This paper describes the experience in Brazil with Casing Drilling Technology, which was developed to reduce costs and eliminate wellbore instability and loss circulation problems. This system integrates the drilling and casing running processes into a single operation, providing a more efficient way to drill a well.

Two service companies currently are using casing as the drillstring; however, the systems being offered are different. One utilizes a conventional BHA, which is tripped in/out with a wireline, while the other one utilizes cutters on the casing shoe. Only the first system has been tested in Brazil so far, but a test of second system is being planned.

Four tests performed in Northeast Brazil proved the Casing Drilling System has a great potential. The first and fourth tests were done on land. The second and third tests were done offshore using a jack up rig. The first test was simply aimed at introducing the technology in Brazil. The others tests were targeted at overcoming specific troublesome borehole instability and loss circulation zones.

Small changes made in the casing connection allowed the casing string to be rotated, even when utilizing Buttress connections. Experience gained during the Casing Drilling tests refuted the conception that casing was fragile and easily damaged, thus allowing casing reaming and drilling operations to be employed with more confidence.


The Casing Drilling technique consists of drilling and casing simultaneously. The casing is used to transmit mechanical and hydraulic energy to the bit. The main reasons to use this technique are to reduce trip time, eliminate well conditioning time before running casing into the well, overcome troublesome formations with well instability and loss circulation problems, and improve well control.

There are two primary casing drilling techniques available in the market: Casing Drilling®, which allows the BHA to be changed without tripping the casing, and Drilling with Casing®, which uses a fixed cutter drill shoe. This paper describes the techniques, preparation, operation, and results of Casing Drilling® tests performed in Brazil.

Casing Drilling® Technology

This process1,2 eliminates the conventional drillstring by using the casing string to transmit mechanical and hydraulic energy to the bit.

A pilot hole is drilled using a conventional bit and an underreamer enlarges the well diameter. Tessari2 describes how the retrieval system works. The BHA is attached to a DLA (Drill Lock Assembly), which connects the BHA to a profile nipple immediately above the casing shoe joint. The BHA can be tripped with wireline, coiled tubing or drill pipe. When the BHA is run into the well, spring-loaded dogs in the DLA stop the tool at the proper depth to lock it to the profile nipple. The locking process is accomplished by shifting a sleeve downward to positively extend lock dogs into recesses in the profile nipple.

Any type of BHA can be used, depending on the operation. For vertical wells, the BHA may consist of a pilot bit, stabilizers, and underreamer. For directional wells, the BHA would include a downhole motor and MWD (or LWD).

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