It is difficult to define safe drilling mud density window for shale sections.To solve this problem,the general Biot effective stress principle developed by Heidug and Wong was modified.The Weibull statistical model w...It is difficult to define safe drilling mud density window for shale sections.To solve this problem,the general Biot effective stress principle developed by Heidug and Wong was modified.The Weibull statistical model was used to characterize the hydration strainrelated strength damage.Considering drilling fluid sealing barrier on shale,a calculation method of safe drilling mud density has been established for shale formation under drilling fluid sealing-inhibition-reverse osmosis effect,combined with a flow-diffusion coupling model.The influence of drilling fluid sealing and inhibiting parameters on safe drilling mud density window was analyzed.The study shows that enhancing drilling fluid sealing performance can reduce the pore pressure transmission and solute diffusion;the inhibiting performance of drilling fluid,especially inhibition to strength damage,is crucial for the wellbore collapse pressure of shale section with significant hydration property.The improvement of drilling fluid sealing and inhibition performance can lower collapse pressure and enhance fracturing pressure,and thus making the safe drilling fluid density window wider and the collapse period of wellbore longer.If there is osmosis flow in shale,induced osmosis flow can make the gap between collapse pressure and fracturing pressure wider,and the stronger the sealing ability of drilling fluid,the wider the gap will be.The safe drilling mud density window calculation method can analyze the relationships between collapse pressure,fracturing pressure and drilling fluid anti collapse performance,and can be used to optimize drilling fluid performance.展开更多
Organic rich dark shale of Q Formation can be found in many areas(e.g.,in the North of S Basin).The shale target stratum is easy to hydrate and often undergoes spallation.Therefore,centering the casing in the horizont...Organic rich dark shale of Q Formation can be found in many areas(e.g.,in the North of S Basin).The shale target stratum is easy to hydrate and often undergoes spallation.Therefore,centering the casing in the horizontal section of the irregular borehole is relatively difficult.Similarly,achieving a good cementflushing efficiency under complex borehole conditions is a complex task.Through technologies such as centralizer,efficient preflushing,multi-stageflushing and ductile cement slurry,better performances can be achieved.In this study,it is shown that the cementing rate in the DY2H horizontal section is 97.8%,which is more than 34%higher than that of adjacent wells.This cementing matching technology for sidetracking horizontal wells can be used to improve the cementing quality of continental shale and provides a reference for future applications in thisfield.展开更多
Well Wutan 1 is a wildcat well deployed in the DazhoueKaijiang paleo-uplift,eastern Sichuan Basin and its design depth is 7570 m.The Cambrian and Sinian strata are its main exploration targets,and the strata below the...Well Wutan 1 is a wildcat well deployed in the DazhoueKaijiang paleo-uplift,eastern Sichuan Basin and its design depth is 7570 m.The Cambrian and Sinian strata are its main exploration targets,and the strata below the Silurian in this well are geologically uncertain with a high risk.A large section of gypsum-salt layer may be encountered in the Cambrian and the longitudinal pressure system is complex.It is predicted that the bottom hole temperature is up to 175 C,and the bottom hole liquid column pressure exceeds 140 MPa,and there is hydrogen sulfide.As a result,the casing program design is confronted with great challenges.In this paper,the difficulties and risks of drilling engineering were analyzed.Then,a casing program was designed and optimized referring to the successful drilling experience of subsalt ultra-deep wells at home and abroad,combined with the pressure system characteristics of Well Wutan 1 and the creep performance of gypsum-salt layers.Finally,the casing program was applied on site.And the following research results were obtained.First,in order to prevent lost circulation,blowout and differential pressure induced stuck pipe in the open hole section,it is determined that the casing program shall be in the pattern of six-section casing with 5 setting points.Second,no setting point is needed in the Carboniferous pressure depleted reservoir for it is lithologically tight and differential pressure induced stuck pipe and lost circulation are less risky.Third,to better isolate the salt layer,one section of casing is specially designed for the Cambrian gypsum-salt layer and its collapse strength is 160 MPa to prevent collapse by salt creep.Fourth,Well Wutan 1 is drilled successfully to the expected strata and its total depth is 8060 m.In conclusion,the unconventional six-section casing program with 5 setting points to ensure the subsalt drilling safety in the eastern Sichuan Basin is rational.The successful drilling of Well Wutan 1 provides experiences and references for the follow-up exploration of deep-seated gas in the DazhoueKaijiang paleo-uplift.展开更多
Deep gas wells and gas fields have the characteristics of high pressure. The vibration of the tubing string during the production of gas wells causes the string to be subjected to severe stress and even dynamic fatigu...Deep gas wells and gas fields have the characteristics of high pressure. The vibration of the tubing string during the production of gas wells causes the string to be subjected to severe stress and even dynamic fatigue failure. Therefore, this article is based on the dynamic finite element theory, aiming at the characteristics of large-size tubing strings in deep gas wells. The finite element mechanics model and mathematical model of the tubing string vibration of the packer of high-pressure gas wells were established, and the ANSYS software was re-developed. The finite element analysis program for the vibration dynamics of the unbuckled and buckled strings of gas wells was compiled with APDL, and the displacement of the longitudinal vibration of the tubing string of high-pressure gas wells was studied. According to different sizes of tubing strings currently used in deep gas wells and gas fields, simulation calculations are carried out, and the axial impact load and buckling damage laws of the tubing strings of the entire well section under different production rates are obtained. It provides a theoretical basis for the prediction of tubing string vibration law and measures to prevent tubing string vibration.展开更多
基金Supported by the China National Science and Technology Major Project(2016ZX05020-003).
文摘It is difficult to define safe drilling mud density window for shale sections.To solve this problem,the general Biot effective stress principle developed by Heidug and Wong was modified.The Weibull statistical model was used to characterize the hydration strainrelated strength damage.Considering drilling fluid sealing barrier on shale,a calculation method of safe drilling mud density has been established for shale formation under drilling fluid sealing-inhibition-reverse osmosis effect,combined with a flow-diffusion coupling model.The influence of drilling fluid sealing and inhibiting parameters on safe drilling mud density window was analyzed.The study shows that enhancing drilling fluid sealing performance can reduce the pore pressure transmission and solute diffusion;the inhibiting performance of drilling fluid,especially inhibition to strength damage,is crucial for the wellbore collapse pressure of shale section with significant hydration property.The improvement of drilling fluid sealing and inhibition performance can lower collapse pressure and enhance fracturing pressure,and thus making the safe drilling fluid density window wider and the collapse period of wellbore longer.If there is osmosis flow in shale,induced osmosis flow can make the gap between collapse pressure and fracturing pressure wider,and the stronger the sealing ability of drilling fluid,the wider the gap will be.The safe drilling mud density window calculation method can analyze the relationships between collapse pressure,fracturing pressure and drilling fluid anti collapse performance,and can be used to optimize drilling fluid performance.
基金funded by the CNPC Science and Technology Department Project(2021ZZ10-03)。
文摘Organic rich dark shale of Q Formation can be found in many areas(e.g.,in the North of S Basin).The shale target stratum is easy to hydrate and often undergoes spallation.Therefore,centering the casing in the horizontal section of the irregular borehole is relatively difficult.Similarly,achieving a good cementflushing efficiency under complex borehole conditions is a complex task.Through technologies such as centralizer,efficient preflushing,multi-stageflushing and ductile cement slurry,better performances can be achieved.In this study,it is shown that the cementing rate in the DY2H horizontal section is 97.8%,which is more than 34%higher than that of adjacent wells.This cementing matching technology for sidetracking horizontal wells can be used to improve the cementing quality of continental shale and provides a reference for future applications in thisfield.
基金supported by Major Science and Technology Project of PetroChina Company Limited“Research and application of key exploration and devel opment technologies to achieve 30-billion-m3 production in Southwest Oil and Gas Field”(No.:2016E-0608)Major Science and Technology Project of Southwest Oil&Gas Field Company“Research and application of key gas exploration and development technologies for Eastern Sichuan Basin”(No.:2016ZD01).
文摘Well Wutan 1 is a wildcat well deployed in the DazhoueKaijiang paleo-uplift,eastern Sichuan Basin and its design depth is 7570 m.The Cambrian and Sinian strata are its main exploration targets,and the strata below the Silurian in this well are geologically uncertain with a high risk.A large section of gypsum-salt layer may be encountered in the Cambrian and the longitudinal pressure system is complex.It is predicted that the bottom hole temperature is up to 175 C,and the bottom hole liquid column pressure exceeds 140 MPa,and there is hydrogen sulfide.As a result,the casing program design is confronted with great challenges.In this paper,the difficulties and risks of drilling engineering were analyzed.Then,a casing program was designed and optimized referring to the successful drilling experience of subsalt ultra-deep wells at home and abroad,combined with the pressure system characteristics of Well Wutan 1 and the creep performance of gypsum-salt layers.Finally,the casing program was applied on site.And the following research results were obtained.First,in order to prevent lost circulation,blowout and differential pressure induced stuck pipe in the open hole section,it is determined that the casing program shall be in the pattern of six-section casing with 5 setting points.Second,no setting point is needed in the Carboniferous pressure depleted reservoir for it is lithologically tight and differential pressure induced stuck pipe and lost circulation are less risky.Third,to better isolate the salt layer,one section of casing is specially designed for the Cambrian gypsum-salt layer and its collapse strength is 160 MPa to prevent collapse by salt creep.Fourth,Well Wutan 1 is drilled successfully to the expected strata and its total depth is 8060 m.In conclusion,the unconventional six-section casing program with 5 setting points to ensure the subsalt drilling safety in the eastern Sichuan Basin is rational.The successful drilling of Well Wutan 1 provides experiences and references for the follow-up exploration of deep-seated gas in the DazhoueKaijiang paleo-uplift.
文摘Deep gas wells and gas fields have the characteristics of high pressure. The vibration of the tubing string during the production of gas wells causes the string to be subjected to severe stress and even dynamic fatigue failure. Therefore, this article is based on the dynamic finite element theory, aiming at the characteristics of large-size tubing strings in deep gas wells. The finite element mechanics model and mathematical model of the tubing string vibration of the packer of high-pressure gas wells were established, and the ANSYS software was re-developed. The finite element analysis program for the vibration dynamics of the unbuckled and buckled strings of gas wells was compiled with APDL, and the displacement of the longitudinal vibration of the tubing string of high-pressure gas wells was studied. According to different sizes of tubing strings currently used in deep gas wells and gas fields, simulation calculations are carried out, and the axial impact load and buckling damage laws of the tubing strings of the entire well section under different production rates are obtained. It provides a theoretical basis for the prediction of tubing string vibration law and measures to prevent tubing string vibration.
