Secondary Recovery
Secondary recovery refers to methods employed in oil and gas production to extract additional crude oil from a reservoir after the natural reservoir pressure has diminished. As a crucial stage in the energy sector, these techniques aim to maintain or restore the energy within the reservoir to push remaining hydrocarbons towards producing wellbores. This stage typically follows primary recovery, which relies on the initial natural pressure of the Earth.
History and Origin
Early methods of oil extraction primarily relied on the natural pressure within the Earth's geological formations to push oil to the surface. However, as these natural forces depleted, much of the oil remained trapped underground. The concept of artificially re-pressurizing reservoirs emerged in the late 19th and early 20th centuries to recover this remaining oil. One of the most significant early developments in secondary recovery was waterflooding, which began accidentally in Pithole, Pennsylvania, around 1865 and became common practice in the 1880s, particularly in Pennsylvania's oil fields. [An Overview and History of Oil Recovery from on-shore Oil Reserves]. These pioneering efforts laid the groundwork for modern secondary recovery techniques, demonstrating that external fluids could effectively displace oil and extend a field's productive life.
Key Takeaways
- Secondary recovery aims to extract additional oil after natural reservoir pressure declines.
- The primary goal is to maintain or increase reservoir pressure and displace hydrocarbons.
- Common methods include waterflooding and gas injection.
- These techniques significantly increase the total recoverable oil from a field, typically yielding 20% to 40% of the original oil in place.3
- Secondary recovery is distinct from enhanced oil recovery (EOR), which involves more complex processes to alter oil properties.
Interpreting Secondary Recovery
Secondary recovery methods are implemented when the natural pressure maintenance of a reservoir is insufficient for continued economic drilling. By injecting fluids like water or natural gas into the reservoir, operators can create an artificial drive mechanism to "sweep" the oil toward production wells. The effectiveness of secondary recovery is measured by the incremental oil recovered beyond what would have been extracted through primary methods. This recovery factor can vary significantly based on the reservoir's geological characteristics and the specific method employed.
Hypothetical Example
Consider an oil field that has been producing oil for several years through primary recovery. Initially, the reservoir's natural pressure was sufficient to bring oil to the surface. Over time, however, the production rate has significantly decreased, indicating a drop in reservoir pressure.
To implement secondary recovery, the operating company drills several injection wells around the existing production wells. They then begin to inject large volumes of water into these injection wells. This injected water travels through the porous rock of the reservoir, increasing the overall pressure. As the water moves, it pushes the remaining oil towards the production wells, where it can then be brought to the surface. This process of waterflooding helps to restore the flow of oil, allowing the company to recover a substantial amount of crude oil that would otherwise have remained trapped.
Practical Applications
Secondary recovery techniques are widely applied in mature oil fields globally to maximize the economic lifespan of assets. The two most common methods are waterflooding and gas injection.2 Waterflooding involves injecting water into the reservoir to sweep oil toward production wells, while gas injection uses gases like natural gas or carbon dioxide to maintain pressure and displace oil. These methods are crucial for increasing overall return on investment from a given oil field by significantly boosting the total volume of recoverable crude oil. According to the Department of Energy, secondary recovery typically yields an additional 20% to 40% of the original oil in place.
Limitations and Criticisms
While secondary recovery methods are effective in increasing oil yields, they come with certain limitations and criticisms. A significant challenge is the substantial volume of water required for waterflooding, which can lead to concerns about water scarcity in some regions. The disposal of produced water—which often contains brine, heavy metals, and other contaminants—also poses an environmental challenge, requiring careful management to prevent ground and surface water pollution. Fur1thermore, the effectiveness of secondary recovery can be limited by the geological characteristics of the reservoir, such as permeability and heterogeneity. These operations also entail significant capital expenditures and ongoing production costs, which can impact the economic viability, especially when oil prices are low.
Secondary Recovery vs. Primary Recovery
Primary recovery and secondary recovery represent sequential stages in the life of an oil field, distinguished by the source of energy used to extract oil. Primary recovery relies solely on the natural energy present in the reservoir, such as natural pressure, gravity, or dissolved gas expansion, to drive oil to the surface. This initial phase typically recovers only a fraction of the original oil in place, often around 10%. Once this natural energy depletes and oil flow significantly diminishes, secondary recovery methods are employed. Unlike primary recovery, secondary recovery introduces external energy into the reservoir through the injection of fluids, most commonly water or natural gas, to artificially maintain pressure and physically displace the remaining oil towards production wells. This distinction is critical in oil and gas production, as secondary recovery extends the productive life of a field and significantly increases the total amount of recoverable hydrocarbons.
FAQs
What is the main purpose of secondary recovery?
The main purpose of secondary recovery is to increase the amount of crude oil extracted from a reservoir after the natural pressure has declined. This is achieved by injecting fluids to maintain or restore reservoir pressure and push oil towards production wells.
What are the most common methods of secondary recovery?
The two most common methods of secondary recovery are waterflooding, where water is injected into the reservoir, and gas injection, where natural gas or carbon dioxide is injected. Both methods aim to displace oil and enhance its flow.
How much additional oil can secondary recovery typically yield?
Secondary recovery techniques can significantly increase the amount of oil recovered, typically yielding an additional 20% to 40% of the original oil in place, beyond what was recovered through primary recovery.
Is secondary recovery the same as enhanced oil recovery (EOR)?
No, secondary recovery is distinct from enhanced oil recovery (EOR), also known as tertiary recovery. While secondary recovery focuses on maintaining reservoir pressure and displacing oil, EOR involves more complex processes that alter the physical or chemical properties of the oil itself to make it easier to extract, such as thermal, chemical, or miscible gas injection methods.