Decline Curve Analysis Examples

2.1 Decline Curve Analysis
Decline curve is the most widely used method of data analysis. It is applied in the evaluation of gas reserves and prediction of future production. The technique is dependent on the assumption of earlier production trends with their controlling factors that would continue in the future. Furthermore, the curve represents the decline in production rate of either oil or gas versus time. Rate-cumulative plot is known as another technique, which is the production rate plotted with cumulative oil or gas. In other words it is defined as reduction of production rate as the time of production increases. However, the production of a well would stop, if the oil production rate is to be dropped to the economic limit. The economic

Before analyzing the production decline-curves with any level of dependability, several conditions should be prevailed. For example, the production should be remained at a constant wellhead pressure or unchanging choke size, and the pumping well should be produced with a stable fluid level. These would prove that the production is at ability controlled under a certain set of condition. The observed decline of production is suppose to be a reflecting the reservoir productivity, and it should not be a outcome of any external causes like well damage, equipment failure, or change in production condition.

2. Extrapolation of decline curves with any degree of dependability should be performed after the stable reservoir conditions are succeeded. This type of condition would normally be met when the production method is not changed. However, in case of any taken action toward the improvement of gas recovery, as fracturing, acidizing, infill drilling, or fluid injection, the decline-curve would be used to predict the performing well or reservoir in the absence of the alteration and then could be compared the real performance with the change occurring. The result of the comparison would allow others to determine the technical and commercial success of their

They used modified time function for analysis of single-phase liquid or gas wells performance. One of the weaknesses of their method is that despite of the underestimation or overestimation of reserves that results when the method is applied, it completely neglects the data of flowing pressure. Moreover, it also neglects the changing production situation and therefore is not able to always produce reliable evaluations of recoverable hydrocarbons. Moreover, the gas reserves are usually underestimated due to the varying gas properties that are not