Geochemical Correlation of Windalia Oil and Extracts of Winning Group (Cretaceous) Potential Source Rocks, Barrow Subbasin, Western Australia

Abstract

Windalia oil is a commercial accumulation in a Cretaceous reservoir at Barrow Island, Western Australia. A chemical correlation study has been made between this oil and hydrocarbons extracted from 37 Cretaceous sedimentary rock samples from different stratigraphic levels in seven wells on and around Barrow Island. Seven established correlation parameters and one new parameter have been applied to establish oil:source rock relations. The new parameter is the ratio of pristane + heptadecane to phytane + octadecane. The influence of maturation on several correlation parameters has been investigated by pyrolyzing source rocks at 300°C for varying times. The changes observed in these experiments have been used to infer the effects which maturation processes have on the co relation parameters. To assess the overall degree of correlation between source rock extracts and oil, each method has been assigned a weighting which reflects its power as a correlation technique. An overall correlation score was obtained for each potential source rock by totaling the contributions from the eight individual methods. It appears likely that the Windalia oil had its source within the Winning Group of sedimentary rocks, the most probable source formations being the Middle shale of the Windalia sandstone member, the Muderong Shale, and the Windalia Radiolarite. Several mechanisms of formation of Windalia oil from these source beds are possible.