Tangent Section Drilling
Tangent or hold sections can prove to be very economical using NDS, although NDS performance drilling will not usually match that of straight motor performance drilling. Long sections of hole can be drilled faster than with conventional rotary assemblies, and corrections can be performed, if required, to keep the well on course. Basic design principles include:
- An undergauge first string stabilizer is required to maintain inclination when rotary drilling with NDS.
- The assembly should be capable of producing an acceptable dogleg rate to allow for shorter corrective oriented intervals.
- Decreasing the diameter of the first string stabilizer versus increasing "L" is preferred because TGDS is affected less. This practice also limits the number of variables to one, the OD of the first string stabilizer.
A typical BHA for drilling a 12-1/4" hole tangent section is:
- 12-1/4" PDC bit
- 9-1/2" Mach 1 motor, AKO or DTU, 12-1/8" UBHS
- Crossover
- 11-3/4" string stabilizer
- 8" NMDC
- 8" MWD tool
- 11-3/4" non-magnetic stabilizer
- 2 x 8" NMDC
- 2 x 8" DC
- Jars
- 8" DC
- Crossover
- HWDP as required
When drilling a tangent or hold section with NDS, the following should be observed:
- After observing NDS directional tendencies over a minimum of 200 ft of rotary drilled interval, a plan for drilling long distances between orientations should be established. This plan should minimize the number of orientation toolsets and maximize penetration rate.
- Oriented drilling intervals should be minimized. Oriented drilling in a tangent or hold section is performed to correct the present wellpath and to compensate for anticipated trends.
- Never let the drilled wellpath get too far from the planned trajectory, because "drilling on the line" can be significantly more expensive. As surveys are obtained, calculate and plot the position on both horizontal and vertical plans. At all times there must be a feasible course to drill from the current location to the intended target.
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