Following discovery of the Arun Gas Field in 1971 and subsequent appraisal drilling to obtain essential reservoir data, a development project based on delivery of sufficient gas to supply a six train LNG plant, with a coincident cycling operation, was planned. High wellstream temperatures, pressures, gas throughput rates and corrosive CO2 content, placed producing, safety, security and environmental constraints on the design of surface wellstream gathering and processing facilities and led to the selection of the cluster development concept.
Producing capacity, dedicated to LNG plant demand, has resulted in a two phase Producing capacity, dedicated to LNG plant demand, has resulted in a two phase field development program. Program I, consisted of two producing clusters each containing two producing trains and five high rate gas wells, a central control and power site (point "A"), a gas cycling system consisting of three injection compressors, eight injection wells and injection lines, and a 16-inch condensate transmission pipeline to the LNG plant. Production from the two clusters has supplied the three train (first phase) LNG plant, completed in late 1978, and the Arun Field cycling project. Program II commencing in 1981, will provide for an additional two producing clusters, each consisting of two producing trains and six producing wells, as dictated by the LNG plant expansion program.
This paper will provide an overview of the Arun Field production mode design concepts, detail the problems encountered in the surface producing facilities following start-up, i.e. corrosion, separator carryover and recycling compressor limitations, and define how these problems have been, or are being, resolved. This will include a projection of anticipated equipment modifications and additions which will be required to accommodate to changing reservoir conditions during the producing life of the Arun Gas Field.
The Arun Field, discovered by Mobil Oil Indonesia Inc. in late 1971, is located in the Bee Block Contract Area in North Aceh Province at the northeast corner of the island of Sumatra, Republic of Indonesia. The discovery well Arun A-1, spudded in August 1971, encountered a limestone reef containing gas and condensate. The produced gas contained 15 percent carbon dioxide. 0.32 percent nitrogen, a trace of hydrogen sulfide and condensate; with a liquid to percent nitrogen, a trace of hydrogen sulfide and condensate; with a liquid to wellhead gas ratio of 55 BPMMCF.
The follow-up appraisal well, Arun A-2 drilled during the spring of 1972 confirmed the results obtained from the discovery well. The field boundaries were defined by drilling eleven additional wells. The north-south trending reef is approximately 18.5 kilometers long and 5.3 kilometers wide.
Development planning for the Arun Field began in mid-1972. The scope of work defining producing facilities required and a bid package were approved in mid-1974. Based on these a prime contractor was selected for final design, engineering, procurement, project management and construction of the initial phase of development. Markets were developed for sale of the LNG from Arun phase of development. Markets were developed for sale of the LNG from Arun Field with initial delivery scheduled for late-1978. An Indonesian company, P.T. Arun Natural Gas Liquification Company, was formed to operate the LNG P.T. Arun Natural Gas Liquification Company, was formed to operate the LNG Plant; ownership being 55% by Pertamina, 30% by Mobil Oil Indonesia, Inc. and Plant; ownership being 55% by Pertamina, 30% by Mobil Oil Indonesia, Inc. and 15% by Japan Indonesia LNG Company.
LNG requires dedicated processing, transportation and receiving facilities and its supply is usually contracted for a specific delivery schedule. A very high degree of reliability must therefore be designed into the entire system.
The initial P.T. Arun Plant development provided three trains, each designed to process 300 MMSCFD of gas feed stock with provision for later expansion of three additional trains of similar capacity. Each Arun Field production separation unit was designed with sufficient capacity to supply one LNG plant process train. The initial scope for the Arun Field Development program was process train. The initial scope for the Arun Field Development program was to provide a wellstream producing capacity of one and one-half billion cubic feet per day. Of this total, 900 MMCFD would supply the requirements of the three-train P.T. Arun LNG plant. The 600 MMCFD back-up wellstream capacity made feasible the installation of recycling facilities for additional condensate recovery from the Arun reservoir.
Alternate means of development the surface facilities of the Arun Field were studied and the 'cluster' concept was selected. Major factors in the selection were:
The need to minimize the use of cultivated land.
Centralization of process facilities and gas compressor plant would be realized.
The flowline length from wellhead to a central gathering point for the high pressure, corrosive produced wellstream was greatly reduce.
To meet the initial sales commitment, two producing clusters, a central location for field support facilities and power generation, three gas compressors, eight injection wells with connecting pipelines, and gas and condensate transfer lines from the clusters to the central location were constructed.
The cluster design provides for sixteen producing wells, wellstream cooling and separation and control and pipeline facilities in a rectangular plot 680 × 960 meters which is about 65 hectares. The layout includes space for gas compressor and a produced water disposal plant, as well as for additional process equipment necessary for producing the field in the latter phase of process equipment necessary for producing the field in the latter phase of operations. The wells, located in two rows of eight locations each on 80 meter spacing, with 160 meter spacing between rows, occupy about one-half of the cluster area.
The gas process and compression equipment requires about one-sixth of the cluster area.