WorldWide Drilling Resource

Notes from the Groundwater Guy by Thomas E. Ballard, P.G., C.H.G. Southeast Hydrogeology, PLLC Well Development: The Good, The Bad, and The Ugly We see many wells, including new ones, not performing as they should, with specific capac- ity and well efficiency much lower than should be for the hydro- geological conditions. It can often be a bit of mystery why these wells do not perform as well as they should. Our experience has been that many times the answer lies with incomplete well development. The well development process is an integral part of establishing a well which produces at its maximum capacity, but can often be an afterthought during the well drilling and construction process. The process of well development is really just a series of techniques to repair borehole damage caused by the drilling - remove drilling mud and establish as clear a flow path as possible for groundwater to move in the well. Well development can be as simple as using a surge block and air lift system to remove the drilling debris from the well, filter pack, and surrounding formation, but drilling mud can be tricky to remove, especially when a significant volume gets lost into the formation, and it can require extra effort to recover in those cases. Dispersants and chlorine can help with recovering bentonite-based drilling mud out of the formation. Screen size, filter pack, formation characteristics, and other factors all need to be accounted for when implementing effective well development. Where well development can go wrong is with a lack of proper measurement techniques which should be spelled out in the drilling contract. Well development should continue beyond just obtaining clear water if there are still sanding or turbidity issues, if specific capacity is seeing improvement each time it is measured, and if well efficiency is still showing improvement, as well. By having measurable standards for well development in the drilling contract, it becomes a "no negotiation" issue and the development process must continue until those standards are met. Examples of measurement standards during well development can include: Sand: Measure sand using a sand tester. Sand content should average not more than 5 mg/L (milligrams per liter) for a complete pumping cycle of two-hour duration when pumping at the design-discharge capacity. No fewer than 10 measurements should be taken at equal intervals to permit plotting of sand content as a function of time and production rate, and to determine the average sand content for each cycle. Turbidity: Turbidity should be measured using standard Environmental Protection Agency methods and be less than 5 NTU (nephelometric turbidity unit) at the completion of development. Specific Capacity: Specific capacity should be calculated during the development process and continue as long as the well’s specific capacity continues to increase significantly. Well Efficiency: Well efficiency requires an observation well for reliable calculations. Well efficiency is calculated as the ratio of actual drawdown as measured in the well versus projected drawdown based on observation well data, as calculated on a semilog scale. Awell efficiency of 70-80% is considered to be an efficient well where well efficiency of below 60% indicates an impaired flow path to the well, which can often be traced to well development or poor well design. By having clearly measurable standards for well development in the drilling contract, it becomes a "no negotiation" issue and the development process must continue until those standards are met. Tom michele@ worldwidedrillingresource.com 25 WorldWide Drilling Resource ® NOVEMBER 2017