ABU DHABI - The Offshore Fields - Abu Dhabi Marine Operating Co.
Umm Shaif, the first offshore field found by Abu Dhabi Marine Areas (ADMA) in March 1958, is one of the biggest in the Middle East - 20x15 km. It went on stream in 1962 as the first oil producing and exporting field in Abu Dhabi. But it is a complex field with fractured reservoirs. Its pay zones are: Lower Cretaceous (Thamama I & II), Upper Jurassic (Arab A-C & D-Darb carbonates) and Middle Jurassic (Upper Araej, Uwainat & Lower Araej limestones). It needs advanced technology, mainly for pressure support and infill drilling. The crude's water cut is also a problem. The field has about 150 producing wells and 62 injection wells. About 40 of its wells are horizontal. Oils in place at Umm Shaif exceed 20 bn barrels.
Like ADCO, ADMA-OPCO applies advanced techniques in 3D and horizontal drilling. Horizontal drilling, which costs much more than vertical drilling but yields four times as much oil, has involved 44 wells since the company introduced this in 1989.
Umm Shaif's sustainable capacity has been expanded from less than 200,000 b/d in the 1980s to 250,000 b/d in 1991. But in recent years that was not sustainable beyond 220,000 b/d. The company spent considerably in raising its sustainable capacity to 265,000 b/d by end-1995. However, this has dropped to 250,000 b/d. ADMA-OPCO now is embarked on a $1.2 bn project to maintain this capacity through injection of 600 MCF/d of gas into the field's Arab D and C oil reservoirs. The gas will come from the Khuff reservoir deep beneath Umm Shaif. In July 2002 Worley of Australia won the FEED contract for this project, with its work to be completed by mid-2003. The EOR system will involve gas compression, processing and accommodation platforms as well as the drilling of new wells. The project should be completed in 2006.
A Thamama gas injection pilot system was commissioned in October 1994 to optimise the long-term development of the Thamama zone, from which sustainable oil production was to average 60,000 b/d. A special technique was used in the last stage of the gas injection pilot, whereby an environment-friendly radioactive tracer material, known as tritiated methane, was injected with the gas at the start-up.
The Permian Khuff reservoir of non-associated gas is a huge limestone structure discovered in 1979. It lies beneath the oil-bearing zones and a Thamama reservoir. But the gas has a high content of sulphur and other impurities. The first phase of its development, in a $350m ADNOC plan, was completed in September 1994. The gas output, 1,200 MCF/d, is piped to Das Island to feed a major LNG complex whose third train went on stream in late 1994. Bechtel was the main contractor for the gas development programme.
A further development of the Khuff reservoir at both Umm Shaif and the nearby offshore field of Abu Bukhoosh, a project delayed since 1998, was contracted in September 2000 to ABB Lummus Global in partnership with ADNOC affiliate NPCC for $260m. To be completed in mid-2004, this will allow for production to rise from 300 MCF/d now to 640 MCF/d in the initial phase. The project involves five new wells at Abu Bukhoosh, a platform for each of the two fields to process dry sour gas, marine pipelines to gather the gas and link the platforms, a pipeline from Abu Bukhoosh to Umm Shaif, a modification and upgrading of 13 existing gas platforms, a pipeline to Das island, and a two-train gas processing system. Foster Weeler won the $10m PMC contract in September 2000. Kvaerner Engineering of Norway did the basic designs under a contract awarded in May 1997. Later on this system should produce almost 1,000 MCF/d.
Associated gas has been produced at Umm Shaif since 1988 from two 150 MCF/d wellhead platforms and two producer/injector platforms all connected to the Umm Shaif Supercomplex. Gas is also produced from the field's Uwainat reservoir, and from four gas cap wells repressurised in 1990 by installation of four wellhead towers for drilling deep into the Khuff formation.
Lower Zakum is ADMA-OPCO's largest oilfield found in July 1963 and developed in 1966. It produces from Thamama IV and V reservoirs. Its capacity has been raised from 270,000 b/d in 1991 to 300,000 b/d. But now its sustainable capacity is limited to 280,000 b/d.
To maintain pressure, 200 MCF/d of Khuff gas will be extracted for re-injection into Lower Zakum's Thamama reservoir. The project is to be completed in 2004. Another project worth $50m is to enable Lower Zakum and Umm Shaif together to raise oil production by 100,000 b/d. This will involve debottlenecking of crude processing facilities on Das island. Tebodin of the Netherlands was to complete the project's feasibility study by end-2002.
The Zakum Central Supercomplex, mothballed in 1986 as a result of output restrictions, was recommissioned in early 1994. In October 1990 the company recommissioned ADNOC's gas gathering plant (GG-II) on the Zakum West Supercomplex, mothballed in 1986, to allow the field's associated gas to be recovered rather than flared. The plant can collect and compress 250 MCF/d from both the Lower and Upper Zakum fields and pump it to the Das Island LNG complex through the Umm Shaif Supercomplex.
The Zakum system (Lower & Upper) is rated as the third biggest oil zone in the Middle East next to Ghawar (Saudi Arabia) and Greater Burgan (Kuwait), although geologists say Iraq's Great Rumaila Triangle could potentially prove to be bigger than Ghawar. Lower Zakum is 30 km long and 25 km wide, lying to the south-east of Umm Shaif. Oil in place at Lower Zakum has been estimated at 16 bn barrels, Oil in place at Upper Zakum, which belongs to ZADCO, has been estimated at 50 bn barrels.
ADMA-OPCO also has the capacity to produce 70,000 b/d from smaller fields which are satellites to the Umm Shaif and Lower Zakum systems. Nasr, discovered by ADMA in 1971, is one of the ADMA-OPCO fields awaiting development. It lies 20 km north-east of Umm Al Shaif and has Arab reservoirs with the oil of 30-35 deg. API. Beneath them lie Permian Khuff gas carbonates proven in 1982. The field's development, initially planned to be on stream in 1993 with a first-phase capacity of 50,000 b/d, was deferred in 1992 and in the subsequent years because of OPEC quota limitations and the priority to Upper Zakum granted by ADNOC.
ADMA-OPCO is spending $300m to replace about 260 km of ageing marine oil and water supply pipelines. In late 2002 it was evaluating bids made by Thales of the UK and Fugro for a contract to do an engineering survey. Bids for a second contract, to do the FEED study, were made by Worley and Tebodin. After the restructuring of the hydrocarbon sector in the late 1980s, ADMA-OPCO managed to reduce costs across the board. As a result, offshore production costs were cut from $4.50 to $1.50/b.