Petrology And Facies Analysis Of The Upper Sand, Hyland Bay Formation, The Petrel Gas Field, Bonaparte Gulf, Northern Australia.

Ahsan, Abul

Honours Degree, 1996

University of Adelaide

Abstract

The upper sands of the Late Permian, Cape Hay Member of the Hyland Bay Formation in the Petrel Gas Field were studied using variety of methods. Palynology and core and thin section analyses of samples from Petrel #3, Petrel #4, Petrel #5 and Petrel #6 suggest that the two uppermost sand units (U1 and U2) which DST results show to be the best reservoir units respectively at Petrel #4 and Petrel #5, are genetically the same and deposited under upper shoreface (or delta front) reworking conditions. Thin section, X-Ray Diffraction (XRD), Scanning Electron Microscopy (SEM) and Cathodoluminescence (CL) data prove the presence of carbonate and/or silica cements in almost all samples, and that the dissolution of carbonate cements controls reservoir quality. CL data reveal that the presence of early carbonate cements prevented the development of quartz overgrowths. Petrographic analyses reveal that the moderately to well sorted sands are likely to be cemented by carbonate. There was no lack of availability of carbonate cements and the better sorted sands have gone through several stages of carbonate cementation and dissolution.

Palynology, and core and thin section analyses show a good correlation between progressive marine transgression, the associated reworking activity and the degree of sorting of the upper sands. The distribution of moderate to well sorted sands, possibly cemented by carbonate is fundamental to exploration in this area. The distribution, however, is difficult to assess because of limited data, only six wells penetrated the studied section and the upper sands were cored partially or completely in only four wells. Log data quality is poor with common bad hole conditions induced by weighted drilling mud. A wave-dominated deltaic sedimentary depositional model is consistent with the data gathered from all the methods associated with this study.