Incorporating Seismic Attribute Modeling into a Flow Model of the Grayburg Reservoir in the Foster-South Cowden Field, An Update.

The Grayburg and San Andres reservoirs in the Foster ? South Cowden Field have been producing since 1939, and under waterflood since 1962. Production had declined to near abandonment level at the start of this project. The objective of the project was to utilize low cost, state-of the-art technologies available to small independent operators to preserve access to well bores and extend the economic life of mature fields. The use of an integrated team of a geologist, geophysicist, and engineer is not new to major oil producers. However, utilizing a team of experienced consultants along with in-house personnel is new at the smaller independent level. The initial approach of this study was to construct a flow model with conventional data. Logs and cores provided the basis for the geological model. Production data was assembled and validated along with the few measured pressures taken early in the field's history. Production testing of all wells was initiated to provide accurate current production data. Pressure transient testing of all wells was initiated to provide accurate current bottom hole pressures. History matching of pressure and water-cut data validated the flow model, and the flow model has since guided field operations, subject to the limits imposed by the spacing of the well data (one reliable well log per 18 acres of reservoir). At this scale, compartmentalization and heterogeneity of the reservoir is obvious. The engineering history match and reservoir simulation, however, is conducted at one-acre (220 x 220 feet) spacing or less. 3-D seismic is required to define porosity in the areas between the wells and reduce the uncertainty inherent in data sets from old fields. The 3-D seismic data set was processed to retain high frequencies, thereby improving vertical resolution to the range of 50 feet. Seismic bin size is 110 x 110 feet, equal to the scale utilized in the history match and reservoir simulation. Traces from the seismic inversion model exhibit a high degree of correlation with the well log data. A correlation was developed between seismic velocities and porosity for each geologic zone. The correlation was used to develop porosity maps for each zone in the flow model. The seismic derived/geologically guided maps delineated small-scale reservoir heterogeneities with a degree of confidence here-to-fore unavailable. The history match and reservoir simulation grids were reoriented to make use of a porosity barrier identified on the porosity maps. The resulting flow model was validated through the history match process, and used to guide the realignment of the waterflood. The recommendations made during the project to date have resulted in the production of an additional 114,000 Barrels of Oil to date, an increase in the injection water quality, and a paradigm shift in the approach to data collection for day to day decision making. The initiation of the waterflood realignment program is aimed at extending the life of the field and the recovery of significant incremental oil. Five wells have been restimulated and the production from these wells has increased from 16 BOPD to 134 BOPD.

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