Abstract
Decline curve analysis in unconventional reservoirs is challenging due to the extremely low reservoir flow capacity coupled with the completion techniques and production practices used to achieve economic rates. The primary flow regimes for these wells include transient bilinear flow, transient linear flow, boundary-influenced flow and possibly long-term linear flow. It is commonly believed that the dominant flow regime in unconventional developments will be transient linear flow; however, boundary-influenced flow may be even more important. Classical decline curve analysis techniques are applicable only during the boundary-influenced flow period. Frequently, a hyperbolic form equation is utilized and this practice used by the industry over the entire life of the well results in excessively high decline exponents which can lead to optimistic forecasts of future performance. This technique can be improved for unconventional plays by imposing limits to the final decline. However, current methods to constrain the final decline are based on historical vertical well performance and rules of thumb which introduce a high degree of uncertainty. A number of these plays have now reached a level of maturity that will allow characterization of their long term decline performance. This paper presents a comprehensive technique to analyze production history using a flow regime based workflow to guide classic decline curve analysis. The technique identifies the onset of boundary-influenced flow and thus provides a consistent approach to evaluate late time decline characteristics which will improve the forecast results. In addition to providing guidance for decline curve analysis, the proposed workflow can also be used to evaluate completion efficiency by relating the time to boundary-influenced flow to the stimulated reservoir volume. The practical application of this this technique will be presented using field studies of active unconventional developments.
