Increase In Mud Weight Due To Cutting

Cutting generated while drilling will increase drilling fluid density and it will finally affect equivalent circulating density while drilling. In this topic, we will talk about how to determine mud weight increase due to cutting.

Figure 1 – Cutting Increases Mud Density

Effective mud density due to cuttings in the hole can be determined by the empirical equation below;

Where;

ρ_eff is effective mud density in ppg.

ρ_m is mud density in ppg.

Q is flow rate in gpm.

ROP is rate of penetration in fph.

d_b is wellbore diameter or bit diameter in inch.

The effective mud density is the combination of drilling mud density and cutting density. We can write in term of equation below.

ρ_{eff =} ρ_{m +} ρ_c — Equation 2

Equivalent Circulating Density (ECD) consists of three components given by the equation below;

ECD = ρ_{m +} ρ_{c +} ρ_a — Equation 3

Where;

ρ_eff is effective mud density in ppg.

ρ_m is mud density in ppg.

ρ_c is cutting density in ppg.

ρ_a is annular pressure loss in ppg.

As you can see from the equation 1 and 3, the more the well is drilled, the more effective mud density which will increase ECD of the well.

Example: The well was drilled with 12-1/4” bit and the average ROP is 150 fph. Flow rate while drilling is 900 gpm and the rig was using 9.2 ppg mud (Figure 2). Determine the effective mud density from the information.

Figure 2 - Drilling information

 The parameters given are listed below;

ρ_m = 9.2 ppg

Q = 900 gpm

ROP = 150 pfh

d_b = 12.25 inch

Using the equation#1, we will get the effective mud density.

ρ_{eff =} 9.39 ppg

The effective mud density is 9.39 ppg. It means that you will have 2% increase in mud weight due to cutting with these drilling parameters.

Reference book => Formulas and Calculations for Drilling Operations