Traditional Decline Curve Analysis
Notation: 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.

Exponential: 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: 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: Hyperbolic decline uses two parameters, Di and b. 
Additional calculations with Exponential References: 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, V1529 V1531. 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. 