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Abstract

Water-base drilling fluids containing glycol additives have become established for cost-effective drilling of many reactive shale formations. Existing fluids function most effectively when the glycol is used in conjunction with moderate to high levels of salt; potassium chloride is most commonly used, although this can sometimes be replaced by sodium or calcium chloride or by more expensive acetate or formate salts.

In many onshore locations, discharge of saline drilling wastes poses environmental problems because of contamination of groundwater and soil which may make the water unsuitable for drinking or irrigation and agriculture. In these situations, either expensive pollution control measures or low-salinity drilling fluids are required. Unfortunately, the glycols in common use for shale control do not function well in salt-free or low-salt fluids, so their benefits cannot be fully exploited in these environmentally sensitive areas.

This paper discusses the technical performance and environmental benefits of a new class of glycol inhibitors, specifically designed to provide high levels of shale inhibition in freshwater and low-salinity water-base drilling fluids. Waste disposal implications are considered and inhibitive properties are compared with other currently available fluids.