Tri-axial fracturing studies were carried out to understand the impact of lateral mechanical parameters on fracture propagation from multiple in-plane perforations in horizontal wells. Additionally, the discussion cov...Tri-axial fracturing studies were carried out to understand the impact of lateral mechanical parameters on fracture propagation from multiple in-plane perforations in horizontal wells. Additionally, the discussion covered the effects of geology, treatment, and perforation characteristics on the non-planar propagation behavior. According to experimental findings, two parallel transverse fractures can be successfully initiated from in-plane perforation clusters in the horizontal well because of the in-plane perforation, the guide nonuniform fishbone structure fracture propagation still can be exhibited. The emergence of transverse fractures and axial fractures combined as complex fractures under low horizontal principal stress difference and large pump rate conditions. The injection pressure was also investigated, and the largest breakdown pressure can be also found for samples under these conditions.The increase in perforation number or decrease in the cluster spacing could provide more chances to increase the complexity of the target stimulated zone, thus affecting the pressure fluctuation. In a contrast, the increase in fracturing fluid viscosity can reduce the multiple fracture complexity. The fracture propagation is significantly affected by the change in the rock mechanical properties. The fracture geometry in the high brittle zone seems to be complicated and tends to induce fracture reorientation from the weak-brittle zone. The stress shadow effect can be used to explain the fracture attraction, branch, connection, and repulsion in the multiple perforation clusters for the horizontal well.The increase in the rock heterogeneity can enhance the stress shadow effect, resulting in more complex fracture geometry. In addition, the variable density perforation and temporary plugging fracturing were also conducted, demonstrating higher likelihood for non-uniform multiple fracture propagation. Thus, to increase the perforation efficiency along the horizontal well, it is necessary to consider the lateral fracability of the horizontal well on target formation.展开更多
Multi-cluster perforation and multi-staged fracturing of horizontal well is one of the main technologies in volumetric fracturing stimulation of unconventional oil and gas reservoirs,but unconventional reservoirs in C...Multi-cluster perforation and multi-staged fracturing of horizontal well is one of the main technologies in volumetric fracturing stimulation of unconventional oil and gas reservoirs,but unconventional reservoirs in China are generally of strong heterogeneity,which causes different fracture initiation pressures in different positions of lateral,making it difficult to ensure the balanced fracture initiation and propagation between clusters in multi-cluster perforating.It is in urgent need to precisely evaluate the difference in rock strength in lateral and determine the well section with similar rock strength to deploy fractures,so as to reach the goal of balanced stimulation.Based on the drilling and logging data,this paper establishes an unsupervised clustering model of mechanical specific energy of bit at the bottomhole the lateral.Then,the influence of drill string friction,composite drilling and jet-assisted rock breaking on the mechanical specific energy is analyzed,and the distribution and clustering categories of bottomhole mechanical specific energy with decimeter spatial resolution are obtained.Finally,a fracture deployment optimization method for horizontal well volumetric fracturing aiming balanced stimulation is developed by comprehensively considering inter-fracture interference,casing collar position,plug position,and clustering result of bottomhole mechanical specific energy.The following results are obtained.First,compared with brittleness index,Poisson's ratioandstressdifference,perforation erosion area isina strongercorrelationwith themechanical specific energy,andthemechanical specific energy can effectively characterize the difference in the amount of proppant injected into the perforation clusters in the lateral,so it can be served as one of the important indicators for the selection of fracture deployment position.Second,the drilling and logging data cleaning and smoothing and the clustering number selection by the elbow method are the key steps to obtain the clustering results of bottomhole mechanical specific energy,which can tell the difference in the mechanical specific energy with decimeter-level resolution.Third,the interval with mechanical specific energy within 10%of the averagevalue in the section is selected for deploying perforation clusters,and the compiled computer algorithm can automatically determine the optimal position of fracturing section and cluster,so as to realize the differential design of stage spacing and cluster spacing.In conclusion,the research results can further improve the fractures deployment efficiency and balanced stimulation of volumetric fracturing in unconventional oil andgasreservoirs,and this technology is expected to provide ideas andnew methods forthe fracturedeployment optimization of horizontal well volumetric fracturing in unconventional oil and gas reservoirs.展开更多
An oriented cluster perforating technology,which integrates both advantages of cluster and oriented perforating,will help solve a series of technical complexities in horizontal well drilling.For realizing its better a...An oriented cluster perforating technology,which integrates both advantages of cluster and oriented perforating,will help solve a series of technical complexities in horizontal well drilling.For realizing its better application in oil and gas development,a series of technologies were developed including perforator self-weight eccentricity,matching of the electronic selective module codes with the surface program control,axial centralized contact signal transmission,and post-perforation intercluster sealing insulation.In this way,the following functions could be realized,such as cable-transmission horizontal well perforator self-weight orientation,dynamic signal transmission,reliable addressing&selective perforation and post-perforation intercluster sealing.The combined perforation and bridge plug or the multi-cluster perforation can be fulfilled in one trip of perforation string.As a result,the horizontal-well oriented cluster perforating technology based on cable conveying was developed.This technology was successfully applied in unconventional gas reservoir exploitation,such as shale gas and coalbed methane,with accurate orientation,reliable selective perforation and satisfactory inter-cluster sealing.The horizontal-well oriented cluster perforating technology benefits the orientation of horizontal well drilling with a definite target and direction,which provides a powerful support for the subsequent reservoir stimulation.It also promotes the fracturing fluid to sweep the principal pay zones to the maximum extent.Moreover,it is conductive to the formation of complex fracture networks in the reservoirs,making quality and efficient development of unconventional gas reservoirs possible.展开更多
Under the general trend of stepping-up oil and gas exploration and development in China,the unconventional oil and gas resources such as shale oil and gas have become an important alternative.Abundant continental shal...Under the general trend of stepping-up oil and gas exploration and development in China,the unconventional oil and gas resources such as shale oil and gas have become an important alternative.Abundant continental shale oil resources are developed in Member 2 of Kongdian Formation(Ek2)of the Cangdong sag in the Huanghua depression of the Bohai Bay Basin which has complex structure,strong heterogeneity,and large buried depth,thus,the geological characteristic of shale oil accumulation and key exploration technologies are investigated on base of the system coring of 635.8 m,centimeter-level fine description and analysis of over ten thousand samples,therefore,the“four accurate”technologies have been developed,including the accurate selection of sweet spot areas,accurate drilling of sweet spot layers,accurate fracturing of sweet spot layers and accurate measure of fracture-rich sections.The results show that the continental shale strata in Member 2 of Kongdian Formation can be divided into three types:felsic shale,limy dolomitic shale and mixed shale.The Member 2 of Kongdian Formation is characterized by diverse mineral components,abundant laminae,good source rocks and medium thermal evolution degree,tight reservoir with rich micropore and microfractures,high oil saturation and brittle mineral content,indicating good prospect of shale oil exploration.Through sedimentological study,TOC and Ro evaluation,brittle mineral calculation,and seismic fusion inversion,a total of 126 km^(2) of Class I sweet spots in Member 2 of Kongdian Formation was delineated comprehensively,which guides horizontal well deployment(Well GD1701H and Well GD1702H).The drilling rate of sweet spot of these two horizontal wells is up to 96%by tracing thin layer through fine calibration,locating compartment through fine inversion,ensuring window entry through precise positioning,and tracking sweet spot through adjustment.The “one-excellent and five-highs”criterion is used to select perforation points to realize differential designs of fracturing intervals and clusters.Micro-seismic and potentiometry monitoring show that the artificial fractures formed by volumetric fracturing are 300e400 m long and 120 m high,and control a volume of about 0.07 km^(3).The maximum daily oil production of two horizontal wells is 48 t and 66 t respectively to realize the economic exploitation of shale oil reserves controlled by fractures.The shale oil exploration in Member 2 of Kongdian Formation shows that the continental shale oil has great potential of exploration and development,and the above technologies are critical and effective for shale oil efficient recovery.展开更多
基金financially supported by the National Natural Science Foundation of China (51704324, 52374027)Natural Science Foundation of Shandong Province (ZR2023ME158, ZR2022ME025)Open Fund of Key Laboratory of Tectonics and Petroleum Resources (TPR-2020-14)。
文摘Tri-axial fracturing studies were carried out to understand the impact of lateral mechanical parameters on fracture propagation from multiple in-plane perforations in horizontal wells. Additionally, the discussion covered the effects of geology, treatment, and perforation characteristics on the non-planar propagation behavior. According to experimental findings, two parallel transverse fractures can be successfully initiated from in-plane perforation clusters in the horizontal well because of the in-plane perforation, the guide nonuniform fishbone structure fracture propagation still can be exhibited. The emergence of transverse fractures and axial fractures combined as complex fractures under low horizontal principal stress difference and large pump rate conditions. The injection pressure was also investigated, and the largest breakdown pressure can be also found for samples under these conditions.The increase in perforation number or decrease in the cluster spacing could provide more chances to increase the complexity of the target stimulated zone, thus affecting the pressure fluctuation. In a contrast, the increase in fracturing fluid viscosity can reduce the multiple fracture complexity. The fracture propagation is significantly affected by the change in the rock mechanical properties. The fracture geometry in the high brittle zone seems to be complicated and tends to induce fracture reorientation from the weak-brittle zone. The stress shadow effect can be used to explain the fracture attraction, branch, connection, and repulsion in the multiple perforation clusters for the horizontal well.The increase in the rock heterogeneity can enhance the stress shadow effect, resulting in more complex fracture geometry. In addition, the variable density perforation and temporary plugging fracturing were also conducted, demonstrating higher likelihood for non-uniform multiple fracture propagation. Thus, to increase the perforation efficiency along the horizontal well, it is necessary to consider the lateral fracability of the horizontal well on target formation.
基金supported by the Science Fund for Excellent Youth of the National Natural Science Foundation of China"Well hydrodynamics and engineering"(No.52122401).
文摘Multi-cluster perforation and multi-staged fracturing of horizontal well is one of the main technologies in volumetric fracturing stimulation of unconventional oil and gas reservoirs,but unconventional reservoirs in China are generally of strong heterogeneity,which causes different fracture initiation pressures in different positions of lateral,making it difficult to ensure the balanced fracture initiation and propagation between clusters in multi-cluster perforating.It is in urgent need to precisely evaluate the difference in rock strength in lateral and determine the well section with similar rock strength to deploy fractures,so as to reach the goal of balanced stimulation.Based on the drilling and logging data,this paper establishes an unsupervised clustering model of mechanical specific energy of bit at the bottomhole the lateral.Then,the influence of drill string friction,composite drilling and jet-assisted rock breaking on the mechanical specific energy is analyzed,and the distribution and clustering categories of bottomhole mechanical specific energy with decimeter spatial resolution are obtained.Finally,a fracture deployment optimization method for horizontal well volumetric fracturing aiming balanced stimulation is developed by comprehensively considering inter-fracture interference,casing collar position,plug position,and clustering result of bottomhole mechanical specific energy.The following results are obtained.First,compared with brittleness index,Poisson's ratioandstressdifference,perforation erosion area isina strongercorrelationwith themechanical specific energy,andthemechanical specific energy can effectively characterize the difference in the amount of proppant injected into the perforation clusters in the lateral,so it can be served as one of the important indicators for the selection of fracture deployment position.Second,the drilling and logging data cleaning and smoothing and the clustering number selection by the elbow method are the key steps to obtain the clustering results of bottomhole mechanical specific energy,which can tell the difference in the mechanical specific energy with decimeter-level resolution.Third,the interval with mechanical specific energy within 10%of the averagevalue in the section is selected for deploying perforation clusters,and the compiled computer algorithm can automatically determine the optimal position of fracturing section and cluster,so as to realize the differential design of stage spacing and cluster spacing.In conclusion,the research results can further improve the fractures deployment efficiency and balanced stimulation of volumetric fracturing in unconventional oil andgasreservoirs,and this technology is expected to provide ideas andnew methods forthe fracturedeployment optimization of horizontal well volumetric fracturing in unconventional oil and gas reservoirs.
基金Project supported by the National Major S&T Project“Shale gas reservoir stimulation technology”(No.:2012ZX05018-004).
文摘An oriented cluster perforating technology,which integrates both advantages of cluster and oriented perforating,will help solve a series of technical complexities in horizontal well drilling.For realizing its better application in oil and gas development,a series of technologies were developed including perforator self-weight eccentricity,matching of the electronic selective module codes with the surface program control,axial centralized contact signal transmission,and post-perforation intercluster sealing insulation.In this way,the following functions could be realized,such as cable-transmission horizontal well perforator self-weight orientation,dynamic signal transmission,reliable addressing&selective perforation and post-perforation intercluster sealing.The combined perforation and bridge plug or the multi-cluster perforation can be fulfilled in one trip of perforation string.As a result,the horizontal-well oriented cluster perforating technology based on cable conveying was developed.This technology was successfully applied in unconventional gas reservoir exploitation,such as shale gas and coalbed methane,with accurate orientation,reliable selective perforation and satisfactory inter-cluster sealing.The horizontal-well oriented cluster perforating technology benefits the orientation of horizontal well drilling with a definite target and direction,which provides a powerful support for the subsequent reservoir stimulation.It also promotes the fracturing fluid to sweep the principal pay zones to the maximum extent.Moreover,it is conductive to the formation of complex fracture networks in the reservoirs,making quality and efficient development of unconventional gas reservoirs possible.
基金The work was supported by the the PetroChina Science and Technology Major Project“Research and Application of Key Technologies for Increasing Reserves and Stabilizing Production in Dagang Oilfield”(No.2018E-11).
文摘Under the general trend of stepping-up oil and gas exploration and development in China,the unconventional oil and gas resources such as shale oil and gas have become an important alternative.Abundant continental shale oil resources are developed in Member 2 of Kongdian Formation(Ek2)of the Cangdong sag in the Huanghua depression of the Bohai Bay Basin which has complex structure,strong heterogeneity,and large buried depth,thus,the geological characteristic of shale oil accumulation and key exploration technologies are investigated on base of the system coring of 635.8 m,centimeter-level fine description and analysis of over ten thousand samples,therefore,the“four accurate”technologies have been developed,including the accurate selection of sweet spot areas,accurate drilling of sweet spot layers,accurate fracturing of sweet spot layers and accurate measure of fracture-rich sections.The results show that the continental shale strata in Member 2 of Kongdian Formation can be divided into three types:felsic shale,limy dolomitic shale and mixed shale.The Member 2 of Kongdian Formation is characterized by diverse mineral components,abundant laminae,good source rocks and medium thermal evolution degree,tight reservoir with rich micropore and microfractures,high oil saturation and brittle mineral content,indicating good prospect of shale oil exploration.Through sedimentological study,TOC and Ro evaluation,brittle mineral calculation,and seismic fusion inversion,a total of 126 km^(2) of Class I sweet spots in Member 2 of Kongdian Formation was delineated comprehensively,which guides horizontal well deployment(Well GD1701H and Well GD1702H).The drilling rate of sweet spot of these two horizontal wells is up to 96%by tracing thin layer through fine calibration,locating compartment through fine inversion,ensuring window entry through precise positioning,and tracking sweet spot through adjustment.The “one-excellent and five-highs”criterion is used to select perforation points to realize differential designs of fracturing intervals and clusters.Micro-seismic and potentiometry monitoring show that the artificial fractures formed by volumetric fracturing are 300e400 m long and 120 m high,and control a volume of about 0.07 km^(3).The maximum daily oil production of two horizontal wells is 48 t and 66 t respectively to realize the economic exploitation of shale oil reserves controlled by fractures.The shale oil exploration in Member 2 of Kongdian Formation shows that the continental shale oil has great potential of exploration and development,and the above technologies are critical and effective for shale oil efficient recovery.
