263-4 Patterns of Risk to Groundwater Resources at the Cat Canyon Oil Field, California, USA

Session: Exploring Groundwater Recharge and Management: Managed Aquifer Recharge and Other Innovative Tools for Water Supply Development and Operations (Posters)

Poster Booth No.: 75

Presenting Author:

Michael Stephens

Authors:

Stephens, Michael J.¹, Shimabukuro, David H.², Anders, Robert³, Sowers, Theron A.⁴, Chang, Will⁵, Imperato, Emily⁶, Gillespie, Janice M.⁷

(1) U.S. Geological Survey, Sacramento, CA, USA, (2) California State University, Sacramento, Sacramento, CA, USA, (3) U.S. Geological Survey, San Diego, CA, USA, (4) California State University, Sacramento, Sacramento, CA, USA, (5) Hypergradient, LLC, Berkeley, CA, USA, (6) U.S. Geological Survey, San Diego, CA, USA, (7) U.S. Geological Survey, San Diego, CA, USA,

Abstract:

Groundwater resources near oil fields can be exposed to quality degradation from natural and anthropogenic features and processes. Within oil fields, complex and dense oil operations bring together several groundwater risk factors. Yet these risk factors are rarely assessed together in space and time, leaving critical gaps in our understanding of where and when groundwater may be vulnerable. This study aims to characterize the spatiotemporal distribution of groundwater risk, identify the operational and hydrogeological features responsible, and provide information for monitoring strategies.

The U.S. Geological Survey, in cooperation with the California State Water Resources Control Board, compiled and integrated four primary datasets to evaluate risk factors at the Cat Canyon Oil Field in California: 1) geologic layer depths, 2) comprehensive hydrocarbon well records, including well age, annular cement, well casing extent, perforation depths, injection/production fluid volumes, and fluid pressures from idle oil wells, 3) groundwater elevations to define hydraulic gradients, and 4) geophysical and geochemical data for mapping three-dimensional groundwater salinity distributions. Geospatial and geostatistical analyses integrated these datasets to explore locations where subsurface conditions and operational practices intersect to elevate risk to groundwater resources.

Preliminary results show pronounced heterogeneity of risk through space and time. The West Area, on the southwestern margin of the oil field, exhibits a higher risk profile, driven by large injection volumes, variable idle well fluid levels, proximity to irrigated agriculture, and older wells with long extents of open annular space potentially linking zones of different salinity. Conversely, the Sisquoc and East Areas of the oil field may be lower risk due to newer wells with cemented annular space; however, proximity to fresh groundwater and localized geochemical evidence of hydrocarbons mixing with shallow groundwater suggests risks are still present. Preliminary findings demonstrate the value of high-resolution, multifaceted assessment to capture the dynamic nature of groundwater risk in oil fields.

Geological Society of America Abstracts with Program. Vol. 57, No. 6, 2025

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