Material Balance
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Material Balance - Concepts

Vol. produced = Expansion of oil & dissolved gas + expansion of gas cap + water influx + expansion of connate water and reduction of pore volume
F/(E_o+E_fw) = N + W_eB_w/(E_o+E_fw)

F = vol. produced
E_o = expansion of oil & dissolved gas
Esub>fw = expansion of formation wtr and PV reduction
W_e = water influx
N = OOIP

Relevance & Model selected

Importance in reservoir characterization

identify drive mechanism
confirm reservoir volumetric
aquifer fitting

Bottom water drive - above bubble point

water influx - Carter Tracy Aquifer model
simplified eq. - F/E = N + W_e/E

E = E_o+E_fw
B_w = 1

Tabular Inputs – left side

Inputs - time versus

N_p, W_p, P_ravg(res.) - user defined
B_o = B_oi(1 + c P)
E = B_oi*c_eff* P
F = N_pB_o + W_p
F/E

Eq. - F/E = N + W_e/E
B_o, B_oi - from PVT module

Tabular calculations – right side

Inputs - time versus

tD = 0.00634*K*t/(** c * r_o²)
P(t_D) = f(t_D)
P’(t_D) - calculate
We = f(U, P, P’(t_D), P(t_D) ,t_D)

U = aquifer constant = 1.119fhcr_o²
f = fractional encroachment angle
W_e = cumulative water influx

W_e/E– calculate

Eq. - F/E = N + W_e/E
, c - from PVT module

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This page updated October 2002
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