The Lifecycle of Unconventional Oil Development

The Lifecycle of Unconventional Oil Development


Unconventional oil development begins with the search for rock formations with oil deposits. This process involves locating subsurface structures that may contain oil. Once a site has been identified, an exploratory well is drilled to confirm both the presence and quantity of oil in the subsurface formation.

Well Development


The drilling process begins after a deposit has been determined to be recoverable. Traditional oil wells are typically vertical or slant wells but the oil industry now uses new technologies to drill horizontally in order to expose more reservoir rock to the well and extract more oil from reservoirs. A well is first drilled vertically to reach the appropriate depth of the shale deposit. In California’s Monterey Shale this would be between 8,000 and 14,000 feet.  As the hole is drilled, well casing is placed to stabilize the hole and prevent caving and then cemented in place. Once the required depth is reached, the drill turns and moves horizontally. Currently, wells can be drilled very long distances and stretch over 8,000 feet away from the original point of vertical entry.1


It is estimated that up to 84 gallons of drilling waste are produced for each vertical foot drilled during well development. This waste is composed of drilling fluids and rock fragments and often contains contaminants including mercury, cadmium, arsenic, hydrogen sulfide, and natural gas. Even though this waste has contaminants that present significant risks to human health, it is exempted from regulation as hazardous waste both under Federal and California law.2

Drilling operations also produce air emissions from the diesel engines and turbines that power the drilling equipment. Air pollutants from these devices include particulate matter and ozone, which contribute to poor air quality and are linked to a host of public health issues. Read more about health impacts of air pollution.



Wells are stimulated in order to produce oil. Well stimulation techniques break down rock to release water, oil, natural gas and dissolved minerals.

Fracking is one of the most commonly used well stimulation techniques in unconventional oil development. It involves injecting a mixture of water, sand and chemicals such as acids, biocides and corrosion inhibitors – into the ground under high pressure. These chemicals can flow through gaps in the wellbore, creating fractures in the adjacent shale formation. The sand in the mixture holds the newly created fractures open, allowing formerly trapped water, oil,  gas and dissolved minerals to flow into the wellbore through perforations in the casing. When this fluid is released from the formation, it creates high pressure in the reverse direction forcing fluid back to the surface.

In California, fracking is often combined with other unconventional oil development techniques that use large volumes of corrosive acid to disintegrate rock. Read more about well stimulation techniques.


Fracking uses a vast number of potentially hazardous chemicals in the fracking fluid. At least 750 chemicals have been identified in fracking fluid; many are extremely toxic, including benzene, lead and the most widely used chemical, methanol, is a hazardous air pollutant. The chemicals and dangerous industrial processes put communities and workers at risk. Learn more about fracking’s threats to our health and safety.

Fracking also uses an immense amount of water, using anywhere from two to nine million gallons per well. If the Monterey Shale formation was fully developed, they could require over 220 billion gallons of fresh-water.3 This presents significant water management challenges and could put California at greater risk of water shortages. Learn more about fracking’s impact on California’s water supply.

The chemicals and water used in fracking fluid is transported to fracking sites by truck. It’s estimated that an individual well could require up to 1,365 truckloads to transport water, chemicals, sand, and other equipment needed for drilling and fracturing. These trucks often travel great distances through urban and rural areas, putting a heavy strain on local roads. Unconventional oil development production also exposes affected communities to significant health and safety risks from potential chemical spills, as well as air pollution from increased traffic. Read more about the potential impact of these truck trips on public health.


Produced Water

Once a well has been stimulated with fracking fluid, oil and natural gas flow to the surface, along with massive amounts of produced water. Produced water is a by-product from the process of lifting oil and gas from water-bearing formations. In California, it’s not uncommon for an oilfield to be composed of 80-90% water, which means that California oilfields produce far more water than oil.4 This water is often contaminated with radioactive material, heavy metals, minerals, and salts.5  This water cannot be recycled without costly, energy intensive treatments, so it is often disposed of via underground injection into waste wells.

The transportation of this water and disposal into wastewater wells across California poses a major risk, as potential leaks or spills of produced water could contaminate soil and groundwater with radioactive material and salt making land unproductive and water non-potable.

Another risk posed by produced water is the induction of earthquakes. Experts around the country have linked the disposal of water into injection wells with increased earthquake activity.6 In fault-laden California, these risks could have even more serious consequences for public safety and infrastructure.7 Read more about fracking’s impacts on earthquakes. 


Unconventional oil development poses specific risks when being transported

Oil tankers wait at a rail station next to Bakersfield High School. (Credit: Henry A. Barrios/The Bakersfield Californian)


The majority of oil produced by unconventional oil development and fracking in California is extra-heavy or heavy oil. This means it has high carbon intensity.8 Refining this oil requires energy intensive processes to break large hydrocarbons down and thus makes it more difficult to refine.

Many of California’s refineries operate in heavily populated areas. The highest concentration of refineries is located in Wilmington, CA where refineries process 650,000 barrels of crude oil per day. These refineries emit half the smog-forming volatile organic compounds (VOCs) for the Los Angeles area.  In addition, the emissions include benzene and particulate matter. All three are linked to serious health risks for communities who live near refineries, such as cancer, asthma and premature death.9

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