Assessment of Simultaneous Water and Gas Injection SWAG Pilot in a Giant Offshore Carbonate Reservoir

Abstract

Gas injection has been widely used by industry for improving oil recovery. A common variation of gas injection is to have water-alternating-gas (WAG) injection which attempts to overcome gas override in an oil reservoir. In this paper, a simultaneous water and gas injection pilot is discussed. Water and gas are injected simultaneously using two strings in the same well with water injected into an upper zone and immiscible hydrocarbon lean gas injected into a lower zone. This is referred as SWAG in the paper. The subject reservoir is part of a large field located offshore in the Middle East. Water flood started in this under-saturated oil reservoir since 1980’s. Five immiscible gas injection pilots (GIPs) including the SWAG pilot were initiated in late 2001 in this reservoir to assess the benefits of immiscible gas injection in improving oil recovery. This paper describes the performance analysis from field surveillance data of the SWAG pilot which is also aided by a sector simulation model. Performance comparisons of the SWAG pilot versus the earlier completed gas injection pilots is also demonstrated. The history matched model successfully predicts gas arrival timing in the pattern producer. The model results are used to infer the swelling effect of the injected gas as well as to estimate gas sweep efficiency. Both RST log and simulation results show that simultaneous water injection introduced in the upper zone is not able to mitigate gas override. The model analysis, coupled with results from special core analysis, suggests the immiscible gas is not as effective as water injection in maximizing oil recovery from this reservoir. The volumetric sweep efficiency of the injected immiscible gas is estimated to be less than 10% pore volume (PV) and the swelling benefit is less than 1% OOIP at the time of gas breakthrough.

Experimental Investigation of the Impact of CO2 Injection Strategies on Rock Wettability Alteration for CCS Applications

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An Integrated Oil Production Enhancement Technology Based on Waterflooding Energy Recovery

“…The corresponding mathematical formulation with defining relations is presented in the form of Eqs. ( 4)- (15). However, the numerical implementation of the solution of the stationary problem, carried out by the solver of the ANSYS CFX package, is carried out using psuedo-time as a iteration method to converge to the final steady solution.…”

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