As a mud Engineer it pays to be able to identify what causes a mud weight to change while drilling.
A Drilling fluids Engineer should be able to observe or carry out a test and subsequently identify the reason for a high or a low mud weight in a water-base mud or an oil-base mud system.
Before looking at the reason why the mud weight reduced or increased from the given mud program specification, it’s good to know that the major function of drilling fluids is to provide sufficient pressure to check influx of gas, oil, and water into the well bore from the drilled formation.
The hydrostatic head of the mud column must be at least equal to that of the formation pressure, and hopefully greater, but not so high as to cause loss of circulation (except where an over balanced / under balanced drilling are specifically desired).
The mud weight materials could be barite, calcium carbonate or soluble salts such as sodium chloride (NaCl), potassium chloride (KCl) and calcium chloride (CaCl2). Sometimes the desired mud weight can be achieved by combining additions of salts and barite.
POTENTIAL CAUSES OF MUD WEIGHT PROBLEMS
HIGH MUD WEIGHT
Possible causes of excessively high mud weight are:
a. Over-treatment with weight material
Solution– Use the right formula for calculation.
b. Drilled solids buildup
Solution – maximize usage of solids control equipment
c. Contamination from rig operations such as cement job
solution – Isolate Cement and Spacer returns during displacement
High mud weight can cause the following problems:
a. lost circulation b. Decreased penetration rate c. Hole erosion d. Stuck pipe e. Damage to subsurface formations etc
LOW MUD WEIGHT
Possible causes of excessively low mud weight are:
a. Barite Sagging
Solution– Use the right viscosity for improved suspension of weight material
b. Air or gas entrained in the mud
Solution–avoid over treating with deformers / soap
c. Over dilution
Solution–- Use the right formula for calculation
d. Improper use of solids control equipment
Solution–– Avoid discarding weight material along with drilled solids instead recover barite and remove undesirable solids
e. Under treatment with weight material
Solution–- Use the right formula for calculation
Low mud weight can cause the following problems:
a. Sloughing b. Hole collapse c. Gas kicks d. Stuck pipe e. Blowouts
MUD TEST INDICATORS OF POSSIBLE MUD WEIGHT PROBLEMS
a. Mud Weight (Density) Test: The mud balance may indicate that mud weight is too high or too low. b. Retort Test: The test may indicate that the percent solids by volume is high, and your solids content calculations (lb/bbl low and high gravity solids) may indicate that barite content is too high or too low. c. Rheology tests: Indicates increase or decrease in viscosity
Thanks for the online lecture
Every mud Engnr should read this.
Thanks for the lectures,may God crown your efforts.
Thank you for the intention and time you put into this, only God can reward your efforts, man can but just appreciate you.
am still thinking when i will attain such height of intelligence from a mentor and a coach….May God Continue to bless u more.
Every mud Engr needs this.God bless you my mentor
Thanks Samuel
I have gained a lot from this manuscript
I have learnt a lot from this Manuscript. Thanks
You are welcome