STABILITY ANALYSIS OF A HORIZONTAL OIL WELL IN A STRIKE-SLIP FAULT REGIME

Fault regimes have significant effects on the stability of oil wells. Although vertical wells have different geo-mechanical behaviors, horizontal wells have more critical conditions when they encounter fault regime changes. In this study, a horizontal oil well is considered at a specific depth in the Mansouri oil field including the poroelastic state of rock mass and anisotropic horizontal stresses. The simulation of stability analysis is conducted with a Finite Element simulator (ABAQUS) and consists of two steps: (1) geostatic and (2) drilling. The geostatic step shows the initial in-situ stress conditions before drilling; in the drilling step, the well pressure has been increased continuously from the formation pore pressure (lower limit of allowable mud pressure window) to fracture pressure limit (tensile failure limit). The mud pressure optimization has been conducted based on the stress and plastic strain reduction at the borehole wall. The general results confirmed that the best direction for drilling horizontal oil wells in formations with anisotropic horizontal stresses is along the minimum horizontal stress and the optimum mud pressure in horizontal wells is higher than the minimum level of the well pressure (formation pore pressure). In addition, this analysis showed that the determination of critical well pressure which can create plastic strain on wellbore wall is very useful for stability evaluation of horizontal oil and gas wells.