The Research Of Shale Wellbore Stability And Software Programming

Wellbore stability is a common problem need to be solved during oil and gas exploitation,almost all oil gas fields in the world have the problem of wellbore stability,and it's prevalent in China's major oil fields.It's very common to appear wellbore stability phenomenon in shale formation,such as collapse of shale,necking of shale and sticking and so on.The research of this thesis and conclusions as following:(1)The thesis researched the calculation of overburden pressure,horizontal stress and pore pressure deeply.At the same time,by the research of wellbore stability mechanics we know how the well stress distribution and how to calculate it.(2)By the analysis of some strength criterions we know that they don't consider the influences of intermediate principal stress to the strength of rock,but the Twin shear unified strength theory can solve this problem,and by the use of this theory to research the wellbore stability of shale,we obtain the accurate and actual result.(3)This thesis determined the relationship between the water content of shale and rock mechanics parameters by the Triaxial stress test.With the hydration of shale the strength and elastic modulus was been reduce,but the poisson's ratio was been increases.With the increase of water content,the cohesion of shale and internal friction angle is getting smaller and smaller.(4)By the sensitivity analysis of safety drilling fluid density window we know poisson's ratio and internal friction angle have closely relationship with it.But we think they are constant,in this thesis it's not a constant,so the result we obtain is more accurate.(5)Based on the above several aspects of research,a software used to prediction the safety drilling fluid density window was been made.After use the software we find that the result obtained is accurately,so it has a practical guiding significance to drilling engineering.