Research On Wellbore Stability And Drilling Fluid System In Liujiagou-Shuangshi Well Section Of Yanchang Gas Field

Yanchang natural gas well construction block is located in yishan slope of ordos basin.However,the lithology of the liugou-shuangshi formation(shiqianfeng formation,shixiexi formation)is mainly hard and brittle(broken)mud shale,which is easy to collapse and drop,and the shaft wall is unstable and protruding.Therefore,this paper studies the borehole wall instability mechanism of liujiagou formation and shuangshi formation(shiqianfeng formation and shibox formation)and the anti-collapse drilling fluid technology.By adjacent well data are collected,analysis in gas Wells of extended Liu Gugou group-ShuangShi(shi feng group,stone box)strata borehole wall is easy to broken,collapse,use the means such as mineral composition,the structure of the sample analysis,reveals the mechanism of sidewall instability for this section is the mechanical,physical and chemical factors,drilling mechanical disturbance and the result of comprehensive action.Therefore,the key to solve the well wall instability of liugou-shiqianfeng formation in yanchang gas field lies in strong inhibition and effective plugging.Rheology,dehydrate wall building,give attention to two or morethings inhibitory,sealing,lubrication performance,such as optimizing fluid loss agent,flow pattern regulator,inhibitors,blocking agent,lubricant,such as treating agent,experiments were made on the approximation formulations,formed by KCOOH inhibitors,CaC03 as fillers,the final piece together into a strong inhibition against the collapse of water-based drilling fluid system(KCOOH polysulfide drilling fluid system):?4.0%bentonite+0.15%XC+0.50%CHL-1+25.0%KCOOH+1.5%SMP-2+1.0%M-SMC+2.0%CMJ-2+5.0%CaCO3(150-200mesh)+2.0%EP-2+1.5%AAMB+0.5%JN303;?4.0%bentonite+0.15%XC+0.50%CHL-1+25.0%KCOOH+3.0%SMP-2+1.5%M-SMC+2.0%CMJ-2+7.0%CaCO3(150-200mesh)+2.0%EP-2+1.0%AAMB+0.5%JN303.The comprehensive performance of the drilling fluid system is evaluated,and the results show that the drilling fluid system has reasonable rheology,effective plugging,excellent wall building,adequate inhibition,good lubricity,strong anti-pollution ability and good thermal stability.The experiment tested the influence of this system on the formation collapse pressure.The results showed that,compared with the original formation,the incremental collapse pressure of liujiagou formation,shiqianfeng formation and shibox formation was 0.120g/cm3,0.095g/cm3 and 0.105g/cm3,respectively,due to the field slurry action of the original formation.The collapse pressure increment of liujiagou formation is 0.070g/cm3 due to the action of drilling fluid system with no.The collapse pressure increment of the shiqianfeng formation and shibox formation was 0.023g/cm3 and 0.038g/cm3,respectively,due to the action of drilling fluid system(no.2)in the original formation.Compared with the field slurry,KCOOH polysulfonate drilling fluid system has a strong ability to stabilize the borehole wall,which is the result of the combined action of strong inhibition and effective plugging of KCOOH polysulfonate drilling fluid system.The application technology of anti-sag drilling fluid is put forward,including the measures of preparation and maintenance of anti-sag drilling fluid,basic technical scheme and operation rules.