Decline Analysis

Related Topics

Decline analysis is a reservoir engineering empirical technique that extrapolates trends in production data from oil & gas wells. The technique is most reliable for wells producing at high drawdown against relatively constant flowing pressures, such that the production rate decline mirrors the decline in reservoir pressure. Because of this tie to reservoir pressure, most practitioners restricted its use to the boundary-dominated flow period. However, development of tight and unconventional reservoirs has extended its usage in the transient flow period, necessitating the development of alternative techniques that generally attempt to match the transient and boundary-dominated flow periods using separate parameters.

The purpose of a decline analysis is to generate a forecast of future production rates and to determine the expected ultimate recovery (EUR) of reserves. Performing a decline analysis requires production rate or volume information for a well — as such, it is best conducted after a consistent production trend has been established.

Harmony provides the following types of decline analysis:

• Traditional Decline — generates a forecast of future production rates based on the equations defined by Arps. The traditional decline analysis can also be modified to a Terminal / Limiting Decline Rate. For information on these calculations, see Terminal Decline Calculation Methods.
• Stretched Exponential Decline — a variation of the traditional Arps method, but is better suited to unconventional reservoirs due to its bounded nature.

If well performance data warrants a modification of the decline curve, see Using Segments.

• Duong Decline — an empirical method developed specifically for low permeability systems exhibiting long periods of transient flow.
• Multi-Segment Decline — generates a three-segment Arps decline where each segment can be used to capture distinct flow regimes, including transient flow (b > 1), boundary-dominated flow (0 < b < = 1), and exponential decline (b = 0). This method is well-suited for unconventional reservoirs that exhibit multiple flow regimes.

Note:   The decline analysis is available with an IHS DeclinePlus license.