The Securities & Exchange Commission requires that ‘reliable technology’ be used to estimate reserves, but no method can truly be considered reliable when the data does not yet exist to validate it. This is the case for shale wells with modern completions and limited production history, which is exacerbated in newer shale plays, such as the Vaca Muerta. In order to achieve reliability from our reserves evaluation methodology, the authors suggest that a multi-faceted approach is required.

Although Rate Transient Analysis (RTA) has been previously introduced as a reserves evaluation technique, it has not become mainstream, primarily because it is more cumbersome than rate-time decline curve analysis (DCA). Nevertheless, in the presence of valid supporting data, RTA is certainly defensible. In comparison to DCA, RTA captures more performance behavior elements of unconventional reservoirs through physics-based reservoir modeling. It can accommodate changes to the reservoir, well and fracture properties, while also accounting for differences in operational practices (e.g. draw-down controlled wells).

In this study, wells with truncated production datasets in the Vaca Muerta are evaluated and forecasted, using two fundamentally different approaches-

RTA workflow- which focuses on detailed modeling of the underlying physics of fluid flow with the end objective of individual well forecasts under prescribed constraints and

Standard reserve evaluator workflow– which focuses on delivering a repeatable and scalable forecasting methodology whose reliability is measured in the aggregate, rather than by individual well samples. The evaluations are validated by comparing short-term well forecasts against the withheld well production, in a blind experiment. Our results show that RTA provides useful insight into what drives production, but does not always result in a better forecast. The results also demonstrate that RTA provides an excellent complement to the standard evaluator workflow when data is both limited and sparse – helping to understand the potential impact of recovery on future field development considerations (well spacing) as well as individual well operating conditions.