Wellbore Stability Mechanism and Countermeasures of Igneous Formations in Shunbei Oilfield

Abstract

Shunbei oilfield is located in the Midwest of Tarim Basin. Since 2018 many wells in the block have encountered broken formation, directional wells wellbore collapsed seriously, resulting drilling sidewells, with a huge loss of drilling costs. The influencing factors of igneous formation stability include internal and external factors. The internal cause refers to the formation instability caused by the strength anisotropy and strong in-situ stress nonuniformity of igneous formation. The external cause refers to various factors that cause the change of the external environment of the formation caused by drilling engineering, including the physical and chemical interaction between the drilling fluid and the formation, well trajectory and mechanical disturbance of the drilling string, etc. Based on the analysis of the influencing factors of wellbore stability in igneous rock, the technical countermeasures of wellbore stability in igneous rock formation are put forward and field tests are carried out. In the Permian fractured formation of Shunbei oil field,the idea of “prevention first, combination of prevention and blocking” is adhered to the first principles. Low density and low viscosity drilling fluid with low displacement is adopted to prevent the occurrence of lost circulation. The wellbore of the igneous rock intrusion in santamu formation of Ordovician is easy to collapse. By adopting special sealing structure and strengthening plugging and anti-collapse, combined with slurry plugging and well washing and refining engineering measures, the safe drilling of the igneous rock can be ensured.