Sealing properties of faults and their influence on water-alternating-gas injection efficiency in the Snorre field, northern North Sea

Within the Snorre field, faults need careful consideration in reservoir modeling and simulation work. In this field, a static seal capacity for oil as much as about 5 bar (3.44 104 Pa) is observed across important faults. In a dynamic setting, the seal capacities for oil become about one order of magnitude higher than for the static situation. Water-alternating-gas (WAG) injection has been chosen as the main recovery mechanism. Because capillary seal capacities as much as 15 bar (1.03 105 Pa) are found for gas to flow across faults in the reservoir, the distribution of gas and efficiency of WAG to a large degree depend on the fault patterns. For the purpose of evaluating the flow paths of the injected fluids, tracer data and time-lapse seismic data were used.Tracer and time-lapse data confirm that the WAG process in Snorre depends on the geometry and properties of medium- to small-scale faults. As a consequence of intrareservoir faults, injected gas is trapped in fault-bounded segments, whereas the water is allowed to spread out laterally. The observations suggest that flow of oil and gas across faults in the Snorre field must be treated individually in flow simulators.

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