EXTENT OF UNCASED AND UNPLUGGED BOREHOLE IN DRY OIL AND GAS WELLS LOCATED OUTSIDE OF OIL FIELDS IN KERN COUNTY, CALIFORNIA

Oil and gas wells that do not produce economically viable amounts of hydrocarbons are usually left uncompleted and quickly abandoned. In California, over 11,000 of these wells, termed “dry holes,” are outside of oil and gas fields.

Completion and abandonment practices in these dry holes vary widely. In some cases, the wells were only partially cased, or had casing pulled during abandonment, leaving uncased borehole filled only with drilling mud. Cement plugs were generally placed during the abandonment process, but often limited to critical zones above the hydrocarbon zone and across the base of fresh water (3,000 ppm total dissolved solids (TDS)). Together, these practices have the potential for leaving extents of uncased borehole acting as vertical pathways connecting deeper saline aquifers with shallower and potentially usable groundwater aquifers (10,000 ppm TDS).

Here we investigate the extent of open borehole present in dry holes outside of oil and gas fields Kern County, California by collecting drilling, casing, and plug data from publicly available well histories. These data were then compared to the depth of perforations from groundwater wells in Kern County. Preliminary results show long extents of open borehole between plugged intervals. Some of these open boreholes extend above the deepest perforation of nearby groundwater wells, leaving open the possibility that groundwater pumping could induce migration of higher TDS fluids into fresher waters.