Premiminary tests on modified clays for electrolyte contaminated drilling fluids

The quality of a bentonite suspension declines in aggressive systems like brackish or saline pore water. An engineered clay (HYPER clay) was developed for sealing materials with enhanced resistance to aggressive conditions. The modified clay is produced by treating a sodium activated bentonite with a cellulose polymer following the HYPER clay process method. This study investigates the suitability of the modified clay for electrolyte contaminated drilling fluids. Drilling fluids become contaminated with saline pore water, e.g. pick up an electrolyte contamination, while drilling a formation at for example an estuary or near the coast. Preliminary laboratory tests were performed to study drilling fluid resistance to electrolytes. Therefore the drilling fluids were contaminated with sea water. Subsequently drilling fluid functionality was characterized by its filtration performance, thixotropic behavior, rheology (gel strength, yield point and viscosity) and bleeding behavior. Drilling fluid performance was analyzed at various electrolyte concentrations (7.6, 14 and 28 volume percentage sea water by total volume). Filter press tests (API, 13B-I) showed that the filtration performance improved significantly due to polymer treatment. Moreover, results showed that the rheology properties can be controlled using Xanthan Gum as an additive