Department of Petroleum Engineering
School of Earth Sciences –MU
Advanced Drilling Fluid (PETR 404)
Drilling fluid Design project
Frist and for most we are thankful GOD who
allowed to start this project and then again allowed us to finish. Secondly we
are thankful of our honorable instructor that encourage always more than what
we deserve Mr. Tekleberhan T/haymanot we have big respect to you, we know you
sacrifice more what you expect as instructor thanks. You will be our heart
forever, thanks your guidance for every aspect. GOD belles you were ever you
are. Than On the behalf of my group am very thankful specially with my group
mate who gives this project their maximum time and their efforts am really
appreciated them the way they participated this project. Finally, I will never
forget to thank my whole classmate that we were sharing and exchanges different
is a key process in the development of oil and gas field, whether at the
exploration stage or in a fully developed field. It set up up to 35-50% of
project costs to Successful completion of a well at minimal cost is therefore vital.
One area that highly affects both successful completion of a well and its cost
is the drilling fluid program. Drilling fluids is any fluid which is circulated
through a well in order to remove cuttings from a wellbore so it have advanced
over the years, more so in petroleum drilling; however, it is imperative to
design a simple drilling fluid program that will not only ensure a quality well
but also minimize the cost of the well. This project seeks to address the
selection of a drilling fluid best fit for oil and gas field .
Introduction to Drilling fluid
worked this project in different topics although Coal bed methane have very
broad topics but we tried our best according to different sources/references as
well as our experiences to complete this project. Drilling fluid, also known as Drilling mud, is a section which is
used in the process of drilling deep boreholes. These holes may be drilled for
oil and gas and a wide variety of other reasons. The mud can be an essential
part of the drilling process, serving a number of functions. One of the most
critical roles of drilling mud is as a lubricant and other which is going to be
discussed later on. The mud also acts as a carrier for the materials being
drilled, with material becoming on hold in the mud and then being carried
Definition of drilling
by the American Petroleum Institute (API), it is defined as combinations of
natural and synthetic chemical compounds as circulating fluid, used in rotary
drilling. Drilling fluids should retain several required characteristics, which
greatly improve the productivity of the drilling operation These include
anticipated rheological properties (plastic viscosity, yield value, low-end
rheology, and gel strengths), fluid loss prevention, stability under numerous
temperature and pressure operating conditions, stability against contaminating
fluids, such as salt water, calcium sulfate, cement, and potassium contaminated
fluids Wetting ability, penetration improvement characteristics.
2. How to design Drilling Fluid?
drilling operations, there must be proper and a general planning (How to
design) of the well in order to select the best drilling mud to drill well
bore. criteria for selecting drilling fluid are based on how to use
(performance of drilling fluid), not too expensive and environmentally friendly
(like skin irritation and contact dermatitis). selecting drilling fluid system
starts with identifying a drilling fluid family, according to the nature of
formation and choice of the mud formulation will be the second step. The three key factors that drive decisions about the type of drilling
fluid selected for a specific well are:
2.1 Cost –it
covers about 10% of the total cost of drilling the well. cost savings resulted
when mud engineers and the fluids performs correctly. Most of oil based muds
are more expensive than water based muds. Water is also used with cost free
emulsifiers, wetting agents and gel among the expensive fluids which have
generally a cost of 78.20$ per barrel. Potassium chloride /KCl/ polymer
drilling fluids have a cost of 43.01$ per barrel while water based drilling
fluids have a cost of 40.80$ per barrel.
2.2 Performance-The working capacity of drilling fluids is the most
important in drilling activity by designing correctly. There must be proper and
extensive planning of the well in order to select the best fluid to drill wells
that are usable, safe and minimum cost.
2.3 Environmental impact. Drilling
muds cause an effect on the environment due to the presence of some toxic
chemicals. Drilling mud disposal near the drilling area can make a great impact
on living things such as human life, animal and plants. This is mostly
happening by oil based drilling muds which are potentially toxic.
Make-up of a Drilling Fluid
Drilling fluid is
composed of a liquid either water or oil and some sort of viscosifying agent.
If nothing else is added, on every case the hydrostatic pressure is greater than
the formation pore pressure and the formation is porous and permeable a portion
of the fluid will be flushed into the formation. Since extreme filtrate can
cause borehole problems, some sort of filtration control additive is generally
added. In order to provide sufficient hydrostatic pressure to balance abnormal
pore pressures, the density of the drilling fluid is increased by adding a weight
material generally barite.
4. Relationship between drilling fluid
function and their properties:
Remove cuttings from well is one function which have a property as Viscosity, if viscosity is too low,
cuttings will settle to the bottom. And Thixotropic,
as it’s viscosity increases during static condition, this keeps cuttings
suspend when mud is not flowing. Fluids with shear thinning and elevated
viscosity efficient for hole cleaning.
E.g.: – during maintenance.
Seal permeable formation is functions of drilling fluid by which
Filter cake and filter loose, mud should be designed to deposit thin, low
permeable and flexible to limit invasion of fluids to the formation.
control formation pressure stability Density, formation pressure
increases mud density also increases to balance the pressure and keep well bore
maintain well bore stability: chemicals inhibitor, such as ca, k, oil,
salt Best for water sensitive formation such shale, to add inhibition use cacl2
to reduce water Absorption activity by a shale.
transmit hydraulic energy to the bit: as solid content, low solids, shear
thinning Drilling muds such as polymer fluids give more efficient hydraulic
principle of drilling muds
of rely on function for which it is designed so to describe their operation of
drilling muds, we have to consider the core functions of drilling mud such as
hole cleaning, well control, protection of formation and well bore stability
Hole cleaning It is a concerned with continues removal of cuttings
under bit to the surface and is the main controlling factor in drilling mud
design The main factor to affect cutting removal or transportation are,
drilling mud and cutting velocity. The cutting can experience downward movement
as a result of gravity which it leads to in negative velocity Relative to
fluids velocity. This negative velocity referred to as cutting slip velocity
and it Is Best in determining cutting transport. The movement of cuttings up
through the annuls is the result of cutting transport velocity, which is
different between fluid annular velocity and cutting slip velocity. This
implies in design drilling mud for efficient for hole cleaning we must consider
how the cutting acts and calculate the expected cutting slip velocity depending
on type of fluid and flow regime. For laminar flow there is effect of fluids
rheological properties, but in the case of turbulent flow there is no effect of fluids rheological
Well control It is
all about the controlling and eliminating kicks, so we limit the chance of blow
out. Kick and blow out occur when formation pressure goes beyond pressure of
drilling mud in the well. When kicks not stopped it leads to blow out which is
more difficult situation such as loss of life, damage of equipment’s,
environmental impact etc. the key parameter to be checked here is that mud
The hydrostatic pressure due to drilling fluid
is obtained from (P=0.052*MW*TVD). Another key parameter is ECD (equivalent
circulating density) this is the density on mud due to the effect of pump
pressure applied on it for circulation during drilling when there is movement of the drilling
fluid. Mathematically it is given by(ECD=MW+Pa/0.052*TVD): – MW= mud weight,
Pa= sum of annular pressure loses, TVD= true vertical depth it results BHCP
(bottom hole circulating pressure) which is the actual pressure the drilling
fluid has during circulation. It is important to consider BHCP during designed
process to ensure its kept low. Given by, BHCP=ECD*0.052*TVD.
Protecting formation from damage: This is
an important task of drilling fluids. For example, in geothermal drilling,
aerated fluids are used in the producing zone with aim of reducing formation
damage. Formation damage is mainly as result of plugging of the formation
natural porosity, permeability, either by solids or plugging with fluid
filtration. When we design drilling muds to reduce formation damage involves
considering of drilling window, which is the margin between the fracture and
pore pressure.as drilling practice well bore pressure must always exceed pore
pressure, both in circulating and non-circulating conditions. It should not
exceed fracture gradient, otherwise; costly drilling challenges such as loss of
circulation and formation damage occur.
6. Application of drilling fluid and types
1. Calcium treated mud
it prevents the swelling of formation shale, manage sloughing shale, whole
enlargement and also to prevent formation damage.
2. Polymer mud is used
in stabilize the formation and reduce filtrate less.
3. Low solid mud help
in improving rate of penetration.
4. Work over fluid
used for acidizing and fracturing operation and in inhibiting swelling
formation shale and minimize formation damage
5. Oil or synthetic
fluid is Useful in in hole stabilization, in high temperature wells, deviated
holes and pipe sticking problem.
6. Mixed metal
hydroxide mud used for stabilization of borehole and protection of producing
formation, to lower pump resistance and for
suspension of solid
during shut down and it improve drilling rate and cutting removal.
7. Oil based drilling
fluid is used to stabilize clay formation and for tolerating salt formation.
or completion fluids are fluids placed across the producing zones before or directly
after perforating, or any fluid placed across the formation during reworking,
undreaming, drill-in, or gravel pack procedures. These fluids help ensure that
production is steady with the estimated potential of the well. The primary
functions of completion/workover fluids are to: provide pressure control by
preventing formation fluids from entering the borehole maintain borehole
stability, minimize formation damage and control fluid loss with minimal solids
invasion. These fluids also keep the borehole “clean” of perforation debris,
solids such as drill cuttings, sand, etc., or any other contaminants by providing
a transportation medium that for circulating loose material to the surface. workover fluid has the following
density to control subsurface pressures
capable solids removal during circulation through filtration systems
nontoxic, low corrosively, and bacterial growth retardant
to other soluble salts, minerals, cement, etc.
8. Drilling fluid
is any fluid that is used in a drilling
operation in which that fluid is circulated or pumped from the surface, down
the drill string, through the bit, and back to the surface via the annulus.
8.1 Types of drilling fluid: there are two primary types of drilling
fluids: Water Based Fluids (WBFs) and Non-Aqueous Drilling Fluids (NADFs) or
8.1.1 Water Based Fluids (W BFs): consist
of water mixed with bentonite, clay and barium sulphate (barite) to control mud
density and thus, hydrostatic head. Other substances are added to increase the
desired drilling properties. These additives include thinners (e.g.
lignosulphonate, or anionic polymers), filtration control agents (polymers such
as carboxymethyl cellulose or starch) and lubrication agents (e.g.,
polyglycols) and numerous other compounds for specific functions.
8.1.2 Non-Aqueous Drilling Fluids
(NADFs): are emulsions where the
continuous phase is the Non-Aqueous Base Fluid with water and chemicals as the
internal phase. The NADFs comprise all non-water and non-water dispensable base
fluids. Similar to WBFs, additives are used to control the properties of NADFs.
Emulsifiers are used in NADFs to stabilize the water-in oil emulsions.
Mud cake: Mud filter cake is a
layer formed by solid particles in drilling mud against porous media due to
differential pressure between hydrostatic pressure and formation pressure.it is
better the filter cake to be impermeable and thin. External filter cake is
important in minimize solid invasion and fluid loss to a formation from
completion fluid and drilling and also in controlling formation damage due to
mud cake permeability decrease with increasing with increasing overbalance
pressure. Filtrate and mud cake are managed by mud particle type, concentration
and size so a mud cake must be thin, low permeability that helps near well bore
stability and strengthen the well bore in addition to reduce the amount of mud
flowing to the formation.
of mud cake on a drilling operations?
Torque and drags: If the
drilling mud becomes a thick filter cake across the wall of wellbore, torque
will increase. Furthermore, it will result in high drag while tripping out of
the hole or logging.
Differential sticking: Since
the formation is permeable during drilling there is a chance of getting stuck
across the formation.