Integrated Identification of Possible Compartmented Gas Reservoirs: A Case Study

Abstract

This paper presents a method to identify and calculate hydraulically connected gas reserves in compartmented gas reservoirs. The 3-D seismic amplitude analyses and edge detection indicate the possible compartmented sands in the same geological flow units identified in this study. Petrophysical properties of adjacent wells also change abruptly that indicate the deltaic nature of sand deposition in Frio Marine and Frio Non-Marine formations.The "material balance" method to calculate original gas in place (OGIP) and remaining gas reserves utilizes a plot of p/Z values versus cumulative gas production. The assumption is that all wells should drain from the hydraulically connected tank-type gas sand body. The isolation of wells draining from different sand bodies is important to determine the correct OGIP for each sand body. Therefore, measured shut-in reservoir pressures were plotted against time for each geological flow unit. Plotted pressure profiles for each well made it possible to identify wells draining from a common sand body. Wells draining from a single gas pool had a uniform pressure decline. However, the well that produced from a different gas pool had a distinct pressure decline trend. Several wells encountered initial reservoir pressures even though the corresponding formation that was completed in was put on production 20 years ago.This paper provides three examples of integrating 3-D seismic amplitudes, production bubble maps and pressure analyses to differentiate hydraulically connected sand bodies. The material balance calculations provide accurate OGIP and remaining gas reserves. This method identifies significant volumes of remaining gas reserves that lead to reopening of shut in gas wells utilizing minor workovers.