Proppant transport and distribution within fractures is an important part in hydraulic fracturing. At present, the majority of the experiments and simulations are applied to parallel planar fracture consideration. The transport and distribution of proppant within tortuous fractures and more realistic uneven fracture faces is not yet clear. Thus, it is important to investigate proppant transport and distribution within this type of fracture.
In this study, a 3D numerical solution coupled with Dense Discrete Phase Model (DDPM) is applied to simulate proppant transport and distribution in tortuous and uneven fractures. First, a tortuous fracture model with dimensions of 1.5m (length)×0.3m (height)×0.004m (width) is built. Two different locations of tortuous fracture are firstly studied. Five different size diameters of proppant are used including 0.800mm, 0.739mm, 0.653mm, 0.522mm and 0.425mm. Three cases of slurry (0.1m/s, 0.2m/s, and 0.4m/s) velocity are applied to investigate the effect of tortuous fracture behavior on proppant transport and placement. Then, a hydraulically fractured outcrop core model with the dimensions of 300mm× 300mm×300mm is obtained from a 3D laser scanner. And a realistic uneven fracture can be created, upon which tests can be conducted to explore the impact of fracture unevenness on the proppant transport in more detail.
From the simulation results, near well bore tortuous fractures increase the equilibrium height of the created sand bank and decrease the effective length of the sand bank. The tortuous fracture can apparently decrease the horizontal velocity of proppant and lead to a shorter propped length. A smaller size of proppant can be transported much deeper into the tortuous fracture. Large size proppants may form a sand plug near the fracture inlet when the dimensions of the fracture width and mean proppant diameters are similar. A higher flow rate can reduce the equilibrium height of sand bank in a tortuous fracture which can prevent the formation of a sand plug and also transport proppant deep into the fracture. In the case of the synthesized realistic fracture, an uneven distribution of proppant occurred.
This study provides a new method to understand the impact of tortuous fractures on the proppant transport and distribution behavior. Furthermore, proppant transport and distribution in a synthetic realistic fracture have been investigated which can explain the nonuniformity of proppant distribution and the short propped length in hydraulic fractures.