> 214 m thick, 14.6 x 5.2 km wide.
Gas field.
Abstract ref. 1708:
The Westerose field produces hydrocarbon from a dolomitized Upper Devonian reef. The reef is 1.6 km by 5.5 km and up to 214 m thick and is not well differentiated into organic reef margin and reef interior facies. Laterally continuous tidal flat and restricted lagoon sediments, which create vertical permeability barriers with the interiors of other reefs, were not observed. Secondary pore systems dominate porosity. The large vugs and fossil molds are well connected throughout the  reef by a pervasive vertical to subvertical fracture system. The equicrystalline xenotopic dolomite matrix has low porosity (3.2%) and permeability and does not contribute to effective intervug communication. The effect of diagenesis on the depositional fabric has made it difficult to subdivide the reef using depositional facies-reservoir quality relationships. Nonparametric statistical techniques were applied to core data to identify trends in permeability and porosity within the reef. Reef  cores were assigned to flank, margin or interior positions based on reef  morphology, an arbitrarity divided into vertical layers 25 m thick giving a total of 17 layer-position combinations. Horizontal permeability, vertical permeability and porosity increase from reef flank to reef interior and from the upper reef to the base of the cored reef. Cumulative probability plots of horizontal permeability data, grouped by reef  position, each exhibit the characteristics of the log-normal distribution but with a portion of the highest permeability values truncated from the data set. Truncation is due to poor core recovery from the highest permeability regions as well as to the limitations of the permeability measuring procedure on high permeability core. Vertical permeability data are not truncated. Truncation effects must be taken into account when estimating average horizontal permeability. Although significant trends in the magnitude of permeability are present within the reef, the reservoir fluid flow model for the rock volume being drained by a single well is best described as a random arrangement of blocks of differing permeability. Permeability calculated for the oil zone from a pressure build-up test is 1115 mD. When corrected for truncation, the geometric average of the core data from within the producing zone of the pressure test is 760 mD, consistent with the pressure test result; the arithmetic mean of the corrected data set would be much too large. The similarity between the geometric average of the horizontal permeability calculated from the pressure build-up test at Westerose is expected from the disordered arrangement of units of differing permeability. 

