STRAY METHANE GAS INVESTIGATIONS CAUSED BY HYDRAULIC FRACTURING IN PENNSYLVANIA

STRAY METHANE GAS INVESTIGATIONS CAUSED BY HYDRAULIC FRACTURING IN PENNSYLVANIA

One of the most important issues associated with oil and gas exploration and development pertains to the effective engineering and construction of oil and gas wells. If wells are not constructed or operated properly, there is a potential risk for natural gas to escape from the well bore and into subsurface geologic strata or groundwater sources. If this happens, it is called “stray gas” migration and the responsible operator is required by law to correct or mitigate the situation.

Through efficient communication and collaboration with district oil and gas operations staff, the Pennsylvania Office of Oil and Gas Management has created a database of stray gas case investigations. The information compiled dates back to 1987 and allows for critical data trend analysis and some level of forensic work aimed at identifying causes and solutions in the rare instances when operating oil and gas wells in the state have been found to not provide adequate protection of water resources. This invaluable summary of information helps to direct policy decisions and inform the development of focused new regulations.

Stray gas investigations are primarily driven by complaints from individuals who believe their property may have been impacted by gas migrating into a water well or surface water body such as a pond, stream or wetland. Since natural gas is colorless and odorless, the most common indicators suggesting potential gas migration are the appearance of many tiny “bubbles” (i.e., effervescence) in tap water drawn from the supply or off-gassing from a water well or surface water body; or the sound of “knocking” in a water well that results when infiltrating gas disturbs the well pump. In some cases, an initial review of the complaint may reveal that the condition is, in fact, not related to gas migration. Such cases are tracked and responded to via DEP’s Complaint Tracking System and are not cataloged as gas migration events. In other cases, the investigation might require a lengthy series of site visits and multiple rounds of lab analyses to reach a determination concerning the alleged gas migration event. It could take many months or even years to reach a final determination.

After a thorough inspection, review of all laboratory analyses, an assessment of construction and integrity data and a geological assessment, DEP renders a determination regarding the event. The determination may result in either of the following findings:

Positive Determination: The migration of gas is confirmed and is the result of hydrocarbon exploration and production activities. These findings are either documented through issuance of an official determination letter to the complainant, or, if no formal complaint is filed with DEP, the department documents which water supplies or residences have been impacted as a result of hydrocarbon exploration and production activities and responds as appropriate.

Negative Determination: The presence of gas is either confirmed, but cannot be positively attributed to hydrocarbon exploration and production activities or, in certain cases, no gas is found.

There are generally two classifications of natural gas – “biogenic gas” and “thermogenic gas”. Biogenic gas is formed by microbial decomposition of organic matter nearer to the earth’s surface; whereas, thermogenic gas is formed when organic matter in sedimentary rock is subjected to heat and pressure deep under the earth’s surface. In some cases, Negative Determinations result when it is found that the type of gas detected is “biogenic” rather than “thermogenic” gas that is targeted during natural gas exploration and production activities. However, both gas types are found to exist naturally in portions of Pennsylvania’s fresh groundwater system.

The following bar chart identifies the number of confirmed Positive Determinations from 2008 through 2013 for gas migration cases investigated by DEP. If a stray gas investigation does not result in a confirmed Positive Determination, then it is not included in this bar graph. If a stray gas investigation extends from one calendar year into a future calendar year, the confirmed positive determination is reported in the year in which the investigation was initiated. DEP is currently conducting several investigations that are expected to be completed during 2014.

The Pennsylvania Oil and Gas Regulation at 25 Pa. Code, Chapter 78, Subchapter D provides specific requirements for the construction of oil and gas wells including, but not limited to, casing and cementing practices. It also details requirements that operators must fulfill when a potential gas migration incident has occurred. The department updated these subsurface activities regulations to strengthen well construction practices that are required of operators and place many of the responsibilities of investigating stray gas incidents on the oil and gas industry. The revised rulemaking went into effect on Feb. 5, 2011. The department intends to further strengthen these subsurface activity regulations through a subsequent rulemaking package that it will initiate in 2014.

The bar chart above identifies the number of drinking water supplies impacted by confirmed gas migration events. It is not uncommon for a single confirmed gas migration to affect multiple water sources.

The Oil and Gas Act of 2012 presumes that an operator of an unconventional well is responsible for pollution of a water supply when the source is located within 2,500 feet of the unconventional well and when the pollution occurred within 12 months of the drilling, stimulation or completion of the unconventional well. Unless, the operator can successfully demonstrate that the pollution was not caused by its actions based on specific statutory defenses, the operator must restore or replace the affected water supply with an alternate water source.

Source: 2013 Oil and Gas Annual Report, PADEP, Office of Oil and Gas Management