Abstract

A fracture acidizing simulator has been written which incorporates many of the recent advances in fracture geometry and temperature calculations and the acid spending process with the many complex variables which affect acid spending. All the various effects have been coupled to reduce errors and improve simulation. A procedure which should effectively correlate laboratory acid-etched conductivity tests with anticipated field results has also been introduced.

Introduction

The proper design of any stimulation treatment should be based on at least a general understanding of the interactions between the stimulation fluid and the formation. Such designs allow producers to reap the most benefits in terms of production, costs, and treatment success. In a non-acid fracturing treatment the effect of a poor design can be very evident by the column of sand left in the wellbore. Such failures have helped prompt the many advances in fracturing knowledge and treatment simulation. Fracture acidizing lacks this feature of instant embarrassment for a failed treatment design. Many fracture acidizing simulators available have incorporated gross assumptions in modeling the process in attempts to reduce execution time. These assumptions include:

  1. the notion of infinite reactivity,

  2. no heat of reaction,

  3. a single final temperature profile or even a single average temperature,

  4. turbulent mass transfer alone or laminar flow with no convection,

  5. poor conductivity correlations,

  6. an over-simplified or single final geometry,

  7. and almost no coupling of the various factors affecting acid spending rates.

Fortunately, the recent times have caused concern regarding the economic quality of fracture acidizing treatments. Such a scrutiny has demanded better treatment justification and, thereby, better simulators. This paper introduces a simulator that has most of the major rigid assumptions set free to become dynamic variables. The result is a simulator with a highly coupled acid spending process. While the use of default or classical input values is still possible, the improved use of laboratory test data should allow more accurate simulations and improved treatment designs.

GEOMETRY CONSIDERATIONS

Lee and Daneshy offer a method of simulating two dimensional geometry when multiple fluids with changing rheological properties are used in fracturing treatments with proppant. To implement this technique in a computer simulation program, a data base or empirical formula which can relate the changing rheological properties of fluids with time and temperature is required. Lee has simplified this method by allowing each fluid to have constant but different rheological properties and then applied this to acidizing. In the examples discussed in this paper, geometries were determined with this latter method.

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