Date of experiment: February 25th
Mr. Pshtiwan Jaf &
Eng. Muhammad Jamal
Aim of experiment:
The aim of this experiment is to illustrate the mud filtration
during static mud condition.
The filtration andwall buildingcharacteristics of a drillingmudare importantfor
providinga relative measure of the amount of mud filtrate invasion into a porous and
permeable formation and the amount of filter cake that will be deposited on the wall
of the well bore wherever filtration occurs.From a drillingviewpoint these properties
give an indication of the amount of water (or oil) wetting that can take place in filtrate
sensitive formations and the potential for tight hole or differential stickingproblems.
For productive, hydrocarbon bearing formations these properties give an indication
of the amount of filtrate invasion and permeability damage that can be expected.
(Azar & Robelloa, 2007)
The flow of mud filtrate through a mud cake is described by Darcy’s law. Thus,
the rate of filtration is given by:
Combining with the continuity equation gives:
Vf - the volume of the filtrate, cm3 ; t – time, s ; k – permeabilityof the
A – the area of the filter paper, cm2 ; Dp – the pressure drop across the mudcake,
atm. Accordingto API standard, Dp = 100 psig
m – the viscosity of the mud filtrate, cp ; hmc – the thickness of the filter cake
fsm, fsc – the volume fraction of solids in the mud and the volume fraction of solids
in the cake
The standard API filter press has A = 45 cm2; operated at a DP = 100 psig (6.8 atm).
The filtrate volume collectedin a 30-min time period is reported as the standard
water loss. (Lyons, et al., 2015)
A test to measure static filtration behavior of water mud at
ambient (room) temperature and 100-psi differential pressure,
usually performed according to specifications set by API, using a
static filter press. The filter medium is filter paper with 7.1 sq. in.
filtering area. A half-size cell is sometimes used, in which case the
filtrate volume is doubled.
Other Apparatus & materials:
Mud balance Electronic balance Beaker
Syringe Electric mixer & steel vessels
Water Barite Bentonite
1. Loosen the T-screw until the filter cell can be removed from the
2. Remove the filter cell and disassemble it.
3. Assure that all parts of the filter cell are dry and clean.
4. Check to see that the rubber gasket in the base cap is
5. Check the filtrate tube in the base cap to be certain it is free of
6. Place the screen in the base cap with the wide rim up.
7. Place filter paper on the top of the screen.
8. Place the second rubber gasket on top of the filter paper.
9. Replace the cell body.
10. Turn the cell body clockwise until it securely fastens into the J
11. Check to see that the rubber gasket is evenly fitted into
the top cap.
12. Fill the filter cell within the drilling mud sample.
13. Check to see that the hole in the top cap is free of
14. Place the top cap on the filter cell.
15. Place the cell body into the frame.
16. Tighten the T-screw securely.
17. Place a graduated cylinder under the filtrate tube and
adjust the support to keep the cylinder under the filtrate
18. Close the pressure-relief valve until the pressure is 100 ± 5
psi. Start timing immediately.
19. Allow the test to continue for 30 minutes.
20. Read and make note of the amount of filtrate in the
graduated cylinder to the nearest 0.1 cc.
21. Open the valve on the regulator by turning counterclockwise.
22. Wait until all pressure is released.
23. Remove the cell from the frame by loosening the T-screw.
24. Remove the top cap and pour the mud out.
25. Remove the bottom cap from the cell.
26. Turn the bottom cap upside down on a solid surface
and remove the filter paper.
27. Measure the thickness of the filter cake to the nearest 1/32
Mud cake thickness=3mm
Volume of mud filtrate=25ml
Q1) why the rubber gaskets are necessary?
A1) to prevent any leakage.
Q2) why is the screen used for this test?
A2) the screen is used beneath the filter paper to distribute the
pressure evenly on the paper and prevent the rupture of the
Q3) in real wellbore condition, what forms the mud cake?
A3) in wellbore condition the mud cake is formed of the rock
cuttings mainly in permeable zones and the mud filtrates into the
walls of the wellbore.
Q4) what are the advantages of the mud cake?
A4) the mud cake stops the loss of drilling fluids and can be a
sign to identify porous and permeable zones.
Azar, J. & Robelloa, S., 2007. Drilling Engineering.
Lyons, W., Plisga, G. J. & Lorenz, M., 2015. Standard
Handbook of Petroleum and Natural Gas Engineering. New
York: Gulf Professional Publishing.