Determining reasonable fracturing stage spacing is the key to horizontal well fracturing.Different from traditional stage spacing optimization methods based on the principle of maximum stimulated reservoir volume,in t...Determining reasonable fracturing stage spacing is the key to horizontal well fracturing.Different from traditional stage spacing optimization methods based on the principle of maximum stimulated reservoir volume,in this paper,by considering the integrity of the wellbore interface,a fracture propagation model was established based on displacement discontinuity method and the competition mechanism of multifracture joint expansion,leading to the proposal of an unequal stage spacing optimization model.The results show that in the first stage,the interfacial fractures spread symmetrically along the axis of the central point during that stage,while in the second and subsequent stages,the interfacial fractures of each cluster extend asymmetrically along the left and right sides.There are two kinds of interface connectivity behaviour:in one,the existing fractures first extend and connect within the stage,and in the other,the fractures first extend in the direction close to the previous stage,with the specific behaviour depending on the combined effect of stress shadow and flow competition during hydraulic fracture expansion.The stage spacing is positively correlated with the number of fractures and Young’s modulus of the cement and formation and is negatively correlated with the cluster spacing and horizontal principal stress difference.The sensitivity is the strongest when the Young’s modulus of the cement sheath is 10-20 GPa,and the sensitivity of the horizontal principal stress difference is the weakest.展开更多
The expansion of shale gas exploration into deeper reservoirs introduces increasing cementing challenges,primarily caused by cement sheath integrity failure through interfacial debonding.This study performed mechanica...The expansion of shale gas exploration into deeper reservoirs introduces increasing cementing challenges,primarily caused by cement sheath integrity failure through interfacial debonding.This study performed mechanical property characterization and interfacial bond strength evaluation of compositetoughened oil well cement to quantify the mechanical behavior of cement sheaths and cementing interfaces.Cavity pressure experiments were performed to obtain pressure-time curves of methane deflagrationfracturing under different fillingpressures.A whole-life-cycle well integrity model was established using a phased modeling approach,with the measured pressure data as input loads,and the cohesive zone model(CZM)was applied to simulate interfacial debonding evolution.Parametric analysis focused on the effects of perforation section length,deflagrationparameters(peak pressure,duration),and cement formulations on interfacial debonding.Numerical results reveal that the casingcement interface exhibits longer axial debonding lengths than the cement-formation interface,while the latter experiences faster debonding propagation.Sensitivity analysis highlights that composite toughened cement sheaths with reduced elastic modulus and enhanced bond strength significantly enhance wellbore integrity under methane deflagration.Interfacial debonding can be mitigated by optimizing perforation section length in staged fracturing operations and carefully controlling deflagration peak pressure and duration.This work enables predictive analysis of cement sheath debonding development and integrity evaluation,offering practical strategies for optimizing methane deflagration fracturing operations.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
基金This work was supported by the Natural Science Foundation of Heilongjiang Province of China(YQ2021E005)the National Natural Science Foundation of China(No.51774094)+2 种基金the Youth Fund Project of National Natural Science Foundation of China(52004065)the Heilongjiang Natural Science Foundation Project(excellent youth project)(YQ2021E006)"Reveal the top"Science and Technology Project of Heilongjiang Province(2021ZZ10-04).
文摘Determining reasonable fracturing stage spacing is the key to horizontal well fracturing.Different from traditional stage spacing optimization methods based on the principle of maximum stimulated reservoir volume,in this paper,by considering the integrity of the wellbore interface,a fracture propagation model was established based on displacement discontinuity method and the competition mechanism of multifracture joint expansion,leading to the proposal of an unequal stage spacing optimization model.The results show that in the first stage,the interfacial fractures spread symmetrically along the axis of the central point during that stage,while in the second and subsequent stages,the interfacial fractures of each cluster extend asymmetrically along the left and right sides.There are two kinds of interface connectivity behaviour:in one,the existing fractures first extend and connect within the stage,and in the other,the fractures first extend in the direction close to the previous stage,with the specific behaviour depending on the combined effect of stress shadow and flow competition during hydraulic fracture expansion.The stage spacing is positively correlated with the number of fractures and Young’s modulus of the cement and formation and is negatively correlated with the cluster spacing and horizontal principal stress difference.The sensitivity is the strongest when the Young’s modulus of the cement sheath is 10-20 GPa,and the sensitivity of the horizontal principal stress difference is the weakest.
基金supported by the National Key R&D Program of China(Grant No.2020YFA0711802).
文摘The expansion of shale gas exploration into deeper reservoirs introduces increasing cementing challenges,primarily caused by cement sheath integrity failure through interfacial debonding.This study performed mechanical property characterization and interfacial bond strength evaluation of compositetoughened oil well cement to quantify the mechanical behavior of cement sheaths and cementing interfaces.Cavity pressure experiments were performed to obtain pressure-time curves of methane deflagrationfracturing under different fillingpressures.A whole-life-cycle well integrity model was established using a phased modeling approach,with the measured pressure data as input loads,and the cohesive zone model(CZM)was applied to simulate interfacial debonding evolution.Parametric analysis focused on the effects of perforation section length,deflagrationparameters(peak pressure,duration),and cement formulations on interfacial debonding.Numerical results reveal that the casingcement interface exhibits longer axial debonding lengths than the cement-formation interface,while the latter experiences faster debonding propagation.Sensitivity analysis highlights that composite toughened cement sheaths with reduced elastic modulus and enhanced bond strength significantly enhance wellbore integrity under methane deflagration.Interfacial debonding can be mitigated by optimizing perforation section length in staged fracturing operations and carefully controlling deflagration peak pressure and duration.This work enables predictive analysis of cement sheath debonding development and integrity evaluation,offering practical strategies for optimizing methane deflagration fracturing operations.
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.
