Effective Permeability

Test Your Knowledge

Quiz on Effective Permeability

Instructions: Choose the best answer for each question.

1. What is the primary difference between absolute permeability and effective permeability?

a) Absolute permeability refers to a single fluid, while effective permeability considers multiple fluids. b) Absolute permeability is measured in Darcy, while effective permeability is measured in milliDarcy. c) Absolute permeability is a theoretical concept, while effective permeability is a practical measure. d) Absolute permeability is constant, while effective permeability varies with fluid saturation.

2. How does the presence of multiple fluids affect the effective permeability of a phase?

a) It increases the effective permeability. b) It decreases the effective permeability. c) It has no effect on the effective permeability. d) It depends on the type of fluids present.

3. Which of the following factors DOES NOT influence effective permeability?

a) Fluid saturation b) Fluid viscosity c) Rock porosity d) Reservoir pressure

4. What is the significance of relative permeability in understanding effective permeability?

a) It measures the flow rate of a single phase. b) It quantifies the resistance a phase encounters due to the presence of other phases. c) It determines the total permeability of the reservoir. d) It is only relevant for gas-water systems.

5. Effective permeability is a crucial factor in which of the following applications?

a) Reservoir simulation b) Well design c) Enhanced oil recovery d) All of the above

Exercise on Effective Permeability

Scenario: A reservoir contains oil and water, with a total porosity of 20%. The absolute permeability to oil is 100 milliDarcy. The oil saturation is 60%, and the water saturation is 40%. The relative permeability to oil at this saturation is 0.6, and the relative permeability to water is 0.3.

Task: Calculate the effective permeability to oil and water using the given data.

Techniques

Effective Permeability: A Key Concept in Multiphase Flow in Oil & Gas Reservoirs

Chapter 1: Techniques for Determining Effective Permeability

Determining effective permeability requires a combination of experimental and analytical techniques. The most common methods include:

1. Laboratory Measurements:

• Steady-State Methods: These involve establishing a constant flow rate of fluids through a core sample and measuring the pressure drop. This allows for the calculation of effective permeability for each phase at various saturation levels. Variations exist, such as using different boundary conditions (e.g., constant pressure or constant rate).
• Unsteady-State Methods: These methods involve measuring the pressure response of a core sample to a change in flow rate. Analysis of the pressure transient data allows for the determination of effective permeability. Pulse decay and drainage/ imbibition tests are common examples.
• Porous Media Characterization: Accurate determination of effective permeability requires a thorough understanding of the rock properties. This often involves techniques like mercury injection capillary pressure (MICP) measurements to determine pore size distribution, and image analysis of thin sections to visualize the pore network.

2. Numerical Methods:

• Reservoir Simulation: Effective permeability values are often incorporated into numerical reservoir simulation models. These models predict fluid flow based on various input parameters including relative permeability curves. Calibration and history matching of these models can indirectly help refine effective permeability estimates.
• Upscaling: Laboratory measurements are typically performed on small core samples. Upscaling techniques are used to translate these measurements to the reservoir scale, accounting for the heterogeneity of the reservoir rock.

Chapter 2: Models for Predicting Effective Permeability

Several models exist to predict effective permeability, each with its own assumptions and limitations:

1. Empirical Correlations: These are based on experimental data and are often specific to a particular reservoir type or fluid system. They are relatively simple to use but lack the physical basis of more complex models. Examples include the Corey-type relative permeability models and Brooks-Corey model for capillary pressure.

2. Analytical Models: These models are based on theoretical considerations of fluid flow in porous media. They provide a deeper understanding of the underlying physical processes but often require simplifying assumptions. Examples include the capillary bundle model and various network models.

3. Numerical Models: These employ computational methods to solve the governing equations of multiphase flow. They can handle complex pore geometries and fluid properties more accurately than empirical or analytical models. However, they require significant computational resources and careful calibration.

Chapter 3: Software for Effective Permeability Calculations and Simulations

Several commercial and open-source software packages are available to assist in effective permeability calculations and reservoir simulations:

• Commercial Software: CMG (Computer Modelling Group) STARS, Eclipse (Schlumberger), and Petrel (Schlumberger) are widely used commercial simulators that incorporate various models for calculating and applying effective permeability.
• Open-Source Software: OpenFOAM and others offer functionalities for simulating multiphase flow, although setting up and running simulations can be more challenging than with commercial software.

These software packages typically provide tools for:

• Importing rock and fluid properties
• Defining relative permeability curves
• Running simulations
• Analyzing results (e.g., pressure, saturation profiles)

Chapter 4: Best Practices for Effective Permeability Determination and Use

Accurate determination and application of effective permeability are crucial for reservoir management. Best practices include:

• Careful Core Selection and Preparation: Selecting representative core samples and properly preparing them for laboratory measurements are crucial.
• Appropriate Experimental Techniques: The choice of experimental technique should be based on the specific characteristics of the reservoir and fluids.
• Data Quality Control: Thorough quality control of experimental data is necessary to ensure accuracy and reliability.
• Robust Modeling Techniques: Utilizing reliable and validated models for predicting effective permeability is essential.
• Sensitivity Analysis: Performing sensitivity analysis to assess the impact of uncertainties in input parameters on the predicted effective permeability.
• Integration with Reservoir Simulation: Integrating effective permeability data into reservoir simulations for accurate prediction of reservoir performance.

Chapter 5: Case Studies Illustrating Effective Permeability Applications

Several case studies highlight the application of effective permeability in different scenarios:

• Case Study 1: Improved Oil Recovery (IOR) in a Carbonate Reservoir: Analysis of effective permeability data helped optimize waterflooding strategies, leading to significant increases in oil recovery. This case study demonstrates how understanding effective permeability contributes to enhanced recovery techniques.
• Case Study 2: Gas Coning Prevention in a Gas-Cap Reservoir: Prediction of gas coning based on effective permeability and fluid mobility helped design optimal well completion strategies and minimize gas production while maximizing oil recovery. This highlights how permeability analysis assists in preventing undesired fluid production.
• Case Study 3: Water Management in a Fractured Reservoir: Understanding the effective permeability in the fracture network and matrix was essential in managing water production and optimizing production strategies in a fractured reservoir. This emphasizes the complexity and importance of accounting for the different pathways of fluid flow.

These case studies illustrate the crucial role of effective permeability in understanding and optimizing oil and gas reservoir production. The selection of appropriate techniques, models, and software is essential for achieving accurate predictions and effective reservoir management.