--> Reservoir Connectivity, Compartmentalization and Overpressure Conditions in the Sable Subbasin (Nova Scotia, Canada) and Porcupine Basin (Ireland)

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Reservoir Connectivity, Compartmentalization and Overpressure Conditions in the Sable Subbasin (Nova Scotia, Canada) and Porcupine Basin (Ireland)

Abstract

Overpressure is abnormally high subsurface pressure exceeding hydrostatic pressure at a given depth, and occurs when fluids become trapped in the pores of sedimentary rocks. Overpressure has been identified as a risk element in the Sable Subbasin of Nova Scotia, and has been identified as a poorly understood risk element in the Porcupine Basin of Ireland. The Sable Subbasin and Porcupine Basin formed as a result of rifting and extension associated with the formation of the North Atlantic Ocean. Both basins represent diverse tectonic styles and depositional environments including early-stage rifting, passive margin, carbonate bank, fluvial-deltaic-lacustrine, and deep water. The Sable Subbasin is southwest-northeast trending and is part of the Scotian Basin; it comprises Mesozoic to Cenozoic sediments (up to 18,000 m) overlying a Paleozoic basement. The Porcupine Basin is a north to south trending basin located on the Irish continental margin, and comprises sediments from the Carboniferous to Holocene. Understanding the formation and distribution of overpressure in reservoir compartments can reduce risk during exploration and development of offshore resources. Previous work has demonstrated overpressure in the Sable Subbasin is variable in magnitude and not associated with specific depths or formations. Faults in the Sable Subbasin were assumed to be either dynamic (allow communication) or static (does not allow communication), which is an inaccurate assumption. Utilizing 3D seismic datasets, with wireline log and pressure data, we have completed a reservoir connectivity analysis of the Sable Subbasin to determine the effect of fault behaviour on connectivity and pressure migration. This study uses 3D geometric models to demonstrate the location and magnitude of overpressured reservoir compartments, integrating reservoir architecture, fault behaviour, and pressure data to generate a preliminary map for de-risking future exploration. Abnormal pressure and pressure distribution has received limited study in the Porcupine Basin. Pressure measurements have been collected (repeat formation tests, formation leak off tests, and drill stem tests) in several wells, providing a preliminary dataset to begin investigating pressure behavior in the basin. We have completed a petrophysical analysis of the wells to determine if there is overpressure present and potential lateral pressure connectivity across the basin.