The Arun Gas Field in Indonesia: Resource Management of a Mature Field

Abstract

Abstract The Arun gas field is a giant hydrocarbon resource in Indonesia and has been supporting Liquified Natural Gas (LNG) sales to the Asian market since 1978. The ultimate gas recovery is expected to be about 94% of initial gas in place, and the ultimate condensate recovery is expected to be a very high 87% of initial condensate in place. As the field has matured, reservoir pressure has declined and well productivities have declined. Mechanical wellbore failures have increased because of increased downhole stresses. The lower reservoir pressure has also increased the water vapor content in the gas, and producing wells have started to loadup as flow rates have decreased. The application of new technologies has generated numerous opportunities to extend field life. Recent work has focused at maintaining productivity despite declining reservoir pressures. This paper presents a summary of Arun history and examples of recent resource management practices, including compression upgrades to reduce wellhead pressures, under-balanced drilling into a pressure-depleted reservoir and problem well restarts. Introduction The Arun gas condensate field in North Sumatra, Indonesia has been and continues to be a prolific producer of gas for the Asian LNG market. ExxonMobil Oil Indonesia Inc. operates the field as a Production Sharing Contractor to the Indonesian Oil and Gas Upstream Regulatory Body, BADAN PELAKSANA KEGIATAN USAHA HULU MINYAK DAN GAS BUMI (hereinafter called "BPMIGAS"). The discovery of this massive resource in October 1971 by the drilling and testing of the Arun-1 discovery well spawned the birth of the Indonesian LNG industry. Since then, Arun has been a valuable resource that has been carefully developed and nurtured to maximize its potential. Field performance has been excellent and the application of the latest petroleum technologies has extended field life. Arun remains a great success story with excellent recovery and high well productivity. Arun has now matured and this paper presents the challenges associated with managing this mature asset to meet market commitments. The Arun Field is located in the Aceh Province of North Sumatra, straddling the coastal plains between the Straits of Malacca on the north and the Barisan Mountains on the south (Figure 1).1 After the Arun-1 discovery well encountered more than 1000 ft of productive limestone in the thickest part of the reefal structure, 13 additional delineation wells were drilled to map the outer limits of the reservoir. Arun was developed from 4 clusters, and a total of 118 wells have been drilled, most of them deviated holes (Figure 2). The initial reservoir pressure was 7115 psi and the temperature 351 °F at a datum depth of 10,050 ft (Table 1). The field is approximately 18.5 km long and 5 km wide and covers approximately 23,240 acres. The average thickness of the Arun limestone is 495 ft, and the formation has an average porosity of 16.1%, with a low connate water saturation of 10.7%.