Identification of sand injectite facies in core: their significance to developing a reservoir model for the Chestnut oilfield, UK Continental Shelf

A reinterpretation of the only core (taken in 1988) through the reservoir sandstone in the Chestnut oilfield changed the interpretation of the reservoir from a base-of-slope turbidite system downdip from a known slope channel to a sand injectite reservoir. Using the base-of-slope turbidite model, four unsuccessful appraisal wells were drilled, and it was concluded that the reservoir was more complex than anticipated, or that the sedimentary model was incorrect. A new examination of the core identified numerous well-preserved characteristics associated with sand injectite reservoirs, including internal structures and hydrofractures. No firm evidence of depositional structures was found. The new interpretation led to changes in the field-wide reservoir model that transformed the Chestnut Field from an uneconomic discovery into a producing oilfield that exceeded expectations. Examples of the injectite facies, including evidence of erosion during sand injection, are provided, together with evidence of hydrofractures along lithological boundaries and in mudstone intervals that allow association between hydrofractures and sand injection.