Wellbore Storage Calculator
Calculate wellbore storage coefficient (C), dimensionless storage (CD), and duration of storage-dominated flow for pressure transient analysis.
Wellbore & Fluid Properties
Reservoir Properties (for CD & Duration)
Vwb = (π/4) × (ID² - OD²) × depth / 144 × (1/5.615)
C = Vwb × cf | CD = 5.615 C / (2π φ ct h rw²)
tend ≈ (200000 + 12000 S) × C / (kh/μ) hours
Annular Volume
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Wellbore Storage C
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Dimensionless Storage CD
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Duration of Storage Effects
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Additional Results
Annular Area
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Rising Fluid C
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Unit Slope End Time
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How this was calculated
Wellbore volume: Vwb = (pi/4) * (ID^2 - OD^2) * depth / 144 converted to barrels (divide by 5.615).
Compressible storage: C = Vwb * cf (bbl/psi). Applies when the wellbore is filled with a single compressible fluid (below bubble point).
Rising fluid level (changing liquid level): C = Aw / (144 * rho * 0.052) where Aw is the annular area in sq inches and rho is fluid density in ppg. This applies when the fluid level is rising or falling in the annulus.
Dimensionless storage: CD = 5.615 * C / (2 * pi * phi * ct * h * rw^2). Values typically range from 10^2 to 10^5.
Duration of storage effects: tend = (200,000 + 12,000*S) * C / (kh/mu) in hours. This estimates when the unit-slope line ends and radial flow begins on a log-log diagnostic plot.
Assumptions: Single-phase fluid. Constant wellbore geometry. No phase segregation.
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Book a free strategy call →Understanding Wellbore Storage in Well Testing
Wellbore storage is a phenomenon that occurs at the beginning of every well test when the wellbore itself, rather than the reservoir, dominates the flow response. When a well is shut in for a buildup test, the fluid in the wellbore continues to compress (or the fluid level changes), masking the true reservoir response. Understanding and quantifying wellbore storage is essential for accurate pressure transient analysis.
The wellbore storage coefficient C (bbl/psi) quantifies how much fluid the wellbore can store per unit pressure change. For a fluid-filled wellbore below the bubble point, C = Vwb * cf, where Vwb is the wellbore volume and cf is the fluid compressibility. For a well with a rising fluid level (e.g., gas cap above liquid), the storage is governed by the annular area.
The dimensionless wellbore storage coefficient CD allows comparison across different well and reservoir systems. High CD values indicate that wellbore storage will dominate the early-time response for a longer period, potentially masking important near-wellbore features like skin effects or fracture behavior.
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