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Oil and Gas: Operations
Table of Contents
Background and Overview
P2 Alternatives
Reasons for Change
Pollution Prevention Overview
Where to Go for Help
Complete List of Links

Essential Links:

Energy.Gov--DOE Web Site
This web site has some good information regarding DOE's research in the oil and gas industry.

EPA Sector Notebook: Profile of the Oil and Gas Industry
This a guiding document that provides a deep analysis of all activities relating to the oil and gas ...

Fact Sheet - Beneficial Reuse of Drilling Wastes
There are many relatively simple processes that can be used on drilling rigs to capture clean mud th...

Pollution Prevention Best Management Practices for the New Mexico Oil and Gas Industry
This manual provides an in-depth look at oil and gas operations, its wastes, and pollution preventio...

This section provides a general overview of the waste streams associated with various oil and gas operations. It is presented in an outline format for easy reference. Separate sections are presented for drilling operations, oil and gas production operations, gas plant operations, and pipeline operations. Examples of wastes potentially generated by each type of operation are included in each section. This may help during a thorough audit of the wastes generated in each operation. Developing a list of the wastes generated in an operation, with a description of the regulatory status of each waste, is an important first step in preparing an effective waste management and minimization plan (Step 7 and Step 8 of the Waste Management Plan).

Drilling Operations

Construction and Rigging

Once a drilling site has been selected, the first step that is taken is drill site preparation (construction and rigging). Drill site construction includes clearing and leveling land; building access roads; digging and lining the drilling mud reserve pit; installing underdrains; and digging and preparing the cellar, rathole, and mousehole.

Rigging up includes erecting the rig, guardrails, walkways, and stairways; installing auxiliary equipment to supply electricity, compressed air, and water; and setting up storage facilities. Rotary rigs are the most common in the oil patch today. Most are portable, moved in and assembled to drill the hole, and then disassembled and moved to another drilling site.

Drilling Rig Operation

Drilling activities basically include the operation of the rig, a drilling mud system, and drill string to make the hole.

The drilling rig is used to handle the drill pipe and bit and to set casing to complete the well. Rig operation and maintenance uses numerous systems and various types of machinery. At some depth when the hole has permeated beyond the near-surface strata, drilling stops and the drill stem is withdrawn from the hole to change bits or run samples (called ?tripping out?). Once the pipe is out, the casing crew runs the surface casing. An oil well cementing service company usually cements the casing in place. After the cement hardens and tests indicate that the job is satisfactory, the rig crew attaches and tests the blowout preventer stack, and drilling is stemmed.

To resume drilling, the drill stem and a new, smaller bit that fits inside the casing must be tripped back into the hole (called ?tripping in?.) At a specific depth, drilling stops again to run another string of casing that is smaller in diameter than the initial run. The final part of the hole is drilled using a smaller bit. The bit and drill stem are tripped in and the intermediate casing shoe is drilled out. Drilling (to the final depth) resumes, and the cuttings are examined and/or well logging is conducted to determine whether to formation contains sufficient hydrocarbons to produce enough oil or gas to cover the costs associated with casing and completing the well. If the well is determined to be a dry hole, it is plugged.

Wastes that are usually associated with drilling are:

  • Pipe dope,
  • hydraulic fluids,
  • used oils and oil filters,
  • rigwash,
  • spilled fuel,
  • drill cuttings,
  • drums and containers,
  • spent and unused solvents,
  • paint and paint wastes,
  • sandblast media,
  • scrap metal,
  • solid waste, and
  • garbage.

Drilling fluid (?mud?) is used to maintain hydrostatic pressure for well control, carry drill cuttings to the surface, and cool and lubricate the drill bit. Drilling fluids may be fresh water-based, salt water-based, oil-based, or synthetic-based depending upon the conditions encountered. Water used to make up the drilling fluid (make-up water) may require treatment to remove dissolved calcium and/or magnesium. Soda ash may be added to form a precipitate of calcium carbonate. Caustic soda (NaOH) is added to form magnesium hydroxide. Wastes associated with this process include:

Wastes: Soda ash, calcium carbonate, caustic soda (NaOH), magnesium hydroxide.

Drilling fluid treating chemicals and additives include:

  • acids and caustics;
  • bactericides;
  • defoamers;
  • emulsifiers;
  • filtrate reducers;
  • shale control inhibitors;
  • thinners and dispersants;
  • weighting materials
  • lost circulation materials.

Solid additives are usually introduced into the mud system in a mixing (jet or ?shotgun?) hopper. Other chemical additives used to control mud viscosity and gel strength are mixed in tanks connected to the mud stream. Several devices used to remove solids from the mud as it circulates include shale shakers, centrifuges, and cone-type desanders/desilters.

Wastes: Drilling fluid additives (used and unused), spilled chemicals, empty containers.

Lined reserve pits or tanks constructed during drilling preparation receive spent mud, drill cuttings and solids, rig wash, and surface runoff from the drilling location. If the location is an ecologically sensitive area, trucks are used to transport waste material to a proper disposal site. [Note: Resource Conservation and Recovery Act (RCRA)-regulated hazardous waste should not be allowed to be allowed to enter the reserve pit.]

If the operating company decides to set casing, a contract casing crew with special equipment for running and making up the casing is called in to haul pipe to the test site, test the pipe, and make all other necessary preparations to run the pipe into the well.

Drilling operations generate an abundance of paper and plastic waste from packaging and wrappers on parts and equipment. Metal and wood debris are also generated. Roll away trash trailers can be placed conveniently and emptied as needed to encourage their use.

Oil Production

Production is defined as the operations involved in bringing well fluids to the surface and preparing the fluids for transport to a refinery via pipelines or trucks. The first step in production is to start the well fluids flowing to the surface (called ?well completion?). Well servicing and workover consists of performing routine maintenance operations (such replacing worn or malfunctioning equipment) and performing more extensive repairs, respectively. Well servicing and workover are an intermittent step and necessary to maintain the flow of oil and gas. Next, the fluid must be separated into its components of oil, gas, and water; stored; and treated (for purification), measured, and tested before being transported to the refinery.

[Click here to view a flowchart of oil production]

Steps in Oil and Gas Production

Step 1: Wells produce oil and/or gas by natural flow or artificial lift.

A. Flowing wells consist of the wellhead assembly and associated equipment used for well treatment.

- Wastes: Paraffin, slop oil, oil and produced water-contaminated soils, produced water, scale, treating chemicals, sand, and paint.

B. Artificial lift is accomplished by use of beam pumps, gas lift, or submersible pumps.

- Wastes: Used lubrication oil and filters, gas lift engine fuel, released crude oil (from stuffing box), paraffin, slop oil, produced water contaminated soils, produced water, scale, treating chemicals, sand, and paint.

C. Flare pits collect unburned materials from the flare.

- Wastes: Overflow hydrocarbon condensate, produced water (condensed from flare).

Step 2: Flowlines (gathering systems) are used to move produced oil to treatment and storage facilities (e.g., tank batteries).

- Wastes: Paraffin, produced water, treating chemicals, contaminated soil, scale, and other materials collected in pig traps. Scale may be contaminated by naturally occurring radioactive material (NORM).

Step 3: Separation and processing are often conducted at points along the gathering system.

A. Two-phase separation of produced liquids from gases, three-phase separation of produced water from liquid hydrocarbons, and/or gas floatation treatment may be installed.

- Wastes: Separator bottoms, blowdown, produced sand and scale, skim oil.

B. Free water knockouts are used to separate oil and water at appropriate locations in the gathering system.

- Wastes: Produced water, produced sand and scale, bottom sludges.

C. Heater treaters and electrostatic treaters separate emulsified oil and water.

- Wastes: Produced water, produced sand and scale, bottom sludges, oil absorption media.

D. Filtering improves the quality of liquids and produced water.

- Wastes: Used filters, filter media, backwash.

E. Centrifugal desanders remove excessive volumes of produced sand and other solids.

- Wastes: Produced sand, scale.

Step 4: Tank batteries consist of separation and treatment equipment and storage tanks.

A. Stock tanks are used to store treated crude oil and produced water. The tanks require periodic cleaning to remove tank bottoms or basic sediment and water (BS&W).

- Wastes: Produced sand, scale, BS&W.

B. Crude oil custody transfer is typically accomplished by moving the oil onto tank trucks via a loading line or into a pipeline.

- Wastes: Spilled crude oil, crude oil-contaminated soil.

Step 5: Handling of produced water is often required in preparation for recycling or proper disposal.

A. Produced water may be stored in pits for remaining solids and oil separation.

- Wastes: Solids and additional oil.

B. Underground injection, using electric or gas engine powered pumps to pressurize water, is a common method for management of produced water.

- Wastes: Used lubricating oil and filters, produced water filters and filter media, filter backwash, produced water-contaminated soil, and unused or spent chemicals.

Step 6: Completions and workovers are conducted to facilitate the production of a well.

A. Workover rigs are used for well completions and well workovers (i.e., treatment and/or stimulation). Workover rigs are generally mobile units.

- Wastes: Hydraulic fluids, rigwash, spent solvents, used lubricating oil and filters.

B. Well workovers may involve recompleting in a different pay zone by deepening the well or plugging back. Operations may generate wastes with the volume and characteristics of drilling operation waste.

- Wastes: Refer to drilling operations.

C. Well treatment and stimulation use various chemicals and products to improve the producing characteristics of a well.

- Wastes: Drums and containers, weighting agents, surfactants, muds, produced water, acids, frac fluids, inhibitors (scale/corrosion), gel, solvents, and other materials.

D. Workover pits are sometimes constructed to receive oil and gas wastes generated during workover operations.

- Wastes: Drilling solids, drilled cement, liners or contaminated soil and metal (e.g., bridge plugs).

Step 7: Enhanced oil recovery operations (EOR) typically involve the injection of water into a producing formation, as well as injection of certain chemicals.

- Wastes: Unused or spent chemicals, polymers, etc.

Step 8: Thermally enhanced oil recovery (TEOR) operations use injected steam for enhanced recovery of crude oil. Steam generators are fueled by crude oil, fuel oil, or natural gas. Feed water is conditioned (softened) to prevent scaling.

- Wastes: Fuel oil filters, refractory waste, combustion scale, flue duct ash, sulfur dioxide and particulate matter air emissions, sulfur dioxide liquor, spent water-softening resin, water-softener regeneration brine, soft water blowdown, surplus deionized water.

Gas Production and Gas Plant Operations

Well Treatement

Well treatment is conducted to optimize production and waste such as produced water and sand must be separated from the production stream.

A. Corrosion inhibitors are chemicals used to counter the reaction between the acid in the gas and the iron of the tubing or other equipment. Usually it is accomplished at the wellhead, either by batch treatments or continuous injection.

- Wastes: Surplus chemicals, spilled chemicals.

B. Hydrate inhibition at the wellhead is accomplished by injection of glycol, ammonia, methanol, or brine.

- Wastes: Surplus inhibitor chemicals, spilled inhibitor chemicals.

Also, hydrate inhibition may be accomplished by the use of indirect heaters that use bath solutions containing calcium chloride or glycol.

- Wastes: Surplus bath chemicals or solution.

C. Impurities such as sand and excessive amounts of water are sometimes separated at the wellhead.

- Wastes: Produced sand, produced water.

Gathering Systems

Gathering systems are used to transport produced gas to a central treatment facility (i.e., gas plant).

A. Scraping or slug catching equipment (separators) on the pipeline removes slugs of liquid (hydrocarbons and/or water). Facilities for handling liquid hydrocarbons may be installed at these locations.

- Wastes: Produced water and wastes associated with processing of hydrocarbon liquids.

B. Hydrate inhibition is conducted at appropriate locations in the gathering system.

1. Glycol, ammonia, methanol, or brine are injected to lower the freezing point of water in the flow line.

- Wastes: Surplus inhibitor chemicals, spilled inhibitor chemicals.

2. Indirect heaters sometimes use bath solutions containing calcium chloride or glycol.

- Wastes: Surplus chemicals or solution.

C. The produced gas is compressed to facilitate its transport to the gas plant.

- Wastes: Engine cooling water, used lubricating oil, used lubricating oil filters, oil-contaminated soil, spent solvents, oily rags and sorbents.

Gas Plant Processing

Gas plant processing removes impurities from the produced gas and, in some cases, includes the fractionation of the treated gas.

Oil absorption plants remove hydrocarbon products form natural gas. Oil absorption plants include:

  • Stage separators (Economizers)
  • Gas chillers
  • Rich oil flash tank
  • Presaturators
  • Accumulators
  • Rich oil demethanizers (RODs)

- Wastes: Surplus or spilled chemicals for hydrate and corrosion inhibition, vessel blowdown.

Dehydration is the removal of water from the produced natural gas and is accomplished by various methods.

1. Ethylene glycol (glycol injection) systems use: a) filters to remove solids from solution prior to reboiler (that removes water) and b) charcoal filters on glycol pump discharge, if the glycol separator is not efficiently removing hydrocarbons.

- Wastes: Glycol, filters, solids, activated charcoal filter media, filter backwash.

2. Triethylene glycol (TEG) and diethylene glycol (DEG) systems use an absorber tower (contactor tower).

Also, stripping gas is used for additional water removal to get very high TEG concentration into the contactor tower. Excess stripping gas will increase TEG losses.

Excessively high reboiler temperature may cause decomposition of glycol.

- Wastes: TEG, DEG (decomposed glycol).

3. Dry-bed dehydrators use desiccants for the adsorption of water:

Silica gel Sorbead

Activated alumina Molecular sieves

Regeneration of desiccants is accomplished by application of hot gas (vaporizes water).

- Wastes: Spent filter media, spent molecular sieve.

Recovery of natural gas liquids (NGL) is sometimes conducted at the gas plant.

1. Cryogenics may be used to remove NGL. Natural gas liquids (e.g., propane) are used as refrigerants and fuels. Filters are used for gas preparation (gas that is free of impurities is required for process). Electrostatic precipitators are sometimes used. Filtered substances include FeS2, crude oil, wax, and lube oil.

- Wastes: FeS2, slop oil, wax, lube oil, filter media.

2. Absorption may be used to remove NGL. An absorption oil removes the heavier compounds from the process stream.

- Wastes: Spent or degraded absorption oil, vessel blowdown.

Gas and product treating includes the removal of sulfur compounds (primarily H2S) and CO2 from gas. ?Sweetening? processes include adsorption using various amines or a dry bed adsorbent.

1. Amine adsorption is accomplished by passing the gas through the amine liquid where the impurity is dissolved or captured by chemical reaction. The amine can be regenerated. The most common systems use MEA (monoethanolamine) or DEA (diethanolamine). Lean amine is filtered.

a. The reclaimer removes solids and heat-stable salts (amine degraded in the presence of air) and other MEA/DEA degradation products.

b. Charcoal filters may be used to remove liquid contaminants when foaming is a problem. Defoamers may also be added to control foaming.

c. The largest amine losses are usually due to: carry-over from contactor due to foaming; continuous small leaks in piping, pump packing, and other fugitive emission points; and sulfur compounds (e.g., COS, CS2; compounds that cannot be regenerated, see reclaimer above).

d. Charcoal filter beds are used to remove corrosion inhibitors, amines, absorber oils, glycol and other sieve contaminants.

- Wastes: Released amine, amine filters, filter backwash, reclaimer solids (bottoms), heat-stable salts, other MEA degradation products, iron sponge, charcoal filter media, defoamers, acid gases.

2. Dry bed adsorption uses one of a variety of absorbent materials (iron sponge is commonly used) to selectively remove sulfur compounds and CO2.

- Wastes: Spent absorbent materials, spent iron sponge, iron sulfide scale.

Sulfur Removal

Sulfur is removed from the H2S recovered from the produced gas.

The Claus process is typically used to remove elemental sulfur from the H2S (acid gas). Tail-gas cleanup systems remove remaining sulfur from the exhaust.

- Wastes: Emissions resulting from the burning of H2S gas (e.g. SO2), released acid gas, catalysts (e.g., activated natural bauxite, aluminum oxide), vessel blowdown, spilled elemental sulfur.

Pipeline Transportation

Pipelines transport crude oil and natural gas from the wellhead to storage tanks, gas processing plants, and to market. Transportation of oil and gas includes the equipment and facilities used to move products through the pipelines.

Oil and Gas Pipelines (Comparison)

Gas and oil pipelines are essentially similar, with the greatest operational difference resulting from the varying needs of transporting gas versus liquid. Oil pipelines require pumps to propel their liquid contents, while gas lines rely on compression to force the resource through the pipe. In both pump and compressor stations, corrosion of piping and vessels must be monitored constantly to prevent failure. Pipelines can be cleaned and surveyed with cleaning pigs used to prevent unwanted materials from contaminating the pumps or compressors. Pigs with high technology instrumentation are used to monitor pipeline conditions and detect potential problems.

Oil Pipelines - Oil pumped from the ground travels through pipes to lease tanks, where it is treated, measured, and tested. Typically, a separator is used to separate oil, gas, and water. A fired heater is used to break water/oil emulsions to promote removal of water from the oil. Tanks store oil until it is shipped as crude oil by truck or, more commonly, by a gathering line connected to storage tanks. From these tanks, the oil is moved through large-diameter, long-distance trunk lines to refineries or other storage terminals.

Trunk lines rely on pumps to initiate and maintain pipeline pressure at the level required to overcome friction, changes in elevation, or other pressure-decreasing factors. Pumps are required at the beginning of the line and are spaced along the pipeline to adequately propel the oil along the line.

Gas Pipelines - Gas pipelines operate at high pressures and use compressors (instead of pumps) to force the gas along the line. Unlike oil, gas does not undergo refining, and transmission lines connect directly to utility companies that distribute the gas to consumers via small, metered pipelines. Gas is often treated in scrubbers or filters to ensure that it is ?dry? prior to distribution. Gas-well flow lines connect individual gas wells to field gas-treating and processing facilities or to branches of a larger gathering system. The gas is processed at the treating facility to remove water, sulfur, acid gases, hydrogen sulfide, or carbon dioxide. Most field gas processing plants also remove hydrocarbon liquids from the produced gas stream. From field processing facilities, the dried, cleaned natural gas enters the gas transmission pipeline system (analogous to the oil trunk line system). Downstream from compressor stations, lubricating oil from the compressors is removed from the gas lines.

Pipeline Transportation Operations


Pipelines transport crude oil and natural gas from the wellhead to storage tanks, gas processing plants, and to market. This operation includes the following:

A. Routine maintenance on pipelines includes painting, repairing, pigging, and replacing.

- Wastes: Paraffin, solvents, sand blast media, asbestos, hydrotest water, NORM, hydrocarbon contaminated soil, iron sulfide, scale, pigging waste, scrap pipe, welding wastes, produced sand, produced water, BS&W, and paint waste.

B. Compressor stations boost the fluid in pipelines to help it travel long distances.

- Wastes: Lube oil, filter media, hydrocarbon contaminated soil, chemicals, solvents, sand blast media, used filters, filter media, scale, NORM, sorbent pads, air emissions, antifreeze, batteries, and stormwater.

C. Corrosion inhibitors are used to minimize the reaction between acid in the fluid and iron in the tubing.

- Wastes: Surplus chemical, spilled chemicals.

D. Lead acetate tape is commonly used for detection of acid gases
(e.g., H2S) in pipelines:

- Wastes: Spent lead acetate tape.

General Operational Wastes

Several wastes are common to most, if not all, types of oil and gas operations:

  • Contaminated soil: Any uncontrolled release of chemicals, brine, oil, drilling fluid, or other materials, will result in soil contamination.
  • Used or spent solvents: Solvents are used in tasks such as cleaning, degreasing, and painting. Unused solvent intended for disposal is considered a waste.
  • Used oil and used oil filters: Engines and other machinery in all areas of operations require lubricating oil and oil filters.

  • Drums and containers: Drums and containers are required for delivery and storage of chemicals and materials used in all areas of operations.

  • Sandblast media: Sandblasting is typically used to prepare equipment for painting and to remove scale from equipment.
  • Paint and paint wastes: Painting is generally required for maintenance of equipment. Paint thinners, solvents, and unused paint are generated wastes.
  • Pesticides and herbicides: These chemicals are used to control insects and vegetation at various locations (e.g., drilling locations).

  • Vacuum truck rinsate: Vacuum trucks recover waste liquids generated by various operations.
  • Radioactive tracers: Tracers are used to observe downhole fluid or gas movements.

  • Scrap metal: Scrap metal consists of damaged tubulars or other equipment, crushed drums, remnants of welding operations, cut drill line, etc. Scrap metal may contain naturally occurring radioactive materials (NORM)


The Topic Hub™ is a product of the Pollution Prevention Resource Exchange (P2Rx)

The Oil and Gas Topic Hub™ was developed by:

Southwest Network for Zero Waste
Southwest Network for Zero Waste
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Hub Last Updated: 4/19/2007