Exercise 3 Cost per Foot Whilst Drilling
The decision to pull a bit should be based on the performance of the bit over a period of time. Table Solution 3 and Figure Solution 3 shows that after 8 hours the cost per foot of the bit run has reached its minima and started to increase. Therefore consideration to pull the bit should be made at this point.
It should be noted that only ‘consideration’ is given to pulling the bit at this point. The engineer should first check with the mud loggers that the bit had not entered a new type of formation, since this may affect the performance of the bit. The engineer should also consider the proximity to the next casing or logging point and the consequent cost of running a new bit to drill what may be a relatively short section of hole. This must be weighed against the possibility of the bit breaking up and losing teeth or even a cone.
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RIG RATE |
400 |
|
BIT COST |
1600 |
|
trip time 1 8 |
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DRILLING TIME |
FOOTAGE DRILLED |
TOTAL COST OF RUN |
COST PER FOOT |
|
1 |
34 |
5200 |
152.94 |
|
2 |
62 |
5600 |
90.32 |
|
3 |
86 |
6000 |
69.77 |
|
4 |
110 |
6400 |
58,18 |
|
5 |
126 |
6800 |
53.97 |
|
6 |
154 |
7200 |
46.75 |
|
7 |
180 |
7600 |
42.22 |
|
a |
210 |
8000 |
38.10 |
|
9 |
216 |
8400 |
38.89 |
|
1 0 |
226 |
8800 |
38.94 |
|
11 |
234 |
9200 |
39.32 |
|
1 2 |
240 |
9600 |
40.00 |
Notes:
1. TOTAL COST OF RUN = BIT COST + RIG RATE(TRIP TIME + TIME ON BOTTOM)
Table Solution 3 Bit Run Evaluation
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Figure Solution 3 Bit Run Evaluation |
1. INTRODUCTION
2. FORMATION PRESSURES
3. OVERBURDEN PRESSURES
4. ORIGIN OF ABNORMAL PRESSURES
4.1 Origin of Subnormal Formation Pressures
4.2 Origin of Overpressured Formations
5. DRILLING PROBLEMS ASSOCIATED WITH ABNORMAL FORMATION PRESSURES
6. TRANSITION ZONE
7. PREDICTION AND DETECTION OF ABNORMAL PRESSURES
7.1 Predictive Techniques
7.2 Detection Techniques
7.2.1 Detection Based on Drilling Parameters
7.2.2 Drilling Mud Parameters
7.2.3 Drilled Cuttings
7.3 Confirmation Techniques
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8. FORMATION FRACTURE GRADIENT
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