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Oil and Gas Extraction

Impacts, Risks and Regulations


Six hundred million years ago, for no obvious reason, life on this planet was suddenly becoming more complicated.  Having existed in the oceans for several times that span as primitive single-celled organisms, creatures were suddenly experimenting with new body plans and new chemistries.  As countless generations developed, died, and settled to the bottom, their remains began a slow process of decomposition.  Most of their carbon was eventually recycled back into the great planetary cycles that characterize the fate of light elements in the planet's outer layers.  But in a few situations, the carbon, gradually reduced to gaseous or liquid hydrocarbons and rising up slowly through the denser rock and water in the subsurface, was trapped under domes or peaks of overlying impermeable strata.  And there it came to rest, remaining undisturbed for tens to hundreds of millions more years.

Two hundred years ago, for no obvious reason, some distant descendants of those organisms suddenly began to develop a complicated technology that required the consumption of unprecedented quantities of energy.  Within fifty years after modern industrialization had begun its exponential ascent, the potential of those ancient deposits to supply the energy had been recognized and tapped.  At an ever increasing rate, carbon has been withdrawn from its traps, burned, and pumped into the atmosphere as the oxide.  A substantial fraction of hundreds of millions of years worth of production has been released in the last hundred years.  And many expect the earth's climate to change significantly and unpredictably as a consequence.

Well, it seemed like a good idea at the time.

The business of extracting fluids from the earth is, if one takes a localized viewpoint, somewhat less disruptive to the earth's surface than the extraction of solids.  One need not extend tunnels directly to each bit of material to be removed, or strip away the overburden altogether.  One has only to extend a tube into the general vicinity of the desired material and maintain the pressure on the upper end of the tube at something less than the pressure at the lower end.  The fluid will come to the tube.  While the drilling of a borehole requires the displacement of a perhaps surprising amount of material, the amount of product that can then be withdrawn through that borehole makes the volume of the cuttings seem minor by comparison. 

However, one would not want to characterize the process of oil and gas extraction as surgical.  While a completed, producing well has a relatively small footprint, its potential environmental impact can be much larger.  First, oil and gas are not the only fluids that the tube conducts to the surface.  Huge quantities of water, bearing complex mixtures of salts including those of toxic metals, as well as toxic organics, both from the natural formation and from additives to facilitate production, also issue from the wells.  Second, opening a passageway between previously isolated strata can also result in an undesired flow of subsurface fluids bearing contaminants into otherwise usable groundwater.  In addition, as with any production process, there are the inevitable air emissions and solid wastes generated as materials are separated and moved.  And finally, the sheer number of holes multiplies the problems of each isolated well over a very wide total area of impact.

The sector's performance in minimizing these impacts has steadily improved, as its capabilities have increased.  Blowouts and fires have become rare events.  Routine releases from producing wells are declining.  Oil and gas can now be recovered from ecologically sensitive areas, and from very inhospitable locations -- offshore in stormy seas and relatively deep water -- with much less damage and risk than would have been the case in earlier years.  And the industry is learning how to produce more from existing wells, an enterprise that can only be fostered by a conservation-minded approach to the resource being tapped.

Companies in the business of oil and gas extraction are getting steadily better at what they do.  They have no choice.  Most of the easy fossil fuel is gone.  The environments in which they must work can only become steadily less forgiving, as will the attitude of the public, whose demand for oil and gas will increase as surely as its tolerance level for damage declines.


Industry profile

Environmental impacts and risks

   Issues List

  Quantitative impact data

Effects of existing and future regulations on impacts

Information sources

Industry profile

This industry locates promising formations, drills exploratory wells, installs and maintains production wells, carries out preliminary separations of materials extracted from the wells, and (ideally) plugs wells that have reached the end of their economically useful life, removes their surface penetrations, and restores their sites.

On the face of it, an oil or gas well is a much less disruptive installation than a typical mine.  It is a common site in some areas of the country to see a field of production wells, each well placidly rocking up and down while sharing the field with rows of corn and soybeans, a form of dual use not typically associated with, say, strip mines.

But drillers have been going after oil and gas for 150 years, and their activities have left their mark.  According to the OECA Sector Notebook on this industry (page 9) quoting figures from the Independent Petroleum Association of America, there were 573,504 active oil wells in the United States, and 303,724 natural gas wells.  (A note on classification:  many wells produce both oil and gas.  Wells are assigned to one or the other category based on the primary material being extracted from it.)

That's a lot of wells.  Looking at just the active ones, we can derive some interesting aggregate impact statistics.  According to data from the American Petroleum Institute (see the OECA Sector Notebook, page 17), the average depth of a well drilled in 1997 was 5,601 feet.  Taking this as historically typical, and folding in another piece of data (page 37), that a quantity of the order of magnitude of one barrel (42 gallons) of drilling waste (mostly cuttings and drilling muds) are produced for each vertical foot drilled, we can calculate that the drilling of the currently active wells involved the production of 135 billion gallons, or 18 billion cubic feet of waste.  That would form a conical mountain a mile across and a half a mile high.  Even spread across the years, that's a lot of waste.

Apart from drilling, oil and gas extraction can impact the environment during routine production operations.  From some wells where gas is produced along with the oil, but where there is no economical way to move the gas to market, the gas is flared, with consequent emissions (and waste of a potential energy resource).  Large quantities of water are often withdrawn from wells, as well as fine sediment.  These materials are generally separated before transportation of the product from the wellhead to the refinery or gas conditioning plant.  The water may be contaminated both with metals and organics from the formation, and with additives introduced to aid the flow of oil from the well, or to help separate desired from undesired materials.  Among the additives are:

Well are also subject to periodic maintenance operations (termed "workovers") that can introduce additional potential contaminants, such as acids to help unclog pores and loosen scales.

Finally, there are risks associated with unintended consequences, such as migration of water or oil into otherwise usable aquifers, and the risk of surface and groundwater contamination resulting from leaks and spills, or from the occasional catastrophic blowout.

Types of producers

According to IPAA (see below), "independent producers drill 85 percent of wells in the United States, produce 65 percent of the country's natural gas, and produce 40 percent of the oil (60 percent in the Lower-48 states.)"

Trade and research organizations

Environmental impacts and risks

Issues list

Quantitative impact data

Air emissions data for certain key criteria pollutants (ozone precursors) are available from the National Emission Trends (NET) database (1999), and hazardous air pollutant emissions data are available from the National Toxics Inventory (NTI) database (1996 is the most recent year for which final data are available).  For the SIC codes 13xx (Oil and gas extraction), the total emissions for volatile organic compounds (VOC), nitrogen oxides (NOx) and hazardous air pollutants (HAPs) are as follows (in tons per year):

SIC Subsector VOC NOx HAP
1311 Crude Petroleum & Natural Gas 60,040 178,207 2,846
1321 Natural Gas Liquids 34,195 187,278 899
1381 Drilling Oil And Gas Wells 59 753 20
1382 Oil And Gas Exploration Service 12 13  
1389 Oil And Gas Field Services, NEC 243 542 1
  Total, all oil and gas extraction subsectors 94,549 366,820 3,766

In terms of VOC emissions, crude petroleum and natural gas is the seventh largest emitter among all SIC sectors at the four digit level, and is sixth largest in NOx emissions.  Natural gas liquids is the fifth largest NOx emitter.   Their HAP impact is somewhat less, presumably since the predominant emissions, light hydrocarbons, are not considered HAPs.  The two lightest, methane and ethane, are not considered VOCs either (since they contribute less significantly than "official" VOCs to ground level ozone formation), so these data actually understate the sector's emissions in that regard.

To complete the picture, one can turn to the Inventory of U.S. Greenhouse Gas Emissions and Sinks, issued by the EPA's Office of Atmospheric Programs.  This document provides extensive data on sources of greenhouse gas emissions, and includes data on methane, which is a powerful greenhouse gas (a ton of methane has the global warming potential of 21 tons of carbon dioxide).  Methane emissions from U. S. natural gas field production in 2000 are estimated (page 58) at 26.2 teragrams (Tg, or million metric tons), expressed as carbon dioxide equivalents, and methane emissions from petroleum field production for that year (page 60) at 21.2 Tg CO2 equivalent.  These are significant contributions to the total, on a par with manufacturing sector emissions, such as that from automobile manufacturing.  And this does not include the greenhouse gas impact from fuels burned to support field production operations.

Incidentally, the figures are also given in terms of the unconverted weight of methane;  they are 1.25 million metric tons of methane from natural gas field production, and 1.01 million metric tons from petroleum field production in 2000.  These numbers dwarf the VOC numbers given in the table above, which amount "only" to tens of thousands of tons (short tons at that). 

Another interesting incidental point which can be gleaned from the greenhouse gas emissions inventory is a comparison of field production losses with processing and distribution losses.  Total methane emissions from the entire natural gas supply chain (field production, processing, transmission and storage, and distribution) were 5.54 million metric tons, and the corresponding total from the petroleum supply chain, including refining, was 1.04 million metric tons.  Thus, while field production of the two fuels accounts for roughly the same quantity of methane emissions, by the time the fuel is ready for distribution to the end user, a disparity emerges.  Field production is only about 23% of the total methane loss for natural gas, but accounts for nearly the entire methane loss for petroleum.  According to the Energy Information Administration, total U. S. natural gas production in 2000 was 20 trillion cubic feet.  Since 1 trillion cubic feet of natural gas weighs 20 million metric tons, U. S. natural gas production in weight units was 400 million metric tons.  The loss of 1.4% of this total to the atmosphere during production and distribution, and the potency of methane as a greenhouse gas, should be taken into account when the relative environmental merits of petroleum and natural gas are being compared.

The oil and gas extraction sector is not considered a "manufacturing" sector, and is not currently required to report under TRI.  Future revisions to TRI reporting requirements might introduce TRI reporting to this sector.


The ever-present risk of a major blowout or spill, particularly in an ecologically sensitive area, is a fact of life for this sector.  As the more easily accessible deposits of oil and gas are depleted, the extraction operations will become more difficult, and the risks will increase in proportion.

Special risks are associated with offshore drilling operations.  Blowouts can be extremely difficult to control.  Deposition of cuttings on the sea floor can have adverse effects on the marine ecology in the vicinity of the waste. 

Effects of existing and future regulations on impacts

Effluent Limit Guidelines:

MACT Standards:

***  [RCRA categorical wastes?]

The Oil Pollution Act of 1990, passed following the Exxon Valdez oil spill in Alaska, applies to spills in general, but in practice probably affects the transportation of oil more than its production.

Information sources

The OECA Sector Notebook for the oil and gas sector is recent (2000), and is particularly rich in interesting detail, even in comparison with the other generally illuminating documents in this series.  It also features an extensive discussion, with exemplary specificity, of pollution prevention methods.  It is available at