INTEGRATING AMPLITUDE VARIATION WITH OFFSET AND ROCK PHYSICS MODELING FOR RESERVOIR CHARACTERIZATION OVER “TOLUJOBI” FIELD, OFFSHORE, NIGER DELTA

Abstract

The drive for finding hydrocarbon reserves has led to various development in the oil and gas industry. Integration of amplitude variation with offset (AVO) and rock physics modeling for reservoir characterization was carried out over “Tolujobi” field, offshore, Niger Delta with a view to evaluate reservoir quality beyond area covered by wells. The data set used for the study includes prestack seismic and a suite of well logs from one well. The methods of reservoir delineation, AVO fluid replacement modeling, AVO gradient analysis using the two term Aki and Richard’s synthetic gather and seismic to well tie was carried out. Porosity and permeability values were calculated and rock physics modeling templates was used to accurately characterize the reservoirs. Elastic log was also generated from the insitu log so as to help in characterizing the reservoir within the study area. Three reservoirs were delineated from the well logs with porosity values ranging from 16 to 26%, indicating that the reservoir rocks in the well have enough pores space to accommodate fluids. The fluid replacement modeling reveals how the reservoir properties change with different fluids. The AVO gradient analysis reveals class IV as the predominant class of gas sand within the study field. Well log data using appropriate rock physics relations were analysed using crossplots over the study field, these cross-plots has shown the greatest ability to discriminate the reservoir fluids and lithology based on large separation between the gas sand and background trend. So far, the log based rock physics and AVO modeling have established the presence of an anomaly due to variations in gas saturation in the reservoir, whose amplitude decrease with increasing offset. In this research, the methods (welllog analysis, fluid replacement modeling, AVO modeling, rock physics analysis, and inversion processes) have helped to discriminate the reservoirs and also helped in characterizing the study field.