Water Well Journal
Issue link: https://read.dmtmag.com/i/643500
So how does one achieve a well aligned borehole? With rotary drilling equipment, using well designed stabi- lizers with a stiff stem—usually a drill collar—will assure an aligned borehole. When choosing a stabilizer design, one must take into consideration the geological conditions found in the area you will typically drill in. For example, if there are large deep fractures that could be found in limestone formations, a longer stabilizer may be in order to be sure the stabilizer will hold the hole while it goes through the large void. My experience has taught me when drilling in creviced limestone formations to try to design stabilizers that are within an inch of the borehole that one is drilling. The design of these stabilizers includes a large diameter drill collar, and usually a larger diameter piece of heavy wall pipe centered on the drill collar. Last, we often run vertical ribs that are some- what spiraled onto the outside of the pipe. These ribs are hard faced the entire length. If the stabilizer is large enough, we will allow the design to be a "flow through," meaning the cuttings will flow between the drill collar and the outer casing. This design minimizes the potential for cuttings to become lodged between the borehole and stabilizer, thus causing the stabilizer to become potential- ly stuck. It is important to make certain one has adequate hole clean- ing capability to prevent the cuttings from accumulating and causing the sta- bilizer to become stuck. When a pneumatic hammer is used on larger diameter holes, we will use an "over the hammer" stabilizer that incorporates the same design on the outer surface of the pipe that covers the hammer (for example, ribs with hard facing). There are various ways to attach the over the hammer stabilizer to the hammer. In some instances and in some formations, typically unconsolidated, we make use of full-hole diameter stabilizers that are of the vertical blade type. These types of stabilizers are also built on drill collars and the blades go directly to the top of the bit with a sub to connect to the bit, built directly into the stabilizer. The bits used on this type of stabilizer are either roller cone or polycrystalline diamond compact bits. The ribs will vary in thickness depending on the size of stabilizer. Our stabilizers of this type use only vertical ribs with no spiraling to them. In many cases we will use another smaller supplemental stabilizer above the primary stabilizer farther up the drill string in order to minimize any mud ring development. Stabilizers can be designed and built by contractors who have good fabrication skills. However, I would recommend if you are doing large diameter hole drilling, using fabrication shops to build the stabilizers will minimize the risks of the stabilizers coming apart down the hole. These shops often have the knowledge and skill sets to advise you in design and have the abilities to assure good weld penetration when fabricating these heavy stabilizers. Full-hole stabilization is critical to making sure a borehole will meet alignment specifications. In today's world, proper tool design will in most cases ensure a well aligned well. WWJ Gary Shawver, MGWC, is president of Shawver Well Co. Inc., an employee stock ownership plan company in Fredericksburg, Iowa. He has been in the water well industry for 40 years and is a Master Groundwater Contractor. He has served as president of the Iowa Water Well Association, the Iowa Groundwater Association, and most recently served on the NGWA Board of Directors. Shawver is semi-retired, having recently sold his business to his employees. He contributes to NGWA's member e-publication and can be reached at grs@shawverwell.com. DACUM Codes To help meet your professional needs, this article covers skills and competencies found in DACUM charts for drillers and pump installers. DO refers to the drilling chart. The letter and number immediately following is the skill on the chart covered by the article. This article covers: DOD-1, DOD-6, DOE-1, 3, 4, 14 More information on DACUM and the charts are available at www.NGWA.org. Become a Certified Well Driller Author Gary Shawver, MGWC, is a Master Groundwater Contractor. Find out more about certification at www.ngwa.org/ Professional-Resources/certification-exams/pages/default.aspx. Twitter @WaterWellJournl WWJ March 2016 47