Infill Drilling To Increase Reserves—Actual Experience in Nine Fields in Texas, Oklahoma, and Illinois

Evaluation of reservoir discontinuity has been used by industry to estimate potential oil recovery to be realized from infill drilling. That this method may underestimate the additional recovery potential is shown by continuity evaluation in a west Texas carbonate reservoir, as infill drilling progressed from 40-acre (162 X 10/sup 3/-m/sup 2/) wells to 20-acre (81 X 10/sup 3/-m/sup 2/) wells and eventually to 10-acre (40.5 X 10/sup 3/-m/sup 2/) wells. Actual production history from infill drilling in nine fields, including carbonate and sandstone reservoirs, shows that additional oil recovery was realized by improving reservoir continuity with increased well density. The conclusions formulated from this infill drilling study are as follows. Infill drilling in nine fields has resulted in per-wellrecovery improvements that are attractive under current economic conditions. Increased oil recovery from the drilling of 870 infill wells in 9 fields ranges from 56% to 100% of their wellbore production. Total additional reserves from these wells will be 60.8 million bbl (9.7 X 10/sup 6/ m/sup 3/) oil. Continuity calculations made after infill drilling indicated the pay zones to be more discontinuous than when calculations were made before infill drilling. The experience in these nine fields indicates that the ultimate wellmore » density in any given field can be determined only after several years of field performance provide sufficient information on reservoir continuity and recovery efficiencies.« less