Interpretation of well tests in acute fracture-wellbore systems

Aydin, Adnan (1994) Interpretation of well tests in acute fracture-wellbore systems. Doctoral (PhD) thesis, Memorial University of Newfoundland.

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Abstract

The problem of well test Interpretation in acute systems has been investigated both theoretically and experimentally. This investigation : a) establishes a basic understanding of the near wellbore flow mechanism in acute systems; b) formalizes the intersection angle-dependent variations in the streamline pattern and hence in pressure distribution and observed response; and c) provides mathematical tools to predict these variations. -- The theoretical component of this study involves: a) the derivation, for acute systems, of the governing differential equation of flow in fractures; b) the introduction of analytical models for constant-flux tests under transient and steady-state conditions; c) the formulation of the streamline-equipotential network created by injection/pumping through acute systems under initially non-uniform heads; and d) the development of a general, semi-analytical model accounting for the roughness, turbulence and intersection effects in interpreting single-well, constant-flux tests. -- The experimental investigation is intended: a) to verify the formation of the idealized streamline pattern and examine the effects of likely interactions at the acute intersections, particularly during injection tests; and b) to quantify the exit/entry loss coefficients as a function of the intersection angle. The experimental set-up designed to carry out this investigation includes three distinct fracture-wellbore system models with 90°, 20° and 10° intersection angles. The laboratory programme involved testing these models for three different apertures under steady, constant-flux, injection and pumping conditions. The overall experimental set-up successfully simulated the conceptual testing environment which the mathematical model is expected to reproduce. -- The pumping pressure distribution observed in the acute system model tests is in good agreement with the predictions whereas the injection pressure distribution at large intersection angles proves to be directionally variable. Although the latter poses a theoretical limitation, the mathematical models, in practice, are equally capable of interpreting single-well. Injection as well as pumping test data, and are valid for the design of the wellbore activities.

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