Capturing secondary permeability and fracture connectivity through geological time by fracture back-stripping

Abstract

Fractured rock petrophysical studies rarely use temporal constraints, thus hindering fracture-related permeability (K) and connectivity (CB) estimation during past geofluid migration. Presenting a new conceptual approach, we use a stochastic method incorporating absolute ages to reconstruct fracture arrays back in geological time. Generating ‘grown’ discrete fracture network (DFN) models, we simulate the hydraulic behaviour of fractured rock volumes from the late-Cretaceous/Palaeocene to the Devonian, via progressive fracture back-stripping. Our study reveals that maximum bulk permeability (K1) increased through time from 9.47e-14 m2 to 4.44e-13 m2 (~ 3 orders of magnitude) along with the maximum horizontal permeability orientation (KHmax) shifting from NE-SW to NW-SE. Similarly, CB increased (1.01 to 1.79) with fracture saturation, peaking in the mid-Cretaceous. Validating our method, timing of dated offshore hydrocarbon activity fit our results. Back-stripping of time-constrained fracture sets is therefore a powerful method to investigate and quantify the dynamic evolution of petrophysical properties through geological time.