Calculation of Hole Collapse Pressure Considering the Influence of Borehole Diameter

Abstract

To solve the wellbore instability problem of slimhole, this paper presents a calculation method of collapse pressure base on the scale effect theory of rock strength. Based on the empirical relation between the uniaxial compressive strength and the specimen diameter proposed by Hoek, a modified empirical relation is studied in which the size effect of internal frictional angle is considered. A modified Mohr-Coulomb failure criterion with the influence of scale effect of rock strength is established. The collapse pressure which considers the influence of borehole diameter is calculated, and two evaluation method of size effect of rock strength is presented. The results show that the collapse pressure of slimhole is related to the borehole diameter. Meanwhile, the scale effect of formation with different properties is also different. The reduction in strength is due to the nonhomogeneity and fracture development of rocks. This provides important reference for the evaluation of collapse risks of wells with different diameters.  Index terms-slimhole, borehole diameter, scale effect, collapse pressure, fracture development He is major in petroleum engineering which includes water flooding development, hydraulic fracturing and well stability. He entered China University of Petroleum (Huadong) in 2005, and got Bachelor degree in 2009.Then he was recommended for admission to graduate school after graduation in 2009. and in 2012, he got master degree in China University of Petroleum(Huadong). He has presented 2 paper: "Ground Anti-Collision monitoring and warning system for directional wells" and "Feasibility analysis on application of casing head vibration signal in wellbore anti-collision monitoring". He has been involved in the area of anti-collision method during cluster well drilling, and currently he is major in water flooding development, hydraulic fracturing and well stability.