The Fracture Characterization and Fracture Modeling of a Tight Carbonate Reservoir—The Najmah-Sargelu of West Kuwait

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Summary This paper presents an innovative and promising, multidisciplinary approach that includes geology (borehole images, cores, and wireline logs); geophysics (seismic facies analysis), and reservoir engineering data (production data, PLT, and well test) that were combined to identify the main types of fractures, to predict their occurrence in the reservoir, and to determine the hydraulic properties of the different fractures sets. The Najmah-Sargelu of west Kuwait is an oil-bearing reservoir made of tight carbonates where porosity and permeability are provided mainly by the fracture network. In this paper, we first introduce the method used to identify and predict the two main scales of fractures: joints and large-scale fractures (faults and fracture swarms). The shale content (Vshale) and mechanical-beds thickness were found to be the two main geological drivers on joints occurrence. The thickness of individual beds was recorded from borehole acoustic images, which enabled us to measure a fracture spacing/bed thickness (S/T) ratio for each fracture set and for different shaliness. Second, we used an innovative solution to deliver an accurate map of the location of large-scale fractures. This approach concurrently uses a set of relevant attributes per selected fracture in a multivariable statistical process called seismic facies analysis (SFA). A 3D-stochastic fracture model was then generated, incorporating the two scales of fractures and this model was constrained by the shaliness of the reservoir, the S/T ratio, and the seismic facies map. In this approach, the two scales of fractures are modeled independently. The model of large-scale fractures is conditioned by the picking of lineaments on the SFA map and validated at wells, whereas small-scale fractures are modelled according to geological driven statistics on fracture density and fracture orientation. The calibration of the hydraulic properties of the fractures was achieved through the second innovation presented in this paper: the simulation of a synthetic well test using the 3D-fracture model and matched with the real data. This resulted in the calibration of effective hydraulic conductivity for each fracture type. These values were combined with the 3D-stochastic fracture model to produce 3D-fracture-properties models (porosity, permeability, and block size) for the Najmah-Sargelu.