times and timing of temporary plugging on temporary plugging control are simulated,and the influences of temporary plugging balls on fracture propagation morphology and SRV(stimulated reservoir volume)distribution are analyzed by taking Sinopec's one deep shale gas well in Dingshan-Dongxi structure of southeast Sichuan Basin as an example.And the following research results are obtained.First,fracture-opening temporary plugging can significantly promote the balanced propagation of multiple fractures,and the simulation confirms that the number of temporary plugging balls and the times and timing of temporary plugging play an important role in fracture control.Second,as the number of temporary plugging balls increase,the SRV increases firstly and then decreases,so there is an optimal number of temporary plugging balls.Third,increasing the times of temporary plugging can improve the fault tolerance rate of temporary plugging and diverting process,but it is necessary to increase the number of temporary plugging balls appropriately.Fourth,when the timing of temporary plugging is appropriate,the balanced propagation of multiple fractures is achieved and the maximum SRV is reached.In conclusion,this method is of great significance to optimizing the design of temporary plugging fracturing,improve the implementation level of field process and develop deep and ultra-deep shale gas efficiently.展开更多
High oil production from the Proterozoic formation of Shen 229 block in Damingtun Depression, Liaohe Basin, China, indicates the presence of natural fractured reservoir whose production potential is dominated by the s...High oil production from the Proterozoic formation of Shen 229 block in Damingtun Depression, Liaohe Basin, China, indicates the presence of natural fractured reservoir whose production potential is dominated by the structural fracture. A con- sistent structural model and good knowledge of the fracture systems are therefore of key importance in reducing risk in the de- velopment strategies. So data from cores and image logs have been collected to account for the basic characteristics of fracture, and then the analyzed results were integrated with the structural model in order to restrict the fracture network development during the structural evolvement. The structural evolution of the Proterozoic reservoir with time forms the basis for understanding the de- velopment of the 3D fracture system. Seismic interpretation and formation correlation were used to build a 3D geological model. The fault blocks that compose the Proterozoic formation reservoir were subsequently restored to their pre-deformation. From here, the structures were kinematically modeled to simulate the structural evolution of the reservoirs. At each time step, the dilatational and cumulative strain was calculated throughout the modelling history. The total strain which records the total spatial variation in the reservoir due to its structural history, together with core data, well data and the lithology distribution, was used to simulate geologically realistic discrete fracture networks. The benefit of this technique over traditional curvature analysis is that the structural evolution is taken into account, a factor that mostly dominates fracture formation.展开更多
In-situ stress is a critical factor influencing the permeability of coal reservoirs and the production capacity of coalbed methane(CBM)wells.Accurate prediction of in-situ stress and investigation of its influence on ...In-situ stress is a critical factor influencing the permeability of coal reservoirs and the production capacity of coalbed methane(CBM)wells.Accurate prediction of in-situ stress and investigation of its influence on coal reservoir permeability and production capacity are significant for CBM development.This study investigated the CBM development zone in the Zhengzhuang area of the Qinshui Basin.According to the low mechanical strength of coal reservoirs,this study derived a calculation model of the in-situ stress of coal reservoirs based on the multi-loop hydraulic fracturing method and analyzed the impacts of initial fractures on the calculated results.Moreover,by combining the data such as the in-situ stress,permeability,and drainage and recovery data of CBM wells,this study revealed the spatial distribution patterns of the current in-situ stress of the coal reservoirs and discussed the impacts of the insitu stress on the permeability and production capacity.The results are as follows.(1)Under given fracturing pressure,longer initial fractures are associated with higher calculated maximum horizontal principal stress values.Therefore,ignoring the effects of the initial fractures will cause the calculated values of the in-situ stress to be less than the actual values.(2)As the burial depth increases,the fracturing pressure,closure pressure,and the maximum and minimum horizontal principal stress of the coal reservoirs in the Zhengzhuang area constantly increase.The average gradients of the maximum and minimum horizontal principal stress are 3.17 MPa/100 m and 2.05 MPa/100 m,respectively.(3)Coal reservoir permeability is significantly controlled by the magnitude and state of the current in-situ stress.The coal reservoir permeability decreases exponentially with an increase in the effective principal stress.Moreover,a low lateral pressure coefficient(less than 1)is associated with minor horizontal compressive effects and high coal reservoir permeability.(4)Under similar conditions,such as resource endowments,CBM well capacity is higher in primary structural coal regions with moderate paleotectonic stress modification,low current in-situ stress,and lateral pressure coefficient of less than 1.展开更多
Machine learning is a good method for predicting fracture by integrating multi-source information. Post-stack seismic attributes are commonly used to predict medium to large fractures, while pre-stack seismic attribut...Machine learning is a good method for predicting fracture by integrating multi-source information. Post-stack seismic attributes are commonly used to predict medium to large fractures, while pre-stack seismic attributes are proven to be more sensitive to small and micro sized fractures through forward modeling. Using machine learning algorithm to fuse information from different scales to predict fracture can greatly improve the accuracy of fracture prediction. On the basis of In-Situ stress prediction, the paper conducted post-stack seismic attribute analysis and pre-stack seismic attribute analysis, further studied on the sensitivity of seismic attributes to fracture and selected sensitive attributes, used the sensitivity log of well-bore fractures as the target log for learning, ultimately obtained a comprehensive body of fracture. Through blind well verification, the prediction results match well with the we1l data and the prediction results is highly consistent with the production data. The results of fracture prediction are reliable, and the research method has certain reference significance for fracture prediction.展开更多
The “well factory” mode's high-density well placement and multi-stage hydraulic fracturing technology enable efficient development of unconventional oil and gas resources.However,the deployment of platform wells...The “well factory” mode's high-density well placement and multi-stage hydraulic fracturing technology enable efficient development of unconventional oil and gas resources.However,the deployment of platform wells in the “well factory” model results in small wellbore spacing,and the stress disturbances caused by fracturing operations may affect neighboring wells,leading to inter-well interference phenomena that cause casing deformation.This study investigates the issue of inter-well interference causing casing deformation or even failure during multi-stage hydraulic fracturing in the “well factory”model,and predicts high-risk locations for casing failure.A flow-mechanics coupled geomechanical finite element model with retaining geological stratification characteristics was established.Based on the theory of hydraulic fracturing-induced rock fragmentation and fluid action leading to the degradation of rock mechanical properties,the model simulated the four-dimensional evolution of multi-well fracturing areas over time and space,calculating the disturbance in the regional stress field caused by fracturing operations.Subsequently,the stress distribution of multiple well casings at different time points was calculated to predict high-risk locations for casing failure.The research results show that the redistribution of the stress field in the fracturing area increases the stress on the casing.The overlapping fracturing zones between wells cause significant stress interference,greatly increasing the risk of deformation and failure.By analyzing the Mises stress distribution of multi-well casings,high-risk locations for casing failure can be identified.The conclusion is that the key to preventing casing failure in platform wells in the “well factory” model is to optimize the spatial distribution of fracturing zones between wells and reasonably arrange well spacing.The study provides new insights and methods for predicting casing failure in unconventional oil and gas reservoirs and offers references for optimizing drilling and fracturing designs.展开更多
Multipole array sonic logging tools have widely been employed in Chinese oilfields in recent years. We have developed a software package for rock mechanical analysis with multipole array sonic logs. This advanced data...Multipole array sonic logging tools have widely been employed in Chinese oilfields in recent years. We have developed a software package for rock mechanical analysis with multipole array sonic logs. This advanced data processing method and software have been applied to the Tahe oilfield in Northern West China to provide guidance to acid hydraulic fracturing design and evaluation. In this paper, we present the field examples of such data processing and applications to demonstrate the validity and advantages of our method and software package.展开更多
Geological characteristics,geomechanical behavior and hydraulic fracture propagation mechanism in the Marcellus shale gas play are analyzed and compared with China’s Fuling shale play.Successful experiences in hydrau...Geological characteristics,geomechanical behavior and hydraulic fracture propagation mechanism in the Marcellus shale gas play are analyzed and compared with China’s Fuling shale play.Successful experiences in hydraulic fracturing and shale gas development in the Marcellus shale gas play are summarized,which might be applicable in other shale plays.The main factors contributing to the successful development of the Marcellus shale gas play include adoption of advanced drilling and completion technologies,increases of hydraulic fracturing stages,proppant concentration and fluid injection volume.The geological and geomechanical mechanisms related to those technologies are analyzed,particularly the in-situ stress impacts on hydraulic fracturing.The minimum horizontal stress controls where the fractures are initiated,and the maximum horizontal stress dominates the direction of the hydraulic fracture propagation.Hydraulic fracturing performed in the shale reservoir normally has no stress barriers in most cases because the shale has a high minimum horizontal stress,inducing hydraulic fractures propagating beyond the reservoir zone,resulting in inefficient stimulation.This is a common problem in shale plays,and its mechanism is studied in the paper.It is also found that the on-azimuth well has a higher productivity than the off-azimuth well,because shear fractures are created in the off-azimuth well,causing main fractures to kink and increasing fracture tortuosity and friction.The Fuling shale gas play has a markedly higher minimum horizontal stress and much smaller horizontal stress difference.The high minimum horizontal stress causes a much higher formation breakdown pressure;therefore,hydraulic fracturing in the Fuling shale gas play needs a higher treatment pressure,which implies higher difficulty in fracture propagation.The small difference in the two horizontal stresses in the Fuling shale gas play generates shorter and more complex hydraulic fractures,because hydraulic fractures in this case are prone to curve to preexisting fractures.To overcome these difficulties,we recommend reducing well spacing and increasing proppant concentration to increase gas productivity for the Fuling shale gas development.展开更多
基金supported by the National Natural Science Foundation of China(Grant No.52374043)the Southwest Oil&Gas Field Branch in PetroChina(Grant No.JS2023-115)。
文摘Over more than a decade of development,medium to deep shale gas reservoirs have faced rapid production declines,making sustained output challenging.To harness remaining reserves effectively,advanced fracturing techniques such as infill drilling are essential.This study develops a complex fracture network model for dual horizontal wells and a four-dimensional in-situ stress evolution model,grounded in elastic porous media theory.These models simulate and analyze the evolution of formation pore pressure and in-situ stress during production.The investigation focuses on the influence of infill well fracturing timing on fracture propagation patterns,individual well productivity,and the overall productivity of well clusters.The findings reveal that,at infill well locations,the maximum horizontal principal stress undergoes the most significant reduction,while changes in the minimum horizontal principal stress and vertical stress remain minimal.The horizontal stress surrounding the infill well may reorient,potentially transitioning the stress regime from strike-slip to normal faulting.Delays in infill well fracturing increase lateral fracture deflection and diminish fracture propagation between wells.Considering the stable production phase and cumulative gas output of the well group,the study identifies an optimal timing for infill fracturing.Notably,larger well spacing shifts the optimal timing to a later stage.
基金National Natural Science Foundation of China (51974176, 52174194, 51934004)Shandong Provincial Colleges and Universities Youth Innovation and Technology Support Program (2019KJH006)+1 种基金Taishan Scholars Project (TS20190935)Shandong outstanding youth fund (ZR2020JQ22).
文摘The viscosity of fracturing fluid and in-situ stress difference are the two important factors that affect the hydraulic fracturing pressure and propagation morphology. In this study, raw coal was used to prepare coal samples for experiments, and clean fracturing fluid samples were prepared using CTAB surfactant. A series of hydraulic fracturing tests were conducted with an in-house developed triaxial hydraulic fracturing simulator and the fracturing process was monitored with an acoustic emission instrument to analyze the influences of fracturing fluid viscosity and horizontal in-situ stress difference on coal fracture propagation. The results show that the number of branched fractures decreased, the fracture pattern became simpler, the fractures width increased obviously, and the distribution of AE event points was concentrated with the increase of the fracturing fluid viscosity or the horizontal in-situ stress difference. The acoustic emission energy decreases with the increase of fracturing fluid viscosity and increases with the increase of horizontal in situ stress difference. The low viscosity clean fracturing fluid has strong elasticity and is easy to be compressed into the tip of fractures, resulting in complex fractures. The high viscosity clean fracturing fluids are the opposite. Our experimental results provide a reference and scientific basis for the design and optimization of field hydraulic fracturing parameters.
基金financial support for this work comes from the Science Foundation of CUPB(No.2462017YJRC023)supported by the Exploration and Development Research Institute of Petro China Tarim Oilfield Branch Company
文摘The tight sandstone in the Tarim Basin has the characteristics of large burial depth and development of nature fractures due to concentrated in-situ stress. Identifying the present-day in-situ stress orientation is important in hydrocarbon exploration and development, but also a key scientific question in understanding naturally fractured reservoirs. This paper presents a case study where we integrate various methods using wireline and image-log data, to identify present-day in-situ stress direction of ultra-deep fractured tight sandstone reservoirs, in the Kuqa depression. We discuss the formation mechanism of the elliptical borehole, compares the advantages and applicable conditions of the double caliper method,resistivity image logs and array sonic logs method. The well borehole diameter is measured orthogonally,then the ellipse is fitted, and the in-situ stress orientation is identified by the azimuth of the short-axis borehole, but it fails in the borehole expansion section, the fracture development section and the borehole collapse section. The micro-resistivity image logs method reveals the borehole breakouts azimuth, and also the strike of induced fractures, which are used to determine the orientation of in-situ stress. However, under water-based mud conditions, it’s hard to distinguish natural fractures from induced fractures by image logs. Under oil-based mud conditions, the induced fractures are difficult to identify due to the compromised image quality. As for the sonic log, shear waves will split when passing through an anisotropic formation, shear waves will split during propagation, and the azimuth of fast shear waves is consistent with the orientation of in-situ stress. However, it is usually affected by the anisotropy caused by the excessively fast rotation of the well log tools, so that the azimuth of fast shear wave cannot effectively reflect the orientation of the in-situ stress. Based on comprehensive assessment and comparison, in this paper we propose a method integrating various logging data to identify the orientation of in-situ stress. Among various types of logging data, the breakouts azimuth identified by image logs is proved to be the most credible in identifying the orientation of in-situ stress, while using the direction of induced fractures under water-based mud conditions is also viable. However, the azimuth of the fast shear wave is consistent with the orientation of maximum in-situ stress only when the rotation speed of the logging tool is low. The caliper method can be used as a reference for verifying the other two methods. Using this integrated method to study the orientation of in-situ stress in the Keshen8 trap, the results show that faults are an important factor affecting the direction of in-situ stress, while multi-level faults will produce superimposed effects that cause the current direction of in-situ stress to change.
基金supported by the National Natural Science Foundation of China (No. 50490271)
文摘In-situ stress measurement using the hydraulic fracturing technique was made at Wanfu Coal Mine in Shandong Province, China. To solve problems caused by great measuring depth and extra thick overburden soil layers in the mine, a series of improved techniques were developed for the traditional hydraulic fracturing technique and equipment to increase their pressure-enduring ability and to ensure safe and flexible removal of the sealing packers with other experimental apparatus. Successful in-situ stress measurement at 37 points within 7 boreholes, which were mostly over 1000 m deep, was completed. Through the measurement, detailed information of in-situ stress state has been provided for mining design of the mine. The improved hydraulic fracturing technique and equipment also provide reliable tools for in-situ stress measurement at great depth of other mines.
文摘A new method, which is based on formation fracturing test and Kaiser effect method, has been developed for confirming the oilfield in-situ stress in this paper. The new method has been used in a certain oilfield of China and the determined oilfield in-situ stresses is more accurate than that based on one single method.
基金the auspice of National Key Basic Project(973)(granted No.2008CB425702)National Science and Technology Project(granted No.SinoProbe-06)
文摘Four months after the Wenchuan Ms 8 earthquake in western Sichuan, China, in situ stress measurements were carried out along the Longmenshan fault zone with the purpose of obtaining stress parameters for earthquake hazard assessment. In-situ stresses were measured in three new boreholes by using overcoring with the piezomagnetic stress gauges for shallow depths and hydraulic fracturing for lower depths. The maximum horizontal stress in shallow depths （-20 m） is about 4.3 MPa, oriented N19°E, in the epicenter area at Yingxiu Town, about 9.7 MPa, oriented N51°W, at Baoxing County in the southwestern Longmenshan range, and about 2.6 MPa, oriented N39°E, near Kangding in the southernmost zone of the Longmenshan range. Hydraulic fracturing at borehole depths from 100 to 400 m shows a tendency towards increasing stress with depth. A comparison with the results measured before the Wenchuan earthquake along the Longmenshan zone and in the Tibetan Plateau demonstrates that the stress level remains relatively high in the southwestern segment of the Longmenshan range, and is still moderate in the epicenter zone. These results provide a key appraisal for future assessment of earthquake hazards of the Longmenshan fault zone and the aftershock occurrences of the Wenchuan earthquake.
基金funded by the National Key R&D Program of China(Grant No.2019YFB1504101)the China Postdoctoral Science Foundation(Grant No.2019M663087)the National Natural Science Foundation of China(Grant No.42002189)。
文摘Geothermal energy plays an important role in urban construction of the Xiong’an New Area.Geothermal reservoir fracture distribution of the Mesoproterozoic Jixianian Wumishan Formation(Fm.)carbonate reservoir in the Rongcheng geothermal field are evaluated based on FMI log from Wells D19 and D21.The results show carbonate reservoir fracture density of Well D19 is 15.2/100 m,greater than that of Well D21 with a value of 9.2/100 m.Reservoir porosity and permeability of Well D19 are better than that of Well D21,and the water saturation is bimodally distributed.The movable fluid volume ratio(BVM)of Well D19 is 2%to 8%with some zones exceeding 20%,while the value of Well D21 is less than 4%.Therefore,reservoir fractures in Well D19 are more conducive to fluid flow.Reservoir fractures have a similar occurrence to normal faults,indicating that the tensile stress field controlled the formation of such fractures.Developed reservoir fractures provide a good channel for groundwater convection.The circulation of regional groundwater and the heat exchange between water and rock and the multiple heat accumulation patterns form a stable and high potential heat reservoir in the Rongcheng geothermal field.
基金Supported by the Natural Science Foundation of Heilongjiang Province of China(YQ2019E007).
文摘To predict fracture height in hydraulic fracturing, we developed and solved a hydraulic fracture height mathematical model aiming at high stress and multi-layered complex formations based on studying the effect of plastic region generated by stress concentration at fracture tip on the growth of fracture height. Moreover, we compared the results from this model with results from two other fracture height prediction models(MFEH, Frac Pro) to verify the accuracy of the model. Sensitivity analysis by case computation of the model shows that the hydraulic fracture growth in ladder pattern, and the larger the fracture height, the more obvious the ladder growth pattern is. Fracture height growth is mainly influenced by the in-situ stresses. Fracture toughness of rock can prohibit the growth of fracture height to some extent. Moreover, the increase of fracturing fluid density can facilitate the propagation of the lower fracture tip.
基金This work was financially supported by the National Natural Science Foundation of China (No. 50490271)
文摘To solve the technical cruxes of the conventional system in deep rock mass, an automatic testing system for hydraulic fracturing that includes a single tube for hydraulic loop, a pressure-relief valve, central-tubeless packers, and a multichannel real-time data acquisition system was used for in-situ stresses measurement at great depths （over 1000 m） in a coalfield in Juye of Northern China. The values and orientations of horizontal principal stresses were determined by the new system. The virgin stress field and its distributing law were decided by the linear regression from the logged 37 points in seven boreholes. Besides, the typical boreholes arranged in both the adjacent zone and far away zone of the faults were analyzed, respectively. The results show that a stress concentration phenomenon and a deflection in the orientation of the maximal horizontal stress exist in the adjacent zone of the faults, which further provides theoretical basis for design and optimization of mining.
基金Major Project of National Natural Science Foundation of China Basic Theory of Efficient Development of Shale Oil and Gas(No.51490653)Theory and Method of Efficient Con struction of Fracture Network in Deep and Ultra-Deep Shale Gas Horizontal Wells(No.U19A2043)National Natural Science Foundation of China Theory and Method of Long term Propping for Deep Shale Gas Hydraulic Fractures based on DEM-LBM Hydro-Mechanical Coupling(No.52104039).
文摘When deep and ultra-deep shale gas well fracturing is carried out,multi-cluster fracturing can hardly realize synchronous initiation and propagation of hydraulic fractures due to the combined effects of heterogeneity of deep in-situ stress and"dense cluster"fracture arrangement,and the strong interference between fractures aggravates the unbalanced fracture propagation degree.Field practice proves that the fracture-opening temporary plugging fracturing technology can effectively control the unbalanced propagation of multiple fractures.In addition,the application effect of temporary plugging process can be improved by developing a method for simulating fracture control during fracture-opening temporary plugging fracturing of deep/ultra-deep shale-gas horizontal wells.Based on rock mechanics,elasticity mechanics,fluid mechanics and fracture propagation theory,combined with the flow distribution equation of horizontal-well multi-cluster fracturing and the plugging equation of temporary plugging balls,this paper establishes a fracture propagation model and a fracture control simulation method for the fracture-opening temporary plugging fracturing of deep/ultra-deep shale gas horizontal wells.Then,the influences of the number of temporary plugging balls and the times and timing of temporary plugging on temporary plugging control are simulated,and the influences of temporary plugging balls on fracture propagation morphology and SRV(stimulated reservoir volume)distribution are analyzed by taking Sinopec's one deep shale gas well in Dingshan-Dongxi structure of southeast Sichuan Basin as an example.And the following research results are obtained.First,fracture-opening temporary plugging can significantly promote the balanced propagation of multiple fractures,and the simulation confirms that the number of temporary plugging balls and the times and timing of temporary plugging play an important role in fracture control.Second,as the number of temporary plugging balls increase,the SRV increases firstly and then decreases,so there is an optimal number of temporary plugging balls.Third,increasing the times of temporary plugging can improve the fault tolerance rate of temporary plugging and diverting process,but it is necessary to increase the number of temporary plugging balls appropriately.Fourth,when the timing of temporary plugging is appropriate,the balanced propagation of multiple fractures is achieved and the maximum SRV is reached.In conclusion,this method is of great significance to optimizing the design of temporary plugging fracturing,improve the implementation level of field process and develop deep and ultra-deep shale gas efficiently.
文摘High oil production from the Proterozoic formation of Shen 229 block in Damingtun Depression, Liaohe Basin, China, indicates the presence of natural fractured reservoir whose production potential is dominated by the structural fracture. A con- sistent structural model and good knowledge of the fracture systems are therefore of key importance in reducing risk in the de- velopment strategies. So data from cores and image logs have been collected to account for the basic characteristics of fracture, and then the analyzed results were integrated with the structural model in order to restrict the fracture network development during the structural evolvement. The structural evolution of the Proterozoic reservoir with time forms the basis for understanding the de- velopment of the 3D fracture system. Seismic interpretation and formation correlation were used to build a 3D geological model. The fault blocks that compose the Proterozoic formation reservoir were subsequently restored to their pre-deformation. From here, the structures were kinematically modeled to simulate the structural evolution of the reservoirs. At each time step, the dilatational and cumulative strain was calculated throughout the modelling history. The total strain which records the total spatial variation in the reservoir due to its structural history, together with core data, well data and the lithology distribution, was used to simulate geologically realistic discrete fracture networks. The benefit of this technique over traditional curvature analysis is that the structural evolution is taken into account, a factor that mostly dominates fracture formation.
基金sponsored by the National Natural Science Foundation of China(42002181)projecta public bidding project of 2020 Shanxi Provincial Science and Technology Program(20201101002-03).
文摘In-situ stress is a critical factor influencing the permeability of coal reservoirs and the production capacity of coalbed methane(CBM)wells.Accurate prediction of in-situ stress and investigation of its influence on coal reservoir permeability and production capacity are significant for CBM development.This study investigated the CBM development zone in the Zhengzhuang area of the Qinshui Basin.According to the low mechanical strength of coal reservoirs,this study derived a calculation model of the in-situ stress of coal reservoirs based on the multi-loop hydraulic fracturing method and analyzed the impacts of initial fractures on the calculated results.Moreover,by combining the data such as the in-situ stress,permeability,and drainage and recovery data of CBM wells,this study revealed the spatial distribution patterns of the current in-situ stress of the coal reservoirs and discussed the impacts of the insitu stress on the permeability and production capacity.The results are as follows.(1)Under given fracturing pressure,longer initial fractures are associated with higher calculated maximum horizontal principal stress values.Therefore,ignoring the effects of the initial fractures will cause the calculated values of the in-situ stress to be less than the actual values.(2)As the burial depth increases,the fracturing pressure,closure pressure,and the maximum and minimum horizontal principal stress of the coal reservoirs in the Zhengzhuang area constantly increase.The average gradients of the maximum and minimum horizontal principal stress are 3.17 MPa/100 m and 2.05 MPa/100 m,respectively.(3)Coal reservoir permeability is significantly controlled by the magnitude and state of the current in-situ stress.The coal reservoir permeability decreases exponentially with an increase in the effective principal stress.Moreover,a low lateral pressure coefficient(less than 1)is associated with minor horizontal compressive effects and high coal reservoir permeability.(4)Under similar conditions,such as resource endowments,CBM well capacity is higher in primary structural coal regions with moderate paleotectonic stress modification,low current in-situ stress,and lateral pressure coefficient of less than 1.
文摘Machine learning is a good method for predicting fracture by integrating multi-source information. Post-stack seismic attributes are commonly used to predict medium to large fractures, while pre-stack seismic attributes are proven to be more sensitive to small and micro sized fractures through forward modeling. Using machine learning algorithm to fuse information from different scales to predict fracture can greatly improve the accuracy of fracture prediction. On the basis of In-Situ stress prediction, the paper conducted post-stack seismic attribute analysis and pre-stack seismic attribute analysis, further studied on the sensitivity of seismic attributes to fracture and selected sensitive attributes, used the sensitivity log of well-bore fractures as the target log for learning, ultimately obtained a comprehensive body of fracture. Through blind well verification, the prediction results match well with the we1l data and the prediction results is highly consistent with the production data. The results of fracture prediction are reliable, and the research method has certain reference significance for fracture prediction.
基金supported by the National Natural Science Foundation of China (No.52104008&No.52274042)the Natural Science Foundation of Sichuan,China (No.2024NSFSC0963)。
文摘The “well factory” mode's high-density well placement and multi-stage hydraulic fracturing technology enable efficient development of unconventional oil and gas resources.However,the deployment of platform wells in the “well factory” model results in small wellbore spacing,and the stress disturbances caused by fracturing operations may affect neighboring wells,leading to inter-well interference phenomena that cause casing deformation.This study investigates the issue of inter-well interference causing casing deformation or even failure during multi-stage hydraulic fracturing in the “well factory”model,and predicts high-risk locations for casing failure.A flow-mechanics coupled geomechanical finite element model with retaining geological stratification characteristics was established.Based on the theory of hydraulic fracturing-induced rock fragmentation and fluid action leading to the degradation of rock mechanical properties,the model simulated the four-dimensional evolution of multi-well fracturing areas over time and space,calculating the disturbance in the regional stress field caused by fracturing operations.Subsequently,the stress distribution of multiple well casings at different time points was calculated to predict high-risk locations for casing failure.The research results show that the redistribution of the stress field in the fracturing area increases the stress on the casing.The overlapping fracturing zones between wells cause significant stress interference,greatly increasing the risk of deformation and failure.By analyzing the Mises stress distribution of multi-well casings,high-risk locations for casing failure can be identified.The conclusion is that the key to preventing casing failure in platform wells in the “well factory” model is to optimize the spatial distribution of fracturing zones between wells and reasonably arrange well spacing.The study provides new insights and methods for predicting casing failure in unconventional oil and gas reservoirs and offers references for optimizing drilling and fracturing designs.
基金This project is sponsored by Natural Science Foundation of China supported project No. 50674098.
文摘Multipole array sonic logging tools have widely been employed in Chinese oilfields in recent years. We have developed a software package for rock mechanical analysis with multipole array sonic logs. This advanced data processing method and software have been applied to the Tahe oilfield in Northern West China to provide guidance to acid hydraulic fracturing design and evaluation. In this paper, we present the field examples of such data processing and applications to demonstrate the validity and advantages of our method and software package.
文摘Geological characteristics,geomechanical behavior and hydraulic fracture propagation mechanism in the Marcellus shale gas play are analyzed and compared with China’s Fuling shale play.Successful experiences in hydraulic fracturing and shale gas development in the Marcellus shale gas play are summarized,which might be applicable in other shale plays.The main factors contributing to the successful development of the Marcellus shale gas play include adoption of advanced drilling and completion technologies,increases of hydraulic fracturing stages,proppant concentration and fluid injection volume.The geological and geomechanical mechanisms related to those technologies are analyzed,particularly the in-situ stress impacts on hydraulic fracturing.The minimum horizontal stress controls where the fractures are initiated,and the maximum horizontal stress dominates the direction of the hydraulic fracture propagation.Hydraulic fracturing performed in the shale reservoir normally has no stress barriers in most cases because the shale has a high minimum horizontal stress,inducing hydraulic fractures propagating beyond the reservoir zone,resulting in inefficient stimulation.This is a common problem in shale plays,and its mechanism is studied in the paper.It is also found that the on-azimuth well has a higher productivity than the off-azimuth well,because shear fractures are created in the off-azimuth well,causing main fractures to kink and increasing fracture tortuosity and friction.The Fuling shale gas play has a markedly higher minimum horizontal stress and much smaller horizontal stress difference.The high minimum horizontal stress causes a much higher formation breakdown pressure;therefore,hydraulic fracturing in the Fuling shale gas play needs a higher treatment pressure,which implies higher difficulty in fracture propagation.The small difference in the two horizontal stresses in the Fuling shale gas play generates shorter and more complex hydraulic fractures,because hydraulic fractures in this case are prone to curve to preexisting fractures.To overcome these difficulties,we recommend reducing well spacing and increasing proppant concentration to increase gas productivity for the Fuling shale gas development.
