Observations of water-clay reactions in water-sensitive sandstone and mudrocks using an environmental scanning electron microscope

• Published in: Journal of petroleum science & engineering Vol. 10; no. 3; pp. 211 - 222
• Main Authors: Huggett, Jennifer M., Uwins, Philippa J.R.
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier B.V 01.02.1994; Elsevier Science
• Subjects: Applied sciences; Crude oil, natural gas and petroleum products; Drilling fluids; Drilling. Casing. Preparing wells for production; Energy; Exact sciences and technology; Fuels; Prospecting and production of crude oil, natural gas, oil shales and tar sands; Drilling mud; Swelling clay; Scanning electron microscopy; Wettability; Sludge bulking; Smectite; Illite; Sodium chloride
• ISSN: 0920-4105; 1873-4715
• DOI: 10.1016/0920-4105(94)90082-5

The experimental in situ wetting and drying of water-sensitive mudrocks in an environmental scanning electron microscope (ESEM) is described. Fluids used in the tests were freshwater (tap water) and a KCl-based drilling mud. By examining the extent to which illite-smectite and smectite swell when treated with water, it has been possible to assess the importance of clay swelling as a drilling problem in these rocks. Smectite in mudrocks obtained from fresh outcrop (WH10 and WH13) and illite-smectite in sandstone (Sample B of Baker et al., 1992) reacted with fresh water to form a gel-like mass, a process which was only slowly reversed by drying. Less swelling was observed in the mudrocks containing Mg/Ca smectite than in those containing predominantly Na in the interlayer sites. Samples treated with KCl-based drilling mud showed no clay swelling with the exception of the most smectite-rich mudrock (1554). This is attributed to the clay having a residual coating of oil from the original oil-based mud used in drilling. Either a residue of this mud, or the solvents which were used to remove it from the cuttings prior to their being supplied to us may have interacted with the KCl-based drilling mud. The swelling rate for the samples used was pure Na-smectite>interstratified illite-Na smectite>Ca/Mg smectite>interstratified illite-Ca/Mg smectite.