Risk Mitigation Strategy Improves Drilling Performance with Geomechanical Modelling in Horizontal Wells

Abstract

The problem of wellbore instability is a worldwide technical problem in the field of the drilling engineering and one of the core problems for the safe and efficient drilling. After the drill bit drills the formation and a borehole is formed, the drilling fluid column pressure replaces the support provided by the drilled rock stratum, upsetting the original stress balance of the formation, and causing the stress redistribution of the rock around the borehole. If the redistributed stress exceeds the maximum load that the rock can bear, it will lead to wellbore instability. At the same time, the invasion of the drilling fluid filtrate into the formation will cause an increase in the formation pore pressure and a decrease in rock strength, further aggravating the instability of the wellbore. In tight gas development, the particularity of the drilling of the long-horizontal wells, during which the unstable bedded sandstone is taken as the target layer, the distribution of the secondary stress around horizontal wells, which is very different from that of vertical wells, the complex stress environment of tight gas reservoirs, and the well-developed bedding/fractures all increase the risk of wellbore collapse and instability. Based on the pore elasticity and single structural plane strength theory, this paper establishes a mechanical analysis model for the wellbore stability of horizontal wells in layered shale to analyze the effects of bedding plane occurrence (strike, dip angle), wellbore trajectory (wellbore orientation), and weakening of bedding plane strength on wellbore stability of horizontal wells. Besides, this paper establishes a three-dimensional geomechanical model of Zhongqian 1 block based on the geomechanical modeling technology to precisely characterize the distribution characteristics of mechanical parameters in three-dimensional space to provide technical support for the optimization of horizontal well drilling plan.