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Reservoir EngineeringMaterial Balance and Production

Oil in Place in Saturated Oil Reservoirs Formula

N=NpBo+(GpNpRs)BgBoBoi+(RsiRs)BgN=\frac{N_pB_o+(G_p-N_pR_s)B_g}{B_o-B_{oi}+(R_{si}-R_s)B_g}

Oil in Place in Saturated Oil Reservoirs calculates oil in place for material balance and production workflows in reservoir engineering.

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How engineers use this formula

Use this formula when the listed inputs (N_p, B_o, G_p, R_s, B_g, B_oi, R_si) are known and the assumptions behind the cited material balance and production relationship match the engineering case being checked.

Assumptions

  • Input values are representative for the well, reservoir, fluid, or equipment case being evaluated.
  • The declared units match the field-unit constants used in the formula.
  • The cited formula applies to the selected petroleum engineering workflow.

Limitations

  • The calculation does not replace a full engineering model or operating procedure.
  • Accuracy depends on the source correlation, assumptions, input quality, and unit consistency.

Common mistakes

  • Mixing unit systems without converting the inputs.
  • Using default example values as field recommendations.
  • Applying the formula outside the source assumptions.

Default example

Using the default inputs, N equals 384,210.526316 STB.

N_pSTB

100000

B_obbl/STB

1.15

G_pSCF

100000000

R_sSCF/STB

500

B_gbbl/SCF

0.005

B_oibbl/STB

1.2

R_siSCF/STB

700

Inputs

N_p

STB

Cumulative Oil Production

B_o

bbl/STB

Oil Formation Volume Factor

G_p

SCF

Cumulative Gas Production

R_s

SCF/STB

Current Gas Solubility

B_g

bbl/SCF

Gas Formation Volume Factor

B_oi

bbl/STB

Initial Oil Formation Volume Factor

R_si

SCF/STB

Initial Gas Solubility

Outputs

N

STB

Oil in Place

G_p

SCF

Cumulative Gas Production

N_p

STB

Cumulative Oil Production

Source and review

reviewed

Advanced Reservoir Engineering, Ahmed, T., McKinney, P. D. (2005)

Ahmed, T. and McKinney, P. D. 2005. Advanced Reservoir Engineering, Gulf Publishing of Elsevier, Chapter 5, Page 334.

Source

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