Numerical study of supercritical CO2 and proppant transport in different geometrical fractures

Supercritical CO2 (SC-CO2) fracturing, as a kind of waterless fracturing method, is an effective treatment in the unconventional oil and gas industry. Due to its characteristic lower viscosity, supercritical CO2 fracturing is likely to create thin and long fractures that connect pre-existing natural fractures and generate complex fractures. It is therefore very challenging to predict how far supercritical CO2 carrying proppant can go and how proppant will be transported in natural fractures, when natural fractures are contacted or penetrated by induced fractures. In this paper, proppant transport with supercritical CO2 in fractures was analyzed using the computational fluid dynamics method. Three types of fractures - planar fractures, T-shape fractures and crossing-shape fractures - were modeled. Five parametrical cases were studied using the T-shape and crossing-shape models. Results show that, for T-shape fracture cases, a turbulent flow regime might develop at a fracture junction, which can make proppant propagate to natural fractures. For crossing-shape fractures, a turbulent flow takes place behind the fracture junction, which causes a little sand dune to form downstream of the induced fracture. With the reduction in the width of the natural fracture, the height of the sand bank at the thinner natural fracture is higher than that at the wider natural fracture. Using a proppant whose density and diameter are respectively less than 1540 kg/m(3) and 0.25 mm, as well as a sand-carrying fluid whose sand ratio ranges from 8% to 10% and injection rate exceeds 2 kg/s, is beneficial to prop natural fractures. Moreover, the larger the intersection angle of the crossing-shape fracture is, the more difficult it is for proppant to enter natural fractures. This study reveals the influence of fracture geometry on proppant transport with SC-CO2. (c) 2018 Society of Chemical Industry and John Wiley & Sons, Ltd.