Introduction to Drilling Fluid /or Mud used to drill Oil and Gas Wells into the sub-surface Hydrocarbon Reservoir. Overview of the rheological properties and general description.

1. भारतीय प्रौद्योगिकी संस्थान (भारतीय खनन विद्यापीठ), धनबाद
INDIAN INSTITUTE OF TECHNOLOGY (ISM), DHANBAD
पेट्रोलियम अलभयांत्रिकी विभाि
Department of Petroleum Engineering
Term Presentation on;
‘Rheology and Filtration Characteristics of Drilling
Fluids for Efficient Drilling Operations’
PRITISH BARMAN 2nd Semester,
M.Tech (2016-18)

2. Content
 OBJECTIVE
 INTRODUCTION
 Properties Of Drilling Fluids
 Rheology Characteristics
 Filtration Control
 Case Study
 CONCLUSION
 REFERENCES

3. Objective
 Describe Drilling Fluid
 Properties of Drilling Fluid
 μ, ρ,Fluid Loss, pH, PV, YP, gel, Alkalinity
 Discuss Rheological Characteristics
 Rheology & Hydraulics, Fluid Types
 Filtration Loss Control
 Filtration Control Agents
 Lost Circulation Materials
 API Fluid Loss Description
 Case Study
 Summarize

4. Introduction to Drilling Fluids
 (a.k.a Mud) -complex mixture of a base, either water, oil or air
and various additives.
 Water Based Mud (WBM), Oil Based Mud (OBM), and
Aerated Mud (ABM)
 weighting, rheology, filtration control, eccentricity and hole
cleaning etc.
 overbalance to contain kick and blowout
 cutting lifting
 shale inhibition
 borehole stability
 keeping the bit and the drill string cool,
 prevent pipe sticking
 drag and torque on the drill string

5. Properties of Drilling Fluids
Viscosity
 internal resistance provided by a fluid to its flow
 attraction between molecules of a liquid
 adhesion and cohesion on suspended particles and liquid
 most familiar instrument used on field is ‘Marsh Funnel’
 Unit of viscosity in oil industry is centipoises (cp)
Density
 The term mud weight is used in connection with mud often than
density
 quantity of solids in the liquid phase
 ρm = Mw+Ms /Vw+Vs

6. Properties of Drilling Fluids
Fluid Loss
 Fluid loss is defined as the loss of a mud filtrate (liquid
phase) into a permeable formation
 Mud solids are deposited on the walls of the hole, and
filtrate invades the formation
 object is to form a thin, tough filter cake to prevent
excessive loss of filtrate

7. Properties of Drilling Fluids
pH
 The pH, or hydrogen ion concentration, is a measure of the relative
acidity or alkalinity.
 Generally, the pH of mud falls between 8 and 11
 major role in controlling the solubility of calcium
 At high pH values, calcium solubility is very limited
 high-pH mud suitable for use in the drilling of carbonate formation
 pH value is also an important indicator for the control of corrosion
 A minimum value of 9.5 should be maintained to prevent oxygen
corrosion
 high pH tends to disperse (disintegrate) the active clays in the mud
 Starch is used as a fluid loss additive.
 Starch is susceptible to bacterial attack at pH values below 11.5

8. Properties of Drilling Fluids
Alkalinity
 Alkalinity or acidity of a mud is indicated by the pH.
 The pH scale is logarithmic and hence a high pH mud may vary
considerably without a noticeable change in pH.
 The filtrate and mud can both be measured to show the
phenolphthalein alkalinity.
 The test for filtrate is carried out by putting 1 or more milliliters of
filtrate into a titration dish and adding 2 or 3 drops of phenolphthalein
indicator solution.
 Drops of 0.02 normal nitric or sulfuric acid solutions are then added
until the pink coloration just disappears.
 The alkalinity is measured as the number of milliliters of acid per
milliliter of filtrate.
 The test for mud is similar except that to one milliliter of mud, 25 to 50
milliliters of water are added for dilution and 4 or 5 drops of
phenolphthalein are added. The result is measured the same as for the
filtrate.

9. Rheological Characteristics
Rheology and Hydraulics
 Rheology and hydraulics are interrelated studies of
fluid behavior.
 Fluid rheology and hydraulics are engineering terms
that describe the behavior of fluids in motion.
 Rheology is the science of deformation and flow of
matter.
 Primarily concerned with the relationship between
shear stress and shear rate and the impact they have
on fluid flow characteristics inside tabular and annular
spaces.

10. Rheological Characteristics
Plastic Viscosity
 The plastic viscosity (PV) is calculated by measuring the
shear rate and stress of the fluid. These values are
derived by using a Fann viscometer, which is a rotating
sleeve viscometer, and may be a simple hand operated
two speed model or a more complex variable speed
electric model. The two speed model operates at 300
and 600 rpm.
 i.e. PV (cp) =Ɵ600-Ɵ300

11. Rheological Characteristics
Yield Point
 Yield point, the second component of resistance to
flow in a drilling fluid, is a measurement of the electro-
chemical or attractive forces in a fluid. These forces are
a result of negative and positive charges located on or
near the particle surfaces.
 Mathematically yield point is calculated from the
equation:-
YP = Ɵ300 – PV
YP = (2 × Ɵ300) – Ɵ600
Unit of YP is lbs /100ft².

12. Rheological Characteristics
Gel Strength
 It is the measurement of the attractive forces of the
mud while at rest or under static conditions.
 The magnitude of gelation, as well as the type of gel
strength, is important in the suspension of cuttings
and weight material.
 Two readings: 10 second and 10 minute with the speed
of the viscometer set at 3 rpm.
 The fluid must have remained static prior to each test,
and the highest peak reading will be reported.
 The unit of gel strength is same as yield point,
i.e. lbs/100 ft²

13. Table: Comparison of non-Newtonian, Newtonian, and viscoelastic properties
Viscoelastic
Kelvin material,
Maxwell material
"Parallel" linear
combination of elastic and
viscous effects
Some lubricants, water
Time-dependent
viscosity
Rheopecty
Apparent
viscosity increases with
duration of stress
Synovial fluid, printer ink,
Thixotropic
Apparent
viscosity decreases with
duration of stress
xanthan gum solutions,
some clays, some drilling
many paints
Non Newtonian
Viscosity
Shear thickening
(dilatant)
Apparent viscosity
increases with increased
stress
Suspensions of corn -starch in
water
Shear thinning
(pseudoplastic)
Apparent
viscosity decreases with
increased stress
paper pulp in water, latex
paint, ice, blood, sand in
Generalized
Newtonian fluids
Viscosity is constant.
Stress depends on normal
and shear strain rates and
also the pressure applied
on it
Blood plasma,
custard, water

14. Graphical Representation:
Shear Stress Vs. Shear Rate
ShearStress
Shear Rate

15. Rheology Control Agents
Viscosifier (Suspending Agents)
 Additives in drilling fluid which serve the purpose to provide desired
viscosity required for various functions such as cutting carrying
capacity and gel strength of mud.
These include:
 a.Bentonite Clay
 b.CMC, Carboxymethyl Cellulose
 c. Xanthan Gum
 d.Guar Gum
 e.PAC HV, Poly Anionic Cellulose (High Viscosity)

16. Rheology Control Agents
Flocculants
 Are used to increase viscosity for improved hole cleaning, to
increase bentonite yield and to clarify or de-water low solids drilling
fluids. Flocculants cause colloidal particles in suspension to group
into clusters or flocs causing solids to settle out. Flocculants
commonly used in the oilfield include:
 Drill Salt (Brine), NaCl, Sodium Chloride
 KCL, Potassium Chloride
 Hydrated Lime, Calcium Hydroxide
 Gypsum, Calcium Sulfate
 Soda Ash, Sodium Carbonate
 Sodium Bicarbonate (Bicarbonate of Soda)
 TSPP, Tetrasodium Pyrophosphate
 Polyacrylamide Polymers

17. Rheology Control Agents
Thinning (De-flocculants) Agents
 Modify the relationship between viscosity and percentage of solids
in a drilling fluid. Thinning agents can be used to reduce gel
strength to improve pump-ability of a drilling fluid. Thinning agents
function as a de-flocculants to prevent the flocculation of clay
particles which produce high viscosity and gel strength.
 a.Lignosulphonates
 b.Ligthin (Caustized Lignite)
 c. Lignite

18. Rheology Control Agents
Emulsifiers
 To create a homogeneous mixture (an emulsion) of two insoluble
liquids. Emulsifiers may be anionic (negatively charged), non-ionic
(neutral) or cationic (positively charged) chemicals, depending on
whether they are used as primary or secondary emulsifiers.
 Fatty acid and amine based chemicals are used in oil base drilling fluids.
 Detergents and soaps
 Organic acids
 Water based surfactants are used for water base drilling fluids.

19. Filtration Control Additives:
Filtration Control Agents
 These products reduce fluid loss of a drilling fluid in various
operating conditions including water base drilling systems, oil base
drilling systems, high temperature and high temperature drilling
environments.
Water Based Drilling Fluids
 a.Bentonite
 b.CMC, CarboxyMethyl Cellulose
 c. PHPA, Partially Hydrolyzed Polyacrylamide
 d.PAC LV, Poly Anionic Cellulose (Low Viscosity)
 e.PAC HV, Poly Anionic Cellulose (High Viscosity)
 f. Drill Amyl, Modified Starch

20. Filtration Control Additives:
Loss Circulation Materials (LCM)
 The primary function of Loss Circulation Materials is to
physically plug the zone in the formation that is losing
drilling fluids. Commonly used products offered by include:
 Nut Plug
 Mica (Medium grade)
 Mica (Fine grade)
 Mica (Coarse grade)

21. Case Study:
‘Future Direction of Research and Challenges in
Mud Engineering’
Developing environment-friendly OBM for Field Application
 Formulation of an environmentally friendly drilling fluid with zero impact on
the environment.
 Ammnullah (2010) proposed the use of waste vegetable oil in the
formulation of environment friendly OBM.
 Ogunrinde and Dosunmu (2010) suggested the use of palm-oil. A major
multinational oil company for off-shore drilling operations had used highly
de-aromatized aliphatic solvents to formulate low toxicity mud system.
 Challenge is to bring down the cost of formulation of these muds.

22. Case Study:
‘Future Direction of Research and Challenges in
Mud Engineering’
Development of environment friendly mud additives
 Hazardous effects of additives on marine and human life had been reported.
 Effect ranges from minor physiological changes to reduced fertility and
higher mortality rates.
For example,
 1) Jonathan et al. (2002) reported that
 ferro-chrome lignosulfonate (a thinner and deflocculant) affected the survival and
physiological responses of fish eggs and fry.
 The filtration control additive CMC (carboxymethylcellulose) causes the death of
fish fry at high concentrations (1000-2000 mg/ml) and physiological changes start
the level of at 12-50 mg/ml.
 2) On the other hand, corrosion inhibitors such as phosphoxit-7, EKB-2-2,
and EKB-6-2 cause genetic and teratogenic damages in humans.

23. Case Study:
‘Future Direction of Research and Challenges in
Mud Engineering’
Development of mud and/or additives for HTHP Applications
 At extreme high temperature and high pressure (HTHP) conditions, mud
systems formulated with macro and micro based materials (chemicals and
polymers) become drastically altered.
 This is due to the breakage or association of polymer chains and branches by
 vibration,
 Brownian motion and
 thermal stress
causing drastic reduction in gelling and viscous properties.
 To solve this problem, nanos with excellent thermal stability and with extreme
pressure consistency should be developed.

24. Conclusion
 The success and smooth operation of the entire drilling program is
based on optimum designing and monitoring of the drilling fluid, is
mud.
 Various additives are added to each mud system to achieve desired
mud characteristics of rheology, weighting and filtration control.
 Weighting is primarily achieved by adding weighting agents commonly
barite, lignite etc.
 Rheology control includes monitoring the parameters of plastic
viscosity, apparent viscosity, yield point, equivalent circulation density,
and gel strength.
 High Filtration may cause serious damages to the formation
 To keep the fluid loss in check, it is necessary to design the mud
according to the particular geo technical order of the well.
 Filtration control additives are used to condition the mud for reducing
the fluid loss, additionally,
 lost control materials like mica flakes are pumped to arrest abnormal
filtrate loss by forming physical barriers between the wellbore and the
formation.

25. References
 Devereux, S., 1999. Drilling Technology: In Nontechnical Language,
PennWell Books.
 Fink, J., 2011. Petroleum engineer’s guide to oil field chemicals and
fluids, Access Online via Elsevier.
 Hawker, D., 2001. Drilling Fluid Hydraulics.
 Max R. Annis, M.V.S., 1996. Drilling Fluid Technology Exxon Manual.
 Skalle, P., 2010. Drilling Fluid Engineering, Bookboon.

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