WorldWide Drilling Resource

Environmental Monitoring by Thomas Kwader, Ph.D., P.G. WorldWide Drilling Resource ® Hydrogeologist Losing Circulation - Usually a Bad Sign Drilling using circulating fluids has been around for a very long time. Drilling with fluids (mud) allows us to drill to deep depths and drill large-diameter holes without worrying about a collapse, as long as the hole is filled with the proper drilling fluid. Drilling with the proper drilling fluid facilitates the circulation of “mud” to lift the cuttings out of the bore- hole and “drop” them in a mud pit as the velocity slows down in a “wider” section of the drilling circulation system. The cuttings settling out in the mud pit are occasionally cleaned out of the pit as the drill bit advances deeper. Circulating fluids have other benefits, such as keeping the temperature down at the drill bit, retrieving fresh drill cuttings to the surface that reveals the type of strata being penetrated, and minimizing friction between the drill bit and rod within the borehole. The “weight” and velocity of the drilling fluid also help lift the cuttings dislodged by the drill bit. If the drill bit encounters a cavity of a very porous and permeable material, the weight of the drill fluid column may begin to flow rapidly into the porous borehole wall. This can develop quickly into a serious situation for the drill operator and drilling rig. Prior to losing circulation, a positive pressure kept the borehole wide open and stable. The sudden loss of pres- sure into the formation or cavity could allow the borehole and formation near the bit to collapse and create a void or depression at the borehole. Even the most experienced drill operator will be torn between running away from the drilling rig and borehole, or to try and stay with the rig and save the borehole by increasing the volume of drill mud headed down the borehole. At the time the lost circulation first occurs, there is no way to determine the size or extent of the events about to follow. I personally know of at least six drill operators who were unfortunately taken to a depth below ground level and smothered by sediment and soil falling on top of them. Prevention techniques include: 1) Building a wide base or platform beneath the back of the rig to spread the rig’s weight over a wider area; 2) Watching closely for the onset of lost circulation and cease drilling immediately, and if it can be done safely, disconnect the last drill rod from the kelly or tophead drive and move the rig off the hole. Tom Tom Kwader may be contacted via e-mail to michele@ worldwidedrillingresource.com 17 WorldWide Drilling Resource ® NOVEMBER 2019 ENV On November 20, 1908, Howard Hughes Sr. applied for a patent for his dual-roller bit, which improved rotary drilling.