CO_(2) drilling is a promising underbalance drilling technology with great advantages,such as lower cutting force,intense cooling and excellent lubrication.However,in the underbalance drilling,the mechanism of the cou...CO_(2) drilling is a promising underbalance drilling technology with great advantages,such as lower cutting force,intense cooling and excellent lubrication.However,in the underbalance drilling,the mechanism of the coupling CO_(2) jet and polycrystalline-diamond-compact(PDC)cutter are still unclear.Whereby,we established a coupled smoothed particle hydrodynamics/finite element method(SPH/FEM)model to simulate the composite rock-breaking of high-pressure CO_(2) jet&PDC cutter.Combined with the experimental research results,the mechanism of composite rock-breaking is studied from the perspectives of rock stress field,cutting force and jet field.The results show that the composite rock-breaking can effectively relieve the influence of vibration and shock on PDC cutter.Meanwhile,the high-pressure CO_(2) jet has a positive effect on carrying rock debris,which can effectively reduce the temperature rising and the thermal wear of the PDC cutter.In addition,the effects of CO_(2) jet parameters on composite rock-breaking were studied,such as jet impact velocity,nozzle diameter,jet injection angle and impact distance.The studies show that when the impact velocity of the CO_(2) jet is greater than 250 m/s,the CO_(2) jet could quickly break the rock.It is found that the optimal range of nozzle diameter is 1.5–2.5 mm,the best injection angle of CO_(2) jet is 60,the optimal impact distance is 10 times the nozzle diameter.The above studies could provide theoretical supports and technical guidance for composite rock-breaking,which is useful for the CO_(2) underbalance drilling and drill bit design.展开更多
The exploitation of shale gas is promising due to depletion of the conventional energy and intensification of the greenhouse effect.In this paper,we proposed a heat-fluid-solid coupling damage model of supercritical C...The exploitation of shale gas is promising due to depletion of the conventional energy and intensification of the greenhouse effect.In this paper,we proposed a heat-fluid-solid coupling damage model of supercritical CO_(2)(SC-CO_(2))compound fracturing which is expected to be an efficient and environmentally friendly way to develop shale gas.The coupling model is solved by the finite element method,and the results are in good agreement with the analytical solutions and fracturing experiments.Based on this model,the fracture propagation characteristics at the two stages of compound fracturing are studied and the influence of pressurization rate,in situ stress,bedding angle,and other factors are considered.The results show that at the SC-CO_(2)fracturing stage,a lower pressurization rate is conducive to formation of the branches around main fractures,while a higher pressurization rate inhibits formation of the branches around main fractures and promotes formation of the main fractures.Both bedding and in situ stress play a dominant role in the fracture propagation.When the in situ stress ratio(δ_(x)/δ_(y))is 1,the presence of bedding can reduce the initiation pressure and failure pressure.Nevertheless,it will cause the fracture to propagate along the bedding direction,reducing the fracture complexity.In rocks without bedding,hydraulic fracturing has the lengthening and widening effects for SC-CO_(2)induced fracture.In shale,fractures induced at the hydraulic fracturing stage are more likely to be dominated by in situ stresses and have a shorter reorientation radius.Therefore,fracture branches propagating along the maximum principal stress direction may be generated around the main fractures induced by SC-CO_(2)at the hydraulic fracturing stage.When the branches converge with the main fractures,fracture zones are easily formed,and thus the fracture complexity and damage area can be significantly increased.The results are instructive for the design and application of SC-CO_(2)compound fracturing.展开更多
Although several theoretical calculation methods for high-pressure jet are available,there is currently no theoretical model for the high-pressure CO_(2)jet based on the high-precision equation of state(EOS).To invest...Although several theoretical calculation methods for high-pressure jet are available,there is currently no theoretical model for the high-pressure CO_(2)jet based on the high-precision equation of state(EOS).To investigate the flow field of the high-pressure CO_(2)jet in cases of the composite rock-breaking under the high-pressure CO_(2)Jet and PDC cutter,a semi-analytical approach of the high-pressure CO_(2)jet is developed based on the Span-Wagner EOS and CO_(2)jet theory.The semi-analytical calculations and the physical property calculations under the action of the high-pressure CO_(2)jet are conducted with consideration of the jet pressure,the jet distance,the nozzle diameter and the jet angle.The results indicate that the distribution of the physical properties calculated by the semi-analytical approaches is similar to that obtained by experimental monitoring and numerical simulation,which indicates that the calculation method of the high-pressure CO_(2)jet presented in this paper is effective and reliable.The properties of the CO_(2)jet obtained by the theoretical calculation see a significant difference between the initial region and the jet impact region.At the temperature of 300 K,the increase of the initial pressure can effectively increase the impact force and the cooling ability of the jet.The proportion of the jet core lengths in the jet on the axis increases with the increase of the ratio of the nozzle diameter to the jet length,accompanied with the increase of the impact force of the jet.The increase of the jet angle can effectively increase the impacting force of the jet,but hampers the fluid diffusion.The study combines the theoretical calculation of the jet with the calculation of the physical properties of the high-pressure CO_(2),for comprehensively understanding the CO_(2)jet field in the composite rock-breaking under the action of the high-pressure CO_(2)jet and PDC cutter.This theoretical calculation of the CO_(2)jet based on the high-precision EOS provides an option for the convenient calculation of the CO_(2)drilling in practical engineering.展开更多
基金This work was supported by the National Natural Science Foundation of China(No.52004236)Sichuan Science and Technology Program(No.2021JDRC0114)+4 种基金the Starting Project of Southwest Petroleum University(No.2019QHZ009)the China Postdoctoral Science Foundation(No.2020M673285)the Open Project Program of Key Laboratory of Groundwater Resources and Environment(Jilin University)Ministry of Education(No.202005009KF)the Chinese Scholarship Council(CSC)funding(No.202008515107).
文摘CO_(2) drilling is a promising underbalance drilling technology with great advantages,such as lower cutting force,intense cooling and excellent lubrication.However,in the underbalance drilling,the mechanism of the coupling CO_(2) jet and polycrystalline-diamond-compact(PDC)cutter are still unclear.Whereby,we established a coupled smoothed particle hydrodynamics/finite element method(SPH/FEM)model to simulate the composite rock-breaking of high-pressure CO_(2) jet&PDC cutter.Combined with the experimental research results,the mechanism of composite rock-breaking is studied from the perspectives of rock stress field,cutting force and jet field.The results show that the composite rock-breaking can effectively relieve the influence of vibration and shock on PDC cutter.Meanwhile,the high-pressure CO_(2) jet has a positive effect on carrying rock debris,which can effectively reduce the temperature rising and the thermal wear of the PDC cutter.In addition,the effects of CO_(2) jet parameters on composite rock-breaking were studied,such as jet impact velocity,nozzle diameter,jet injection angle and impact distance.The studies show that when the impact velocity of the CO_(2) jet is greater than 250 m/s,the CO_(2) jet could quickly break the rock.It is found that the optimal range of nozzle diameter is 1.5–2.5 mm,the best injection angle of CO_(2) jet is 60,the optimal impact distance is 10 times the nozzle diameter.The above studies could provide theoretical supports and technical guidance for composite rock-breaking,which is useful for the CO_(2) underbalance drilling and drill bit design.
基金the funding support from the National Natural Science Foundation of China(Nos.52274093 and 52004236).
文摘The exploitation of shale gas is promising due to depletion of the conventional energy and intensification of the greenhouse effect.In this paper,we proposed a heat-fluid-solid coupling damage model of supercritical CO_(2)(SC-CO_(2))compound fracturing which is expected to be an efficient and environmentally friendly way to develop shale gas.The coupling model is solved by the finite element method,and the results are in good agreement with the analytical solutions and fracturing experiments.Based on this model,the fracture propagation characteristics at the two stages of compound fracturing are studied and the influence of pressurization rate,in situ stress,bedding angle,and other factors are considered.The results show that at the SC-CO_(2)fracturing stage,a lower pressurization rate is conducive to formation of the branches around main fractures,while a higher pressurization rate inhibits formation of the branches around main fractures and promotes formation of the main fractures.Both bedding and in situ stress play a dominant role in the fracture propagation.When the in situ stress ratio(δ_(x)/δ_(y))is 1,the presence of bedding can reduce the initiation pressure and failure pressure.Nevertheless,it will cause the fracture to propagate along the bedding direction,reducing the fracture complexity.In rocks without bedding,hydraulic fracturing has the lengthening and widening effects for SC-CO_(2)induced fracture.In shale,fractures induced at the hydraulic fracturing stage are more likely to be dominated by in situ stresses and have a shorter reorientation radius.Therefore,fracture branches propagating along the maximum principal stress direction may be generated around the main fractures induced by SC-CO_(2)at the hydraulic fracturing stage.When the branches converge with the main fractures,fracture zones are easily formed,and thus the fracture complexity and damage area can be significantly increased.The results are instructive for the design and application of SC-CO_(2)compound fracturing.
基金This work was supported by the Sichuan Science and Technology Program(Grant No.2021JDRC0114)the Starting Project of Southwest Petroleum University(Grant No.2019QHZ009)+2 种基金the China Postdoctoral Science Foundation(Grant No.2020M673285)the Open Project Program of Key Laboratory of Groundwater Resources and Environment,Ministry of Education,Jilin University(Grant No.202005009KF)the Chinese Scholarship Council funding(Grant No.202008515107).
文摘Although several theoretical calculation methods for high-pressure jet are available,there is currently no theoretical model for the high-pressure CO_(2)jet based on the high-precision equation of state(EOS).To investigate the flow field of the high-pressure CO_(2)jet in cases of the composite rock-breaking under the high-pressure CO_(2)Jet and PDC cutter,a semi-analytical approach of the high-pressure CO_(2)jet is developed based on the Span-Wagner EOS and CO_(2)jet theory.The semi-analytical calculations and the physical property calculations under the action of the high-pressure CO_(2)jet are conducted with consideration of the jet pressure,the jet distance,the nozzle diameter and the jet angle.The results indicate that the distribution of the physical properties calculated by the semi-analytical approaches is similar to that obtained by experimental monitoring and numerical simulation,which indicates that the calculation method of the high-pressure CO_(2)jet presented in this paper is effective and reliable.The properties of the CO_(2)jet obtained by the theoretical calculation see a significant difference between the initial region and the jet impact region.At the temperature of 300 K,the increase of the initial pressure can effectively increase the impact force and the cooling ability of the jet.The proportion of the jet core lengths in the jet on the axis increases with the increase of the ratio of the nozzle diameter to the jet length,accompanied with the increase of the impact force of the jet.The increase of the jet angle can effectively increase the impacting force of the jet,but hampers the fluid diffusion.The study combines the theoretical calculation of the jet with the calculation of the physical properties of the high-pressure CO_(2),for comprehensively understanding the CO_(2)jet field in the composite rock-breaking under the action of the high-pressure CO_(2)jet and PDC cutter.This theoretical calculation of the CO_(2)jet based on the high-precision EOS provides an option for the convenient calculation of the CO_(2)drilling in practical engineering.
