Труды российских конференций

During drilling operations typical clay minerals encountered are smectite, illite, kaolinite, chlorite as well as interstratified clays. Clay hydration is considered as having three mechanisms: external surface hydration, hydration of exchangeable cations and crystalline swelling. Surface hydration of various clays depends on the degree of hydrophilicity which, in turn, is determined by the individual mineralogical and crystallographic features of clay. The other two hydration mechanisms vary from clay to clay due to the strength of their interactions with exchangeable cations, expandability of the crystal lattice, layer charge etc.

The role of hydrophilicity of clays and their surface acidity is considered in this presentation as the most crucial factor of their wetting behavior during drilling operations. It was assumed that it was the hydrophilicity that should be controlled in both non-swelling and swelling clays and shales as a primary factor.

Hydrophilicity may be determined as a specific enthalpy of wetting (Van Oss & Good, 1988). Recent developments in the theory of surface thermodynamics provided a basis for quantitative definition of hydrophilicity and hydrophobicity, in terms of free energy of interfacial interaction between two surfaces in aqueous environment (Van Oss & Giese, 1995). According to (Van Oss, 1994) montmorillonite clays are usually highly hydrophilic, however, the actual hydrophilicity varies depending on the magnitude of layer charge and the nature of exchangeable cation. This is the reason of their high dispersibility in water causing serious complications during drilling operations. Kaolinite clays normally have low hydrophilicity that prevents them from spontaneous dispersion in water.

The theory of surface acidity says that there are Lewis acids and bases on the surface of clay minerals that are transformed into Broensted acids and bases, such as Al(OH)₆^3- and Si(OH)³⁺, as a result of surface hydration (Van Oss, 1994). This enabled us to develop a method of surface modification in order to change the nature and amount of surface active sites of clay similar to (Bondarenko et al., 1986). A new method has been developed to control hydrophilic properties of clay minerals (Pavlova & Wilson, 1999) based on these theories. The method allowed development of highly efficient water-based drilling fluid using silicon-organic liquids. The fluid enabled effective suppression of swelling and dispersion in shale samples in salt-free environment.

Van Oss C. J. and Good R. J, (1988). On the mechanism of “hydrophobic” interactions. Journal of Dispersion Science and Technology, 9, 355-362.

Van Oss C.J. and Giese R.F., (1995). The hydrophilicity and hydrophobicity of clay minerals. Clays and Clay Minerals, 43, 474-477.

Van Oss C. J., (1994). Interfacial Forces in Aqueous Media, Marcel Dekker, New York, 400 pp.

Bondarenko SV, Nazarenko AV, Tarasevich YI. 1986. Liquid phase modification of support for gas chromatography. Ukrainskiy Khimicheskij Zhurnal 52(3), 254-258 (in Russian).

Pavlova L.A. ,Wilson M. J., (1999). Colloid chemical control of kaolinite properties related to ceramic processing. Clays Clay Miner., Vol. 47, No.1, 36-43.