How do you measure bottom hole pressure?
When the well is static, you’re mostly looking at a simple calculation of fluid density and true vertical depth:
BHP (lb/sq in) = Fluid density (lb/gal) x True vertical depth (ft) x 0.052 (conversion factor)
The math changes when you start moving fluid. Once the well is active, BHP becomes a dynamic number because the environment inside your wellbore is constantly shifting. Several key variables affect your pressure reading, and you need to account for all of them to get accurate measurements.
- Fluid Density: The most direct factor is the weight of the fluid column itself, no matter what fluid you’re running. Multiplying the density of that fluid by the well’s true vertical depth creates the baseline hydrostatic pressure. Any change in fluid weight or thermal expansion will immediately change your BHP.
- Friction: As fluid rubs against the walls of the casing or tubing, it creates resistance that reduces the total pressure felt at the bottom. The faster the fluid moves, the more friction and less pressure are generated.
- Backpressure: Any restriction placed on the flow at surface travels straight down the hole. By adjusting a choke or holding backpressure on the wellhead, you’re stacking the extra pressure on top of the fluid column's weight.
- Wellbore Geometry: The physical shape of the well matters just as much as the fluid inside it. A highly deviated or horizontal well has a much longer measured depth than its vertical depth, meaning there’s more pipe surface area creating friction. Changes in tubing size also create bottlenecks that can cause localized pressure spikes or drops.
READ MORE: Oriented perforating strategies and frac plug performance
How is bottom hole pressure data used?
In the field, bottom hole pressure is an essential measurement for keeping the well stable and the production profitable. Here’s how BHP affects operational decisions:
- Maintaining Stability: The most critical use for BHP is staying within the drilling window. You need enough pressure to stay overbalanced against the formation to prevent a kick, but not so much that you exceed the fracture gradient and start losing returns. By monitoring BHP in real time, crews can adjust fluid weights or surface backpressure to keep the wellbore from collapsing.
- Evaluating Performance: Flowing BHP shows engineers how well the reservoir is giving up its oil and gas. By comparing BHP to the static reservoir pressure, they can see if the tubing size is right or if the well is loading up with liquids. This data helps forecast how much the well will produce over its lifetime.
- Refining Completion Designs: BHP data tells you if your artificial lift is doing its job. If the BHP is too high, the pump might not be drawn down enough. If it’s too low, you might be gassing out the pump. Accurate pressure data helps you fine-tune these systems so you can move the maximum amount of fluid for the lowest possible cost.
How does your frac plug affect well performance?
Your frac plug is a mechanical barrier that isolates a section of the wellbore so pressure can build in a targeted interval. As a result, frac plugs control where pressure goes during stimulation. Without isolation, you can’t generate the bottom hole pressure needed to initiate and propagate fractures in the right zone.
Here’s how plug performance influences BHP and production:
1. Pressure placement
A frac plug seals off the lower stages so surface pressure can translate into bottom hole pressure at the active stage. If the plug seals properly, bottom hole pressure builds where intended and fractures initiate in that zone. If the plug leaks, pressure bleeds off below the stage. Without complete isolation, your frac wont perform anything like what you planned.
2. Pressure containment
Multi-stage completions often push high treating pressures to overcome breakdown pressure and extend fracture networks. A properly set frac plug has to hold differential pressure from above, withstand dynamic pressure spikes during pump ramps, and maintain seal integrity under temperature and proppant loading. If the plug slips or fails under pressure, you lose stage isolation and compromise fracture geometry.
READ MORE: What’s making your frac plug fail?
3. Pressure distribution
Bottom hole pressure during a frac stage determines fracture initiation pressure, height growth, and the fracture’s lateral extension, as well as the efficiency of your proppant placement. Poor plug isolation can cause crossflow into previously treated stages, uneven cluster treatment, and reduced fracture complexity.
4. Pressure communication
After drill-out, plug debris and incomplete removal can restrict flow paths. In the case of poorly performing dissolvables, restrictions decrease full wellbore contribution and limit early production rates. Inconsistent mill-out performance can also leave residual restrictions that alter pressure gradients along the lateral.
READ MORE: What copy-paste engineering means for your completion
Your choice of frac plug decides whether perforations treat as designed, whether you achieve the intended bottom hole pressure during stimulation to promote fracture growth, and whether you maximum resource recovery. At Repeat Precision, we engineer PurpleSeal™ frac plugs to provide the zonal isolation needed to achieve your planned bottom hole pressure.
Need a frac plug that seals every time? Contact us and let’s talk about your completions.
