--> --> Abstract: An Innovative Geostatistical Approach to Oil Volumetric Calculations: Rock Creek Field, West Virginia, by R. R. McDowell, D. L. Matchen, M. E. Hohn, and A. G. Vargo; #90984 (1994).

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Abstract: An Innovative Geostatistical Approach to Oil Volumetric Calculations: Rock Creek Field, West Virginia

Ronald R. McDowell, David L. Matchen, Michael E. Hohn, Ana G. Vargo

Detailed analysis of production trends in heterogeneous reservoirs requires local estimates of production, original oil in place (OOIP), and recovery efficiency. In older fields, calculating these values is hampered by incomplete well records, inconsistent reporting of production (well by well vs. lease by lease), unknown effective drainage radius, and poorly constrained completion interval. Accepted methods of estimation rely heavily on the use of average values for reservoir properties. We have developed an alternative method for calculating local and field-wide estimates, and have compared our results to published values.

Our study of the Lower Mississippian Big Injun sandstone reservoir in Rock Creek field, central West Virginia, used production data obtained from operators. Production for the first 10 yr was reconstructed, when necessary, by comparison to decline curves for 70 wells with complete production records. Similarly, curve fitting techniques were used to interpolate data for missing years.

Cumulative production values for 667 producing wells were kriged over the extent of the field; the resulting grid was sampled to provide an estimate of cumulative production at each well location. Kriged estimates of pay thickness, porosity, and water saturation were used to calculate OOIP for a given value of effective drainage radius. Changing the drainage radius was observed to affect the range of values for OOIP and recovery efficiency (cumulative production + OOIP), but not geographic distribution of these two parameters. An optimal radius of 270 ft gave recovery efficiencies ranging between 18.75% and 21.9%, comparing favorably with a published value of 22.3%.

Summing the OOIP value for all producing wells in the field yields a value of 139.6 million bbl, significantly higher than the published value of 37.8 million bbl. Our estimate reflects a more complete data set and revised values for reservoir parameters. Discussions with the principal operator in the field suggest that the higher figure is more correct.

AAPG Search and Discovery Article #90984©1994 AAPG Annual Convention, East Lansing, Michigan, September 18-20, 1994