Three phases of production
Crude oil production in traditional reservoirs can include three different phases of recovery: primary, secondary and tertiary. During primary recovery, the natural pressure of the reservoir is the primary force driving the oil to the well bore. The natural movement of oil can be enhanced using pumping equipment to provide an additional artificial lift. Only 10-20% of the reservoir's original oil in place (OOIP) is typically recovered during this phase. Secondary recovery involves the injection of water (known as waterflooding), or gas to displace oil and drive it to the production well bore which lengthens the field's productive life and results in the recovery of 20-40% of OOIP. The tertiary recovery phase is also known as Enhanced Oil Recovery (EOR) in the oil & gas industry and refers to the recovery of the oil that is left behind after the primary and secondary recovery phases. This phase uses several more sophisticated methods to extract the oil which can be expensive and unpredictable, but can ultimately allow for up to 60% OOIP recovery. Three major categories of these EORs have been tested and proven successful in various fields: thermal recovery, chemical injection and gas injection.
Enhanced Oil Recovery
According to the Energy Information Administration, nearly two-thirds of the OOIP discovered in US fields remains in the ground after conventional recovery (primary and secondary) operations and nearly 400 billion barrels of domestic oil is estimated to be technically recoverable. This problem, as well as an increased desire for the nation to become more energy independent, has led to the creation of "enhanced" oil recovery techniques to increase oil recovery. The recovery of even a small portion of this residual oil could greatly affect the future of the domestic oil industry and dictate national policies regarding energy, security and the economy. The EOR program must be designed specifically for each reservoir and take into account for characteristics of the formation being produced and the economics involved. These types of proven enhanced recovery methods will increase production, reduce exposure to economic risk, and enable Underground Energy to more effectively exploit the potential of its hydrocarbon resources. More information about specific EOR techniques is shown below:
Thermal Recovery:
There are several types of thermal recovery methods, each involving the introduction of heat to reduce the viscosity of oil and improve its ability to flow through the reservoir into a wellbore. The most common method for applying heat to a reservoir is steam. The two most common thermal recovery methods using steam are called cyclic steaming and steamflooding. Cyclic steaming produces the reservoir in specified intervals or "cycles". Each cycle includes an injection period, a soaking period, and a producing (or flow back) period. The exact lengths of each period of the cycle are determined by the characteristics of each reservoir in order to maximize production. Once injected through the well into the reservoir, the steam is allowed time to "soak" to allow the heat to spread throughout the formation and soften the oil that was originally resistant to flow. This method is especially effective in deposits of heavy, viscous oil.
Chemical Injection:
Chemical injection is primarily used in conjunction with water and steam flooding. Dissolved chemicals called polymers work by combining with the oil and water to carry it out of the reservoir. Polymers work much like laundry detergent which are designed to "grab ahold" of dirt and oil and carry it (through water) out of your clothes. These polymers reduce natural tensions between oil and water to enable them to "work together" and flow as one liquid out of the wellbore. Another form of chemical injection is called a surfactant. In the tertiary phase, the attractive force between the oil and rock is a great inhibitor of oil flow. The free oil located in pore spaces has already been removed and most of the residual oil is on the surface of rocks. A surfactant works to break the bond between the oil and surface of the rock, enabling oil to flow. If a field is found to be a suitable candidate for recovery using chemical injection, extensive laboratory testing is conducted on soil samples to determine the combination of chemicals most effective in purging the reservoir of oil. Recovery using chemical injection requires a sophisticated separation facility once removed from the ground to separate the oil from the water and chemical agents. Recovery through chemical injection has been used extensively worldwide and has proven successful in recovering an additional 15-25% OOIP.
Gas Injection:
Gas injection uses gases to expand in a reservoir and displace the oil, pushing it to a nearby wellbore. Gases can also be dissolved in the oil, which reduces its viscosity and increases flow. Types of gases used include: carbon dioxide, nitrogen and natural gas, which are injected into the oil-bearing reservoir under high pressure. According to EcoGeneration Solutions, gas injection is one of the most popular & growing EOR techniques, accounting for 50% of all EOR production in the United States. The high initial investment cost for gas and equipment purchase, however, has created a barrier to entry for smaller, independent companies to use this type of recovery.
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