Production wells also pose other challenges:
Produced water – When oil and gas are brought up to the surface, they emerge along with water that coexists with hydrocarbons in the reservoir. This is a significant waste stream by volume in oil-and-gas extraction operations. Where extraction is enhanced through flooding the reservoir with water, the quantities of produced water can be even greater. Depending on the age of the well and the nature of production, between two and nine barrels of produced water can be generated for every barrel of oil extracted.
Produced water is highly saline and corrosive, and will contain hydrocarbons like the toxic benzene, polycyclic aromatics, heavy metals and naturally occurring radioactive material like dissolved uranium, radon and radium. Pipelines or vessel interiors used to store or transport these effluents are prone to corroding and developing scales and salt deposits. The scales themselves tend to concentrate the toxins within the effluent, and ought to be handled as hazardous wastes.
ONGC’s delta operations claim to have 21 effluent treatment plants (ETP) to handle 70 million litres of produced water per day. Some of the treated water is reused in injection wells for waterflooding hydrocarbon reservoirs and the remainder disposed by pumping into old wells. Deepwell injection for disposal or for waterflooding are governed by dedicated rules in other countries and followed up with monitoring as well as informing the public of it.
However, produced water is dealt with casually in India. The EIA reports, which ought to dedicate entire sections to predicting and managing the impact of produced water, has nothing more than one passing reference to the waste stream. No information is available in the public domain about the performance of these ETPs either.
Groundwater contamination can occur if the well casing in production wells fail or wells collapse, exposing the aquifers to produced water and hydrocarbons emerging from the bore. They can also occur in abandoned or idle wells that may not be plugged, or where the plugs get damaged over time. Where and when this happens, hydrocarbons, gases and associated water can enter drinking-water aquifers. Idle wells that are not plugged should be subjected to routine checks for fractures in the casing or other defects. The exploratory well near Neduvasal has not been monitored since it was capped in 2009.
Groundwater, surface water and land contamination can also occur due to improper handling of waste streams – e.g., spills of produced water, temporary or long-term surface storage of produced water or oily wastes, leaks from crude oil pipelines, etc.
Air pollution can occur due to fugitive emissions or leaks. Volatile organic compounds (VOCs), including toxic chemicals like benzene (which causes leukaemia), ethylbenzene, xylene and toluene, can be mobilised in the air. Flaring or venting of gases is generally not a good practice as it represents a waste of the fuel that is to be harvested.
However, where this is done, ground-level air quality tends to deteriorate and pose a localised health hazard. Many of the VOCs can combine with nitrous oxides emitted from diesel exhaust to form ground-level ozone, a respiratory irritant.
Since methane – a potent greenhouse gas – is a major constituent of natural gas, venting the gases into the atmosphere can appreciably worsen global warming risks.
Blow-outs and explosions – Hazardous incidents such as blow-outs – caused by sudden surges in pressure inside the bore – result in gases erupting and exploding from the well mouth. These are the most hazardous incidents that can occur at a well site, and result in the discharge of large quantities of pollutants into the atmosphere. A single blow-out can last from a few minutes to several days. The 2010 Deepwater Horizon spill at BP’s oil installation in the Gulf of Mexico has been the worst blowout incident to date. It took five months to tame.
Blow-out risks are sought to be reduced by safety devices and good practices, and are relatively rare.
Land subsidence and salinity intrusion – Large-volume extraction of fluids, such as water or hydrocarbons, can result in land-subsidence. According to the US Geological Service, “This induced subsidence, which is either sub-regional or local in extent, has its greatest impact on flat coastal plains and wetlands near sea level where minor lowering of the land surface results in permanent inundation.”
This is particularly problematic for the delta region, which is already facing sea-water intrusion owing to rising sea levels, rampant sand-mining and the exploitation of underground resources like groundwater, apart from oil and gas.
Note: The sections on oil and gas extraction and environmental/health effects of hydrocarbon production has been sourced from several documents, including those already cited above. More herehere and here.
Nityanand Jayaraman is a Chennai-based writer and social activist.