WorldWide Drilling Rescource

29 WorldWide Drilling Resource ® OCTOBER 2019 Notes from the Groundwater Guy by Thomas E. Ballard, P.G., C.H.G. Southeast Hydrogeology, PLLC Common Causes of Well Failure - Well Design and Construction We look at many examples of problem wells around the country, and some common themes stand out. One of the most common causes of well failure is in the well design and construction process. The six main areas where we see issues with well construction and design are: 1. Well Seals: Many wells are constructed using state standards as de facto construction standards when geology should really be the guide. We find that problems with things like nitrates and total coliform are often directly traceable to inade- quate seal depth. 2. Screen and Casing Materials: It may seem like a great idea to save money on a well using low-carbon steel casing and stainless steel screen, but you are really setting yourself up for galvanic corrosion of the low-carbon steel, substantially shortening the life span of the well. Using dissimilar metals in a well without a dielectric coupling. 3. Screen and Gravel Size: The wrong choices here can lead to a sanding well if the screen openings are too large and the gravel not sized appropriately for the screen. Similarly, too small of a screen opening can lead to an inefficient well which is also challenging to develop properly. 4. Bridging Issues: Installation of gravel pack during well construction can result in voids due to bridging, which can result in later sanding issues. Settling can have a similar effect, if inadequate gravel is placed over the top of the upper screen section, settles during development, and well use causes the top of the gravel to drop below the top of the upper screen section. 5. Welds: Welds are a common point of failure due to preferential corrosion of welds due to differences in metal types. Video logs of wells should be conducted after well completion to verify construction, and later video logs should pay at- tention to welds to check for corrosion issues. 6. Plumbness and Alignment: A well that is not straight and plumb will often have problems with construction and pump operation, although submersible pumps can be a bit more tolerant of well deviation than turbine pumps. Most of these issues can be addressed by paying attention to the geology while drilling or, even better, understanding the geology and aquifer characteristics at the well location prior to drilling. A preliminary well design modified by geologic conditions encountered during drilling, is often the most effective approach. Tom Tom Ballard may be contacted via e-mail to michele@worldwidedrillingresource.com WTR