Abstract

The San Andres “C” Field in the Permian Basin is one of 44 fields successfully redeveloped as part of a 1980’s – 1990’s program to find new reserves within and adjacent to existing mature fields. The fields purchased were identified by small multidisciplinary teams of geoscientists and petroleum engineers. The teams scanned more than 350 mature fields in the Permian Basin and the coastal portion of the Gulf of Mexico Basin. The fields that were identified as candidates for purchase had the possibility of “undiscovered” low-to-moderate-risk reserves amounting to at least 5 percent of the cumulative reserves already produced.

The fields purchased added over 650 million barrels of oil equivalent (BOE) of proved and probable reserves at a cost of $2.69 per BOE (in 2000 dollars).

The “C” reservoir was a failed waterflood unit in the San Andres dolomite. The reservoir was originally deposited as oolite bars and a tidal channel. The original operator mapped the reservoir as two “layer-cake” units instead of three off-lapping units separated from each other by impermeable shaly carbonate flow barriers. The original 40-acre peripheral waterflood was ineffective for sweeping the remaining oil after primary production. Because of the distribution of reservoir pore space and the intervening flow barriers, a 20-acre five-spot flood pattern proved to be optimal. Pay cutoffs were proven by flow test to be 4 percent porosity and 0.1 md permeability instead of 8 percent porosity and 1 md permeability. The new ratio of secondary to primary production (S/P) is 1.75 instead of 0.55 at the time of field purchase. The new ultimate recovery is expected to increase more than 19 million barrels.