A Fluid Selection Expert System for Matrix Treatments
Authors: Chavanne Christophe , Perthuis H.G. 
Published: December 2007

Abstract
This paper presents an expert system-based tool used in the matrix treatment area to determine the sequence of fluids to pump. The reasoning is performed in two steps and is based on chemical rules. Multiple solutions which are ranked are provided, along with dynamic explanations. Corresponding generic chemical descriptions and proprietary products occurs in the final mapping phase, which also ensures product compatibility. The software has been tested by compassing the conformity of the predicted sequence of fluids against actual expert designs.

Introduction
To increase the production of damaged wells, matrix treatments are performed. Matrix treatments consist of injecting chemicals into the formation below fracturing pressure in order to remove or bypass the damage. Determining the proper fluid sequence is a difficult task reserved for experts in acidizing. This is difficult because it involves numerous chemical rules for selecting fluids and adjusting their concentrations according to well, damage and formation data and because this process requires a thorough knowledge of products to avoid incompatibilities. In the past, Cram and Hendrickson have studied the feasibility of applying an expert system to matrix treatments with different commercial shells. Matteini et al. have developed an expert system for context evaluation which includes economical and operational constraints. Damage diagnosis was attempted also by Trussell et al., with only generic treatments. Only Blackburn et al. have developed an expert system able to provide a customized matrix treatment design with chemical description. We have developed a software program using an expert system that assists the user in determining different fluid sequences appropriate to a problem. The fluid sequences are ranked by efficiency and include dynamic chemical explanations. Chemical concentrations are indicated, generic chemicals are mapped into products and compatibility between final products is checked. This module presents qualitative information about the nature of the selected fluids and their concentrations, but does not calculate the volume to inject or the flow rate. No recommendation for placement is currently available. Nevertheless, the outputs of the software can be transferred to other modules for complementary calculations.

Statement of the Problem and Definitions

What is a fluid sequence ?
Fig. 1 is an example of a fluid sequence as it is used in the field. It lists a series of stages (or steps) containing fluids that have to be injected sequentially into the formation. Each stage has a name corresponding to a specific purpose as explained in Table 1.
Fig. 2 shows the same fluid sequence now expressed in terms of chemical species, replacing the coded products with their chemical composition. The transformation of the chemical form into product form is relatively straightforward. A fluid database is browsed to select the appropriate products. This task, called "mapping", will be detailed in a following section. Each elementary component of a fluid sequence is selected for chemical reasons. Depending on the role the fluid is to perform in the stage, the chemical is categorized as detailed in Table 2.
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