Abstract
Traditionally, Inflow Performance Relationships (IPRs) are generated using correlations such as Vogel or Fetkovich, which were developed for conventional reservoirs. These methods do not work for unconventional reservoirs. We present a methodology for generating an IPR for unconventional reservoirs. It uses a simulation model of the reservoir and has been applied to transient linear flow, the predominant flow regime of unconventional wells.
The transient linear flow IPR resulted in curves with shapes that are very different from the conventional IPRs. These unexpected shapes were validated using multiple simulators, refined gridding and a semi-analytical method. It was shown that, in certain situations, the flow rate decreases when the flowing pressure is lowered. This counter-intuitive result was shown to be consistent with the physics of multi-phase flow, and is caused by the interplay between the competing opposite effects of drawdown, compressibility and relative permeability.
Transient IPRs are not based on average reservoir pressure, but on specified times. In fact, we propose a triple combo IPR consisting of a set of 3 flow durations (e.g. 30-, 90- and 180-days, or 1-, 3- and 6-months) to replace the conventional IPR (which is based on the average reservoir pressure). The triple combo IPR does for unconventional reservoirs what the traditional (Vogel) IPR does for conventional wells. It maintains the practicality of using IPRs for production engineering in unconventional reservoirs.
The Inflow Performance Relationship (IPR), is a relationship between flow rate and flowing sandface pressure. It is used by production engineers in conjunction with a Tubing Performance Curve (TPC), to determine the deliverability at the wellhead. Conventionally, the IPR reflects Boundary Dominated Flow, in predominantly radial flow geometry. For unconventional wells, because of the extremely low permeability and the unconventional completion (multi-fracture horizontal wells), boundary dominated flow is rarely achieved and the flow is predominantly transient linear flow. There are more complicated flow regimes possible, but this paper focuses only on linear flow, and addresses both transient and boundary dominated flow conditions.
