Ventura Oil Field

The oil field is on and beneath the ranges of hills northwest, north and northeast of the city of Ventura. The Ventura River, flowing down from Ojai, cuts through the field, and empties into the Pacific Ocean at Ventura. Native vegetation in the hills is predominantly chaparral and coastal sage scrub, and riparian woodland is found along the course of the Ventura River. Terrain on the hills is steep, and the roads to well pads, tanks, and other infrastructure make numerous switchbacks. Most of the field is hidden from view from the city because of the first steep range of hills. The oil field is one of several following the east–west trend of the Transverse Ranges at this point: to the west are the San Miguelito Oil Field and the Rincon Oil Field, and to the east, across the Santa Clara River valley, the large South Mountain Oil Field adjacent to Santa Paula and the smaller Saticoy Oil Field along the Santa Clara River east of Saticoy. To the north are the smaller Ojai and Santa Paula fields. Total productive area of the field, projected to the surface, encompasses . California State Route 33, which follows the route of the Ventura River through the hills and through the field, provides much of the vehicular access, and other access roads come directly from the city of Ventura to the south. Climate in the area is Mediterranean, with cool, rainy winters and mild, dry summers, cooled by morning coastal clouds. Elevations on the field range from about above sea level along the Ventura River to around on the highest ridges both east and west of the river. Runoff from the oil field is into the Ventura River, although some of the eastern portions of the field drain south into the Santa Clara River. ==Geology==

In the Ventura field, the large-scale structural feature responsible for petroleum accumulation is the Ventura Anticline, an east–west trending geologic structure long, visible in the numerous rock outcrops in the rugged topography of the area. This anticline dips steeply on both sides, with the dip angle ranging from 30 to 60 degrees, resulting in a series of rock beds resembling a long house with a gabled roof, under which oil and gas collect in abundance. Within this feature, the primary petroleum-bearing unit is the Pico Formation, a sedimentary unit of turbidite sands of high porosity (16 to 20 percent)). Additionally, oil is found in the underlying Santa Margarita Formation. Eight different oil-bearing zones have been identified by number, 1st through 8th based on depth, with the 2nd zone the first to be discovered, in March 1919 by the Shell Oil Company. The pools range in depth from to over , although depth within each pool varies greatly; the discovery well into the 2nd zone, which has an average depth of , had a total depth of only . Even with the impermeable caps and structural traps, there are enough breaks in the structure for significant natural tar seeps to occur; indeed the entire region is riddled with natural seeps, and tar was used by the native Chumash peoples as a sealant for their watercraft. Oil gravity and sulfur content is similar in all pools in the field, with an API gravity of 29-30 and approximately 1 percent sulfur by weight. ==History, production and operations==

The area was worked initially in 1885, followed by Ventura County Power Company drilling 7 shallow gas wells in 1903. While they reached depths of between 400 and , it is not known if they produced oil. In May 1916 the first commercially viable well, No. "Lloyd" 1, was drilled by State Consolidated Oil Company to a depth of 2,555 feet. Initial production consisted of 100 barrels a day. While the field was productive from the earliest years, it had a reputation for difficulty, and challenged the technological skill of the early 20th-century drillers. The Lloyd No. 102 well, operated by the Associated Oil Company, was the deepest production well in the world in 1928, producing from a depth of . Later wells reached even greater depths, as drillers attempted to find the bottom of this extraordinarily productive but challenging field. Shell Oil Company's Taylor 653 reached a depth of , penetrating into the Miocene age Monterey Formation, but found no oil at those depths. Deeper reservoir oil was extremely hot; the temperature of oil in the 4th zone, discovered in 1925, and determined later to have an average depth of , was approximately . In 1954 alone the field produced over 31 million barrels of oil. Their neighbor on the abutting San Miguelito and Rincon fields to the west is Vintage Petroleum, a subsidiary of Occidental Petroleum. In 2009 Aera was still producing an average of 11,600 barrels of oil a day from the field, making the company the largest oil and gas producer in Ventura County. Aera reported the production of 14,000 barrels of crude oil and 7.8 billion cubic feet of natural gas a day in 2016 from 414 wells in an area of . Shell and ExxonMobil agreed in 2022 to sell the all the assets of Aera to a German asset management group IKAV. ==Notes==