Evaluation of Volatile and Semi-Volatile Organic Compounds Potentially Associated with the Gas Shale Fracturing Process in the Fayetteville and Marcellus Shale.

摘要

With the recent growth of the natural gas industry coupled with technological advancements, gas shale fracturing has become an effective and highly profitable method for natural gas production. Unlike conventional natural gas extraction which may require vertical fracturing, gas shale fracturing relies on a method known as horizontal fracturing to remove gas trapped within the impermeable facies. Compared to vertical fracturing, horizontal fracturing requires larger amounts of fluids to be injected downhole under high pressure. These fracturing fluids can contain high concentrations of petroleum hydrocarbons with known adverse health effects. Due to the large volumes used, the potential for groundwater contamination has caused concern in the public. In this study, groundwater quality was evaluated in regions associated with gas shale fracturing. Groundwater samples were collected from 15 shallow aquifer wells at varying depths in areas near gas shale fracturing sites in north-central Arkansas. Samples were also collected from 7 groundwater monitoring wells in proposed gas shale production areas in New York State. Concentrations of volatile (VOC) and semi-volatile (SVOC) organic compounds in groundwater samples, including gasoline range organics (GRO) and diesel range organic (DRO), were analyzed using gas chromatography.;This study also investigated flowback water quality from both horizontally and vertically fractured wells. Flowback water is water that returns to the surface within 14 days of the initial fracturing event. Flowback data made available by the Shale Network were collected using geographic information systems (GIS). Flowback sample analytes of interest were DRO and GRO compounds. These samples came from gas shale fracturing wells located within the Marcellus Shale region in Pennsylvania and West Virginia.;Noticeable patterns were present in DRO and GRO flowback data. Flowback water results showed differences between horizontally and vertically fractured well DRO patterns. Vertically fractured wells showed a sharp decrease in DRO concentrations following fracture events. Horizontally fractured wells exhibited a peak in loading when flowback water shifted to produced water. This pattern suggests the method of completion has a large effect on DRO loading. GRO loadings appeared to not be effected by the method of completion. A horizontally fractured well and vertically fractured well within 16km showed similar loading patterns. GRO data suggest factors such as geographic location, may be responsible for VOC loading trends.;VOCs and SVOCs were present at detectable levels in groundwater samples. Average concentration of GROs in groundwater samples collected from wells in Arkansas was 14.7+/-13.0 microg/L. Monterey CF was the only New York site with GROs above the detection limit, with a mean concentration of 11.4+/-3.1 microg/L. Concentrations of GROs in New York were found to be statistically lower compared to Arkansas locations (P = 0.042). DRO concentrations in groundwater samples collected from Arkansas ranged from non-detect to 4.48+/-0.81 mg/L. DROs were detected in two groundwater samples collected from New York State. DRO concentrations in New York groundwater samples were found to be statistically lower compared to samples collected in Arkansas (P = 0.029). Results from this study also support that methane was detected in 10 out of 22 groundwater samples from Arkansas and New York State. The average concentration for the 6 groundwater samples collected in Arkansas with detectable levels of methane was 0.05+/-0.06 mg/L. Methane was detected in groundwater samples collected from four sites in New York State. However, no statistical difference was found between New York and Arkansas samples. A relationship between the distances of Arkansas groundwater samples to gas shale fracturing operations was not found for any measured organics.