The hazards of fault reactivation caused by fluid injection are a growing concern.However,traditional evaluation methods of fault stability are likely to underestimate the risk in fault segments with a high clay conte...The hazards of fault reactivation caused by fluid injection are a growing concern.However,traditional evaluation methods of fault stability are likely to underestimate the risk in fault segments with a high clay content.Therefore,an extended evaluation method of fault stability(ECPP)incorporating the heterogeneity in friction strength caused by variation in the clay content within the fault zone is established in this study.After characterizing the current stress field of the BZ34-2 Oilfield in the Huanghekou Sag,Bohai Bay Basin,the reactivation potential of faults is evaluated using both traditional and ECPP methods.Traditional evaluation of fault stability shows that all faults are stable in the present stress field.Faults oriented ENE have a relatively high risk.The maximum sustainable fluid pressure Δp is approximately 8.8-8.9 MPa and 9.3-9.9 MPa.When considering the heterogeneity in fault friction strength,the fault stability is clearly controlled by the clay content of the faults.The high-risk fault segments assessed using traditional methods are no longer obvious,which reflects the importance of incorporating friction strength heterogeneity in the process of fault evaluation.Moreover,the results also show that most fault segments are activated when the fault zone is dominated by montmorillonite,reflecting the strong influence of clay mineral types on fault stability.The factors influencing the heterogeneity of fault friction strength are very complicated in actual situations.Therefore,future work should focus on establishing a database through a large number of experiments and investigating the relationship between the friction coefficient and the main controlling factors.展开更多
Although many intact rock types can be very strong,a critical confining pressure can eventually be reached in triaxial testing,such that the Mohr shear strength envelope becomes horizontal.This critical state has rece...Although many intact rock types can be very strong,a critical confining pressure can eventually be reached in triaxial testing,such that the Mohr shear strength envelope becomes horizontal.This critical state has recently been better defined,and correct curvature or correct deviation from linear Mohr-Coulomb（MC） has finally been found.Standard shear testing procedures for rock joints,using multiple testing of the same sample,in case of insufficient samples,can be shown to exaggerate apparent cohesion.Even rough joints do not have any cohesion,but instead have very high friction angles at low stress,due to strong dilation.Rock masses,implying problems of large-scale interaction with engineering structures,may have both cohesive and frictional strength components.However,it is not correct to add these,following linear M-C or nonlinear Hoek-Brown（H-B） standard routines.Cohesion is broken at small strain,while friction is mobilized at larger strain and remains to the end of the shear deformation.The criterion ＇c then σn tan φ＇ should replace ＇c plus σn tan φ＇ for improved fit to reality.Transformation of principal stresses to a shear plane seems to ignore mobilized dilation,and caused great experimental difficulties until understood.There seems to be plenty of room for continued research,so that errors of judgement of the last 50 years can be corrected.展开更多
Discarded train brake shoes mainly consist of steel-backed friction material. To be better reutilized, its essential features and its interaction in cement-based material need to be studied. Consequently, particle siz...Discarded train brake shoes mainly consist of steel-backed friction material. To be better reutilized, its essential features and its interaction in cement-based material need to be studied. Consequently, particle size analysis, SEM, IR and TGA were used to investigate two types of waste brake shoes, i e, mechanical grinding friction reclaimed material of waste brake-shoe（G-FRMWBS） and pyrolysis-friction reclaimed materials of waste brake-shoe（P-FRMWBS）. The latter exhibited less organic content, larger range of particle size distribution and smaller medium particle diameter. Both types contained inorganic particles of spherical and irregular shapes, striped with steel fiber. Upon isometric substituting fine aggregates, G-FRMWBS lifted the strength of mortar effectively that was increased by 16.6% and 17.5% when the replacing rate was 5%; the value went up to 19.2% and 19.2% when the replacing rate was 10%. Moreover, inclusion of FRMWBS enhanced the chloride penetration resistance, and optimized the pore characteristic and ITZ（interfacial transition zone） as well.展开更多
This paper presents the results of the shear strength（frictional strength） of cemented paste backfillcemented paste backfill（CPB-CPB） and cemented paste backfillerock wall（CPB-rock） interfaces. The frictional be...This paper presents the results of the shear strength（frictional strength） of cemented paste backfillcemented paste backfill（CPB-CPB） and cemented paste backfillerock wall（CPB-rock） interfaces. The frictional behaviors of these interfaces were assessed for the short-term curing times（3 d and 7 d） using a direct shear apparatus RDS-200 from GCTS（Geotechnical Consulting ＆ Testing Systems）. The shear（friction） tests were performed at three different constant normal stress levels on flat and smooth interfaces. These tests aimed at understanding the mobilized shear strength at the CPB-rock and CPB-CPB interfaces during and/or after open stope filling（no exposed face）. The applied normal stress levels were varied in a range corresponding to the usually measured in-situ horizontal pressures（longitudinal or transverse） developed within paste-filled stopes（uniaxial compressive strength, s c 150 k Pa）. Results show that the mobilized shear strength is higher at the CPB-CPB interface than that at the CPB-rock interface. Also, the perfect elastoplastic behaviors observed for the CPB-rock interfaces were not observed for the CPB-CPB interfaces with low cement content which exhibits a strain-hardening behavior. These results are useful to estimate or validate numerical model for pressures determination in cemented backfill stope at short term. The tests were performed on real backfill and granite. The results may help understanding the mechanical behavior of the cemented paste backfill in general and, in particular, analyzing the shear strength at backfillebackfill and backfill-rock interfaces.展开更多
In recent years,shale gas production horizontal well types mainly include conventional horizontal well,highly deviated well and scoop-shape horizontal well.For the sake of construction decision making,it is necessary ...In recent years,shale gas production horizontal well types mainly include conventional horizontal well,highly deviated well and scoop-shape horizontal well.For the sake of construction decision making,it is necessary to study these three types of wells from the aspects of drag and torque characteristic,weight on bit transferring efficiency,key hole sections or links and extreme penetration length.In this paper,these three types of horizontal wells were taken as the study objects.Their drag and torque,load transfer and extended reach drilling were explored based on the dynamic model of full hole drilling string and the simulation calculation of dynamic characteristics of full hole drilling string system.And the results were applied and tested on site in three shale gas wells(a conventional horizontal well,a highly deviated well and a scoop-shape horizontal well)in the Changning area,Sichuan Basin.And the following research results were obtained.First,the contact friction strength of the deeper part of the buildup section in the scoop-shape horizontal well is very high,and it is 1.67 times that of the hold section.The total contact force of buildup section in the scoop-shape horizontal well is 1.62 times that in the highly deviated well.Second,the contact friction strength of the hold section in highly deviated well is not only higher than that of its buildup section,but also higher than any characteristic section in the three well types of the same depth.Third,the operating stress of drilling strings during the drilling of three well types is not high,but during the extended reach drilling in the curved section of the scoop-shape horizontal well,it is necessary to focus on the twist off of drilling string in the hold section.Fourth,the weight on bit transferring efficiency of scoop-shape horizontal well is lower than that of conventional horizontal well and highly deviated well.In conclusion,the research results preliminarily reveal the drag and torque characteristics and active load transferring mechanisms of conventional horizontal well,highly deviated well and scoop-shape horizontal well for shale gas production,and present important hole sections for safety assessment.They can be used as references for efficient and safe construction of shale gas horizontal wells.展开更多
基金the financial support from the National Natural Science Foundation of China(Grant Nos.42002152 and U20A2093)National Key Research and Development Program of China(Grant No.2022YFE0206800).
文摘The hazards of fault reactivation caused by fluid injection are a growing concern.However,traditional evaluation methods of fault stability are likely to underestimate the risk in fault segments with a high clay content.Therefore,an extended evaluation method of fault stability(ECPP)incorporating the heterogeneity in friction strength caused by variation in the clay content within the fault zone is established in this study.After characterizing the current stress field of the BZ34-2 Oilfield in the Huanghekou Sag,Bohai Bay Basin,the reactivation potential of faults is evaluated using both traditional and ECPP methods.Traditional evaluation of fault stability shows that all faults are stable in the present stress field.Faults oriented ENE have a relatively high risk.The maximum sustainable fluid pressure Δp is approximately 8.8-8.9 MPa and 9.3-9.9 MPa.When considering the heterogeneity in fault friction strength,the fault stability is clearly controlled by the clay content of the faults.The high-risk fault segments assessed using traditional methods are no longer obvious,which reflects the importance of incorporating friction strength heterogeneity in the process of fault evaluation.Moreover,the results also show that most fault segments are activated when the fault zone is dominated by montmorillonite,reflecting the strong influence of clay mineral types on fault stability.The factors influencing the heterogeneity of fault friction strength are very complicated in actual situations.Therefore,future work should focus on establishing a database through a large number of experiments and investigating the relationship between the friction coefficient and the main controlling factors.
文摘Although many intact rock types can be very strong,a critical confining pressure can eventually be reached in triaxial testing,such that the Mohr shear strength envelope becomes horizontal.This critical state has recently been better defined,and correct curvature or correct deviation from linear Mohr-Coulomb（MC） has finally been found.Standard shear testing procedures for rock joints,using multiple testing of the same sample,in case of insufficient samples,can be shown to exaggerate apparent cohesion.Even rough joints do not have any cohesion,but instead have very high friction angles at low stress,due to strong dilation.Rock masses,implying problems of large-scale interaction with engineering structures,may have both cohesive and frictional strength components.However,it is not correct to add these,following linear M-C or nonlinear Hoek-Brown（H-B） standard routines.Cohesion is broken at small strain,while friction is mobilized at larger strain and remains to the end of the shear deformation.The criterion ＇c then σn tan φ＇ should replace ＇c plus σn tan φ＇ for improved fit to reality.Transformation of principal stresses to a shear plane seems to ignore mobilized dilation,and caused great experimental difficulties until understood.There seems to be plenty of room for continued research,so that errors of judgement of the last 50 years can be corrected.
基金Funded by National Natural Science Foundation of China(Nos.51408380,No.51478278)Science and Technology Plan of Hebei Province,China(No.14273805D)+1 种基金He Bei Education Department(No.QN2016156)the Young Top Talent Science Research Project of Colleges and Universities in He Bei Province(No.BJ2014053)
文摘Discarded train brake shoes mainly consist of steel-backed friction material. To be better reutilized, its essential features and its interaction in cement-based material need to be studied. Consequently, particle size analysis, SEM, IR and TGA were used to investigate two types of waste brake shoes, i e, mechanical grinding friction reclaimed material of waste brake-shoe（G-FRMWBS） and pyrolysis-friction reclaimed materials of waste brake-shoe（P-FRMWBS）. The latter exhibited less organic content, larger range of particle size distribution and smaller medium particle diameter. Both types contained inorganic particles of spherical and irregular shapes, striped with steel fiber. Upon isometric substituting fine aggregates, G-FRMWBS lifted the strength of mortar effectively that was increased by 16.6% and 17.5% when the replacing rate was 5%; the value went up to 19.2% and 19.2% when the replacing rate was 10%. Moreover, inclusion of FRMWBS enhanced the chloride penetration resistance, and optimized the pore characteristic and ITZ（interfacial transition zone） as well.
文摘This paper presents the results of the shear strength（frictional strength） of cemented paste backfillcemented paste backfill（CPB-CPB） and cemented paste backfillerock wall（CPB-rock） interfaces. The frictional behaviors of these interfaces were assessed for the short-term curing times（3 d and 7 d） using a direct shear apparatus RDS-200 from GCTS（Geotechnical Consulting ＆ Testing Systems）. The shear（friction） tests were performed at three different constant normal stress levels on flat and smooth interfaces. These tests aimed at understanding the mobilized shear strength at the CPB-rock and CPB-CPB interfaces during and/or after open stope filling（no exposed face）. The applied normal stress levels were varied in a range corresponding to the usually measured in-situ horizontal pressures（longitudinal or transverse） developed within paste-filled stopes（uniaxial compressive strength, s c 150 k Pa）. Results show that the mobilized shear strength is higher at the CPB-CPB interface than that at the CPB-rock interface. Also, the perfect elastoplastic behaviors observed for the CPB-rock interfaces were not observed for the CPB-CPB interfaces with low cement content which exhibits a strain-hardening behavior. These results are useful to estimate or validate numerical model for pressures determination in cemented backfill stope at short term. The tests were performed on real backfill and granite. The results may help understanding the mechanical behavior of the cemented paste backfill in general and, in particular, analyzing the shear strength at backfillebackfill and backfill-rock interfaces.
基金supported by Sichuan Youth Science and Technology Innovation Team Project“Drilling Speed Increase”(No.:2017TD0014)Sichuan Science and Technology Plan International Cooperation Program“Non-linear Vibration Characteristics of Reaming while Drilling System and Optimization of Reaming Parameters”(No.:2016HH0008).
文摘In recent years,shale gas production horizontal well types mainly include conventional horizontal well,highly deviated well and scoop-shape horizontal well.For the sake of construction decision making,it is necessary to study these three types of wells from the aspects of drag and torque characteristic,weight on bit transferring efficiency,key hole sections or links and extreme penetration length.In this paper,these three types of horizontal wells were taken as the study objects.Their drag and torque,load transfer and extended reach drilling were explored based on the dynamic model of full hole drilling string and the simulation calculation of dynamic characteristics of full hole drilling string system.And the results were applied and tested on site in three shale gas wells(a conventional horizontal well,a highly deviated well and a scoop-shape horizontal well)in the Changning area,Sichuan Basin.And the following research results were obtained.First,the contact friction strength of the deeper part of the buildup section in the scoop-shape horizontal well is very high,and it is 1.67 times that of the hold section.The total contact force of buildup section in the scoop-shape horizontal well is 1.62 times that in the highly deviated well.Second,the contact friction strength of the hold section in highly deviated well is not only higher than that of its buildup section,but also higher than any characteristic section in the three well types of the same depth.Third,the operating stress of drilling strings during the drilling of three well types is not high,but during the extended reach drilling in the curved section of the scoop-shape horizontal well,it is necessary to focus on the twist off of drilling string in the hold section.Fourth,the weight on bit transferring efficiency of scoop-shape horizontal well is lower than that of conventional horizontal well and highly deviated well.In conclusion,the research results preliminarily reveal the drag and torque characteristics and active load transferring mechanisms of conventional horizontal well,highly deviated well and scoop-shape horizontal well for shale gas production,and present important hole sections for safety assessment.They can be used as references for efficient and safe construction of shale gas horizontal wells.
