John Gould, Jerl Wackler
Mobil E. & P. U. S.
John Quiren and John Watson
Mobil E. & P. Services, Inc.
ABSTRACT
The East Mallet Unit in Hockley County, Texas, has been under CO2 flood since June 1989. Four observation wells were drilled to monitor the CO2 flood. The locations of the four observation wells were chosen to provide information in different parts of the Unit and to help account for well performance and geologic variation in the reservoir. The wells were drilled to an approximate depth of 5,200 feet and cased with fiberglass casing. Open-hole togs were run to establish a baseline for comparison to cased-hole togs. The open-hole logging program consisted of a lithodensity log, a dual porosity neutron log and a phasor induction log. Drill-stem tests were taken in the first three wells for water samples. These water samples were analyzed for salinity and water resistivity. Cased-hole base togs were run shortly after the casing was cemented. The cased-hole base log suite consisted of a dual porosity neutron tog, a phasor induction tog and a cement evaluation log.
The cased-hole monitor program includes the same logging program as the base cased-hole suite with the exception of the cement evaluation tog. Two passes were made on each eased-hole monitor run. Both passes from run one and run two neutron togs were averaged to give a base cased-hole log. Subsequent passes from each neutron logging run were averaged to give one log per run. Cased-hole neutron porosity was normalized to open-hole neutron porosity for each run. The neutron matrix response was calculated for the base log from open-hole porosity, then a hydrogen index was calculated for each cased-hole run. Volumes of gas, oil and water were calculated for each monitor run and compared to the base log to evaluate the CO2 flood front
Results show effective vertical sweep in one of the observation wells in the southern end of the Unit. This well is between an injector and a producer on a line of preferred fracturing. Sweep in the northern part of the Unit has not been as effective away from the line drive, and the monitor logs show that the flood has not yet moved through the lower past of the completed interval.