reservoir · volumetrics
Pore Volume & Hydrocarbon Pore Volume (PV & HCPV)
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Inputs
acres
ft
fraction
fraction
Description
Computes reservoir pore volume (PV) and hydrocarbon pore volume (HCPV) directly from drainage area, net pay, porosity, and water saturation — the same intermediate steps already embedded inside the OOIP and GIIP volumetric equations, exposed here as a standalone result for use before a fluid formation volume factor is applied (e.g., PVT screening, reserve-in-place comparisons across fluid types, or reporting pore volume independent of Bo/Bg assumptions).
Variables
| Symbol | Unit | Description |
|---|---|---|
| PV | bbl | Pore Volume |
| HCPV | bbl | Hydrocarbon Pore Volume |
| A | acres | Areal extent of the drainage area or reservoir compartment. 259 ha (≈640 acres / 1 section) is a common single-well drainage assumption for unconventional spacing. |
| h | ft | Net (hydrocarbon-bearing, reservoir-quality) pay thickness, after applying porosity/Sw/Vcl cutoffs from the net pay calculation. |
| φ | fraction | Average effective porosity of the net pay interval — typically a thickness-weighted average from log analysis. |
| Sw | fraction | Average water saturation of the net pay interval. (1−Sw) gives the hydrocarbon saturation used in the volumetric calculation. |
Assumptions
- Porosity, Sw, and net pay are representative averages of the drainage area (not just the wellbore)
- Drainage area and net pay are reasonably well constrained by seismic, offset wells, or analogy
- HCPV is reported at reservoir conditions — converting to stock-tank or standard volume requires dividing by Bo or Bg, as in OOIP/GIIP
Limitations
- A single-point volumetric estimate does not capture reservoir heterogeneity — use a distribution (P10/P50/P90) for reserves reporting
- Does not distinguish oil from gas saturation within the hydrocarbon pore volume — for a two-phase (oil+gas) system, HCPV must be split by relative saturation before further use
- Sensitive to the area and net pay estimates, which are often the largest sources of uncertainty early in field life
Use Cases
- → PVT-independent resource screening: Compare hydrocarbon pore volume across prospects before committing to a fluid-specific Bo/Bg assumption, isolating the rock-and-saturation part of the volumetric estimate.
- → OOIP/GIIP cross-check: Verify the HCPV feeding into an OOIP or GIIP calculation independently, or reuse a previously computed HCPV across multiple FVF scenarios without recomputing the geometry.
- → Reserve booking support: Report pore volume and hydrocarbon pore volume as intermediate, auditable quantities alongside OOIP/GIIP in a reserves report.
Related Calculations
Region Notes
Permian Basin
Unconventional spacing units of 1280 ac (DSUs) are common; per-well drainage area is often modeled as 1 section (≈259 ha) or less depending on well spacing within the DSU.
Global
Report HCPV alongside the porosity and saturation cutoffs used to define net pay — HCPV is only as reliable as the net pay interval it's computed over.
References
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