Rock characterization of rupelian-chatian Asmari carbonate formation using the simultaneous pre-stack inversion technique and lame parameters in the Kopal oilfield, Dezful embayment, Zagros basin

Abstract

The main aim of this study is to integrate the results of sedimentology, strontium isotope with the results simultaneous inversion of 3D seismic data for rock characterization of Rupelian-Chatian Asmari Formation. Using the simultaneous inversion of prestack seismic data variations of rock properties in the Rupelian-Chatian Asmari Formation were interpreted. In this regard, lame coefficients, compressive velocity (Vp), shear velocity (Vs) and compressive-to-shear velocity ratio (Vp/Vs) were extracted from prestack 3D seismic data. Converting shear impedance (SI) and acoustic impedance (AI) to LMR (Lambda-Mu-Rho) provides a more comprehensive understanding of the subsurface rock properties. Based on AI, SI, and lame coefficients, the Rupelian-Chatian Asmari Formation was divided into the lower part and the upper part. The upper part of the Asmari Formation shows a relatively low lame parameters indicating sigmoid patterns composed of shale and sandstone. In contrast, the upper part of Asmari Formation is composed of cyclic carbonate sediments mainly mainly limestone and dolomite. This interval is associated with variations in the lame coefficients, P and S- impedances indicating clinoform patterns. The downlap and top lap termination observed in lame coefficient sections indicate the movement of clinoforms from southwest (shallow) to northeast (deep). The results of this study show that during the Rupelian Chatian time, the coastal part of the Asmari Sea was situated in the southwest of the Kopal Oilfield, while the deeper part was located in the northeast of the field. This study shows that the simultaneous inversion of seismic data combined with sedimentological and geochemical can effectively aid in lithology detection, sequence stratigraphy and depositional setting analysis.