RTA — Flowing Material Balance
Estimate original oil-in-place (OOIP) and identify flow regimes from production & pressure data. Replaces $20-50K/yr software for screening-level analysis.
Input Data
Est. OOIP (FMB)
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Cumulative Prod.
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Recovery Factor
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FMB Slope
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Flowing Material Balance Plot
q/ΔP vs Np/ΔP — x-intercept = OOIP × ct × ΔP
Normalized Rate vs Material Balance Time
q/ΔP vs tMB — decline trend
Linear Flow Diagnostic: 1/q vs √tMB
Straight line indicates linear (fracture-dominated) flow
How this was calculated
Material Balance Time: tMB = Np / q, where Np = cumulative production (STB), q = instantaneous rate (STB/d).
Normalized Rate: q / ΔP where ΔP = Pi - Pwf. This removes pressure drawdown effects.
FMB Plot: Plot q/ΔP (y) vs Np/ΔP (x). Under boundary-dominated flow this is a straight line. The x-intercept gives Np/ΔP at q=0, from which OOIP = x-intercept / ct.
Linear Flow ID: 1/q vs sqrt(tMB) yields a straight line during linear (fracture) flow, common in tight/unconventional wells.
Assumptions: Single-phase oil, slightly compressible fluid, constant ct, bounded reservoir (for FMB).
Need advanced RTA with type-curve matching, multi-phase flow, or DFIT analysis for your unconventional assets?
Book a free strategy call →Understanding Rate Transient Analysis & Flowing Material Balance
Rate transient analysis (RTA) uses production rate and flowing pressure data to characterize reservoir properties and estimate hydrocarbons in place. Unlike traditional pressure transient analysis that requires shut-in tests, RTA works with readily available production data, making it particularly valuable for unconventional wells where shut-ins are costly.
The flowing material balance (FMB) method, introduced by Mattar and McNeil (1998), transforms production data into a material-balance-like plot. By plotting normalized rate (q/ΔP) against normalized cumulative production (Np/ΔP), boundary-dominated flow data falls on a straight line whose x-intercept yields the contacted hydrocarbon volume. This is mathematically equivalent to the p/Z plot for gas reservoirs but applicable to flowing data without shut-in pressures.
The material balance time concept (tMB = Np/q) was introduced by Blasingame et al. to convert variable-rate production data into an equivalent constant-rate response. When 1/q is plotted against sqrt(tMB), a straight line indicates linear flow, typical of hydraulically fractured tight reservoirs. The transition from linear to boundary-dominated flow provides information about drainage area and fracture geometry.
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