Use of chemicals within the oil & gas sector
Module 1

Contents

Chemicals in the Sector Harmful v Hazardous Drilling fluids Cementing Chemicals Completion Chemicals Production Chemicals Radio-Active Substances

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Chemicals – intrinsic properties

	Is the component toxic? To humans To animals (fish, algae, crustacean, earthworms etc.) Is the component bio-degradable? What is the half life, how long will it take to break it down? Is the component bio-accumulative? Is it soluble in fat and will be transferred up the food chain?

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Harmful vs hazardous

	Harmful substances may cause adverse effects as a result of: Amount of discharge Time of discharge Concentration of discharge Mode of discharge Hazardous substances may cause adverse effects as a result of Intrinsic properties (toxicity, & potential for bioaccumulation).

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Chemicals in the oil & gas sector

	Drilling and well chemicals Production chemicals Injection chemicals Pipeline chemicals Gas treatment chemicals Utility chemicals Chemicals added to the export flow Water trace components Emergency preparedness

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Main activities in the oil and gas value chain

Oil and gas production

Transportation to market

Geological mapping, seismic surveys

Opening of new fields and licensing

Exploration and exploration drilling

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Discharges to environment

	Drill cuttings (rocks and sand from the well) Drilling fluids (drilling muds) Produced water (containing oil and chemicals from production) Drainage water Domestic water Sewage Cooling water Solid waste Spills

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What are drilling and completion fluids?

	Water-based drilling fluids (WBDF) or oil-based drilling fluids (OBDF) used during well drilling. More recently, synthetic based drilling fluids have been developed – based upon a synthetic fluid rather than an oil – typically used offshore, greater environmental acceptance than OBDF.

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Drilling fluid

	Drilling fluid forms the continuous face within the well and in which all components are carried. Due to material costs and environmental concerns, WBDF is always the first drilling fluid to be considered Drilling fluid and drill cuttings = drilling mud

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Drilling fluids

	Primary function of drilling fluids in drilling operations include: Removal of drilled cuttings (rock chippings) from the wellbore to the surface Control of the formation pressure Cooling of the drill bit

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Drilling fluids and cuttings

	Removal of cuttings from well: Drilling fluid must have sufficient viscosity and velocity. In WBDF this is achieved through adding bentonite clay or polymers (compound of high molecular weight with large individual particles). At the surface, drilling fluid is separated from the cuttings and the drilling fluid is re-circulated through the well.

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Drilling fluids functions

	Seal permeable formations and maintain well stability: Prevent the ingress of formation fluids into the well Prevent the wall of the well caving-in Avoid fluid loss, especially when drilling through porous and permeable formations WBDF tend to react with salt-bearing and clay formation OBM reduce interaction

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Drilling fluid, functions continued

	Cool and lubricate the drilling tools and drill bit: Especially important at depth and inclined drilling Lubricate & transmit hydraulic power to the drill bit Both water and oil are effective at cooling the drill bit but at depths with higher temperatures problems result due to the boiling point of water OBDF better retain their properties at high temperatures and pressures

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History of drilling chemicals

Only partly successful in removing cuttings

1845

1901

1920

1935

1970

Increased transport of cuttings away from the bit

Bentonite introduced

Water was

used

Finely ground hole cuttings and clay was added

Inclusion of a weighting agent- barite

Prevented incursion of high pressure formation fluids

Diesel used, but banned due to environmental considerations

Better thermal stability

Largely replaced use of barite

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Water-based drilling fluids (drilling muds)

	Water is the base of the WBDF Used in exploration wells, top hole sections and in simple wells WBDF can, within Europe, normally be allowed to be discharged to environment following pre-treatment

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WBDF – additives

Additive	Function
Salts/brine Polymers	Inhibitor for reactive clays, in combination with polymers
Viscosifier/clay	Get the right viscosity, gel strength and filtration rate
Shale inhibitor, scale inhibitor	Prevent interaction with shale, prevent precipitation of scale
Lubricant	Reduce friction (aromatic and naphthenic compounds)
Defoamer (e.g. aluminium stearate)	Minimize foaming
Corrosion inhibitor (alkaline chemicals, NaOH)	Minimize corrosion of drill pipe and casing
Biocide	To reduce the biological growth
Weighting agent (barite)	Match formation pressure, achieve desired density
Fluid loss additives (starch, polyanionic cellulose)	Added to reduce loss rate
Bridging agent (sized salt, calcium carbonate)	Added to bridge across pores or fractures to prevent loss of drilling mud
Emulsifier	Disperse small amounts of oil from the formation or added to increase lubricity

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Oil-based drilling fluid

	Oil is the base fluid (mineral oil, paraffin etc) Used in long, complicated & horizontal wells within complex geology Used in the reservoir zone (high temperature and pressure) Normally contain components that are toxic in nature OBDFs are not allowed to be discharged to the environment OBMs require treatment and disposal

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OBDF – additives

Additive	Function
Brine phase (salt)	Minimize interaction between the mud and formation clays and salt, adds density to the mud
Emulsifiers / surfactants	Create a stable invert emulsion, oil wet cuttings to ensure good transport
Lime (calcium hydroxide)	Minimize corrosion, convert additives into oil soluble forms
Viscosifier (organo clay)	Get the right viscosity
Weighting agent (barite)	As for water based systems
Organic fluid loss additive (asphaltine, rubber, coke resin, lignite-based)	As for water based systems
Bridging material (calcium carbonate, dolomite, marble, graphite)	As for water based systems

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Water-based drilling fluids

	Why use water-based drilling fluids? Reduced costs Healthier working environment (fewer noxious fumes) Reduced harm to the marine environment Avoidance of waste problems

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Effects of WBDF

	Pre-treatment prior to discharge is recommended. WBDF have little effect when discharged offshore or on land (inert, low toxicity, but high pH and high salt content). Offshore: will cover the seabed if discharged, will temporarily change the seabed as feeding ground for fish. Land based: need to be placed in holding pits prior to treatment.

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Effects of OBDF

	Severe effect if discharged offshore or on land May also be harmful to people’s health Drilling fluids and cuttings must be taken to treatment plants to be reclaimed or destroyed Trials ongoing on cleaning the cuttings on board, and discharge if oil content is less than 1%

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Use of cementing chemicals

	After drilling, once well section conductor casing is installed Cement slurry is used for fixation and sealing Used for safety reasons to ensure pressure integrity Support for BOP/well head

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Cementing chemicals

Chemical	Function
Cement	Strength/hardening
Dispersants and surfactants	Keep particulates and droplets suspended
Retarder	Ensure the right hardening rate
Polymers/glycol	Minmize loss to formation
Vegetable oils	Anti foam

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Completion

	Completion is the process of making a drilled well ready for production testing and ultimately production This will only be carried out if the reservoir is going to be produced Could be an exploration well that is turned into a production well

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Completion chemicals

	Keep the integrity of the well until it is ready to produce hydrocarbons Secure the well from ingress of unwanted formation fluid Cleaning/clearing the well Establishing the production tubing and its associated down hole tools

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Completion chemicals

	Keeping the integrity of the well: Salt brine, surfactants Cleaning of the well: Surface active agents, inhibition fluids Advanced polymers Preventing biological growth and corrosion: Biocide, inhibition fluids

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Other chemicals

Chemical	Function
Wash chemicals	Oil rig cleaning Normally green or yellow Some may be discharged
Grease	Used when the drill string and conductors are connected Could have red or black components May partly be discharged
BOP-fluid	Used when valves are pressurized and activated Parts will be discharged (when testing BOP) Could have red components
Hydraulic fluids	Used in closed systems Could have red or black components Normally not discharged, only if leakage/sweating

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Production process

	The production phase involves taking the oil and gas from the well-head to stabilized marketable products.

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Production chemicals

	Both chemical and physical changes can occur to the well stream fluids, as they are transported from the reservoir through the processing system. Production chemicals can help to address or minimise these changes.

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Production chemicals – application

Situation	Consequence
Foaming	Reduced production
Corrosion	Damage process equipment, production lines and export lines
Scaling	Reduced production, scaling on process equipment and reduced functionality
Emulsions	Discharge water with high oil content and high water content in exported oil
Waxing	Scaling, reduced production, separation problems
Biolological growth	Injection problems, presssure loss, corrosion and fouling in process equipment
Hydrate formation	Ice pig formation in pipelines and process equipment (hydrocarbons and water)

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Production chemicals – how they work

Situation	Consequence
Defoamer	Reduced the surface tension on the gas bubbles
Corrosion inhibitors	Establish a protective layer on the surface of the metal
Anti scale agent	Hamper formation of crystal growth
Emulsion breakers Flocculants	Reduce surface tension on the water droplets. The droplets coagulate to bigger droplets that separated due to the self-weight or gravity
Anti waxing	Reduce the wax particles ability to grow
Biocides	Toxic towards bacteria and limit the bacterial growth
H2S/O2- Scavenger	React with H2S, clean the gas. Reduce the O2-content in the gas
Hydrate inhibitor	Change the freezing point for ice plugs that is formed at a certain pressure and temperature

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Oil export string

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Production chemicals

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Discharge of production chemicals

Production chemicals normally contain green, yellow and some red components. Biocide can contain red components. If chemicals are water soluble, may be discharged through produced water. Ideally, produced water is injected down injection wells – but, in many cases this is not happening. Gas treatment chemicals normally follow the gas (injected as fuel or exported). Support chemicals (cleaning, hydraulic fluids, biocides, slop tanks).

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Radioactive substances used in oil industry

Bit cuttings from any well dug will contain Naturally Occurring Radioactive Materials (NORM), with the actual amount the same as was present in the earth removed at that location. There are reports where cuttings have set off radiation alarms at disposal facilities due to elevated NORM levels in the soil. Typically, the removed soil from drilling is substantially below the NORM levels required to set off a radiation portal alarm. Common examples of NORM include uranium, thorium, potassium and radium.

Thank you
UNEP-Norway Partnership
United Nations Avenue, Gigiri PO Box 30552 – 00100 GPO Nairobi, Kenya	www.unep.org

Chemical content and properties

	Is the chemical made up of one component or a mixture of components? Gas, liquid or solid? Soluble in water or in oil? The properties of the chemical determines fate in the environment.

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