Geological Context

Geology plays a large role in determining how fluids flow - or do not flow - through the subsurface system, and where water and petroleum resources are likely to be found. The characteristics of the geologic units are also important factors in salinity mapping.

Constructing Geologic Framework Models

Geologic framework models include images constructedto help scientists explore the geometry and characteristics of the subsurface. Past research has resulted in framework models covering many of the COGG study areas.

Extrapolating to Formation Maps

Geologic modelers transform well-specific data into interpolated three dimensional (3d) frameworks using techniques ranging from fairly simple layer models, such as the one shown in the first example below, to geostatistical models of lithologies (Burow and others, 2005; Faunt and others, 2009; Faunt and others, 2010).

We can also use the lithology data to create 3D images of the boundaries between geologic formations. These are important because flow properties change from one formation to another. The following 3D visualization is an example of how we map formation boundaries and was constructed using data from the Fruitvale field (a detailed report and complete peer reviewed data set on Fruitvale are planned for publication).

visualization of cross-section showing wells superimposed over geology

Conceptual cross-section combining geology with well locations, well depths, and measured salinity at each well. (Based on example by Ponti and others, 2014.)

Image shows different geological layers and locations and oil and gas wells and water wells in the top two formations

Example of a layer model showing geologic formation (Fm) thickness at Fruitvale oil field with overlay of salinity measured in groundwater samples. (Point values of salinity color coded according to concentration of total dissolved solids (TDS) in milligrams per liter.) (Hosford Scheirer, 2007; California Department of Water Resources, 2015; California State Water Resources Control Board, 2015; U.S. Geological Survey, 2015; Blondes and others, 2016; Division of Oil, Gas, and Geothermal Resources, 2015).

Using the Geologic Framework Models

The COGG program uses geologic framework data and models in several ways, including:

  • Designing regional monitoring networks
  • Comparing salinity within and between formations
  • Mapping fault locations within a study area to support interpretative analyses of whether they are serving as conduits or barriers
  • Exploring flow gradients in study areas
  • Identifying where oil and water wells are located in 3D in relation to the geology, including where fluid movement between these resources is most likely due to close proximity and/or relatively permeable sediments

Water management programs can also use these data to build or refine groundwater-flow models. An example of a regional scale flow model constructed using geologic framework models is the USGS Central Valley Hydrologic Model.

References

Burow, K.R., Shelton, J.L., Hevesi, J.A., and Weissmann, G.S., 2004, Hydrogeologic characterization of the Modesto area, San Joaquin Valley, California: U.S. Geological Survey Scientific Investigations Report 2004-5232, 54 p.

https://pubs.usgs.gov/sir/2004/5232/

California Department of Water Resources, 2015, Water quality data reports: Digital spatial data with water quality data for groundwater wells; data received June 2015 via email.

http://www.water.ca.gov/waterdatalibrary/waterquality/index.cfm/

California State Water Resources Control Board, 2015, Electronic Data Transfer Library, accessed February 2015 at

http://www.waterboards.ca.gov/drinking_water/certlic/drinkingwater/EDTlibrary.shtml

Division of Oil, Gas, and Geothermal Resources, 2015, DOGGR Well Finder: Digital spatial data for oil wells in California; California Department of Conservation, accessed February 28, 2015 at

http://www.conservation.ca.gov/dog/Pages/Wellfinder.aspx

Faunt, C.C., ed., 2009, Groundwater Availability of the Central Valley Aquifer, California: U.S. Geological Survey Professional Paper 1766, 225 p.

https://pubs.usgs.gov/pp/1766/

Faunt, C.C., Belitz, K., and Hanson, R.T., 2010, Development of a three-dimensional model of sedimentary texture in valley-fill deposits of Central Valley, California, USA: Hydrogeology Journal, v. 18, p. 625-649, http://dx.doi.org/10.1007/s10040-009-0539-7.

https://ca.water.usgs.gov/projects/central-valley/HydrogeologyJournal-2010-18.pdf

Hosford Scheirer, Allegra, ed., 2007, Petroleum systems and geologic assessment of oil and gas in the San Joaquin Basin Province, California: U.S. Geological Survey Professional Paper 1713.

https://pubs.usgs.gov/pp/pp1713/

Ponti, D.J., Wagner, B.J., Land, M., and Landon, M.K., 2014, Characterization of potential transport pathways and implications for groundwater management near an anticline in the Central Basin area, Los Angeles County, California: U.S. Geological Survey Open-File Report 2014-1087, 84 p., https://dx.doi.org/10.3133/ofr20141086.

http://pubs.er.usgs.gov/publication/ofr20141087

Sweetkind, D.S., Faunt, C.C., and Hanson, R.T., 2013, Construction of 3-D geologic framework and textural models for Cuyama Valley groundwater basin, California: U.S. Geological Survey Scientific Investigations Report 2013-5127.

https://pubs.er.usgs.gov/publication/sir20135127

U.S. Geological Survey, 2015, National Water Information System - Web interface: U.S. Geological Survey water database, accessed February 3, 2015, at http://dx.doi.org/10.5066/F7P55KJN.

http://waterdata.usgs.gov/ca/nwis/