Proppant Selection
After the pumping process has been completed and the fracture created, it must now be held open. This requires the proppant, it will physically hold or prop the fracture open thus promoting the flow. The most important characteristic of the proppant is its ability to withstand compressive forces, thus its compressive strength is very important.
Typically the proppant is selected on the basis of in-situ stress. This is where knowledge of the geology and the geophysical characteristics of the formation come into play.
With fluid flow, typically, the larger the orifice the greater the flow, so to with fractures, a larger fracture would promote better flow. Now the proppant needs to be larger thus a large proppant would help to promote greater flow. However we must again consider the physical properties of the formation, can it or did it fracture to a degree that would allow the admittance of larger proppant. So ultimately the size of the fracture determines the size of the proppant, which in turn would determine the permeability.
Treatment Pressure
The maximum pressure that will be applied during the job would be applied to induce formation breakdown. This pressure is what will produce and help to propagate the fracture. Topside the pumps will be used to generate the pressures needed to increase the bottom hole pressure to the desired value.
The treatment pressure will take into consideration the formation breakdown pressure, which would be obtained from either geo-mechanical studies, or drilling or logging data or a combination of all those. The fluid characteristics in the well-bore, must be accounted for, this would provide the information about the hydro-static pressure drop, as well as the frictional pressure drop. These 3 pressure points help determine the the pressure the surface pumps would need to apply.
