Abstract

Depending on the type of fracture propagation regime when the injection stops, the closure of the fracture may occur exactly after the injection ceases, in the case where the fracturing process is dominated by fracture energy, or the fracture propagate for a while due to the elastic energy stored in the rock, when fluid viscous dissipation dominates. In any cases, fluid losses in the surrounding porous media ultimately stops fracture growth and the fracture closes (on the proppant pack in practice). Some recent theoretical solutions have been reported for the recession and closure of a hydraulic fracture in the absence of proppant. These solutions are relevant in the context of micro hydraulic fracturing tests for in-situ stress determination. In this work, we report a laboratory hydraulic fracture experiments performed in sandstones with the aim to study experimentally fracture closure. In our experimental set-up, an extensive passive acoustic monitoring is performed and provide un-precedented spatio-temporal evolution of fracture development and closure.

Introduction and Motivation

Hydraulic fracturing is one of the methods for stimulating oil and gas wells. In this method, high-pressure fluid injection causes tensile fractures, which leads to an increase in rock permeability and conductivity, and as a result, increases oil and gas production (Madyarova and Detournay, 2003).

Investigating the behavior of fracture propagation in hydraulic fracturing operations is one of the topics that researchers are working on. Fracture propagation in rocks follows different regimes. When the energy is dissipated to overcome the toughness of the rock to form new fracture surfaces, the regime is toughness dominated and when the energy is dissipated in the flow of viscous fluid in the fracture, it is viscosity dominated (Lecampion et al, 2017). In addition, when this fracture is created in permeable and porous rocks, in which there is fluid loss into the rock, these regimes are converted to toughness-leak off dominated and viscosity-leak off dominated regimes respectively (Detournay, 2016).

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