Downhole operating pressure in the context of hydraulic fracturing (also called fracking) is the pressure exerted within the wellbore at a specific depth (downhole) during the fracturing process. Hydraulic fracturing is a technique used to extract oil and natural gas from underground reservoirs, typically in low-permeability formations like shale or tight sandstone. This process involves injecting a high-pressure fluid mixture, usually water, sand (as a proppant), and chemical additives, into the well to create fractures in the rock, allowing hydrocarbons to flow more freely to the surface.
Downhole Operating Pressure (Hydraulic Fracturing) Formula |
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| Symbol | English | Metric |
| \( p_f \) = Downhole Operating Pressure (psi) | \(lbf \;/\; in^2\) | \(Pa\) |
| \( G_f \) = Fracture Gradient | \(ft\) | \(m\) |
| \( D \) = Fracture Elevation Depth | \(ft\) | \(m\) |
Downhole operating pressure is the pressure measured at the depth of the target formation, as opposed to surface pressure, which is measured at the wellhead. It accounts for the hydrostatic pressure of the fluid column, friction losses, and the pressure required to initiate and propagate fractures in the rock. This pressure varies depending on the depth, formation characteristics, and the specifics of the fracturing operation.
The downhole pressure must exceed the formation's fracture gradient (the pressure required to break the rock) but stay below the equipment’s safety limits or the formation’s burst pressure. Typical downhole pressures in hydraulic fracturing can range from 5,000 to 15,000 psi (34.5 to 103.4 MPa) or higher, depending on the depth and geology.
Downhole Operating Pressure (Hydraulic Fracturing) Formula |
||
| Symbol | English | Metric |
| \( G_f \) = Fracture Gradient | \(ft\) | \(m\) |
| \( p_{inj} \) = Injection Pressure | \(lbf \;/\; in^2\) | \(Pa\) |
| \( \Delta p_h \) = Hydrostatic Pressure Change | \(lbf \;/\; in^2\) | \(Pa\) |
| \( \Delta p_f \) = Pressure Loss Sourced by Friction | \(lbf \;/\; in^2\) | \(Pa\) |
| \( \Delta p_p \) = Pressure Loss Sourced by Perforations | \(lbf \;/\; in^2\) | \(Pa\) |
| \( D \) = Fracture Elevation Depth | \(ft\) | \(m\) |
