Inflow Performance Relationship (IPR) describes a well's inflow rate at various flowing pressures. The conventional IPR assumes stabilized (i.e. boundary dominated) flow conditions. Unconventional reservoirs may take several years to reach stabilization and their performance evaluation involves complex modeling of stimulated reservoir volume (SRV) and requires advanced reservoir engineering knowledge. As a result, some of the traditional IPR concepts and notions are not applicable.

This paper discusses the behaviour of "transient" IPR in comparison to "stabilized" IPR, the meaning of slope and intercept in transient IPR, and the differences between IPR of conventional and unconventional reservoirs. In addition, the effect of production history on transient IPR of a well is examined.

The result of this study is a methodology for generating a "practical" transient IPR for multi-frac'ed horizontal wells. After history-matching the well's performance, the resulting reservoir model is used in a straightforward procedure to obtain the transient IPR in a form similar to the conventional IPR. This means that it can be used with nodal analysis for determining the effect of changing flowing pressure on the inflow rate.

The methodology presented in this paper maintains the simplicity of use of IPRs, yet accounts for unconventional reservoir complications. The "practical" transient IPR can be used directly by the production engineer for optimizing the production performance of a well without the need to get involved in the complexities of reservoir modeling.

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