Reservoir EngineeringReserves and Recovery
Exponential Decline Time to Economic Limit Formula
Exponential Decline Time to Economic Limit calculates time to economic limit for reserves and recovery workflows in reservoir engineering.
How engineers use this formula
Use this formula when the listed inputs (q_i, q_econ, D_i) are known and the assumptions behind the cited reserves and recovery 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, t_econ equals 2,995.732274 day.
q_iSTB/day
1000
q_econSTB/day
50
D_i1/day
0.001
Inputs
q_i
STB/dayInitial Production Rate
q_econ
STB/dayEconomic Limit Rate
D_i
1/dayNominal Decline Rate
Outputs
t_econ
day
Time to Economic Limit
q_econ
STB/day
Economic Limit Rate
Source and review
reviewedArps, J.J. 1945. Analysis of Decline Curves, Trans. AIME. Exponential decline economic-limit expression.
Source