Tag Archives: Basic Drilling Formulas

According to the previous post, you have learnt about Mixing Fluids of Different Densities with Pit Space Limitation. This post you will learn about how to mix different fluid densit withour limitation of mud pit space (Case#2: You don’t have limitation of pit space). For this case, the calculation will be easier because you can directly input value of each variation into the equation to get answer.

First of all, let’s review the formula for mixing fluid density.

(V1 x D1) + (V2 x D2) = VF x DF

Where;

V1 = volume of fluid 1 (bbl, gal, etc.)

D1 = density of fluid 1 (ppg,lb/ft3, etc.)

V2 = volume of fluid 2 (bbl, gal, etc.)

D2 = density of fluid 2 (ppg,lb/ft3, etc.)

VF = volume of final fluid mix

DF = density of final fluid mix

Let’s read and understand this example so you will know how to use the formula.

Example 2: No limit is placed on volume:

Determine the final mud weight and the final volume when mixing 10.0 ppg and 14.0 ppg drilling mud. There is no limitation regarding the pit space.

Mud in mud pits :

200 bbl of 10.0 ppg mud in pit A

300 bbl of 14.0 ppg mud in pit B

Solution:

Apply formula of mixing different fluid density.

(V1 x D1) + (V2 x D2) = VF x DF

Where;

V1 = 200 bbl

D1 = 10.0 ppg

V2 = 300 bbl

D2 = 14.0 ppg

VF = V1+V2 =500 bbl

Formula: (V1 x D1) + (V2 x D2) = VF x DF

(200x 10.0) + (300 x 14.0) = 500 x DF

12.4 ppg = DF

You will have total fluid 500 bbl of 12.4 ppg.

Please find the Excel sheet to calculate how to mix different fluid density without pit space limitation.

Ref book: Formulas and Calculations for Drilling, Production and Workover, Second Edition

You sometimes need to reduce your mud weight in hole. The method to reduce mud weight is dilution. The concept of dilution is to add light weight fluid into heavy fluid and when they mix together whole drilling fluid weight will decrease. The light weight fluid frequently used are fresh water, sea water, base oil, diesel, synthetic oil, etc which are normally your based fluid.

You can calculate how much light weight fluid in barrel required reducing original mud weight to new mud weight with this following formula:

Mud weight reduction by diluting with light weight fluid

Light weight fluid volume in bbl = V1 x (W1 – W2) ÷ (W2 – Dw)

Where;

V1 = Intial volume in bbl

W1 = Initial drilling fluid weight in ppg

W2 = Final drilling fluid weight in ppg

Dw = Density of light weight fluid in ppg

Example: Determine the number of barrels of base oil 7.2 ppg (Dw) required to reduce 200 bbl (V1) of 13.8 ppg (W1) to 10.0 ppg (W2):

Light weight fluid volume in bbl = V1 x (W1 – W2) ÷ (W2 – Dw)

Light weight fluid volume in bbl = 200 x (13.8 – 10) ÷ (10 – 7.2)

Light weight fluid volume in bbl = 271.4 bbl

You need to mix 271.4 bbl of base oil 7.2 ppg into 200 bbl of 13.8 ppg in order to achieve final mud weight of 10.0 ppg

Please find the Excel Sheet to calculate mud dilution.

Ref book: Formulas and Calculations for Drilling, Production and Workover, Second Edition

You know how much volume will be increased due to adding  Hematite into the system; however, you sometimes are limited to total volume due to limit pit volume on the rig so you need to calculate starting volume to achieve the predetermined final volume of desired mud weight. This formula below is used to determine the staring volume of mud with Hematite.

Starting volume in bbl = VF x (40 – W2) ÷ (40 – W1)

Where; W1 = current mud weight in ppg

W2 = new mud weight in ppg

VF = final volume in bbl

Example: Determine the barrel of starting volume of 10.0 ppg (W1) mud required to achieve 100 bbl (VF) of 13.0 ppg (W2) mud with Hematite:

Starting volume in bbl = VF x (40 – W2) ÷ (40 – W1)

Starting volume in bbl = 100 x (40 -13.0) ÷ (40 – 10.0)

Starting volume = 90 bbl

In order to achieve 100 bbl of 13.0 ppg mud weight up with Hematite, you must have 90.0 bbl starting volume of 10.0 ppg mud.

Please find the Excel Sheet for calculating starting volume of original mud weight up with Hematite.

Ref book: Formulas and Calculations for Drilling, Production and Workover, Second Edition

The concept of mud volume increase due to adding Hematite is as same as the mud volume increase by adding barite and calcium carbonate. The formula for calculating volume increment is just different only one factor which is 40 for hematite but 22.5 is usedfor calcium carbonate and 35 is used for barite. Please follow the formula below for determining volume increase because of adding Hematite.

Volume increase per 100 bbl of mud = 100 x (W2 – W1) ÷ (40 – W2)

Where; W1 = current mud weight

W2 = new mud weight

Please read and follow the example below for more understanding.

Example: Determine the volume increase when increasing the density with hematite from 10.0 ppg (W1) to 13.0 ppg (W2):

Volume increase per 100 bbl of mud =100 x (13.0 – 10.0) ÷ (40 – 13.0)

Volume increase per 100 bbl of mud = 11.11 bbl

If you have total volume of 500 bbl of mud, the volume increase due to adding calcium carbonate will be equal to 55.56 bbl (11.11 x 500 ÷ 100).

Please find the Excel sheet used to calculate how much volume increased due to adding Hematite.

Ref book: Formulas and Calculations for Drilling, Production and Workover, Second Edition