Abstract: Pickerill Field Geophysical Reservoir Analysis

G. Dorn, K. Tubman, D. Cooke, R. O'Connor, C. Hawkes

The combination of petrophysics and geophysics adds significantly to the understanding of a hydrocarbon reservoir and can help guide the location of development wells. The objective of the Pickerill Field study was to develop seismic criteria that could be used to optimize the location of development wells. Primary products included a detailed fault map and an estimate of gross reservoir porosity. These are being used to help select development well locations.

The Pickerill Gas Field is located in Blocks 48/11a, 48/11b, 48/12b and 48/17b in the UK Southern Gas Basin. The 100^prime to 250^prime thick, Permian Rotliegend reservoir consists primarily of dune and interdune deposits overlying generally poorer quality fluvial sands. There is a rapid lateral change in reservoir quality due to variations in facies, diagenesis, and the effects of faulting.

A set of seismic horizon attributes were generated from a refined Top Rotliegend interpretation and were used for detailed fault trace interpretation. Reservoir faults with throws of as little as fifteen feet were mapped and avoided in subsequent development drilling locations.

Synthetic seismic studies of existing exploration wells indicated a linear relationship between reservoir reflection amplitude and average reservoir porosity. The actual surface seismic amplitude-porosity relationship is particularly sensitive to the phase of the seismic data, and a frequency-dependent phase correction operator was designed based upon extracted wavelets at several wells. The effect of uncompensated transmission losses due to lateral variation in the overburden needed to be quantified and corrected.

Phase-corrected amplitude from the Top Rotliegend reflection was correlated with porosity at existing wells to produce an estimated porosity map, which was superimposed in color on the three-dimensional time structure of the reservoir. The empirical amplitude-porosity relationship has been used successfully to predict gross reservoir porosity in several wells drilled since the work was concluded.

AAPG Search and Discovery Article #90986©1994 AAPG Annual Convention, Denver, Colorado, June 12-15, 1994