Skin Factor & Flow Efficiency
Calculate skin factor, flow efficiency, productivity index, and pressure drop due to skin from reservoir and well test parameters.
Steady-State Skin & Flow Efficiency
S = (kh / 141.2qμBo) × (Pr−Pwf) − ln(re/rw) + 0.75
FE = ln(re/rw) / [ln(re/rw) + S]
Results
Skin Factor (S)
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Flow Efficiency (FE)
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Actual PI (STB/d/psi)
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Ideal PI (STB/d/psi)
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ΔPskin (psi)
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Effective Wellbore Radius (ft)
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Damage Ratio
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How this was calculated
Steady-state Darcy radial flow: q = kh(Pr-Pwf) / [141.2*mu*Bo*(ln(re/rw)-0.75+S)]. Rearranged to solve for S.
Buildup test (Horner): S = 1.1513*[(P1hr-Pwf)/m - log(k/(phi*mu*ct*rw^2)) + 3.2275]
Flow Efficiency: FE = ln(re/rw) / [ln(re/rw) + S]. FE=1 means no damage, FE<1 means damage, FE>1 means stimulated.
Pressure drop due to skin: dP_skin = 141.2*q*mu*Bo*S / (k*h)
Effective wellbore radius: rwa = rw * exp(-S). Negative skin (stimulation) gives rwa > rw.
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Book a free strategy call →Understanding Skin Factor and Flow Efficiency
The skin factor (S) quantifies the additional pressure drop near the wellbore caused by formation damage, partial penetration, perforation geometry, or other near-wellbore effects. A positive skin indicates damage (reduced productivity), while negative skin indicates stimulation (enhanced productivity from fracturing or acidizing). A skin of zero represents an ideal, undamaged well.
Flow efficiency (FE) compares actual well productivity to its ideal potential: FE = J_actual / J_ideal. An FE of 0.5 means the well is producing at only 50% of its undamaged capacity, suggesting significant stimulation potential. Values above 1.0 indicate the well has been stimulated beyond its natural capacity (e.g., through hydraulic fracturing).
The pressure drop due to skin (dP_skin) directly translates skin factor into lost production pressure. This value quantifies the economic impact of wellbore damage and helps justify stimulation treatments. The effective wellbore radius (rwa = rw * exp(-S)) provides a physical interpretation of skin.
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