Geomechanical assessments of a sandstone reservoir using 3D pre-stack seismic and wellbore data

Abstract

The main objective of this study is to identify the hydrocarbon-bearing zones of a reservoir layer using the combination of several geomechanical parameters in a horizontal slice. A two-step assessment procedure was designed and used on three-dimensional pre-stack seismic data accompanied by information from four wells. In the first step, an integrated attribute consisting of the Zp, Vp/Vs, Young's modulus, Poisson's ratio, and Mu-Rho geomechanical parameters were prepared. The method to extract those parameters was a simultaneous inversion. By performing the inversion, acoustic impedances and density were obtained. Then the geomechanical parameters were extracted using several equations. To identify and assess zones with high hydrocarbon potential, the integrated attribute was accomplished laterally and vertically at the various zones of a reservoir layer. We found that when a lower value of the integrated attribute appears at the higher thickness of the reservoir layer, it indicates the zones with higher hydrocarbon potential. To distinguish the shale, brine, and hydrocarbon-bearing intervals the higher hydrocarbon potential zones, which were identified in the first step, were used to obtain five scatter plots in the second step. The scatter plots determine the correlation between every two of the geomechanical parameters. The plots consist of Young's modulus versus Poisson's ratio, Zp versus Vp/Vs, Zp versus Poisson's ratio, Mu-Rho versus Lambda-Rho (LMR), and Mu-Rho/Lambda-Rho versus Lambda-Rho. It was concluded that this procedure is able to find the best location of the reservoir with the highest hydrocarbon potential within a short time, which is so useful in the petroleum industry. We validated our results using the existing well information. The correlation, in this case, was about 90% for P impedance and 80% for geomechanical parameters which was considered satisfactory. Therefore the two-step assessment procedure proved to be a sensitive tool to identify and quantify the high hydrocarbon potential zones as well as distinguishing between shale, brine, oil, and gas-bearing, intervals of a reservoir layer.