Physical Model of the West Willmar Rich Gas Pilot

Abstract A physical model of the West Willmar Frobisher Beds reservoir in southeastern Saskatchewan has been developed by assembling 31 core plugs into a 1.5-metre horizontal pore system. Studies conducted range from simple gas flow through immiscible, miscible and water-and-gas displacements, with results confirmed by compositional simulation n runs wherever practical. The discussion of the data develops new insights into laboratory methods and simulation concepts. The interpretation of results indicates the impact of flow conditions on potential oil recovery from the miscible swept zone in the West Willmar Rich Gas Pilot. Introduction The initial objective of the core flood studies for the Willmar Pilot was simple: to find out how much stock-tank oil could be recovered from the reservoir rock by water flood, gas flood and hydrocarbon miscible flood. As this objective was achieved, it became equally important to develop better insight into the process and its key parameters, not only for the optimization of the West Willmar Pilot, but also for use in designing other gas miscible projects in Western Canada. Subsequent investigations into the effect of the preliminary water flood on miscible flood recovery led to investigations of water-alternating- gas (WAG) flood cycle size, gas-water ratio and effectiveness of chase gas in improving oil recovery and recovering miscible fluid during the latter part of the flood. The attainment of the above objectives was a stepwise process, with each new core flood building upon data previously acquired. The amount of data derived from the experiments- (Figure in full paper) also increased progressively, leading to improvements in equipment and procedures to their current status. Experimental Apparatus and Procedure Apparatus and Procedures The apparatus used in performing the core displacement tests is shown in Figure 1. The novel feature of this apparatus and associated procedures is that inlet injection rate and outlet production rate are equal and constant. These boundary conditions have been found to enhance mechanical reliability and ease of operation. This technique is also useful in avoiding problems with pressure surging that commonly occur with back-pressure control. In situations where two- and three-phase production occurs, the method improves mass and volumetric balances. In situations where the three phases are intimately mixed limits can easily be put on inlet pressure and pressure drop across the core to prevent development of unnecessarily unfavorable reservoir conditions. Where both incompressible and compressible fluid are used in the same test, the procedure provides data equivalent to those obtained in conventional constant injection rate – constant outlet pressure experiments(l). In the case where compressible materials (gases) are injected, the volumes of material injected and collected from the core are determined knowing the pump injection and withdrawal reading, the fluid compressibilities, and the volumes of the fluid injection and collection reservoirs. To measure pressure drop across the core a differential pressure transducer is placed in parallel. High-pressure visual cells permit observation of the phase behaviour of the injected and produced fluids.