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Selection and Application of Drilling Fluids
Research · April 2015
DOI: 10.13140/RG.2.1.3243.4722
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MSc Petroleum Engineering
Drilling Engineering and Well Completion
(CBE4015-N-CF1-2014)
Assignment on
Selection and Application of Drilling Fluids
By
NWAICHE JASON
N3264679
Submitted to
Dr Sina R. Gomari
January, 2015.
1
TABLE OF CONTENTS
TITLE PAGE ………………………………………………………………………………………………………………..
1
TABLE OF CONTENTS …………………………………………….…………………………………………………..
2
LIST OF TABLES ………………………………………………………………………………………………………….
3
LIST OF FIGURES …………………………………………………………………........................................
4
1.0
INTRODUCTION ……………………………………………………………………………………………..
5
1.1
Drilling Fluids …………………………………………………………………………………………………
5
2.0
TYPES AND APPLICATIONS OF DRILLING FLUIDS …………………………………………….
6
2.1
Water-Based Mud (WBM) ……………………………………………………………………………..
6
2.2
Oil-Based Mud (OBM) …………………………………………………………………………………….
6
2.3
Synthetic Based Mud (SBM) ………………………………..............................................
6
2.4
Emulsion Drilling Mud (EDM) ………………………………............................................
7
2.5
Invert Emulsion Mud (IEM) ………………………………...............................................
7
2.6
Air Drilling Fluid ……………………………….................................................................
7
2.7
Foam Drilling Fluids ………………………………...........................................................
8
3.0
SELECTION FACTORS AND PROPERTIES OF DRILLING FLUIDS ………….................
9
3.1
Factors to Consider While Choosing a Drilling Fluid ………………………………………..
9
3.2
Properties of Drilling Fluids …………………………………………………………………………….
9
REFERENCES ………………………………………………………………………………………………………………
11
APPENDIX ………………………………………………………………………………………………………………….
12
a) Tables …………………………………………………………………………………………………………….
12
b) Figures ……………………………………………………………………………………………………………
13
2
LIST OF TABLES
Table 1:
Comparison between the merits of drilling mud/fluid systems
12
Table 2:
Typical drilling mud composition
12
LIST OF FIGURES
Fig 1:
A Drilling mud cycle system
13
Fig 2:
Types of drilling fluids
13
Fig 3:
Reversible invert emulsion mud
14
3
1.0 INTRODUCTION
Over the years, the discovery of petroleum in various parts of the world has led to
the development of techniques and equipment to enhance and optimize the
production of this natural resource. Drilling fluids (mud) happens to be one of these
developed technologies used for efficient drilling and to control drilling pressure,
stabilize wellbore as well as control fluid losses during drilling.
From Fig. 1, during drilling, drilling mud is pumped through the kelly and the drill
string using mud pipes which connects the drilling fluid and a swivel device
connected to the kelly. This device ensures that the mud is circulated while rotating
the kelly and drill string. Drilling fluids are pumped from the mud tanks by the pump.
This fluid is passed through the kelly, drill pipe, drill collars, and drill bit and goes
back to the surface through well bore and the conductor pipe unto the shale shaker
which then removes cuttings from the drilling mud and sends back the mud to the pit
(Teymournejad, 2010).
1.1
DRILLING FLUIDS
AES Drilling Fluids (2012) defined drilling fluids as “a fluid used to drill boreholes into
earth and are used while drilling oil and natural gas wells and on exploration rigs”.
Drilling fluid is most times also referred to as ‘drilling mud’.
The major functions of a drilling fluid include;
 Improving the hydrostatic pressure while drilling so as to eliminate formation
fluids from fi ding their way back into the wellbore.
 Cools, cleans and supports the drill bit and its assembly during drilling.
 Prevents damage to the formation and avoiding the corrosion of drill pipes.
 Pushes out and suspends drill cuttings (debris of rock materials and mud)
during drilling.
4
 Seals permeable formations thereby reducing circulation loss.
 Minimizes environmental impacts and hazards resulting from drilling.
Although a drilling fluid has been noted for some of these above functions, it is also a
peculiar thing to note that the functionality of drilling fluids depends a lot on the
drilling fluid properties (Ljones, 2013) and by modifying the composition of these
fluids, the required properties may be obtained.
5
2.0 TYPES AND APPLICATIONS OF DRILLING FLUIDS
There exist many types of drilling fluids presently used today in the drilling and
petroleum industry. Each used according to the prevailing drilling conditions
encountered. The following are some of the existing drilling fluids used in the drilling
industry today as classified under three (3) groups:
2.1
WATER-BASED MUD (WBM)
This is a class of drilling fluid that has fresh or seawater as its continuous phase. Its
composition includes mixtures of aqueous polymers, clay and brine. It is the most
predominant type of drilling fluid.
2.2
OIL-BASED MUD (OBM)
This class of drilling fluids have oil (usually gas oil) as its continuous phase, an
average molecular weight of about 120 to 1000 and being synthesized from one or
more olefin monomers with a carbon chain of about C2 to C14. It is used mainly in
cases where the WBM is considered inadequate. They are mainly composed of as
reverse-emulsions of saltwater (brine) in a continuous oil phase which is stabilized by
surfactants (Khodja et. al., 2010). Although OBM are amongst the less used drilling
fluids today because of their expensive nature, they also guarantee better results
when used.
2.3
SYNTHETIC BASED MUD (SBM)
This category of drilling mud are quite similar to the OBM, but less harmful in terms
of its toxicity and environmental impact. They are mainly composed of olefins, esters
and sometimes paraffins. In terms of its application, SBM have a low kinetic viscosity
and thus could be use under low pressure conditions.
6
2.4
EMULSION DRILLING MUD (EDM)
These are a group of drilling mud that have emulsion-based phases. It is composed of
two (2) phase; the outer and inner phases respectively. The outer phase consists of
salt water (brine) whereas the inner phase component consists of oil. In terms of its
application and uses, surfactants are applied to make the two phases miscible due to
the opposing emulsion effect. They are also very cheap and environmentally friendly
to apply, with comparison to OBM, but more expensive when compared to WBM
(Shah et al., 2010).
2.5
INVERT EMULSION MUD (IEM)
This category is quite similar to the EDM in terms of its chemical composition, cost,
environmental impacts and applications, but differs in the phase distribution. Just as
the name implies, it is the inverse composed form of the EDM. It also has two (2)
phases, but the outer phase consists of oil while the inner phase consists of salt
water (brine). In terms of their application, they have a light viscosity and suitable for
high temperature and be easily degraded by micro-organisms.
2.6
AIR DRILLING FLUID
This category of drilling fluids are basically aerosols and are used mainly for
underbalanced pressure drilling where there exists little or no connection between
the reservoir oil or water (Shah et al., 2010). Its advantage over other forms of
drilling fluids comes from its high penetration rate, little damage to formation, zero
circulation loss, little or no contamination. According to Shah et al., (2010), in the
application, an understanding of the formation hydraulics is a key factor to a
successful use.
7
2.7
FOAM DRILLING FLUIDS
Foam drilling fluids are composed of about 5-25% liquid and 75-95% gas phases
respectively (Shah et al., 2010). And because they are used most times when their
pressure is lower than the pressure of hydrocarbons located within the pores of the
rock formation. They are mainly applied in underbalanced or deep-water wells,
which is why they are most times called ‘underbalanced fluids’ (Khodja et. al., 2010).
This is also one of the best drilling fluids as tests from controlled drilling rates have
shown that air or gas is a faster drilling fluid than water or oil, while water is
considered the fastest drilling liquid than oil.
8
3.0 SELECTION FACTORS AND PROPERTIES OF DRILLING
FLUIDS
3.1
FACTORS TO CONSIDER WHILE CHOOSING A DRILLING FLUID
The choice of a drilling fluid type or system usually starts with selecting a drilling fluid
(mud) family according to the nature of the rock formation and considering its
financial implications as well as environmental impacts. This is because drilling fluids
may cover for 5% to 15% of total drilling cost but could lead to a 100% of drilling
problems (Bloys et.al., 1994).
In choosing a drilling fluid, emphases are based on the following factors;
 Well design
 Formation pressure
 Rock mechanics
 Chemistry of the formation
 Limiting negative impacts on the producing formation
 Environmental issues and regulations
 Logistics
 Cost
It is important to note that the ability to simulate down-hole conditions and optimize
fluid design will always contribute to a reduction in non-productive time.
3.2
PROPERTIES OF DRILLING FLUIDS AND WELL CONTROL EFFECTS
To address these considerable factors, a drilling fluid should consist of about five (5)
basic properties, namely; rheology, fluid loss, chemical properties, solid contents and
density. For any type of drilling fluid, all five properties may be influenced with
chemicals and other additives (Bloys et.al., 1994).
i.
Rheology: This is a property of fluid that talks about viscosity. A high
viscous fluid may be able to carry drill cuttings to the surface freely
alongside other weighting agents in the mud.
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ii.
Density: Requires enough hydrostatic pressure to avoid the drilled
borehole from caving in, thereby keeping the formation fluid from entering
the borehole. Drill muds with high density than the cuttings density makes
cleaning of wellbore easier and faster.
iii.
Fluid Circulation Loss: A good drilling fluid should be able to have a lowpermeability effect so as to be able to seal the pores between the
formation and wellbore.
iv.
Solid Content: Solids could be high gravity (HGS) e.g. barite and other
weighting materials or low gravity (LGS) e.g. clays, polymers and bridging
materials. Drilling fluids with high solid contents (i.e. LGS) usually increase
plastic viscosity and gel strength because they have more thicker filter
cakes and slow drilling rates than low solid content fluids (i.e. HGS).
v.
Chemical Properties: This is a major property of drilling fluids that affects
performance and wellbore stability. It monitors salt formations, pH and
corrosion effects of a drilling fluid.
By modifying some of these properties and factors, for example the viscosity and
mud weight, the negative effects resulting from kick during drilling prevents
formation fluid from entering back in the wellbore.
10
REFERENCES
AES Drilling Fluids (2012) Drilling fluids. Available at:
http://www.aesfluids.com/drilling_fluids.html (Accessed: 23 December, 2014).
Al-Ansary, M. S., & Al-Tabbaa, A. (2004) ‘Stabilisation/solidification of synthetic north sea
drill cuttings containing oil and chloride’ Proceedings of the international RILEM conference
on use of recycled materials in building and structures, Barcelona, Spain, 8 to 11 November
2004, pp. 833-842.
Baars, D.L., Watney W. L., Steeples, D.W., and Brostuen, E.A. (2001) Petroleum: a primer for
Kansas. Available at: http://www.kgs.ku.edu/Publications/Oil/primer12.html (Accessed: 28
December 2014).
Bloys, B., Davis, N., Smolen, B., Bailey, L., Houwen, O., Reid, P. and Montrouge, F. (1994)
‘Designing and managing drilling fluid’, Oilfield Review, 6(2), pp.33-43 (Accessed: 22
December 2014).
Chilingarian, G. V. and Vorabutr, P. (1983) Drilling and drilling fluids. Amsterdam: Elsevier
Scientific.
Khodja, M., Khodja-Saber, M., Canselier, J. P., Cohaut, N. and Bergaya, F. (2010) ‘Drilling
fluid technology: performances and environmental considerations’, Product and Services,
From R&D to final solutions, pp. 227-232. Available at: http://cdn.intechopen.com/pdfswm/12330.pdf
Ljones, .T. (2013) Drilling mud property estimator. M.Sc dissertation. Norwegian University
of Science and Technology. Available at: http://www.divaportal.org/smash/get/diva2:649714/FULLTEXT01.pdf (Accessed: 20 December 2014).
Patel, A. D. (1999) ‘Reversible invert emulsion drilling fluids: a quantum leap in
technology’, SPE Drilling & Completion, 14(4), pp. 274-279. Available at:
https://www.onepetro.org/download/journal-paper/SPE-59479-PA?id=journalpaper%2FSPE-59479-PA
Shah, S. N., Shanker, N. H. and Ogugbue, C. C. (2010) ‘Future challenges of drilling fluids and
their rheological measurements’ AADE fluids conference and exhibition, Houston, Texas, 5-7
April 2010.
Teymournejad, .H. (2010) Drilling materials databank. Availabe at:
http://petroiran.blogfa.com/8904.aspx?p=1 (Acessed: 12 December 2014).
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APPENDIX
a) TABLES
Source: Al-Ansary, M. S., & Al-Tabbaa, A. (2004)
12
b) FIGURES
Fig 1: A Drilling mud cycle system (Teymournejad, 2010)
Fig 2: Types of drilling fluids (Khodja et. al., 2010)
13
Fig 3: Reversible invert emulsion mud (Patel, 1998)
14
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