Abstract

The emphasis on providing protection to sensitive clays in a variety of reservoir types has led to the development and application of specific chemistries. These range from monovalent to polyvalent salts and more recently, to polymer based systems. In numerous published (bases exotic interaction studies have been performed to evaluate the potential effectiveness of these clay protection additives.

The need for a simple standard screening technique to allow comparative testing and ultimately specific designs for clay additive usage is obvious. This technique will illustrate the significance of clay species interaction with clay stabilizing fluids and point to any harmful side effects on reservoir permeability that may be caused by the clay stabilizer.

The study presents a simple procedure for indexing clay stabilizing additives in order to insure-that the most effective one is chosen and implemented as a "specific" agent to control a "specific" clay situation. Use of a packed column in addition to berea core allows the designer to vary the type and amount of clay in the column in order to simulate the clay content of the formation in question.

Factors affecting the performance of clay stabilizers will be prioritized. They include compatibility with other additives, permeability damage, and ability to prevent clay migration in a packed column.

An attempt will be made to document results with respect to clay chemical/clay species interaction. This will be done before and after permeability flow tests using scanning electron microscopy.

The evaluation of stabilizers examined in this study will be documented by indexing each chemical. This index will be shown to be a useful tool in differentiating among the numerous clay stabilizers available in the market today.

Introduction

Many sandstone formations contain significant amounts of materials detrimental to the success of hydraulic fracturing treatments. These materials are mixtures of clays, clay minerals, silica fines and other fines. Upon contact with an alien fluid, these materials will tend to swell and/or migrate. This often results in reduced permeability within the pore spaces of the formation. The more common types of migrating and non-swelling clays are illite and kaolinite. Montmorillonite is the most common swelling clay.

Large agglomerations of clay particles usually won't be picked up and transported by moving fluids. Less tightly bound or smaller aggregations may be moved and eventually lodged in a pore throat. This tends to restrict fluid flow to the well bore, and to reduce or stop production of oil and gas.

The sensitivity of a formation is dependent upon the permeability of that formation as well as upon the content of these clay-type particles. A tight formation may be more affected by migrating particles than by swelling particles. A formation with high permeability will be more difficult to bridge with migrating fines and may be more susceptible to damage by swelling clays. Of course a formation may be damaged by a combination of migrating and swelling clays.

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