Investigation of Reactivation of Fault and Wellbore Stability Analysis by the Depletion of Hydrocarbon Reservoirs

Over time and production from the reservoir, the pore pressure of the production layer decreases if there is no source of pressure supply. This reduction in pressure directly alters the amount and direction of stresses. Changes in the amount of stresses can cause geomechanical changes in the reservoir and production layers. If the reservoir layers are faulted, reducing the reservoir pressure can activate these faults and also change the tensile strength of the well bore for new drilling in the discharged layer. This research was conducted in one of the reservoirs of southwestern Iran. In this reservoir, three production layers with different thicknesses were examined and the probability of reactivation of faults and tensile strength in the initial state and after the pressure drop of 1800 psi was evaluated. In layer 1, the value of the stress path was 0.67, which due to the fact that it is tangent to the critical stress value, the faults will be reactivated by producing from the reservoir and reducing the reservoir pressure in this layer. Also in this layer, the maximum weight of the drilling mud allowed for non-failure of rock traction in the initial state is 17.81- 25.13 PPG and after a reduction of 1800 psi of layer pressure, it is in the range of 15.07- 23.42 PPG. . In addition, the most resistant state of the well bore is drilling with an angle of 60 degrees and in the direction of minimum horizontal stress.