Tracer-Test Simulation on Discrete Fracture Network Models for the Characterizationof Fractured Reservoirs

摘要

The presence of fractures at various scales affects the flowrndynamics within a reservoir, thus casting uncertainty on thernassessment of the field productivity and reserves.rnMethodologies and tools are now available (I) to reconstructrngeologically-realistic models of the fault/fracture network (ii)rnto turn these models into simplified conceptual models usablernfor field-scale simulations of multi-phase production methods.rnHowever, a critical intermediate step remains that ofrnvalidating the geometry of the geological fault/fracturernnetwork and characterizing it in terms of flow properties.rnAn original 3D Discrete Fracture Network simulator enablingrnone to fulfil this characterization step has already beenrnpresented by the authors1. This simulator can compute thernsingle-phase flow response of any type of fractured reservoir,rnwhatever the scale, density and connectivity of fractures. Anrnextension of this simulator to compute tracer tests is presentedrnin this paper. Compared with pressure tests, tracer tests mayrnprovide additional information about the reservoirrnheterogeneity due to the convective nature of these tests.rnThis simulator is based on the dual-medium conceptrnapplied to an explicit representation of the geological model ofrnfault/fracture network and matrix medium. The transport andrndispersion of non-reactive tracers are modelled by introducingrna convection-dispersion equation into the existing dual-rnporosity flow model. A hybrid scheme discretizes thernconvective term implicitly within densely fractured regions forrnstability purposes, and explicitly via a double-upstreamrnscheme everywhere else for reducing spurious numericalrndispersion.rnAfter demonstrating the reliability of this tracer model onrnvalidation cases, a realistic case that combines diffusernfracturing and major objects such as seismic and sub-seismicrnfaults is studied. Tracer tests are simulated for wells in a five-rnspot injection/production pattern. Effects of a fracture/matrixrntracer exchange as well as a Taylor-Aris dispersion onrnbreakthrough curves are analyzed. The potentiality of tracerrnresponses for providing information on the distribution ofrnreservoir heterogeneities is discussed.