PE Petroleum cheat sheet

Volumetric OOIP: N = 7758 * A * h * phi * (1 - Swi) / Boi, with A in acres, h in ft of net pay, and Boi in res bbl/STB; 7758 converts acre-ft to bbl.

Radial steady-state oil flow (field units): q = 0.00708 * k * h * (Pe - Pw) / (mu * Bo * [ln(re/rw) + s]), q in STB/day, k in mD, mu in cp.

Pseudosteady state replaces the denominator bracket with [ln(re/rw) - 0.75 + s] and uses average reservoir pressure P-bar instead of Pe.

Skin adds a pressure loss dp = 141.2 * q * mu * B * s / (k * h); s > 0 means damage, s < 0 means stimulation such as fracturing or acidizing.

Gas material balance: plotting p/Z versus cumulative gas produced gives a straight line whose extrapolation to p/Z = 0 gives OGIP for a volumetric, normally-pressured gas reservoir.

Arps decline: exponential q = qiexp(-Dt) (straight line on semilog); hyperbolic q = qi*(1 + bDit)^(-1/b) with 0 < b < 1; harmonic is the special case b = 1.

Volumetric waterflood recovery factor: RF = (1 - Swi - Sor)/(1 - Swi); mobility ratio M = (krw/mu_w)/(kro/mu_o), with M < 1 giving stable, favorable displacement.

Archie: Sw = [(a * Rw)/(phi^m * Rt)]^(1/n); typical clean-sand values are a about 1, m about 2, and n about 2.

Hydrostatic pressure: p (psi) = 0.052 * mud weight (ppg) * TVD (ft); the 0.052 factor converts ppg and feet directly to psi.

ECD/EMW = total bottomhole pressure / (0.052 * TVD); ECD includes annular friction, so it exceeds static mud weight while circulating.

Kill mud weight = current mud weight + SIDPP / (0.052 * TVD); SIDPP plus slow-circulating pressure defines the initial and final circulating kill weights.

MAASP = (fracture gradient - current mud weight) * 0.052 * shoe TVD; it is the maximum casing pressure allowed before the shoe breaks down.

Dogleg severity = 100 * (angle change in degrees) / (course length in ft), expressed in deg/100 ft; high DLS raises torque, drag, casing wear and fatigue.

Annular velocity AV (ft/min) = 24.5 * Q / (Dh^2 - Dp^2), Q in gpm and diameters in inches; AV must exceed cuttings slip velocity for hole cleaning.

Bit hydraulic horsepower HHP = dP_bit * Q / 1714 (psi and gpm); total nozzle flow area is selected to maximize HHP or jet impact force at the bit.

Casing design checks burst (internal pressure), collapse (external hydrostatic) and tension (string weight), with commonly used minimum design factors near 1.1, 1.125 and 1.8.

Vogel IPR: q/qmax = 1 - 0.2*(Pwf/Pr) - 0.8*(Pwf/Pr)^2, applicable to solution-gas-drive wells producing below bubble point.

Productivity index J = q/(Pr - Pwf) in STB/day/psi; for radial flow J = 0.00708kh/(muB[ln(re/rw) - 0.75 + s]).

Separator gas capacity from Souders-Brown: v_max = K*sqrt((rho_liquid - rho_gas)/rho_gas), where K depends on vessel type and mist eliminator.

Separator liquid sizing uses residence time: typically 1-3 minutes for two-phase and 3-5 minutes for three-phase vessels between inlet and weir.

API RP 14E erosional velocity: Ve = C/sqrt(rho_mixture), with C about 100 for continuous service; it caps line velocity to limit erosion.

Gas flow through a choke becomes critical when Pwf/Pup falls below about 0.55; the rate then depends on choke size only, not downstream pressure.

Beam pump displacement PD (bbl/day) = 0.1166 * D^2 * S * N, D and S in inches, N in strokes per minute; actual output is reduced by volumetric efficiency.

Water cut WC = qw/(qw + qo); total liquid rate = qo/(1 - WC), which sizes separators, flowlines and emulsion-treating equipment.