Drag BITS

what is drag bit?

A drag bit is a drill bit usually designed for use in soft formations such as sand, clay, or some soft rock. However, they will not work well in coarse gravel or hard rock formations. Uses include drilling water wells, mining, geothermal, environmental and exploration drilling. Whenever possible, they should be used to drill pilot holes because they produce cuttings that are easiest to log

Historically there were two types of drill bits used in or natural gas drilling rigs , a drag bit and a rock bit:

1.a polycrystalline diamond compact hammer bit( pdc bits) is used for soft rocks, like sand and clay. The drill string is rotated along with pneumatic pressure, and nibs on the bit shear the rock.

2.a deep hole (also called a roller bit ) consists of teeth on wheels which turn as the drill string is rotated. These teeth apply a crushing pressure to the rock, breaking it up into small pieces.

In today's modern industry the two main types of drill bits are now classed as PDC (polycrystalline Diamond Compact) and Roller Cone; although the tri-cone dominates, bi-cone and mono cone bits do exist. Natural and synthetic diamonds are used in coring bits, as well as for very hard rock drilling with mud motors and turbines.drag bit type bits are used for mining and construction and also for oil and gas work over wells.

What PDC bit?

A drilling tool that uses polycrystalline diamond compact (PDC) cutters to shear rock with a continuous scraping motion. These cutters are synthetic diamond disks about 1/8-in. thick and about 1/2 to 1 in. in diameter. PDC bits are effective at drilling shale formations, especially when used in combination with oil-base muds.

Advantages of PDC bits:

Bit Brokers International introduces PDC bits to their line-up of products. These bits are designed for high speed drilling in shale, limestone, and sandstone formations. Unlike roller cones, these PDC bits are a one piece matrix bodies with no moving parts. The fixed-cutters shave away the rock, making it possible to operate with higher rotation speeds more efficiently in consolidated formations.

Bit Brokers offers PDC bits in a variety of sizes and number of blades.

Variables affected PDC bits design

1.Bit body material.

2.Bit profile.

3.Grave protection.

4.Cutter shape.

5.Number of concentration of cutter.

6.Locations of cutter.

7.Cutter orientation.

8.Cutter exposures.

9.Hydraulics.

Roller cone bit

A roller-cone bit is adrill bit used for drilling through rock, for example when drilling for oiland gas.

There are three types of roller cone bit:

1.The two cone bit: is used for soft formation only.

2.The three cone bit: is the most widely used.

3.The four cone bit: is used for drilling large hole size.

oil traps

There are three basic forms of a structural trap in petroleum geology:

• Anticline Trap
• Fault Trap
• Salt Dome Trap

The common link between these three is simple: some part of the earth has moved in the past, creating an impedence to oil flow.
Anticline Trap

An anticline is an example of rocks which were previously flat, but have been bent into an arch. Oil that finds its way into a reservoir rock that has been bent into an arch will flow to the crest of the arch, and get stuck (provided, of course, that there is a trap rock above the arch to seal the oil in place

Fault Trap

Fault traps are formed by movement of rock along a fault line. In some cases, the reservoir rock has moved opposite a layer of impermeable rock. The impermeable rock thus prevents the oil from escaping. In other cases, the fault itself can be a very effective trap. Clays within the fault zone are smeared as the layers of rock slip past one another. This is known as fault gouge

Salt Dome Trap
Salt is a peculiar substance. If you put enough heat and pressure on it, the salt will slowly flow, much like a glacier that slowly but continually moves downhill. Unike glaciers, salt which is buried kilometers below the surface of the Earth can move upward until it breaks through to the Earth's surface, where it is then dissolved by ground- and rain-water. To get all the way to the Earth's surface, salt has to push aside and break through many layers of rock in its path. This is what ultimately will create the oil trap

Stratigraphic Traps

A stratigraphic trap accumulates oil due to changes of rock character rather than faulting or folding of the rock. The term "stratigraphy" basically means "the study of the rocks and their variations". One thing stratigraphy has shown us is that many layers of rock change, sometimes over short distances, even within the same rock layer. As an example, it is possible that a layer of rock which is a sandstone at one location is a siltstone or a shale at another location. In between, the rock grades between the two rock types. From the section on reservoir rocks, we learned that sandstones make a good reservoir because of the many pore spaces contained within. On the other hand, shale, made up of clay particles, does NOT make a good reservoir, because it does not contain large pore spaces. Therefore, if oil migrates into the sandstone, it will flow along this rock layer until it hits the low-porosity shale. Voilà, a stratigraphic trap is born!

Combination Traps

As the name implies, a combination trap is where two (or more) trapping mechanisms come together to create the trap. In reality, many successful oil traps are combination traps.

Filter Calculation

In all actual filters the resistance to the flow
of filtrate varies with time as the precipitate
deposit on the filtering sand in sand bed
filters, or as the filter cake building up on
the cloth, screen or other filter medium. The
filter medium holds back the solids as the
filtrate passes through, and the filter cake
continues to increase in thickness, adding
its resistance to the flow of filtrate. This
action continues during filtration. At the end
of the filtration, the products are filtrate
porous filtrate cake, and fluid in the porous
of the cake.
During filtration the operation is laminar
flow and the linear velocity V are
v = (1/A) (d V/d t) = (K ρ Lw)/ L μ
= K (-Δ P) / L μ [1]
where
v linear velocity
V volume f iltrate
A area of filter media
(gc Dp
2 FRe)
K permeability of cake K = -----------
32 ff
L thickness of cake

t time of filtration
ΔP pressure drop through the cake
Relation between Volume of filtrate
and Time of filtration
In order to obtain an expression relating
filtration capacity (expressed as either the
quantity of filtrate V or the cake thickness L
) with the time of filtering t, it is necessary
to obtain the relation between the variable, L
and V . This can be done by making a
material balance between solid in slurry
filtered and the solid in cake.
Mass of solid in cake = mass of solids in
slurry.
(V+ε L A) ρ x
( 1- ε ) L A ρ s = [2]
(1-x)
where
L A volume of cake
( 1- ε ) L A volume of solid in cake
ρs density of solid in cake
ρ density of filtrate
x mass fraction of solid in slurry
ε porosity of cake
note: [(mass of filtrate/total mass) /(mass of solid
/total mass)] = (1-x)/x
Then,
mass of solid = mass of filtrate ( x / 1-x )
Then
ρ s (1-x) ( 1- ε ) - ρ x ε
V = [ ] L A [3]
ρ x
V ρ x
L = [ ] [4]
A [ρ s (1-x) ( 1- ε ) - ρ x ε]
According to equation [1]
(d V/d t) = K A (-Δ P) / L μ
K A2 [ρ s (1-x) (1- ε ) - ρ x ε ] (-ΔP)
∴(dV/dt)= [5]
μ V ρ x
This equation is an expression for the
instantaneous rate of filtration in term of
properties of the slurry, cake, quantity of
filtrate and pressure drop through the cake.
For a given slurry, the only variables subject
to
the control of the operator are pressure drop
(-ΔP), filtrate volume V, an time t. If we but :
μ ρ x
Cv = [62 K [ρ s (1-x) (1- ε ) - ρ x ε]
A2 (-ΔP)
∴ (d V/d t) = [7]
2 Cv V
If the cake porosity remains essentially
constant during filtration (as is true with a
so-called non-compressible cake and may
also occur for constant pressure drop
filtration in general).
Cv may be considered as a constant, and
equation [7] is easily integrated. For
constant pressure drop and constant
porosity, this integrates to:
Cv V2
t = [8]
A2 (-Δ P)]. absolute viscosity of filtrate

FILTERATION

Filtration may be de defined as the
separation of solids from liquids by passing
a suspension through a permeable medium,
which retains the particles. Filtration is
considers one of the most common
applications of the flow of fluids through
packed bed. As carried out in industrially, it
is exactly analogues to the filtration carried
out in the chemical laboratory using filter
paper in a funnel. In every case, the
separation is accomplished by forcing the
fluid through porous media (membrane). The
solid particles are trapped within the pores
of the membrane and build up as a layer on
the surface of this membrane. The fluid,
which may be either gas or liquid, passes
through the bed of solid and through the
retaining membrane.
Industrial filtration differs from laboratory
filtration only in the bulk of material
handled and in the necessity that it be
handled at low cost. Thus, to attain a
reasonable throughput with a moderatesized
filter, the pressure drop for flow may
be increased, or the resistance to flow may
be decreased. Most industrial equipment
decreases the flow resistance by making the
filtering area as large as possible without
increasing the overall size of the filter
apparatus.
The choice of filter equipment depends
largely upon economics, but the economic
advantages will very depending upon the
following:
1. Fluid viscosity, density, and chemical
reactivity2.
Solid particle size, size distribution,
shape of particles’ flocculation
tendencies and deformability.
3. Feed slurry concentration.
4. Amount of material to be handled.
5. Absolute and relative value of liquid
and solid particles.
6. Completeness of separation required.
7. Relative costs of labor, capital, and
power

OVERALL REFINERY FLOW

The crude oil is heated in a furnace and charged to an atmospheric distillation
tower, where it is separated into butanes and lighter wet gas, unstabilized
light naphtha, heavy naphtha, kerosine, atmospheric gas oil, and topped (reduced)
crude (ARC). The topped crude is sent to the vacuum distillation tower and separated
into vacuum gas oil stream and vacuum reduced crude bottoms (residua,
resid, or VRC).
The reduced crude bottoms (VRC) from the vacuum tower is then thermally
cracked in a delayed coker to produce wet gas, coker gasoline, coker gas oil, and
coke. Without a coker, this heavy resid would be sold for heavy fuel oil or (if
the crude oil is suitable) asphalt. Historically, these heavy bottoms have sold for
about 70 percent of the price of crude oilThe atmospheric and vacuum crude unit gas oils and coker
gas oil are used
as feedstocks for the catalytic cracking or hydrocracking units. These units crack
the heavy molecules into lower molecular weight compounds boiling in the gasoline
and distillate fuel ranges. The products from the hydrocracker are saturated.
The unsaturated catalytic cracker products are saturated and improved in quality
by hydrotreating or reforming.
The light naphtha streams from the crude tower, coker and cracking units
are sent to an isomerization unit to convert straight-chain paraffins into isomers
that have higher octane numbers.
The heavy naphtha streams from the crude tower, coker, and cracking units
are fed to the catalytic reformer to improve their octane numbers. The products
from the catalytic reformer are blended into regular and premium gasolines for
sale.
The wet gas streams from the crude unit, coker, and cracking units are
separated in the vapor recovery section (gas plant) into fuel gas, liquefied petroleum
gas (LPG), unsaturated hydrocarbons (propylene, butylenes, and pentenes),
normal butane, and isobutane. The fuel gas is burned as a fuel in refinery furnaces
and the normal butane is blended into gasoline or LPG. The unsaturated hydrocarbons
and isobutane are sent to the alkylation unit for processing.
The alkylation unit uses either sulfuric or hydrofluoric acid as catalyst to
react olefins with isobutane to form isoparaffins boiling in the gasoline range.
The product is called alkylate, and is a high-octane product blended into premium
motor gasoline and aviation gasoline.
The middle distillates from the crude unit, coker, and cracking units are
blended into diesel and jet fuels and furnace oils.
In some refineries, the heavy vacuum gas oil and reduced crude from paraffinic
or naphthenic base crude oils are processed into lubricating oils. After removing
the asphaltenes in a propane deasphalting unit, the reduced crude bottoms
is processed in a blocked operation with the vacuum gas oils to produce lubeoil
base stocks.
The vacuum gas oils and deasphalted stocks are first solvent-extracted to
remove the aromatic compounds and then dewaxed to improve the pour point.
They are then treated with special clays or high-severity hydrotreating to improve
their color and stability before being blended into lubricating oils.
Each refinery has its own unique processing scheme which is determined
by the process equipment available, crude oil characteristics, operating costs, and
product demand. The optimum flow pattern for any refinery is dictated by economic
considerations and no two refineries are identical in their operations..

PROPERTIES OF NATURAL GAS

Treated natural gas consists mainly of methane; the properties of both
gases (natural gas and methane) are nearly similar. However, natural gas
is not pure methane, and its properties are modified by the presence of
impurities, such as N2 and CO2 and small amounts of unrecovered heavier
hydrocarbons.
An important property of natural gas is its heating value. Relatively
high amounts of nitrogen and/or carbon dioxide reduce the heating value
of the gas. Pure methane has a heating value of 1,009 Btu/ft3. This value
is reduced to approximately 900 Btu/ft3 if the gas contains about 10% N2
and CO2. (The heating value of either nitrogen or carbon dioxide is zero.)
On the other hand, the heating value of natural gas could exceed
methane’s due to the presence of higher-molecular weight hydrocarbons,
which have higher heating values. For example, ethane’s heating value is
1,800 Btu/ft3, compared to 1,009 Btu/ft3 for methane. Heating values of
hydrocarbons normally present in natural gas are shown in Table 1-4.
Natural gas is usually sold according to its heating values. The heating
value of a product gas is a function of the constituents present in the mixture.
In the natural gas trade, a heating value of one million Btu is
approximately equivalent to 1,000 ft3 of natural gas.

Water Removal

Moisture must be removed from natural gas to reduce corrosion problems
and to prevent hydrate formation.
Hydrates are solid white compounds
formed from a physical-chemical reaction between hydrocarbons
and water under the high pressures and low temperatures used to transport
natural gas via pipeline. Hydrates reduce pipeline efficiency.
To prevent hydrate formation, natural gas may be treated with glycols,
which dissolve water efficiently. Ethylene glycol (EG), diethylene glycol
(DEG), and triethylene glycol (TEG) are typical solvents for water
removal. Triethylene glycol is preferable in vapor phase processes
because of its low vapor pressure, which results in less glycol loss. The
TEG absorber normally contains 6 to 12 bubble-cap trays to accomplish
the water absorption. However, more contact stages may be required to
reach dew points below –40°F. Calculations to determine the number of
trays or feet of packing, the required glycol concentration, or the glycol
circulation rate require vapor-liquid equilibrium data. Predicting the interaction
between TEG and water vapor in natural gas over a broad range
allows the designs for ultra-low dew point applications to be made.6
A computer program was developed by Grandhidsan et al., to estimate
the number of trays and the circulation rate of lean TEG needed to dry natual
gas. It was found that more accurate predictions of the rate could be
achieved using this program than using hand calculation.7
Figure 1-4 shows the Dehydrate process where EG, DEG, or TEG
could be used as an absorbent.8 One alternative to using bubble-cap trays
is structural packing, which improves control of mass transfer. Flow passages
direct the gas and liquid flows countercurrent to each other. The use
of structural packing in TEG operations has been reviewed by Kean et al.9
Another way to dehydrate natural gas is by injecting methanol into gas
lines to lower the hydrate-formation temperature below ambient.10 Water
can also be reduced or removed from natural gas by using solid adsorbents
such as molecular sieves or silica gel.
Condensable Hydrocarbon Recovery
Hydrocarbons heavier than methane that are present in natural gases
are valuable raw materials and important fuels. They can be recovered by
lean oil extraction. The first step in this scheme is to cool the treated gas
by exchange with liquid propane. The cooled gas is then washed with a
cold hydrocarbon liquid, which dissolves most of the condensable hydrocarbons.
The uncondensed gas is dry natural gas and is composed mainly
of methane with small amounts of ethane and heavier hydrocarbons. The
condensed hydrocarbons or natural gas liquids (NGL) are stripped from
the rich solvent, which is recycled. Table 1-2 compares the analysis of
natural gas before and after treatment.11 Dry natural gas may then be
used either as a fuel or as a chemical feedstock.
Another way to recover NGL is through cryogenic cooling to very low
temperatures (–150 to –180°F), which are achieved primarily through
adiabatic expansion of the inlet gas. The inlet gas is first treated to
remove water and acid gases, then cooled via heat exchange and refrigeration.
Further cooling of the gas is accomplished through turbo
expanders, and the gas is sent to a demethanizer to separate methane
from NGL. Improved NGL recovery could be achieved through better
control strategies and use of on-line gas chromatographic analysis.12

NATURAL GAS TREATMENT PROCESSES

Raw natural gases contain variable amounts of carbon dioxide, hydrogen
sulfide, and water vapor. The presence of hydrogen sulfide in natural
gas for domestic consumption cannot be tolerated because it is poisonous.
It also corrodes metallic equipment. Carbon dioxide is undesirable,
because it reduces the heating value of the gas and solidifies under the
high pressure and low temperatures used for transporting natural gas. For
obtaining a sweet, dry natural gas, acid gases must be removed and water
vapor reduced. In addition, natural gas with appreciable amounts of heavy
hydrocarbons should be treated for their recovery as natural gas liquids.
Acid Gas Treatment
Acid gases can be reduced or removed by one or more of the following
methods:
1. Physical absorption using a selective absorption solvent.
2. Physical adsorption using a solid adsorbent.
3. Chemical absorption where a solvent (a chemical) capable of reacting
reversibly with the acid gases is used.
Physical Absorption
Important processes commercially used are the Selexol, the Sulfinol,
and the Rectisol processes. In these processes, no chemical reaction
occurs between the acid gas and the solvent. The solvent, or absorbent, is
a liquid that selectively absorbs the acid gases and leaves out the hydrocarbons.
In the Selexol process for example, the solvent is dimethyl ether
of polyethylene glycol. Raw natural gas passes countercurrently to the
descending solvent. When the solvent becomes saturated with the acid
gases, the pressure is reduced, and hydrogen sulfide and carbon dioxide
are desorbed. The solvent is then recycled to the absorption tower.
Physical Adsorption
In these processes, a solid with a high surface area is used. Molecular
sieves (zeolites) are widely used and are capable of adsorbing large
amounts of gases. In practice, more than one adsorption bed is used for
continuous operation. One bed is in use while the other is being regenerated Regeneration is accomplished by passing hot dry fuel gas through the
bed. Molecular sieves are competitive only when the quantities of hydrogen
sulfide and carbon disulfide are low.
Molecular sieves are also capable of adsorbing water in addition to the
acid gases.
Chemical Absorption (Chemisorption)
These processes are characterized by a high capability of absorbing
large amounts of acid gases. They use a solution of a relatively weak
base, such as monoethanolamine. The acid gas forms a weak bond with
the base which can be regenerated easily. Mono- and diethanolamines are
frequently used for this purpose. The amine concentration normally
ranges between 15 and 30%. Natural gas is passed through the amine
solution where sulfides, carbonates, and bicarbonates are formed.
Diethanolamine is a favored absorbent due to its lower corrosion rate,
smaller amine loss potential, fewer utility requirements, and minimal
reclaiming needs.3 Diethanolamine also reacts reversibly with 75% of
carbonyl sulfides (COS), while the mono- reacts irreversibly with 95% of
the COS and forms a degradation product that must be disposed of.
Diglycolamine (DGA), is another amine solvent used in the
Econamine process (Fig 1-2).4 Absorption of acid gases occurs in an
absorber containing an aqueous solution of DGA, and the heated rich solution (saturated with acid gases) is pumped to the regenerator.
Diglycolamine solutions are characterized by low freezing points, which
make them suitable for use in cold climates.
Strong basic solutions are effective solvents for acid gases. However,
these solutions are not normally used for treating large volumes of natural
gas because the acid gases form stable salts, which are not easily
regenerated. For example, carbon dioxide and hydrogen sulfide react
with aqueous sodium hydroxide to yield sodium carbonate and sodium
sulfide, respectively.
CO2 + 2NaOH (aq) r Na2 CO3 + H2O
H2S + 2 NaOH (aq) r Na2S + 2 H2O
However, a strong caustic solution is used to remove mercaptans from
gas and liquid streams. In the Merox Process, for example, a caustic solvent
containing a catalyst such as cobalt, which is capable of converting
mercaptans (RSH) to caustic insoluble disulfides (RSSR), is used for
streams rich in mercaptans after removal of H2S. Air is used to oxidize
the mercaptans to disulfides. The caustic solution is then recycled for
regeneration. The Merox process (Fig. 1-3) is mainly used for treatment
of refinery gas streams .