12.5: Natural Resources of the Great Valley
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\(\newcommand{\avec}{\mathbf a}\) \(\newcommand{\bvec}{\mathbf b}\) \(\newcommand{\cvec}{\mathbf c}\) \(\newcommand{\dvec}{\mathbf d}\) \(\newcommand{\dtil}{\widetilde{\mathbf d}}\) \(\newcommand{\evec}{\mathbf e}\) \(\newcommand{\fvec}{\mathbf f}\) \(\newcommand{\nvec}{\mathbf n}\) \(\newcommand{\pvec}{\mathbf p}\) \(\newcommand{\qvec}{\mathbf q}\) \(\newcommand{\svec}{\mathbf s}\) \(\newcommand{\tvec}{\mathbf t}\) \(\newcommand{\uvec}{\mathbf u}\) \(\newcommand{\vvec}{\mathbf v}\) \(\newcommand{\wvec}{\mathbf w}\) \(\newcommand{\xvec}{\mathbf x}\) \(\newcommand{\yvec}{\mathbf y}\) \(\newcommand{\zvec}{\mathbf z}\) \(\newcommand{\rvec}{\mathbf r}\) \(\newcommand{\mvec}{\mathbf m}\) \(\newcommand{\zerovec}{\mathbf 0}\) \(\newcommand{\onevec}{\mathbf 1}\) \(\newcommand{\real}{\mathbb R}\) \(\newcommand{\twovec}[2]{\left[\begin{array}{r}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\ctwovec}[2]{\left[\begin{array}{c}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\threevec}[3]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\cthreevec}[3]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\fourvec}[4]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\cfourvec}[4]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\fivevec}[5]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\cfivevec}[5]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\mattwo}[4]{\left[\begin{array}{rr}#1 \amp #2 \\ #3 \amp #4 \\ \end{array}\right]}\) \(\newcommand{\laspan}[1]{\text{Span}\{#1\}}\) \(\newcommand{\bcal}{\cal B}\) \(\newcommand{\ccal}{\cal C}\) \(\newcommand{\scal}{\cal S}\) \(\newcommand{\wcal}{\cal W}\) \(\newcommand{\ecal}{\cal E}\) \(\newcommand{\coords}[2]{\left\{#1\right\}_{#2}}\) \(\newcommand{\gray}[1]{\color{gray}{#1}}\) \(\newcommand{\lgray}[1]{\color{lightgray}{#1}}\) \(\newcommand{\rank}{\operatorname{rank}}\) \(\newcommand{\row}{\text{Row}}\) \(\newcommand{\col}{\text{Col}}\) \(\renewcommand{\row}{\text{Row}}\) \(\newcommand{\nul}{\text{Nul}}\) \(\newcommand{\var}{\text{Var}}\) \(\newcommand{\corr}{\text{corr}}\) \(\newcommand{\len}[1]{\left|#1\right|}\) \(\newcommand{\bbar}{\overline{\bvec}}\) \(\newcommand{\bhat}{\widehat{\bvec}}\) \(\newcommand{\bperp}{\bvec^\perp}\) \(\newcommand{\xhat}{\widehat{\xvec}}\) \(\newcommand{\vhat}{\widehat{\vvec}}\) \(\newcommand{\uhat}{\widehat{\uvec}}\) \(\newcommand{\what}{\widehat{\wvec}}\) \(\newcommand{\Sighat}{\widehat{\Sigma}}\) \(\newcommand{\lt}{<}\) \(\newcommand{\gt}{>}\) \(\newcommand{\amp}{&}\) \(\definecolor{fillinmathshade}{gray}{0.9}\)Natural Resources of the Great Valley
The Great Valley, CA, is known for its abundant geologic-based natural resources, with some of the main resources consisting of oil and natural gas, groundwater, and mineral deposits, including metallic ores.
The valley is home to significant reserves of oil and natural gas. Oil exploration and extraction have been a vital industry in the region for many years, contributing to California's overall energy production. The underground sedimentary formations within the valley hold substantial reserves of these valuable fossil fuels.
Petroleum: Oil and Natural Gas
Petroleum, also known as crude oil, forms over millions of years through the decomposition of organic materials such as diatoms and plankton that settle at the bottom of ancient oceans. In fact, the Great Valley was once the home of a shallow inland sea where algae, such as plankton and diatoms, once thrived. Figure 12.6.1 is a map of the San Joaquin basin during the late Miocene (10.4-5 Ma). This map reflects the source and deposition of principle sediments and source rocks that make up the Great Valley Sequence in the San Joaquin Valley. Thus, once living oceanic microorganisms are the ultimate source of petroleum found in the Great Valley. Furthermore, in California, the process of petroleum formation is similar to other regions on the globe where petroleum may be found. The elements of a petroleum system include formation, source rocks, migration, and trapping.
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The petroleum formation process begins with the deposition of organic materials in ancient marine environments, such as ancient seabeds, deltas, some river systems, and carbonate reefs. Over time, these organic remains accumulate and are buried under layers of sediment. As more sediment accumulates, heat and pressure increase, transforming the organic matter into kerogen—a wax-like substance.
The rocks containing the kerogen are known as source rocks. In the Great Valley, significant petroleum deposits are found in source rocks from the Eocene Kreyenhagen and Miocene Monterey Formations (45 Ma and 22 Ma, respectively). These rocks have suitable conditions for the conversion of kerogen into petroleum due to the right combination of heat, pressure, and organic material.
Once petroleum forms, it migrates upward through porous and permeable rocks, such as sandstones, until it reaches a trapping mechanism. Traps can be formed by various geological structures, including anticlines (folded rock formations), fault traps (resulting from movement along faults), and stratigraphic traps (changes in rock layers). These traps prevent the petroleum from further migration and trap it. Where the petroleum is trapped, this is known as a reservoir (often referred to as “reservoir rock”). Figure 12.5.2 exhibits a typical petroleum system as may be found in the Great Valley. Figure 12.5.3 provides a closer look at the types of oil and gas traps that may exist globally. Additionally, Video 15.5.1, "How Oil and Gas Reservoirs Form" further complement the cycle of petroleum formation, migration, and trapping.
Video 12.5.1: "Oil and Gas Formation" by EarthScience Western Australia is in the public domain. Access a written description.
The concept of wildcatting, or the risky practice of drilling for petroleum in an area where no oil has been discovered, was practiced in the early part of the 20th century. Rural California was no different. Figure 12.5.4 shows an oil discovery at McKittrick Oil Field, southwest of Bakersfield, where enormous deposits of oil were discovered, and working-class rig hands became multimillionaires. Back then, drilling for oil was more luck than it was science as geology was coming of age in the oil boom.
Geologists used a whole toolbox when it comes to understanding what is going on in the subsurface. Petroleum geologists, as with many other geologists, use their skills to map the subsurface to identify oil reservoirs, water in the pore space, faults, and more. Subsurface mapping is a crucial geophysical technique used to visualize and understand the structures and properties of the Earth's subsurface layers. The primary objective of subsurface mapping is to create detailed, 2D and 3D representations of the geological features and formations beneath the Earth's surface.
To achieve this, subsurface mapping employs a range of advanced tools and technologies. Among the most commonly used are magnetic surveys, seismic reflection, electrical resistivity tomography (ERT), the collection of drill core, borehole logging, and exploratory drilling. Magnetic surveys used to detect variations in the Earth's magnetic field caused by subsurface rock formations, and usually help identify steep discontinuities such as faults. Magnetic surveys survey are usually conducted alongside seismic reflection, which utilizes controlled energy sources and receivers to analyze the reflected energy waves to create a subsurface image.
Electrical resistivity tomography measures the electrical resistivity of subsurface materials, helping identify variations in composition, and borehole logging involves analyzing rock samples retrieved from drilled boreholes to provide detailed information about the lithology and physical properties of the subsurface.
Gravity surveys measure variations in Earth’s gravitational fields to identify subsurface structures. Collecting drill core is a process by which cylindrical rock samples are obtained from the subsurface, providing a continuous record of the geological formations and structures encountered (Figure 12.5.5). Cores like this may be found throughout the Great Valley, but many are held by private companies, such as energy companies, to be used in subsurface mapping and to confirm the presence of hydrocarbons. Subsurface mapping is very similar to surface mapping of a region’s geology but brings together many physics-based tools and techniques to put together a view into the geology hundreds and even thousands of feet below the Earth’s surface. Figure 12.5.6 is a subsurface map showing the overall thickness of what is known as the Corcoran Clay. This subsurface map exhibits a dominant clay layer found in the San Joaquin Valley. The colored portions of the map indicate where the clay is found, based on well logs and drill core. The contour lines define the thickness (in feet) along the lines. Thicknesses are inferred between contour lines. Where no color or contours are shown, the clay will not found in the subsurface. The Corcoran Clay is discussed in detail in Chapter 18. This map was generated using information observed in drill core and from well logs consisting of measurements of resistivity, gamma ray, density and porosity. Of note, clays give off natural gamma ray, something that is also recorded on well logs and subsequently interpreted to identify clay-rich intervals in the subsurface.
By combining these tools, scientists and engineers can gain valuable insights into the Earth's subsurface, such as locating natural resources and assessing geological hazards. Once a promising location is identified, wells are drilled to access the reservoirs and extract petroleum.
Figure 12.5.7 is a map displaying the Great Valley Province and its oil and gas fields, all which have been well defined through subsurface mapping and historical oil production. A notable pattern can be observed on the western side of the Valley, particularly in the Kern County area, where the fields are arranged en echelon relative to the San Andreas Fault. By examining the geological history of the Valley, which involves subduction and subsequent strike-slip movement, it becomes evident that the geological formations and their structures, including anticlines and synclines, where oil and gas are trapped, align with the northwest-to-southeast direction of the San Andreas Fault's motion.
In California, petroleum extraction involves both conventional and unconventional methods. Conventional extraction typically involves drilling vertical wells into reservoirs and utilizing natural reservoir pressure to bring the petroleum to the surface. Unconventional methods, such as hydraulic fracturing (fracing) and steam injection are also used in specific areas to access petroleum trapped in tight rocks or in sands where there is high-viscosity oil. Interest in steam-assisted production was limited before the 1973 oil embargo and the ensuing jump in petroleum prices. In 1979 most of the United States proved the potential for heavy oil reserves in California and the concept has been present in the Valley ever since. This is an important fact associated with California’s petroleum production history, as the vast majority of California’s oil fields are comprised of heavy oil.
Most of California’s heavy oil is in the San Joaquin Valley. The Bakersfield area (i.e Kern County), alone, counts for about 72% of the proved heavy-oil reserves in the state. In 1983, Kern County accounted for about 404,000 barrels of oil per day of the 669,000 produced in California (roughly 60%). In 2023 that number was down to 326,000 barrels of oil per day of the 463,000 produced in California (roughly 70%). Video 12.5.2 is from the Kern River Oil Field and exhibits the large number of wells that cover a large geographic area on the west side of Bakersfield. These wells are extracting oil from the late Miocene to Pliocene Kern River Formation comprised of sandstones and mudstones deposited in a braided fluvial environment. The Kern River Formation reaches a maximum thickness of 800 m (2600 ft)!
Video 12.5.2: "Oil Fields - Kern County" by The Drone Guy. Used with permission.
It's important to note that environmental considerations and regulations play a crucial role in petroleum extraction in California, especially given the state's focus on sustainability and minimizing environmental impacts. This is one reason why a new geologically related industry known as carbon capture and sequestration (CCS) is on the rise.
Carbon capture and sequestration in California's Great Valley involves capturing carbon dioxide (CO2) emissions from the air, known as direct capture, or from industrial sources, such as power plants and refineries. The captured CO2 is then injected deep underground into suitable geological formations to prevent its release into the atmosphere, thus helping to mitigate climate change impacts. In partnership with the Federal and State government, petroleum geologists are using their knowledge of deep geologic formations, the mapping of pore space, and geologic trapping mechanisms of faults, stratigraphic pinch-outs, and structural traps (e.g. anticlines and synclines) to identify candidate formations for CCS. In 2023 there were approximately three CCS projects that have been federally approved and are waiting on state approval to start injection and storage.
Geothermal Energy
The Great Valley is situated within a region of active tectonic activity and volcanic hotspots. This geothermal energy potential has been harnessed, making the valley an ideal location for geothermal power plants. The heat from underground sources is tapped to generate electricity, providing a renewable and sustainable energy source.
The Great Valley does not have significant geothermal plays. While the region does have some geothermal potential, it is not as prominent as in other areas of the state. The primary geothermal resources in California are concentrated in the northern part of the state, particularly in the areas around The Geysers, located in the Mayacamas Mountains of Sonoma and Lake Counties, and the Imperial Valley in the southern part of the state. Each of these active geothermal plays, and those geographical areas within California that are currently being explored, are found within highly faulted and tectonically active areas. As already noted, tectonic activity in the Great Valley is minimal. However, trapped and existing heat from steam injection operations are being considered for geothermal potential, but oil and gas reservoirs would either need to be depleted, or operations stopped to allow access to the injected steam. At this time, the economics of geothermal energy do not look as good as the economics behind existing oil and gas operations. It should be noted that several hot springs exist within the Great Valley on the westside of the San Joaquin Valley near Firebaugh, but as of 2023, there are no geothermal plays that hold economic viability.
Groundwater
The valley's geology plays a crucial role in storing and supplying groundwater. Underground aquifers and permeable formations provide ample water resources for agricultural irrigation and drinking water supplies. Groundwater pumping from the valley supports the region's extensive agricultural activities.
The Great Valley is renowned for its fertile soil and extensive agricultural activities, making it one of the most productive agricultural regions in the United States. Groundwater, through wells and irrigation systems, provides a reliable and sustainable water source for irrigation, allowing farmers to cultivate a wide range of crops throughout the year. The availability of groundwater enables the agriculture sector to flourish, contributing significantly to the local and regional economy through job creation, export revenue, and food production.
In addition to agriculture, groundwater plays a crucial role in supporting the industrial sector in the Great Valley. Many industries, including food processing, manufacturing, and beverage production, rely on a steady and accessible water supply for their operations. Groundwater sources provide a reliable and cost-effective solution for meeting industrial water demands, contributing to the growth and development of various industrial activities in the region. The availability of groundwater resources attracts investment, facilitates business expansion, and enhances the overall economic competitiveness of the Great Valley.
Furthermore, groundwater serves as a crucial resource for domestic water supply in the Great Valley. Many communities and households in the region depend on groundwater wells for their daily water needs. The accessibility and quality of groundwater sources provide a reliable and safe drinking water supply, reducing reliance on external water sources and associated costs. The availability of groundwater for domestic use promotes residential growth, facilitates population stability, and contributes to the overall quality of life in the Great Valley.
Many of the confined and unconfined aquifers would not exist if not for the Great Valley Sequence. Thus, the Great Valley’s geology drives the success of agricultural productivity, industrial growth, and economic productivity.
Mineral Deposits
The Great Valley is known for its diverse mineral resources. The region has significant deposits of minerals such as chromite, copper, gold, mercury, and tungsten. Other minerals used in construction or industrial applications include asbestos, high-grade clay, diatomite, granite, gypsum, and limestone. These minerals are essential for construction materials, cement production, glass manufacturing, and various industrial processes.
The valley is also recognized for its deposits of metallic ores. Copper, zinc, gold, silver, and manganese are among the minerals that have been extracted from the region's mines. These metals have economic importance and are used in various industries, including electronics, construction, and manufacturing.
The geologic-based natural resources in the Great Valley have shaped its economy, providing valuable energy sources, raw materials for industry, and supporting agricultural productivity.
References
- Bartow, J. A. (1987). The cenozoic evolution of the San Joaquin valley, California US Geological Survey. doi:10.3133/ofr87581
- California Department of Conservation & Division of Oil, Gas, and Geothermal Resources. (1983). California Oil & Gas Fields: Northern California (TR10 ed., Vol. 3).
- California Department of Conservation & Division of Oil, Gas, and Geothermal Resources. (1991). California Oil & Gas Fields: Southern, Central coastal, and Offshore California (TR12 ed., Vol. 2).
- Geothermal Resources. (n.d.). California Department of Conservation. Retrieved July 1, 2023, from https://www.conservation.ca.gov/calgem/geothermal
- Faunt, C. C., Sneed, M., Traum, J., & Brandt, J. T. (2016). Water availability and land subsidence in the Great Valley, California, USA. Journal of Hydrogeology, 24, 675-678.
- Guerard Jr., W. F. (1998). Heavy Oil in California. California Department of Oil and Gas, Publication No. TR28.
- Hill, F. L. (1964). Harvester gas field: California Department of Conservation, Division of Oil and Gas, Summary of Operations, California Oil Fields, 50, 1, 11-15.
- McPherson, J. G., & Miller, D. D. (1990). Depositional Settings and Reservoir Characteristics of the Plio-Pleistocene Tulare Formation, South Belridge Field, San Joaquin Valley, California. Structure, Stratigraphy and Hydrocarbon Occurrences of the San Joaquin Basin, California, The Pacific Section American Association of Petroleum Geologists. doi: 10.32375/1990- GB65.17
- Webb, G. W. (1983). Stevens and earlier Miocene turbidite sandstones, southern San Joaquin Valley, California. American Association Petroleum of Geologists, Bulletin 65, 438-465.