page_title: Guijarral Hills Oil Field
section_title: Geology
hierarchical_section_title: Guijarral Hills Oil Field / Geology
caption_attribution_description: English: The last active well on the Guijarral Hills field; photo by self, GFDL/equiv.
context_page_description: The Guijarral Hills Oil Field is a formerly-productive oil and gas field near Coalinga on the western side of the Central Valley in central California in the United States. Discovered in 1948, and having produced 5.4 million barrels of oil during its peak year in 1950, it now has but one active oil well producing a little over a barrel of oil a day, and is very near to exhaustion, with only 343,000 recoverable barrels of oil remaining throughout its 2,515-acre extent according to the official California State Department of Conservation estimate. As of 2010, the only active operator was Longview Production Company.
context_section_description: The field, like many in and adjacent to the California Central Valley, is an anticlinal structure, in which oil has accumulated through both structural and stratigraphic mechanisms. The Guijarral Hills are a segment of a long anticline which includes the Kettleman Hills to the southeast, and which continues to the northwest as the large eastern extension of the Coalinga Oil Field (named there the Coalinga Anticline, and Anticline Ridge on United States Geological Survey maps). The uppermost productive units in the field are sand lenses within the Miocene-age Temblor Formation, named the Smith and Allison respectively from upper to lower. The most productive unit, and the first to be discovered, is the Leda Sands, which reside in the Miocene-age Vaqueros Formation, underlying the Temblor. The impermeable Salt Creek member of the same Vaqueros Formation is above the Leda Sands, trapping the oil and preventing its natural upward movement.
  Other oil pools were found later, including the Gatchell, Dessell, McAdams, Sanger, Bourdieu, and Smith, with the most recent discovery being the Dessell pool in 1962. These pools are accumulations of oil in permeable sand lenses within less permeable lithologic units. Oil quality varies throughout the field but is always medium to light, with API gravity between 27 and 38. Sulfur content is generally low, with no pool over 0.63 percent by weight. In 2008 the remaining active well reported a water cut of 96%, a high value typically indicating a field near the end of its useful life (once that much of the fluid pumped from the reservoir is water, the cost to extract oil exceeds the revenue generated by selling it).
caption: Oil well with pumpjack, oil-water separator, and storage tanks on the Guijarral Hills field
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