Abstract:

Bottom-hole differential pressure is one of the important factors which affect the drilling penetration rate; and it is proved that underbalanced drilling is usually more efficient than conventional drilling. The purpose of the article is to study the effect of bottom-hole differential pressure on the vertical bottom-hole stress field. Based on the of mechanical analysis of the bottom-hole rock, the fluid-solid coupling model with the bottom-hole differential pressure is established under axisymmetric condition and the numerical simulation calculation of the bottom-hole stress field under different differential pressures is calculated with the finite element method. The comparison between the numerical and theoretical solutions and analysis of the stress state of bottom-hole rock to break are carried out. The results show that the numerical solution is consistent with the theoretical solution and the fluid-solid coupling model is reasonable. The bottom-hole rock is divided into three regions: triaxial tension region, biaxial compression region and triaxial compression region. Study of the bottom hole rock stress field under different drilling methods is the theoretical basis for faster and more efficient drilling.

Key words: bottom-hole differential pressure, fluid-solid coupling, finite element method, stress field, rock breaking