WorldWide Drilling Resource

39 JUNE 2021 WorldWide Drilling Resource® Artesian Flows by Ronald B. Peterson Drilling Products Specialist, Mountainland Supply Company Phil, a WorldWide Drilling Resource® reader, presented the following observation and question: “Think back to the domestic water well drilling business. The rules that apply are a lot different from that of the oil & gas industry, so it’s not uncommon a few corners get cut in the interest of money. One corner is surface casing not being installed, which brings me to my question. As the drill operator advances the drill bit and enters a water-bearing sand (desirable or not) and he quickly discovers it is now an artesian (free flowing) well, excitement tends to overwhelm him. This also generates a lot of attention from a lot of people nearby. I dabble in the mud business. Often, I’m asked how to stop the flow of water. My first thought is - how much pressure is behind all this water? With no casing installed, how would you recommend a person determine what mud weight is needed to kill the flow? Certainly you wouldn’t want to pump cement down hole and ruin a perfectly good water well. Keep in mind there is a growing audience around this well site - some informed and some not so. Your comments are welcome.” This is an excellent observation and a complex question. Unfortunately, it happens more often than it should. We try to save some time and reduce the overall cost of the well, but because we do not recognize some of the critical pitfalls, the result is we take more time than expected and ultimately cost ourselves a lot of money. Situations like this are why I stress preplanning! The success of any drilling project starts before the first turn of the bit. Actually, success is in the evaluation of the project and the effort put into fully understanding the project and the potential problems or issues which may be encountered. It is critical that we understand the full scope of the project to determine the design of the drilling program, well design, and the measures which need to take to be taken to ensure its successful completion. Shallow artesian flows or pressure zones with no surface casing in place, are problematic at best. It can be downright scary since lack of depth makes artesian flows difficult to control and the lack of surface casing compromises the stability of the ground around the borehole along with the security of the drilling rig. Another problem may be the operational, environmental, and/or regulatory issues that are presented in controlling the water generated by the free-flowing well. A free-flowing artesian water zone tends to self-develop once it starts to flow and almost always becomes more severe with time, so time is critical. Since you are at a shallow depth and have minimal money invested in the well, at this point the quickest and most economical solution frequently is to pump cement to stop the flow and reevaluate. This is almost always the last thing to be considered. Then, if it is determined that this water zone is not critical, you should abandon the initial hole and start a new hole. Since you now know the inherent problem ahead, you should install appropriate surface casing. To control the problematic well using drilling fluid, you must know the depth at which the pressure is generated and the amount of pressure. With no surface casing, you usually cannot shut the well in to determine the pressure, as there is no confining casing to get a pressure reading, and if the surface casing is too shallow, it will simply force the water to come up around the casing and compromise the stability of the borehole and the location. One way to determine the pressure is to identify how far above the ground surface the water will rise. This can be done by placing a large enough piece of casing over the open hole, then allow the water level to stabilize, and see how far up the casing the water comes. Every foot aboveground the water rises in the casing indicates 2.31 psi. If you know the depth the water is coming from, you can then calculate the weight increase needed by dividing the apparent pressure by the depth of the artesian zone, which gives you the needed increase in drilling fluid weight. If the water comes up 3 feet in the casing, you have (3 x 2.31) or 6.93 psi. If it is coming from a depth of 50 feet, you divide the 6.93 by 50 and you have 0.1386 or 0.14 psi per foot. You would need to raise the drilling fluid (mud) weight by 0.14 pounds per gallon to control the water flow. Mud scales are difficult to read in hundredths, so you would raise the weight by 0.2 pounds. per gallon. You need to be careful, as very often a water zone may become a lost circulation zone if the mud weight is raised too high. I have been on wells where WTR Artesian Flows cont’d on page 40.