ABSTRACT
Large reserves are present and economically recoverable in many mature oil fields. Small multidisciplinary teams studied several basins in North America and a few large fields in South America searching for large volumes of low risk reserves in poorly performing fields. The fields studied include those producing by primary recovery with or without secondary recovery potential, and fields undergoing waterflooding. In the United States over 350 mature oil fields were examined from 1981 – 1997 looking for fields to purchase. The majority of the fields were in the USA Permian basin of West Texas/New Mexico and in a coastal portion of the Gulf of Mexico basin. Some large fields were studied for the property owners to rejuvenate or increase production.
Finding large volumes of low risk, presently non-producing reserves within fields involves several steps. First, the teams search in reservoir systems that appear more massive and homogeneous than they are. Second, the geoscience and engineering data is scanned to estimate original oil-in-place, percent recovery, and bypassed reserves. Third, the teams make an economic analysis including improvement costs. Candidate fields for purchase all have new low to moderate risk reserves amounting to at least 5% of the cumulative reserves already produced.
New reserves are found or exploited by applying one or more of the following: (1) improved drilling/completion technology, (2) identification of bypassed pay, especially very low resistivity pay, (3) new 2D and 3D seismic, and (4) sequence stratigraphic concepts. Additional reserves are found in both land-derived clastic and carbonate reservoirs in mature fields.
Forty-six mature fields were purchased in the Permian basin of Texas/New Mexico and in the Gulf of Mexico basin. In the fields purchased, 625 × 106 barrels of oil equivalent (BOE) of proved and probable reservoirs were added at a cost of US$ 2.69 per BOE. The average after tax rate of return of the 46 fields is 21 percent.
