WorldWide Drilling Resource

20 JUNE 2013 WorldWide Drilling Resource ® Drilling Fluid Updates by Ray McLarty Drilling Fluids & Grouts Questions & Answers Question We are drilling a city water well in DeSoto County, Mississippi, to a depth of 500 feet. At approximately 40 feet, we hit a lot of gravel. The first few feet, the majority of the gravel was the size of pea gravel, and slightly larger. We didn’t have a problem removing this. As we continued to drill, the gravel got much bigger and we are not having much success getting the gravel out, and the log indicates it is approximately 12-15 more feet of the gravel. What do you recommend we do? Answer Upon visiting the jobsite, we found the well you were drilling was to be a 20-inch municipal city well. You started drilling a 20-inch hole. At approximately 45 feet you hit gravel of various sizes, most of which was pea gravel size and slightly larger. You drilled to 50 feet and changed over to 9¾-inch bit. At that point, we thickened up the mud consid- erably by the addition of QUIK-GEL ® , a high-yield bentonite drilling mud; and QUIK-TROL ® , a dry modified cellulose (PAC) polymer. We later added a fibrous loss circulation material ( N-SEAL™ ) to control fluid loss and as an aid in lifting the cuttings. N-SEAL™ is acid soluble and can be broken down fairly easily with a mild acid. We were able to get a lot of the smaller gravel out, but we were not having much success getting the larger gravel out of the hole. The problem was not only the size of the grav- el, but the size of the hole. You were drilling a 9¾-inch hole that changed to a 20-inch hole approx ima t e l y 50 feet below the surface. To carry cuttings out of the hole, the ascending velocity (av) is recommended by Ground Water and Wells Second Edition to be between 80 and 120 feet per minute. You were using a 3½-inch drill pipe and estimated your pump gallons per minute (gpm) was 300. The formula to determine the ascending velocity of a drill fluid is: V = 25 x Q D2- d2 V = velocity Q = pump discharge in gpm D = hole diameter squared d = drill pipe size squared Using the above formula, you find when drilling in the 9¾ hole, your av will be 90.6. When drilling in a 20-inch hole using the same formula, your av drops to 19.35. So, you have plenty of velocity while drilling a 9¾-inch hole, but when the fluid hits the last 50 feet of hole the pressure drops and you do not have suf- ficient velocity to transport the cuttings the last 50 feet out of the hole. The solution to your drilling problem, which you came up with yourself, was to use an open-top bailer made from an 8-inch section of pipe, to remove the large size cuttings. It was a slow process, but by raising and lowering your mud you were able to get the cutting to flow into the bailer where they could be lifted to the surface and washed out of the bailer by hand. Note: QUIK-GEL ® , QUIK-TROL ® , and N-SEAL™ are Baroid IDP products. Similar products to Quik Gel would be CETCO ® SUPER GEL-X ® or Wyo-Ben EXTRA HIGH YIELD™ . Similar products to QUIK-TROL ® would be CETCO ® REL-PAC ® , Wyo-Ben DRIL-TROL™ “QD” , and M-I SWACO POLYPAC R . Similar products to Baroid IDP N-SEAL™ would be CETCO ® MAGMA FIBER . The statements and comments in this article are my own and are based on information and references believed to be true and factual. If you have a ques- tion on bentonite drilling fluids, grouts, and sealants, or a comment or question on this article, please forward them to me in care of WWDR . Ray Ray McLarty may be contacted via e-mail at admin@ worldwidedrillingresource.com Gravel samples at the jobsite. # # " " $ $ $ ! $ ! # "