SPEE Monograph 4 establishes recommended best practices for decline curve analysis of unconventional wells through the use of specialized diagnostic plots such as the square-root of time plot. These diagnostic plots are important for flow regime identification and selection of an appropriate b-factor for predicting a well’s EUR. However, in practice, because of familiarity with the Arps decline equation and its ease of use, typically a single b-factor is selected despite multi-fractured horizontal wellbores demonstrating changes in flow regime and consequently the b-factor. This paper introduces the Modified Arps Equation, an iterative formulation of the Arps equation. The Modified Arps Equation maintains use of the form of the original Arps equation with a few modifications to allow for a changing b-factor. These modifications allow a single equation to be used with a vectorized b-factor in order to model a well as it transitions from linear flow to boundary dominated flow and eventually back to pseudo-linear flow. This equation may be applied broadly across unconventionals where wells transition over years from linear flow to boundary dominated flow and later return to pseudo-linear flow as simulation data suggest.
Number of Pages
Anderson, D., Nobakht, M., Moghadam, S., & Mattar, L. F. (SPE Unconventional Gas Conference, Pittsburgh, PA 2010). Analysis of Production Data from Fractured Shale Gas Wells. SPE 131787.
Arps, J. (Houston Meeting, May 1944). Analysis of Decline Curves. SPE 945228-G.
El-Banbi, A. H., & Wattenbarger, R. A. (SPE Gas Technology Symposium in Calgary, Alberta, Canada, 15-18 March 1998.). Analysis of Linear Flow in Gas Well Production. SPE 39972.
Fetkovich, M. (1980). Decline Curve Analysis Using Type Curves. SPE 4629.
Ibrahim, M. S., & Wattenbarger, R. T. (Abu Dhabi International Petroleum Exhibition, November 2006). Analysis of Rate Dependence in Transient Linear Flow in Tight Gas Wells. SPE 100836.
SPEE Monograph 4 - Estimating Ultimate Recovery of Developed Wells in Low-Permeability Reservoirs. (2016). Houston, TX: SPEE.
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