Home / News / Schlumberger-TESCO offer directional casing while drilling

Most casing while drilling (CwD) is done by attaching a non-retrievable bit to the bottom of the casing and leaving the bit in the hole. Directional casing while drilling (DCwD) uses a steerable BHA that is retrieved, making DCwD a viable alternative to conventional directional drilling in depleted or mature fields that have severe lost-circulation and wellbore stability problems, said Schlumberger during a press conference held at its exhibit booth on Tuesday.

Well construction in mature fields with standard drillpipe sometimes requires extra casing strings to avoid well stability problems caused by depleted formation pressures. Because they improve wellbore stability, the DCwD techniques developed through collaboration between Schlumberger and TESCO may reduce the number of casing strings needed.

Schlumberger-TESCO offer directional casing while drilling

DCwD also improves well control because it allows circulating while the BHA is being retrieved or run into the well. They also leave the casing at or near the bottom while the BHA is out of the well. During drilling, DCwD rotation strengthens the borehole wall because of the plastering effect, also known as smear or stress cage, which occurs in the narrow annulus. 

Used successfully in the North Sea

The first deployment of DCwD offshore was on a well drilled from the ConocoPhillips-operated Eldfisk Bravo platform in the Norwegian sector of the North Sea. Both the 10 ¾-in. and 7 ¾-in. sections of Well 2/7B-16A, totaling 10,968 ft, were drilled successfully and positioned as planned using retrievable BHAs that incorporated Schlumberger’s PowerDrive X5 rotary steerable systems, PowerPak straight positive displacement motors (PDMs), and Pulse telemetry and surveying systems. The casing strings were rotated at 20-30 rpm from the surface, and the PDMs provided an additional 130 rpm to the RSS, PDC bits and under-reamer. ROP was as high as 80 ft/hr. All directional objectives for the wellbore were achieved, with a maximum dogleg severity of 4.83deg/100 ft.

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