oa Geomechanical behavior of reservoir rocks in the Sarvak Formation southwest Iran

Cost-effective improvements in the technology needed to develop and manage reservoirs in challenging environments require an increase in our understanding of geomechanical behavior. The knowledge of rock strength is important in assessing wellbore stability problems, effective sanding and the estimation of in-situ stress field. Geomechanical properties are determined directly from in-situ tests and core analysis in laboratory in reservoir conditions. This method is time-consuming, expensive and can only be applied in limited intervals in wells. Reservoir rocks are generally layered, fractured, faulted and jointed, and these factors have an influence on their mass properties. Moreover cutting and recovering cores in these rocks is very difficult. Alteration of cores during and after drilling may also influence the results. In this study a method has been used that is based on down-hole measurements of sonic-wave velocity and other petrophysical logs. In most wells the shear-wave velocity (Vs) is not measured. We therefore measured compressional and shear wave velocities from 31 core plugs taken from the Sarvak carbonate formation in four wells. The measurements were conducted in both dry and saturated samples under reservoir condition. The laboratory results were calibrated with compressional and shear wave velocities measured using the DSI tool in one well, and a suitable relationship was obtained for estimating the shear wave velocity from compressional wave velocity and porosity logs. We then used compressional<br>and shear wave velocity logs, in conjunction with the bulk density log, to interpolate the in-situ measurements and calculate the geomechanical parameters on continuous logs. Using these parameters, unstable intervals and sand-productive zones were identified in the reservoir.