Traditional Decline Curve Analysis
qi = Initial rate, q(t) = rate at time t, Q(t) = Cumulative Production, Di = decline rate, b = used in hyperbolic decline, b = 1 for harmonic. Keep units consistent. Decline rate is not annual decline, but used as a parameter in the equation.
The plots on the left side are based on a common 15 year rate for all three methods. (Ref 1, page 215)
DCA is applicable when the plot of rate vs. log(time) has a constant slope, Di. Plot of rate vs. cum oil, also has a straight line.
The exponential model is:
Harmonic decline is a special case of the hyperbolic curve for b = 1. The slope of ln(q) vs cumulative production plot is equal to or on log base 10, the slope is:
Hyperbolic decline uses two parameters, Di and b.
Additional calculations with Exponential
1. Lee, J. and Wattenbarger, R.A.,Gas Reservoir Engineering, pages 215- 219.
2. Harrell, R. and Cronquist, C, Estimation of Primary Reserves of Crude Oil, Natural Gas and Gas Condensate, Petroleum Engineering Handbook, 2007, V-1529- V-1531.
3. Bradley, H., Estimation of Oil and Gas Reserves, Petroleum Engineering Handbook (H. Bradley, Ed), 1987.
4. Cronquist, C, Estimation and Classification of Crude Oil, Natural Gas and Condensate, 2001.