Incremental Remaining Resource Assessment of a Large Turbidite Sandstone Reservoir, California

Locating and quantifying remaining resources in mature fields is challenging due to uncertainties in geologic characterization and water movement trends. Identifying areas of incremental remaining resource leads to high-graded infill locations and increased net present value. This study offers a quick and robust technique to map and quantify remaining resource in producing fields, with a specific example from a large sandy-turbidite reservoir, onshore California.

Oil cut model contour grids of the reservoir are built from producing oil cut and injection data reviewed over the reservoir history as well as integrating basic geologic principles of structure and contour mapping. The resulting oil cut map grids simulate a flood-front map as a proxy to current average water saturation across the reservoir. Current net pay maps are generated by integrating the oil cut models with fractional flow data and original net-pay maps. A range of models are developed to capture the potential low to high cases of remaining resource. With the resulting range of net-pay maps, the recovery factor are calculated and three quality controls applied: 1) the recovery factors calculated from the maps are compared with recovery factor analog databases and the waterflood recovery efficiency equation; 2) a visual review of mapped water movement trends; and 3) past infill results compared to map values.

The remaining net pay maps highlight areas of potential remaining resource, which are then quantified through a Monte Carlo simulation of the entire field. Variables modeled in the simulation include ranges of current oil in place from the net pay maps, recovery factors, and remaining production from active wells. The resulting outputs are P10-P50-P90 incremental-oil estimates that illustrate high-graded sub-areas for infill drilling. The results are compared to the EUR of active wells to assess the number of infills to target the incremental oil.

The results from this California reservoir study identified 14 infill locations within two areas for strategic infill drilling to increase production and maximize EUR in the reservoir. This mapping and remaining resource quantification technique was applied to a total of six Chevron reservoirs, both onshore and offshore, over a 6 month period in 2011, resulting in 110 million barrels of incremental potential remaining resource. This technique has also been used as an independent assessment to compare to 3D-volume modeling and simulation.

AAPG Search and Discovery Article #90142 © 2012 AAPG Annual Convention and Exhibition, April 22-25, 2012, Long Beach, California