Tests show no leakage from fracking
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NETL project demonstrates that hydraulic fracturing of a well does not result in upwards contamination by gas or other fluids
Alan Bailey Petroleum News
In the interest of establishing some objective data in response to a continuing debate over potential contamination of groundwater and other subsurface resources from the hydraulic fracturing of oil and gas wells, the National Energy Technology Laboratory, or NETL, has conducted a project to test for fluid contamination following the “fracking” of wells in the gas producing Marcellus shale in Pennsylvania. The project found no evidence of the upwards migration of gas or brine from the Marcellus shale as a result of the fracking of six horizontal wells in the shale, NETL has reported.
The objectives of the research project were to determine the maximum height of the fractures created by the hydraulic fracturing of the wells, and to determine if natural gas or brine had migrated 3,800 feet upwards into an overlying gas field during or after fracturing, NETL said.
Small-scale seismic monitoring of the fracturing operations indicated that some fractures had propagated through a limestone layer about 280 feet above the Marcellus - that layer had been thought to be a barrier to upward fracture growth. Nevertheless, the shallowest fracture penetrations appeared to be at least 2,000 feet below the overlying gas field and more than 5,000 feet below drinking water aquifers, NETL reported.
Chemical monitoring The NETL research team tested for fluid and gas migration before, during and after the well fracking operations by monitoring the gas field above the test wells, with monitoring continuing for two months following the fracking. The team monitored the field’s gas pressure; the gas production history; the produced gas isotopic and chemical composition; and the possible presence of chemical markers that had been incorporated into the hydraulic fluid used to fracture the Marcellus wells.
Any breakthrough of fluids from the Marcellus into the overlying gas field would have caused some measurable gas pressure change in the field. And, with the gas and water in the Marcellus shale having distinctly different isotopic contents from those of the fluids in the overlying field, any movement of Marcellus fluids into the field would have been detectible. Similarly, should some fluid breakthrough have occurred, chemical tracers injected into the Marcellus should have appeared in the gas field during the monitoring exercise following the well fracking operations.
The research concluded that the impact of hydraulic fracturing in the Marcellus did not extend upwards into the gas field and that there had been no migration of gas or aqueous fluids from the Marcellus into the field during the two-month monitoring period, following the fracking of the Marcellus wells.
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