Formation damage and the resultant reduction in hydrocarbon production rates due to clay expansion are long-recognized problems (Ohen, 1991). The clay damage may occur during the drilling, completion and production phases of well operations. Often the remediation of clay damage is inadequate, providing only temporary improvements in hydrocarbon production. The prevention of clay expansion presents a challenge; fit-for-purpose chemistries exist, and are a function of clay identity and operational phase of the well.
Two broad subsets of clay damage mechanisms are chemical and mechanical considerations (Bennion, 2002). The focus of this study is to evaluate the minimization of clay hydration by coating clays to prevent chemical or reactive damage. An example of chemically induced formation damage would be clay swelling. On exposure to introduced aqueous fluids, other than interstitial water, sensitive clays will hydrate detrimentally. The end result can be subsequent hydrocarbon flow restrictions due to a decrease in pore space and detrimental formation softening allowing embedment of proppant. Chemical methods of ameliorating clay expandability potential fall into two broad categories: temporary and permanent stabilizers. The temporary clay control additives prevent clay swelling by increasing the ionic strength of treatment fluids, e.g., potassium chloride. Permanent clay stabilizers create a protective sheath around the clay.
The formation of a self-assembled monolayer (SAM), where the chemical covalently bonds to the siliceous formation surface, offers a more robust chemical coating on the clay surface. This coating acts as a chemical shield, which prevents subsequent wellbore fluids from interacting with the formation surface.
A new chemical treatment has been evaluated and, as discussed in this paper, the laboratory test results indicate the application of a hydrophobic coating offers substantial clay protection in water sensitive environments.