PT (well test)

Test Your Knowledge

PT (Well Test) Quiz

Instructions: Choose the best answer for each question.

1. What is the primary purpose of a PT (Well Test)? (a) To determine the age of the reservoir. (b) To assess the characteristics of the underground reservoir. (c) To identify the type of rock formations present. (d) To measure the depth of the well.

2. Which type of well test involves gradually increasing the production rate and monitoring the pressure response? (a) Buildup Test (b) Drawdown Test (c) Interference Test (d) Injection Test

3. What information can a Buildup Test provide? (a) Reservoir pressure and permeability. (b) Fluid properties and reservoir size. (c) Well productivity index and injection rate. (d) Reservoir connectivity and interference between wells.

4. How are PT (Well Tests) used in the context of reservoir management? (a) To predict future oil prices. (b) To identify new oil and gas fields. (c) To monitor reservoir performance and optimize production. (d) To analyze the environmental impact of drilling.

5. Which of the following is NOT a parameter typically measured during a PT (Well Test)? (a) Pressure (b) Flow rate (c) Well depth (d) Fluid composition

PT (Well Test) Exercise

Scenario:

An oil well has been producing for 6 months. During a recent drawdown test, the following data was recorded:

| Time (hours) | Pressure (psi) | Flow Rate (bbl/day) | |---|---|---| | 0 | 3000 | 1000 | | 1 | 2900 | 1200 | | 2 | 2800 | 1400 | | 3 | 2700 | 1600 |

Task:

Using the provided data, calculate the productivity index (PI) of the well.

Formula:

PI = Flow Rate / (Pressure Difference)

Instructions:

1. Choose a time interval from the table (e.g., between 1 hour and 2 hours).
2. Calculate the pressure difference between the two time points.
3. Calculate the average flow rate during that time interval.
4. Apply the PI formula to determine the well's productivity index.

Techniques

PT (Well Test): A Comprehensive Guide

This document expands on the introduction to PT (Well Tests) provided previously, delving into specific aspects through dedicated chapters.

Chapter 1: Techniques

Well testing encompasses a range of techniques designed to elicit specific reservoir properties. The choice of technique depends heavily on the objectives of the test and the reservoir characteristics. Key techniques include:

1.1 Drawdown Tests: These tests involve gradually increasing the production rate from a well and continuously monitoring the resulting pressure decline. Analysis focuses on the pressure-time relationship to determine reservoir parameters such as permeability, skin factor (a measure of near-wellbore damage or stimulation), and wellbore storage coefficient (the capacity of the wellbore to store fluids). Different drawdown test types exist, including:

• Constant Rate Test: Production rate is maintained constant throughout the test.
• Variable Rate Test: Production rate is changed during the test, allowing for a more comprehensive analysis.

1.2 Buildup Tests: Following a drawdown test, a buildup test involves shutting in the well and monitoring the pressure increase as the reservoir re-pressurizes. This provides independent verification of drawdown test results and allows for the determination of reservoir properties such as permeability, skin factor, and even reservoir boundaries under certain conditions. Variations include:

• Conventional Buildup Test: Simple shut-in after a constant-rate drawdown.
• Modified Isolate Buildup Test: Isolates specific zones for a more focused analysis.

1.3 Interference Tests: These tests involve monitoring the pressure response in one or more observation wells while producing from a test well. This allows for the determination of reservoir connectivity, permeability distribution, and the location of reservoir boundaries. The pressure changes in observation wells reflect the influence of production from the test well.

1.4 Injection Tests: These tests involve injecting fluids (water, gas, or steam) into a well and monitoring the resulting pressure increase. Injection tests are vital for evaluating reservoir injectivity, crucial for enhanced oil recovery (EOR) techniques like waterflooding or steam injection. Analysis yields parameters like injectivity index and formation characteristics affecting fluid flow.

1.5 Pulse Tests: These are short-duration tests where a small, controlled change in flow rate is introduced and the pressure response is observed. This method is especially useful in tight formations or where subtle changes in reservoir properties need to be measured.

1.6 Drill Stem Tests (DSTs): These tests are conducted during drilling, providing early assessments of reservoir properties. While less precise than surface tests, DSTs offer valuable information during the exploratory phase.

Chapter 2: Models

Interpreting well test data requires sophisticated mathematical models that simulate fluid flow in porous media. Several models are commonly employed, each with its own assumptions and limitations:

2.1 Analytical Models: These models utilize simplified mathematical equations to describe the pressure transient behavior. Examples include:

• Radial Flow Model: Assumes radial flow of fluids towards the wellbore.
• Linear Flow Model: Assumes linear flow in fractured reservoirs.
• Composite Reservoir Model: Accounts for reservoirs with varying properties (e.g., layered reservoirs).

Analytical models offer quick solutions but often require simplifying assumptions that might not accurately reflect reservoir complexity.

2.2 Numerical Models: These employ numerical techniques (finite difference, finite element) to solve the governing equations of fluid flow. They can handle complex reservoir geometries, heterogeneities, and boundary conditions, but require significant computational resources.

2.3 Semi-Analytical Models: These models combine aspects of analytical and numerical approaches, leveraging the strengths of both. They can efficiently handle some complexities while maintaining a degree of analytical tractability.

Chapter 3: Software

Specialized software packages are essential for analyzing well test data and interpreting the results. These software packages typically offer:

• Data Input and Preprocessing: Tools to import, validate, and clean raw pressure and flow rate data.
• Model Selection and Parameter Estimation: Selection of appropriate reservoir models and estimation of reservoir parameters through history matching and optimization algorithms.
• Data Visualization and Reporting: Generation of plots and reports to communicate the well test results effectively.

Examples of widely used well test analysis software include:

• SAPHIR
• MBT (Multirate Buildup Test)
• PAPRI
• INTERSECT

Chapter 4: Best Practices

Successful well testing requires meticulous planning and execution. Best practices include:

• Proper Well Preparation: Ensuring the well is in optimal condition to avoid complications during the test.
• Accurate Data Acquisition: Utilizing high-quality pressure and flow rate gauges and ensuring accurate data recording.
• Thorough Data Analysis: Employing rigorous data analysis techniques and appropriate reservoir models to ensure reliable interpretation.
• Documentation and Reporting: Maintaining comprehensive records of the test procedures, data, and analysis.
• Safety Considerations: Adhering to strict safety protocols throughout the testing process.

Chapter 5: Case Studies

Real-world examples illustrate the application and value of well tests. Case studies often include:

• Case Study 1: A Drawdown/Buildup Test in a Homogenous Reservoir: This case would describe the successful application of a simple well test to characterize a relatively straightforward reservoir.
• Case Study 2: Interference Testing in a Multi-well System: This might show how interference tests helped map reservoir connectivity between multiple wells in a field.
• Case Study 3: The Impact of Wellbore Skin on Production: This case might showcase how a significant skin factor affected production and how that was identified and mitigated.
• Case Study 4: Using Well Tests to Design and Monitor EOR Projects: This could describe the role of well tests in monitoring an enhanced oil recovery operation, such as waterflooding.

These case studies will showcase different test types, data analysis methods, and the insights gained. By studying real-world applications, engineers and geoscientists can gain valuable experience in using well tests effectively.