By inducing a gas (non-wetting fluid) into a water saturated rock, the gas will displace the water (wetting fluid), but this process just take place, when the capillary pressure is above the capillary entry pressure (gas pressure difference). First the largest pores near the sample surface are drained (drainage process). At higher capillary pressures even the smallest pores are filled with gasThe relation between capillary pressure and pore radius is given by the Washburn equation (1921), “The intrusion of a non-wetting fluid into a cylindrical capillary of radius r only occurs if the capillary pressure Pc […] within a pore is exceeded”: [...]
Table of Contents
I. Introduction: Principle Measurement
II. Results steady state experiment
II. 1. Steady-State single-phase gas permeability on a dry sample
II. 2. Steady-State gas permeability on a saturated sample
II. 3. Non-steady state single-phase flow on a saturated sample
III. Error calculation
IV. Conclusion
Objectives and Topics
This report documents a laboratory study investigating gas breakthrough phenomena in rock samples under both steady-state and non-steady-state conditions to determine permeability characteristics.
- Measurement of gas permeability in dry and saturated sandstone samples.
- Application of the Klinkenberg correction for compressible gas flow in porous media.
- Analysis of drainage and imbibition processes during gas-water displacement.
- Calibration and pressure-volume relationship determination in experimental cells.
- Calculation of error margins for experimental permeability measurements.
Excerpt from the Book
I. Introduction: Principle Measurement
By inducing a gas (non-wetting fluid) into a water saturated rock, the gas will displace the water (wetting fluid), but this process just take place, when the capillary pressure is above the capillary entry pressure (gas pressure difference). First the largest pores near the sample surface are drained (drainage process). At higher capillary pressures even the smallest pores are filled with gasThe relation between capillary pressure and pore radius is given by the Washburn equation (1921), “The intrusion of a non-wetting fluid into a cylindrical capillary of radius r only occurs if the capillary pressure Pc […] within a pore is exceeded” [1]:
At gas breakthrough gas starts to flow through the sample and displace water from the pore system (drainage path). The effective permeability of the gas-phase after the gas breakthrough is a function of the gas/water saturation and is no longer a rock property like the absolute permeability (single-phase flow). The effective permeability can be determined using the following equation:
A decrease of capillary pressure leads to an imbibition of water and gas saturation decreases until the last capillary pore is blockaded and gas flow is restricted (snap-off pressure). Complete pressure equilibrium is not established.
Summary of Chapters
I. Introduction: Principle Measurement: Outlines the physical principles of gas displacement in saturated rock and introduces the governing equations for capillary pressure and effective permeability.
II. Results steady state experiment: Presents the experimental data and permeability calculations for dry and saturated sandstone samples using steady-state conditions.
II. 1. Steady-State single-phase gas permeability on a dry sample: Details the specific results and Klinkenberg-corrected permeability measurements for a dry sandstone core.
II. 2. Steady-State gas permeability on a saturated sample: Discusses the two-phase flow experiments conducted on saturated samples and the calculation of effective permeability.
II. 3. Non-steady state single-phase flow on a saturated sample: Describes the calibration of the experimental setup and the methodology for non-steady-state gas breakthrough testing.
III. Error calculation: Describes the methodology used to determine the maximum relative and absolute errors for the calculated permeability coefficients.
IV. Conclusion: Summarizes the key findings regarding gas breakthrough pressures and the influence of capillary forces on flow behavior in different sample states.
Keywords
Petrophysics, Gas Breakthrough, Permeability, Darcy’s Law, Klinkenberg Correction, Capillary Pressure, Drainage, Imbibition, Steady-state, Non-steady-state, Porous Media, Sandstone, Fluid Flow, Pore Radius, Snap-off Pressure
Frequently Asked Questions
What is the fundamental focus of this laboratory report?
This report focuses on analyzing gas breakthrough and permeability in sandstone samples under both steady-state and non-steady-state experimental conditions.
What are the primary thematic areas covered?
The core themes include fluid dynamics in porous media, the physical effects of capillary pressure, and the practical application of Darcy’s Law for compressible gas flow.
What is the primary objective of these experiments?
The primary goal is to determine the absolute and effective permeability of rock samples and to observe how gas displaces water within the pore structure.
Which scientific methods are utilized?
The report utilizes steady-state flow measurements with bubble flow meters and non-steady-state pressure equilibration methods, supplemented by the Klinkenberg correction.
What topics are discussed in the main section?
The main section covers the theoretical principles of gas intrusion, experimental calibration procedures, raw data analysis for dry and saturated samples, and error calculation methodologies.
Which keywords characterize this work?
Key terms include Petrophysics, Permeability, Gas Breakthrough, Klinkenberg Correction, Darcy’s Law, and Capillary Pressure.
Why is the Klinkenberg correction applied in this study?
It is applied to dry samples to determine absolute gas permeability, as it accounts for slip flow effects at the pore walls that occur at low mean fluid pressures.
How is the snap-off pressure relevant to the results?
The snap-off pressure represents the state where gas flow is restricted because capillary forces block the remaining gas within the pore system after the imbibition process.
What does the comparison between dry and saturated samples reveal?
The study reveals that saturated samples require a higher entry pressure for gas breakthrough compared to dry samples, as capillary forces are active in the saturated state.
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- Amalia Aventurin (Autor:in), 2013, Gas Breakthrough, München, GRIN Verlag, https://www.hausarbeiten.de/document/272606
