As injection of frac fluid continues, the fracture tends to grow in width as fluid pressure in fracture, exerted on the fracture face, works against the elasticity of the rock material. After sufficient frac fluid “pad”has been injected to open the fracture wide enough to accept proppant, sand is added to the frac fluid and is carried into the fracture to hold it open after the job.
A vertical fracture groes in length upward, downward and outward. The growth upward or downword may be stopped by a barrier formation; downward growth may also be stopped by fallout of sand to the bottom of the fracture. The growth outward away from the wellbore ( as well as upward or downward) will be stopped when the rate of frac fluid leakoff through the face of the fracture into the formation equals the rate of fluid injection into the fracture at the wellbore.
When sufficient sand has been injected, the pumps are shut down, the pressure in the fracture drops, and the earth compressive stress closes the fracture on the proppant.