Compartmentalization
Learning objectives
- Read a pressure step across a barrier as evidence of a seal
- Require the step to exceed the gauge noise before calling a seal
- Explain that sealed compartments deplete independently
- Connect compartmentalization to different contacts and reserves risk
One Tank or Many?
The single most valuable thing pressures tell you is whether a reservoir is one connected tank or several sealed compartments. Run the tester through a sealing shale or a fault and the pressure-depth trend steps: the rock above and the rock below carry the same fluid on the same gradient but sit at different pressures. That step is the seal.
The Step Must Beat the Noise
The trap is the gauge. A pressure step proves a seal only when it clearly exceeds the gauge scatter; a three-psi step under three-psi noise proves nothing. Engineers look for a step of many psi, or a step that grows over time as one block is produced and the other is not, before they will draw a barrier on the map.
Why It Decides the Field
Sealed compartments deplete independently. Each empties on its own as it is produced, each can sit on its own fluid contact, and a compartment with no well of its own is never drained at all. Miss a seal and you over-count connected volume and plan a depletion that strands oil; invent one that is not there and you drill a needless well. Few interpretations move more money than the call this pressure step forces.
References
- Dake, L. P. (1978). Fundamentals of Reservoir Engineering. Elsevier.
- Cosentino, L. (2001). Integrated Reservoir Studies. Editions Technip.