Hydraulic Efficiency
The effects of increased hydraulic horsepower at the bit are similar to their effect on roller cone bits. However manufacturers will often recommend a minimum flowrate in an attempt to ensure that the bit face is kept clean and cutter temperature is kept to a minimum. This requirement for flowrate may adversely affect optimisation of HHP
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Figure 28 Penetration Rate vs. Rotary Speed |
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Pbh
Figure 29 Static chip hold down effect |
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Figure 30 Dynamic hold down effect |
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Exercise 2 Cost per foot of a Bit Run
The following bit records are taken from the offset wells used in the design of the well shown in Appendix 1 of Chapter 1.
Assuming: that the geological conditions in this well are the same as those in the offset wells below; that the 12 1/4” section will be drilled from around 7000ft; an average trip time of 8 hrs; and a rig rate of Ј400/hr. select the best bit type to drill the 12 1/4" hole section.
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WELL |
BIT |
COST |
DEPTH |
DEPTH |
TIME ON |
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IN |
OUT |
BOTTOM |
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(Ј) |
(FT.) |
(FT.) |
(HR.) |
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I |
A |
350 |
7100 |
7306 |
14.9 |
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II |
B |
1600 |
7250 |
7982 |
58.1 |
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III |
C |
1600 |
7000 |
7983 |
96.3 |
Exercise 3 Cost Per Foot Whilst Drilling
Whilst drilling the 12 1/4" hole section of the new well the following drilling data is being recorded and provided to the company man. At what point in time would you have suggested that the bit be pulled and why? Assume an average trip time of 8 hrs, a rig rate of Ј400/hr and the bit type selected above had been run in hole.
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TIME ON |
FOOTAGE |
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BOTTOM |
(FT) |
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(HRS) |
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1 |
34 |
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2 |
62 |
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3 |
86 |
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4 |
110 |
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5 |
126 |
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6 |
154 |
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7 |
180 |
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8 |
210 |
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9 |
216 |
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10 |
226 |
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11 |
234 |
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12 |
240 |
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