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Heavy oil reservoirs in Alaska provide for major production challenges. The diverse set includes proximity to permafrost layers, very high viscosity oil and low mechanical strength pay zones. The Ugnu deposits of Alaska North Slope (ANS) hold more than 6 billion barrel of oil in place. The dead oil viscosity at reservoir temperature ranges from 1,000 to 1,000,000 cp1. In an effort to achieve sustained well life, this paper focuses on the unique set of challenges occurring in the Ugnu reservoir and presents the best possible way of maximizing production.The paper accentuates on the observations derived from the field data which shows that deliberate sand production with the hydrocarbon stream while employing a Progressive Cavity Pump (PCP) as artificial lift method has favorable effect on the primary oil recovery. The developments have led to the advent of technique called Cold Heavy Oil Production with Sand (CHOPS) as initial production method for shallow heavy oil reservoirs. Sand production leads to the formation of high porosity channels or wormholes that can range up to hundreds of meters. The co-mingling of heavy oil and sand develops the behavior of foamy oil by creating a bubbly flow inside the reservoir. The combination of these wormholes with foamy oil behavior are the primary factors that result in enhanced production during CHOPS. One of the major hindrances to its successful application is the selection of post CHOPS production method, that has been addressed in this paper with the help of modeling and simulation The present research is based on modeling one of the wells drilled into the M80 sands of the Ugnu formation and then analyzing the post CHOPS recovery for the well. The research uses modeling of CHOPS well with the help of a wormhole fractal pattern and a foamy oil model. Simulation of polymer injection is then being employed from a nearby well. The recovery obtained from the simulations have been analyzed to provide a basis for selecting the appropriate enhanced oil recovery method after CHOPS.Alternative recovery techniques following the primary cold production include water flooding, polymer injection, miscible gas injection and thermal recovery methods. Water flooding becomes unviable because of the mobility contrast between the highly viscous oil and water. The high permeability zones provide a bypass for water, producing elevated water cuts as a consequence. Another aspect unique to Alaskan heavy oil reservoirs is the proximity to the permafrost layer with the hydrocarbon bearing zone making thermal recovery methods unappealing. Polymer injection and miscible gas injection become favorable non-thermal secondary and tertiary recovery methods in this case. This paper analyses the performance of polymer flooding on a reservoir that has been produced with CHOPS. The results indicate almost 12% increment in recovery with polymer flooding as compared to the natural depletion. |
