Advances in the characterization of rough fractures in hydrocarbon reservoirs

A multitude of factors control the flow of fluids through fracture systems in hydrocarbon reservoirs. For example, closed fractures i.e. (deformation bands) may seal or baffle hydrocarbon flow (Fossen & Hesthammer 1998 ) whereas open fractures are considered to be conductive to hydrocarbon flow. However, fracture surface roughness has much control upon fluid flow through open fractures and is demonstrated to effect significant departures from the Cubic Law for predicting flow through fracture apertures (Isakov et al. 2001a). Such considerations are crucial in igneous and metamorphic reservoir rocks since fractures in these rocks may form the only significant pathways for fluid migration (Isakov et al. 2001b) (Fig. 1). We present a five-stage approach for the full characterization of rough fracture surfaces in rocks and their incorporation into reservoir flow models. Each stage is aided by in-house developed software (Fig. 2). 1. Optical profiling of resin replicas of rough fracture surfaces in a suite of rocks (Fig. 2), using OPTPROF (Isakov et al. 2001a; Ogilvie et al. 2001a), 2. Parameterization and statistical analysis of the surfaces using PARAFRAC software (Isakov et al. 2001c), 3. Creation of synthetic fractures tuned to the properties of the real rock fractures using SYNFRAC software (Isakov et al. 2001c), 4. Experimental investigation of fluid flows (Ogilvie et al. 2001b). 5. Computational fluid flow modelling in 2D cross sections of fractures [boundary conditions from 1 to 4]. The objective is to replace the parallel-plate model assumed in larger multi-fracture models with a model that fully accounts for rough fractures at a range of scales.