Effect of Natural Fracture Characteristics on Proppant Transport and Placement in an Irregular, Nonplanar Fracture

Hydraulic fracturing is recognized as the primary stimulating technique to enhance recovery in unconventional reservoirs. Connecting natural fractures and filling proppant are crucial elements to achieve the effective development of the reservoirs. Many studies have investigated the interaction characteristics between hydraulic fracture and natural fracture and proppant transport in complex fracture systems. However, few studies show how natural fracture affects proppant migration and placement. In this work, we experimentally explore proppant transport in an irregular, nonplanar fracture containing hydraulic fractures and a natural fracture. The objective is to identify the influence of natural fractures on proppant transport and placement. In this paper, proppant transport in a nonplanar fracture with bends is studied experimentally by a laboratory size slot, and the bending section represents a natural fracture. A high--resolution particle image velocimetry (PIV) system is used to detect the instantaneous velocity field in the complex pathway to understand particle transport behaviors. Proppant placement is quantitatively evaluated by the proppant coverage area as the proppant bed reaches the equilibrium state. Also, the effects of natural fracture width and height, intersection angle with hydraulic fracture, and relative location with the inlet on proppant placement are investigated. The results identify that the natural fracture would significantly increase the complexity of proppant transport and lead to a discontinuous and irregular proppant bed in the complex fracture. The vorticity flow appears around the bend and resuspends deposited proppants through the bending section. The small natural fracture width and height increase flow erosion and are not conducive to proppant settlement, resulting in no proppant. The more the bending angle, the lower the coverage area and bed height. When the natural fracture is close to the inlet, a depleted region without proppants would be formed around the wellbore. The multiple linear regression method developed two reliable models expressed by four normalized parameters to predict the bed coverage areas. The experimental results and laws provide ways to quantitatively analyze natural fracture characteristics' effect on proppant transport and placement in unconventional reservoirs and fissured formations.