Exponential Decline

The Decline Curve analysis of the oil and gas wells model examines the production forecasting for oil and gas wells, i.e., the exponential decline curve. The standard equation, q = qie-at (3.3), can be used with random variables for both qi (the initial production rate, sometimes called IP) and a (the constant decline rate). Here the model has an additional parameter, t (time), which makes the output (Rate, STB/YR) more complicated than the volumetric reserves output. The distributions of numbers for output and forecasts or graphs are needed. The worksheet has two input cells, IP and Decline, and a column of outputs for the Rate of production in STB/YR over 15 years. After the simulation, a summary graph is generated. This graph shows uncertainty over the 15 years. Two colors signify 1) the 5th and 95th percentiles and 2) the 25th and 75th percentiles, thus representing a 90% confidence interval.