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;
Where;
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;
Vc in gallon per hour is shown below;
Vc in gallon per minute is shown below;
Example: Determine volume of cutting in gallon per hour entering into the well bases on the following information.
Well depth 9,500’ MD/8,000’ TVD.
Average ROP = 80 fph
Average formation porosity = 20 %
Bit size = 8-1/2”
Assume gauge hole
Figure 2 - Well and Drilling Information
Vc in gallon per hour is shown below;
Vc = 188.8 gallon/hr
This figure tells you that with the drilling parameter, you must be able to remove the cutting faster than what you generate in order to eliminate operation issues as stuck pipe.
Reference book => 
Formulas and Calculations for Drilling Operations