Predicting Fracture Density In The Eagle Ford (Boquillas) Formation, Val Verde Basin, Texas
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Fracture density in hydrocarbon reservoirs is an important variable for efficient production of oil and gas in tight reservoirs. Fracture density is the fracture surface area per unit of volume, and the higher the reservoir fracture density, the higher its recovery factor. Being able to estimate the induced fracture density in advance of hydraulic fracturing will therefore help increase the knowledge of the reservoir and production efficiency. Theoretical considerations indicate that fracture density is related to strain energy. The purpose of this study is to verify the hypothesis that fracture density can be predicted under constant strain conditions using the elastic properties, rock density and fracture toughness. The hypothesis has been framed in the form of an equation, the validity of which is to be tested. In order to do so, a number of field and laboratory measurements were made. In the field, the fracture densities of outcrops were measured and samples collected. In the laboratory, density and elastic properties of the rocks were measured using ultrasonic techniques. In order to maintain the assumption that the strain in the strata where measurements are made remains constant, samples are taken from different sedimentary layers in the same outcrop, as well as fracture measurements from the same joint set. The hypothesis was not confirmed. Two of the possibilities for the outcome could be either the samples' spatial distribution, with the samples being either from the same outcrop or outcrops in excess of 20 miles apart, or the assumption of constant strain throughout the samples, which may not be valid in the sample area.