California Oil, Gas, and Groundwater Program

Monitoring Wells Drilled as part of COGG


The COGG Program includes drilling new wells when there is no existing infrastructure in a location where more robust information is needed about subsurface conditions between protected groundwater and oil and gas development activities. These sites can yield new insight on vertical profiles of water quality, groundwater flow, aquifer layers that may impede groundwater flow, and changes in aquifer conditions over time in response to recharge and well pumping. These multi-well monitoring sites are expensive and can cost up to $1 million to install, depending on depth, site conditions, and the number of analyses completed during the well installation process. The first two multi-completion monitoring sites were installed in 2018. Data from the Lost Hills site are available online; similar records will soon be available from a site drilled later in 2018 adjacent to the North/South Belridge oil fields.

Geophysical and well construction information for wells drilled by the USGS are published in the USGS GeoLog Locator. Monitoring data from the sites, such as water levels and water quality, are published in the NWISWeb. For multi-completion monitoring wells installed as part of COGG, there will be multiple “sites” at a single location, each representing one of the completed wells.

<abbr>USGS</abbr> Drill Rig, Lost Hills, California 2018.
USGS Drill Rig, Lost Hills, California 2018.

Lost Hills

The LHSP lies about 1700 FT east of the Lost Hills oil field administrative boundary.

The borehole was drilled to 1,860 FT.

Boreholes at each site were drilled by the USGS Western Region Research Drilling Unit using the mud-rotary method. Borehole diameter decreased with depth, ranging in diameter from 20 to 7-5/8 inches. After total hole depth was attained, geophysical log surveys were completed, and the monitoring wells were installed.

Electrical conductivity of drill mud was monitored.

EC of the drilling mud was monitored every 10 FT during the drilling process. Drill rig operations, such as mixing new mud, that can alter the mud properties were also monitored. EC of the source water, collected from a local hydrant, used for mixing and EC of the fresh drill mud was also noted. Changes in the EC of the drill mud can indicate changes in either the salinity of the native water or the formation encountered at a given depth.

Location of drilling sites.
Location of drilling sites.
<em>Diagram showing depth of each well and geologic interval each was completed in.</em>
Diagram showing depth of each well and geologic interval each was completed in.

Drill cuttings were collected and described every 10 FT.

Two sets of drill cuttings are collected throughout the drilling process. Cutting samples, denoted as “sieve,” were composited along 20-foot drill intervals at the borehole surface using a No. 120 sieve. Cutting samples, denoted as “shaker,” were collected at 10-foot intervals and at distinguishable changes in lithology from a No. 60-mesh screen mounted on the drill rig’s shaker tank. Detailed lithologic logs were compiled from descriptions of drill cuttings collected at each borehole site and from observations recorded during drilling. Sieve and shaker cuttings are described in the office by grain size, texture, sorting, rounding, color, and any other noticeable features, such as wood or shell fragments. Texture descriptions follow the National Research Council (National Research Council, 1947) grain-size classification. Color, determined on moist samples, follows the numerical color designations in Munsell Soil Color Charts (Munsell Color, 1994). Photos of the drill cuttings and detailed lithologic descriptions are available through the United States Geological Survey GeoLog Locator.

A number of geophysical logs were collected: Caliper, gamma, resistivity, spontaneous potential (SP), EM induction, full wave form sonic, Nuclear Magnetic Resonance (NMR) porosity.

To access this information, click here, close the “Welcome to GeoLog locator pop-up, select “USGS NWIS Site Numbers” on the left-hand side of the page, enter site ID 354048119445001 and select “Go,” select the site (red dot) on the map to view the list of available logs.

To assist in the identification of lithologic and stratigraphic units, geophysical log surveys were completed in the uncased, fluid-filled borehole prior to well construction using techniques described in USGS Techniques of Water-Resources Investigations Reports (Keys and MacCary, 1971; Shuter and Teasdale, 1989; Keys, 1990). Geophysical log surveys run to total borehole depth included caliper, bulk-natural gamma, spontaneous potential, 16- and 64-inch normal resistivity, EM induction, acoustic logs, and nuclear magnetic resonance. Subsequent high-resolution temperature logs and EM logging will be performed in the deepest well at each site to assess if changes in temperature or salinity occur.

Drill cuttings collected during drilling process at LHSP borehole site.
Drill cuttings collected during drilling process at LHSP borehole site.
<em>Example of water level time series data from multi-completion well (</em><abbr>USGS</abbr> Site 354048119445001)
Example of water level time series data from multi-completion well (USGS Site 354048119445001)

Water level monitoring sensors installed.

Each well is equipped with a pressure transducer and data logger set up to measure water levels (depth to water below land surface), on an hourly basis. Periodic manual measurements of water levels were made to verify the time-series data. The discrete water levels along with the computed unit values, and daily maximum, minimum, and median values for all time-series water-level data for these sites are available through the USGS NWIS Web.


USGS installed a multiple-well monitoring site in the southern San Joaquin Valley groundwater basin adjacent to the North and South Belridge oil fields, about 7 miles southwest of Lost Hills, Calif. Data collected at the Belridge multiple-well monitoring site (BWSD) provide information about the geology, hydrology, geophysical properties, and geochemistry of the aquifer system, thus enhancing understanding of relations between adjacent groundwater and the North and South Belridge oil fields in an area where there are few groundwater data.

Construction, lithology, and geophysical logs for the Belridge multiple-well monitoring site

Everett, R.R., Brown, A.A., Gillespie, J.M., Kjos, A., and Fenton, N.C., 2020, Multiple-well monitoring site adjacent to the North and South Belridge Oil Fields, Kern County, California: U.S. Geological Survey Open-File Report 2020-1116, 10 p.,