While drilling, cuttings are generated every footage drilled and this topic will demonstrate how to determine volume of cutting entering into the wellbore.
Figure 1 – Cutting Generated While Drilling
The following formula is used to calculate cutting volume generated while drilling;
Vc is volume of cutting in bbl/hr.
Ø is formation porosity (%).
D is wellbore diameter in inch.
ROP is rate of penetration in feet per hour.
Vc can be presented in several unit as follows;
Buoyancy Factor is the factor that is used to compensate loss of weight due to immersion in drilling fluid and you can find more information from this article > buoyancy factor calculation . In that article, it demonstrates the buoyancy formula only for one fluid in the wellbore. However, this time, we will have the details about buoyancy factor when inside and outside fluid are different.
Buoyancy factor with different fluid inside and outside of tubular is listed below;
Ao is an external area of the component.
Ai is an internal area of the component.
ρo is fluid density in the annulus at the component depth in the wellbore.
ρi is fluid density in the component depth in the wellbore.
ρs is steel weight density. Steel density is 65.4 ppg.
Buoyancy factor is the factor that is used to compensate loss of weight due to immersion in drilling fluid and you can find the calculation from here http://www.drillingformulas.com/buoyancy-factor-calculation/.
We have created a simple table to help people determine the buoyancy factor quickly. Let’s take a look at the table. In Figure 1, it shows the main page and you can select the mud weight range from 4.0 ppg to 19.0 ppg.
Figure 1– Main Page BF Table
For instant, we choose 8.0 ppg and the table will show buoyancy from 8.0 – 8.9 ppg (Figure 2)
Figure 2 – Buoyancy Factor for 8 ppg Range
Frictional pressure is pressure loss acting in the opposite direction of fluid flow and today we will look into each component in pressure therefore you will get clearer picture about the frictional pressure in drilling system.
Let take a look at the simple diagram below.
A mud pump creates power to move drilling fluid from point A to C and the frictional pressure or pressure loss is the amount of pressure required to transfer fluid.
Pump pressure is 2,000 psi at the starting point (“A”) and at the end point (“C”), pressure is 0 psi. This tells you that you need 2,000 psi to overcome the frictional pressure in order to move the fluid from point “A” to point “C”.
“Differential pressure between two points in the system is pressure loss while fluid is moved from one to another point.”
Margin of overpull is additional tension to be applied when pulling the stuck drill string without breaking the tensile limit of the drill string. This is the difference between maximum allowable tensile load of drill string and hook load.
There are several factors when consider about the margin of over pull as listed below;
• Overall drilling conditions
• Hole drag
• Likelihood of getting stuck
• Dynamic loading