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The Natih Field in North Oman is a complex domal fractured limestone structure with a STOIIP of some 500 million m3. Initially subjected to a depletion drive, rapidly dropping pressures resulted in a switch to water injection and then to gas injection to promote gas oil gravity drainage.

In determining which production mechanism to promote an integrated approach has been taken. Held tests used tracers to investigate the problems associated with water injection; fracture orientation and intensity has been determined using core data including palaeomagnedcs, FMS logs and out-crop studies; initial oil saturations have been determined within a given range using resistivity and pulsed neutron logs as well as capillary pressure curves to overcome problems of mixed wettability; to monitor gas saturation development in the matrix recourse has been made to the Borehole Gravity Meter; special core analysis on restored state cores has been utilized to characterize wettability and relative permeability as input to both monitoring the water influx and to reservoir simulation.

Development of a simulator to incorporate all the necessary physics of gravity drainage, including block to block interaction, has been undertaken at the research laboratories in the Netherlands and, using the understanding of the field built up through the above studies, a successful history match was achieved. A field development plan is now emerging requiring a ring of wells to be drilled to a downdip target completion interval to further promote gas oil gravity drainage. The plan will attempt to create a balanced offtake from around the

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