2. MUD CIRCULATION
Drilling fluids are generally pumped from the
surface tanks down through a hollow drill – pipe to
the bit and to the bottom of the hole, it returned
to the surface through the annular space,
i.e. between drill pipe and wall of the drilled hole.
This phenomenon is known as mud circulation.
3. INTRODUCTION
■ All fluids used in the wellbore, during drilling
operations are termed as drilling fluids.
■ Each drilling fluid consists of following four
constituents:
➢ Continuous Phase
➢ Discontinuous Phase
➢ Inert solids
➢ Chemicals
Drilling mud may be defined as a suspension of solids
in a liquid phase; the liquid may be water or oil.
4. PROPERTIES OF THE DRILLING FLUID
■ Density/Specific Gravity
■ Viscosity
■ pH (Alkalinity)
■ Salinity
■ Filtration – filter cake & water separation
■ Lost circulation (fluid loss control)
■ Compressibility
■ Chemical composition
- interaction between the mud
and the drilled formations must
have a minimal effect on the
mechanical properties of the
formation
5. FUNCTIONS OF THE DRILLING FLUID
❑ Cooling and lubricating the bit, drill pipe and drill collar.
❑ Controlling the formation pressure (Pm-Pf ~ 100-200 psi)
❑ Carry cutting from beneath the bit, transport them up the annulus and permit their separation at the surface
(Cleaning of the bottom of the hole)
❑ Acting as medium for settling out cuttings in the surface pit
❑ Assist in the collection and interpretation of information available from
drill cuttings, cores and electrical logs
❑ Form a thin, low–permeable filter cake which seals pores and other openings in formations penetrated by the bit
❑ Preventing caving – in of the formation
❑ Avoiding damage to productivity of producing formations
❑ Partial aid in supporting the weight of drill string and casing
❑ Preventing corrosion and fatigue of drill pipe
❑ Suspension of cuttings and weight materials on stopping the circulation
7. CUTTING CARRYING CAPACITY OF MUD
Depends on
■ Annular velocity, Vr
■ Plastic viscosity, PV
■ Yield point of mud, YP
■ Slip velocity of generated cuttings, Vs
Lift (resultant) velocity of cuttings = Annular velocity – Slip velocity
Vr = volume flow rate (Q)/annular area (A)
Dp = equivalent particle
diameter (inch)
ρp = density of particle (ppg)
ρm = density of mud (ppg)
μe = effective mud viscosity (cP)
Based on power law model, transitional flow
9. CERTAIN LIMITATION/RESTRICTION ARE PLACED ON THE DRILLING FLUIDS
❑ Not injurious to drilling personnel, norbe damaging or offensive to the
environment (non toxic)
❑ Not corrode nor cause excessive wear of drilling equipment
❑ Not require unusual or expensive methods of completion of the drilled hole
10. DEVELOPMENT
• As early as 1887 water was used as circulating fluid.
• Later on it was observed that drilled clays after getting mixed with circulating
water possesses better carrying capacity, so the use of plastic clay material
with water recommended.
• It was only in 1916 that a gradual recognition of drilling mud as an aid to safer,
faster and economical drilling was established.
11. CLASSIFICATION/TYPES OF DRILLING FLUIDS
The choice for a particular type of mud is usually
made on the basis of the:
- type of formation to be drilled,
- expected formation temperature,
- pressure and oil gas zones, etc.,
Types of drilling mud:
❑ Water based muds - constituents of mud are added in crude oil
❑ Oil based muds - constituents of mud are added in (crude)
oil
❑ Emulsion muds (O/W)
❑ Invert Emulsion Mud (W/O)
12. CLASSIFICATION/TYPES OF DRILLING FLUIDS
• Air is the best drilling fluid
- Easily available
- Free of cost
- Need not to be cleaned before circulation
- Doesn’t contaminate cuttings and formation
- Provides best cooling
- Used for blast hole drilling, water well
drilling, mineral drilling.
DISADVANTAGES
- When circulation stops, cuttings fall down
- Doesn’t have viscosity
- Doesn’t support the wall
- Doesn’t give counter pressure to
formation fluid
- Doesn’t provide lubrication to bit
Air: 1000-2000 m/min
Water: 80m/min
Mud: 30-40 m/min
• Water
• Air + Water
• Foam/Mist
- Make the fluid viscous
- Looses its viscosity and foaming properties and becomes liquid all of sudden
13. WATER BASED MUD
■ Liquid water – continuous phase and used to provide initial viscosity
■ Reactive fractions – to provide further viscosity and yield point –
(low gravity solids)
- Clays – Bentonite and Attapulgite
■ Inert fractions – to provide the required mud weight –
(high gravity solids)
– Sand, barite, limestone, chert
■ Chemical additives – to control mud properties
Solid
components
of mud
14. CLAY
Natural, earthy, fine grained materials that develop plasticity
when wet.
Two types of clay are currently in use:
❑ Bentonite clay – only used with fresh water. (since high
viscosity and high yield point do not develop in salt water)
❑ Attapulgite clay – can be used for both fresh and saline
water
15. NATURE OF CLAY
They posses an atomic structure in which the atoms form layers.
Three types of atomic layers;
1. Tetrahedral layer
-sheets of tetrahedra - a central silicon atom surrounded
by 4 oxygen atoms
-the tetrahedra are linked to form a sheet by sharing 3
of their oxygen atoms by adjacent tetrahedra
2. Octahedral layer
3. Exchangeable layers
-layers of atoms or molecules bound loosely into
structure → which can be exchanged with other atoms
or molecules
16. NATURE OF CLAY
(K, Na, Ca, Mg atoms or H2O
or organic molecules)
Tetrahedral silica
Octahedral Alumina/Mg
Tetrahedral silica
Interchangeable layer
Tetrahedral silica
The nature of these layers and the way these are stacked
together on top of one another define the type of clay mineral.
Cation Exchange Capacity (CEC) –
measure of how easily exchange
can take place
17. NATURE OF CLAY
■ The layers A and B are held together by exchangeable layers.
■ The bond is very weak.
■ Layers split easily along exchangeable layers.
■ The separated layers carries electric charge on their faces and edges.
■ The edge carries +ve charge & the faces carries –ve charge.
■ So due to repulsion or bombarding between each other, the layers remains in suspension and separated.
■ When exchange layer (Montmorillonite);
“Ca” → Ca based clay “Na” → Na based clay
Hydration of clay🡺 high CEC clay → high adsorption of water into exchangeable layer → expansion
of the clay structure → high viscosity and yield point of clay. (dry powder → plastic slurry)
Clay yield → the number of barrels of 15 cp mud which can be obtained
from 1 ton (2000 lb) of dry clay.
18. FUNCTIONS OF ADDITIVES/CHEMICALS
❑ Weighing materials
❑ Viscosifiers
❑ Thinners, dispersants,
deflocculants
❑ Lost circulation
control materials
❑ Filtration control
materials
❑ Surface active
agents/Emulsifiers
❑ Foaming agents
❑ Alkalinity and pH control
additives
❑ Bactericides
❑ Calcium removers
❑ Corrosion inhibitors
❑ Defoamers
❑ Flocculants
❑ Lubricants
❑ Shale stabilizing materials
19. WEIGHTING MATERIAL (INERT FRACTION)
■ Sand
■ Barite
-Barium Sulphate (BaSO4) -Low cost and high purity
-Specific gravity- 4.2 gm/cc: used to prepare mud of over 10 ppg
■ Lead Sulphides – Galena
- specific gravity – 6.5-7: mud weight upto 35 ppg
■ Calcium Carbonate (2.7-2.8 gm/cc) – 12 ppg max. mud density
- ability to react and dissolve in HCL → any cake formed in the producing zone can
be easily removed.
■ Iron Minerals – Iron oxides - Hematite (4.9 – 5.3), magnetite, Illmenite (4.5-5.1)
-more erosive -contains toxic material
20. WEIGHTING MATERIAL
■ High pressure formations like Shale requires SG of
mud to be 2.4 gm/cc
■ At high mud weight, rheological properties
becomes difficult to control due to increased solid
content.
S.G. of
Bentonite – 2.6
Barite - 4.2
22. EFFECTS OF SOLIDS
HP – Hydrostatic pressure
(Kg/cm2)
ρ𝑚 - mud weight (gm/cc)
TVD – true vertical depth of well
bore (m)
HP =
ρ𝑚∗𝑇𝑉𝐷
10
■ Hydrostatic Pressure
or, HP (psi) = 0.052 * ρ𝑚 (ppg) * TVD(ft)
■ Density of mud,
ρ𝑠 = specific gravity of solid X = fraction
of solid in m3 ρ𝑙 = specific gravity of
liquid ρ𝑚 = specific gravity of mud
Vm = volume of mud (Vs +Vl)
ρ𝑠*x + ρ𝑙*(1-x) = ρ𝑚*1
ρ𝑠*Vs + ρ𝑙*Vl = ρ𝑚*(vm)
■ For 1 m3 of mud,
23. VISCOSITY MODIFIERS
Used to control viscosity, yield point, gel and fluid loss properties of mud –
Mud thickeners and Mud thinners
24. MUD THICKENERS (VISCOSIFIERS)
■ Bentonite (Sodium/calcium Aluminosilicates)
■ Attapulgite
■ Spiolite
■ Hectorite
■ Polymers
Polymers are used for filtration
control
• Viscosity modification
• Flocculation
• Shale stabilization
-Xanthum Gum
-Guargum
-Polyacrylate/Polyacrylamide
-Hydroxy ethyl cellulose (HEC)
-Carboxy methyl cellulose (CMC)
-Poly anionic cellulose (PAC)
-Starch
Increase in viscosity primarily due to flocculation of clay plates, resulting
from replacement of Na+ cations by Ca+ cations
25. MUD THINNERS (DEFLOCCULANT/DISPERSANT)
Decrease in viscosity primarily due to breaking in the attachment of clay plates, and then
attaching itself to clay plates → preventing the maintenance of attractive forces between
the sheets
❑ Phosphates
-Sodium tetraphosphate
-Sodium acid pyrophosphate
❑ Chrome lignosulphates
-Decomposes at 300 ℉ (177℃ )
❑ Lignite- Lignin- Water loss control agent
❑ Surfactants- reduce water loss, and used as emulsifiers
-Modified lignosulphates
o Suitable for any pH value
o Temperature limitation of
175 °F (79 °C)
They increase fluid loss control
& reduce filter cake thickness
• Qudracho
• Reacted caustic Tenyon
• Reacted Caustic Lignite
• Mangrove Bark
26. LOST CIRCULATION MATERIAL
Granular, flaky and fibrous type of mud.
■ Blend of cane and wood fibers
■ Blend of long fibers
■ Cellofane flakes
■ Short fibers
■ Leather products
■ Granide Mica
■ Shredding
■ Ground walnut shell
■ Cement
■ Shredded rubber tires
■ Fibrous Material wool
27. ADDITIVES CONTROLLING FILTRATION PROPERTIES AND FREE WATER
▪ Polymers (PAC, CMC)
PH additives – to improve pH value
(water based fluid)
▪ NaOH, KOH
▪ Soda Ash (Na2CO3)
▪ Sodium Bicarbonate
▪ Potash
▪ Lime
▪ magnesia
Lubricating Materials
▪ Oil (Diesel, Mineral,
Animal or Vegetable Oils)
▪ Surfactants, Polymers
▪ Graphite
▪ Asphalt
▪ Gilsonite, And Glass Beads
28. SHALE STABILIZING MATERIAL
■ Shale – highly hydratable – swells in contact with water
■ Minimized by the prevention of water contacting the open shale section.
■ High molecular weight polymers
■ Hydrocarbons
■ Potassium and calcium salts (e.g. KCl)
■ Glycols
A specific ion of additive such as potassium actually enters the exposed shale section
and neutralizes the charge on it.
29. OIL BASED MUD || INVERT EMULSION MUD
Oil – continuous phase
Solids – discontinuous phase Water & solids – discontinuous phase + surfactant
■ Useful in drilling; (since clay do not swell in oil)
– Production zones, or other water sensitive zones
– Shales
■ IEFs are cost effective for
– Shale stability
– Temperature stability
– Lubricity
– Corrosion Resistance
– Stuck pipe prevention
– Contamination
– Production prevention
30. FUNDAMENTAL PROPERTIES OF MUD
■ Weight (or Density)
■ Rheological Properties
■ Filtrate and filter cake
■ pH value
31. FUNDAMENTAL PROPERTIES OF MUD
■ Depends on quantity of solids in liquid phase
For water
■ Sp. Gr. = 1
■ Lb/gallon (ppg) = 8.33
■ Lb/ft3 (pcf) = 64.5
■ Lb/100 ft3 = 434.5
■ Calibrate Mud Balance first with water. (corrections can be done by taking out shots).
■ Fill the mud in 200 cc cup (excess mud comes out through hole).
■ Move the rider till the bubbles come in middle of glass window.
■ Take readings of density, specific gravity and pressure gradient.
Steps
33. VISCOCITY – MARSH FUNNEL
➢ Body - thermoplastic material
➢ Opening – Gun Metal tube
■ Marsh funnel viscosity (sec) – The Time taken by one quartz (946
cc) of mud to flow through marsh funnel at temperature of 70 °F
■ Calibration of Marsh funnel is done with water at 70 °F.
– Water – 26.5 ± 0.5 sec
Preparation of standard mud sample:
■ Take 220 gm bentonite → mix in 350 cc of distilled water → stir at 1800 rpm for 15 min
(Hamilton stirrer) → leave the sample for 24 hr.
■ Before test → again stir it for 5 min.
35. VISCOCITY-FANN VISCOCITY GEL(VG) VISCOMETER
■ Three available types
i. 6 speed – for educational
purpose/field
ii. 8 speed
iii. 12 speed – for developing new muds
■ Motor is operated at 3 gear & 2 speeds.
■ Instead of linear motion, rotary motion is
used to measure viscosity.
37. DRILLING FLUID – BINGHAM PLASTIC RHEOLOGICAL MODEL
Yield point – measure of forces that cause mud to gel once it is motionless, and it directly
effects the carrying capacity of mud.
Gel Strength- measure of the ability of mud to develop and retain a gel structure.
A. Plastic viscosity (PV or μp), cp = ф600 – ф300
B. Yield point (𝛕γ), lb./100 ft2 = ф300 – μp
C. Apparent viscosity (AV or μa), cp = ф600/2
D. Gel strength
• Mud is stirred at high speed → allowed to rest for 10 sec (for initial gel strength) or 10 min
(for final gel strength)
• Gel strength – take torque reading at 3 rpm (lb./100 ft2)
Rheological properties of mud:
38.
39.
40.
41. APPARENT VISCOSITY CALCULATION AT EACH ROTOR
SPEED
■ Apparent viscosity (at each rpm)
θN : Dial reading in degrees
N : Revolution speed (rpm)
The dimension of bob and motor are chosen so that
the dial reading is equal to the apparent
Newtonian viscosity in centipoise at 300 rpm rotor
speed.
42. API FILTER PRESS - LPLT
A. Ordinary filter press (LPLT) – 100 Psi pressure
B. HPHT filter press – simulates actual reservoir- (with half filtration area), but can
be used in P upto 1200 psi and T up to 500 ◦F
Two properties are tested:
▪ Filtrate loss – Amount of water mud will loose in formation
▪ Mud cake thickness – that will be formed during drilling
There are 2 caps:
– Top cap
– Bottom cap – acts as formation
Mesh Size – 60
Filter paper diameter– 3.5 inch
44. PROCESS TO MEASURE FILTRATION LOSS
i. Fill the cup with mud sample
ii. Open cart, apply pressure, test starts.
iii. Under pressure some liquid will fill cylinder.
iv. Test is done for 30 min, and amount of water collected in the
graduated cylinder is noted as filtration loss.
(Amount of water should not exceed 11-13 ml)
v. Reading should be taken every 4 min.
vi. Plot graph between amount of filtrate loss Vs. time.
(Initially the rate of filtrate loss is more and gradually decreases) –
(initially, rock is clean, so flow is fast, then pores fill up → less loss )
**Some people also test it for 15 min or 7.5 min & convert the result to 30 min
𝑉2 = 𝑉1
𝑇2
𝑇1
V2 – volume at 30 min
V1 – volume at 15 min
45. PROCESS TO MEASURE FILTER CAKE THICKNESS
i. Remove the pressure source, and open the screw.
ii. Remove bottom cap and take out the filter paper (on hard surface).
iii. Wash it under tap and remove loose constituents.
iv. Take a scale, with graduation starting from bottom, and insert it in
the cake to measure the thickness.
(Thickness should be 1 mm at max)
v. Check if the film made is permeable or not.
**Mud cake thickness is reported as 1/32 of an inch
46. DETERMINATION OF SAND CONTENT
■ Sands/solids → abrasive → wear out all the equipment they
get in contact with, drilling rate also gets reduced.
■ In a fresh mud → zero sand content
■ Sands/solids need to be removed before recirculation.
■ Since sands become more fine → 100% removal not possible
Maximum allowed sand content → 2.5%
**If sand is not checked, it will continue to recycle and harm. A point will come
where san can no longer be removed, and new mud needs to be made.
(Which Gets Added Due To Borehole Cuttings)
47. DETERMINATION OF SAND CONTENT
Sand Content Kit
Sieve (Plastic)
Funnel (Plastic)
Glass Tube
Water bottle
Wire mesh -
200
48. PROCESS TO DETERMINE SAND CONTENT
■ Fill mud till mud level, and then water till “water to here” level.
■ Shake it vigorously ( to remove thixotropic properties) → so that separation of sand from
mud takes place.
■ Put funnel on the bottom of the sieve.
■ Gentle hammering is done so that water goes down.
■ Wash it with water again & repeat so that components like CMC also passes down.
■ Reverse the sieve, also put a funnel & put the solid (washed with water) back in glass
tube.
■ Measure the % sand in mud. (Scale is calibrated)
49. pH VALUE TEST
■ Should be between→ 8.5 – 9.5
■ If mud is very acidic/ basic → bentonite will not remain in dilution but
will precipitate.
Tested using:-
■ Litmus Paper
■ Electronic pH calculator
50. EQUIVALENT ANNULAR CIRCULATION DENSITY
Dynamic Pressure = Hydrostatic pressure (HP) + Annular Pressure Loss (ΔP)
Dynamic pressure → total pressure exerted on hole bottom
Dynamic pressure = equivalent circulation density (ECD) x g x hole depth
𝑬𝑪𝑫 = 𝝆𝒎 +
𝚫𝑷
𝟎. 𝟎𝟓𝟐 + 𝑯
Question-
For a well bore, Annular pressure losses are 200 psi, true vertical depth (TVD) is
10,000 ft and mud column weigh is 9.6 ppg. Calculate the equivalent circulation
density.
52. PUMPS
Circulation of Drilling fluid Reciprocating Pump (Duplex double
acting or triplex single acting)
To pump mud into degaser/ desander/
desilter
Centrifugal Pump
For increasing pressure of oil for hydraulic
system (so that it can rotate motor)
Rotary/Piston Pump
Water supply Pump Centrifugal Pump
Fuel pump in engine to circulate coolants Rotary pump/centrifugal pump
Cement pump Reciprocal Pump
53. PUMPS
Advantages of the reciprocating PDP when compared to centrifugal pumps are:
■ ability to pump fluids with high abrasive solids contents and with large solid
particles,
■ easy to operate and maintain,
■ sturdy and reliable,
■ ability to operate in a wide range of pressure (P) and flow rate (Q).
54. CALCULATION OF MUD WEIGHT INCREASE
𝑊𝑡𝐵 = wt. of barite required to add mud weight (lb/gal)
𝑉𝑜 = initial volume of mud (gal)
ρ𝑜 = initial mud density (lb./gal)
ρ𝑓 = final mud density (lb./gal)
ρ𝐵 = (Barite density (lb./gal)
𝑾𝒕𝑩 =
𝒗𝟎 𝝆𝒇 − 𝝆𝟎
𝝆𝑩 − 𝝆𝒇
Practice Question –
■ Determine the quantity/sacks of barite required to change the density of mud from
1.5 kg-J-l (12.53 ppg) to 2 kg-J-l (16.7 ppg). Calculate the increase in pit volume due to
the addition of such a quantity of barite for an initial mud volume of 10m3 (63 bbl.).
55. CALCULATION OF MUD WEIGHT INCREASE
𝑊𝑡𝑤 = wt. of water required to decrease mud weight (lb/gal)
𝑉𝑜 = initial volume of mud (gal)
ρ𝑜 = initial mud density (lb./gal)
ρ𝑓 = final mud density (lb./gal)
ρ𝑤 = (water density (lb./gal)
𝑾𝒕𝒘 =
𝒗𝟎 𝝆𝒐 − 𝝆𝐟
𝝆𝒇 − 𝝆𝒘
Practice Question –
(a) How much fresh water must be added to 1000 bbl. of 12 lb./gal mud to reduce its
density to 10 lb./gal?
(b) (b) What will be the resulting volume?
56. Thank You for your undivided attention !
We are now open to questions.
