Magnus Water-Alternating-Gas-Pattern Optimization Through Data Integration

Abstract

This article, written by Special Publications Editor Adam Wilson, contains highlights of paper SPE 169167, “Magnus WAG-Pattern Optimization Through Data Integration,” by Demet Erbas, SPE, Matthew Dunning, Timothy M. Nash, David Cox, SPE, John A. Stripe, and Euan Duncan, BP, prepared for the 2014 SPE Improved Oil Recovery Symposium, Tulsa, 12–16 April. The paper has not been peer reviewed. Several studies explored the possibility of improving both areal and vertical sweep efficiency in mature water-alternating-gas (WAG) patterns in the Magnus oil field. Key surveillance data, such as 4D seismic, production-logging-tool (PLT) data, and well performance and openhole saturation logs, have been coupled with simulations to study options for sweep improvement. Optimizing the WAG patterns enables a more efficient use of the available gas, which makes this a more-commercially-viable and –cost-effective tertiary-recovery option. Introduction The Magnus oil field was discovered in 1974 and is on the UK continental shelf of the North Sea. The field started production in 1983 through seven predrilled subsea wells by use of a fixed, steel- jacket platform. The first of the 20 platform well slots was drilled out in 1984, followed by water-injection startup in the same year to provide pressure support and sweep. The plateau production was maintained until 1995 at 150,000 STB/D, and, after 7 years of decline, miscible-gas injection through a WAG scheme started in 2002. In the WAG enhanced-oil-recovery (EOR) scheme, lean hydrocarbon gas is injected. The minimum miscibility pressure is 5,000 psi, which is the current target operating pressure. The average net-gas-use efficiency to date is 3,500 cf/STB. So far, EOR has been implemented in three panels—A3:B3, Central, and South (Fig. 1). This paper focuses on analyzing 10 years of data from running the WAG scheme and on investigating how to improve recovery in mature patterns, specifically in the Central panel.