This paper presents a coupled fluid flow and geomechanics model for analysis of two-phase flow and deformation behaviors in naturally fractured porous media. The discrete fracture model (DFM) is used to model two-phase fluid flow. The zero-thickness interface element method coupled with a modified Barton-Bandis’s constitutive model is applied to model the mechanical behavior of natural fractures. The finite volume (FVM) and finite element (FEM) methods are used for the discretization of flow and geomechanical equations, respectively. The coupled problem is iteratively solved using the fixed-stress splitting algorithm. Then the proposed model is applied to investigate the two-phase fluid flow in fractured porous media under various in-situ stress conditions. The results show that fracture aperture significantly increases as the differential stress increases due to shear dilation, which accordingly enhances the equivalent permeability of the fractured medium. Channelized flow is formed through the dilated fractures, which results in early water breakthrough and reduces the water sweep efficiency. This study illustrates the importance of shear dilation on two-phase flow behaviors in fractured porous media and highlights the necessity of considering shear dilation for accurate prediction of saturation distributions. The simulations also demonstrate the capacity of our model to capture the complex coupled behavior induced by the interaction between pore pressure and in-situ stress loadings.
{"title":"A coupled hydro-mechanical model for simulation of two-phase flow and geomechanical deformation in naturally fractured porous media","authors":"Lijun Liu, Yongzan Liu, Xiaoguang Wang, J. Yao","doi":"10.56952/arma-2022-0493","DOIUrl":"https://doi.org/10.56952/arma-2022-0493","url":null,"abstract":"This paper presents a coupled fluid flow and geomechanics model for analysis of two-phase flow and deformation behaviors in naturally fractured porous media. The discrete fracture model (DFM) is used to model two-phase fluid flow. The zero-thickness interface element method coupled with a modified Barton-Bandis’s constitutive model is applied to model the mechanical behavior of natural fractures. The finite volume (FVM) and finite element (FEM) methods are used for the discretization of flow and geomechanical equations, respectively. The coupled problem is iteratively solved using the fixed-stress splitting algorithm. Then the proposed model is applied to investigate the two-phase fluid flow in fractured porous media under various in-situ stress conditions. The results show that fracture aperture significantly increases as the differential stress increases due to shear dilation, which accordingly enhances the equivalent permeability of the fractured medium. Channelized flow is formed through the dilated fractures, which results in early water breakthrough and reduces the water sweep efficiency. This study illustrates the importance of shear dilation on two-phase flow behaviors in fractured porous media and highlights the necessity of considering shear dilation for accurate prediction of saturation distributions. The simulations also demonstrate the capacity of our model to capture the complex coupled behavior induced by the interaction between pore pressure and in-situ stress loadings.","PeriodicalId":418045,"journal":{"name":"Proceedings 56th US Rock Mechanics / Geomechanics Symposium","volume":"68 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":"115165039","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}
Ala Eddine Aoun, V. Rasouli, Youcef Khetib, Atir Kaunain, Olivia Kost, Abdelhakim Khouissat
Unconventional resources have become the core business of many petroleum companies to meet the increasing demand for energy. Several technologies and methods have been developed and deployed to unlock the potential of tight and ultra-tight formations. Hassi Tarfa (HTF) oil field is a thin and tight sandstone reservoir in Algeria, with an average permeability of less than 0.5 mD. However, all drilled wells in this field are vertical. Hydraulic Fracturing (HF) is the prime stimulation technique that is applied to increase oil recovery in unconventional reservoirs. Although the well production tremendously increases after fracking operation, it does not sustain for longer period of time, which keeps the estimated ultimate recovery (EUR) to be relatively low. In this study, a reservoir model was built and history matched, in order to consider three scenarios to optimize the horizontal lateral length in the HTF field. Then, multistage HF design was simulated using advanced 3D finite element software and exported to the model to estimate the potential increase of EUR. Sensitivities on number of HF stages, fluid volumes, and proppant were conducted to identify the optimal number of HF stages. The results of this study showed that, employing multistage hydraulic fracturing along horizontal drilling can significantly improve the oil recovery in HTF formation. Fracture length and the number of stages showed to be important design parameters. This study also identified the optimal range of operational parameters such as pumping schedule, proppant mass and perforation interval which are crucial to the cost reduction and operation efficiency.
{"title":"Technical Assessments of Horizontal Drilling with Multistage Fracturing to Increase Production from Hassi Tarfa Field, Algeria","authors":"Ala Eddine Aoun, V. Rasouli, Youcef Khetib, Atir Kaunain, Olivia Kost, Abdelhakim Khouissat","doi":"10.56952/arma-2022-0523","DOIUrl":"https://doi.org/10.56952/arma-2022-0523","url":null,"abstract":"Unconventional resources have become the core business of many petroleum companies to meet the increasing demand for energy. Several technologies and methods have been developed and deployed to unlock the potential of tight and ultra-tight formations. Hassi Tarfa (HTF) oil field is a thin and tight sandstone reservoir in Algeria, with an average permeability of less than 0.5 mD. However, all drilled wells in this field are vertical. Hydraulic Fracturing (HF) is the prime stimulation technique that is applied to increase oil recovery in unconventional reservoirs. Although the well production tremendously increases after fracking operation, it does not sustain for longer period of time, which keeps the estimated ultimate recovery (EUR) to be relatively low. In this study, a reservoir model was built and history matched, in order to consider three scenarios to optimize the horizontal lateral length in the HTF field. Then, multistage HF design was simulated using advanced 3D finite element software and exported to the model to estimate the potential increase of EUR. Sensitivities on number of HF stages, fluid volumes, and proppant were conducted to identify the optimal number of HF stages. The results of this study showed that, employing multistage hydraulic fracturing along horizontal drilling can significantly improve the oil recovery in HTF formation. Fracture length and the number of stages showed to be important design parameters. This study also identified the optimal range of operational parameters such as pumping schedule, proppant mass and perforation interval which are crucial to the cost reduction and operation efficiency.","PeriodicalId":418045,"journal":{"name":"Proceedings 56th US Rock Mechanics / Geomechanics Symposium","volume":"7 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":"124299765","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}
It is well known that rock porosity reduces rock Young’s modulus of intact rock specimens. However, it is not well understood how different types and amount of macroporosity in forms of non-connected or isolated cavities (e.g., vesicular basalt, lithophysal tuff) or interconnected vugs (e.g., vuggy limestone) affect rock elastic properties. Such macroporosity leads to challenges in deriving engineering properties of rock. This paper compiles an existing database for porosity and Young’s modulus of macroporous rocks. The database includes Young’s modulus determined from unconfined compression testing on intact rock specimens and analogue specimens used to prepare rock-like test samples and numerical simulations of compression testing on similar materials. The database is used to develop the relationship between porosity and Young’s modulus. In addition to the porosity, the macropore shapes, sizes, locations, and proximity of a macropore to its neighboring macropore play a role in how porosity affects intact rock Young’s modulus.
{"title":"Relationship between macroporosity and Young’s modulus through UCS tests on rock and analogue models, and numerical modeling – a literature review","authors":"N. Hudyma, B. Avar","doi":"10.56952/arma-2022-0131","DOIUrl":"https://doi.org/10.56952/arma-2022-0131","url":null,"abstract":"It is well known that rock porosity reduces rock Young’s modulus of intact rock specimens. However, it is not well understood how different types and amount of macroporosity in forms of non-connected or isolated cavities (e.g., vesicular basalt, lithophysal tuff) or interconnected vugs (e.g., vuggy limestone) affect rock elastic properties. Such macroporosity leads to challenges in deriving engineering properties of rock. This paper compiles an existing database for porosity and Young’s modulus of macroporous rocks. The database includes Young’s modulus determined from unconfined compression testing on intact rock specimens and analogue specimens used to prepare rock-like test samples and numerical simulations of compression testing on similar materials. The database is used to develop the relationship between porosity and Young’s modulus. In addition to the porosity, the macropore shapes, sizes, locations, and proximity of a macropore to its neighboring macropore play a role in how porosity affects intact rock Young’s modulus.","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":"128314679","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}
Xiyang Xie, J. D. Ytrehus, A. Taghipour, Raghavendra B. Kulkarni
Grooves makes easier to remove casing from cemented wellbore by pulling with lower force, which has been observed in lab-scale experiments. The simulation based on lab-scale geometry verifies the experimental observation, meanwhile frictional cohesion, as the key parameter controlling pulling force, is quantified. Field-scale simulation indicates the significant drawdown of the pulling force with small grooves (5 mm width). The peak of the pulling force also illustrates the possibility of pulling a 10-meter grooved casing without cutting into pieces, which may shorten the non-productive time and save cost on plug and abandonment task.
{"title":"How grooves can improve casing tripping-out from cemented borehole","authors":"Xiyang Xie, J. D. Ytrehus, A. Taghipour, Raghavendra B. Kulkarni","doi":"10.56952/arma-2022-2179","DOIUrl":"https://doi.org/10.56952/arma-2022-2179","url":null,"abstract":"Grooves makes easier to remove casing from cemented wellbore by pulling with lower force, which has been observed in lab-scale experiments. The simulation based on lab-scale geometry verifies the experimental observation, meanwhile frictional cohesion, as the key parameter controlling pulling force, is quantified. Field-scale simulation indicates the significant drawdown of the pulling force with small grooves (5 mm width). The peak of the pulling force also illustrates the possibility of pulling a 10-meter grooved casing without cutting into pieces, which may shorten the non-productive time and save cost on plug and abandonment task.","PeriodicalId":418045,"journal":{"name":"Proceedings 56th US Rock Mechanics / Geomechanics Symposium","volume":"17 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":"116851195","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}
J. Burghardt, H. Knox, T. Doe, D. Blankenship, P. Schwering, M. Ingraham, Timothy J Kneafsey, P. Dobson, C. Ulrich, Y. Guglielmi, W. Roggenthen
Engineering a robust hydraulic connection between wells is one of the most difficult aspects of enhanced geothermal systems (EGS). Designing and constructing such hydraulic connections requires an understanding of the in-situ state of stress and the heterogeneities and discontinuities that naturally exist and may control the stimulation. Even with comprehensive stress and formation characterization programs, substantial uncertainty remains in these key parameters. This is especially the case in high-temperature EGS environments where drilling conditions are often difficult and far fewer logging and testing options are available. This paper presents a new approach for explicitly quantifying the uncertainties in the state of stress using a Bayesian Markov Chain Monte Carlo method. This approach produces a probability distribution for the stress tensor, including a general 3D orientation, that reflects the uncertainties in all the observations or indicators used to constrain the stress state. This method is demonstrated using the characterization data for the EGS Collab Experiment 2 site. The output of the analysis is used to guide the design of the planned stimulations. In the case of research projects like EGS Collab, explicitly quantifying the uncertainties in the stress state allows for more rigorous hypothesis testing by allowing conclusions drawn from the experiments to be interpreted in the context of the uncertain knowledge about conditions in the test bed.
{"title":"EGS Stimulation Design with Uncertainty Quantification at the EGS Collab Site","authors":"J. Burghardt, H. Knox, T. Doe, D. Blankenship, P. Schwering, M. Ingraham, Timothy J Kneafsey, P. Dobson, C. Ulrich, Y. Guglielmi, W. Roggenthen","doi":"10.56952/arma-2022-0723","DOIUrl":"https://doi.org/10.56952/arma-2022-0723","url":null,"abstract":"Engineering a robust hydraulic connection between wells is one of the most difficult aspects of enhanced geothermal systems (EGS). Designing and constructing such hydraulic connections requires an understanding of the in-situ state of stress and the heterogeneities and discontinuities that naturally exist and may control the stimulation. Even with comprehensive stress and formation characterization programs, substantial uncertainty remains in these key parameters. This is especially the case in high-temperature EGS environments where drilling conditions are often difficult and far fewer logging and testing options are available. This paper presents a new approach for explicitly quantifying the uncertainties in the state of stress using a Bayesian Markov Chain Monte Carlo method. This approach produces a probability distribution for the stress tensor, including a general 3D orientation, that reflects the uncertainties in all the observations or indicators used to constrain the stress state. This method is demonstrated using the characterization data for the EGS Collab Experiment 2 site. The output of the analysis is used to guide the design of the planned stimulations. In the case of research projects like EGS Collab, explicitly quantifying the uncertainties in the stress state allows for more rigorous hypothesis testing by allowing conclusions drawn from the experiments to be interpreted in the context of the uncertain knowledge about conditions in the test bed.","PeriodicalId":418045,"journal":{"name":"Proceedings 56th US Rock Mechanics / Geomechanics Symposium","volume":"12 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":"114641954","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}
The Boise Valley contains several columnar jointed basalt cliffs, which were deposited approximately 1.4 to 0.5 Ma on terraces formed by downcutting of the Boise River. Three runout talus deposits on Whitney Terrace were characterized using unmanned aerial vehicle visual imagery. Although the runout talus deposits were from different areas and were of varying size, they contained roughly the same dimensions and distributions of blocks. Images of the cliff face indicated that blocks were detached from the base of columns along horizontal discontinuities which lacked support (undercut columns) and by toppling of basalt columns. The mapped block sizes in the cliff face were larger than the blocks in the associated runout, indicating the cliff blocks were fragmented during impacts in the runout.
{"title":"Mapping and Characterization of Rockfall Runout Talus Deposits from Columnar Basalt Cliffs in Boise, ID","authors":"N. Hudyma, N. Walker, B. Chittoori","doi":"10.56952/arma-2022-0132","DOIUrl":"https://doi.org/10.56952/arma-2022-0132","url":null,"abstract":"The Boise Valley contains several columnar jointed basalt cliffs, which were deposited approximately 1.4 to 0.5 Ma on terraces formed by downcutting of the Boise River. Three runout talus deposits on Whitney Terrace were characterized using unmanned aerial vehicle visual imagery. Although the runout talus deposits were from different areas and were of varying size, they contained roughly the same dimensions and distributions of blocks. Images of the cliff face indicated that blocks were detached from the base of columns along horizontal discontinuities which lacked support (undercut columns) and by toppling of basalt columns. The mapped block sizes in the cliff face were larger than the blocks in the associated runout, indicating the cliff blocks were fragmented during impacts in the runout.","PeriodicalId":418045,"journal":{"name":"Proceedings 56th US Rock Mechanics / Geomechanics Symposium","volume":"133 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":"130630983","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}
Wencheng Jin, P. Dobson, C. Doughty, N. Spycher, T. McLing, G. Neupane, Robert W. Smith, T. Atkinson
Reservoir thermal energy storage (RTES) is a promising technology to balance the mismatch between energy supply and demand. In particular, high temperature (HT) RTES can stabilize the grid with increasing penetration of renewable energy generation. This paper presents the investigation of the mechanical deformation and chemical reaction influences on the performance of HT-ATES for the Lower Tuscaloosa site. Thermo-hydraulic (TH), thermo-hydro-mechanical (THM), and thermo-hydro-chemical (THC) coupled simulations were performed with different operational modes and injection rates for a fixed five-spot well configuration and a seasonal cycle. The results show that (1) geomechanical-induced porosity change is mainly contributed by effective stress change, and the porosity change is distributed through the whole system; (2) geochemistry-induced porosity change is located near the hot well, and its change is one order of magnitude higher than the geomechanical effect; (3) both the operation mode and the injection rate have a huge influence on the RTES performance and lower injection rate with push-pull operation mode has the best performance with recovery factor around 70% for this RTES system. These results shed light on the deployment of HT-RTES in the US and around the world.
{"title":"Influence of mechanical deformation and mineral dissolution/precipitation on reservoir thermal energy storage","authors":"Wencheng Jin, P. Dobson, C. Doughty, N. Spycher, T. McLing, G. Neupane, Robert W. Smith, T. Atkinson","doi":"10.56952/arma-2022-0083","DOIUrl":"https://doi.org/10.56952/arma-2022-0083","url":null,"abstract":"Reservoir thermal energy storage (RTES) is a promising technology to balance the mismatch between energy supply and demand. In particular, high temperature (HT) RTES can stabilize the grid with increasing penetration of renewable energy generation. This paper presents the investigation of the mechanical deformation and chemical reaction influences on the performance of HT-ATES for the Lower Tuscaloosa site. Thermo-hydraulic (TH), thermo-hydro-mechanical (THM), and thermo-hydro-chemical (THC) coupled simulations were performed with different operational modes and injection rates for a fixed five-spot well configuration and a seasonal cycle. The results show that (1) geomechanical-induced porosity change is mainly contributed by effective stress change, and the porosity change is distributed through the whole system; (2) geochemistry-induced porosity change is located near the hot well, and its change is one order of magnitude higher than the geomechanical effect; (3) both the operation mode and the injection rate have a huge influence on the RTES performance and lower injection rate with push-pull operation mode has the best performance with recovery factor around 70% for this RTES system. These results shed light on the deployment of HT-RTES in the US and around the world.","PeriodicalId":418045,"journal":{"name":"Proceedings 56th US Rock Mechanics / Geomechanics Symposium","volume":"48 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":"131372208","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}
G. Kim, Sang-Gyu Cho, Chanhwi Shin, Pureun Jeon, Seoyeong Lee, Hanlim Kim, G. Min, Juseok Yang, Kyungjae Yoon
For an underground excavation at depth in highly stressful conditions, it is important to mitigate the risk of stress-induced failure, e.g., rockburst, and improve miner safety concerning the stability of underground workplaces and the prevention of fatalities. In general, the cause of rockburst is classified into three categories: strainburst due to stress-induced fracturing, rock ejection by seismic energy transfer, and rockfall associated with mining-induced seismicity. In this study, the Split Hopkinson Pressure Bar (SHPB) modified configuration of bar drop apparatus was developed by attaching a direct shear test box and a long bar. As a result, the modified bar drop system enabled to replicate and control of a seismic velocity that was an incident on the joint rock surfaces installed in the direct shear testing box. The long bar installed in the modified bar drop system provides a longer stress wavelength to overcome the relatively shorter duration of the stress waves in the SHPB system. The dynamic shear test on the jointed rock samples using the bar drop apparatus also provided the information to estimate the rock joint shear strengths.
{"title":"Laboratory Test on Direct Shear Behavior of Rock Joints Using a Bar Drop Impact System","authors":"G. Kim, Sang-Gyu Cho, Chanhwi Shin, Pureun Jeon, Seoyeong Lee, Hanlim Kim, G. Min, Juseok Yang, Kyungjae Yoon","doi":"10.56952/arma-2022-0734","DOIUrl":"https://doi.org/10.56952/arma-2022-0734","url":null,"abstract":"For an underground excavation at depth in highly stressful conditions, it is important to mitigate the risk of stress-induced failure, e.g., rockburst, and improve miner safety concerning the stability of underground workplaces and the prevention of fatalities. In general, the cause of rockburst is classified into three categories: strainburst due to stress-induced fracturing, rock ejection by seismic energy transfer, and rockfall associated with mining-induced seismicity. In this study, the Split Hopkinson Pressure Bar (SHPB) modified configuration of bar drop apparatus was developed by attaching a direct shear test box and a long bar. As a result, the modified bar drop system enabled to replicate and control of a seismic velocity that was an incident on the joint rock surfaces installed in the direct shear testing box. The long bar installed in the modified bar drop system provides a longer stress wavelength to overcome the relatively shorter duration of the stress waves in the SHPB system. The dynamic shear test on the jointed rock samples using the bar drop apparatus also provided the information to estimate the rock joint shear strengths.","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":"134427417","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}
Rotary-percussive drilling technique is an efficient rock-breaking method and can be applied in geothermal drilling. The rock's fragmentation mechanism was investigated using the distinct element method with the consideration of pre-existing cracks. We developed a cutter-rock interaction model to simulate the rotary-percussive drilling. In this model, a discrete fracture network (DFN) was used to reflect the rock's complex behavior. Bonded Block Model (BBM) was used to simulate cracks initiation that can merge and propagate to fracture the rock. As a dynamic problem, the rock's damping effect was introduced into our model by fitting it to the laboratory tests. Results represented the rock's fragmentation process under the cutter indentation and the coupling of impact load and lateral movement well. The pre-existing cracks can significantly enhance the drilling speed, which demonstrates the significance of considering the rock's non-continuous nature. Raising dynamic impact load is good for improving the penetration results in our study. For the back rake angle, 50 is the best choice in the evaluated range. But the cutter with the back rake angle of 20 obtains the highest fragmentation volume and lowest specific energy under the coupling of impact load and lateral velocity. This paper's research is of great significance to guide the application of rotary-percussive drilling and reduce the cost of developing geothermal resources.
{"title":"Numerical analyses of the granite fragmentation in rotary-percussive drilling with the consideration of pre-existing cracks","authors":"Z. Ji","doi":"10.56952/arma-2022-0346","DOIUrl":"https://doi.org/10.56952/arma-2022-0346","url":null,"abstract":"Rotary-percussive drilling technique is an efficient rock-breaking method and can be applied in geothermal drilling. The rock's fragmentation mechanism was investigated using the distinct element method with the consideration of pre-existing cracks. We developed a cutter-rock interaction model to simulate the rotary-percussive drilling. In this model, a discrete fracture network (DFN) was used to reflect the rock's complex behavior. Bonded Block Model (BBM) was used to simulate cracks initiation that can merge and propagate to fracture the rock. As a dynamic problem, the rock's damping effect was introduced into our model by fitting it to the laboratory tests. Results represented the rock's fragmentation process under the cutter indentation and the coupling of impact load and lateral movement well. The pre-existing cracks can significantly enhance the drilling speed, which demonstrates the significance of considering the rock's non-continuous nature. Raising dynamic impact load is good for improving the penetration results in our study. For the back rake angle, 50 is the best choice in the evaluated range. But the cutter with the back rake angle of 20 obtains the highest fragmentation volume and lowest specific energy under the coupling of impact load and lateral velocity. This paper's research is of great significance to guide the application of rotary-percussive drilling and reduce the cost of developing geothermal resources.","PeriodicalId":418045,"journal":{"name":"Proceedings 56th US Rock Mechanics / Geomechanics Symposium","volume":"37 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":"129969712","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}
Drilling mud loss is of crucial importance in drilling. Lost circulation will extend the well construction period, cause investment losses, and even cause serious downhole accidents. In the Mizhi block of Changqing Oilfield targeted by this research, serious leakage occurred in many wellbore drilling processes, which has seriously affected the development of the block and caused economic losses. This paper focuses the mud loss during the drilling process of more than 200 wells in the Mizhi block, and counts the key loss data such as the lost horizons, the amount of lost drilling fluid, the average leak rate, and the density of the drilling fluid, and fully analyzes the possible reasons of the lost circulation. Collecting logging data, modeling geomechanics of some key wells and formations, taking cores and the geomechanical model is established. Analyzing the logging data and the specific leakage situation, the leakage mainly comes from fractured leakage, and the leakage horizon is mainly located at the bottom of the Liujiagou Formation, the entire interval of the Shiqianfeng Formation and the top of the Shihezi Formation. Most of the mud loss sections are sand-mudstone interbeds. Geomechanical analysis shows that the rock mechanical strength of the entire interval is difficult to support the stability of the wellbore under the drilling fluid density of 1.1 grams per cubic meter, but the block loss pressure is generally between 1.1 - 1.2 grams per cubic meter. Collapse and leakage coexist in the wellbore. This study gives the method of drilling fluid optimization, and gives the possible reasons for the leakage from the perspective of geomechanics, which has important guiding significance for the further development of the Mizhi block.
钻井泥浆漏失是钻井过程中至关重要的问题。漏失会延长井的施工周期，造成投资损失，甚至造成严重的井下事故。本研究所针对的长庆油田米脂区块，多次井筒钻井过程中发生了严重的泄漏，严重影响了区块的开发，造成了经济损失。本文重点分析了米脂区块200多口井钻井过程中的泥浆漏失情况，统计了漏失层数、钻井液漏失量、平均漏速、钻井液密度等关键漏失数据，并对可能的漏失原因进行了充分分析。收集测井资料，对部分重点井和地层进行地质力学建模，取岩心，建立地质力学模型。通过对测井资料和具体泄漏情况的分析，发现泄漏主要来自裂缝性泄漏，泄漏层位主要位于刘家沟组底部、石千峰组全段和石河子组顶部。大部分失泥段为砂泥岩互层。地质力学分析表明，在钻井液密度为1.1 g / m3下，整个段段岩石机械强度难以支撑井筒的稳定性，但块体损失压力一般在1.1 - 1.2 g / m3之间。井筒内塌陷与泄漏并存。本研究给出了钻井液优化的方法，并从地质力学角度给出了泄漏的可能原因，对米脂区块的进一步开发具有重要的指导意义。
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