Revitalizing a Mature Sand-Prone Field by Installing Enhanced Gravel-Pack Completions - A Case Study

Abstract

The Dulang oilfield is located some 130 km offshore Terengganu in Peninsular Malaysia and is structurally complex. Production from the field began in March1991, and oil production averaged 26,000 STB/D with peak production reaching approximately 50,000 STB/D. As with the other field developments in the MalayBasin, sand production was not anticipated under normal drawdown or producing conditions, and thus, all the wells in Dulang field were completed without any sand-control measures. In the later stages of the field's life, however, a significant amount ofsand production was observed. This condition gradually increased over time,resulting in reduced hydrocarbon production, additional costs for routinewellbore sand clean-outs, and platform shutdowns for surface vessel sandclean-up. In 1991, eight years after initial development, a wellbore opportunity study was initiated to revitalize a section of Dulang field. The objectives of the study were toidentify remaining reserves, andidentify new completion options to maximize recovery. The study identified three major activities that would improve oil production:Develop by-passed reserves behind casingReactivate idle wells that had been closed in, some as a result of sand production.Provide additional drainage points for undeveloped reserves. From the proposed wellbore opportunities study, ten wells were identified for a workover campaign, and six wells were identified for infill drilling or sidetracks. Sand production mitigation using a gravel-pack technique was identified as a requirement in the completion plan for the majority of the targeted reservoirs. However, the increase in mechanical skin that would result from a sand control installation was also recognized. Hence, it was determined that the best approach for production optimization in these wells would be a combination of a sand control and a stimulation technique. Several technologies, which included frac-andpack, extension pack with conductivity enhancer, and highrate water-pack (HRWP) gravel packing, were suggested. The use of a special completion tool that would enable greater flexibility on short string selective production in multi-zone gravel-packed wells was also identified. After careful review of the options, a combination of sand control and stimulation technique (frac pack, extension pack and high-rate water pack) was selected, and the combined strategies have successfully increased the productivity and prevented sand production in the Dulang wells. Introduction The Dulang oilfield is located about 130 km offshore Kuala Terengganu, Malaysia. Fig. 1 shows the Dulang Field location. The main reservoir is comprised of Dulang E sands, which are of late Miocene age and consist ofalternating sequences of sands deposited in a tidal flat environment. The reservoir faults are complex and are in a westward plunging anticline. They compartmentalize the Dulang field into 16 subblocks. Stratigraphically, 20reservoir units have been identified in Dulang field. Drive mechanism is edge water, gas cap expansion and solution gas drive. Fig. 2 is a 3-D visualization of the Dulang Field, and Fig. 3 shows the field blocks. When production from the field began, the average production was 26,000STB/D, and during peak production from the field, it was producing nearly double that amount.