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Abstract: Multi-Phase Flow in Several Layers Limits the Applicability of Conventional Buildup Analysis


Conventional buildup analysis techniques are based on analytical solutions to the diffusivity equation that are subject to certain assumptions. Single-fluid flow in a homogeneous reservoir is the most important of them. However, in actual well tests multi-phase flow in several layers with different properties often occurs.

We showed that using single-layer single-phase analysis for the interpretation of such complex cases could lead to significant errors in average oil permeability and skin calculation. In our study we estimated the degree of error we should expect when conventional techniques are used.

Our work showed that calculated values of average effective oil permeability and skin factor depend on a wide range of parameters, such as contrast in layer properties, production mode, production rate and production time prior to shut-in. Both average oil permeability and skin can be either over- or under-estimated by up to 100% and more. A statistical summary of 283 tests illustrates the results of our study. Overall, simplified techniques should not be used if there is a strong evidence of reservoir layering and the contrast in layer properties is great.


AAPG Search and Discovery Article #90911©2000 AAPG Pacific Section and Western Region Society of Petroleum Engineers, Long Beach, California