Advanced planning on these types of wells is vitally important.
By Gary Shawver, MGWC
Preplanning is vitally important if you live and work in an area where flowing wells are part of your regimen.
In Iowa, there is a story about a flowing well—“Old Jumbo” it was called. In 1886, a driller was hired to drill a 3-inch-diameter well. However, he didn’t have the necessary tools for a 3-inch well, so he drilled a 2-inch hole with the thought in mind the water flowing out of the well would ream the hole to the 3 inches necessary.
Well, the power of flowing water worked! When it was all said and done—13 months later!—the well was finally sealed, but not before it consumed numerous strings of pipe, including 163 feet of 18-inch casing, along with several other smaller strings of casing. (More details about the “Jumbo” well can be read here.)
I had my own problems years later with a flowing well and while it did not get away from me, there were several moments where I was deeply concerned.
Flowing wells, especially those drilled through unconsolidated formations, are nothing to fool with and advanced planning on these types of wells is vitally important.
Most drillers with experience in a given area are usually familiar where these types of wells will occur. If one is not, checking existing records of previously drilled wells through a state database is advised before tackling such a project.
One of the practices I adopted with my company was to set temporary casing that ranged from 15 feet to 30 feet in depth. The depth at which we set the temporary casing depended on where we would find a zone of stiff clay.
With a domestic type of well, we typically fluid drill a 12¼-inch hole to a given point and set 10-inch temporary casing. If a 20-foot length of temporary casing was to be set, we would drill a 12¼-inch hole to 17 feet and set the string of 10-inch casing in the hole and pressure grout the casing in place with a high solids bentonite grout using the Haliburton method.
After the annulus was filled with grout, we would then push the casing into the underlying clay another foot or so. This would give the base of the casing a good seal and we would still have 2 feet of temporary casing above grade. The casing would always be equipped with a threaded 10-inch coupling.
Having the 10-inch threaded coupling on the top gave us flexibility—should the flow get away from us prior to having the permanent casing set and grouted and we needed to screw a premade, 10-inch threaded cap onto the well to shut the flow down and allow us to reformulate our plan.
The premade cap was typically 15 inches long and always accompanied drillers to jobsites such as this. The cap also had a 2- or 3-inch coupling welded into the side of the 10-inch cap to allow us to install a 2- or 3-inch valve—so if we wanted to allow water to discharge from the hole while completing the well, we could. The valve gave us the flexibility of pumping a heavy grout back down the bore and redrilling later after the grout had set, or closing the hole and beginning a new bore.
In addition, having the 10-inch temporary casing extend approximately 2 feet above grade allowed us to be able to push the casing farther into the clay if water began to flow around the outside of the temporary casing.
When we grouted the casing on flowing wells, we would in most instances use neat cement grout in lieu of a high solids bentonite grout. The set strength of neat cement is far superior to that of a high solids grout. If time was a factor, we would use Type III Portland cement rather than Type I as Type III has a cure time of 24 hours in contrast to 72 hours for Type I.
In instances where we anticipated a flow of less volume or pressure, we would use a high solids bentonite grout, but would typically place approximately 10 feet of graded bentonite at the bottom of the annulus prior to pumping the high solids grout. The shear point of graded bentonite, once hydrated, is significantly higher than the set strength of a high solids bentonite grout.
If the well was to be finished in a sand and gravel formation, we would typically try to set the primary casing about 5 to 10 feet above the anticipated aquifer of where the flow would originate.
After the casing was grouted and the grout allowed to cure, we would drill out the end of the grouted casing and into the underlying sand and gravel formation. Typically, a stainless screen with a PVC riser pipe would be telescoped out the end of the casing, using a riser pipe of appropriate length with a rubber K-packer. The riser pipe would extend a minimum of 10 feet back up into the primary casing. In most cases, the well would be flowing at the time of installing the screen.
Upon completion of the well, the 10-inch temporary casing would be removed and salvaged for future use.
I have spoken with many contractors over the years who have had their own issues with flowing wells. The fallout from a failed flowing well construction can be catastrophic. There is story after story of scenarios of flowing well issues.
While there are many different approaches when drilling a well anticipated to flow, I can’t emphasize enough the importance in preplanning for the worst-case scenario—so you don’t end up having your own “Jumbo” problem.
Gary Shawver, MGWC, is president of Shawver Well Co. Inc. in Fredericksburg, Iowa. He has been in the water well industry for more than 40 years and is a Master Groundwater Contractor. He served on the NGWA Board of Directors. Shawver is semi-retired, having sold his business to his employees. He can be reached at firstname.lastname@example.org.