APPROACHES TO IDENTIFYING RESERVOIR HETEROGENEITY AND RESERVE GROWTH OPPORTUNITIES IN THE HUTTON SANDSTONE, JACKSON FIELD, AUSTRALIA

Abstract

An integrated geologic and engineering approach was applied to identify heterogeneities in the subsurface that might lead to reserve growth opportunities in the analysis of the Hutton Sandstone within the Jackson field, Eromanga Basin, Australia. The devised approach involves four key steps:

determine geologic reservoir architecture;

investigate trends in reservoir fluid flow;

integrate fluid flow trends with reservoir architecture; and

estimate original oil-in-place, residual oil saturation, and remaining mobile oil, to identify opportunities for reserve growth.

Although the Hutton reservoir is interpreted as the deposit of a continental-scale bed-load fluvial system and is dominated by highly permeable sandstone, the genetic stratigraphic analysis identified numerous thin but widespread lacustrine shale units that periodically interrupted episodes of coarse clastic Hutton deposition. These shales represent chrono-stratigraphically significant surfaces, but more importantly, the trends established in reservoir fluid flow from monitoring aquifer encroachment, production response to workovers, and differential depletion indicate that these shale units act as efficient barriers to vertical fluid flow. Erosion of the upper part of the Hutton reservoir by the younger Birkhead mixed-load fluvial system caused further strati- graphic complexity introducing additional barriers to vertical and lateral migration of mobile oil and aquifer encroachment. These stratigraphic complexities were not fully appreciated in previous field development and production strategies and potential exists for incremental reserve growth through geologically-targeted infill drilling and recompletions.