Analysis on borehole stability of gas drilling with complete stress–strain and thermal stress theory

Abstract In conventional mud drilling, sufficient drilling fluid density is required to maintain wellbore stability. However, in gas the support ability of very weak, and stability usually good. This shows that borehole instability mechanism different from drilling. wall rock still has a certain bearing capacity after reaching peak strength. this paper, studied by using complete stress–strain model. The deformation around can be divided into elastic zone, plastic broken zone. radii zone were used evaluate wall. method good general applicability case no thermal stress rock. due throttling cooling as flows out bit nozzle during occurs when cryogenic flow annulus meets hot formation. Therefore, introduced calculation are calculated according actual data, compared with measured diameter. results show model reasonable effective. Analysis process, temperature much lower than original formation near bottom borehole, higher upper part borehole. Thermal significant effect on makes shrink offset expansion situ surrounding rock, thus enhancing top expands under action stress, toward aggravating better explain it more intuitive use radius characterize