In-Situ Stress Constrain: A Geomechanics Study To Evaluate the Influence of the Structural Geology

Abstract

Abstract The in situ stresses constraint is one of the most difficult parameter in a geomechanics model. Most of them are simple models in which is not involved the influence of geological discontinuities such as complex fault system, bedding plane, folds and joints. Recent studies have pointed out that these can significantly impact on the in situ stress states, leading to changes in magnitudes and rotations of stress tensor along formation sections. However, taking into account the structural geology and projecting the stress state underground, its uncertainty can be reduced. It results in an improvement during the well construction design to obtain a safer operational fluid density window, optimum well trajectories and an effective borehole stability analysis. This paper presents an integrated methodology to interpolate the magnitude of the stresses and their orientation, including the effect of structural geology. A case of study from Eastern Basin Venezuela, SJ Field, was analyzed. First, a review of the structural geology model was done to identify its origin and the fault history. Then, a geomechanics 1D model with the pore pressure calculation, rock mechanics properties and in situ stress estimations was developed to be integrated with a kinematic analysis in which the structural restoration was defined. Besides, dynamic analysis using a numerical simulation with finite element in a 2D structural section was performed. The results confirmed that stress state changed not only in orientation, but also in magnitude near to the Anaco Thrust. As a main consequence, the boreholes located next to this structural element experiment variations in depth from normal to strike-slip regime.