fundamentals of oil and gas

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List the major parts of the wellhead?

"Casing head
Tubing head
Christmas Tree
Pressure Gauges"

Why is hydrogen sulfide gas a concern in production operations?

Hydrogen sulfide is potentially damaging to equipment and potentially dangerous to people and animals.

What purpose does the water analysis serve in the production of oil and gas?

Water analyses are used for formation identifications and compatibility studies between formation zones. It is also used to determine scale and corrosion potential.

Describe the process of acidizing a formation.

Acid or stimulation chemicals are pumped into the formation to increase the porosity and permeability of the formation near the well bore.

What are gas hydrates?

Gas hydrates are ice-like crystalline compounds formed in natural gas in the presence of free water under conditions of high pressure and turbulence.

Describe how a gas lift system works.

Gas under pressure is injected into the space between the casing and tubing of the producing well. Gas then enters the tubing through the gas lift valves and lifts the fluid above the valve to the surface. The gas is either fed continuously for high volume wells or intermittently for lower volume wells.

Draw a typical offshore production flow diagram. Label all equipment and fluid paths.

...

What are the three conditions that must exist to form a stable emulsion?

"Two immiscible liquids
An emulsifying agent
Sufficient agitation to disperse one liquid as a droplet in the other"

Describe three preferred injection points for emulsion breakers and tell why they are preferred for this application.

"At the wellhead
In the flowline as close to the wellhead as possible
In the header if several wells are manifolded together
All these injection points provide adequate mixing and chemical contact time."

What are the three parts of a bottle test and what is the purpose of each?

"Ratio Test - defines the parameters of the bottle test and determines agitation, dosage, heat, and retention time.
Elimination Test - screens all desired compounds and identifies promising ones for further testing.
Confirmation Test - determines the best compound to treat the emulsion."

What are the five key factors used to determine the best emulsion breaker based on the results of the bottle test?

""1. Speed of water drop
2. Color and brilliance of oil
3. Low BS&W
4. Oil/Water Interface
5. Water Quality"

Name three goals of all emulsion treating practices.

"1. Increasing the size of the water droplets.
2. Increasing the gravity difference between oil and water.
3. Decrease the viscosity of the oil."

Why is the condition of the oil-water interface important in selecting an emulsion breaker?

If the interface is too loose or contains an excessive amount of unresolved emulsion, the interface pad can eventually displace the clean oil and cause the oil to be rejected due to high BS&W. Additionally, excessive interface can drag into the water phase and can cause oil carry-under and other related problems.

What problems can result from iron in produced water?

Iron can precipitate as it comes in contact with oxygen. Precipitated iron plugs injection wells, causes iron oxide interfaces in vessels, and can cause a sheen when water is discharged from offshore platforms.

What are the basic problems that should be examined when troubleshooting water clarifier problems in an offshore facility?

"Excessive oil
Lack of floatation
Gas blanket
Excessive gas
Oil removal
Outside interferences
Wet oil tank"

List three types of chemistries typically used for oil field water clarification.

"Polyamines
Solution of metal salts
Cationic high molecular weight latex polymers
Dithiocarbamates"

Why would you not overfill a sample being collected for an oil-in-water analysis?

Oil will tend to adhere to the bottle wall and separate from the water. If the bottle is filled more than once, oil from each filling is likely to stay in the bottle, giving erroneously high results. Alternatively, free oil may be carried out of the bottle by overflowing, giving low results.

Name several water properties that can change quickly after sampling and would need to be measured in the field for accuracy.

"pH
Temperature
Dissolved Gasses
Bacterial Population
Bicarbonates"

Describe two methods used to determine oil and grease content in produced water.

"Gravimetric Method - A Freon extraction is evaporated and the residual oil and grease is weighed.

Infrared Method - The Freon is extracted and the infrared absorption is measured at a wavelength of the carbon hydrogen bond."

Does the solubility of gases in water increase or decrease with higher temperatures?

Decrease

Name two places where water pumps can experience oxygen intrusion.

"Pump Suctions
Leaking Seals"

Tell the difference between a rotor type and eductor type float cell.

"Rotor type float cell generates a liquid vortex resulting in a gas-liquid interface, which extends through the interior of the rotor to a point just above the bottom of the cell. The gas cavity within the vortex is at a sub-atmospheric pressure, resulting in the flow of gas from the vapor space in the cell through the rotor, where it is mixed with the water.

Eductor type float cell uses clean water pumped from the discharge of the cell through an eductor. This causes a localized low pressure area at the nozzle so natural gas flows from the vapor space into the eductor where it mixes with water leaving the nozzle."

What is a CPI, and how does it work?

A CPI is a Corrugated Plate Interceptor. As oily water passes between the plates, free oil particles rise until they reach the underside of a plate where they collect and coalesce. The coalesced oil travels upstream along the plate until it reaches the water surface, where it is skimmed off and collected.

How do hydrocyclones work?

Water is introduced tangentially through a rectangular port in a conically shaped chamber. As the water rotates rapidly around the chamber and moves downward, the decreasing diameter causes high centrifugal acceleration of the water to the outer wall while the lighter oil droplets move to the center of the cone. The oil rises to the top and flows out, while the water exits the bottom of the cone.

What three factors are required for foam stability?

"1. Liquid
2. Gas
3. Foam stabilizing agent with surfactant properties"

List four Key Performance Indicators for defaoming applications.

"1. Chemical usage
2. Chemical related downtime
3. Gas mist carry-over and gas carry-under in separators
4. Excessive loss of glycol or VRU lube oil"

What two types of defoamers can generally be used together in a deep-water system?

Silicone defoamer in a kerosene solvent and a flurosilicone type product in a special carrier.

List four ways in which the performance of a defoamer can be monitored.

"1. White rag test
2. Foam probe
3. Trend graphs
4. Liquids carry-over"

Define Cloud Point.

The cloud point is the temperature at which paraffin begins to crystallize.

What are the three general classifications of paraffin chemicals.

"1. Solvents
2. Dispersants
3. Wax Crystal Modifiers"

List three methods available for monitoring a paraffin treatment program.

Available methods include field history, visual inspection, well records, pressure changes, coupons and test nipples, pig returns, and production changes.

Which of the following has the greatest influence on paraffin disposition: flow velocity, Co2 content, temperature, pressure, or pH?

Temperature

Describe the Paraffin Solvent/Dispersant Field Test and tell what information it provides.

A ball of paraffin is made from field samples, one for each product to be tested. These samples are placed in the appropriate products and the results noted. Effective products will show dissolution of the ball of wax.

Name three places in the production process that are likely locations to find paraffin.

Flowlines, tubing, pipelines, tank bottoms, and formations

Briefly describe the difference in the mechanism between paraffin solvents, dispersants, and wax crystal modifiers.

"Solvents - dissolve was that has already formed.
Dispersants - prevent wax particles from depositing on equipment surfaces.
Wax Crystal Modifiers - prevent the crystallization of wax from the oil."

What are asphaltenes?

Asphaltenes are high molecular weight compounds that are insoluble in hexane and soluble in aromatics.

What happens when the thermodynamic equilibrium of asphaltenes, resins, maltenes, and the oil in a flowline is disturbed?

The resins become disassociated from the asphaltenes and flocculation of these asphaltenes often occurs as a result. It is flocculated asphaltenes that cause production problems.

What types of solvents are effective in treating asphaltenes? Give examples.

Aromatic solvents such as xylene, toluene, and heavy aromatic naptha

Name three field monitoring techniques that are used to indicate the possibility of an asphaltene problem.

"1. Tracking production for signs of flow restrictions
2. Tracking flowline pressures, looking for increases
3. Asphaltene Dispersant Test"

Which of the following molecular structures best describes asphaltenes?

Cyclical compounds

Name two processes or operational changes that could lead to asphaltene destabilization/precipitation.

"Mixing incompatible crudes
Acid work-overs
Using condensate in work-overs on wells"

What type of process is corrosion, and what are the factors required for this process to proceed?

Corrosion is an electrochemical process. As corrosion occurs, an electrical current passes through the corroding metal. For this process to proceed, there has to be a voltage source and a completed electrical circuit.

How long should corrosion coupons be left in place?

A minimum of two weeks is acceptable. Once control is established, coupons should be left in place for 30 to 90 days. In any event, time must be allowed for the coupons to attain steady state corrosion.

Why are iron counts not reliable means for monitoring hydrogen sulfide corrosion?

Hydrogen sulfide attack may not release any dissolved iron in the fluids, which could lead to inaccurate results.

What are the four principal ways to prevent corrosion?

"1. Corrosion resistant materials in construction
2. Coatings and linings
3. Cathodic protection
4. Chemical corrosion inhibitors"

Why is temperature of the system being treated important when selecting a corrosion inhibitor?

Corrosion inhibitors lose their effectiveness above certain temperature limits. Further, selecting an inhibitor that is suitable for the temperature of the system avoids problems that might be caused by the heat-induced degradation of the inhibitor.

List four methods of treating a producing well with corrosion inhibitor.

...

Why is water chemistry important in the corrosion process?

Water's electrical conductivity increases as the amount of dissolved salts or ions increase.

What three gases are of the greatest concern regarding corrosion in oil and gas production?

"1. Hydrogen Sulfide
2. Carbon Dioxide
3. Oxygen"

What are the guidelines for using carbon dioxide partial pressure to predict corrosivity?

"1. Partial pressure above 30 psi indicates that corrosion is almost certain
2. Partial pressures between 7 and 30 psi indicates that corrosion is possible
3. Partial pressure below 7 psi indicates non-corrosive conditions"

What are two limitations of using electrical resistances probes to monitor corrosion?

"1. Pitting and stress corrosion cannot be detected
2. Sulfide deposits interfere with results"

When would a galvanic probe be used to detect corrosion?

A galvanic probe is used to detect corrosion when dissolved oxygen is suspected.

Explain how organic corrosion inhibitors function.

The polar head of the molecule is attached to the metal surface, while the non-polar (hydrocarbon soluble) end extends outward from the metal surface and forms a hydrophobic layer. This hydrophobic layer keeps water away from the metal surface.

Rank the film persistency of corrosion inhibitors according to their solubility classification.

"Greatest: limited solubility
oil-soluble/water-dispersible
oil-soluble
Least: water-soluble"

Why does the corrosion rate generally increase as pH becomes lower?

A lower pH indicates an increase in the concentration of hydrogen (H*) ions. An increase in hydrogen ions at the cathode will generally increase the amount of metal loss at the anode.

What part does pressure play in the corrosion process?

Pressure increases the solubility of gases in the water and thus increases the corrosion rate.

Why would a water-soluble inhibitor be selected for a low-velocity pipeline?

Water-soluble inhibitors will be able to reach the metal surface in low areas where water is standing undisturbed. Oil-soluble and oil-soluble/water-dispersible inhibitors would not reach the metal in these places.

Why should temperature be considered when selecting a corrosion inhibitor for a gas pipeline?

If the temperature is too high for the selected inhibitor, the solvents flash off, resulting in gunking of the inhibitor.

What type of corrosion inhibitor should be used in oil lines?

Water-soluble inhibitors are generally most effective.

Why are iron and manganese counts often misleading when monitoring a pipeline?

It's not possible to determine where the iron and manganese came from as they could come from either the producing wells or the pipeline. Additionally, wells are shut-in during certain times of the year. When wells are brought back on line, it is common for iron and manganese concentrations to be many times higher than normal initially.

Describe the influence of slime-forming bacteria on corrosion.

Slime formers give off acid by-products such as sulfuric acid and carboxylic acids. A deposit of slime on a surface can cause an oxygen concentration cell to form due to partial screening of the metal surfaces. Metal under the slime becomes anodic and loses iron while the exposed metal becomes the cathode.

Why will a water sample produce an inaccurate assessment of the levels of SRB in a system?

Since SRB are sessile bacteria and grow attached to surfaces, the number that have sloughed off into the water is likely to be poor guide to the total number living in the system.

List two monitoring techniques used to detect sessile bacteria.

Coupons, corrosion probes, and side streams

Where are SRB most likely to be found in a production system?

SRB normally predominate in stagnant and slow moving areas, such as s large vessels and pits, as well as in slow-flowing systems. Although the optimum environment for SRB is oxygen-free, they can readily create a local anaerobic condition and flourish in what appears to be an aerobic one.

How do you determine the optimal dosage rate (ppm) and contact time for a biocide treatment program?

Use the Time Kill Test

What is the most important consideration in selecting a biocide for a batch/slug treatment?

The most important consideration is the amount of contact time necessary for the biocide to be effective, since it must be matched to the residence time of the system.

Name the scale species commonly encountered in oil fields.

Calcium carbonate, calcium sulfate, barium sulfate, strontium sulfate, and iron deposits

List three reasons why scale precipitation can occur.

"Mixing incompatible crudes
Changes in physical conditions
Changes in chemical equilibrium"

A water analysis is being used to predict scaling tendency. What parts of the test must be run on-site to ensure accuracy?

pH and bicarbonate parts must be run on-site.

How do scale inhibitors function?

Scale inhibitors can either interfere with the nucleation or crystal growth

Should phosphate esters be used in high temperature environments? Explain.

Phosphate esters break down at temperatures above 90 C, causing loss of effectiveness and precipitation of ortho phosphate.

In what circumstances would you recommend a polymer-based scale inhibitor?

Polymers are good for high-calcium-level brines and provide high thermal stability.

List four analytical procedures that can be used to characterize injection water.

"Suspended solids by membrane filtration
Particle size distribution by Coulter Counter
Turbidity by light meter
Plugging tendency by filtration"

Why is it necessary to remove suspended particles form injection water?

To maintain well injectivity.

What two chemicals are most commonly used as oxygen scavengers in water injection systems.

"Ammonium Bisulphite liquid (NH4HSO3)
Sodium Bisulphite liquid (NaHSO3)"

Why is it that, in most systems, large numbers of bacteria typically survive the primary chlorination treatment?

Chlorine is 99.9% efficient if there is sufficient contact time (30 minutes). Reduced contact time and chlorination upsets will allow some bacteria to survive.

What are the two common points where supplementary biocides should be applied?

"1. To the inlet of the deaerator or recylce line to deaerator sump
2. To the outlet of the deaerator"

What two areas in seawater injection systems are potentially at the greatest risk for scale formation and why?

The heat exchangers and the injection wells are both enviroments that bring the temperature of the seawater above 32 C, a point which scale deposition of calcium carbonate is probale.

List three specific things that must be monitored in a produced water injection system.

"Water Quality
Microbiological
Corrosion"

In water infection systems, what measurement are necessary for monitoring?

"Iron
Suspended solids
Turbidity
Water quality measurements (membrane filter analysis)
Corrosion rate
Oxygen concentration
Filter operation
Bacteria counts."

What are the major components of natural gas?

Methane ethane, propane, and butane

List two reasons why it is important to know the amount of water produced with natural gas.

"Condensed water will affect the potential for corrosion.
Condensed water may result in the formation of hydrates."

What operational problems are observed in gas inlet separators?

"A pad or rag layer at the interface.
Foaming.
Paraffin or asphaltene deposition.
Scale precipitation and deposition, especially across dump valves in water outlets.
Corrosion due to acid gas and/or bacteria."

Describe the purpose and methods of dehydration in gas production operations. What are the typical specification for dry gas?

"Dehydration is the removal of water from a gas stream. It is usually achieved in gas production operations through the use of solid or liquid desiccants - substances that have a high affinity for water. The purpose of dehydration in gas production operations is to prevent hydrates and corrosion in gas-gathering and transmission systems. Gas transmission companies achieve these objectives by setting water content specificatio0ns in the gas. The typical transmission line specification for ""dry gas"" in the U.S. is 7 pounds of water per mmscf of gas, and 4 pounds per mmscf of gas in Canada and other regions around the world.

The common methods for dehydration natural gas are:

Absorption of water by a glycol dehydration.
Adsorption of water by solid desiccant.
Refrigeration."

The selection of gas-gathering system corrosion inhibitors is based on the corrosion mechanism to be treated, the method of application, and the hydrocarbon/water content of the gas. Water-soluble inhibitors are preferred in pipelines; however, there are two conditions that exclude their use. What are these conditions?

"1. Gas is dehydrated to the point where the dew point is less than the typical operating conditions. The gas will remove the water carrier in the product, and the amine can form a chemical gunk.
2. Batch treating between pigs on an infrequent basis. Oil-soluble film-persistent corrosion in inhibitors should be used."

What is the standard rule-of-thumb for calculating the amount of corrosion inhibitor required in a gathering line batch application?

One U.S. gallon per diameter inch of line per mile of line.

What is the base antifoam chemistry recommended by Nalco in gas systems? Why is this chemistry preferred over the alternative?

The PEG type antifoam is the base chemistry recommended by Nalco for foam control in gas systems. They are preferred over silicones because they do not cause fouling in closed high-temperature systems such as glycol and amine units.

List three common problems associated with the formation of hydrates in oil and gas facilities.

Any three of these: reduction in the gas throughput, plugging of flowlines, increased pressure, erosion, damage to downstream equipment, and increased safety concerns.

What are the four components that must be present for gas hydrate crystals to form?

"Gas
Water
High pressure
Low temperature."

What is the impact of presence of acid gases like carbon dioxide or hydrogen sulfide on hydrate formation?

The presence of these acid gases shifts the hydrate equilibrium curve to the right; that is they raise the temperature and pressure thresholds for hydrate formation, thus raising the probability for hydrate formation.

Name two thermodynamic hydrate inhibitors and tell briefly how they work.

Methanol and ethylene glycol are called thermodynamic inhibitors because they shift the hydrate equilibrium curve toward higher pressures and lower temperatures by changing the activity of water molecules.

What are the advantages of using anti-agglomerate type hydrate inhibitors?

the anti-agglomerates can handle a higher degree of sub-cooling and sustain a longer shut-in period.

What are the disadvantages of using anti-agglomerate type hydrate inhibitors?

Because these chemicals are usually more toxic than kinetic hydrate inhibitors require a minimum oil cut of at least 50% to work and may cause production problems such as bad water quality and emulsions.

"If hydrate formation is suspected in a system, what is the required response time?
A. One day
B. One week
C. One hour"

One hour is the correct response time.

What are the reasons for pigging a pipeline?

"Flow assurance
Corrosion mitigation"

What is meant by "progressive pigging"?

Progressive pigging would consist of running a low-density pig and monitoring the returns. Depending on the volume of returns received, a higher density pig would be run successivley until the received volume was low enough to run a disk pig to scrap the walls.

What is a pig, as used in oil pipeline management?

A semi-hard projectile, usually foam or metal with scraping surfaces used to clean the pipeline.

An operator tells you, "A lot of wax was recovered during the last pig run." What four questions should you ask before deciding on a course of action?

...

What tests can be run on the pig returns from gas or oil transmission lines?

"Analyses of wax or asphaltene samples
Deposition rate simulators"

Explain how to calculate the volumes of chemicals required for a chemical pigging application.

v = 0.823pdl

Name the types of scale that may be found in a distillation unit.

"Calcium carbonate
Calcium sulfate"

How can oxygen corrosion be avoided in steam generators and LP boilers?

Injection of a sulphite oxygen scavenger.

What is the control range for the pH of boiler water?

9.5 to 10.5

Why is nitrite used in heating/cooling systems, and how much should be used?

To prevent corrosion, the nitrite reserve in the water must be maintained at 800 to 1,000 ppm as NO3.

What pH should be maintained in a heating/cooling system?

9.0 to 10.0

List nine typical components of a chemical feed system.

Typical components are: a base tank, drum, or porta-feed; suction lines; a pump; injection points; a sight glass; filters; check valves; fill lines; and injection quills.

In terms of the chemical requirements, what is the primary difference between an umbilical chemical feed system and a land-based or platform-based system?

The primary differences are that feed systems that supply umbilical's must be extremely clean and temperature-stable, and have complete compatibility with all soft goods and materials used in the umbilical's. This is because any loss of production due to failure of an umbilical could be extremely costly.

List two possible reasons why chemical in a sight glass appears to go down and then return to the same level when timing a pump.

"1. The pump is air locked.
2. The suction check is dirty or leaking."

What precautions should be taken when filling chemical tanks?

All tanks and fill hoses must be clearly marked and each tank and product must have a designated fill hose to eliminate contamination of chemical. Nalco personnel should be responsible for training and hazards identification.

Why is an injection quill used on all injection points?

The injection quill is used to deposit chemicals directly into the fluid stream so that high pH materials are neutralized before contacting pipe or vessel internals and to ensure enhanced mixing.

HARD QUESTIONS

...

Why would you not overfill a sample being collected for an oil-in-water analysis?

Oil will tend to adhere to the bottle wall and separate from the water. If the bottle is filled more than once, oil from each filling is likely to stay in the bottle, giving erroneously high results. Alternatively, free oil may be carried out of the bottle by overflowing, giving low results.

Tell the difference between a rotor type and eductor type float cell.

"Rotor type float cell generates a liquid vortex resulting in a gas-liquid interface, which extends through the interior of the rotor to a point just above the bottom of the cell. The gas cavity within the vortex is at a sub-atmospheric pressure, resulting in the flow of gas from the vapor space in the cell through the rotor, where it is mixed with the water.

Eductor type float cell uses clean water pumped from the discharge of the cell through an eductor. This causes a localized low pressure area at the nozzle so natural gas flows from the vapor space into the eductor where it mixes with water leaving the nozzle."

...

What is a CPI, and how does it work?

A CPI is a Corrugated Plate Interceptor. As oily water passes between the plates, free oil particles rise until they reach the underside of a plate where they collect and coalesce. The coalesced oil travels upstream along the plate until it reaches the water surface, where it is skimmed off and collected.

How do hydrocyclones work?

Water is introduced tangentially through a rectangular port in a conically shaped chamber. As the water rotates rapidly around the chamber and moves downward, the decreasing diameter causes high centrifugal acceleration of the water to the outer wall while the lighter oil droplets move to the center of the cone. The oil rises to the top and flows out, while the water exits the bottom of the cone.

How long should corrosion coupons be left in place?

A minimum of two weeks is acceptable. Once control is established, coupons should be left in place for 30 to 90 days. In any event, time must be allowed for the coupons to attain steady state corrosion.

Why is temperature of the system being treated important when selecting a corrosion inhibitor?

Corrosion inhibitors lose their effectiveness above certain temperature limits. Further, selecting an inhibitor that is suitable for the temperature of the system avoids problems that might be caused by the heat-induced degradation of the inhibitor.

Why is water chemistry important in the corrosion process?

Water's electrical conductivity increases as the amount of dissolved salts or ions increase.

What are two limitations of using electrical resistances probes to monitor corrosion?

"1. Pitting and stress corrosion cannot be detected
2. Sulfide deposits interfere with results"

Explain how organic corrosion inhibitors function.

The polar head of the molecule is attached to the metal surface, while the non-polar (hydrocarbon soluble) end extends outward from the metal surface and forms a hydrophobic layer. This hydrophobic layer keeps water away from the metal surface.

Why does the corrosion rate generally increase as pH becomes lower?

A lower pH indicates an increase in the concentration of hydrogen (H*) ions. An increase in hydrogen ions at the cathode will generally increase the amount of metal loss at the anode.

What part does pressure play in the corrosion process?

Pressure increases the solubility of gases in the water and thus increases the corrosion rate.

Why would a water-soluble inhibitor be selected for a low-velocity pipeline?

Water-soluble inhibitors will be able to reach the metal surface in low areas where water is standing undisturbed. Oil-soluble and oil-soluble/water-dispersible inhibitors would not reach the metal in these places.

Why should temperature be considered when selecting a corrosion inhibitor for a gas pipeline?

If the temperature is too high for the selected inhibitor, the solvents flash off, resulting in gunking of the inhibitor.

Why are iron and manganese counts often misleading when monitoring a pipeline?

It's not possible to determine where the iron and manganese came from as they could come from either the producing wells or the pipeline. Additionally, wells are shut-in during certain times of the year. When wells are brought back on line, it is common for iron and manganese concentrations to be many times higher than normal initially.

Describe the influence of slime-forming bacteria on corrosion.

Slime formers give off acid by-products such as sulfuric acid and carboxylic acids. A deposit of slime on a surface can cause an oxygen concentration cell to form due to partial screening of the metal surfaces. Metal under the slime becomes anodic and loses iron while the exposed metal becomes the cathode.

Why will a water sample produce an inaccurate assessment of the levels of SRB in a system?

Since SRB are sessile bacteria and grow attached to surfaces, the number that have sloughed off into the water is likely to be poor guide to the total number living in the system.

List two monitoring techniques used to detect sessile bacteria.

Coupons, corrosion probes, and side streams

Where are SRB most likely to be found in a production system?

SRB normally predominate in stagnant and slow moving areas, such as s large vessels and pits, as well as in slow-flowing systems. Although the optimum environment for SRB is oxygen-free, they can readily create a local anaerobic condition and flourish in what appears to be an aerobic one.

How do you determine the optimal dosage rate (ppm) and contact time for a biocide treatment program?

Use the Time Kill Test

What is the most important consideration in selecting a biocide for a batch/slug treatment?

The most important consideration is the amount of contact time necessary for the biocide to be effective, since it must be matched to the residence time of the system.

Name the scale species commonly encountered in oil fields.

Calcium carbonate, calcium sulfate, barium sulfate, strontium sulfate, and iron deposits

List three reasons why scale precipitation can occur.

"Mixing incompatible crudes
Changes in physical conditions
Changes in chemical equilibrium"

A water analysis is being used to predict scaling tendency. What parts of the test must be run on-site to ensure accuracy?

pH and bicarbonate parts must be run on-site.

How do scale inhibitors function?

Scale inhibitors can either interfere with the nucleation or crystal growth

Should phosphate esters be used in high temperature environments? Explain.

Phosphate esters break down at temperatures above 90 C, causing loss of effectiveness and precipitation of ortho phosphate.

In what circumstances would you recommend a polymer-based scale inhibitor?

Polymers are good for high-calcium-level brines and provide high thermal stability.

List four analytical procedures that can be used to characterize injection water.

"Suspended solids by membrane filtration
Particle size distribution by Coulter Counter
Turbidity by light meter
Plugging tendency by filtration"

Why is it necessary to remove suspended particles form injection water?

To maintain well injectivity.

What two chemicals are most commonly used as oxygen scavengers in water injection systems.

"Ammonium Bisulphite liquid (NH4HSO3)
Sodium Bisulphite liquid (NaHSO3)"

What are four problems that can be caused by bacteria in oil and gas systems?

"Corrosion of steel
Souring of produced oil and gas
Toxic hydrogen sulfide gas release
Poor oil-water separation"

Name at least three mechanisms that result in corrosion in oil and gas systems that can be defines as MIC.

"Sulfide related mechanisms caused by SRB
Inorganic acid mechanisms caused by thiobacillus
Metal precipitation processes caused by iron bacteria
Organic acid mechanisms caused by heterotrophic bacteria"

What are the four main areas where souring of oil and gas production can occur?

"Oil-water separation systems
During transportation
Drains and storage tanks
Oily water separation systems"

Why are sessile bacteria important?

The growth of marine bacteria is associated with surfaces. Moreover, the corrosion problems associated with bacterial activity are dependent on the growth of these bacteria on a metal surface within a biofilm.

How do you determine the optimal dosage rate (ppm) and contact time for a biocide treatment program?

Use the Time Kill Study

What is vital in applying a biocide for a batch/slug treatment, and how is this factored into the application?

"Between the batch treatments there is no bacterial control in the system.
The frequency of treatments should be related to how quickly the bacteria can grow from low numbers to a level where a problem may be initiated. "

In water infection systems, what measurement are necessary for monitoring?

Iron, suspended solids, turbidity, water quality measurements (membrane filter analysis), corrosion rate, oxygen concentration, filter operation, and bacteria counts.

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