Multiphase Fluid Flow in Porous and Fractured Reservoirs - Yu-Shu Wu

Multiphase Fluid Flow in Porous and Fractured Reservoirs (eBook)

Yu-Shu Wu (Autor)

eBook Download: PDF | EPUB

2015 | 1. Auflage
418 Seiten
Elsevier Science (Verlag)
978-0-12-803911-3 (ISBN)

Multiphase Fluid Flow in Porous and Fractured Reservoirs discusses the process of modeling fluid flow in petroleum and natural gas reservoirs, a practice that has become increasingly complex thanks to multiple fractures in horizontal drilling and the discovery of more unconventional reservoirs and resources. The book updates the reservoir engineer of today with the latest developments in reservoir simulation by combining a powerhouse of theory, analytical, and numerical methods to create stronger verification and validation modeling methods, ultimately improving recovery in stagnant and complex reservoirs. Going beyond the standard topics in past literature, coverage includes well treatment, Non-Newtonian fluids and rheological models, multiphase fluid coupled with geomechanics in reservoirs, and modeling applications for unconventional petroleum resources. The book equips today's reservoir engineer and modeler with the most relevant tools and knowledge to establish and solidify stronger oil and gas recovery. - Delivers updates on recent developments in reservoir simulation such as modeling approaches for multiphase flow simulation of fractured media and unconventional reservoirs - Explains analytical solutions and approaches as well as applications to modeling verification for today's reservoir problems, such as evaluating saturation and pressure profiles and recovery factors or displacement efficiency - Utilize practical codes and programs featured from online companion website

Yu-Shu Wu is currently a tenured Professor and the Reservoir Modeling Chair for the Department of Petroleum Engineering at the Colorado School of Mines in Golden, Colorado, USA. Dr. Wu's research and teaching areas include reservoir engineering, specifically reservoir characterization and simulation, fractured reservoir characterization, and non-Newtonian and non-Darcy flow behavior. Previously, Yu-Shu has worked as a Scientist at the Lawrence Berkeley National Laboratory researching unconventional natural gas resources, Adjunct Professor at Peking University in Bejiing, the China University of Geosciences in Beijing, and the China University of Petroleum in Qingdao as well as a Researcher at SINOPEC and PetroChina. Yu-Shu has published over 300 conference articles, 100 peer-reviewed journal papers, contributed to mulitiple book chapters, and remains active on many journal publications as technical editor. He is a Fellow and member of the Geological Society of America, a member of the Society of Petroleum Engineers, American Geophysical Union, and a member of the International Professionals for the Advancement of Chinese Earth Sciences. Yu-Shu earned a BS in Petroleum Engineering from Daqing Petroleum Institute, a MS in Petroleum Engineering from Southwest Petroleum Institute (China), and a MS and PhD both in Reservoir Engineering from University of California at Berkeley.

Chapter 2

Multiphase Fluids in Porous Media

Abstract

This chapter discusses fundamentals of multiphase flow through porous media. It focuses on physics and quantitative analysis of flow processes in porous media. Because of unknown nature of porous media and complex interactions of fluids and rock in reservoirs, this chapter argues that some macroscopic continuum approach has to be used to study flow processes of multiphase fluids in reservoirs. It concludes that almost all theories on flow phenomena in porous media lead to macroscopic laws using a representative elementary volume (REV) concept. Flow-governing equations can be derived from conservation of mass, energy, and momentum. It further discusses basic concepts of fluids and porous media and flow-driving mechanisms as well as extensions of Darcy's law to non-Newtonian fluid and non-Darcy flow. In addition, it shows that macroscopic laws in association with capillary pressure and relative permeability concepts make it possible to quantify flow and transport in porous media.

Keywords

Capillary pressure; Continuum approach; Darcy's law; Flow driving mechanisms; Flow potential; Porous media; Primary recovery; Relative permeability; REV (representative elementary volume); Wettability

2.1. Introduction

The physical processes associated with flow and transport of multiphase fluids in porous media are governed by the same fundamental conservation laws as those used in any branch of the sciences and engineering. Conservation of mass, momentum, and energy governs the behavior of multiphase fluid flow, chemical transport, and heat transfer through porous and fractured media. These physical laws in porous media are well known at the pore level; however, in practice for a particular study of laboratory or field application, one may be interested only in global behavior or volume averaging of the porous medium system. Because of the complexity of pore geometries and the heterogeneity of a porous medium system, the macroscopic behavior is not easily deduced from that on the pore level or micro scale. For example, any attempts to directly apply the Navier–Stokes equation to flow problems through a lot of pores in an actual reservoir porous-medium system will face tremendous difficulties. These include poorly defined or unknown pore geometries or flow boundaries, complex dynamic phenomena of physical and chemical interactions between pores and fluids or between fluids and solids, and too many unknowns or equations, with too many undefined parameters or correlations, which cannot be solved at present for field-scale applications.

The macroscopic continuum approach is most commonly used in studies of flow and displacement processes in reservoirs from laboratory to field scale. For practical application, almost all theories on flow phenomena occurring in porous media lead to macroscopic laws applicable to a finite volume or a subdomain of the system under investigation, the dimensions of which are large compared with those of pores. Consequently, these laws lead to equations in which the porous medium and fluid system are treated as if they were continuous and characterized by the local values of a number of thermodynamic variables and rock and fluid parameters, defined for all points with appropriate averaging or representative elementary volume (REV) (Bear, 1972). Then, flow equations, derived from combining conservation of mass, energy, and momentum and based on the REV concept, are used to describe flow processes in reservoirs.

2.2. Basic Science and Engineering Concepts, Fluids and Porous Media

There are two basic goals for analysis of multiphase fluid flow in reservoirs: one is determination of in situ mass distribution spatially at a given time and the other is calculation of flow or movement of fluids in reservoirs. To determine mass distribution and calculate movement or “flow” of fluids in a porous-medium system of rock, we need to introduce a number of physical concepts, such as those describing fluid and rock properties. There are a number of excellent books in the literature to define and discuss these rock and fluid properties (e.g., Bear, 1972; Scheidegger, 1974; McCain, 1990; Dullien, 1991).

Determination of spatial mass distribution or local mass balance is a volumetric and static concept. To estimate how much water, oil, or gas is in place, in addition to geological data and geophysical logs, we need to introduce many physical parameters of reservoir rock, such as effective porosity, fluid density, fluid saturation, and their residual values, fluid-phase pressure, fluid and rock compressibility, solution gas–oil ratio, etc. These fluid and rock properties and parameters are not only necessary to estimate mass distribution in a reservoir system, but also provide the bases for mass balance calculation, needed for deriving flow-governing equations of multiphase fluids in reservoirs.

Flow and movement of fluids in porous media is a dynamic process and is driven by energy that is stored within reservoirs or supplied by injection. The key question for reservoir engineers and hydrologists to answer is how much fluid, water, oil, or gas can be produced under given geological and operational conditions. Or, how can the performance of the reservoir be optimized for maintaining long-term productivity or higher recovery rate? The flow and displacement in reservoirs is controlled by conservation laws of mass, energy, and momentum. To calculate flow in porous media, we need to introduce and determine many fluid flow and rock properties, such absolute permeability, fluid viscosity, interface tension (IFT), wettability, relative permeability, and capillary pressure concepts, etc. We also need to know the driving forces or flow mechanisms, i.e., the main energy driving fluid to flow from reservoir to well, such as pressure and potential gradient, potential energy, or capillary force.

Continuum approaches of fluid mechanics and thermodynamics have been traditionally used for flow analysis in porous and fractured media. Reservoir rock of interest is a porous medium, containing pores (voids) and skeleton (solids). For any engineering application of flow in porous media, we are interested in only the porous medium that has interconnected pores that fluids are able to flow through. The skeletal portion of a porous medium is called the “matrix” and is normally solid and impermeable to fluids. The pores of porous media are typically filled with one or several fluids (e.g., water, oil, or gas). Because the fluids in porous media are not spatially “continuous” per se, the REV or volumetric averaging concept has to be used in practice, together with a local thermodynamic equilibrium assumption, to define rock and fluid parameters (e.g., porosity, tortuosity, specific surface area, etc.), and thermodynamic state variables (pressure, temperature, density, concentration, etc.). Then, we treat both fluids and solids as though they were continuous in space all the time. Using continuum concepts, therefore, we are able to define the parameters and state variables needed for mass conservation and flow calculation. As a result, quantitative approaches and tools, developed in fluid dynamics or thermodynamics, are directly applied in analysis of flow through porous media.

The continuum approaches, even though widely applied, have certain limitations. Past investigations of displacement of a more viscous fluid by less viscous fluid, such as a crude oil displaced by gas, and water seepage in thick unsaturated zones of fractured rocks, have indicated that flow and transport processes in such an environment may occur in non-volume-averaged fashion and proceed, in part, by means of localized preferential pathways (Pruess, 1999). Conventional continuum concepts and modeling approaches may not adequately capture the physics of multiphase flow displacement along those preferential flow pathways if the spatial variability is not properly represented by constraints of the computational requirements.

2.3. Physical Processes and Flow-Driving Mechanisms

For a fluid to be able to flow toward a well in a reservoir, there must be some energy in the reservoir to impel it. Flow-driving forces or mechanisms control fluid flow behavior and performance of reservoirs. Taking a petroleum reservoir as an example, primary recovery is naturally occurring flow toward wells, but this will not persist without enough energy either stored within the reservoir or supplied from outside. To maintain long-term productivity of oil or gas, a secondary recovery method, such as waterflooding and gas injection, is most commonly used to supply energy to reservoirs. In addition, tertiary oil recovery (or Enhanced Oil Recovery, EOR) has been routinely used to inject chemicals or thermal energy into petroleum reservoirs to enhance production or performance of the reservoir.

A primary recovery stage of petroleum reservoirs is the production time period when flow to wells relies on the natural energy of the reservoir or before a secondary or tertiary recovery approach is implemented. During this stage, the overall performance of reservoirs is controlled by the nature of the energy, i.e., driving mechanism(s), available for mobilizing the oil to the wellbore. There are a number of driving mechanisms that provide the natural energy necessary for oil to flow into wells (Craft et al., 1959; Willhite, 1986; Ahmed and McKinney, 2011):

Rock and liquid expansion drive: This usually is the main production mechanism for...

Erscheint lt. Verlag	23.9.2015
Sprache	englisch
Themenwelt	Naturwissenschaften ► Physik / Astronomie ► Strömungsmechanik
	Technik ► Elektrotechnik / Energietechnik
	Technik ► Maschinenbau
	Technik ► Umwelttechnik / Biotechnologie
ISBN-10	0-12-803911-6 / 0128039116
ISBN-13	978-0-12-803911-3 / 9780128039113

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