Drilling and stray natural gas migration

From Wikimarcellus

(Difference between revisions)
Jump to: navigation, search
Revision as of 22:11, 10 November 2012
Tcopley (Talk | contribs)
(Identifying Stray Gas)
← Previous diff
Revision as of 22:38, 10 November 2012
Tcopley (Talk | contribs)
(Marcellus Shale Coalition Recommended Practices on shale gas)
Next diff →
Line 31: Line 31:
The Marcellus Shale Coalition is a membership organization made up of natural gas exploration and production companies as well as suppliers to that industry. In October, 2012 the Coalition issued a guidance document on how operators should handle stray gas incidents. Operators are advised to act very proactively in event of any report of gas migration. The Marcellus Shale Coalition is a membership organization made up of natural gas exploration and production companies as well as suppliers to that industry. In October, 2012 the Coalition issued a guidance document on how operators should handle stray gas incidents. Operators are advised to act very proactively in event of any report of gas migration.
 +
 +The group advises its members to make a site survey as soon as possible after being notified of a stray gas incident. It should interview workers on the scene and make a reconnaissance survey. Operators are expected to be good communicators with owners, emergency responders (if required) and state regulatory agencies. In the event of a critical incident, emergency response organizations will need to be made fully aware so that evacuation and/or ventilation can take place.
 +
 +The initial reconnaissance survey should include monitoring all buildings, out buildings and water wells to detect possible migration paths for the gas
 +
 +If necessary, the operator should take immediate action to vent any water wells with high concentrations of dissolved methane, install monitors and alarms when needed, and/or provide an alternative drinking water source for the home owner/landowner.
 +
 +The operator should essentially document everything about the incident, and in fact it may be a state requirement to do so. The end objective is to obtain permission from the state regulatory agency to close its file on the incident. An operator can document either that the migrating gas was already there, or else if it does have some responsibility, then to provide a remedy for the migration.

Revision as of 22:38, 10 November 2012

Typical stray natural gas migration scenariosSource: The Pittsburgh Geological Society, Natural Gas Migration Problems In Western Pennsylvania (Pamphlet).
Typical stray natural gas migration scenarios
Source: The Pittsburgh Geological Society, Natural Gas Migration Problems In Western Pennsylvania (Pamphlet).

Stray natural gas migration refers to the movement of natural gas (mostly methane) through bedrock and soil. It can leak from a variety of sources, including reservoir rock, coal seams, landfill, or pipelines. It can also occur from drilling any well--gas, oil or water--as well as from abandoned wells. Whenever the water table is penetrated by drilling a well, methane gas may be given an escape route. It tends to move from areas of high pressure to low.

Contents

Identifying Stray Gas

Stray gas is quite common in regions of North America that are undergirded by hydrocarbon deposits, such as in southwestern and northeastern Pennsylvania. It can be found throughout the central and northern Appalachian Basin. When it occurs, it can be broken down into three main categories:

  • Sub-surface microbial gas. These originate in deep sea sediments and may be identified as drift gas.
  • Near-surface microbial gas often from landfills or naturally occurring marsh gas.
  • Thermogenic gas consisting of natural gas or coal-bed gas.

These gasses can blend together into a mixture. The origin of stray natural gas may only reliably be determined by its chemical signature.

Factors Affecting Gas Migration

The general rule is that stray natural gas moves from areas of high pressure to ones of lower pressure. However several factors can, come into play that influence migration. These include changes in barometric pressure, porosity and permeability of soil and bedrock, temperature differentials, rain or snow.

Stray Gas Regulatory Environment

Pennsylvania has taken an aggressive stance towards regulating stray gas originating from drilling operations. Obviously, there is little that can be done to regulate naturally-occurring gas migration. The state issued new drilling regulations in 2011 to help combat gas leaks from drilling operations.

The Pennsylvania Oil and Gas Act

The Pennsylvania Oil and Gas Act of 2011 automatically assumes whenever a new well is drilled within 1,000 feet of a drinking water supply, and contamination such as stray gas or chemical occurs within six months of drilling, that the operator is at fault. Thus, in order to either establish or else avoid blame, it is important for both the water supply owner/homeowner in addition to the well operator to obtain test samples of the drinking water before drilling begins. Well operators must report any incidents of contamination to PDEP within 24 hours once it is in fact discovered.

Regulation of Well Casings

The Act focuses regulating well casings and cementing as one possible source of stray gas, and specifies construction standards and requirements that bring Pennsylvania' drilling regulations up to the same standard as several other states. The purpose is to provide greater protection for home and property owners from contaminated drinking water. Also blow-out preventers--essentially large valve or a series of valves that can be triggered remotely to close-off a well bore--are required on all natural gas wells.

Operator Held Liable

Under this Act, whenever there is any contamination of drinking water, the well operator is held liable for replacing the damaged water supply. Operators are also required to notify PDEP promptly in the event of any complaints regarding natural gas migration. Emergency responders are to be summonsed when high concentrations of gas are noticed.

Marcellus Shale Coalition Recommended Practices on shale gas

The Marcellus Shale Coalition is a membership organization made up of natural gas exploration and production companies as well as suppliers to that industry. In October, 2012 the Coalition issued a guidance document on how operators should handle stray gas incidents. Operators are advised to act very proactively in event of any report of gas migration.

The group advises its members to make a site survey as soon as possible after being notified of a stray gas incident. It should interview workers on the scene and make a reconnaissance survey. Operators are expected to be good communicators with owners, emergency responders (if required) and state regulatory agencies. In the event of a critical incident, emergency response organizations will need to be made fully aware so that evacuation and/or ventilation can take place.

The initial reconnaissance survey should include monitoring all buildings, out buildings and water wells to detect possible migration paths for the gas

If necessary, the operator should take immediate action to vent any water wells with high concentrations of dissolved methane, install monitors and alarms when needed, and/or provide an alternative drinking water source for the home owner/landowner.

The operator should essentially document everything about the incident, and in fact it may be a state requirement to do so. The end objective is to obtain permission from the state regulatory agency to close its file on the incident. An operator can document either that the migrating gas was already there, or else if it does have some responsibility, then to provide a remedy for the migration.

Personal tools