Investigation of thermal Gas-Oil Gravity Drainage (GOGD) in fractured carbonate reservoirs

In Oman, it is known that the oil content in matrix porosity in fractured carbonate oil reservoirs exceeds more than 90% of the oil originally in place. Minimal recovery factors during the primary stages of production are due to the nature of these carbonate reservoirs; geometry and extent of the fracture network, matrix permeability, wettability tendency, as well as the nature of the fluid system. The occurrence of a strong water drive, in some of the fields, becomes even more detrimental to primary recovery. The Omani oilfield of Qam Alam, with a naturally-fractured Shuaiba carbonate reservoir, is at the center of this investigation. Its reservoir contains 213 million cubic meters of heavy crude (16° API and 220 cp) with an expected ultimate oil recovery of 2% of STOIIP, under primary depletion. Intensive theoretical and experimental studies are carried out in an attempt to quantify potential gains from the Gas-oil Gravity Drainage (GOGD) mechanism that is taking place in the reservoir. Investigations will be undertaken to validate the theory that the combined effects of matrix accessibility to the trapped oil by hot gas, oil viscosity reduction, and the possible oil bank formation are contributing to a higher oil recovery factor during GOGD.