Exxon Corp. last week disclosed an agreement under which one of its units will move toward a multi-billion dollar development program in giant Natural gas field off Indonesia and export liquefied natural gas.
After many years of planning, the accord among Exxon unit Esso Exploration & Production Natuna Inc., the Indonesian government, and Indonesia's Pertamina clears the way for a study of Natuna LNG demand among potential Asian customers. The most likely markets include Japan, South Korea, and Taiwan.
Detailed engineering, infrastructure development, and platform, pipeline, and LNG plant construction is to follow, with the project advancing in phases tied to market demand.
If prospective customers respond as expected, Exxon said, Natuna could become the world's largest offshore gas development. It could involve as many as 200 wells and 18 fixed steel jacketed platforms producing and processing about 2 bcfd of gas for more than 30 years. LNG production could amount to more than 14 million tons/year.
The Natuna project could cost as much as $40 billion because of the development's massive scale, the field's remote site and water depth, and the need to extract and dispose of large volumes of carbon dioxide ' Natuna reserves are estimated at 210 tcf, including about 60 tcf of methane and heavier hydrocarbons. The field lies in 470 ft of water in the southern South China Sea, about 800 miles north of Jakarta.
NATUNA DESCRIBED
Discovered in 1973 in the Natuna Sea, about 140 miles east-northeast of Natuna Island, Natuna field is a 120 sq mile, 15 mile by 10 mile, dome shaped, middle and late Miocene carbonate reservoir below 8,530 ft subsea.
Natuna's productive Terumbu formation is nearly 5,100 ft thick at the reservoir's center.
The field is in Esso Natuna's D-Alpha production sharing block awarded by Pertamina in 1980.
Esso Natuna has drilled five exploratory wells in the field and conducted 15 production tests, analyses of which show the reservoir is highly productive. Tests of well samples show Natuna's gas composition varies only slightly across the reservoir, averaging about 71% CO2, 28% methane and heavier hydrocarbons, and 0.5% of both hydrogen sulfide (H2S) and nitrogen.
Recoverable hydrocarbons are estimated at 45 tcf, about three times the recoverable reserves of Indonesia's Arun field, also a carbonate reservoir.
About 1,000 km of seismic data has been collected over Natuna field.
Natuna's development concept is based on three integrated activities: offshore production and gas treating, onshore gas treating and liquefaction, and offshore disposal of waste gas into subsurface formations near the field.
Processing offshore will separate the well stream into sales gas and waste gas, mostly methane and CO2, respectively. Sales gas is to move through a 140 mile pipeline to Natuna Island for further treating and liquefaction. Waste gas separated offshore and onshore will be shipped by pipeline to offshore platforms for injection into carbonate aquifers at sites 35-75 km northwest of the field.
While gas production and LNG capacities are to be determined by market demand, preliminary plans call for Natuna's initial facilities to supply about 800 MMcfd of gas to the onshore LNG plant. At that rate, LNG production would amount to about 4.8 million tons/year. Capacity expansions based on market growth would occur in 400 MMcfd stages.
Eventually, Natuna gas and LNG could rise to 2.4 bcfd and 14 million tons/year, respectively.
MAJOR COMPONENTS
At full development, the Natuna project would include six offshore processing platforms, six drilling platforms with 36 well slots each, four injection platforms, two quarters platforms, and more than 565 miles of in field and transportation pipelines.
Decks of processing platforms designed to handle as much as 1.8 bcfd of gas could be among the largest built, with dimensions of more than 210 ft by 375 ft and weighing as much as 43,000 tons. Designed for one-piece installation to minimize offshore construction, each deck is to be completed and tested onshore before installation.
Offshore processing units will be equipped for inlet cooling and separation of produced gas, bulk extraction Of CO2, and compression of treated and excess gas streams. Raw gas is to enter treating equipment at 196 F. and 1,265 psi, where a two-step process will condense and separate most CO2 and H2S from the methane.
Esso will warm and compress sales gas for the 140 mile trip by pipeline to the Natuna liquefaction plant.
Condensed excess gas on the platforms will provide cooling for the CO2 removal process before being compressed for pipeline transport and injection into aquifers. The CO2 removal process to be used at Natuna is based on industry experience in low temperature gas separation. Exxon has experience in more than 40 uses of similar low temperature technology.
NATUNA ISLAND PLANT
The Natuna plant is to be built on the northern tip of Natuna Island for additional removal of CO2 and H2S before the methane is liquefied.
The LNG plant site was chosen for proximity to the pipeline landfall, relatively flat terrain, firm soils, access to waterways, and relatively few inhabitants. In addition to the plant and harbor, facilities will be constructed for warehousing and logistical support, an airport, and a self-contained community for offshore and onshore workers and their families.
Development of Natuna LNG plant will be similar to Indonesian LNG plants at Arun and Bontang. The plant's design will draw from Pertamina's knowledge and operating experience in gas liquefaction.
Onshore gas treating is to use a proprietary Exxon process to remove remaining excess gas. Treated gas is to be dehydrated, then chilled to - 260 F. for storage at atmospheric pressure. Porosity and other characteristics of the two carbonate aquifers where Esso plans to dispose of Natuna waste gas have been confirmed by data from 14 wells and extensive studies.
Also part of the Terumbu formation, the aquifers have characteristics better than Natuna's gas pay. Additional wells are planned during the project's engineering phase to confirm aquifer characteristics at the proposed sites of the injection platforms.
With a combined pore volume more than 40 times that of Natuna's gas reservoir, the aquifers could accept more than 100 times the volume of excess gas that could be injected during the life of the project.
Copyright 1994 Oil & Gas Journal. All Rights Reserved.
Issue date: 11/21/94
