Abstract
Formation damage and the associated injectivity loss of wells induced by the produced water re-injection can be often overcome by injecting in the fracturing injection regime. This paper presents an experimental investigation of fracturing mechanisms induced in unconsolidated sand reservoirs under fluid injection using a new radial injection setup. The development of the injection cell is based on a radial injection configuration within a classical triaxial cell to simulate the injection wells conditions and this cell allows the whole specimen to be scanned using X-ray Computed Tomography (X-ray CT). Typical test results exhibit pressure drops during fluid injection corresponding to fracturing of the specimen, and consequently to an increase of the overall permeability. This can be confirmed by the detection of small radial fractures ('pseudo-cracks') around the injection point either by visual observation when disassembling the specimen or by 3D X-ray CT. Fractures appear as localized zones of higher porosity and larger pore size resulting from dilatant shearing and subsequent particles transport. The impact of various parameters (confining pressure, stress ratio coefficient, flow rate, permeability) on the fracturing process in sand specimens is explored. The obtained experimental results suggest that confining pressure is a key parameter controlling fracture initiation.
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