Bottomhole Pressure
Drilling bottomhole pressure, abbreviated as BHP, also called downhole pressure, is the pressure exerted at the bottom of a wellbore during drilling operations. In drilling engineering it helps to ensure that the pressure in the well is managed correctly to prevent issues like blowouts, formation damage, or wellbore collapse.
For non-flow conditions, the downhole pressure is caused by the hydrostatic pressure exerted by the fluid in the wellbore and surface pressure. For flow conditions, when wellbore fluid is being circulated, it is the sum of the hydrostatic pressure and the friction pressure drop in the annulus.
Bottomhole Pressure Formula
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\( BHP \;=\; SP + HP \) (Bottomhole Pressure) \( SP \;=\; BPH - HP \) \( HP \;=\; BPH - SP \) |
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| Symbol | English | Metric |
| \( BHP \) = Bottomhole Pressure | \(lbf \;/\; in^2\) | \(Pa\) |
| \( SP \) = Surface Pressure | \(lbf \;/\; in^2\) | \(Pa\) |
| \( HP \) = Hydrostatic Pressure | \(lbf \;/\; in^2\) | \(Pa\) |
Factors Influencing Bottomhole Pressure
Hydrostatic Pressure - The pressure exerted by the column of drilling fluid (mud) in the wellbore. It depends on the fluid density and the true vertical depth (TVD) of the well.
Annular Pressure Loss - During the circulation, there will be a pressure loss in the annulus. This pressure loss comes mainly from the friction force that was produced due to the mud circulation, causing frictional pressure loss in the annulus between the drill string and the wellbore walls. This force will generate a back pressure, which will be exerted on the bottom of the well.
Surge and Swab Pressures - These are dynamic pressures caused by the movement of the drill string up or down. Surge pressure occurs when the string is lowered, increasing BHP, while swab pressure occurs when it is raised, decreasing BHP.
Equivalent Circulating Density - The effective density of the drilling fluid when it is circulating, which takes into account both the fluid density and the dynamic effects of circulation.
Importance of Managing BHP
Well Control - Proper BHP management helps in preventing the influx of formation fluids (kicks) into the wellbore, which can lead to blowouts.
Formation Stability - Ensuring that the BHP is within a safe range to prevent collapse or fracturing of the formation.
Efficient Drilling - Optimizing BHP can improve the rate of penetration (ROP) and reduce non-productive time.
Bottomhole Pressure for Dry Gas Well Formula
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| \( BHP \;=\; p_{wh} \; e^{ \;(SG / R ) \; TVD \;/\; \Delta T } \) |
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| Symbol | English | Metric |
| \( BHP \) = Bottomhole Pressure (psi) | \(lbf \;/\; in^2\) | \(Pa\) |
| \( p_{wh} \) = Wellhead Pressure (psi) | \(lbf \;/\; in^2\) | \(Pa\) |
| \( e \) = Euler's Constant | \(2.718281828...\) | \(2.718281828...\) |
| \( SG \) = Specific Gravity of Gas | \(dimensionless\) | \(dimensionless\) |
| \( R \) = Gas Constant (53.36 \(lbf-ft\;/\;lbm-R\) for API standard condition air) | \(lbf - ft\;/\;lbm - R\) | \(J\;/\;kg - K\) |
| \( TVD \) = Well True Vertical Depth | \(ft\) | \(m\) |
| \( \Delta T \) = Average Temperature | \(F\) | \(K\) |
Tags: Drilling