Abstract

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 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 cementation, has created a high degree of variability in the porosity distribution across Welch Field. The spacing of wells with porosity measurements is insufficient to describe these variations. A 3-D seismic volume is used to map 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 development drilling has verified the seismic porosity interpretation in the interwell space.