Material Balance Functions

Calculates p/z ratio for gas material balance analysis, [psi].

Calculates modified p/z for geopressured reservoirs, [psi]. Accounts for formation/water compressibility.

Estimates OGIP using standard p/z method, [scf]. Assumes volumetric depletion.

Estimates OGIP using modified p/z for geopressured reservoirs, [scf].

Predicts reservoir pressure at given cumulative production, [psi].

Predicts cumulative production at given reservoir pressure, [scf].

Calculates recovery factor for a gas reservoir, [fraction 0-1].

Calculates ultimate recovery factor based on abandonment pressure, [fraction 0-1].

Estimates OOIP from F vs Et (no water influx), [STB]. N = F / Et.

Estimates OOIP using regression on F vs Et data, [STB]. Least-squares through origin.

Estimates OOIP with water influx, [STB]. N = (F - We) / Et.

Estimates N and m from F/Eo vs Eg/Eo regression. Returns [N, m].

Infers water influx from material balance given known OOIP, [RB]. We = F - N*Et.

Calculates normalized MBE residual for quality check, [fraction]. Should be close to 0.

Calculates oil and dissolved gas expansion term (Eo), [RB/STB]. Eo = (Bo-Boi) + (Rsi-Rs)*Bg.

Calculates gas cap expansion term (Eg) for oil reservoirs, [RB/STB]. Eg = Boi*(Bg/Bgi - 1).

Calculates gas expansion for pure gas reservoirs, [RB/scf]. Eg = Bg - Bgi.

Calculates formation/water expansion term (Efw), [RB/STB]. Accounts for rock compaction and connate water expansion.

Calculates total expansion term (Et), [RB/STB]. Et = Eo + m*Eg + Efw.

Calculates two-phase formation volume factor (Bt), [RB/STB]. Bt = Bo + (Rsi-Rs)*Bg.

Calculates underground withdrawal for oil reservoir, [RB]. F = Np*(Bo + (Rp-Rs)*Bg) + Wp*Bw.

Calculates underground withdrawal for gas reservoir, [RB]. F = Gp*Bg + Wp*Bw.

Calculates Depletion Drive Index (DDI), [fraction 0-1]. DDI = N*Eo / F.

Calculates Gas Cap Drive Index (GDI), [fraction 0-1]. GDI = N*m*Eg / F.

Calculates Water Drive Index (WDI), [fraction 0-1]. WDI = We / F.

Calculates Compressibility Drive Index (CDI), [fraction 0-1]. CDI = N*Efw / F.

Calculates all drive indices. Returns [DDI, GDI, WDI, CDI, Sum]. Sum should be ~1.

Calculates effective compressibility for undersaturated oil reservoir, [1/psi].

Calculates effective compressibility for gas reservoir, [1/psi].

Calculates effective compressibility for geopressured reservoir with gas solubility, [1/psi].

Calculates pore volume compressibility term, [1/psi]. cpv = (cw*Swc + cf) / (1 - Swc).

Calculates total system compressibility, [1/psi]. ct = Sg*cg + Sw*cw + cf.

Calculates aquifer pore volume for pot aquifer model, [bbl].

Calculates instantaneous water influx for pot aquifer, [bbl]. We = ct * Wi * deltaP.

Calculates instantaneous water influx rate (Schilthuis), [bbl/day]. qw = C * (pi - p).

Calculates cumulative water influx (Schilthuis) using trapezoidal integration, [bbl]. We = C × ∫(pi − p)dt.

Calculates maximum encroachable water (Fetkovich), [bbl]. Wei = ct * Wi * pi.

Calculates aquifer productivity index for radial flow (Fetkovich), [bbl/day/psi].

Calculates aquifer productivity index for linear flow (Fetkovich), [bbl/day/psi].

Calculates average aquifer pressure (Fetkovich), [psi]. pa = pi * (1 - We/Wei).

Calculates water influx rate (Fetkovich), [bbl/day]. qw = J * (pa - pr).

Calculates initial water volume in aquifer (radial), [bbl].

Calculates dimensionless time for VEH aquifer, [dimensionless]. tD = 0.00634*k*t / (phi*muw*ct*rr^2).

Calculates dimensionless radius for VEH aquifer, [dimensionless]. reD = ra / rr.

Calculates aquifer constant for VEH model, [bbl/psi]. U = 1.119 * phi * ct * h * rr^2 * (theta/360).

Calculates dimensionless influx for infinite aquifer (VEH), [dimensionless]. Uses Edwardson correlation.

Calculates dimensionless influx for finite aquifer (VEH), [dimensionless].