English Edition (6 MB pdf) - Saudi Aramco

Fig. 9. Thermal integrity; the figure on the left shows good thermal integrity, and the figure on the right shows poor thermal integrity.
Fig. 10. Bit A cutter layout.
came out of the hole. Later analyses and laboratory tests
concluded that in many cases what appeared to be impact
damage was actually cutter degradation as a result of the high
temperatures to which the cutters are exposed during the drilling
operations. Based on this cutter failure mechanism, new cutters
were developed to improve the wear and impact resistance, as
well as the thermal integrity, Fig. 9. After many laboratory and
field tests in various locations, including Saudi Arabia, cutters
for extreme drilling conditions were developed and implemented
in bits used in demanding environments, such as the deep gas
wells in the Ghawar field. With the optimum distribution of
forces on the 12” PDC bit design, cutters for extreme drilling
conditions, and PRSS, it was possible to considerably extend the
bit life to replace up to four PDC bits, as compared to the wells
in which steerable motors and conventional PDC bits were used.
12” PDC BIT DESIGN AND OPTIMIZATION
Base Bit Design (Bit A)
The first two bits used with the PRSS tool were basic designs
that were used previously with conventional steerable motors
and achieved relatively good results. Bit A was set with eight
blades, 13, 16 and 19 mm standard cutters in the bit face, and
13 mm cutters in the gauge. The gauge pad was straight and
3” long. The first two runs in the Haradh zone were not too
demanding from the steerability perspective; the results were
encouraging because the system was able to kickoff the well
Fig. 11. Bit A straight gauge pads.
from the vertical, and the ROP was almost twice that
obtained in the runs with conventional motors. Figure 10
shows the distribution of the three cutter sizes on the Bit A
face. Figure 11 shows the straight gauge pads.
Bit Design Iteration 1 (Bit B)
After analyzing and discussing the results with the operator
and directional drilling company, it was evident the PRSS
50 SUMMER 2010 SAUDI ARAMCO JOURNAL OF TECHNOLOGY