Approaches to Identifying Reservoir Heterogeneity and Reserve Growth Opportunities in a Continental-Scale Bed-Load Fluvial System: Hutton Sandstone, Jackson Field, Australia

Abstract

We applied an integrated geologic and engineering approach devised to identify heterogeneities in the subsurface that might lead to reserve growth opportunities in our analysis of the Hutton Sandstone at Jackson field, Eromanga basin, Australia. Our approach involves four key steps: (1) determine geologic reservoir architecture, (2) investigate trends in reservoir fluid flow, (3) integrate fluid-flow trends with reservoir architecture, and (4) 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, shale units deposited during lacustrine flooding that periodically interrupted episodes of coarse clastic Hutton deposition. These shales represent chronostratigraphically significant surfaces, but more importantly, the trends in reservoir fluid flow, established from monitoring aquifer encroachment, production response to water shut-off workovers, and differential depletion in repeat formation tests, 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 stratigraphic complexities, 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 the potential exists for incremental reserve growth through geologically targeted infill drilling and recompletions.