Mechanism of Shale Inhibition by Polyols in Water Based Drilling Fluids

Abstract

Polyols (e.g. glycols, glycerols, polyalkylene glycols) are now established as effective shale inhibitors in water-based muds (WBM). These water-soluble compounds are typically used at concentrations between 3 and 10% in WBM and are generally found to reduce wellbore problems associated with reactive shales, increase drilling rates and reduce the environmental impact of the drilling operation. The mechanisms by which these molecules provide shale inhibition are not well understood and the aim of this paper is to provide some insights into these mechanisms. The adsorption of three polyols on to a swelling clay mineral (montmorillonite) was studied. The adsorption experiments were carried out from distilled water and from potassium chloride solutions. The resulting clay complexes were characterised by X-ray diffraction and infra-red spectroscopy techniques. Shale inhibition measurements were also made and the results correlated with the adsorption of the polyols. The polyols are shown to be strongly adsorbed by the clay. During the adsorption process, water is displaced from the clay surface and ordered structures of polyol are formed. The nature of these structures and their stability in aqueous fluids is strongly controlled by the presence or absence of potassium cations:Under most conditions, a single polyol layer forms on the clay in the presence of potassium and the resulting complexes are stable in water.A complex containing 2 polyol layers is formed when potassium is absent. This complex is less stable in water. The interaction between potassium ions and polyols at the clay surface is proposed as the critical factor in the provision of shale inhibition. This interaction appears to account for all the observed inhibition in the case of two of the polyols studied. For a 3rd polyol, an additional (minor) contribution may come from interactions between polyol molecules at the clay surface. The selection of the most appropriate polyol for inhibitive muds is discussed. This is a complex issue that must consider cost and environmental acceptability as well as technical performance.

Partially hydrophobized hyperbranched polyglycerols as non-ionic reactive shale inhibitors for water-based drilling fluids

“…It can be observed that, in all cases, the inhibition efficiency increases with the polymer concentration. In aqueous medium, the synthesized polymer structures show a relatively good performance as inhibitors, but the performance is much better in the presence of KCl, probably due to the formation of a complex between the polymers and K + , favoring the polymer interaction with the negatively charged clay layer, as reported previously in the literature for polyglycols and polyols, also non-ionic polymers (Bland et al, 1995;Reid and Dolan, 1995). The results also indicate that the partially Fig.…”

“…The literature also suggests the formation of a stable complex between exchangeable potassium ions on the clay surface and the non-terminal portions of the adsorbed polyol molecules. This leads to the removal of the water molecules and to an increase of the amount of adsorbed polymer for the structures without free hydroxyl groups (Reid and Dolan, 1995).…”

Hyperbranched polyglycerols, obtained from environmentally benign monomer, as reactive clays inhibitors for water‐based drilling fluids

“…5,6 Glycols, poly(ethylene glycol) (PEG), glycerols, and polyglycerol derivatives, also called polyols, have been used as additives in WBFs and are normally employed in conjunction with KCl to reduce clay swelling and dispersion of drilled cuttings. 7 Another common drilling fluid inhibitor is the poly (diallyldimethylammonium chloride) (PDADMAC). Due to its cationic structure, it is very effective to avoid clay swelling, but unfortunately it is also very toxic.…”

How do Anions in Water-Based Muds Affect Shale Stability?

“…In spite of some successes, recently a few questions have been raised on the potassium chloride role in some wellbore failures (shale matrix shrinking 10 , mineralogical transformations 11 , kaolinite hydration/ swelling 12 ) demanding for more work on the topic. Soluble glycols [13][14][15] has been also proposed to control shale hydration, even with modified chemical structure to be used without potassium chloride 16 .…”