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View Full Version : Drill string design questions???

Dorranp
7th Nov '11, 12:33
For my graded unit I have chosen to do a drill string design, just out of random with no prior knowledge in this field. Reason being is the aim of the unit is to test and also teach us how to apply what we are learning to the real world. I therefore have to make up a specification list that I think my client would present to me and then complete it.

Information I have gathered so far are as follow:

Hole dept 9000 ft
Assume a vertical hole
Data from offset wells has shown that 5 heavy-weight drill pipes are desirable
Required over pull margin: 100000 lb
Safety factor for tensile force 1.2
Neutral point design factor 1.13
Mud weight 12lb
Hole size 9 ½”
Maximum Weight on bit: 40000 lb
No crooked hole tendency

I am in the process of choosing a drill collar and so far have picked a 7” x 2 13/16 DC with a NC50 connection. E= 4320X106 lb/ft, Weight of the drill collar in air = 110 lb/ft.

Calculations (in short)

Length Drill collar needed: 510 ft @ 30ft per Drill collar

Therefore:
510 x 0.816 x 110 = 45822.48 lb (buoyed weight which includes the 1.13 design factor)

First order buckling comes in at 11211.79 lb
Second order buckling comes in at 21672 lb etc

Problem

The first order buckling is well below maximum weight required on the bit (40,000lb).

Information I have found so far are telling me that it is best to carry weight on the bit less than the value for 1st order buckling of the Drill collars.

Question

Are my specifications realistic? Does this problem exist? What would be the route to take in solving this problem if it did exist?:cool: