Summary

The ability to describe the interwell heterogeneity of reservoir properties can reduce risk and uncertainty in the advanced development of mature shallow shelf carbonate reservoirs. Oil production at the Welch Field, Dawson County, Texas, is from a stratigraphic trap in a low permeability San Andres reservoir of Permian age. Post depositional diagenesis, mostly anhydritic cementing, has created a high degree of variability in the porosity and permeability distributions across the Welch Field. The spacing of wells with porosity measurements is insufficient to describe these variations. A 3-D seismic volume has been used to extend the porosity into the interwell space.

Porosity was determined from compensated neutron/density logs and integrated with laboratory measurement of porosity on core samples. Three seismic attributes; structure, amplitude and phase were found to have high correlation to the porosity. A multiple variable transform equation was developed and porosity values were estimated at each seismic bin. The seismic-guided porosity map ties to the well data accurately, provides detailed variation in the interwell space and reveals extensions of the reservoir beyond the well control. Subsequent drilling has verified the seismic porosity interpretation, and numerical simulation using the seismic data more efficiently matched the production and injection history of the reservoir than using the well data alone.

AAPG Search and Discovery Article #90937©1998 AAPG Annual Convention and Exhibition, Salt Lake City, Utah