The problem of designing and analyzing well tests for wells producing from multiple zones through the same production string is often complicated by the interaction between the different layers. Often, measurements of both downhole rates vs. depth in addition to downhole pressure is required so as to ascertain how much rate is coming from each layer in order to analyze the response of each layer separately. A complicating factor comes in if the layers are communicating, which may significantly reduce the accuracy of available analytical methods.

This paper describes new applications of a recently developed integrated single well model (ISWM) that couples equations describing dynamic wellbore flow with ones describing transient reservoir flow. This coupling allows the user to assign production, injection, and shut-in of wells at the surface point, where the valves are physically located, instead of downhole for conventional reservoir simulators. The wellbore flow is handled by use of the Bernoulli equation including friction and kinetic contributions to pressure drop.

Another feature of this model is the use of the full rate equation for gas flow in the reservoir, including the inertial-turbulent (forcheimer) term, in order to handle the rate-dependent skin in addition to mechanical skin at the wells. Reservoir and wellbore equations are solved simultaneously using the fully implicit Newton method.

Applications for this model include determining the dynamic wellbore pressure drop versus time for both single phase oil or gas, and multiphase production and shut-in in vertical and deviated wells, and the resultant change in production rates at the wellbore sandface with time. This feature enables the engineer to simulate the actual flow rate coming from each layer and the resultant reservoir response as measured downhole from a pressure recording tool. The degree to which crossflow affects pressure response can also be measured. Examples describing how one can use the model to better design well tests i n commingled formations are also included.

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