4D Seismic for Reservoir Management in Carbonates: Does It Work?

Abstract

This article, written by Senior Technology Editor Dennis Denney, contains highlights of paper SPE 144228, ’Application of 4D Seismic for Reservoir Management in Carbonates: Does It Work?,’ by Mohamed Saleh Efnik, SPE, and Samsudin Haj Taib, University of Malaya, prepared for the 2011 SPE Enhanced Oil Recovery Conference, Kuala Lumpur, 19-21 July. The paper has not been peer reviewed. In the past 10 years, time-lapse (4D) seismic has evolved from an academic research topic to a typical method of monitoring reservoir performance. The method is used to provide evidence of saturation changes within the reservoir at field scale. 4D seismic provides data that describe the dynamic behavior of reservoir fluid between wells that otherwise would be limited to small-scale monitoring at borehole scale. Thus, 4D seismic provides sophisticated techniques of reservoir monitoring and management that rely on the integration of geological models, static and dynamic properties of the reservoir rock, and detailed field-production and -pressure data. Introduction The feasibility of 4D seismic has evolved with studies that showed that certain rock properties, such as acoustics and pressure, are affected by changes caused by hydrocarbon production over the life of the field. The use of 4D-seismic data in conjunction with reservoir-simulation models and production data enables creation of an internally consistent subsurface model. It has been shown that acoustic impedance (AI) and Poisson’s ratio are related closely to porosity and water-saturation changes in Arne chalks. An increase in porosity causes a decrease in AI; increasing water saturation (at constant porosity) results in a strong increase in Poisson’s ratio. An extensive seismic program was carried out over a CO2-injection area during a 5-year span to monitor the CO2 storage in a saline aquifer in the North Sea Utsira sand. 4D seismic and other geo-physical techniques were used to obtain information that could help determine reservoir-quality characteristics and predict fluid contacts. Forward modeling of 4D seismic has been shown to be a useful reservoir-management tool. Here, the simulation model was combined with the streamline method for modeling flow, and the ray-Born method for synthetic seismograms was used to compensate for the numerically expensive model because of the large volumes in the subsurface.