The effect of faults on the 3D connectivity of reservoir bodies: a case study from the East Pennine Coalfield, UK

The connectivity of reservoir bodies has been tested in unfaulted and variably faulted, high resolution 3D geocellular stratigraphic models (16 million cells in a 20 km × 20 km × c. 600 m volume) from the East Pennine Coalfield, UK. These deterministic stratigraphic–structural models are underpinned by high density borehole and mineplan data. The stratigraphy extends from mid-Westphalian A to base Westphalian C and represents a low net:gross (0.03–0.27) coal-bearing, delta top/fluvial reservoir analogue. The models contain up to 1467 post-depositional normal faults with maximum displacements ranging from 1 m to 140 m. Using two sets of facies as net, the effect of fault size on inferred reservoir connectivity has been assessed for stratal intervals with different sedimentary architecture, interval net:gross and thickness.

Faults often disconnect reservoirs in thinner, lower net:gross intervals containing only laterally discontinuous, channelized bodies. By contrast, faults generally increase reservoir connectivity in thick, relatively high net:gross intervals containing laterally extensive, tabular reservoir bodies. The most significant factor for fault-related reservoir connectivity is the dimensionality and scale of reservoir bodies in relation to the displacement distribution along faults. Populations of small, sub-seismic, faults (<5 m throw) can reconnect reservoir bodies that are dissected by larger displacement, seismic resolvable, faults (>20 m throw).