|Geography||Regional Geological Setting||Structure||Stratigraphy|
|Oil and Gas||Peat and Coal||Other Minerals||References|
The Champion field is a complex oil and gas field, situated 40 kilometres north-northwest of Bandar Seri Begawan, in water depths of 10 to 45 metres (Figures 5.51 and 5.52). The shallows in the area are covered with coral reef patches. The field was discovered in 1970 by Champion-1, drilled in its northern part.
The first platform was completed in 1972, to produce from shallow, oil-bearing intervals. A major appraisal drilling campaign followed in 1972 - 1973. At the same time, a field development plan was formulated, with 6 additional in-line platforms. In 1974, a blow-out at Champion-41 caused a delay of the appraisal / development operations. During 1975 - 1976, eight isolated appraisal wells were drilled to compensate for this delay. These wells not only aided in further delineating the main field, but also discovered hydrocarbons beyond the reach of the primary development platforms, namely the separate Champion West structure, to the northwest of the main field, and the very shallow accumulations to the southeast (Champion Southeast). Another blow-out occurred in the northern part of the Champion Main field in well CP-141, in early 1979.
During the early development stages of the field, the extreme complexity, of structure as well as reservoir architecture, was recognised. In 1978, a grid concept for platform location was introduced for the shallow part of the main field, which contains the bulk of the known oil reserves. This decision facilitated the long term engineering planning, and ensured that most of the future draining / injection points are within easy reach of a platform location.
Construction of the centralised field facilities at Champion-7 began in 1980 and was completed in 1983.
To date (1/1/96) 282 wells have been drilled, of which 118 are producing. Average production rates over 1995 were 10,000 m3/d of liquids and 1.2 million m3/d of gas (including production from Champion Southeast). Some 7,000 m3/d of water is injected in order to support the pressure in a number of reservoirs.
The Champion field is highly compartmentalised, characterised by large areas of fault / dip closures, from the seabed downwards. Combined with the multilayered nature of the stratigraphic succession, striking sub-parallel to most of the faults, the numerous hydrocarbon traps are relatively small and generally stacked. Block widths range from 100- 450 metres.
To the north-west of the main anticline, the deep, smaller, early rollover structure is termed Champion West. To the south-east, hydrocarbons are found trapped in fault slivers parallel to the main growth fault and this set of accumulations is termed Champion Southeast. The Peragam gas field is directly below the Champion field
Because of its great thickness, the prospective sequence is divided vertically into 5 levels:
|1. Very Shallow||from seabed to 600 metres||H1.0 and shallower|
600 to 1,500 metres
|H1.0 - P1.0 horizons|
1,500 to 2,150 metres
|P1.0 - S1.0 horizons|
2,150 metres to the top of the hard overpressures
|S1.0 - V1.0 horizons|
hard overpressured section (Peragam)
|V1.0 - V4.0|
Reservoirs are heterogeneous, consisting of mainly fine grained shallow marine to coastal/delta plain sands (i.e., beach/spit, channel, crevasse splay, barrier, distributary and mouth bar deposits). Porosities average between 25 and 30% at shallow levels and 10 to 14% at 3,000 m. Two-thirds of the reservoirs have permeabilities between 100-5,000 mDarcy (0.1-5 m2) The core photograph of Figure 5.53 illustrates reservoir sands of tidal channel facies.
Hydrocarbon migration was almost certainly from the west, filling traps on the westerly flank of the structure with the prospective sequence extending almost from seabed to below 3,000 metres. Salient features of the hydrocarbon distribution are:
The bulk of the Champion oil reserves are contained in the very shallow and shallow intervals of the Main field, At present, there are more than 900 identified oil and gas reservoirs. Most of these reservoirs are small, with 88% having a STOllP of less than 1.0 million m3.
The expected ultimate recovery for the Champion field is 128 million m3 of oil (27 % recovery), 2.18 million m3 of condensate (34% recovery) and 27.7 109 m3 of gas (55% recovery).
Original reservoir pressures are at or near hydrostatic in the very shallow and shallow intervals. Significant over-pressures are first encountered in the intermediate intervals and gradually increase to more than 22,750 kPa (3,300 psi) above hydrostatic in the deep intervals, at about 2,900 metres subsea.
On production, reservoir pressures are observed to drop rapidly. The numerous fault barriers, the absence of large gas caps, and low initial gas-oil ratios, result in generally low natural drive energy. Solution gas is an important drive mechanism. Thus, primary recovery efficiencies are to some extent related to gas/oil ratios, and, less importantly, abandonment pressure policies.
The crestal reservoirs are, in general, more shielded from aquifer drive than those on the flanks and the isolated reservoirs are, in principle, targets for supplementary recovery.
The highly permeable reservoirs in the field are considered favourable for water injection. The relatively low oil viscosity (3 cp) for this heavy (22° API or 920 kg/m3) oil together with the small relative permeability for water (around 0.2) results in a not too unfavourable mobility ratio of about 1.5. However, the significant vertical and lateral permeability heterogeneities may lead to some reduction in sweep efficiency. Another complication is the limited confinement of target reservoirs, caused by the limited sealing capacity of the surrounding faults.
The gas in the Champion field has a CO2 content that varies from less than 1 % to more than 80%. CO2 is highest in the very shallow and shallow reservoirs and decreases with depth. CO2 in Champion is therefore probably related to the biodegradation of hydrocarbons .
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