Effect of Natural Fractures on Eagle Ford Shale Mechanical Properties

Abstract

AbstractNatural fractures widely exist in shale samples, and natural opening-mode fractures reactivate during stimulation and enhance efficiency by widening the treatment zone. The existence of natural fractures is very important to the stimulation treatment and will eventually benefit the shale gas/oil reservoir recovery. The effect of natural fractures on a shale mechanical property study will serve as the basis for the formation evaluation and the sweetspot selection on the hydraulic fracturing treatment. By combining conventional destructive mechanical tests and novel digital rock nondestructive analysis, important conclusions can be determined regarding the mechanical properties changing trend as a function of the fracture structure. The more complex the natural fracture structures, the less resistant the rock. This paper presents, in detail, the changing trend from various shale samples.Studies on the mechanical properties of Eagle Ford shale samples (e.g., Young's modulus, Poisson's ratio, etc.) are performed in a laboratory using a hydraulic load frame, and the core internal fractures are computed tomography (CT) scanned before and after the mechanical tests. The effect of natural fractures on the mechanical properties is analyzed through the testing data. The induced fractures are characterized in several Eagle Ford shale core plugs in terms of orientation, size, and width. Substantial image processing techniques are employed to analyze the three-dimensional (3D) rock microstructures. The statistical properties, such as the width, length, and the tortuosity of the main fractures, are obtained through image analysis. The volume of the fractures and the permeability on all x, y, and z directions on the central part of the core plug are calculated based on the 3D CT images as well. The small fractures can serve as the planes of weakness and reactivate during a hydraulic fracture treatment.This paper elaborates on the data interpretation and measurement correlation methods used to study natural fracture behavior as well as how this behavior affects mechanical tests, which can be very important in the field of geomechanics as well as formation stimulation research.