Journal of Canadian Petroleum Technology, Vol.49, No.3, 22-27, 2010
Experimental Investigations on the Flow Dynamics and Abandonment Pressure for CO2 Sequestration and Oil Recovery in Artificially Fractured Cores
CO2 flooding in naturally fractured reservoirs is becoming increasingly more popular. The Midale Field is a good example of this phenomenon and has gained a great deal of interest, not only from enhanced oil recovery, but also from a CO2 sequestration point of view. To consider future opportunities for greenhouse sequestration in these types of reservoirs while improving oil recovery specifically in the Midale field, a series of experiments were performed. The goal of this work was to study the effect of miscibility (miscible, immiscible and near-miscible regions) and injection rate on incremental oil recovery and sequestration during continuous injection in fractured porous media. Another important aspect considered was to analyze the effect of pressure draw-down or depletion on additional recovery with sequestration optimization. First, artificially fractured Berea sandstone samples were used. CO2 was injected at constant, slow rates into the fracture, while maintaining the high-pressure into the core and the system. At the end of the production life, the pressure into the system was released to different pressure steps and kept for a longer period of time at each of the reduced steps of pressure. In between two pressure steps, the system was shut down for enough time to observe the effect of CO2 and oil diffusion/back diffusion. After a series of Berea sandstone experiments, a few tests were conducted on the Midale cores, which were obtained from a good quality matrix part of the field. Injection and production data were collected using a continuous data logging system, an analysis of the produced liquids and measuring the gas production using a continuous flowmeter, which led to the understanding of the mechanism. The results showed that the pressure blowdown, followed by shut in after continuous injection, can increase oil recovery significantly until a certain critical pressure. Storage capacity of the rock with change in pressure and amount of oil recovered during blowdown period will lead to the critical understanding of abandonment pressure during the project life to achieve the goal of sequestration and recovery optimization.