Among the large group of injection wells working in California's enhanced oil recovery (EOR) sector, state regulators have zeroed in on two dozen that could be candidates for closure as has happened with 23 other wells earlier this year. The latest revelations came in a letter at the end of July from the state to the U.S. Environmental Protection Agency (EPA).
On Thursday the state provided added information to EPA on volumes and sources of water used by oil/gas operators, based on reporting from about 60% of them. Industry data showed that approximately 65,000 acre-feet of water -- mainly unsuitable for other uses -- was produced and typically reinjected to produce more oil. By comparison, state officials said, California's annual use of water for all purposes totals 80 million acre-feet.
California's Division of Oil, Gas and Geothermal Resources (DOGGR) and Water Resources Control Board told EPA Region IX officials in San Francisco that they completed a review of more than 5,000 wells used in EOR that inject into nonexempt aquifers. As a result, the water board targeted 24 wells to obtain additional water quality information, a DOGGR spokesperson told NGI's Shale Daily on Tuesday.
"If we find cause for concern as the review goes on, we will seek more data and, if necessary, shut in additional injection wells," the spokesperson said. "Compliance with the U.S. Safe Drinking Water Act and protecting potential sources of beneficial water are the overriding objectives."
Twenty-three wells earlier this year were shut in, either voluntarily or through state orders (see Shale Daily, March 5).
"The state has conducted a comprehensive review of available data for water supply wells in the vicinity of these 24 nonthermal wells, and it is considering issuing orders to well operators under state water code," said DOGGR Oil/Gas Supervisor Steve Bohlen and water board Chief Duty Director Jonathan Bishop in the letter to EPA.
They explained to EPA the state's criteria to determine if any of the wells pose a potential risk to groundwater with a current beneficial use:
The injection zone water quality is less than 10,000 milligrams/liter of total dissolved solids (TDS); and the well's injection depth is less than 1,500 feet below ground surface; or
The well is within 500 vertical feet and one mile horizontally of the screened portion of an identified water supply well.
The data from each of the operators that the state is collecting data from are to assist regulators in determining if there is a potential risk to groundwater.
"DOGGR and the water board are taking a risk-based approach to the review of injection wells and believe we are making good progress toward ensuring that drinking water supplies are not impacted," the spokesperson said.. "If we find cause for concern as the review goes on, we will seek more data and, if necessary, shut-in additional injection wells.
Most of the injection wells under consideration in the state review (5,475 of 5,625 wells) are involved in thermal-EOR (steam flood and cyclic steam wells), state officials told EPA. Both steam flood and cyclic steam operations employ much smaller volumes of water than water flooding and waste disposal.
"Therefore, the zone of endangering influence is very small for thermal operations," Bohlen and Bishop said in their letter. They said the state has concluded that no further analysis of the thermal wells is needed at this time.