An Independent Scientific Assessment of Well Stimulation in California — Summary Report: An Examination of Hydraulic Fracturing and Acid Stimulations in the Oil and Gas Industry
California Council on Science and Technology
[Abstract] Senate Bill 4 (SB 4) requires an independent study to assess current and potential future well stimulation practices in California, including the likelihood that these technologies could enable extensive new petroleum production in the state; impacts of well stimulation technologies (including hydraulic fracturing, acid fracturing and matrix acidizing); gaps in data that preclude evaluation; potential risks associated with current practices; and alternative practices that might limit these risks.
Publicly available information indicates the vast majority of well stimulations in California are hydraulic fracturing in four oil fields in the San Joaquin Valley. The California experience with hydraulic fracturing differs from that in other states because California wells tend to be shallow and the reservoirs more permeable. California operators generally do not conduct high-volume hydraulic fracturing from long-reach horizontal wells, and for this reason use far less water. Operators use hydraulic fracturing in a small number of offshore wells in state waters, but data on wells in federal waters is sparse. In the next few years, use of hydraulic fracturing in California will likely look much like today, both in terms of the stimulation practices and the expected number of operations. No reliable estimates exist of potential oil production using hydraulic fracturing or acid stimulation in the deep Monterey Formation source rock and the state should request a credible scientific assessment.
Direct impacts of hydraulic fracturing stem from unrestricted chemical use. These appear small but have not been investigated. Significant gaps and inconsistencies exist in available voluntary and mandatory data sources, both in terms of duration and completeness of reporting that limit assessment of the impacts of hydraulic fracturing. However, good management and mitigation measures can address the vast majority of potential direct impacts of well stimulation. The state should limit the use of the most hazardous chemicals and disallow the use of any chemical with unknown environmental characteristics in order to prevent possible environmental and health impacts. Operators currently dispose of wastewater from hydraulically fractured wells in percolation pits and also likely have occasionally injected wastewater contaminated with stimulation chemicals into protected groundwater. These practices should stop. We found no documented instances of hydraulic fracturing or acid stimulations directly causing groundwater contamination in California, but few studies examined this possibility. However, we did find that fracturing in California tends to be in shallow wells, and hydraulic fractures could possibly intersect protected groundwater in a few locations. Also, California reservoirs have many existing boreholes that warrant more attention to ensure they are not leakage pathways. We found the data insufficient to determine if there is a relationship between oil and gas-related fluid injection and any of California’s numerous earthquakes, and this should be studied.
Most impacts associated with hydraulic fracturing are indirect and are caused by oil and gas production enabled by hydraulic fracturing. For example, oil and gas development in general causes habitat loss and fragmentation that should be mitigated and any production facility can incur air emissions. As hydraulic fracturing enables only 20-25% of production in California, only about 20-25% of any given indirect impact is likely attributable to hydraulically fractured reservoirs.
Oil production from hydraulically fractured reservoirs emits less greenhouse gas per barrel than other forms of oil production in California. Air pollutants and toxic air emissions from hydraulic fracturing are mostly a small part of total emissions in oil producing regions except for a few toxic air substances such as hydrogen sulfide and formaldehyde in the San Joaquin Valley. However, pollutants can be concentrated near production wells and present health hazards to nearby communities. California public health studies could determine the magnitude of this issue and the need for any mitigating policies. Studies done outside of California found workers in hydraulic fracturing operations were exposed to respirable silica and volatile organic compounds (VOCs), especially benzene, above recommended occupational levels, but confirmation of this issue awaits specific evaluation in California.
This study highlights many recommendations to change practice, collect data, and investigate risk factors for Californians. However, questions remain at the end of this initial assessment of the impacts of well stimulation in California that can only be answered by new research and data collection. Volumes II and III of this report series provide many detailed recommendations for filling data gaps and additional research.