Abstract
Abstract
The Mereenie Oil and Gas Field, situated in the Amadeus Basin in Central Australia, is the largest onshore oil field in Australia, containing some 367 million barrels of original oil in-place and 900 billion cubic feet of original gas in-place. Oil is contained in an elongated, anticlinal trap in multilayered reservoirs as rims associated with large gas-caps. Expansion of solution and gas-cap gas is the primary oil recovery mechanism. However, most of the oil is contained in narrow, thin rims in tight reservoirs which are considered marginally economic for development.
The Pacoota Sandstone is the major oil bearing unit The rims have been partially developed by drilling wells at a one kilometre spacing. The Pacoota Sandstone is Cambro-Ordovician in age with six to nine percent porosity and 5 to 50 md permeability. Dedicated production wells have been drilled for the upper and lower reservoirs at an optimum distance from the gas-oil contact to maximise primary recovery. Based on production performance, the average, primary oil recovery factor in the developed rim area is estimated at 28% of the original oil in-place.
A previous reservoir simulation study had indicated that two to three percent incremental oil recovery could be achieved by reinjecting the produced gas into the gas-cap. Recent modelling has shown a 10% to 14% incremental oil recovery by reinjecting gas directly into the oil rims. This innovative rim injection technique provides direct displacement of bypassed and unaccessed oil as well as pressure maintenance. The optimum spacing (between producers) for this gas injection technique is estimated at 1.5 km compared to 1 km for the primary development Simulation modelling shows that, unlike primary oil recovery, this secondary recovery is less dependent on well distance from the GOC.
A pilot test is currently underway. Based on the encouraging results from the pilot test and simulation results, a field development strategy is proposed.
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