This paper describes the development, monitoring programs and evaluation methodology of a gas injection pilot project carried out in a fractured carbonate reservoir with a strong water drive. Immiscible gas injection was recognized as a potentially viable economic recovery process, and a gas injection pilot was initiated in the field. The reservoir contained an undersaturated, intermediate gravity oil with a recovery of less than 6 percent after 40 years of primary depletion. The major areas of performance that were monitored thoroughly during the gas injection pilot project were:

  1. Production (oil, gas and water)

  2. Reservoir pressure

  3. H2S concentration of the produced gas

  4. Reservoir gas saturation and gas-cap advance

A numerical reservoir simulator was used to history match reservoir performance under gas injection, and to investigate operative reservoir mechanisms which had resulted in improved oil recovery. The results were also used to confirm the validity of assumptions made in the design and performance prediction of the pilot project. The importance of collecting accurate data during the monitoring phase of the pilot was recognized so that meaningful field expansion guidelines and economic evaluation parameters could be established with a reasonable level of confidence. Immiscible gas injection in this watered-out carbonate reservoir resulted insubstantial increases in oil production rates and is expected to double the recoverable reserves from the field.

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