The hydrofracking that has opened up America’s enormous natural gas resources is a marvel of modern technology, but keeping gas and flowback water from those wells from seeping into drinking water depends on a far more mundane science: cementing.
Cementing is used to seal well bores on- and off-shore, in all types of oil and gas wells, and integrity standards are well established. But those standards “are often difficult to attain,” said James Saiers, a professor of hydrology at Yale University, speaking at a Resources for the Future (RFF) forum on “Managing the Risks of Shale Gas.”
When a well is drilled, it is lined with lengths of steel casing, which are cemented to seal them, a process that some experts say is as much art as science. In hydrofracking, a portion of the water injected flows back to the surface and could include toxic metals leached from deep underground.
If the well casing through the near-surface layers is not properly sealed, gas and possibly flowback fluid can seep into drinking water sources.
Cement Is Not Forever
“How often is the cementing job done right?” asked Karlis Muehlenbachs, professor at the University of Alberta, Canada. He said major industry service companies admit there are often cementing problems, in all kinds of wells. Hydrofracking adds another element, he said, because once cemented, drillers “put big pressure pulses through them.”
Moreover, Muehlenbachs said, in wells that don’t involve fracking, it’s known that well integrity deteriorates with age. He pointed to a survey of Gulf of Mexico off-shore wells indicating 60% showed leakage after 16 years, and said he’d seen a similar level of problems with land-based wells in Alberta.
Those difficulties are why Texas requires routine well testing for leaks, said Mukul Sharma, professor of Petroleum and Geosystems Engineering at the University of Texas, Austin. Any leak, once detected, must be patched before a well returns to production under Texas rules. He said patching technologies are effective.
But states vary widely in their regulations, said RFF Fellow Sheila Olmstead, and many don’t have Texas’ experience with extraction industries.
Learning Quickly Enough?
The speakers are all part of an RFF study looking at risks of shale gas development and whether the growing use of shale gas is a net improvement for the environment, considering emissions at all stages. Hydrofracking has become highly controversial in the Northeast, where some residents and environmentalists charge the process will poison water supplies.
Alan Krupnik, head of RFF’s Center for Energy Economics & Policy which is leading the study, said the industry has “learned fast” in the last decade, extending horizontal wells from 2,000 to 8,000 feet, reducing drilling time from 80 to 20 days, and reducing decline rates for fracked wells, all lowering costs. But there has been “no comprehensive analysis” of environmental impacts, he said.
Sharma said there are “no documented cases” of groundwater contamination due to the frac process, where fluids are injected far deeper than drinking water aquifers. Problems instead center on well integrity and proper handling of return fluids.
Muehlenbachs said one problem for scientists trying to determine the source of alleged drinking water pollution is the lack of pre-drilling data. Only now are neighboring water wells sometimes being tested before drilling starts.
Saiers said there is “great potential” for hydrologists to use “benign tracers” to study frac fluid and aquifer water movements, but added “the industry is not too excited yet” about sponsoring such studies.
Photo Caption: Chinese troops of the People’s Liberation Army use cement mixers to construct a road through Tibet, 1950.
