Wellbore Stability Analysis In Inclined Wells

Wellbore stability analysis is becoming a necessary tool to improve operationaleconomy and to avoid wellbore problems. Essential elements here are estimation of criticalfracturing and collapse pressures to obtain an optimal mud weight window.The input data for this analysis is mainly pore pressure predictions from many sourceslike logs and drilling exponents, overburden stresses from logs or drilled cuttings, leak-offtests at casing shoes and breakout analysis from caliper logs. From these and other data,estimates for in-situ stresses and directions are obtained, which again serves as input forwellbore stability modeling. It is evident that the input data comes from many differentsources and can therefore not be considered consistent.The objective for this study is to conduct wellbore stability based on software system.For this purpose, a computer program in Visual Basic has been written and utilized to predictthree pressures profile. Field data from Kong gas field wells was analyzed to create thegeomechanical model used as the basis for developing safe mud-weight window for thedeviated and horizontal wells. An analytical approach to wellbore stability analysis wasimplemented using Mohr-Coulomb criterion.Three pressure profile is obtained with application of this study to Kong gas field inEast China. The pore pressure of the study area ranges from0.98g/cm3to1.55g/cm3. In theabnormally high pressured layer in the Pinghu formation, collapse pressure as well as fracturepressure in vertical changed quickly and collapse pressure generally ranges between0.8-1.2g/cm3and fracture pressure is1.5-2.2g/cm3.