Experimental Study on Silt Distribution Law at the Front end of Fractures in Volume Fracturing

The role of silt in volume fracturing of tight reservoirs is not yet clear, and so it is with its distribution law at the front end of the fracture. For this reason, a dynamic fluid loss analysis device was used to establish a simulation test method for the distribution of silt sand at the front end of volume fracturing fractures (hereinafter referred as “volume fractures”), and the distribution law and influencing factors of silt were studied on the basis of fracture surface morphology description. It is found by experiments that the sand-carrying fluid was gradually lost in the volume fractures, and the distribution of silt retained at the fracture front end was largely distinct after the fluid loss reached equilibrium. Meanwhile, the pressure in the fractures was gradually elevated and then became stable as the fluid loss continued. The distribution of silt at the front end of fractures can be reasonably characterized by the maximum transport distance and stable pressure. The maximum transport distance increases with widening aperture of the fracture front end, lowering roughness of fracture surfaces, and increasing fracturing fluid viscosity. Small particle size of silt also increases the maximum transport distance. In addition, the stable pressure in the fractures increases as the aperture of fracture front end decreases, the roughness of fracture surfaces increases, the fracturing fluid viscosity increases, and the particle size of silt decreases. The results demonstrate the addition of silt during fracturing can raise the pressure in fractures after plugging their front ends and restrain the fractures from growing too fast in a certain direction, thereby increasing the complexity of the fracture network.