Compositional simulation and optimization of secondary and tertiary recovery strategies in monument butte field, utah
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Monument Butte field produces oil from low-permeability, lacustrine fluvial-deltaic sandstones of the Green River formation. Reservoir sands are heterogeneous, lenticular, and have limited aerial extent and vertical communication, resulting in poor inter-well connectivity. Cumulative recovery to date (primary and secondary) is about 2% of the estimated 2 billion barrels of original oil in place (OOIP). Current water flooding successfully maintains reservoir pressure, but it provides very poor sweep efficiency. The objectives of this study were to assess secondary and tertiary recovery methods and to recommend a reservoir management approach that would increase oil recovery efficiency. To accomplish these objectives, we conducted detailed compositional simulation studies in a pilot area of the field. The reservoir model was calibrated using manual and assisted history matching methods. To reduce simulation time, we grouped fluid components into 10 pseudo-components. The 3-parameter, Peng-Robinson equation of state (EOS) was used to match PVT experimental data. Primary-then-water-flood and water-flood-only strategies were simulated using different water-flood timings. Infill drilling potential was evaluated by simulating downspacing from the original 40-ac to 20-ac well spacing. Immiscible and miscible flooding with CO 2, water alternating with gas (WAG), N 2, and CH 4 were simulated with reservoir pressures below and above minimum miscibility pressure (MMP). Simulation results indicate that water flooding should be started within 6 months of production. A water-flood-only strategy provides more oil recovery than a primary-then-water-flood strategy. Infill drilling may effectively produce unswept oil and double oil recovery. Immiscible gas injection suffers early gas breakthrough and is not an effective way to increase ultimate oil recovery. CO 2 injection is much more efficient than N 2 and CH 4 injection, because it has a lower MMP (2500 psia) and later gas breakthrough. Water-alternating-CO 2 injection is superior to continuous CO 2 injection in oil recovery, because it makes the gas-oil mobility ratio more favorable, controls early CO 2 breakthrough and maintains reservoir pressure. The study results can be used to optimize oil production from other parts of the large Monument Butte field. Copyright 2008, Society of Petroleum Engineers.
