Feet of pay

Test Your Knowledge

Feet of Pay Quiz:

Instructions: Choose the best answer for each question.

1. What does "feet of pay" refer to in the oil and gas industry?

a) The total depth of a well. b) The thickness of a rock formation containing hydrocarbons. c) The amount of oil or gas extracted from a well. d) The time it takes to drill a well.

2. Why is feet of pay a crucial metric for oil and gas projects?

a) It determines the type of drilling rig needed. b) It helps estimate the potential reservoir volume and production rate. c) It indicates the age of the rock formation. d) It measures the environmental impact of drilling.

3. Which of these factors DOES NOT influence feet of pay?

a) Depositional environment b) Weather patterns c) Geological structures d) Lithology

4. Which methods are used to measure feet of pay?

a) Satellite imagery and aerial photography b) Well logs and seismic surveys c) Soil analysis and water sampling d) Birdwatching and wildlife surveys

5. What is the primary reason why high feet of pay is generally considered desirable for oil and gas projects?

a) It indicates a more environmentally friendly drilling process. b) It ensures a quicker drilling time. c) It often translates to greater potential for extracting oil or gas. d) It guarantees a higher oil price in the market.

Feet of Pay Exercise:

Scenario:

You are a geologist evaluating a new oil and gas exploration site. Initial seismic surveys indicate a potential pay zone with a thickness of 50 feet. However, further analysis of core samples reveals that only 30 feet of this zone has good porosity and permeability suitable for holding and flowing hydrocarbons.

Task:

1. What is the true "feet of pay" for this site?
2. Explain how the knowledge of true "feet of pay" affects your assessment of the site's potential.

Techniques

Feet of Pay: A Comprehensive Guide

Chapter 1: Techniques for Determining Feet of Pay

Determining the feet of pay accurately is crucial for evaluating the economic viability of an oil or gas well. Several techniques are employed, each with its strengths and limitations:

1. Well Logging: This is the primary method for determining feet of pay. Various logging tools measure different properties of the formation, providing data to identify hydrocarbon-bearing zones. Key logs include:

• Gamma Ray Logs: Measure the natural radioactivity of the formation. Lower gamma ray readings often indicate the presence of porous and permeable zones, which can be part of the pay zone.
• Neutron Logs: Measure the hydrogen index of the formation. High hydrogen index suggests the presence of hydrocarbons or water. Differentiation requires additional logs.
• Density Logs: Measure the bulk density of the formation. Density logs, combined with neutron logs, can help distinguish between hydrocarbons and water.
• Resistivity Logs: Measure the electrical resistance of the formation. High resistivity often indicates the presence of hydrocarbons.

Analysis of these logs, often in combination, allows geologists and engineers to identify the top and bottom of the pay zone, thereby determining its thickness.

2. Seismic Surveys: While not as precise as well logs for determining exact feet of pay, seismic surveys provide a broader understanding of the subsurface geology. These surveys can identify potential reservoir structures and their approximate dimensions, providing a preliminary estimate of the pay zone thickness before drilling. 3D seismic surveys offer higher resolution and improved accuracy.

3. Core Analysis: Core samples obtained during drilling provide direct observation of the rock formation. Laboratory analysis of core samples helps determine porosity, permeability, and hydrocarbon saturation, ultimately refining the assessment of the feet of pay and its productivity. This is expensive and not always feasible.

4. Production Testing: Once a well is drilled, production testing provides crucial data on the reservoir's productivity. The observed flow rates, in conjunction with other data, can be used to estimate the effective feet of pay (the portion of the gross pay zone that contributes significantly to production).

Chapter 2: Models for Feet of Pay Estimation

Estimating feet of pay isn't simply a matter of measuring thickness; it involves incorporating various geological parameters and uncertainties. Several models aid in this process:

1. Petrophysical Models: These models use well log data to estimate reservoir properties like porosity, permeability, and water saturation. By incorporating these properties within a defined pay zone, the model can predict hydrocarbon volume and potential production.

2. Geological Models: These models integrate geological interpretations (e.g., depositional environment, structural features) with geophysical data (seismic surveys) to create a 3D representation of the reservoir. These models can provide a more accurate estimate of the gross thickness of the pay zone and its distribution within the reservoir.

3. Reservoir Simulation Models: These complex models simulate the flow of fluids within the reservoir, incorporating factors like pressure, temperature, and fluid properties. Simulation models use estimated feet of pay as an input and help predict long-term production performance.

4. Statistical Models: These models can be used to predict feet of pay based on historical data from analogous fields or wells. This is particularly useful in early exploration stages when data is limited.

The choice of model depends on data availability, the complexity of the reservoir, and the required accuracy.

Chapter 3: Software for Feet of Pay Analysis

Several software packages are used for analyzing well log data, creating geological models, and simulating reservoir performance:

• Petrel (Schlumberger): A comprehensive suite of tools for seismic interpretation, reservoir modeling, and production simulation.
• Landmark OpenWorks (Halliburton): Another industry-standard software package offering similar functionalities to Petrel.
• Roxar RMS (Emerson): Offers specialized modules for reservoir characterization and simulation.
• IP (Interactive Petrophysics): Focuses on well log analysis and interpretation.
• Kingdom (IHS Markit): Provides integrated solutions for geoscience and reservoir engineering.

These software packages provide tools for processing and interpreting well logs, creating 3D geological models, and performing reservoir simulations to estimate and refine feet of pay calculations.

Chapter 4: Best Practices for Feet of Pay Determination

Accurate determination of feet of pay requires adherence to best practices:

• Quality Control of Data: Ensuring the accuracy and reliability of well log data and other input data is paramount. This includes proper calibration of logging tools and rigorous quality checks.
• Integrated Approach: Employing an integrated approach that combines well logs, seismic data, core analysis, and production testing data provides a more robust estimate of feet of pay.
• Geologic Understanding: A thorough understanding of the regional geology and the specific depositional environment is essential for accurate interpretation of the data.
• Uncertainty Quantification: Acknowledging and quantifying the uncertainties associated with feet of pay estimations is crucial for realistic project planning and risk assessment.
• Calibration and Validation: Whenever possible, comparing estimated feet of pay with actual production data from producing wells provides a way to calibrate and validate the models used.

Chapter 5: Case Studies on Feet of Pay Analysis

Several case studies demonstrate the importance and application of feet of pay analysis:

(Note: Specific case studies would require detailed data and would be quite lengthy. Here are examples of case study elements):

• Case Study 1: A successful appraisal well: Describe a situation where accurate determination of feet of pay, using a combination of well logs and seismic data, led to the successful appraisal of a new field. Highlight the positive economic impact due to accurate prediction.
• Case Study 2: A challenging reservoir: Discuss a situation where the initial estimate of feet of pay was inaccurate due to complex geological features (e.g., faulting, fracturing). Show how further investigation (e.g., additional well logs, core analysis, reservoir simulation) improved the accuracy and adjusted the project plan accordingly.
• Case Study 3: Impact of inaccurate feet of pay estimation: Provide an example where an inaccurate estimation of feet of pay negatively impacted the economic viability of a project. This could illustrate the high cost of errors in this area.

Each case study would analyze the techniques used, the challenges encountered, and the lessons learned. It would highlight the importance of a rigorous and multi-faceted approach to feet of pay determination.