Handbook of Natural Gas Analysis E-Book

James G. Speight

• Herausgeber: John Wiley & Sons
• Kategorie: Fachliteratur
• Sprache: Englisch

Seitenzahl: 1154

Veröffentlichungsjahr: 2018

Beschreibung

A comprehensive resource to the origin, properties, and analysis of natural gas and its constituents Handbook of Natural Gas Analysis is a comprehensive guide that includes information on the origin and analysis of natural gas, the standard test methods, and procedures that help with the predictability of gas composition and behavior during gas cleaning operations and use. The author--a noted expert on the topic--also explores the properties and behavior of the various components of natural gas and gas condensate. All chapters are written as stand-alone chapters and they cover a wealth of topics including history and uses; origin and production; composition and properties; recovery, storage, and transportation; properties and analysis of gas stream and gas condensate. The text is designed to help with the identification of quality criteria appropriate analysis and testing that fall under the umbrella of ASTM International. ASTM is an organization that is recognized globally across borders, disciplines and industries and works to improve performance in manufacturing and materials and products. This important guide: * Contains detailed information on natural gas and its constituents * Offers an analysis of methane, gas hydrates, ethane, propane, butane, and gas condensate * Includes information on the behavior of natural gas to aid in the planning for recovery, storage, transportation, and use * Covers the test methods that are applicable to natural gas and its constituents * Written in accessible and easy-to-understand terms Written for scientists, engineers, analytical chemists who work with natural gas as well as other scientists and engineers in the industry, Handbook of Natural Gas Analysis offers a guide to the analysis, standard test methods, and procedures that aid in the predictability of gas composition and behavior during gas cleaning operations and use.

Leseprobe

Handbook of Natural Gas Analysis

James G. Speight

CD&W Inc.Laramie, WY, USA

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Library of Congress Cataloging‐in‐Publication Data

Names: Speight, James G., author.Title: Handbook of natural gas analysis / by Dr. James G. Speight.Description: Hoboken, NJ : John Wiley & Sons, 2018. | Includes bibliographical references and index. |Identifiers: LCCN 2018010730 (print) | LCCN 2018014739 (ebook) | ISBN 9781119240303 (pdf) | ISBN 9781119240310 (epub) | ISBN 9781119240280Subjects: LCSH: Natural gas–Analysis–Handbooks, manuals, etc.Classification: LCC TN880.A3 (ebook) | LCC TN880.A3 S74 2018 (print) | DDC 665.7/3–dc23LC record available at https://lccn.loc.gov/2018010730

Cover Design: WileyCover Image: © suns07butterfly/Shutterstock

About the Author

Dr James G. Speight has a BSc and PhD in Chemistry; he also holds a DSc in Geological Sciences and a PhD in Petroleum Engineering. He has more than 50 years of experience in areas associated with (i) the properties, recovery, and refining of reservoir fluids, conventional petroleum, heavy oil, and tar sand bitumen; (ii) the properties and refining of natural gas and gaseous fuels; and (iii) the properties and refining of biomass, biofuels, and biogas and the generation of bioenergy. His work has also focused on environmental effects, environmental remediation, and safety issues associated with the production and use of fuels and biofuels. He is the author (and coauthor) of more than 75 books in petroleum science and engineering, biomass, biofuels, and environmental sciences.

Although he has always worked in the private industry that focused on contract‐based work, Dr Speight has served as adjunct professor in the Department of Chemical and Fuels Engineering at the University of Utah and in the Departments of Chemistry and Chemical and Petroleum Engineering at the University of Wyoming. In addition, he was a visiting professor in the College of Science, University of Mosul (Iraq), and has also been a visiting professor in chemical engineering at the following universities: University of Akron (Ohio), University of Missouri, Technical University of Denmark, and University of Trinidad and Tobago. He has served as a thesis examiner for more than 30 theses and has been an advisor/mentor to MSc and PhD students.

Dr Speight has been honored as the recipient of the following awards:

Diploma of Honor, United States National Petroleum Engineering Society. For outstanding contributions to the petroleum industry, 1995.

Gold Medal of the Russian Academy of Sciences. For outstanding work in petroleum science, 1996.

Einstein Medal of the Russian Academy of Sciences. In recognition of outstanding contributions and service in the field of geologic sciences, 2001.

Gold Medal – Scientists without Frontiers, Russian Academy of Sciences. In recognition of his continuous encouragement of scientists to work together across international borders, 2005.

Methanex Distinguished Professor, University of Trinidad and Tobago. In recognition of excellence in research, 2006.

Gold Medal – Giants of Science and Engineering, Russian Academy of Sciences. In recognition of continued excellence in science and engineering, 2006.

Preface

Natural gas is a flammable gaseous mixture that usually occurs with petroleum in reservoirs as well as in gas reservoirs. It is predominantly methane (CH4) but does contain higher molecular weight hydrocarbon derivatives, such as paraffins (CnH2n+2), generally containing up to eight carbon atoms that may also be present in small quantities. In some gases, benzene and low molecular weight aromatic carbon derivative may also be present. The hydrocarbon constituents of natural gas are combustible, but nonflammable nonhydrocarbon components such as carbon dioxide (CO2), hydrogen sulfide (H2S), nitrogen (N2), and helium (He) are often also present, which detract from the heating value of natural gas. In certain natural gases where the concentration of the nonhydrocarbon constituents is relatively high, they may be extracted as added‐value products.

Effective gas recovery, transportation, storage, and processing operations require that analytical resources are optimized because the application of the relevant analytical methods meets the objectives required at each stage of gas handling. Method validation, as required by the local, state, or national regulatory agencies at the various stages of the approval process, necessitates the need for demonstrating that the analytical procedures applied to the sales gas are suitable for their intended use in terms of defining the sales specifications of the gas. Where appropriate, the results of the analytical test methods are incorporated into MSDS documents that provide valuable information to purchasers. In addition, regulations require chemical manufacturers to prepare and distribute an MSDS for various products, especially those products that might be harmful to the user and to the environment. This includes natural gas products (and natural gas itself) that are flammable, corrosive, explosive, or toxic.

However, to fully understand the results of the analytical test methods as applied to production to sales of natural gas and the various products, it is necessary to understand the composition of natural gas as it is related to its formation and character. For example, analytical data are the media for transmitting information related to the effectiveness of gas processing operations at the wellhead and at the refinery. Prior to transportation in pipelines, it is essential that any corrosive constituents in the gas (such as water, carbon dioxide, and hydrogen sulfide) are separated from natural gas.

Thus, analytical methods are employed to establish the identity, purity, physical characteristics, and potency of natural gas and the associated products. Methods have been developed to support testing against specifications during manufacturing and quality release operations, as well as during long‐term stability studies. Furthermore, the validation of an analytical method demonstrates the reliability of the measurement. It is required to varying extents throughout the regulatory process, and the validation practice demonstrates that an analytical method measures (in the context of natural gas) the amount of the constituent and it is in the allowable range for that constituents.

As a result, it should not be a surprise that at each stage of natural gas production, wellhead treating, transportation, and processing, analysis of the gas to determine its composition and properties by standard test methods is an essential part of the chemistry of natural gas and related technology. Use of analytical methods offers vital information about the behavior of natural gas during recovery, wellhead processing, transportation, gas processing, and use. The data produced from the test methods are based on the criteria involving the suitability of the gas for use and the potential for interference with the environment.

Thus, it is the purpose of this book to identify and describe the criteria that are appropriate to the analysis and testing of natural gas and related gas streams. For this reason, there is reference to the relevant standard test method that falls under the umbrella of ASTM International, an organization that is recognized globally across borders, disciplines, and industries and works to improve performance in manufacturing and materials, products and processes, and systems and services.

This book presents the various aspects of the origin and analysis of natural gas and will provide a detailed explanation of the necessary standard test methods and procedures that are applicable to products to help predefine predictability of gas composition and behavior during gas cleaning operations and use. This information allows the analyst to understand the behavior of the method and to establish the performance limits of the method according to the origin of the sample received by the analytical laboratory. Where appropriate, the book also references process gas (also called refinery gas), coalbed methane, gas from tight formations, gas from gas hydrates, coal gas, biogas, landfill gas, and flue gas.

Each chapter is written as a stand‐alone chapter so that all of the relevant information is at hand especially where there are tests that can be applied to several products. Where this was not possible, cross‐references to the pertinent chapter are included. Several general references are listed for the reader to consult and obtain a more detailed description of natural gas properties, and the focus is to cite the relevant test methods that are applied to natural gas and its constituents.

The book is intended for use within analytical laboratories that specialize on the analysis of natural gas and for managers, professionals, and technicians working in the gas industry as well as gas processing scientists and engineers as a guide for the analysis of gas from other sources. The book will help the reader to understand where the various standard test methods are relevant and how these test methods fit into the technology of natural gas. In summary, it is not merely a matter of knowing which test methods to apply to the analysis of natural gas, but at which point analysis should be applied in the gas train that commences with the origin of the gas and ends with the sales of the gas to the consumer.

This book will serve as a valuable reference work for the application of analysis in the natural gas industry and will introduce the analytical chemist to the origin and production of natural gas and the natural gas engineer to the various methods of analysis that are required (by regulation) as well as the points of application of the relevant test methods.

Dr. James G. Speight

Laramie, WY, USA

January, 2018

Part IOrigin and Properties

1History and Background

1.1 Introduction

Although the terminology and definitions involved with the natural gas technology are quite succinct, there may be those readers that find the terminology and definitions somewhat confusing. Terminology is the means by which various subjects are named so that reference can be made in conversations and in writings and the meaning is passed on. Definitions are the means by which scientists and engineers communicate the nature of a material to each other either through the spoken or through the written word. Thus, the terminology and definitions applied to natural gas (and, for that matter, to other gaseous products and fuels) are extremely important and have a profound influence on the manner by which the technical community and the public perceive that gaseous fuel. For the purposes of this book, natural gas and those products that are isolated from natural gas during recovery (such as natural gas liquids [NGLs], gas condensate, and natural gasoline) are a necessary part of this text.

Thus, the term natural gas is the generic term that is applied to the mixture of gases and low‐boiling liquid hydrocarbon derivatives (typically up to and including hydrocarbon derivatives such as n‐octane, CH3(CH2)6CH3, boiling point 125.1–126.1 °C, 257.1–258.9 °F) (Table 1.1) that is commonly associated with petroliferous (petroleum‐producing, petroleum‐containing) geologic formations (Mokhatab et al., 2006; Speight, 2007, 2014a) and that has been extended to gases and liquids from the recently developed shale formations (Speight, 2017b) as well as gas (biogas) produced from biological sources (John and Singh, 2011; Ramroop Singh, 2011; Singh and Sastry, 2011).

Table 1.1 Constituents of natural gas.

Name

Formula

Vol. %

Methane

CH

4

>85

Ethane

C

2

H

6

3–8

Propane

C

3

H

8

1–5

Butane

C

4

H

10

1–2

Pentane

+

C

5

H

12

1–5

Carbon dioxide

CO

2

1–2

Hydrogen sulfide

H

2

S

1–2

Nitrogen

N

2

1–5

Helium

He

<0.5

Pentane+: pentane and higher molecular weight hydrocarbon derivatives up to octane as well as benzene and toluene.

For clarification, natural gas (also called marsh gas and swamp gas in older texts and more recently landfill gas) is not the same as town gas, which is manufactured from coal, and the terms coal gas, manufactured gas, producer gas, and syngas (synthetic natural gas [SNG]) are also in regular use for gases produced from coal (Speight, 2013b). Also, by way of definition and clarification, town gas is a flammable gaseous fuel made by the destructive distillation of coal. It contains a variety of calorific gases including hydrogen, carbon monoxide, methane, and other volatile hydrocarbon derivatives, together with small quantities of noncalorific gases such as carbon dioxide and nitrogen. Town gas, although not used to any great extent in the United States, is still generated and used in some countries and is used in a similar way to natural gas. This is a historical technology and is not usually economically and environmentally competitive with modern sources of natural gas.

Most town gas‐generating plants located in the Eastern United States in the late nineteenth century and early twentieth century were ovens that heated bituminous coal in airtight chambers to produce coke through the carbonization process. The gas driven off from the coal was collected and distributed through networks of pipes to residences and other buildings where it was supplied to industrial and domestic users – natural gas did not come into widespread use until the last half of the twentieth century. The coal tar collected in the bottoms of the gashouse ovens was often used for roofing and other waterproofing purposes, and when mixed with sand and gravel (aggregate), it was used for paving streets (road asphalt). The coal tar asphalt has been replaced by asphalt produced from crude oil (Speight, 2014a, 2015b). Thus, prior to the development of resources, virtually all fuel and lighting gas was manufactured from coal, and the history of and analysis of natural gas has its roots in town gas analysis and use (Speight, 2013b). Thus, with the onset of industrial expansion after World War II, natural gas has become one of the most important raw materials consumed by modern industries to provide raw materials for the ubiquitous plastics and other products as well as feedstocks for the energy and transportation industries.

From a chemical standpoint, natural gas is a mixture of hydrocarbon compounds and nonhydrocarbon compounds with crude oil being much more complex than natural gas (Mokhatab et al., 2006; Speight, 2007, 2012, 2014a). The fuels that are derived from this natural product supply more than one quarter of the total world energy supply. The more efficient use of natural gas is of paramount importance, and the technology involved in processing both feedstocks will supply the industrialized nations of the world for (at least) the next five decades until suitable alternative forms of energy (such as biogas and other nonhydrocarbon fuels) are readily available (Boyle, 1996; Ramage, 1997; Speight, 2008, 2011a, b, c; Rasi et al., 2011). Any gas sold, however, to an industrial or domestic consumer must meet the designated specification that is designed according to the use of the gas.

As a result, it should not be a surprise that at each stage of natural gas production, wellhead treating, transportation, and processing, analysis of the gas to determine the composition and properties of the gas by standard test methods is an essential part of the chemistry and technology of natural gas. Use of analytical methods offers vital information about the behavior of natural gas during recovery, wellhead processing, transportation, gas processing, and use. The data produced from the test methods are the criteria by means of which the suitability of the gas for use and the potential for interference with the environment.

1.2 History, Use, and the Need for Analysis

Natural gas is a versatile, clean‐burning, and efficient fuel that is used in a wide variety of applications. In the late nineteenth century and in the early twentieth century, natural gas played a subsidiary role to coal gas insofar as coal gas was used for street lighting and for building lighting and provided what was known as gaslight (Mokhatab et al., 2006; Speight, 2013b). However, as the twenty‐first century progresses, the discovery of large reserves of natural gas in various countries as well as improved distribution of gas has made possible a wide variety of uses in homes, businesses, factories, and power plants. The fastest‐growing use of natural gas is for the generation of electric power and, to a large extent, has been a replacement fuel of many formerly coal‐fired power plants and oil‐fired power plants. Natural gas power plants usually generate electricity in gas turbines (which are derived from jet engines), directly using the hot exhaust gases from the combustion process.

Natural gas‐fired plants are currently among the cheapest power plants to construct, which is a reversal of previous trends where operating costs were generally higher than those of coal‐fired power plants because of the relatively high cost of natural gas. In addition, natural gas‐fired plants have greater operational flexibility than coal‐fired power plants because they can be fired up and turned down rapidly. Because of this, many natural gas plants in the United States were originally used to provide additional capacity (peak capacity) at times when electricity demand was especially high, such as the summer months when air conditioning is widely used. During much of the year, these natural gas peak plants were idle, while coal‐fired power plants typically provided base load power. However, since 2008, natural gas prices in the United States have fallen significantly, and natural gas is now increasingly used as for base load power as well as for intermediate load power source in many cities. Natural gas can also be used to produce both heat and electricity simultaneously (cogeneration or combined heat and power [CHP]). Cogeneration systems are highly efficient, able to put 75–80% of the energy in gas to use. Trigeneration systems, which provide electricity, heating, and cooling, can reach even higher efficiencies using natural gas.

Natural gas also has a broad range of other uses in industry, not only as a source of both heat and power but also as a source of valuable hydrogen that is necessary for crude oil refining as well as for producing plastics and chemicals. Most hydrogen gas (H2) production, for example, comes from reacting high‐temperature water vapor (steam) with methane – steam‐methane reforming reaction followed by the water–gas shift reaction:

Furthermore, the hydrogen produced from natural gas can itself be used as a fuel. The most efficient way to convert hydrogen into electricity is by using a fuel cell, which combines hydrogen with oxygen to produce electricity, water, and heat. Although the process of reforming natural gas to produce hydrogen still has associated carbon dioxide emissions, the amount released for each unit of electricity generated is much lower than for a combustion turbine.

As part of the industrial use of natural gas, there is the need for associated (or contract) laboratory operations to perform the necessary high numbers of analyses before the products (in this context, the gaseous products) are used by industrial and domestic consumers. Detection of even the slightest amounts of impurities can be an indication of process inefficiency and whether or not the gas is suitable for the designated use. In fact, one of the most important tasks in gas technology, especially in the context of petroleum‐related natural gas, is the need for reliable values of the volumetric and thermodynamic properties for pure low‐boiling hydrocarbon derivatives and their mixtures. These properties are important in the design and operation of much of the processing equipment (Poling et al., 2001).

For example, reservoir engineers and process engineers analyze pressure–volume–temperature (PVT) relationships and phase behavior of reservoir fluids (i) to estimate the amount of oil or gas in a reservoir, (ii) to develop a recovery process for a crude oil or gas field, (iii) to determine an optimum operating condition in a gas–liquid separator unit, (iv) to determine the need for a wellhead processing system to protect a pipeline from corrosion, and (v) to design suitable gas processing options. However, the most advanced design approaches or the most sophisticated simulation experiments cannot guarantee the optimum design or operation of a unit (or protection of a pipeline) if the physical properties as determined in an analytical laboratory dictate otherwise. For these reasons accurate knowledge of the properties of the gas is an extremely increasingly important aspect of gas technology. Analysis of the gas during production operations is also an essential practice.

Typically, in field operations, the composition of natural the gas (which affects the specific gravity), especially of associated gas, can vary significantly as the product flowing out of the well can change with variability of the production conditions as well as the change of pressure as gas is removed from the reservoir (Burruss and Ryder, 2003, 2014). Constituents of the gas that were in the liquid phase under the pressure of the reservoir can revert to the gas phase as the reservoir pressure is reduced by gas removal. As a result, it is necessary to collect representative samples of gas from high‐pressure cylinders for analysis by gas chromatography in the laboratory (Chapter 6). In terms of gas analysis, the concept of obtaining a representative sample of the gas for analysis cannot be overstressed (Chapter 6).

1.2.1 History

Natural gas has been known for many centuries, but initial use for the gas was more for religious purposes rather than as a fuel. For example, gas wells were an important aspect of religious life in ancient Persia because of the importance of fire in their religion. In classical times these wells were often flared and must have been, to say the least, awe inspiring (Forbes, 1964). In the current contact, it is perhaps at least as awe inspiring – considering the history of the use of other fossil fuels such as coal and crude oil during the twentieth century – that the use of natural gas is superseding the use of crude oil and coal in many countries. During that time, natural gas was generally flared as a product of limited use until the depletion of crude oil reserves in the late twentieth century caused a back‐and‐forth concern about the future lack of energy‐producing fuels (Speight, 2011a, 2014a; Speight and Islam, 2016).

After the discovery by the Chinese more than 2000 years ago that the energy in natural gas could be harnessed and used as a heat source, the use of natural gas has grown (Mokhatab et al., 2006; Speight, 2007, 2014a). However, the uses of natural gas did not necessarily parallel its discovery, and during recorded historical time, there was little or no understanding of what natural gas was; it posed somewhat of a mystery to man. Sometimes, events such as lightning strikes would ignite natural gas that was escaping from vents through the crust of the Earth. This would create a fire coming from the earth, burning the natural gas as it seeped out from underground. These fires puzzled most early civilizations and were the root of much myth and superstition. One of the most famous of these types of flames was found in ancient Greece, on Mount Parnassus approximately 1000 BC. The (realistic or legendary) story is that a goat herdsman came across what looked like a burning spring, a flame rising from a fissure in the rock. The Greeks, believing it to be of divine origin, built a temple on the flame. This temple housed a priestess who was known as the Oracle of Delphi, giving out prophecies she claimed were inspired by the flame.

These types of gas leaks became prominent in the religions of India, Greece, and Persia where the inhabitants of the region were unable to explain the origin of the fires and regarded the origin of the flames as divine, or supernatural, or both. As a result, the energy value of natural gas was not recognized until approximately 900 BC in China, and the Chinese drilled the first known natural gas well in 211 BC. Crude pipelines (probably state‐of‐the‐art pipelines at the time) were constructed from bamboo stems to transport the gas, where it was used to boil seawater, removing the salt as a residue product, after which the water was condensed and, therefore, drinkable (Abbott, 2016).

Natural gas was discovered and identified in America as early as 1620, when French explorers discovered natives igniting gases that were seeping into and around Lake Erie (Table 1.2). However, Britain was the first country to commercialize the use of natural gas, and in 1785 natural gas produced from coal was used to light houses, as well as streetlights. Manufactured natural gas of this type (as opposed to naturally occurring gas) was first brought to the United States in 1816, when it was used to light the streets of Baltimore, Maryland. This manufactured gas was much less efficient, and less environmentally friendly, than modern natural gas that comes from underground.

Table 1.2 Abbreviated timeline for the use of natural gas.

1620

French missionaries recorded that Indians in what is now New York state ignited gases in the shallows of Lake Erie and in the streams flowing into the lake

1785

HousNNatural gas is introduced for home lighting and streetlighting

1803

Gas lighting system patented in London by Frederick Winsor

1812

First gas company founded in London

1815

Metering for households, invented in 1815 by Samuel Clegg

1816

First US gas company (using manufactured gas) founded in Baltimore

1817

First natural gas from the wellhead used in Fredonia, NY, for house lighting

1840

Fifty or more US cities were burning public utility gas

1850

Thomas Edison postulated replacing gas lighting by electric lighting

1859

Carl Auer von Welsbach in Germany developed a practical gas mantle

1885

Depleted reservoirs are used for the first time to store gas

In 1821 in Fredonia, United States, residents observed gas bubbles rising to the surface from a creek. William Hart, considered as America’s father of natural gas, dug there the first natural gas well in North America (Speight, 2007). In 1859, Colonel Edwin Drake, a former railroad conductor (the origin of the title “Colonel” is unknown but seemed to impress the townspeople), dug the first well. Drake found crude oil and natural gas at 69 ft below the surface of the Earth. More recently, natural gas was discovered because of prospecting for crude oil. However, the gas was often an unwelcome by‐product because, as any gas‐containing reservoirs were tapped during the drilling process, the drillers were forced to discontinue the drilling operations to allow the gas to vent freely into the air. Currently, and particularly after the crude oil shortages of the 1970s, natural gas has become an important source of energy in the world.

1.2.2 Use

Throughout the nineteenth century, natural gas was used almost exclusively as source of light, but because of the lack of any transport infrastructure that prevented the transportation of the gas to distant markets, the use was localized to areas close by where the gas was discovered. However, in 1890 with the invention of leakproof pipeline coupling, transportation of natural gas to long‐distance customers became possible and finally achieved practicality in the early 1920s with additional advances in pipeline technology. Finally, after World War II, the use of natural gas underwent a marked increase as pipeline networks and natural gas storage systems underwent rapid development.

Once the transportation of natural gas was possible over considerable distances, the increased use of natural gas led to innovations from the discovery of new uses for natural gas that included the use of natural gas by industrial consumers. As the use of natural gas has increased and diversified, the need for analysis related to gas composition has also increased. Natural gas has many applications: for domestic use, industrial use, and transportation. In addition, natural gas is also a raw material for many common products such as paints, fertilizer, plastics, antifreeze, dyes, photographic film, medicines, and explosives. Along with these newer uses, there has been an increased need not only for the compositional analysis of natural gas but also for analytical data that provide other information about the behavior of natural gas.

1.2.3 The Need for Analysis

To satisfy the modern use of natural gas, analytical methods are applied to all aspects of gas production and use and include (i) gas in the reservoirs, (ii) associated gas, (iii) nonassociated gas, (iv) unconventional gas, including coalbed methane (CBM), tight shale gas, and gas from gas hydrates, (v) determining the quality of gas reserves; (vi) determining the suitability of the gas for use, (vii) the ability of the gas to conform to regulation, and (viii) the effect of natural gas on the environment.

However, the primary need for analysis of natural gas came with the recognition by the producers and the consumers that natural gas – a product of nature – is a gaseous mixture and that the composition of the gas will differ according to the reservoir from which the gas was produced. While natural gas consists predominantly of methane, with higher molecular weight (MW) hydrocarbon derivatives such as ethane, propane, and butane present as minor constituents, there are also the nonflammable (inert) constituents such as nitrogen, carbon dioxide, water (vapor), and helium. It is these other nonmethane constituents that give rise to the need not only for compositional analysis of the gas but also for the determination of other properties that are relevant to the ultimate use of the gas.

Up to the introduction of gas chromatography in the 1950s, the analysis of natural gas and other fuel gases, such as coal gas (Speight, 2013b) and refinery process gas (Speight, 2014a), was performed using chemical absorption (chemisorption) and/or combustion methods (Speight, 2015a). These methods relied upon the selective absorption of different constituents (either in their original form or after reaction with other chemicals), e.g. carbon dioxide was determined by absorption in a solution of potassium hydroxide (chemisorption) followed by titration to determine the amount of the gas absorbed:

But in the early 1960s, chromatography had replaced the adsorption methods as the major analytical method applied to natural gas and other fuel gases.

Although the specification of the natural gas from a source is typically negotiated between the supplier and the customer, the gas must meet specification that is provided by various governmental and environmental bodies. The main aspects that should be covered include, but are not limited to, (i) properties such as gas quality, heating value, and Wobbe index; (ii) impurities, such as oxygen, inert gases, carbon dioxide, and sulfur compounds; (iii) hydrocarbon dew point, which prevents condensation of hydrocarbon liquids in the pipeline; and (iv) water content, which prevents water dropout and hydrate formation and corrosion in the pipeline.

Each of the categories enumerated in the preceding paragraph requires detailed analysis (and thence knowledge) of the properties of natural gas, and to understand the applicability of the analytical methods, it is helpful for the reader to understand (i) the origin of natural gas; (ii) the production of natural gas; (iii) the transportation of natural gas; (iv) the refining of natural gas, including gas cleaning; and (v) the influence of natural gas on the environment.

First and foremost, although covered in name by a generic term, natural gas varies in composition, and therefore quality, as well as other properties depending on the source of the gas. Therefore, it is essential that gas composition and properties should be determined by a series of standard test methods (Chapter 6) in order to choose and predict a suitable use for the gas. For example, it is often assumed that gases with the same heat content (calorific value [CV], heating value) are interchangeable, but this is not necessarily the case. Since all gas‐fired equipment is designed to operate within a particular range of gas specification, the use of gases outside this range can lead to a range of issues from poor quality combustion to equipment damage and ultimately dangerous operation. As a result, gas interchangeability relates to more than just a parameter for the heat content. In fact, interchangeability is governed by a general umbrella property often referred to as gas quality, which is, in turn, a function of gas composition and specific gravity as well as any other property (or properties) that are relevant to the use of the gas. Thus, the essence of natural gas interchangeability relies on knowledge of the necessary properties of the gas, which are derived from application of a series of standard test methods that are accepted on an international basis.

The various purposes to be served by the analytical data and the necessary accuracy with which each constituent of each type of gas must be known in order to serve each specific purpose are then estimated. These estimates afford the first criterion by means of which the suitability of analytical methods and apparatus may be judged, but they are subject to revision when more is known about the limiting attainable accuracies of the analytical methods (Shepherd, 1947). Thus, because of the worldwide use of natural gas and the potential for gas from different wells to vary in composition, there is a need to apply a series of standard test to the gas in order that it can meet sales specifications (Table 1.3).

Table 1.3 Examples of standard test methods for natural gas (ASTM, 2017).

ASTM D1070 Standard Test Methods for Relative Density of Gaseous Fuels

ASTM D1071 Standard Test Methods for Volumetric Measurement of Gaseous Fuel Samples

ASTM D1072 Standard Test Method for Total Sulfur in Fuel Gases

ASTM D1142 Standard Test Method for Water Vapor Content of Gaseous Fuels by Measurement of Dew‐Point Temperature

ASTM D1826 Standard Test Method for Calorific (Heating) Value of Gases in Natural Gas Range by Continuous Recording Calorimeter

ASTM D1945 Standard Test Method for Analysis of Natural Gas by Gas Chromatography

ASTM D1946 Standard Practice for Analysis of Reformed Gas by Gas Chromatography

ASTM D1988 Standard Test Method for Mercaptans in Natural Gas Using Length‐of‐Stain Detector Tubes

ASTM D3588 Standard Practice for Calculating Heat Value, Compressibility Factor, and Relative Density of Gaseous Fuels

ASTM D4084 Standard Test Method for Analysis of Hydrogen Sulfide in Gaseous Fuels (Lead Acetate Reaction Rate Method)

ASTM D4150 Standard Terminology Relating to Gaseous Fuels

ASTM D4810 Standard Test Method for Hydrogen Sulfide in Natural Gas

ASTM D4891 Standard Test Method for Heating Value of Gases in Natural Gas Range by Stoichiometric Combustion

ASTM D4984 Standard Test Method for Carbon Dioxide in Natural Gas Using Length‐of‐Stain Detector Tubes

ASTM D5287 Standard Practice for Automatic Sampling of Gaseous Fuels

ASTM D5454 Standard Test Method for Water Vapor Content of Gaseous Fuels Using Electronic Moisture Analyzers

ASTM D5503 Standard Practice for Natural Gas Sample‐Handling and Conditioning Systems for Pipeline Instrumentation

ASTM D5504 Standard Test Method for Determination of Sulfur Compounds in Natural Gas and Gaseous Fuels by Gas Chromatography and Chemiluminescence

ASTM D5954 Standard Test Method for Mercury Sampling and Measurement in Natural Gas by Atomic Absorption Spectroscopy

ASTM D6228 Standard Test Method for Determination of Sulfur Compounds in Natural Gas and Gaseous Fuels by Gas Chromatography and Flame Photometric Detection

ASTM D6273 Standard Test Methods for Natural Gas Odor Intensity

ASTM D6350 Standard Test Method for Mercury Sampling and Analysis in Natural Gas by Atomic Fluorescence Spectroscopy

Gases analyzed include hydrocarbon derivatives (C1–C6+) such as methane, ethane, propane, isobutane, n‐butane, isopentane, n‐pentane, and hexane, plus higher MW hydrocarbon derivative. Nonhydrocarbon impurities include hydrogen, nitrogen, carbon monoxide, carbon dioxide, oxygen, mercury, sulfur‐containing compounds such as hydrogen sulfide and thiols (also called mercaptans, R ─ SH), and water. As an example of the need for a standard test method, natural gas composition analysis is applied to all phases of natural gas exploration and production, from the reservoir to recovery at the wellhead, initial processing prior to transportation, processing, storage, and distribution as well as liquefied natural gas‐related activities. Natural gas composition includes testing for the following:

Methane, CH

4

Ethane, C

2

H

6

Propane, C

3

H

8

Butane, C

4

H

10

Carbon dioxide, CO

2

Oxygen, O

2

Nitrogen, N

2

Hydrogen sulfide, H

2

S

Thiols (mercaptans), RSH

Trace of rare gases

Trace metals

Because of the presence of the nonmethane constituents, the energy density of the gas also differs. Since delivery of natural gas to the consumer is billed according to the energy quantities calculated from the gas analysis and the measured volume of gas, it is essential to analyze the gas composition as accurately as possible.

Moreover, the analysis of natural gas is carried out for many reasons: (i) identification of specific constituents, commonly minor constituents such as odorants, (ii) identification of the source of the gas either by fingerprinting or by molar composition, (iii) the application areas of increasing importance such as calculation (or estimation) of physical properties, and (iv) the measurement of gas quality when compared to the specification for use. However, the amount of detail that is required from the analysis depends upon the reason for the analysis, i.e. identification of source of the gas by molar composition might be done in some circumstances by an analysis up to pentane with a composite number for the presence of the higher MW hydrocarbon derivatives (such as the hexane and hydrocarbon derivatives up to, and including, C8 or C10 hydrocarbon derivatives). Such data may also be suitable for estimation of the CV, assuming a single bulk contribution to the CV from this higher MW group (Chapter 6).

Direct methods of measurement of physical properties, particularly CV and relative density, are common and in some cases mandatory (Chapter 6). Chromatographic analysis followed by calculation of a property is a popular alternative for several reasons: (i) the apparatus is relatively inexpensive, (ii) the analysis will show why a change in property has occurred in addition to measuring the change, and (iii) a sufficiently detailed analysis allows several properties to be calculated at the same time. Nevertheless, the investigator should be aware of the risks of the use of average values, which may produce data that are not truly representative of the behavior of the gas mixture. Furthermore, in the case of property calculations related to phase changes, such as the hydrocarbon dew point, much more detail is needed about the distribution of the higher MW hydrocarbon derivatives. Briefly, the dew point is the temperature to which a given volume of gas must be cooled, at constant barometric pressure, for vapor to condense into liquid. Thus, the dew point is the saturation point that will vary as the carbon number of the hydrocarbon increases or decreases, thereby leading to results that are not consistent with the true behavior of the gas.

In summary, natural gas testing includes the analysis of conventional and shale gas, liquefied natural gas, and other hydrocarbon condensates and components (ASTM, 2017). The standard test methods that are cited within this book are, for convenience, the standard test methods developed by ASTM International (formerly the American Society for Testing and Materials) (ASTM, 2017). For example, standard test methods that might be used or consulted for comparison are (i) the British Standards (BS), which are the standards produced by BSI Group, located in Chiswick, London, which is incorporated under a Royal Charter and is formally designated as the national standards body (NSB) for the United Kingdom; (ii) the International Organization for Standardization (ISO), located in Geneva, Switzerland; and (iii) the German Institute for Standardization (DIN), located in Berlin, Germany, which publishes a variety of test methods that are applicable to determining the properties and behavior of natural gas and processed gases. Other organizations are available in several countries (Table 1.4) that might also be consulted as source of standard test methods.

Table 1.4 Examples of standards organizations in various countries (listed alphabetically).

Organization

Acronym

Country

American National Standards Institute

ANSI

United States

Badan Standardisasi Nasional

BSN

Indonesia

Brazilian National Standards Organization

ABNT

Brazil

British Standards Institution

BSI

United Kingdom

Bureau of Indian Standards

BIS

India

Bureau of Standards Jamaica

BSJ

Jamaica

Colombian Institute of Technical Standards and Certification

ICONTEC

Colombia

Deutsches Institut für Normung

DIN

Germany

Dirección General de Normas

DGN

Mexico

Ente nazionale italiano di unificazione

UNI

Italy

Estonian Centre for Standardisation

EVS

Estonia

Euro‐Asian Council for Standardization, Metrology and Certification

GOST

Russia (Soviet Union)

Finnish Standards Association

SFS

Finland

French Association for Standardization

AFNOR

France

Instituto Argentino de Normalización y Certificación

IRAM

Argentina

Instituto Português da Qualidade

IPQ

Portugal

Japanese Industrial Standards Committee

JISC

Japan

Jabatan Standard Malaysia

DSM

Malaysia

Korean Agency for Technology and Standards

KATS

Korea (Republic)

Luxembourg Institute for Standardization

ILNAS

Luxembourg

Nederlandse Norm

NEN

Netherlands

Romanian Standards Association

ASRO

Romania

South African Bureau of Standards

SABS

South Africa

Spanish Association for Standardization and Certification

AENOR

Spain

Standardization Administration of China

SAC

China

Standards Australia

SAI

Australia

Standards Council of Canada

SCC

Canada

Standards New Zealand

SNZ

New Zealand

Standards Norway

SN

Norway

Standards Organisation of Nigeria

SON

Nigeria

Swedish Standards Institute

SIS

Sweden

Swiss Association for Standardization

SNV

Switzerland

However, the application of standard test methods need not (or does not) typically end with analysis of the gas. The mineralogy of the reservoir can (and often does) play a major role in the ability of the gas to be produced at the wellhead. Thus, there may be a need for the mineralogical analysis of samples of the reservoir rock.

1.3 Reservoirs

Natural gas is derived from aquatic plants and animals that lived and died hundreds of millions of years ago. Their remains mixed with mud and sand in layered deposits that, over the millennia, were geologically transformed into sedimentary rock. Gradually the organic matter decomposed and eventually formed petroleum (or a related precursor), which migrated from the original source beds to more porous and permeable rocks, such as sandstone and siltstone, where it finally became entrapped. Such entrapped accumulations of petroleum are called reservoirs. A series of reservoirs within a common rock structure or a series of reservoirs in separate but neighboring formations is commonly referred to as an oil field. A group of fields is often found in a single geologic environment known as a sedimentary basin or province.

When a hydrocarbon reservoir is identified, it is important to also identify the types of fluids that are present, along with their main physicochemical characteristics. Generally, that information is obtained by performing a PVT analysis on a fluid sample of the reservoir. Conventional production measurements, such as a drill stem test (DST), are the typical parameters that can be measured almost immediately after a well is completed, as well as to obtain preliminary values of properties such as molar percentage of heptane and heavier components (% mole of C7+), MW of the original fluid, maximum retrograde condensation (MRC), and dew‐point pressure (Pd