Novel simplified method of well performance calculation in multi-well system is considered. Differences between engineering content of various pressures in multi-well system traditionally denoted by one term "reservoir pressure" are shown. A new terminology to designate these pressures and estimation methods based on production and well test data are proposed.

In practice due to the complexity of well productivity analysis in multi-well system single well is often "extracted" from the environment. The influence of neighboring wells is taken into account by assigning for each well a certain value of reservoir pressure at the certain drainage area. At first glance, this simplification procedure seems so natural that does not require any justification. However, unlike the unambiguous and well-defined single well concept of "reservoir pressure", for wells in multi-well system this approach depends strongly on the context. In order to distinguish the concepts traditionally designated a single term "reservoir pressure" the definition of three types of pressure is introduced. Instantaneous and static reservoir pressures are the local parameters describing well performance subject to interference effects. The average (integral) reservoir pressure characterizes the energy state of the reservoir in whole. For the case of a single well system all these pressures are equal that creates the semantic difficulties in multi-well system consideration.

Reservoir pressures proposed can be used to provide well productivity calculations at different time periods after the change of well operation conditions. Instantaneous reservoir pressure enables to determine production rate changes at the end of transient flow regime and static reservoir pressure gives an estimation of production rate reached at the new steady state regime. The impact of well operation condition changes to the performance of surrounding wells can be also analyzed.

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