A Comprehensive Approach to Select Fracturing Fluids and Additives for Fracture Treatments
Authors: Xiong Hongjie , Davidson Brian , Saunders Bryan , Holditch Steve A. 
Published: December 2007

Abstract
The paper describes a new approach used to select fracture fluid systems by applying fuzzy logic for fracture treatments. Based on the given formation information, the system first determines base fluid, viscosifying method, and energization method. Secondly, the system chooses the 3 to 5 best combinations of the possible fluids. Then, the system determines polymer type and loading, crosslinker, gas type if necessary, and other additives for the fluid systems. At the same time, the system also checks the compatibility of the fluid and additives with formation fluids and composition.
The fuzzy logic system described in this paper, which is consisted of several fuzzy logic evaluators, can be applied to study, evaluate, and determine the best fluid systems to stimulate oil and gas production or water injectivity in wells.
The approach can be extended to the solution of many other similar problems associated with drilling, completing, and working over wells.

Introduction
Hydraulic fracturing is one of major methods to increase reservoir production. The success or failure of a fracture treatment heavily depends on the fracturing fluids and additives used in the treatment. Choosing the correct fluid and additives is extremely important to ensure that the formation is not damaged, proppant is placed in formation as designed, and the fluid breaks and cleans up properly.
Fracturing fluids are used to create fractures and to transport proppant down the tubular goods, through the perforations, and deep into the fracture. To pump a successful fracture treatment, an ideal fracturing fluid should have the following characteristics.–The fluid should be compatible with the formation and the reservoir fluids.–The fluid should be able to maintain sufficient viscosity at reservoir temperature, so it can suspend proppant and transport it deep into the fracture.–The fluid should be capable of developing the necessary fracture width to accept proppants or to allow deep acid penetration.–The fluid should have low fluid loss properties or high fluid efficiency.–The fluid should be easy to remove from the formation and have minimal damaging effects on both the proppant and the formation.–The fluid should be easily pumped down the wellbore and exhibit minimal friction pressure losses in both the pipe and the fracture.–The fluid should be easy to prepare and safe to use.–The fluid should be low cost.
Currently available fracturing fluids seldom satisfy all of the above requirements. Of these, however, the most important requirements that we have to consider when selecting a fracturing fluid are (1) the ability to maintain sufficient viscosity at reservoir temperature and (2) compatibility with the formation and reservoir fluids.
Fracture fluids can be divided into four groups:water-based fluids,oil-based fluids,foam-based fluids, andalcohol-based fluids.
Table 1 describes these fluid types, and the conditions under which they are most often used.
The selection of optimal fracturing fluids for a formation is based on consideration of the following factors: formation pressure, water sensitivity of the formation, formation temperature, permeability, and the fracture half-length to be created. Laboratory testing and field experience provide important information that must be considered when choosing a fracture fluid.
These decisions are crucial to the success or failure of the stimulation treatment, and require comprehensive data sets, knowledge, and experience.
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