Casing Drilling: An Emerging Technology
- S.F. Shepard (BP America Production Co.) | R.H. Reiley (BP America Production Co.) | T.M. Warren (Tesco Corp.)
- Document ID
- Society of Petroleum Engineers
- SPE Drilling & Completion
- Publication Date
- March 2002
- Document Type
- Journal Paper
- 4 - 14
- 2002. Society of Petroleum Engineers
- 1.7.5 Well Control, 4.2 Pipelines, Flowlines and Risers, 1.10.1 Drill string components and drilling tools (tubulars, jars, subs, stabilisers, reamers, etc), 1.6.10 Running and Setting Casing, 4.2.4 Risers, 1.6.6 Directional Drilling, 1.7 Pressure Management, 1.14 Casing and Cementing, 1.11 Drilling Fluids and Materials, 1.14.1 Casing Design, 1.2.5 Drilling vibration management, 1.5 Drill Bits, 1.11.2 Drilling Fluid Selection and Formulation (Chemistry, Properties), 1.6 Drilling Operations, 1.6.1 Drilling Operation Management, 1.1.6 Hole Openers & Under-reamers, 3 Production and Well Operations, 1.12.6 Drilling Data Management and Standards, 1.10 Drilling Equipment, 1.6.1 Drilling Operation Management, 2.4.3 Sand/Solids Control
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BP America Production Co. used the Tesco Casing Drilling™* process to drill the surface and production intervals of 15 Wyoming gas wells. These wells range in depth from 8,300 to 9,600 ft. This paper provides a case-history discussion of the critical issues encountered and resolved during the planning and operations phases of this project.
Oilfield casing was used as the drillstring, along with a wireline- retrievable bottomhole assembly (BHA), to reduce the overall time required to drill, run casing, and cement the surface holes. Drilling with casing matched the rate of penetration (ROP) for conventional wells, and both the downhole and surface tools proved to be reliable.
The production-hole interval turned out to be more challenging. Drillstring vibrations were encountered when drilling with the 4 1/2- in. casing, and difficulty was experienced in maintaining a competitive ROP with the wireline-retrievable drilling assembly. The last 11 production holes were drilled with casing and a nonretrievable bit assembly. Nine of these wells were completed without tripping the casing. Drilling times were competitive with conventional drilling in the Wamsutter area. One of the wells was the third-fastest well ever drilled in the field.
The project demonstrated that the casing-drilling process can be used successfully but may not be cost-effective in all situations. It is probably better suited to softer formations and larger casing sizes than those used at Wamsutter. The process seemed to improve wellbore stability, reduce lost circulation, and minimize gas influx, even when drilling with a lower mud weight than is typical for conventional drilling.
Casing drilling, an innovative process for simultaneously drilling and casing a well, is emerging as viable technology for the 21st century. The concept builds on experience gained from drilling liners to the bottom in troublesome holes. With the advent of dependable top-drive systems, wireline-retrievable BHAs, PDC bits, and high-torque casing connections, it is possible to simultaneously drill and case a complete well with the casing as the drillstring.
BP and Tesco undertook a project to drill five gas wells in the Wamsutter area of Wyoming with the casing-drilling process. The casing-drilling program was initiated specifically as a joint technology- evaluation project between an operating and service company. A multiwell program was approved, because experience shows it often takes several trials to successfully implement a new technology. Tesco provided the casing-drilling services as well as the rig for the project under an incentive contract. Casing drilling proved so successful that an additional 10 wells were added to the program.
Casing-Drilling System Overview.
The Tesco Casing Drilling system simultaneously drills and cases a well with normal oilfield casing as the drillstring.1 The casing transfers hydraulic and mechanical energy to a wireline-retrievable drilling assembly suspended in a profile nipple located near the bottom of the casing. A drill lock (DLA) in the top of the drilling assembly provides mechanical (axial and torsional) coupling and hydraulic seals to the casing. It also provides a mechanism to facilitate insertion and retrieval from the casing string. The drilling assembly below the DLA terminates in a pilot bit but may include other conventional drillstring components, such as an underreamer, a mud motor, coring, or a directional assembly.
In most casing drilling applications, an underreamer is used above a pilot bit to open the hole from the pilot-bit diameter to the final wellbore diameter. The pilot bit is sized to pass through the casing, and the underreamer opens the hole to the size that is normally drilled to run casing. For example, a 6 1/4-in. pilot bit and an 8 1/2-in. underreamer are used while drilling with 7-in., 23-lb/ft casing, as shown in Fig. 1.
An underreamer and pilot-bit assembly were used to casing-drill the 7-in. surface casing for all 15 wells in the BP project. A 6 1/4-in. PDC casing shoe and a 3 7/8-in. PDC pilot bit were used with 4 1/2-in. casing to drill the production intervals of the first four wells. The casing shoe was used instead of an underreamer because of reliability concerns with the small underreamer and the desire to evaluate the drilling potential with an even smaller casing size. After the first four wells, the casing shoe/pilot bit combination was abandoned because of the low penetration rate. The remaining wells were drilled with a conventional 6 1/4-in. PDC bit attached directly to the bottom joint of the casing. These wells were drilled to total depth (TD), and the production casing was cemented in place without retrieving the PDC bit.
The casing drilling system uses a top drive to rotate the casing. Single joints of casing are picked up off the pipe rack and set in the mouse hole. The top drive, with an extend feature, is connected to the top of the joint, which is then stabbed into the top of the casing string in the rotary table. The casing joint is drilled down by using the top drive in a conventional manner. The casing string is rotated for all operations except slide drilling with a motor and benthousing assembly for oriented directional work.
The primary objective of the project was to evaluate the potential of casing drilling technology to improve drilling performance, both for Wamsutter and, more generally, for other BP locations worldwide. The operating costs at Wamsutter are significantly less than many other areas where casing drilling might be employed. Openhole logs are normally not required because of a wealth of offset well data. These factors made it a good location to pilot test casing-drilling technology, even though the probability of equaling conventional performance and economics at this location was thought to be low.
The following specific goals were established for the project.
Get Health, Safety, Environment (HSE) right (no accidents, no harm to people, and no damage to the environment).
Capture the key learnings and best practices to improve performance on subsequent wells.
No unplanned tripping of casing.
Drill a useable production well to show that casing drilling is a viable option to conventional drilling.
The Wamsutter area is located in the Greater Green River basin in south-central Wyoming. Gas production has been under development since the early 1970s. The productive formation is primarily the Almond sand, located at depths ranging from 8,000 to 10,000 ft. The Almond is a hard, tight sandstone with native pressures of approximately 11 lb/gal.
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