Data-Acquisition Optimization Maximizes Value of Mature Oil-Rim Reservoirs
Authors: Feder Judy 
Published: December 2019

This article, written by JPT Technology Editor Judy Feder, contains highlights of paper SPE 196208, “Value Creation From the Reservoir, Well, and Facilities Management (RWFM) Planning in Multistacked Mature Oil-Rim Reservoir, Offshore Sarawak, Malaysia,” by Yeek Huey Ho, SPE, Nor Baizurah Ahmad Tajuddin, SPE, Muhammed Mansor Elharith, SPE, Hui Xuan Dan, Kwang Chian Chiew, Kok Liang Tan, SPE, Raj Deo Tewari, SPE, and Rahim Masoudi, SPE, Petronas, prepared for the 2019 SPE Annual Technical Conference and Exhibition, Calgary, 29 September–2 October. The paper has not been peer previewed.

The XamXung field offshore Sarawak, Malaysia, is a 47-year brownfield with thin remaining oil rims that have made field management challenging. The dynamic oil-rim movement has been a key subsurface uncertainty, particularly with the commencing of a redevelopment project. A reservoir, well, and facilities-management (RWFM) plan was implemented to optimize development decisions. This paper is a continuation of paper SPE 174638 and outlines the outcome of the RWFM plan and the results’ effect on development decisions such as infill well placement and gas/water injection-scheme optimization (Fig. 1). Key decisions affected by the RWFM findings are highlighted in the complete paper.

Introduction

The XamXung field was discovered in 1967, with commercial production established in 1972. The field is a simple faulted anticline bounded by two major faults in the north and south. The field consists primarily of clastic deposits characterized by thick sands interbedded with thin shale layers of late Miocene to Pliocene age.

The field consists of multiple stacked gas and oil reservoirs, with key producing intervals being the oil-rim reservoirs XE/XF and XH/XI, and the deeper oil reservoir XL, as well as major nonassociated gas reservoirs XA, XC, XD, XM, and XN. The main discussion of the complete paper focuses on XE/XF and XH/XI reservoir redevelopment.

XE/XF is a saturated oil-rim reservoir with initial oil-rim thicknesses of 95 and 85 ft, respectively. The XE/XF oil rim is overlain by a gas cap with m size (ratio of initial free-gas reservoir volume to initial reservoir oil volume) of 1.1 and 0.4, respectively. XE and XF reservoirs are separated by a fieldwide sealed shale layer of 10–20-ft thickness. Initial reservoir pressure and well log data acquired during the early production his-tory suggested that XE/XF reservoirs originally shared a common gas/oil con-tact (GOC) but different free-water levels. XE/XF reservoirs have an average porosity of 27–32% and average permeability of 500–1500 md. They started production in 1974 and reached peak production in 1977. The reservoir pressure has declined by only 200 psi after 45 years of production, indicating that the reservoir is under a strong aquifer drive. Gas injection into XE reservoir commenced in 1995 following an increasing water-cut trend in most of the producers, with the objective to counteract the aquifer influx and to allow uniform gas-cap gas expansion throughout the reservoir. However, the reservoir historically has produced more free gas compared with the amount of gas reinjected, resulting in the reservoir gas-cap shrinkage.