Wellbore Stability Analysis During Drilling Using Geomechanical Model and FLAC3D Software in Asmari Reservoir, Ahwaz Oil Field

Oil reservoirs are one of the important sources of energy due to which is caused by specific rock mechanical properties, the ability to maintain hydrocarbon fluids. One of the major problems that are occurred during drilling a well is instability of the wellbore. In order to prevent this difficulty its need to predict stability of the rocks by using geomechanical properties and in-situ stresses. A lack of accurate wellbore stability analysis brings many problems such as borehole washout, breakout, collapse, stuck pipes and drill bits. In the present research work the stability of an oil well located in Asmari reservoir of Ahwaz oil field was stimulated by using numerical software FLAC3D and information obtained from well log curves were evaluated and analyzed in two parts and the results were presented. Mud pressure and mud weight in outset of wellbore plastic flow and also outset of shear failure in wellbore were obtained for 7.5 meter of formation which mainly consists of limestone, marl. Well stability analysis was performed in vertical direction, minimum horizontal stress and maximum horizontal stress. Due to plastic movement and shear failure in wellbore, in first stage the mud pressure occurred is 33 and 26.4 Mpa and the second stage it reaches to 45 and 30 Mpa, respectively.It indicates that tensile failure is in direction of maximum horizontal stress and shear failure in direction of minimum horizontal stress. Subsequently, the result shows that the analysis due to the low mechanical properties of the sandstone layer indicates the maximum amount of displacement and loss. The safe mud window is small in this layer.