Proppant transport and placement simulation in bedding opening of coal seams

ABSTRACT: "Horizontal well + hydraulic fracturing" technology is an important technology for coal seam production enhancement and reforming. The transportation and placement of proppant in hydraulic fractures and bedding play a crucial role in hydraulic fracturing of coal seams. Existing fracture models are usually for vertical seam networks, and fewer studies have been conducted under bedding open conditions. In this study, the Eulerian-Eulerian method was applied to establish a numerical model of proppant transport and to verify the validity of its model in comparison. The study was carried out in terms of the effects of laminar opening, distance of laminar compared to hydraulic fracture bottom (HLB), and shot hole location on proppant transport and placement, respectively. The study showed that proppant placement in fracture-layering showed significant differences compared to vertical fracturing. The proppant transportation in fracture-layers is divided into bottom sand sinking stage, layer limiting stage, and layer filling stage. The proppant placement area in the main hydraulic fracture increased with the decrease of bedding opening, but too small bedding opening also increased the risk of sand plugging. Compared with the vertical single bedding, the maximum reduction of the characteristic length of the stabilized sand dike under the condition of bedding opening is 36.69%, and the maximum reduction of the characteristic area is 55.33%; the smaller the HLB is, the smaller the placement area of the stabilized sand dike in the hydraulic main fracture is, and the proppant in the bedding mostly exists in the form of suspended sand; the higher the injection location the higher the height of the sand dike inlet is, but the main body of the sand dike will not be higher than the HLB. This study provides theoretical guidance for the construction design under the presence of bedding-opening conditions in hydraulic fracturing of coal seams.