Drill Collars Weight Design & Calculations
Buoyancy Factor Method Vs Pressure Area Method
|Buoyancy factor method vs pressure area method|
Comparison between the Buoyancy Factor Method and the Pressure Area Method for the Drill Collar weight calculations.
- It can be seen that the Drill Collar length calculated by the Pressure Area Method is almost twice that calculated by the Buoyancy Factor Method and, therefore, is enough to provide all the Weight On Drilling Bit WOB.
- For this reason, In Pressure Area Method only the Drill Collar are in compression while the Heavy Weight Drill Pipe HWDP is in tension.
- The buckling neutral point is the same in both cases.
- Either of the two methods can be used to calculate the length of the Drill Collar.
However, the Pressure Area Method has the following disadvantages:
- Requires more Drill Collars to keep the Heavy Weight Drill Pipe HWDP or Drill Pipes in tension. This serves no useful purpose because whether the pipe above the buckling neutral point is in tension or compression is irrelevant to fatigue damage, if the pipe is not buckled.
- The need to procure, transport, maintain, inspect and handle the extra Drill Collars increase the cost of the drilling operation
- Adding more Drill Collars reduce the available overpull.
- Adding more Drill Collars increases the weight of the Drill String and the tensile stress in the Drill Pipes at all depths. The increase in stress will increase the rate of fatigue attack and reduce the life of the Drill Pipes.