Revitalizing a Mature Sand-Prone Field by Installing Enhanced Gravel-Pack Completions - a Case Study
Authors: Noor Mohamed Zaini B. Md. , Selamat Kasim B. , Kasim Abdullah B. , Salahudin Sharifudin 
Published: October 2008

The Dulang oilfield is located some 130 km offshore Terengganu in Peninsular Malaysia and is structurally complex. Production from the field began in March 1991, and oil recovery averaged 26,000 STB/D with peak production reaching approximately 50,000 STB/D. As with the other field developments in the Malay Basin, 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 of sand production was observed. This condition gradually increased over time, resulting in reduced hydrocarbon production, additional costs for routine wellbore sand clean-outs, and platform shutdowns for surface vessel sand clean-up.

A wellbore opportunity study was initiated in 1999 to revitalize the field. The objectives of the study were to 1) identify remaining reserves, and 2) identify 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 shut-in 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 techniques (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 of alternating 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, 20 reservoir units have been identified in 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 26,000 STB/D, and during peak production from the field, it was producing nearly double that amount.