Petrophysical Evaluation, Construction of a One-Dimensional Geomechanical Model, and Determination of the Safe Drilling Mud Window in the Ilam Formation, One of the Fields in Southwest Iran
Subject Areas :
Keywords: Reservoir Zonation, Permeability, Stoneley Wave, Geomechanical Model,
Abstract :
Investigation of the reservoir and mechanical properties of formations – including permeability calculation, reservoir zonation, and construction of geomechanical models – is among the essential requirements of petroleum engineering studies in all disciplines. Given the significance of geological sciences, well logging, and reservoir geomechanics in petroleum engineering investigations, the present study aims to conduct a comprehensive analysis of formation zonation through the integration of geology and petrophysics, permeability estimation using dipole shear sonic logs, and ultimately the construction of a one-dimensional geomechanical model for the Ilam Formation in the studied well. To this end, in the first stage, using a complete suite of well logs integrated with geological data, the studied reservoir was divided into four zones and sections. In the second stage, considering the very high accuracy of the Stoneley wave in permeability estimation, the Flow Zone Indicator-Stoneley (FZI–Stoneley) method was employed to calculate this sensitive parameter. The correlation coefficient between the estimated permeability and core permeability using the FZI-Stoneley method was obtained as R2 = 0.90. In the third stage, a one-dimensional geomechanical model was constructed for the main reservoir interval under investigation. Accordingly, the directions of the minimum and maximum horizontal stresses in the studied well were determined as S34E and N56E, respectively. Based on the constructed model, the intervals exhibiting breakouts are consistent with the model results, and the applied mud weight in this well is slightly lower than the safe mud window and is consistent with the pore pressure. The safe mud window for the vertical well condition in the studied zone ranges from 12.2 to 15.5 lb/gal. The optimal deviation azimuth from the vertical direction is N120°, with an inclination of 80-90°. The minimum optimal weight in this direction, based on pressure and its equivalent mud weight, was calculated as 5996.7 psi and 11.8 lb/gal, respectively. Moreover, the faulting regime in the studied well, considering the magnitudes of the horizontal and vertical stresses, is identified as a normal-strike-slip regime.
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