Secondary Recovery

Test Your Knowledge

Secondary Recovery Quiz

Instructions: Choose the best answer for each question.

1. What is the main purpose of secondary recovery techniques?

(a) To extract oil from newly discovered reservoirs. (b) To increase the rate of oil production in mature fields. (c) To prevent oil spills and leaks. (d) To refine crude oil into gasoline and other products.

2. Which of the following is NOT a common method for secondary recovery?

(a) Waterflooding (b) Gasflooding (c) Hydraulic fracturing (d) Steam injection

3. How does waterflooding work?

(a) By dissolving the oil and making it easier to extract. (b) By injecting water into the reservoir to increase pressure and push oil towards wells. (c) By replacing the oil with water, reducing the volume of oil in the reservoir. (d) By using water to dissolve and remove impurities from the oil.

4. What is a major advantage of secondary recovery?

(a) It reduces the cost of oil production. (b) It eliminates the need for drilling new wells. (c) It increases the amount of oil extracted from a reservoir. (d) It reduces the environmental impact of oil extraction.

5. What is a major challenge associated with secondary recovery?

(a) The need for specialized equipment and expertise. (b) The risk of contaminating groundwater. (c) The high cost of extracting oil using these methods. (d) All of the above.

Secondary Recovery Exercise

Problem: A hypothetical oil field has been producing oil for 10 years using primary recovery methods. The field is estimated to contain 100 million barrels of oil. Primary recovery has extracted 20 million barrels, leaving 80 million barrels remaining. The company wants to implement a secondary recovery method (waterflooding) to boost production. They anticipate recovering an additional 30% of the remaining oil through waterflooding.

Task:

1. Calculate the total amount of oil that can be extracted through waterflooding.
2. Calculate the total amount of oil that can be extracted from the field using both primary and secondary recovery methods.
3. What percentage of the total oil in the field will be extracted using both primary and secondary recovery?

Techniques

Secondary Recovery: A Comprehensive Overview

Chapter 1: Techniques

Secondary recovery techniques aim to enhance oil production after the initial decline of reservoir pressure. Two primary methods dominate the field:

1. Waterflooding: This involves injecting water into the reservoir to displace the oil towards production wells. The effectiveness depends on reservoir characteristics like permeability and heterogeneity. Variations include:

• Pattern Flooding: Water is injected through a regular grid of injection wells, with production wells strategically placed to maximize oil recovery. Common patterns include five-spot, seven-spot, and nine-spot.
• Polymer Flooding: Adding polymers to the injected water increases its viscosity, improving sweep efficiency and reducing water channeling.
• Surfactant Flooding: Surfactants lower the interfacial tension between water and oil, improving oil mobilization and recovery from low-permeability zones.
• Alkaline Flooding: Alkaline chemicals are injected to alter the wettability of the rock, making it more oil-wet and improving oil displacement.

2. Gasflooding: This involves injecting gas (e.g., natural gas, nitrogen, CO2) into the reservoir. The gas's lower density and mobility displace oil towards production wells. Variations include:

• Miscible Flooding: The injected gas is miscible with the oil, creating a single phase and significantly improving recovery efficiency. This often requires specific gas compositions and reservoir conditions.
• Immiscible Flooding: The injected gas is not miscible with the oil, relying on pressure and buoyancy effects for oil displacement. This is generally less expensive than miscible flooding.

Other less common, but increasingly important techniques include:

• Thermal Recovery: Methods like steam injection and in-situ combustion heat the reservoir, reducing oil viscosity and improving mobility. These are particularly effective for heavy oil reservoirs.
• Chemical Flooding: This encompasses the use of various chemicals (polymers, surfactants, alkalis) to improve oil mobilization and recovery. This is often tailored to the specific reservoir characteristics.

The selection of the most appropriate technique depends on factors like reservoir properties, oil type, economic considerations, and environmental regulations.

Chapter 2: Models

Accurate reservoir modeling is crucial for successful secondary recovery operations. These models simulate fluid flow, pressure changes, and oil displacement within the reservoir. Key model types include:

• Numerical Simulation: This sophisticated approach solves complex equations describing fluid flow and reservoir behavior. It uses reservoir properties (porosity, permeability, fluid properties) and operational parameters (injection rates, well locations) as input to predict future production. Software packages like Eclipse, CMG, and INTERSECT are commonly used.
• Analytical Models: These simplified models offer faster solutions but make assumptions about reservoir properties and geometry. They are useful for preliminary assessments and sensitivity studies. Examples include Buckley-Leverett and material balance models.
• Reservoir Characterization Models: These models integrate geological data (seismic surveys, well logs) to create a detailed 3D representation of the reservoir. This information is essential for optimizing well placement and injection strategies.

Model calibration and validation are critical steps to ensure accuracy and reliability. This often involves comparing model predictions with historical production data. Uncertainty analysis is also vital to assess the range of possible outcomes and manage risks.

Chapter 3: Software

Specialized software packages are essential for planning, executing, and monitoring secondary recovery projects. These tools handle complex reservoir simulations, data analysis, and visualization. Popular software includes:

• Reservoir Simulation Software: Eclipse (Schlumberger), CMG (Computer Modelling Group), INTERSECT (Roxar), and other similar packages provide comprehensive tools for simulating fluid flow, heat transfer, and chemical reactions in reservoirs. These typically involve finite difference or finite element numerical methods.
• Geostatistical Software: GSLIB, Leapfrog Geo, and Petrel are examples of software used for creating 3D geological models of reservoirs, which are crucial input for reservoir simulations.
• Data Management and Visualization Software: Specialized software handles the vast amounts of data associated with secondary recovery projects, enabling efficient storage, retrieval, and visualization of key parameters.

Selecting the right software depends on the specific needs of the project, including the complexity of the reservoir, the desired level of detail, and the available budget.

Chapter 4: Best Practices

Effective secondary recovery requires careful planning and execution. Key best practices include:

• Comprehensive Reservoir Characterization: A thorough understanding of reservoir geology, fluid properties, and rock-fluid interactions is crucial for optimizing recovery strategies.
• Detailed Reservoir Simulation: Accurate reservoir simulation helps predict the impact of different injection strategies and optimize well placement.
• Well Placement Optimization: Strategic placement of injection and production wells is vital for maximizing sweep efficiency and minimizing water/gas channeling.
• Monitoring and Control: Regular monitoring of pressure, flow rates, and fluid composition is crucial for detecting any problems and adjusting the injection strategy as needed.
• Data Integration and Analysis: Integrating data from various sources (geology, geophysics, production) is essential for informed decision-making.
• Environmental Considerations: Minimizing the environmental impact of secondary recovery operations is crucial, including managing wastewater disposal and greenhouse gas emissions.

Adherence to these best practices improves the efficiency and effectiveness of secondary recovery projects.

Chapter 5: Case Studies

Several successful secondary recovery projects demonstrate the effectiveness of these techniques:

• Example 1: The North Sea: Many North Sea oil fields have employed waterflooding and gas injection to significantly extend their productive life and increase overall oil recovery. Specific field examples could be detailed, highlighting the techniques used, the results achieved, and the challenges overcome.
• Example 2: Heavy Oil Reservoirs in Canada: Steam-assisted gravity drainage (SAGD) and cyclic steam stimulation (CSS) are commonly used in Canadian heavy oil reservoirs, showcasing the success of thermal recovery methods. Again, specific examples can be discussed.
• Example 3: CO2 Injection Projects: Several projects demonstrate the potential of CO2 injection for enhanced oil recovery and carbon capture and storage (CCS). These case studies would highlight the environmental benefits and technical challenges involved.

Each case study should illustrate the specific techniques used, the geological context, the results achieved, and the lessons learned. A comparative analysis of different projects can reveal best practices and identify areas for future improvement.