A brief explanation of parameters affecting asphaltene and Wax (Paraffins) Deposition, The document also covers techniques available to alleviate the problem

1. 1
 Paraffin and Asphaltene together pose a serious threat to flow
assurance in the production system. Elaborate it. List out
likely solutions to avoid problems.
Flow Assurance due to Paraffin Deposition
Paraffin (Saturates having Carbon more than 20 and less than 60 – crude oil can
maximum have C-36 in its composition) and asphaltene are major constituents in
crude oils and create severe problems in production system. These are organic
deposits; their deposition causes reduction in effective flow-line diameter so as
reducing production and creates back-pressure to the flowing well and
consequently not allowing more hydrocarbon flow.
High Viscosity and Pressure Losses: High viscosity of oil and wax deposition
on pipe surfaces cause high flowline pressures besides turbulent flow.
Crystallization of wax suddenly increases the crude viscosity. Presence of wax
crystallites increases both the cohesive and the adhesive forces because of their
gel forming tendency which results in increased viscosity and pressure losses.
Pumping pressure increases and crude transportation may get stopped. Such
pressure losses across the tubing cause low flow rates in the well, which in turn
makes the conditions for wax deposition more favourable, thereby slowly
decreasing the flow rate further until the flow stops. In low-temperature
reservoirs, the flow of petroleum has been reported to be reduced by wax
crystallization in the formation, resulting into poor recovery.
High Yield Stress for Restarting the Flow. This problem can be called the
restartability of the flow in a line when the static oil contained therein is allowed
to cool to temperatures below its pour point. In such cases, certain pressure, called
the restarting pressure, is required to break the gel and resume flow. Sometimes
this pressure exceeds the pressure limits of the pumps and pipelines. The line
appears to be chocked. This problem is caused due to wax deposited in the line.
Deposition of Wax Crystallites on Surfaces. When the oil temperature goes
below cloud point, the wax crystals start precipitating out. These crystals deposit
at the surface of handling system (e.g. on tubing, flowlines, tank bottom, process
equipment, and sucker rod assemblies). Wax can deposit even if the bulk oil is at
a temperature above its cloud point. This occurs because of a temperature
difference between the bulk oil and the outer surface of the line. Oil near the pipe
wall may experience a temperature below its cloud point, and wax crystallization
will occur.

2. 2
Flow Assurance due to Asphaltene Deposition
In the Reservoir: -
During gas flooding a miscible fluid, e.g. ethane, carbon dioxide, natural gas etc.,
is injected into the reservoir for displacing the residual oil left after water
flooding. Miscibility of the solvent with the reservoir oil is the property which
can also lead to the precipitation of asphaltenes inside the reservoir matrix and its
deposition on the reservoir rock. Most of the miscible solvents have the potential
for ·causing asphaltene flocculation. As more and more of the solvent dissolves
into the crude. oil, the Asphaltene problem (generally speaking) will increase
The adsorption of asphaltenes and/or resins on the mineral surfaces has been
studied mainly with respect to wettability alterations and its impact on oil
recovery. Several studies have shown that rock wettability can be altered by
treating a core with a solution of petroleum heavy ends. The wettability of the
core can, be shifted from water-wet to intermediate-wet after the treatment. Clays
are important deposition sites and clay stabilization enhances organic deposition.
Hence, Asphaltene deposition can alter permeability and alter wettability thereby
leading to reduced recovery efficiencies.
In Well Bores and Tubing: -
In many instances the asphaltene deposits plug the wells and result in production
losses. To compensate for these losses, the pressure is reduced at the well head
until it cannot be reduced any further. Production losses lead to increased costs
and well clean-ups from asphaltene deposition can adversely ·affect the
economics of the oil recovery project. Besides added cost, asphaltene deposition
inside the wells has the potential of serious accidents. For example,
the malfunction of the down hole safety valves and other valves inside the well
can lead to very serious consequences.
Processing Equipments:
The insidious asphaltene deposition problem is not only limited to the reservoir,
well bore and tubing but can occur in the well head processing equipment,
pipeline and downstream refining facilities.
The main problem is of safety of the process control equipment. Asphaltenes in
the crude oil have a tendency to deposit on all process equipment surfaces. They
can plug safety devices and safety relief valves on processing equipment. When
these fail to open or close when required, the consequences can be disastrous.

3. 3
Bottom Line is: -
The formation of the wax and asphaltene in the pipe during the fluid
production from the bottom hole of the well to the surface can restrict the flow
of crude oil, creating pressure abnormalities and causing an artificial blockage
leading to the reduction or even cessation of production. Wax and asphaltene
formation leads to formation damage near the wellbore, reduction in
permeability, changes in reservoir fluid composition, and fluid rheology due to
phase separation as wax and Asphaltene solid precipitates.
Mitigation Techniques
 Wax Removal Techniques: -
Thermal Technique: -
Wax precipitation is highly temperature dependent; therefore, thermal techniques
can be highly effective both for preventing and removing wax precipitation
problems.
Hot oiling is one of the most popular methods of deposited wax removal in the
flow lines and downhole. Hot oil is heated to a temperature above the melting
point for wax and then pumped into the well, normally through the annular space.
The circulated hot oil melts and dissolves the wax which allows it to be circulated
from the well and the surface producing system. During the hot oil process, a wax
dispersant is usually added to the crude oil to boost the dispersion of the melted
wax with the crude oil. Higher molecular-weight waxes tend to deposit at the
high-temperature bottom end of the well, while lower
molecular-weight fractions deposit as the temperature decreases up the wellbore.
This technique should not be applied to wells where the crude is characterized
by a low flash point. Reports show that hot-oil has been replaced with steam
or hot water to melt the wax in certain operations, but they are rarely used due
to risk of emulsion and corrosion problems.
Hot water treatment: - It does not give the solvency effects typical of the hot
oiling technique, so surfactants are often added to aid wax dispersion in the water
phase. The combined hot water and surfactant method allows the suspension of
solids by the surfactant's bipolar interaction at the interface between the water
and wax. An advantage of this method is that water has a higher specific heat than
oil, and therefore usually arrives at the site of deposition with a higher
temperature.

4. 4
Direct heating: - It has been regarded as an efficient flow in combating the flow
problems associated with wax, due to the advantages to control the temperature
above the formation region. The basic principle involves passing a huge quantity
of electric current through the pipeline wall to generate heat. It is the most
appealing and reliable option for Deepwater field operation of transport flowlines.
Chemical Techniques: -
Solvent treatments: - Solvent Treatment of wax and asphaltene depositions are
often the most successful remediation methods, but are also costlier; therefore,
are reserved for applications where hot oil or hot water techniques have shown
little success. Wax solvents helps to resolve the precipitated wax to ease transport
of crude oil to the surface. Normally the solvents are applied in frequent batch
treatments or continuously. Aliphatic and aromatic solvents are the main groups
of solvents used in the oilfields.
Mixing xylene or toluene together with an aliphatic solvent has shown to increase
the wax removal efficiency.
Other solvents have shown such as benzene, chlorinated hydrocarbons, and
carbon disulfide have shown a good level of success. However, many of these
solvents are not environmental friendly.
Wax crystal modifiers: - It acts at the molecular level to reduce the networking
tendency of wax molecules, and prevents them from forming lattice structures
within the oil. They reduce oil viscosity and lower the wax gel strength. They are
known for high-molecular-weight and thus they have high pour points, so their
use can be limited in cold climates
Dispersants: - They are a type of surfactants that acts to disperse the wax crystals
into the produced oil or water, thereby preventing wax deposition and effect
positively on the viscosity and gel strength. Dispersants breaks up deposited wax
into smaller particles capable of being carried in the oil stream. To remediate
deposited wax, dispersants can be used continuously or in batch treatments. They
generally have a very low pour point making their use suitable for cold climates.
These chemicals are used in low concentrations and can be formulated in both
aqueous and hydrocarbon solutions, making them relatively safe and inexpensive
Surfactants: - They are a general class of chemicals that are most often used to
clean vessels, tanks, pipes, machinery or any place where wax may deposit.
Surfactants or dispersants can also be used in combination with hot oil and water
treatments.

5. 5
MECHANICAL TECHNIQUES
These techniques include manual stripping, pigging, mechanical vibrations, etc.
Mechanical/manual stripping is probably the oldest method known for the
removal of heavy hydrocarbon deposits. It is done by mechanically scraping the
tubing.
Pigging technology is well established, it is most suitable for foams, waxy crude
arteries and wax deposit removal. The traditional answer to the problem of wax
deposition has been to mechanically clean the pipeline using a pig. A pig is an
effectively moving piston driven through the pipe by a pressure differential. Pigs
are generally designed to push any loose material through the pipeline and to
apply a mechanical force between the pig and the pipe wall to remove debris.
Pigging frequencies may range from 2-3 days to 3-4 months. A very important
factor for efficient wax pigging is that the pig has small bypass holes that allows
liquid to be 'flushed' through due to the pressure drop across the pig. Before the
remediation operation, a pigging program must identify type and numbers of pigs.
The use of a non-suitable pig can, in the worst-case scenario lead to full pipeline
blockage. As the pig enters the pipeline, it removes the wax deposit on the pipe
wall and pushes the wax forward. As the pigging length increase, the volume of
wax in front of the pig also increases.
Pigs can also be molded in polyurethane foams of various densities. This type of
pig is usually bullet shaped and, if a more aggressive cleaning operation is
required, bristles or studs can be molded into a hard gel coat. Very hard deposits
such as hard wax and scale require a very aggressive tool; usually a metal-bodied
pig with tooling attached with brushes, ploughs, scrapers and pin-wheels to
increase the efficiency
Screening Criteria of Methods: -
 For the oil wells with water cut below 50%, wax content less than 30% and
Carbon Number distribution of the wax in the range of C13-C40, a good
efficiency may be obtained by using chemical removing and inhibiting
techniques.
 For the wells with water cut more than 50%, the magnetic paraffin inhibiting
technique is generally more economic to apply.
 For the wells with wax content more than 30%, pour point higher than 400C,
irrespective of the water cut, the best choice is to adopt chemical paraffin-removal
or thermal washing method.

6. 6
 For the oil wells with very high Carbon Number of wax, pure chemical paraffin
removing techniques are ineffective. The best economic choice is to apply
chemical paraffin inhibitor or glass/plastic coating or lining of tubing.
 Asphaltene Removal Techniques: -
Chemical Treatment: -
The most popular method for Asphaltene treatment is using chemicals. Their
application areas are wide – chemicals can be used to treat the deposition in
tubing, flowline, wellbore, formation, etc. Major types of chemical treatments
are:
 Aromatic solvents. Solvents will dissolve bulk asphaltene deposits by
breaking asphaltene to asphaltene bonds. Eventually, given enough time, all the
aromatic based solutions will become fully saturated at about 30% asphaltene
loading rate. Xylene alone will not remove asphaltenes that are attached to
formation material such as clay; a dispersant is needed to remove adsorbed
asphaltenes, which best are used to remove solid deposits
 Asphaltene dispersants. They speed the breakup and dissolution of bulk
asphaltene deposits over xylene alone, prevent sticking; best used to prevent the
formation of sludge and rigid film emulsions.
 Asphaltene inhibitors. The following is the list of few chemicals which
showed a good result in inhibition and are applied in many reservoirs: alkyl
phenol; natural resin; non-ionic surfactant such as ethoxylategalcohols and
phenols; vegetable oil (e.g. sweet almond, coconut essential oil); dodecyl benzene
sulfonic acid (DBSA). Efficiency of asphaltene inhibitor can be tested in the
laboratory using PVT cell on the dead oil sample, however core flooding must be
done in order to check the compatibility of inhibitor with reservoir rock
A number of additives can be used to clean up existing rigid film emulsion. The
chemicals should be applied directly on the problem area and allowed to soak for
24 hours to minimize deferment, if the damage is severe longer soaking time is
needed.
The main disadvantage of chemical methods is environmental safety and personal
exposure hazards concerns which may result in restrictions for many chemical-
treatment materials. If well stimulation operations are planned, pre-treatment of
the well using solvent or hot water and surfactant the day prior to any well
stimulation project should be considered as a deposition mitigation strategy.

7. 7
Thermal treatment
This category of treating methods uses hot oiling and downhole heaters, which
described in wax deposition thermal treatment. In addition to them, heat-
liberating chemicals can be used: a mixture of equi-molar concentrations of
ammonium chloride and sodium nitrate is pumped down with a buffer to delay
the exothermic reaction until the fluid reaches the bottom-hole with a large
quantity of nitrogen gas.
Disadvantages: very expensive in comparison to conventional thermal methods,
the process must be designed and closely monitored by a chemist on location.
Bacterial Treatment: -
‘‘It is being found that naturally occurring marine microorganisms, which have
the ability to absorb paraffin, are able to remove effectively Asphaltene and
paraffin deposits or at least reduce the deposition over a certain time period’’ The
mechanism of bacteria involves two processes: 1) degradation of the paraffin and
asphaltene and 2) surfactant, produced by the bacteria cause the paraffin and
Asphaltene to become soluble in the oil again.
Laser Treatment: -
Laser technology proposed a novel technique to clean asphaltenes with laser
energy. In their experiments, they used bitumen/powdered limestone cores and
brine. It was shown that laser energy alters the thermodynamics of the system,
which results in a reversible process: some of the asphaltene redissolved back
into the liquid phase. Laser treatment employed different laser intensities and
different laser exposure times. Higher laser intensity provided better
improvement of the rock - damaged permeability. The effect of exposure time
indicated that there is an optimum exposure time beyond which no additional
improvement on the damaged core permeability was observed.
Combination of Treatment could also be done for e.g. Hot chemical treatment can
be done where chemicals react in an exothermic reaction creating thermal effect.