WorldWide Drilling Resource

17 WorldWide Drilling Resource ® APRIL 2014 Drilling Fluid Updates by Ray McLarty Drilling Fluids & Grouts Questions & Answers Publisher’s Note: In the last issue, we inadvertently changed the manufac- turer name for the EXTRAHIGH YIELD™ and TRU-BORE ® products. These are both Wyo-Ben products. Question Local regulators are looking at writ- ing a regulation for driven casing requiring the use of granular bentonite. I remember you wrote an article several years back about a project where they used ben- tonite in some driven wells and none in others, and measured the well seals over a long period of time. I am not sure how they did this, and I don’t know if you still have this information or not. If you do, could you please send me the results of the test study? Answer In the 1980s and 90s, it was my pleasure to work with a gentleman by the name of James Frazee, now retired from the St. Johns Water District in Florida. Jim was interested in anything that would help protect the Florida aquifers from any type of contamination, be it man-made or naturally occurring. Over the years, he and I worked together at sites using bentonite in various forms, as a sealing medium. This includ- ed bentonite pellets, granular bentonite, hole plug, drilling mud, and various types of mixable pumpable bentonite grouts. One of the more unique, as well as questionable sealing methods, was using granular bentonite with driven casing to form a seal between the casing and wall of the hole. The very top of the hole was hallowed out. Bentonite was poured in the hole and would advance with the casing as it was driven into place. There were a lot of skeptics as to how well the bentonite would advance and seal the casing below surface. I include myself in the skeptical group. In 1994, Leigh Haller and Mark Stewart coauthored a paper for the Department of Geology at the University of South Florida Tampa, titled Bentonite, Dye, and Tracer Study . The study in- volved several wells, half of which were constructed regularly using natural for- mation cuttings. The other half were con- structed with the addition of granular bentonite. I am not sure what Jim’s in- volvement was with this study, but he was the one who called it to my atten- tion and sent me a copy of the report which I will be forwarding to you in its entirety. A thumbnail sketch of the 20 plus pages is as follows: Project A total of 12 wells were drilled at three different sites that were consid- ered a representative sampling of the variety of hydrologic conditions encoun- tered in the Southwest Florida Water Management District. Half of the wells were constructed with granular bentonite placed at the surface around the cas- ing as it was driven. The other half allowed the formation with the addition of cuttings to seal the annular space as the casing was driven. Tracer dye was added at the surface and the water was sampled on a regular schedule. Results Sampling of the water table wells indicated the tracer dye moved quickly from the surface to the water table in all wells constructed without the application of granular bentonite. The movement of the tracer dye from surface to the water table took no more than a few days to a few weeks. After eight months, the tracer dye had not reached the water table adjacent to well casing driven with the dry granular bentonite. Conclusion The use of dry granular bentonite when driving casing provided an effec- tive seal to prevent contaminants from reaching the water table through an open annulus. Therefore, the use of granular bentonite is recommended when driving well casing, to prevent contamination from surface and near-surface sources. The statements and comments in this article are my own and are based on information and references believed to be true and factual. If you have a question or comment on this article, or on bentonite drilling muds, polymers, grouts, or additives, please forward them to me in care of WWDR . Ray Ray McLarty may be contacted via e-mail at admin@ worldwidedrillingresource.com 4< /*2'3* "& > > > > ,'< ? /2+ '6* /3+6 /3+6 ')1/3- " " !8=2+ /7843 4* 4* ')1/3- !+8 5)7 !8'3*'6* $'2:+ 9((+6 6':+2 $'2:+ 9((+6 !+'87 9((+6 $'2:+ 37+687 #6+8.'3+ $'2:+ 37+687 $'2:+ !56/3- ! ! $'2:+ 4:+6 '71+8 ? !;/:+2 ')1/3- ? !+6/+7 ? !+6/+7 ? !+6/+7 ? !+6/+7 ? !+6/+7 ? !+6/+7 < /3+6 < /3+6 < /3+6 < /3+6 < /3+6 6/)+7 !9(0+)8 "4 .'3-+ %/8.498 48/)+ !@ @ < < < < <