Gas Liberation in Tight Porous Media

Wael Fadi Al-Masri*

*Corresponding author for this work

Research output: Book/ReportPh.D. thesisResearch

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Abstract

This thesis addresses the problem of measuring oil relative permeability under the solution gas process, particularly measuring the effective oil permeability when the gas phase is immobile and the critical gas saturation value. The thesis is divided into five chapters. The first two chapters provide a comprehensive literature review and theoretical background that serve as the foundation of this work. Chapters 3 and 4 present the experimental and modeling parts of the study and represent the work's main body. Chapter 5 briefly sums up the work's general conclusions and the suggested future work inspired by the thesis results. The content of each chapter is outlined as follows:

Chapter 1 presents the practical problem statement from which the project was initiated. When the oil reservoirs are developed, the pressure decreases. If it becomes below the so-called bubble point pressure, gas is liberated from oil. The liberated gas bubbles plug the porous space of the reservoir and create additional resistance to the oil flow. This is reflected in the value of the relative permeability for the oil. Experimental and modeling studies of the oil and gas relative permeabilities form the subject of the present thesis.

Chapter 2 provides the framework of fluid flow in porous media and the concept of relative permeability. It also discusses the most common laboratory methods of measuring the relative permeability alongside a brief review of the relative permeability models. The factors affecting the relative permeability are also presented. Finally, the chapter is rounded by a literature review of the solution gas drive experimental and theoretical studies. This chapter aims to present the theoretical background needed to familiarize the reader with the main concepts to benefit from reading this thesis. Finally, the controversy of the results found in the literature is discussed.

Chapter 3 presents the experimental part of the study. A new method to measure oil relative permeability and critical gas for oil-gas systems under depressurization is presented. The oil relative permeability is measured in the presence of immobile gas through the steady-state method. The novelty of this work is the ability of the proposed method to measure the relative permeability outside the active saturation region. Six low permeable chalk core samples from the North Sea region are studied using two binary fluid mixtures. The results show a highly variable amount of immobile gas for North Sea chalk and a significant reduction in oil relative permeability. The relative permeabilities outside the active saturation region were found to be power-law type functions. Applying the model developed in the following chapter allows the reconstruction of both gas and oil relative permeability curves in the whole saturation range. The significance of the presented work is not limited to the new method of measuring the relative permeability but also the addition of such data to the literature, which, to the best knowledge of the author, lack such data set.

Chapter 4 presents the modeling part of the study. The derived model predicts the relative permeabilities under two-phase flows in porous media. The phases may partly mix, and one of the phases is immobile. The model was derived for the purpose of predicting oil relative permeability for the particular case of bubble formation in an oil reservoir when the pressure falls below the bubble point. However, it can be used in the case of condensation and droplet precipitation in a gas-condensate reservoir. The dependencies for the relative permeabilities on the saturation are derived based on a pore-level model of the porous medium, represented as a capillary network. The distribution of the bubbles or droplets in the network is computed statistically using a method adapted from statistical physics. The relative permeabilities of the whole lattice are determined by applying effective medium formalism. Universal correlations between the model parameters and the parameters in the Corey-Brooks dependencies are presented. This allows the extinction of the standard Corey-Brooks formula onto the saturation ranges where one of the phases is immobile. A comparison with the available experimental data is also presented. The result of the comparison indicates the good performance of the model.

Chapter 5 briefly sums up the general conclusions of the study. Additionally, suggested future work based on the conclusions is presented. The main goal is to provide the reader with a broader picture of the results and their application from an engineering perspective.
Original languageEnglish
Place of PublicationKgs. Lyngby
PublisherTechnical University of Denmark
Number of pages134
Publication statusPublished - 2020

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