Proppant transportation in vertical fractures with controlled roughness in different positions

Effective proppant placement is essential to increasing the production of unconventional oil/gas reservoirs. It can substantially affect the fracture roughness. This paper presents a laboratory fracture model to quantify the effect of fracture roughness under well-controlled conditions. This model simulates fracture roughness by embedding particles into the walls. Via this model, the roughness can be well controlled and defined. The effect of fracture roughness location is quantified as an example to demonstrate the usefulness of the controllable fracture model. Using a fracture model with two-sided roughness, the relationships between the roughness location, pump rate, and inlet location were established. The experimental results show that the rough surface in the middle resulted in a large void space in the fracture, which became more evident at a higher pump rate. This phenomenon has unexpected consequences for oil and gas production. Based on these experimental results, different sand injection modes were tested to reduce the void space caused by the surface roughness in the fractured middle. An injection mode that involves alternatively pumping proppants of different sizes was proposed to solve this problem effectively.