Investigation of Fluid Properties and their Effect on Seismic Response: A Case Study of Fenchuganj Gas Field, Surma Basin, Bangladesh

Abstract

The Fenchuganj Gas Field is one of the water-drive gas fields in the Surma Basin, Bangladesh. Due to gas production water saturation is increasing day by day. However, fluid properties of the reservoir at the present state in the gas depleted condition should be addressed with proper prediction. In this paper, we represent some modeling results which evidences that the pore fluids have a significant effect on the acoustic impedance and the Poisson’s ratio of the reservoir rock which is directly correlated with seismic amplitudes at constant pressure with Batzle-Wang model and Gassman-Boit models. Moreover, these models with varying pressure and water saturation conditions show the reasonable predicted fluid modulus against pressure. The reservoir modeling from irreducible water saturation conditions (90% gas saturation) to residual gas conditions (10% gas saturation) provides a pathway to calculate values at reservoir conditions from logging conditions. Fluid bulk density increases when water saturation increases with constant pressure and stay around constant when water saturation increases with pressure fall. But overall it increases through the production path that we assumed. Amplitude versus Offset (AVO) analysis also consistent with other studies models which show that seismic reflection of p-wave changes due to change of pressure and water saturation of the reservoir rock layers. The AVO response decreases with increases of water saturation of the gas zones. The evaluation of fluid properties enables seismic data to be used more powerfully. This study is also showing that both gas zones of the Fenchuganj are under gas sand category 3. We suggest that the modeling of fluid property in determining the usefulness of time lapse seismic, predicting AVO and amplitude response, and making production and reservoir engineering decisions and forecasting in the study field.