Sina Javankhoshdel, T. Ma, B. Cami, T. Yacoub, B. Corkum, J. Curran
The disturbance factor (D) is a parameter in the Generalized Hoek-Brown failure criterion for rock slopes in slope stability. It represents the subsurface damage to the rock material properties resulting from blasting and stress relaxation during excavations. Within the region of assumed damage, a number between zero (undisturbed) and unity (very disturbed) is prescribed as the value of the disturbance factor. Most commonly a uniform value of D is assumed within the entire region of damage, but little research has been done to study the impact of the variation in the D parameter on stability. Through use of an example, this paper examines the effect of various distribution functions of D through the damaged region, such namely, as constant, linearly varying, and exponentially varying. The failure modes and factors of safety for the slope as determined via limit equilibrium are also compared with finite element analyses. Varying the distribution of the damage function was found to significantly affect the failure mode and factor of safety. It is recommended that practitioners adopt care to select an appropriate distribution for slope stability analysis.
{"title":"Effect of Disturbance Factor Distribution Function on Stability of an Open Pit Mine","authors":"Sina Javankhoshdel, T. Ma, B. Cami, T. Yacoub, B. Corkum, J. Curran","doi":"10.56952/arma-2022-0133","DOIUrl":"https://doi.org/10.56952/arma-2022-0133","url":null,"abstract":"The disturbance factor (D) is a parameter in the Generalized Hoek-Brown failure criterion for rock slopes in slope stability. It represents the subsurface damage to the rock material properties resulting from blasting and stress relaxation during excavations. Within the region of assumed damage, a number between zero (undisturbed) and unity (very disturbed) is prescribed as the value of the disturbance factor. Most commonly a uniform value of D is assumed within the entire region of damage, but little research has been done to study the impact of the variation in the D parameter on stability. Through use of an example, this paper examines the effect of various distribution functions of D through the damaged region, such namely, as constant, linearly varying, and exponentially varying. The failure modes and factors of safety for the slope as determined via limit equilibrium are also compared with finite element analyses. Varying the distribution of the damage function was found to significantly affect the failure mode and factor of safety. It is recommended that practitioners adopt care to select an appropriate distribution for slope stability analysis.","PeriodicalId":418045,"journal":{"name":"Proceedings 56th US Rock Mechanics / Geomechanics Symposium","volume":"26 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2022-06-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"128954727","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Xiaohuan Zhang, Shicheng Zhang, Y. Zou, Jianmin Li, Jun-chao Wang, Danyang Zhu, G. Zhou, Can Yang
The shale oil reservoir of Lucaogou Formation is characterized by complex lithology changes in vertical direction and lamination. To simulate the lithology variation of shale oil formation, downhole cores with different lithologies were prepared and bonded to layered samples. After that, the influence of interlaminar difference on propagation behavior of hydraulic fractures (HFs) was investigated through laboratory hydraulic fracturing and mechanical characteristics analysis. The result shows that mechanically weak bedding planes (BPs) leads to obvious anisotropy of rock mechanical properties. The rock samples is unstable when loaded along the parallel BPs direction, the tensile strength decline significantly, which is about 20% of the tensile strength measured perpendicular to BPs. The brittleness of rock samples measured parallel to BPs is greater than that measured perpendicular to BPs, by about two times. This results in HFs induced by low-viscosity slickwater are easily arrested by BPs, can not penetrate interlayer. HFs induced by high viscosity gel can penetrate the bonding interface. The difference of tensile strength between layers increases, the decrease degree of fracture width increases 2.5 times. This will impede proppant placement in interlayer. This research results provide a basis for the optimization of hydraulic fracturing of Lucaogou shale oil reservoir.
{"title":"Effect of interlaminar difference on Height propagation behavior of hydraulic fracture in Lucaogou Shale","authors":"Xiaohuan Zhang, Shicheng Zhang, Y. Zou, Jianmin Li, Jun-chao Wang, Danyang Zhu, G. Zhou, Can Yang","doi":"10.56952/arma-2022-0193","DOIUrl":"https://doi.org/10.56952/arma-2022-0193","url":null,"abstract":"The shale oil reservoir of Lucaogou Formation is characterized by complex lithology changes in vertical direction and lamination. To simulate the lithology variation of shale oil formation, downhole cores with different lithologies were prepared and bonded to layered samples. After that, the influence of interlaminar difference on propagation behavior of hydraulic fractures (HFs) was investigated through laboratory hydraulic fracturing and mechanical characteristics analysis. The result shows that mechanically weak bedding planes (BPs) leads to obvious anisotropy of rock mechanical properties. The rock samples is unstable when loaded along the parallel BPs direction, the tensile strength decline significantly, which is about 20% of the tensile strength measured perpendicular to BPs. The brittleness of rock samples measured parallel to BPs is greater than that measured perpendicular to BPs, by about two times. This results in HFs induced by low-viscosity slickwater are easily arrested by BPs, can not penetrate interlayer. HFs induced by high viscosity gel can penetrate the bonding interface. The difference of tensile strength between layers increases, the decrease degree of fracture width increases 2.5 times. This will impede proppant placement in interlayer. This research results provide a basis for the optimization of hydraulic fracturing of Lucaogou shale oil reservoir.","PeriodicalId":418045,"journal":{"name":"Proceedings 56th US Rock Mechanics / Geomechanics Symposium","volume":"14 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2022-06-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"115097674","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Jinyang Xie, Luo Zuo, B. Hou, Yifan Dai, Jiaxin Li, L. Zhuang, D. Elsworth
With the continuous depth breakthrough of two ultra-deep exploration wells in northeastern Sichuan block, tuff reservoir was finally discovered at the depth of 6700-7300 m. It belongs to ultra-deep tight gas reservoir with low brittle mineral content and high clay content. Hydraulic fracturing is hard to be reformed this special reservoir, easy to appear hydration expansion and other problems. However, the research and development of such tight tuff reservoir with high temperature and high pressure are relatively low in the domestic and overseas until now. Therefore, it is of great significance to carry out experimental research on relevant reservoir reconstruction methods of such rocks and explore the factors of fracture conductivity here. In this study, the influence of acid type, sanding concentrations, proppant size was research by a new experimental installation. The factors of fracture conductivity are analyzed by experimental data and the reconstitution of fracture surface. The results show that before the abnormal point, the acid etching effect of crosslinked acid on tuff is better than that of gelling acid. At the condition of closure pressure is lower 30 MPa, the higher sanding concentrations, the higher fracture conductivity, then narrowed the gap among them. Meanwhile, the larger proppant size, the higher fracture conductivity in low closure pressure. With increasing closure pressure, fracture conductivity of smaller size proppant decreased slowly. In conclusion, it is also convenient for the field operation to choose the best acid and proppant parameters.
{"title":"Influencing Factors of Acid Etching Fracture Conductivity of Tuff Reservoir in Northeastern Sichuan Block","authors":"Jinyang Xie, Luo Zuo, B. Hou, Yifan Dai, Jiaxin Li, L. Zhuang, D. Elsworth","doi":"10.56952/arma-2022-0155","DOIUrl":"https://doi.org/10.56952/arma-2022-0155","url":null,"abstract":"With the continuous depth breakthrough of two ultra-deep exploration wells in northeastern Sichuan block, tuff reservoir was finally discovered at the depth of 6700-7300 m. It belongs to ultra-deep tight gas reservoir with low brittle mineral content and high clay content. Hydraulic fracturing is hard to be reformed this special reservoir, easy to appear hydration expansion and other problems. However, the research and development of such tight tuff reservoir with high temperature and high pressure are relatively low in the domestic and overseas until now. Therefore, it is of great significance to carry out experimental research on relevant reservoir reconstruction methods of such rocks and explore the factors of fracture conductivity here. In this study, the influence of acid type, sanding concentrations, proppant size was research by a new experimental installation. The factors of fracture conductivity are analyzed by experimental data and the reconstitution of fracture surface. The results show that before the abnormal point, the acid etching effect of crosslinked acid on tuff is better than that of gelling acid. At the condition of closure pressure is lower 30 MPa, the higher sanding concentrations, the higher fracture conductivity, then narrowed the gap among them. Meanwhile, the larger proppant size, the higher fracture conductivity in low closure pressure. With increasing closure pressure, fracture conductivity of smaller size proppant decreased slowly. In conclusion, it is also convenient for the field operation to choose the best acid and proppant parameters.","PeriodicalId":418045,"journal":{"name":"Proceedings 56th US Rock Mechanics / Geomechanics Symposium","volume":"16 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2022-06-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"126687478","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
N. Reppas, C. Davie, B. Wetenhall, Y. Gui, Jianjun Ma
In carbon capture and storage schemes, the carbon dioxide (CO2) can be injected at high pressures and low temperatures for permanent storage in deep reservoirs. In the North Sea, the storage sites will be predominantly sandstone. To study the effects of these conditions on the rock surrounding the injection site, triaxial tests on sandstone were conducted until failure using representative in-situ stresses to estimate the mechanical properties of the rock. A theoretical constitutive model, using Finite Element Modelling (FEM), describing the stress-strain behaviour and damage evolution of rock during triaxial testing is presented alongside the results of the tests. The model reproduced the experimental outcomes well and it was used for the estimation of the critical state mechanic parameters. Lower temperature indicated higher strength of sandstone, a decrease in the Poisson’s ratio and consequently an increase in damage.
{"title":"Numerical simulation of triaxial experimental results on Sandstone using critical state mechanics","authors":"N. Reppas, C. Davie, B. Wetenhall, Y. Gui, Jianjun Ma","doi":"10.56952/arma-2022-0383","DOIUrl":"https://doi.org/10.56952/arma-2022-0383","url":null,"abstract":"In carbon capture and storage schemes, the carbon dioxide (CO2) can be injected at high pressures and low temperatures for permanent storage in deep reservoirs. In the North Sea, the storage sites will be predominantly sandstone. To study the effects of these conditions on the rock surrounding the injection site, triaxial tests on sandstone were conducted until failure using representative in-situ stresses to estimate the mechanical properties of the rock. A theoretical constitutive model, using Finite Element Modelling (FEM), describing the stress-strain behaviour and damage evolution of rock during triaxial testing is presented alongside the results of the tests. The model reproduced the experimental outcomes well and it was used for the estimation of the critical state mechanic parameters. Lower temperature indicated higher strength of sandstone, a decrease in the Poisson’s ratio and consequently an increase in damage.","PeriodicalId":418045,"journal":{"name":"Proceedings 56th US Rock Mechanics / Geomechanics Symposium","volume":"34 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2022-06-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"124324632","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Hang Xu, Fu-jian Zhou, Hao Wu, Yuan Li, L. Shen, Erdong Yao
Using heavyweight brines as a base for fracturing fluids is an effective method for solving the problem of exorbitant surface pressure during deep well fracturing process. However, higher fluid densities can lead to higher friction pressures, and with the well depth increases, the travel time to the mudline prolongs, resulting in the demand for extended crosslink delay times. Therefore, fracturing fluids that provide flexibility in density, lower friction and extended crosslink times are required for effective stimulation in ultra-deep reservoirs. This paper presents details of laboratory studies to develop and evaluate a novel weighted fracturing fluid. The main additives of the novel system were sequentially synthesized, including modified guar gum, a new weighting agent and an organic boron-zirconium crosslinker. Afterwards, a series of lab experiments were carried out to test the comprehensive performances of the novel system, such as temperature and shear resistance, friction reduction, gel breaking performance and core damage rate. The optimal formula of fracturing fluid was 54.3 wt.% weighting agent + 0.4 wt.% modified guar gum + 1.0 wt.% pH regulator + 0.5 wt.% crosslinker. Results show that the novel weighted fracturing fluid is a good choice for ultra-deep reservoirs hydraulic stimulation and hence improving the recovery.
{"title":"Development and Evaluation of a Novel Delayed Crosslink, Low Friction, High Density Brine-Based Fracturing Fluid for Ultra-Deep Fracturing Stimulation","authors":"Hang Xu, Fu-jian Zhou, Hao Wu, Yuan Li, L. Shen, Erdong Yao","doi":"10.56952/arma-2022-0085","DOIUrl":"https://doi.org/10.56952/arma-2022-0085","url":null,"abstract":"Using heavyweight brines as a base for fracturing fluids is an effective method for solving the problem of exorbitant surface pressure during deep well fracturing process. However, higher fluid densities can lead to higher friction pressures, and with the well depth increases, the travel time to the mudline prolongs, resulting in the demand for extended crosslink delay times. Therefore, fracturing fluids that provide flexibility in density, lower friction and extended crosslink times are required for effective stimulation in ultra-deep reservoirs. This paper presents details of laboratory studies to develop and evaluate a novel weighted fracturing fluid. The main additives of the novel system were sequentially synthesized, including modified guar gum, a new weighting agent and an organic boron-zirconium crosslinker. Afterwards, a series of lab experiments were carried out to test the comprehensive performances of the novel system, such as temperature and shear resistance, friction reduction, gel breaking performance and core damage rate. The optimal formula of fracturing fluid was 54.3 wt.% weighting agent + 0.4 wt.% modified guar gum + 1.0 wt.% pH regulator + 0.5 wt.% crosslinker. Results show that the novel weighted fracturing fluid is a good choice for ultra-deep reservoirs hydraulic stimulation and hence improving the recovery.","PeriodicalId":418045,"journal":{"name":"Proceedings 56th US Rock Mechanics / Geomechanics Symposium","volume":"1 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2022-06-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"121808357","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Lei Jin, R. Lippoldt, W. Curry, S. Hussenoeder, Peeyush Bhargava
This paper investigates a seismicity sequence that occurred near Stanton, TX between December 2020 and February 2021 with event magnitudes peaking at 4.2. The historically aseismic area has been undergoing shallow salt water disposal (SWD) since the early 1980s, and deep SWD in the last decade. We perform a 3D fully coupled hydro-geomechanical investigation into potential links between the M4.2 event sequence and the surrounding decades-long, multi-zone SWD activities involving 183 SWD wells in a 900 mile2 area. We include faults interpreted from reflection seismic data into the model and survey six fault scenarios with various fault-zone structures and fault upper extents. We compare the modeled Coulomb stress changes against earthquake triggering thresholds obtained from a detailed in-situ stress model, and identify implausible and plausible scenarios. The plausible scenarios yield an excellent match between the critical Coulomb failure function (CFF) propagation and the onset of seismicity in both space and time, and are further supported by their revealing of possible earlier events that were later detected through template matching. Together, these findings strongly suggest a SWD origin of the M4.2 seismicity sequence. The modeling also suggests that near-hypocenter Coulomb stresses are sourced primarily from several deep disposal wells and secondarily from the remaining deep wells and shallower wells given the likely fault configurations. We also analyze roles of fault-zone structures, non-seismogenic faults, and mechanically time-dependent formations. Our work illustrates the importance of physics-based modeling that accounts for faults, formations, wells, and poroelasticity in understanding causes of seismicity.
{"title":"A Numerical Investigation of the 2020 M4.2 Stanton, Texas Seismicity Sequence Using 3D Poroelastic Modeling","authors":"Lei Jin, R. Lippoldt, W. Curry, S. Hussenoeder, Peeyush Bhargava","doi":"10.56952/arma-2022-0285","DOIUrl":"https://doi.org/10.56952/arma-2022-0285","url":null,"abstract":"This paper investigates a seismicity sequence that occurred near Stanton, TX between December 2020 and February 2021 with event magnitudes peaking at 4.2. The historically aseismic area has been undergoing shallow salt water disposal (SWD) since the early 1980s, and deep SWD in the last decade. We perform a 3D fully coupled hydro-geomechanical investigation into potential links between the M4.2 event sequence and the surrounding decades-long, multi-zone SWD activities involving 183 SWD wells in a 900 mile2 area. We include faults interpreted from reflection seismic data into the model and survey six fault scenarios with various fault-zone structures and fault upper extents. We compare the modeled Coulomb stress changes against earthquake triggering thresholds obtained from a detailed in-situ stress model, and identify implausible and plausible scenarios. The plausible scenarios yield an excellent match between the critical Coulomb failure function (CFF) propagation and the onset of seismicity in both space and time, and are further supported by their revealing of possible earlier events that were later detected through template matching. Together, these findings strongly suggest a SWD origin of the M4.2 seismicity sequence. The modeling also suggests that near-hypocenter Coulomb stresses are sourced primarily from several deep disposal wells and secondarily from the remaining deep wells and shallower wells given the likely fault configurations. We also analyze roles of fault-zone structures, non-seismogenic faults, and mechanically time-dependent formations. Our work illustrates the importance of physics-based modeling that accounts for faults, formations, wells, and poroelasticity in understanding causes of seismicity.","PeriodicalId":418045,"journal":{"name":"Proceedings 56th US Rock Mechanics / Geomechanics Symposium","volume":"32 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2022-06-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"131206997","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Sangcheol Yoon, S. Borglin, Chun Chang, C. Chou, Liange Zheng, Yuxin Wu
Bentonite buffer in the geological repository for high-level radioactive waste undergoes the heating from the waste package and hydration from the geological formation and goes through coupled thermo-hydro-mechanical-chemical (THMC) changes over the life span of a repository. For a better understanding of such process under higher temperatures, we report bench-scale laboratory experiments with heating up to 200◦C and the corresponding THM model. The bench-scale laboratory experiments included two test columns, with the non-heated control column undergoing only hydration, and a heated column experiencing both heating in the center up to 200◦C and hydration from a sand-clay boundary surrounding the column. During the experiment, we took frequent X-ray CT images to provide insight into the spatio-temporal evolution of THMC due to heating, hydration, bentonite swelling/compression. Based on the experiment setup, 2-D axisymmetric simulations were performed for the heated column and the mechanical changes were investigated in 3-D. The model first matched the temperature evolution with step-wise temperature boundary conditions at the heater and calibrated the thermal conductivity and specific heat of the materials. Then model interpreted the spatio-temporal distribution of bulk density by considering the combined effect of hydration, fluid pressure, and porosity change due to swelling/compression.
{"title":"Evolution of bentonite under high temperature heating and hydration: bench-scale laboratory experiments and coupled thermo-hydro-mechanical modeling","authors":"Sangcheol Yoon, S. Borglin, Chun Chang, C. Chou, Liange Zheng, Yuxin Wu","doi":"10.56952/arma-2022-0730","DOIUrl":"https://doi.org/10.56952/arma-2022-0730","url":null,"abstract":"Bentonite buffer in the geological repository for high-level radioactive waste undergoes the heating from the waste package and hydration from the geological formation and goes through coupled thermo-hydro-mechanical-chemical (THMC) changes over the life span of a repository. For a better understanding of such process under higher temperatures, we report bench-scale laboratory experiments with heating up to 200◦C and the corresponding THM model. The bench-scale laboratory experiments included two test columns, with the non-heated control column undergoing only hydration, and a heated column experiencing both heating in the center up to 200◦C and hydration from a sand-clay boundary surrounding the column. During the experiment, we took frequent X-ray CT images to provide insight into the spatio-temporal evolution of THMC due to heating, hydration, bentonite swelling/compression. Based on the experiment setup, 2-D axisymmetric simulations were performed for the heated column and the mechanical changes were investigated in 3-D. The model first matched the temperature evolution with step-wise temperature boundary conditions at the heater and calibrated the thermal conductivity and specific heat of the materials. Then model interpreted the spatio-temporal distribution of bulk density by considering the combined effect of hydration, fluid pressure, and porosity change due to swelling/compression.","PeriodicalId":418045,"journal":{"name":"Proceedings 56th US Rock Mechanics / Geomechanics Symposium","volume":"26 3","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2022-06-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"132914617","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
In this work, we have developed a methodology to model the stress evolution in cement plugs during hydration. The model begins with the slurry state of cement and calculates the water consumption and void creation over time as the hydration reactions progress. The void volume change due to chemical shrinkage is imported into a coupled mechanical model that calculates the pore pressure drop and the resulting change in stresses. The results of the proposed modelling methodology are verified using lab experiments from the literature. The results provide new insights in understanding cement behavior under lab and field conditions. Under most scenarios, cement’s pore pressure drops to saturation pressure of water which leads to partial evaporation of the remaining pore water. This pore pressure drop controls the radial stress change, according to the theory of poroelasticity. For a plug set under an initial pressure of 5 MPa, the radial stress drops to 1.6 MPa after 20 hours of curing. This stress drop can cause the cement to debond from the casing, if the fluid pressure above the plug exceeds the final radial stress. This methodology can be extended to annular cements and initial cement stress after placement can be readily calculated.
{"title":"Modelling stress evolution in cement plugs during hydration","authors":"A. Moghadam, A. Corina","doi":"10.56952/arma-2022-0096","DOIUrl":"https://doi.org/10.56952/arma-2022-0096","url":null,"abstract":"In this work, we have developed a methodology to model the stress evolution in cement plugs during hydration. The model begins with the slurry state of cement and calculates the water consumption and void creation over time as the hydration reactions progress. The void volume change due to chemical shrinkage is imported into a coupled mechanical model that calculates the pore pressure drop and the resulting change in stresses. The results of the proposed modelling methodology are verified using lab experiments from the literature. The results provide new insights in understanding cement behavior under lab and field conditions. Under most scenarios, cement’s pore pressure drops to saturation pressure of water which leads to partial evaporation of the remaining pore water. This pore pressure drop controls the radial stress change, according to the theory of poroelasticity. For a plug set under an initial pressure of 5 MPa, the radial stress drops to 1.6 MPa after 20 hours of curing. This stress drop can cause the cement to debond from the casing, if the fluid pressure above the plug exceeds the final radial stress. This methodology can be extended to annular cements and initial cement stress after placement can be readily calculated.","PeriodicalId":418045,"journal":{"name":"Proceedings 56th US Rock Mechanics / Geomechanics Symposium","volume":"10 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2022-06-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"134574769","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Lisa Winhausen, Kavan Khaledi, M. Jalali, F. Amann
For analyzing the influence of structural anisotropy on the hydro-mechanical behavior of a clay shale, we performed three consolidated, undrained triaxial compression tests with different geometric specimen configurations. Opalinus Clay specimens were tested with bedding plane orientations of 30°, 60°, and 90° with respect to the horizontal. Results indicated different peak strengths at failure with highest and lowest values for the 90° and 30°-specimens, respectively. Failure occurred at different mean effective stresses with different magnitudes of pore water pressure built up. The 30°-specimen showed a decreasing effective mean stress up to and beyond failure compared to the initial effective consolidation stress of 10 MPa, while the 90°-specimen increased in effective mean stress during undrained loading. Dilation was found to be highest in the 30°-specimen and lowest in the 60°-specimen, demonstrated by both the effective stress path and the post-experimental microstructural analysis of the shear zones. The macroscopic shear band formed parallel to the bedding plane orientation for the specimen loaded in 60°-orientation. Here, only minor microstructural fabric changes such as increased porosity or deformed grain structures were observed, which verifies the minor volume changes inferred from the effective stress path.
{"title":"Insights into the anisotropic, hydro-mechanical behavior of Opalinus Clay through experimental and microstructural investigations","authors":"Lisa Winhausen, Kavan Khaledi, M. Jalali, F. Amann","doi":"10.56952/arma-2022-0353","DOIUrl":"https://doi.org/10.56952/arma-2022-0353","url":null,"abstract":"For analyzing the influence of structural anisotropy on the hydro-mechanical behavior of a clay shale, we performed three consolidated, undrained triaxial compression tests with different geometric specimen configurations. Opalinus Clay specimens were tested with bedding plane orientations of 30°, 60°, and 90° with respect to the horizontal. Results indicated different peak strengths at failure with highest and lowest values for the 90° and 30°-specimens, respectively. Failure occurred at different mean effective stresses with different magnitudes of pore water pressure built up. The 30°-specimen showed a decreasing effective mean stress up to and beyond failure compared to the initial effective consolidation stress of 10 MPa, while the 90°-specimen increased in effective mean stress during undrained loading. Dilation was found to be highest in the 30°-specimen and lowest in the 60°-specimen, demonstrated by both the effective stress path and the post-experimental microstructural analysis of the shear zones. The macroscopic shear band formed parallel to the bedding plane orientation for the specimen loaded in 60°-orientation. Here, only minor microstructural fabric changes such as increased porosity or deformed grain structures were observed, which verifies the minor volume changes inferred from the effective stress path.","PeriodicalId":418045,"journal":{"name":"Proceedings 56th US Rock Mechanics / Geomechanics Symposium","volume":"413 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2022-06-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"121705652","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
This work presents a well integrity tool based on an analytical model describing the thermo-poroelastic behaviour of wells in the so-called drained conditions and plane-strain conditions. The analytical model takes into account the pore pressure, uniform temperatures changes across the well and the cement's initial state of stress. The well integrity tool estimates the potential for debonding, tensile and shear fracturing of the rock and the cement sheath using computed stress profiles and the Mohr-Coulomb failure criterion. The tool is suited to study vertical well sections consisting of a single casing and cement sheath inside a porous or non-porous rock formation. The tool is built within a Microsoft Excel spreadsheet to make it as accessible, portable and flexible as possible. Furthermore, this work also presents an integrity analysis of a characteristic gas production well re-purposed for CO2 injection. This investigation covers the construction of the well, reservoir depletion, CO2 injection and long-term storage conditions. This demonstrates the type of data necessary for the tool to function, the different results and outputs that may be expected and the type of conclusions that may be drawn from them. This work is part of wider efforts by TotalEnergies to drive the development of safe CO2 storage technology and in particular to progress the understanding of well integrity loss mechanisms.
{"title":"An Open-access Well Integrity Tool to Study Legacy Wells Re-Purposed for CO2 Injection","authors":"C. Joulin","doi":"10.56952/arma-2022-0225","DOIUrl":"https://doi.org/10.56952/arma-2022-0225","url":null,"abstract":"This work presents a well integrity tool based on an analytical model describing the thermo-poroelastic behaviour of wells in the so-called drained conditions and plane-strain conditions. The analytical model takes into account the pore pressure, uniform temperatures changes across the well and the cement's initial state of stress. The well integrity tool estimates the potential for debonding, tensile and shear fracturing of the rock and the cement sheath using computed stress profiles and the Mohr-Coulomb failure criterion. The tool is suited to study vertical well sections consisting of a single casing and cement sheath inside a porous or non-porous rock formation. The tool is built within a Microsoft Excel spreadsheet to make it as accessible, portable and flexible as possible. Furthermore, this work also presents an integrity analysis of a characteristic gas production well re-purposed for CO2 injection. This investigation covers the construction of the well, reservoir depletion, CO2 injection and long-term storage conditions. This demonstrates the type of data necessary for the tool to function, the different results and outputs that may be expected and the type of conclusions that may be drawn from them. This work is part of wider efforts by TotalEnergies to drive the development of safe CO2 storage technology and in particular to progress the understanding of well integrity loss mechanisms.","PeriodicalId":418045,"journal":{"name":"Proceedings 56th US Rock Mechanics / Geomechanics Symposium","volume":"1 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2022-06-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"126057367","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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