Drilling with casing Drilling with casing has been with us now for a few years, however very little has been published about the subject. The drillers club has been following the subject since 2000 and with the help of some very dedicate people have put together quite a bit of information that is constantly being added to. The club is free to join and all questions are welcome Listed below are just a few of the questions and answers that have been contributed buy one of out members. to learn more about this up and coming subject. Since I am [club member that is not me) involved with casing drilling from the operators side, we are continually answering questions from other drillers who are curious about how/why/what we do when drilling with casing. These are few of the most frequent questions being asked. If you have other questions that aren't addressed here, ask away. Q. What is casing drilling? A. Casing drilling is simultaneously drilling & casing a well where the casing is used to transmit both mechanical and hydraulic energy to the bit. The casing acts like drill pipe during the drilling phase, but reverts to casing after TD and cementing operations begin. Q. Do you rotate the casing? A. Yes, the casing is rotated. We will at times also use a downhole motor but our preference is just rotate the casing. Q. How fast do you rotate the casing? A. We will rotate casing up to 180 RPM. Whatever is required for adequate ROP. Q. What is the advantage of casing drilling? A. The original focus of casing drilling was to reduce drilling times by reducing tripping times and other planned/unplanned events. Also, a purpose built casing drilling rig is a smaller, more efficient rig design that will require less mobilization time. Q. What pipe sizes and connections do you use? A. We are using 9 5/8” 36# J-55 Buttress for surface casing. The intermediate casing is 7” 23# Mav 95/100 Buttress. Both these connections utilize Noetic torque rings installed in the J-area of the coupling for additional torque capacity. The production hole is drilled with a combination string of 4½” 11.60# & 13.5# Mav 95 DWC/C. In the near future, we will be utilizing DWC/C connections in 7" and 9 5/8". The DWC/C connection does not require the use of torque ring and is competitively priced with Buttress threads. Q. Any additional problems that were not anticipated prior to drilling the first well? A. We have experienced several mechanical issues. We were not using float equipment when cementing the 7” casing which lead to several cement failures. We have solved the problem temporarily by using a composite set plug, but are looking for a cost savings solution to this. Fatigue cracking of the casing has not been a big problem, but it has occurred. Also, we experienced junk in the hole from the wear protection and centralizers that we started the project with. We have shied away from tools in the hole with welded blades. Q. Anything that surprised the drillers when casing drilling? A. We have experienced problems with pipe in pipe induced whirl. This is mainly observed when a deeper set (>1000’) of surface casing (9 5/8”) is set. We then drill out with 7” casing and have observed surface indications of whirling. For now, we utilize a downhole motor to drill out of the deeper set surface casings. We are currently working on a solution so we will not need to run the motor. We have discovered a cost savings that was unforeseen. We have seen a reduction in open hole trouble time. From lost circulation, stuck pipe and well control. While initially looking at casing drilling, we were concerned the small annulus would lead to higher ECD’s which would lead to more lost circulation than we currently experienced. We found that we actually have fewer problems with lost circulation than a conventional rig. Q. How is the BHA configured and run in the hole? A. A wireline retrievable assembly is run and landed in a profile nipple located near the bottom of the casing of the 9 5/8” and 7” casing strings. The production section is drilled with a detachable 6¼” PDC bit. The wireline retrievable assembly consists of a PDC pilot bit, tandem stabilizer, underreamer, pony drill collar and drill lock assembly (DLA). The pony drill collar and DLA are located inside the 7” casing with the DLA landing inside the profile nipple. The DLA provides the ability to lock and unlock the drilling assembly both axially and torsionally into the casing string and also connect conventional drilling tools to the casing. The BHA may also consist of other conventional BHA components including motors and directional assemblies. As stated, the production hole is drilled with a 6¼” PDC and a packed hole assembly using integral stabilizers. Q. What type of muds are used. A. We use the same basic muds as are being used by the conventional rigs. Gel spud mud for surface casing and the first 5000’ of intermediate hole. We use more polymer than conventional rigs due to keeping the mud shear thinning to reduce ECD’s. Mud weights of 10.5#-11.0# are typical for this area. Regular diesel based OBM is used in the production hole at typical mud weights of 15.0#-16.0#. Q. What other special equipment is required for casing drilling? A. We use a top drive to rotate the casing with the casing string being attached with a Casing Drive System (CDS) without screwing into the top casing coupling. The CDS has a slip assembly to grip the exterior of the casing and an internal spear assembly to provide a fluid seal to the pipe. The CDS is made up to a new joint from the V-door and is stabbed and made up to the stump with the top drive. For retrieving the BHA, a ½” braided wireline unit is used. Q. Whats a purpose built casing drilling rig? A. Casing drilling has been conducted on a conventional kelly drive and also a top drive rig, but the purpose built rigs are designed with hydraulically powered 1000HP mud pumps, drawworks, top drive and wireline unit. Conventional rigs are designed to trip heavy strings of pipe, the casing drilling rig is sized smaller with no sacrifice in operational performance. (Remember…no tripping) The new rigs currently operating are 250 ton and is a total of 12 truckloads. They have a semi-automated pipe handling system designed for Casing Drilling. The pipe is picked up from the pipe rack and delivered to the V-door with an automated power catwalk system. Using a single joint elevator, the joint is picked up and stabbed into the stump in the rotary table. Q. What surface torque is normally observed? A. When drilling w/ 9 5/8” the normal range of torque runs from 2-4000 ft/lbs. Drilling w/ 7” casing, surface torque ranges from 4-6000 ft/lbs. Production hole sees 2-4000 ft/lbs torque. Q. What kind of flowrates and pump pressures are used? A. When drilling surface hole (9 5/8”), flowrates of 550 GPM @ 850# SPP. At TD of intermediate hole (7”) at approx. 8000’, we pump w/ 300 GPM @ 1300# SPP. When drilling the production hole (4½”), we pump 170 GPM @ 1400#. Q. How deep can you drill each hole section? A. We have drilled in 9 5/8” to 2600’, 7” to 9000’ and 4½” to 13000’. Typical depths are 550’ for 9 5/8”, 8500’ for 7” and 4½” to 11200’.