Question

What are secondary and tertiary oil recovery methods? Why is their use related to the price of oil?

Short answer

Secondary and tertiary recovery methods increase oil extraction but are cost-effective only when oil prices are high.

Step-by-step solution

Understanding Oil Recovery Methods

Oil recovery methods are techniques used to extract oil from underground reservoirs. The primary recovery method relies on natural reservoir pressure, but it can generally only extract about 10-20% of the oil in place.

Introduction to Secondary Recovery

Secondary oil recovery methods are initiated when natural pressure is no longer sufficient. It involves injecting substances like water (waterflooding) or gas to maintain reservoir pressure and push additional oil towards the production wells, extracting an additional 20-40% of the reservoir's oil.

Exploring Tertiary (Enhanced) Recovery

Tertiary, or enhanced oil recovery (EOR), involves more advanced techniques: chemical flooding, thermal recovery, or gas injection (e.g., carbon dioxide). These methods modify the properties of the oil or the reservoir to recover an extra 10-20% of the oil.

Relation to Oil Prices

Secondary and tertiary oil recovery methods are more technologically complex and costly than primary methods. Their use becomes economically viable when oil prices are high, justifying the additional investment required to implement these advanced techniques.

Key concepts

Secondary Oil Recovery

Secondary oil recovery is the next step when primary recovery, which depends on natural reservoir pressure, starts to taper off. In order to boost oil output, producers inject substances like water or gas into the reservoir. This helps to maintain the reservoir pressure that naturally pushes the oil to the surface. Since natural pressure decreases as oil is extracted, these methods become essential in prolonging the productive life of an oil reservoir.

**Methods Used in Secondary Recovery**

• Waterflooding: Injecting water to sweep the oil towards the production wells.
• Gas injection: Using gases such as natural gas or nitrogen to keep pressure high.

This method typically accounts for an additional 20-40% of the original oil in place, significantly increasing the amount of oil that can be extracted from a reservoir.

Tertiary Oil Recovery

Often called Enhanced Oil Recovery (EOR), tertiary recovery involves more sophisticated techniques than secondary recovery. These are applied once the secondary methods become less effective and aim to retrieve more oil by altering the physical or chemical properties of the oil or reservoir. These interventions typically occur after primary and secondary measures have extracted as much oil as those methods can.

**Advanced Techniques in Tertiary Recovery**

• Chemical flooding: Introduces chemicals like polymers and surfactants to reduce oil viscosity or enhance its flow.
• Thermal recovery: Employs heat to lower oil viscosity, making it easier to extract (e.g., steam flooding).
• Gas injection: Involves substances such as carbon dioxide to expand and push more oil towards production wells.

Tertiary recovery can squeeze out an additional 10-20% of the oil within a reservoir, contributing significantly to total oil recovery efforts.

Enhanced Oil Recovery

Enhanced Oil Recovery (EOR) is essentially synonymous with tertiary recovery. This advanced stage focuses on extracting the remaining oil that primary and secondary methods could not recover. EOR improves the sweeping efficiency and the displacement of oil, increasing yield from mature reservoirs.

**Impact of EOR**

• Increased extraction rates, maximizing the potential of aging oil fields.
• Application of technological innovations unique to the geological and chemical properties of the reservoir.
• Environmental considerations, as EOR can sometimes make use of industrial byproducts like CO2.

Enhanced methods push the boundaries of what can be extracted economically and technologically, and they extend the life of oil fields.

Reservoir Pressure

Reservoir pressure is a critical factor in the viability of any oil extraction effort. It refers to the pressure exerted by fluids within the underground reservoir. Initially, this natural pressure aids in bringing oil to the surface during the primary recovery phase.

**Maintaining Reservoir Pressure**

• Natural pressure eventually diminishes as oil is extracted, necessitating the use of secondary recovery interventions like water or gas injection to simulate natural conditions.
• Advanced EOR techniques can further address pressure depletion by altering reservoir dynamics to support continued extraction.

Understanding and managing reservoir pressure is key to maximizing oil recovery and extending the productive life of reservoirs.

Oil Prices

Oil prices play a crucial role in determining the adoption of secondary and tertiary recovery methods. These methods are more expensive due to the complexity and technology involved. Thus, higher oil prices justify the investment required for such advanced recovery techniques.

**Why Oil Prices Matter**

• High prices encourage the use of costly recovery methods to maximize extraction efficiency.
• Lower prices can slow down the adoption of advanced methods, making primary recovery or shutting in wells more cost-effective.
• The future price expectations can influence investment decisions related to secondary and tertiary recovery operations.

The economics of oil recovery must balance operational costs with market conditions to remain profitable and sustainable.