WorldWide Drilling Resource

70 MAY 2014 WorldWide Drilling Resource ® Dealmakers Skillings & Sons, Inc. of Amherst, New Hampshire, purchased this drill rig from Northeast Drill Supply of Middletown Springs, Vermont. Pic- tured are Ben Robbins, Alan Maynard, Norman Skillings, Jerry Parker with Northeast, and Justin Skillings. Northeast Drill Supply I want to use this opportunity to appreciate the good work that you guys are doing at the WorldWiiddee Drilling Resource ® . Your magazine has been of great help to me on my job, and I have recommended it to many colleagues who are also en- joying the magazine. Yours truly, Oluwole A. Oyedeji Nigerian Geological Survey Agency Abuja, Nigeria Irrigation Well Essentials Compiled by Amy White, Associate Editor WorldWide Drilling Resource ® Drilled wells can provide clean water with few impurities for a variety of applications. As more and more restric- tions are placed on municipal water supplies, many customers are opting for irrigation wells to supply their agri- cultural needs. The drilled well is the heart of irri- gation systems with groundwater sup- plies, so it must be properly designed and compatible with the pump and dis- tribution system to ensure long life, effi- ciency, and economic operation. The process of installing irrigation wells is a lot like creating wells for drink- ing water, only the water is connected to a sprinkler system instead of being pumped into the home. An irrigation well could be a shallow well - which uses groundwater; or an artisan well - which is a deep well drilled into bedrock. Once the well is drilled, a pump, sprinkler clock, and energy source are installed. Irrigation wells depend on the fol- lowing principles of design and con- struction: Preliminary investigation - This is the foundation of well design. It in- cludes the examination of records, geological data, and the drilling of test holes. Design procedure - Once the preliminary investigation and site selec- tion are complete, a well design can be selected to best utilize the hydrogeo- logical conditions present at the site. Gravel pack - Gravel-pack construc- tion is recommended in aquifers con- sisting of fine sand; loosely cemented sandstone formations; and extensively stratified formations consisting of alter- nating layers of fine and coarse sedi- ments of thin silt and clay. This makes the area immediately surrounding the well screen more permeable by remov- ing formation materials and packing artificially-graded materials in their place. Well screen - It is important to choose the right size well screen. A screen too short affects the efficiency of the well and a screen too long caus- es problems such as cascading water, entrained air, and accelerated corrosion and/or incrustation. The most favorable length of well screen is chosen with regards to thickness of the aquifer, available drawdown, and stratification of the aquifer. Slot openings - Gravel packing retains the water-bearing formation, while the well screen retains the gravel-packed particles. The size of the screen slot in this type of well is selected to retain 90% or more of packed material. Screen diameter - Screen diameter is selected to provide enough total area of screen openings so the average en- High-capacity irrigation well typi- cal of the High Plains irrigated agricultural setting. Image courtesy of usgs.gov trance velocity of water through slot openings does not exceed the design standard of 0.1 feet per second. Screen material - Based on results of preliminary investigations, the well screen should be made of materials as corrosion-resistant as necessary. Irrigation wells can be a valuable resource for farmers and growers. Untimely breakdown of these wells can be avoided by selecting the proper gravel pack and screen slot-opening size in the design phase. A properly constructed irrigation well should have a useful life of at least 25 years. Read more on irrigation wells in this section in upcoming issues.