125285214 Crude Oil Analysis

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ISBN: 978-0-8031-7014-8Stock #: MNL68

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Crude Oils Their Sampling, Analysis, and Evaluation

Harry N. Giles and Clifford O. Mills

Harry N. Giles is retired from the Department of Energy where he was manager of crude oil quality programs for the Strategic Petroleum Reserve. This included development and management of analytical programs for monitoring quality of stocks, and research relat-ed to the biological and geochemi-cal aspects of petroleum stockpiling.

He was employed by the Department of Energy for over 30 years, prior to which he held several positions with other U. S. Government agencies and at the University of Manchester (UK). He has authored or co-authored a number of articles on crude oil analysis, characterization, and storage, and on fuel stability and cleanliness. Mr. Giles has been involved with ASTM Committee D02 on Petroleum Products and Lubricants since the 1980s. He is past chairman of Subcom-mittee D02.14 on Fuel Stability and Cleanliness. He remains active in Subcommittees D02.02, D02.08, D02.14, and D02.EO., and is a technical advisor to ASTM for their Crude Oil Interlaboratory Crosscheck Program (ILCP). In 2005, he and Clifford Mills developed the ASTM training course on Crude Oil: Sampling, Testing, and Evaluation. In 2009, he received the ASTM International George V. Dyroff Award of Honorary Committee D02 Membership. Other memberships include API Committee on Measurement Quality, and IASH, the Inter-national Association for Stability, Handling, and Use of Liquid Fuels. He is chairman emeritus of IASH, and was elected to honorary membership in 2009. Currently, he serves as Executive Director of the Crude Oil Quality Association.

Clifford O. Mills is retired from CONOCO where he served in numerous capacities. At retire-ment, after 35 years, he was a labo-ratory consultant with an emphasis on crude oil analysis. Mr. Mills has been involved with ASTM methods development since the early 1980s. Until recently, he was chairman of ASTM D02.05 on Properties of

Fuels, Petroleum Coke and Carbon Material, and also chaired D02.H0 on LP-Gases for several years. He continues to be active in D02.03, D02.04, D02.05, D02.06 and D02.H0. Mr. Mills has been actively involved in development of numer-ous ASTM methods of analysis. Together with Mr. Giles, he serves as technical advisor to ASTM for their Crude Oil ILCP. For several years, Mr. Mills served as co-instructor for the crude oil training course and, together with Mr. Giles, presented this at numerous locations worldwide. He is a member of the Crude Oil Quality Association, and author of an authoritative paper on crude contaminants and analysis requirements presented at one of their meetings. This paper is now widely referenced and used as an instructional aid. In 2009, he received the ASTM International George V. Dyroff Award of Honorary Committee D02 Membership.

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Crude Oils: Their Sampling, Analysis,and Evaluation

Harry N. Giles and Clifford O. Mills

ASTM Stock Number: MNL68




Library of Congress Cataloging-in-Publication Data

Giles, Harry N.Crude oils: their sampling, analysis, and evaluation/Harry N. Giles and Clifford O. Mills.

p. cm.Includes bibliographical references and index.ISBN: 978-0-8031-7014-8

1. PetroleumAnalysis. I. Mills, Clifford O. II. Title.TP691.G545 2010665.5dc22 2010031882

Copyright 2010 ASTM International, West Conshohocken, PA. All rights reserved. This material may not be repro-duced or copied, in whole or in part, in any printed, mechanical, electronic, film, or other distribution and storagemedia, without the written consent of the publisher.

Photocopy RightsAuthorization to photocopy items for internal, personal, or educational classroom use of specific clients is granted byASTM International provided that the appropriate fee is paid to ASTM International, 100 Barr Harbor Drive, PO BoxC700. West Conshohocken, PA 19428-2959, Tel: 610-832-9634; online: http://www.astm.org/copyright/

ASTM International is not responsible, as a body, for the statements and opinions advanced in the publication. ASTMdoes not endorse any products represented in this publication.

Printed in Newburyport, MANovember, 2010

ii




ForewordTHIS PUBLICATION, Crude Oils: Their Sampling, Analysis, and Evaluation, was sponsored by ASTM com-mittee D02 on Petroleum Products and Lubricants. The authors are Harry N. Giles, Consultant, 2324 N.Dickerson Street, Arlington, Virginia 22207 and Clifford O. Mills, Consultant, 1971 E. Tower Road, PoncaCity, Oklahoma 74604. This is Manual 68 in the ASTM International manual series.

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AcknowledgmentsThis manual is based on the ASTM International Technicaland Professional Training Course of the same name that hasbeen taught by the authors at several locations worldwidenumerous times since 2005. This manual would not havebeen possible without the support and encouragement ofmany of our colleagues and participants in the course. Weare grateful to many individuals and companies for provid-ing us some of the material included herein. We appreciatetheir willingness to share this information because it makesour task easier illustrating some of the topics. The followingindividuals and companies provided some of the materialincluded in this course: Baker Hughes and Larry Kremer;Canadian Crude Quality Technical Association and AndreLemieux; Chevron Energy Technology Company and Anne Sha-fizadeh; Crude Oil Quality Association; DynMcDermott Petro-leum Operating Co.; Google and the WorldWideWeb;

Intertek; KBW Process Engineers; Koehler Instruments; ArdenStrycker, Northrop Grumman Mission Systems; Patrice Per-kins, PetroTech Intel; Professor G. Ali Mansoori, Universityof IllinoisChicago; Professor Bahman Tohidi, Institute ofPetroleum Engineering; Heriot-Watt University; Dan Villa-lanti, Triton Analytics; Anne Brackett Walker, W. L. WalkerCo.; and David Fish, Welker Engineering. We apologize ifwe neglected to mention someone that has assisted us; thisis not intentional. Dr. Arden Strycker of Northrop Grum-man Mission Systems kindly reviewed the manuscript andprovided many valuable comments that helped us improvethe contents. We also thank the staff at ASTM Interna-tional, who helped in making the course a reality, and themembers of the Publications Department for their guid-ance, support, and, most of all, their patience during thepreparation of this manual.

Harry N. GilesArlington, VA

Clifford O. MillsPonca City, OK

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ContentsGlossary of Terms. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ix

Chapter 1: Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

Brief History of Crude Oil Exploitation and Use . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

Strategic Importance of Crude Oil . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

Chapter 2: Sampling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

Manual Sampling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

Automatic Sampling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

Sampling for Vapor Pressure Determination . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

Mixing and Handling of Samples . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

Sample Chain of Custody . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

Sample Archive . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

Chapter 3: Inspection Assays . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

API Gravity and Density . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

Sulfur Content . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

Water and Sediment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

Salt Content . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

FluidityPour Point and Viscosity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

Vapor Pressure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

Total Acid Number . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

Carbon Residue . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

Characterization Factor. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

Trace Elements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18

Nitrogen Content . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20

Organic Halides . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

Asphaltenes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

Boiling Point Distribution . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22

Other Tests. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23

Referee Test Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24

Chapter 4: Comprehensive Assays and Fraction Evaluations. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25

True Boiling Point Distillation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25

Gas. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27

Naphtha Fractions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27

Kerosine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27

Distillate Fuel Oil . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27

Vacuum Gas Oil Fractions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30

Residuum . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30

Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30

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Chapter 5: Quality Assurance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32

Chapter 6: Crude Oil Compatibility and Stability . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34

Asphaltenes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34

Waxes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34

Chapter 7: Crude Oil as Fuel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37

Chapter 8: Future Needs in Crude Oil Characterization. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38

Appendix 1: Procedures for Collection of Samples for Hydrogen Sulfide Determination . . . . . . . . . . . . . . . . . . . 40

Appendix 2: Referenced ASTM and Other Standards . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41

Appendix 3: Excerpts from Standards Used for Sampling, Handling, and Analysis . . . . . . . . . . . . . . . . . . . . . . . . 44

References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 64

Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 67

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Glossary of TermsAdditivesSubstance added to a crude oil stream in rela-tively minor amounts to facilitate its production and trans-portation and minimize adverse effects on equipment. Theseinclude pour point depressants, drag reducing agents, demul-sifiers, and corrosion inhibitors.

API gravityA special function of relative density (specificgravity) 60/60F, represented by:

API = 141.5/(specific gravity 60/60F) 131.5[ASTM D1298]

AssayA combination of physical and chemical data thatuniquely describe a crude oil.

BitumenA category of crude oil that is black, highly viscous,and semisolid at normal temperatures, will not flow withoutdilution, and generally has an API of less than 10.

Challenging (or challenged) crudeSee Opportunity crude.

CompatibilityThe capacity of two or more crude oils to becommingled without asphaltenes or waxes precipitating or floc-culating out of the mixture.

CondensateLiquid mixture usually recovered from naturalgas consisting primarily of hydrocarbons from approximatelyC6C12-15, and having an API gravity greater than 45. The mix-ture may also contain hydrogen sulfide, thiols, carbon dioxide,and nitrogen. Some consider condensate to be a light, sweetcrude oil. Other terms include gas condensate, natural gasliquids, lease condensate, and natural gasoline.

ContaminantAny material added to a crude oil stream thatis not naturally occurring or exceeds the concentration nor-mally present.

Crude oilNaturally occurring hydrocarbon mixture, generallyin a liquid state, which may also contain compounds of sulfur,nitrogen, oxygen, metals, and other elements. [ASTM D4175]

DegradationA lessening in quality of a crude oil stream com-monly resulting frommixing of another stream of poorer quality.Degradation of a crude oil can also result from biological activity.

DifferentiationNatural development of a density differentialfrom top to bottom in a storage container. Cf. Stratification.

ImpurityNonhydrocarbons naturally occurring in crude oil.These typically include sediment; water; salts; organic acids;heteroatomic compounds of sulfur, nitrogen, and oxygen;and metalsparticularly nickel and V.

IncompatibilityAgglomeration or flocculation of asphal-tenes, waxes, or both from a mixture of two or more crudeoils. Cf. Compatibility.

Opportunity crudeA crude oil priced below market value.An opportunity crude may be production from a new fieldwith little or no processing history, a distressed cargo, or acrude oil with a known history that reduces refinery profit-ability. This latter can result from the crude having a hightotal acid number, sulfur content, and/or metals, problem-atic contaminants, or is difficult to upgrade or has unattrac-tive yields.

Referee test methodAn analytical method designated in test-ing protocols to be used in case of disputes.

Relative density (specific gravity)The ratio of the mass of agiven volume of liquid at a specific temperature to the massof an equal volume of pure water at the same or differenttemperature. Both reference temperatures must be explicitlystated. [ASTM D1298]

Representative sampleA portion extracted from a total vol-ume that contains the constituents in the same proportionas are present in the total volume. [ASTM D4057]

SamplingAll the steps required to obtain an aliquot repre-sentative of the contents of any tank, pipe, or other systemand to place the sample into a suitable laboratory samplecontainer. [ASTM D6470]

Slop oilA combination of off-specification fuel, water, refin-ery wastes, and transmix. Slop oil is usually processed in thegenerating refinery but is occasionally exported or shippeddomestically for use as an inexpensive feedstock for process-ing in atmospheric units.

StabilityThe ability of a crude oil when produced, trans-ported, and/or stored to endure without physical or chemicalchange, such as flocculation or precipitation of asphaltenesand/or waxes.

StratificationThe intentional layering of different crudes oilsin a storage container taking advantage of differences in theirdensity. Cf. Differentiation.

Synthetic crude oilStream derived by upgrading oil-sandsbitumen and extra-heavy crude oil. Upgrading processes includehydroprocessing and coking to yield a more fungible, lighter,less viscous stream.

TransmixTransportation mixture is the material present atthe interface between different quality crude oils batched ina common carrier pipeline system. Generally, at a terminal,the mixture will be relegated to the lower quality crude oil.

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1Introduction

This manual is intended for whoever is involved with sam-pling and analysis of crude oils after they are produced andstabilized; essentially the mid- and downstream sectors of theindustry. They will be the operators of pipelines and tankersthat transport the crude oil, the terminals that temporarilystore it, laboratory personnel that are responsible for itscharacterization, refiners that eventually process it, and trad-ers responsible for its sale or acquisition.

Crude oils are a highly complex combination of hydro-carbons; heterocyclic compounds of nitrogen, oxygen, andsulfur; organometallic compounds; inorganic sediment; andwater. More than 600 different hydrocarbons have been pos-itively identified in crude oil, and it is likely that thousandsof compounds occur, many of which probably will never beidentified. In a study sponsored by the American PetroleumInstitute (API) in the 1960s, nearly 300 individual hydrocar-bons were identified in Ponca City, Oklahoma, crude oil [1,2].In another API project beginning in the 1950s, some 200 indi-vidual sulfur compounds were identified in a 20-year system-atic study of four crude oils [3]. In the ensuing 50+ years,hundreds, and perhaps thousands, of other hydrocarbons andsulfur compounds have been identified using increasinglymore sophisticated instrumentation. Not only is the composi-tion of crude oil highly complex, it is also highly variable fromfield to field, and even within a given field it is likely to exhibitinhomogeneity from reservoir to reservoir. Physical and chemi-cal characterization of this complex mixture is further compli-cated for the analyst by the fact that crude oils are not puresolutions but commonly contain colloidally suspended compo-nents, dispersed solids, and emulsified water.

Compared with refined products such as gasoline andaviation turbine fuel, there is relatively little in the literatureon the analysis and characterization of crude oils. Indeed, formany years, there were relatively few ASTM methods specificto crude oils, although several ASTM methods had beenadapted for their analysis. This situation may have resulted,at least in part, from the historical tendency of refinerychemists to independently develop or modify analytical meth-ods specific to their needs and, subsequently, for the methodsto become company proprietary. In recent years, the uniqueproblems associated with sampling and analysis of crude oilshave received more attention, and more methods for determin-ing selected constituents and characteristics of crude oils havebeen standardized.

A series of articles [4-9] illustrates the diversity of crudeoil assay practices used by major refiners in the United Statesand Austria. The dissimilarity of published results [10] and asprovided by several companies on their Web sites [11] is areflection of this independent development of analyticalschemes, although standardized approaches to crude oil analy-sis have been published [12-15]. Despite the complexity of crudeoil composition and the diversity of analytical methodology,

probably more crude oil analyses are routinely performedon a daily basis using inherently similar methods than areanalyses on any single refined petroleum product except, possi-bly, gasoline.

The overriding issue when performing comprehensivecrude oil assays is economics. Crude oils are assayed todetermine (a) the slate of products that can be producedwith a given refinerys process technology, (b) the processingdifficulties that may arise as a result of inherent impuritiesand contaminants, and (c) the downstream processing andupgrading that may be necessary to optimize yields of high-value specification products. Today, analytical data are typi-cally stored in electronic databases that can be accessed bycomputer models that generate refinery-specific economicvaluations of each crude oil or crude slate; that is, a mixtureof crude oils processed together. Linear programming (LP)models are available from several commercial vendors, butseveral companies have developed their own models to meetthe needs of their specific refinery configurations.

Analyses are also performed to determine whether eachbatch of crude oil received at a terminal or the refinery gatemeets expectations. Can the crude oil be commingled into acommon stream pipeline system, or does it need to be batched?Does the crude receipt match the database assay so that theprojected economic valuations and operational strategies arevalid? Has any unintentional contamination or purposeful adul-teration occurred during gathering, storage, or transport of thecrude oil that may increase the processing cost or decrease thevalue of the refined products? The information needed toanswer these questions is often refinery-specifica function ofthe refinerys operating constraints and product slateand, al-most certainly, has considerable financial consequences.

To obtain the desired information, two different analyti-cal schemes are commonly used; namely, an inspection assayand a comprehensive assay. Inspection assays usually involvedetermination of a few key whole crude oil properties suchas API gravity, sulfur content, and pour pointprincipally asa means of determining if major changes in a crude oilstreams characteristics have occurred since the last compre-hensive assay was performed. Additional analyses may beperformed to help ensure that the quality of the cargo orshipment received is that which is expected; to ascertain thequantity of impurities such as salt, sediment, and water; andto provide other critical refinery-specific information. Inspec-tion assays are routinely performed on all shipments receivedat a terminal or refinery. On the other hand, the comprehen-sive assay is complex, costly, and time-consuming and is nor-mally performed only when a new field comes on stream forwhich a company has an equity interest, a crude that has notpreviously been processed arrives at a refinery, or when theinspection assay indicates that significant changes in the streamscomposition have occurred. Except for these circumstances,

1

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a comprehensive assay of a particular crude oil stream maynot be updated for several years.

Moreover, many major pipeline companies require a com-prehensive assay when accepting a new crude oil stream fortransportation in their system on a common stream basis.Thereafter, an inspection assay is used for checking the qual-ity of shipments.

BRIEF HISTORY OF CRUDE OILEXPLOITATION AND USEHerodotus, the ancient Greek historian, recorded about 440BCE that the Mesopotamians in 40th century BCE used bitu-men to caulk their ships and as an adhesive [16]. This isthought to be the first recorded use of petroleum by a civili-zation. Herodotus also recorded that beginning about 1000BCE, the ancient Egyptians used crude oil or a derivative intheir mummification process. The term mummy is derivedfrom the Persian word mummeia, meaning pitch or asphalt.Many ancient civilizations including those of the Persians andSumerians used bitumen for medicinal purposes, a practicealso known to have been used by pre-Columbian cultures inthe Americas. Further documentation of the medicinal uses ofpetroleum was provided by Georgius Agricola, the 16th cen-tury German physician and scientist in his De Natura Fossil-ium [17]. In that, he reported that It is used in medicine Spread on cattle and beasts of burden it cures mange andPliny writes that the Babylonians believed it to be good forjaundice They also believed it to be a cure for leprosy (and)it is used as an ointment for the gout. In this latter respect, ithas been reported by several writers that, in 1539, oil in someform was exported from Venezuela to Spain for use in treatinggout suffered by the Holy Roman emperor Charles V. In hisTravels, Marco Polo wrote of its use in the 13th century inthe Caspian Sea region to treat mange in camels and as a ther-apeutic ointment for various skin conditions in humans [18].From the writings of Agricola and others on the medicinal vir-tues of petroleum, it is no wonder that centuries later snake oilsalesmen were so successful in marketing their concoctionsmany of which contained crude oil or some derivative.

The earliest known oil wells were drilled in China in347 CE to depths of as much as 240 m using bits attachedto bamboo shafts. In 1594, a well was hand dug near Baku,Azerbaijan to a depth of 35 m [19]. Hand dug wells contin-ued to be used in Azerbaijan until the mid-19th century forrecovery of crude oil [18].

The modern history of petroleum perhaps dates from1846 when Abraham Gesner developed a process for extractingwhat he termed keroselain from coal [20]. In 1853, IgnacyLukasiewicz, a Polish pharmacist, made improvements to Ges-ners process and used it to distill kerosene from seep oil [21].In 1854, Benjamin Silliman, a chemist and professor of sci-ence at Yale University, became the first person known to frac-tionate petroleum by distillation. This was followed in 1855 byhis Report on the Rock Oil, or Petroleum, from Venango Co.,PA, with special reference to its use for illumination and otherpurposes [22]. In this, he documented that half of the crude oilhe studied could be economically exploited as an illuminant andthat much of the remaining byproducts had commercial value.

The first commercial oil discovery in North American wasmade in 1858 in Ontario, Canada, when a 3-m deep hand dugpit encountered a pool of crude oil. This predated by one yearthe more famous well drilled by Colonel Edwin Drake nearTitusville, Pennsylvania, to a depth of 21 m. Following Drakes

success, Sillimans report became an important document inpromoting commercial development at Titusville, which islocated in Venango County.

Thereafter, developments in the petroleum industryspread worldwide but were most prevalent in North Americaand in the Caspian Sea region. Many significant developmentsin the exploitation and use of crude oil took place in Azerbai-jan and Russia in the mid- to late 19th century. Azerbaijan isthe oldest known oil-producing region in the world, and itwas there that Russian engineer F. N. Semyenov drilled thefirst modern oil well in 1848. The first offshore well was alsodrilled in the Azerbaijan area of the Caspian Sea at the endof the 19th century [23]. Ludvig and Robert Nobel, brothersof Alfred, the inventor of dynamite and benefactor of hisnamesake Nobel Prize, were responsible for considerable devel-opment of Azerbaijans petroleum resources and for severaltechnological advances. Beginning in 1877, they had a fleetof tankers, several railway tank cars, and a pipeline built fortransporting crude oil. The brothers introduced the use oftanks to store crude oil, rather than in the commonly usedopen vessels and pits [24]. This practice resulted in large lossesthrough evaporation and oil penetrating into the ground andsignificant ecological damage that persisted for decades. By1900, Azerbaijan was the worlds largest producer of crude oil.

Totten provides a comprehensive timeline of the impor-tant events in the history of the petroleum industry fromancient times to the present [19]. Table 1 provides a summaryof some of the highlights in ancient and modern exploitationand use of crude oil.

Zayn Bilkadi, in his introduction to Babylon to Baku[25], accurately portrayed the importance of petroleum intodays world.

There is one natural material which touches almostevery facet of our lives; it assists us to travel long dis-tances, it is an ingredient in many of our medicines, itis used in the manufacture of our clothes and in themicrochips we build into our computers. In fact, it isessential to our daily existence.

That material is, of course, crude oil.A few of the superlatives that can be attributed to crude

oil are Volume produced each day worldwide is sufficient to

fill a string of railroad tank cars over 2100 km in length Basis of worlds first trillion dollar industry Worlds most actively traded commodity Largest single item in balance of payments and exchanges

between nations Employs most of worlds commercial shipping tonnage More than 1 million km of pipelines are dedicated to its

transportation

STRATEGIC IMPORTANCE OF CRUDE OILEarly in the 20th century, Winston Churchill successfullyargued that the British Navy should switch from coal topetroleum to power its warships [26]. In 1907, the Oil & GasJournal in an article titled When Will the United StatesNavy Wake Up! reported on the British Admiralty convert-ing its warships from use of coal to crude oil as fuel [27].The article went on to state that Japan is also aware of thefact that coal is so scarce in (the Pacific Ocean) that the usecrude oil as fuel is absolutely imperative to insure success or

2 CRUDE OILS: THEIR SAMPLING, ANALYSIS, AND EVALUATION




victory (in naval operations). The article noted that U.S.Navy Department reports demonstrated conclusively thesuperiority of crude oil over coal as a fuel. In 1910, withpassage of the Picket Act and support of President WilliamHoward Taft, the United States withdrew oil-bearing lands inCalifornia and Wyoming as sources of fuel for the U.S. Navy.These later became known as Naval Petroleum Reserves. Inthis case, the crude oilwhen neededwould be used to pro-duce Navy Special Fuel Oila heavy fuel oil analogous toNo. 5 burner fuelrather than for direct burning.

In 1919, a German patent was issued to Deutsche ErdolAG for underground storage of petroleum in caverns in saltbeds [28]. At that time, it is likely that little attention wasgiven to its strategic potentialpresent or future. The firstknown use of this technology was in 1950, when a solution-mined cavern in salt was used for operational storage of pro-pane and butane in the Keystone Field in western Texas.

In the years leading up to World War II, several coun-tries, including Sweden and Britain, began stockpiling refinedproducts such as aviation gasolinebut apparently not crudeoil. After its entry into World War II, some senior U.S. politi-cians recognized the strategic importance of crude oil. InDecember 1943, Secretary of the Interior Harold Ickes wrotean article Were Running out of Oil in which he warned ifthere should be a World War III it would have to be foughtwith some elses petroleum, because the United States wouldnthave it. [29,30]. In 1944, Ickes called for the stockpiling ofcrude oil, but no action was taken. Then in 1952, PresidentHarry S Trumans Minerals Policy Commission advocated astrategic oil supply. After the Suez Crisis in 1956, Britain beganstoring crude oil and refined products in solution-mined cav-erns in salt, and President Eisenhower recommended creationof a reserve in the United States. In support of Presidents Tru-man and Eisenhower, the U.S. National Petroleum Council sub-mitted reports promoting the practicality of petroleum reserves.

The large-scale creation of petroleum stockpiles began inthe late 1960s. From 1967 to 1972, France, Germany, Japan,and others commenced stockpiling crude oil and refined prod-ucts in aboveground tanks, underground caverns, and tankships. The United States did not begin stockpiling crude oiluntil after the Arab Oil Embargo of 19731974 when it createdthe Strategic Petroleum Reserve. From 1980 through the pres-ent, there has been a global proliferation of stockpiles [31].Among the major countries currently having or currently devel-oping crude oil stockpiles are Austria, France, Germany, India,Japan, the Netherlands, Spain, Peoples Republic of China,Republic of Korea, and the United States. In 2008, the U.S.Energy Information Administration estimated that over 4 bil-lion barrels of petroleum reserves existed worldwide, withcrude oil comprising somewhat more than half of the total.

Developments in Analysis of Crude OilBenjamin Silliman, professor of chemistry at Yale University, isprobably the father of crude oil analytical chemistry. In late1854, he was sent three barrels of rock oil skimmed from OilCreek in Venango County, Pennsylvania. Over the next 5 monthshe conducted several tests during which he developed a tech-nique that today is known as fractional distillation. Using this, herefined the rock oil and separated it into eight fractions. In hisreport, Silliman described the general properties of the oil andthose of the fractions he had distilled and collected. He deter-mined the boiling range of each and their specific gravity [22].This likely is the first assay of a crude oil every published.

TABLE 1Historical highlights in exploitationand use of crude oil.

Year Event

40th century BCE Mesopotamians use bitumen to caulkships and as an adhesive

1000300 BCE Egyptians use a derivative of crude oilin mummification

2500 BCE1400 CE Crude oil used for medicinal purposesby many Eurasian and westernhemisphere cultures

347 CE Wells drilled in China to depth of240 m using bits attached to bambooshafts

13th century CE Marco Polo in his Travels records itbeing used to treat mange in camelsand as a therapeutic ointment byhumans in the Caspian Sea region

1539 Exported from Venezuela to Spain totreat gout in HRE Charles V

1594 Well hand dug in Azerbaijan to depthof 35 m

1846 Gessner develops process for extractingkeroselain from coal

1853 Lukasiewicz distills kerosene fromseep oil

1855 Silliman publishes his Report on theRock Oil, or Petroleum, from VenangoCo., PA . . .. This is the first knowncrude oil assay.

1859 Col. Drake drills successful well atTitusville, PA

1863 2 diameter cast iron pipeline built atTitusville to transport crude oil 2 1=2 mi

18731890 Nobel brothers develop Azerbaijanspetroleum resources and implementnumerous technological advancesrelated to production, storage, andtransportation

1886 Benz patents carriage with gasolineengine

1891 Thermal cracking process patented byRussian engineer V. Shukhov

1892 Patent issued in Germany for internalcompression (diesel) engine

19141918 Large scale demand created forpetroleum products mostly gasoline

1936 Catalytic cracking process developed byEugene Houdry of Sun Oil Co.

19421943 The Big Inch a 24 diameter pipelinebuilt to transport crude oil from EastTexas to refineries at Linden, NJ andPhiladelphia

CHAPTER 1 n INTRODUCTION 3




Sillimans report was followed just 1 year later by areport that dealt with the artificial destructive distillationand characterization of Burmese Naphtha, or Rangoon Tar[32]. In this, it was noted that the material contains indeedso great a variety of substances, and some of them in soexceedingly minute a proportion, that even the large amountof material at our disposal was insufficient for the completeexamination of several constituents, the presence of whichwe had succeeded in establishing beyond a doubt. In thecourse of the investigation, several aromatic compoundswere separated and studied in great detail.

By the end of the 19th century, great strides had beenmade in determining the composition of crude oil, mostlyby Russian scientists and engineers involved in its refining.

It was clear that crude oil was a greatly varying mix-ture of widely different hydrocarbons, a mixture ofstraight-chain paraffins (sometimes with short sidechains), of aromatic hydrocarbons deriving from ben-zene, and cyclic hydrocarbons or naphthenes having aring structure with five or six carbon atoms as nucleus.Besides these saturated hydrocarbons there might alsobe present small quantities of unsaturated olefins, sul-phur, nitrogen and oxygen compounds, which gave eachcrude a special character and compelled the refiner totake its composition into account [33].

Beginning in 1924, API began supporting several researchprojects on the heteroatomic composition of crude oil. Thefirst two of these, initiated in 1926, were to isolate and studysulfur and nitrogen compounds. This was followed in 1927by a project on the metallic constituents of crude oil [34].These and several other studies that continued into the 1960sused separation, analysis, and compound identification techni-ques, some of which might seem primitive by modern stand-ards, yet they succeeded in separating and identifying over600 individual hydrocarbons and over 200 individual sulfurcompounds. Unquestionably, these studies have been funda-mentally important in our understanding of the origin, chemis-try, and geochemical history of crude oil.

In the last 40 years, advances in instrumentation haveallowed the petroleum chemist to separate and identifycrude oil components that are characterized as novel bysome investigators [35]. However, these are present in suchinfinitesimally small concentrations that they do not haveeven a trivial effect on refining or product quality, yet theymay provide important insight into the origin of petroleumand its transformation in the reservoir. These techniquesinclude gas chromatography (GC), mass spectrometry (MS),atomic absorption and inductively coupled plasma (ICP) spec-trometry, and numerous multihyphenated techniques such asGC-MS, atomic emission spectrometry (AES)-ICP, and ICP-MS,among others [36].





2Sampling

The basic objective of sampling is to obtain a small portion(spot sample) for analysis that is truly representative of thematerial contained in a large bulk container, vessel, or pipe-line shipment. Often, the spot sample may be as little as onepart in greater than ten million. Frequently, a series of spotsamples may be collected and composited for analysis,which can help to minimize randomness and nonhomogene-ity and make for a somewhat more representative sample.Samples to be composited must be thoroughly mixed andvolumetrically proportional.

Crude oil to be sampled may be in static storage in anabove- or underground tank or a marine vessel, or it may beflowing through a pipeline or vessel offloading line. Forstatic storage, samples are collected manually using severaldifferent devices. For streams flowing in a pipeline, auto-matic sampling methods are used. In establishing a samplingprotocol, the analytical tests to be performed will dictate thevolume of sample needed, type(s) of container(s) to be used,and precautions necessary to preserve sample integrity. Thelatter consideration is especially important for samples to becollected for vapor pressure determination or measurementof hydrogen sulfide (H2S) content.

The importance of adhering to a rigorous sampling pro-tocol to ensure that samples are representative of the bulkmaterial cannot be overemphasized. Representative samplesare required for the determination of chemical and physicalproperties used to establish standard volumes and compli-ance with contractual specifications. Maintaining composi-tional integrity of these samples from the time of collectionuntil they are analyzed requires care and effort.

Moreover, it is critically important that the sampling pro-cedure does not introduce any contaminant into the sampleor otherwise alter the sample so that subsequent test resultsare affected. Procedures for collection and handling of sam-ples for H2S determination are especially critical because ofthe highly reactive nature and volatility of this compound.Appendix 1 provides recommended procedures suitable forcollection and handling of samples for determination of H2Sin crude oil. These were developed by the U.S. Department ofEnergys Strategic Petroleum Reserve in support of its crudeoil assay program and underwent rigorous field and labora-tory testing [37]. With proper handling, samples do not exhibitdetectable loss of their H2S for a minimum of 10 days.

MANUAL SAMPLINGASTM D4057: Practice for Manual Sampling of Petroleum andPetroleum Products1,2 provides procedures for manuallyobtaining samples, the vapor pressure of which at ambientconditions is below 101 kPa (14.7 psi), from tanks, pipelines,

drums, barrels, and other containers. This practice addresses,in detail, the various factors that need to be considered inobtaining a representative sample. These considerationsinclude the analytical tests to be conducted on the sample, thetypes of sample containers to be used, and any special instruc-tions required for special materials such as crude oils to besampled. Test Method D5854 provides additional guidance forsample mixing and handling. In many liquid manual samplingapplications, it must be kept in mind that the material to besampled contains a heavy component (e.g., free water) thattends to separate from the main component. Unless certainconditions can be met to allow for this, an automatic samplingsystem as described in ASTM D4177 is highly recommended.

ApparatusSample containers come in various shapes, sizes, and materi-als. To be able to select the right container for a given appli-cation, one must have knowledge of the material to besampled to ensure that there will be no interaction betweenthe sampled material and the container that would affect theintegrity of the other. Additional considerations in the selec-tion of sample containers are the type of mixing required toremix the contents before transferring the sample from thecontainer and the type of laboratory analyses that are to beconducted on the sample. For most samples, the containermust be large enough to contain the required sample vol-ume without exceeding 80% of the container capacity. Theadditional capacity is required for thermal expansion of thesample and to enhance sample mixing efficiency.

SAMPLE MIXING SYSTEMSThe sample container should be compatible with the mixingsystem for remixing samples that have stratified to ensurethat a representative sample is available for transfer to anintermediate container or the analytical apparatus. This isespecially critical when remixing crude oil samples to ensurea representative sample. When separation of entrained con-stituents such as sediment and water is not a major concern,adequate mixing may be achieved by such methods as shak-ing (manual or mechanical) or use of a shear mixer. How-ever, manual and mechanical shaking of the samplecontainer are not recommended methods for mixing a sam-ple for sediment and water analysis. Tests have shown it isdifficult to impart sufficient mixing energy to mix and main-tain a homogeneous representative sample.

SAMPLE TRANSFERSThe number of intermediate transfers from one container toanother between the actual sampling operation and testing

1 Appendix 2 lists the ASTM and other standards referenced in this manual.2 Appendix 3 provides excerpts from the Scope and certain other sections for most of the ASTM standards cited in this manual.

5



MNL68-EB/Nov. 2010






should be minimized to the maximum extent possible. Theloss of light hydrocarbons as the result of splashing, loss ofwater due to clingage, or contamination from external sour-ces, or a combination thereof, may distort test results. Themore transfers between containers, the greater the likelihoodone or more of these problems may occur.

SAMPLE STORAGEExcept when being transferred, samples should be main-tained in a closed container to prevent loss of light compo-nents. Samples should be protected during storage toprevent weathering or degradation from light, heat, or otherpotentially detrimental conditions. Refrigerated storage atapproximately 5C will help preserve compositional integritywhen samples are stored for protracted periods.

SPECIAL PRECAUTIONSCrude oil almost invariably contains sediment and water,which will rapidly settle out, and may contain H2S, anextremely toxic gas. Sampling of tanks through a stand pipethat is not slotted or perforated will not yield a representa-tive sample. When crude oil is to be tested for vapor pres-sure, care must be exercised in sample collection andhandling, and reference should be made to ASTM D5842.

AUTOMATIC SAMPLINGASTM D4177: Practice for Automatic Sampling of Petroleumand Petroleum Products covers information for the extractionof representative samples of petroleum from a flowing streamand storing them in a sample receiver. Several precautionsmust be observed in the use of automatic systems when sam-pling crude oil. Free and entrained water must be uniformlydispersed at the sample point. The sample must be maintainedin the sample receiver without altering the sample composi-tion. Venting of hydrocarbon vapors during receiver filling andstorage must be minimized. A properly designed, installed,tested, and operational automatic sample system is to be pre-ferred to manual sampling and is more likely to provide a rep-resentative test specimen that can be delivered into theanalytical apparatus.

SAMPLING FOR VAPOR PRESSUREDETERMINATIONASTM D5842: Practice for Sampling and Handling of Fuels forVolatility Measurements covers procedures and equipment forobtaining, mixing, and handling representative samples of vol-atile fuels. Although directed to products such as gasoline andreformulated fuels, the guidance provided is also useful insampling and handling of crude oils and condensates.

Vapor pressure is extremely sensitive to evaporationlosses and to slight changes in composition. The precautionsrequired to ensure the representative character of the sam-ple are numerous and depend on the tank, carrier, con-tainer, or pipe from which the sample is being obtained; thetype and cleanliness of the sample container; and the sam-pling procedure that is used. For example, ASTM D323requires that the sample shall be taken in 1-L containersfilled 7080 %. The sample container and its contents haveto be cooled to a temperature of 01C before the containeris opened. With crude oils with a pour point greater than1C, this requirement can affect results. Directions for sam-pling cannot be made explicit enough to cover all cases, andextreme care and good judgment are necessary.

MIXING AND HANDLING OF SAMPLESASTM D5854: Practice for Mixing and Handling of LiquidSamples of Petroleum and Petroleum Products covers thehandling, mixing, and conditioning procedures that arerequired to ensure that a representative sample is deliveredfrom the primary sample container or receiver into the ana-lytical test apparatus or into intermediate containers. Thispractice also provides a guide for selecting suitable contain-ers for crude oil samples for various analyses.

Further guidance and precautions to be observed insampling for specific tests such as water determination andmeasurement of vapor pressure are provided in discussionof the relevant test methods elsewhere in this manual.

Sample ContainersNo single container type will meet requirements of all sam-pling operations or restrictions necessary to ensure samplecompositional integrity for different tests. Sample containersmust be clean and free from all substances that might con-taminate the material being sampled, such as water, dirt,washing compounds, naphtha or other solvent, solderingfluxes, acid, rust, and oil. Table 1 provides a guide for select-ing the sample container most suitable for various crude oilanalyses. It is impossible to cover all sampling containerrequirements; therefore, when questions arise as to a con-tainers suitability for a given application, experience andtesting should be relied upon. Regardless of the containertype, before a sample is transferred from one container toanother, a homogenous mix must be created and maintaineduntil the transfer is complete. Even new containers shouldbe inspected for cleanliness before use.

Sample Mixing MethodsSample mixing methods can be divided into three generalcategories of power mixing, shaking, and no mixing. Thesecategories vary greatly in severity depending on the equip-ment used, the type of analytical test to be conducted, andthe characteristics of the sample. Further, power mixers areof two subtypesinsertion and closed loop. Overmixing withpower mixers may create an oil and water emulsion that willaffect the accuracy of certain analytical tests. Power mixersmay entrain air into the sample that could affect certain ana-lytical tests. Loss of vapor normally associated with rise intemperature may also occur, which could affect test resultsfor water, Reid vapor pressure (RVP), and density. Shakingsimply involves manually or mechanically shaking the sam-ple container to redisperse separated constituents such assediment and water. If a sample is known to be homogene-ous, no mixing is required; however, this is rarely the casewith crude oils. Nevertheless, samples should not be mixedwhen the analytical tests to be conducted may be affected byair, which could be introduced by power mixing or shaking.When the results will be affected by interference from extra-neous material such as water and sediment, the sampleshould not be shaken. Table 2 lists the recommended mixingprocedure to be used before a sample is transferred from acontainer for certain crude oil tests.

SAMPLE CHAIN OF CUSTODYChain-of-custody procedures are a necessary element in a pro-gram to ensure ones ability to support data and conclusionsadequately in a legal or regulatory situation. ASTM D4840:Guide for Sample Chain-of-Custody Procedures contains a





TABLE

1Su

mmaryofContainer

MaterialsforCrudeOils

(ASTM

D5854)

TypeofAnalysis

Den

sity

Chloride

Hyd

ro-Carbon

Distribution

Neu

trali-

zation

Number

Pour

Point

Salt

San

dW

Sulfur

Trace

Metals

Vap

or

Pressure

Viscosity

Hardborosilicateglass

Immed

iate

use

SP

NP

PS

SS

PP

SS

Storage

6months

SP

NP

PS

SS

PP

SS

Reu

seS

PNP

PS

SS

PS

SS

Stainlesssteel

Immed

iate

use

SS

SS

SS

SS

SS

S

Storage

6months

SS

SS

SS

SS

SS

S

Reu

seS

SS

SS

SS

SS

SS

Epoxy-lined

steel

Immed

iate

use

PS

SS

SS

PS

SS

S

Storage

6months

PS

SS

SS

PS

SS

S

Reu

seS

SS

SS

SS

SS

SS

Tin-platedsoldered

steel(Supercleanonly)

Immed

iate

use

SS

SS

SS

SS

NR

SS

Storage

6months

NR

NR

NR

NR

NR

NR

NR

NR

NR

NR

NR

Reu

seNR

NR

NR

NR

NR

NR

NR

NR

NR

NR

NR

Polytetrafluoroethylen

e,Perfluoroalko

xyorFluorinated

ethylen

epropylen

e

Immed

iate

use

SS

NP

SS

SS

SP

SS

Storage

6months

NR

NR

NP

NR

NR

NR

NR

NR

NR

NR

NR

Reu

seS

SNP

SS

SS

SS

SS

High-den

sity

linearpolyethylen

e

Immed

iate

use

SS

NP

SS

SS

SP

SS

Storage

6months

SNR

NP

NR

NR

NR

NR

NR

NR

NR

NR

Reu

seS

NR

NP

NR

NR

NR

NR

NR

NR

NR

NR

Note

1Th

econtainerslistedin

thissummaryshould

notbeusedwithoutconsultingtheap

propriateparag

raphsofthispracticefordetailad

vice.

Note

2WhereREU

SEisindicated

,containersshould

becleaned

inaccordan

cewith6.7priorto

reuse.

Note

3Legen

d:

NR=notrecommen

ded

NP=notpractical

P=preferred

5=suitab

le

CHAPTER 2 n SAMPLING 7




comprehensive discussion of potential requirements for a sam-ple chain-of-custody program and describes the proceduresinvolved. The purpose of these procedures is to provideaccountability for and documentation of sample integrity fromthe time samples are collected until they are disposed of.

SAMPLE ARCHIVESamples, or representative portions thereof, should be main-tained in a sample archive for a minimum of 45 days, althoughthe time requirement can be from 30 to 180 days. Archivedsamples may be needed in case of disputes, should additionaldata become necessary, or to conform to contractual require-ments or environmental or governmental regulations.

SUMMARYIn any sampling operation, whether manual or automatic, itmust be kept in mind that crude oils are not homogeneous.They contain sediment and water that can settle out andasphaltenes and waxes that can flocculate or precipitate outunder certain conditions. In pipeline shipments, differentcrudes will commonly be batched, and some mixing willtake place between the heads and tails of these. When crudeoils are discharged into a storage tank, there will frequentlybe a tank heel that may be of different quality. During stor-age in a tank, crudes oilseven a single crudecan differenti-ate and exhibit a density differential from top to bottom.Also, sediment and water present in the incoming crude oilwill settle during storage. Conversely, sediment and wateralready present in a tank heel can be resuspended by theturbulence created when further crude oil is pumped in.Crude oil can also exhibit a density differential from oneside of a tank to the opposite because of heating by theSuns rays. At a terminal, when storage capacity is at a pre-mium, operators may intentionally layer similar qualitycrudes in a tank. Collection of a representative sample maybe impeded by the presence of deadwood in ships compart-ments and tank stand pipes that are not slotted or perfo-rated. In sampling a pipeline, flow must be turbulent andnot laminar. With dense or viscous crude oils, this canbecome problematic.

In conclusion, it was accurately said Sampling is trulyan art. Failure to use proper techniques can cost companieshuge sums of money daily. Sampling is too critical to beleft to guess work, old outdated methods, or unproventechniques [38].

TABLE 2Summary of Recommended MixingProcedures for Crude Oils

Test Purpose

Recommended Mixing Procedure

Power None

Density X

Sediment and water X

Vapor pressure X

Sulfur by X ray X

Other tests Note 1 Note 1

Note 1 = Refer to specific analytical test procedure.



Path: k:/AST-GILES-10-0701/Application/AST-GILES-10-0701-ch3.3d

Date: 21st October 2010 Time: 16:28 User ID: sebastiang

3Inspection Assays

INTRODUCTIONThe testing of crude oils to determine their quality and toassess refining characteristics generally involves two sequen-tial but complimentary series of tests. An inspection analysisas described in this chapter is performed initially to deter-mine a few to numerous whole crude oil properties. This isfollowed by a detailed comprehensive analysis described inthe next chapter that involves distillation of the crude oilinto several fractions or cuts that are analyzed to determinetheir suitability for use or blending into a host of refinedproducts.

Inspection assays comprise a relatively limited numberof tests generally restricted to the whole crude oil. On thebasis of published data, there is little agreement as to whatconstitutes an inspection assay. Because the data are primar-ily for intracompany use, there is little driving force for astandard scheme. At a bare minimum, American PetroleumInstitute (API) gravity and sulfur, sediment, and water con-tent are usually determined, although it is useful to alsoknow the pour point, which provides some basic perceptionof the crude oils fluidity and composition. A more detailedinspection assay might consist of the following tests: APIgravity (or density or relative density), total sulfur content,pour point, viscosity, carbon residue, salt content, total acidnumber (neutralization number), and water and sedimentcontent. Individual shippers and refiners may substitute oradd tests (e.g., trace metal or organic halide tests) that maybe critical to their operations. Combining the results fromthese few tests and high-temperature simulated distillationdata of a current crude oil batch with the archived datafrom a comprehensive assay, the process engineer will beable to estimate generally the product slate that the crudewill yield and any extraordinary processing problems thatmay be encountered.

In the early 1990s, the API formed an Ad Hoc Crude OilQuality Task Force. The report of this task group recom-mends a set of crude oil quality testing procedures that, ifadopted by a shipper or refiner, would help ensure the qual-ity of crude oil from the wellhead to the refinery [39]. Theseprocedures include tests for API gravity, sediment and watercontent, organohalide compounds, salt, sulfur, and neutrali-zation number, among others. Although not a standard, it isan important aid to members of the petroleum industry inprotecting the quality of common stream crude petroleumfrom contamination by foreign substances or crude petro-leum of unspecified makeup. The report is also a usefulguide for an inspection program using mostly standardizedprocedures widely accepted in the industry for monitoringthe quality of mercantile commodity.

It is important to note that, in the following discussionof test methods, crude oil may not be included in the titleor even in the scope. However, many test methods have

been adapted to and are widely used and accepted for crudeoil analysis.

API GRAVITY AND DENSITYAccurate determination of the density or API gravity ofcrude oil is necessary for the conversion of measured vol-umes to volumes at the standard temperature of 15.56C(60F) using ASTM D1250: Petroleum Measurement Tables.API gravity is a special function of relative density (specificgravity) represented by the following:

API gravity; degrees 141:5specific gravity 60=60F

131:5

1

No statement of reference temperature is required because60F is included in the definition. Fig. 1 depicts the relation-ship between the two. A specific gravity of 1.00that ofwaterequates to an API gravity of 10.0.

API Gravity HistoryIn 1916, the U.S. National Bureau of Standards adopted theBaume scale as the standard for measuring the specific grav-ity of liquids less dense than water. The Baume scale, devel-oped in 1768, used solutions of sodium chloride (NaCl) inwater for degree calibration. When adopted, a large marginof error was unintentionally introduced as later found ininvestigation by the U.S. National Academy of Sciences. Thisresulted in hydrometers in the United States being manufac-tured with a modulus of 141.5 rather than the correctBaume scale modulus of 140. By 1921, the scale was sofirmly established that API created the API gravity scale,which recognized the scale being used by the industry [40].

Density and API gravity are also factors indicating thequality of crude oils. Generally, the heavier (lower the APIgravity) the crude oil the greater the quantity of heaviercomponents that may be more refractory and requiregreater upgrading or more severe cracking to produce sala-ble products. Conversely, the lighter the crude oil the greaterthe quantity of easily distillable products. Crude oil pricesare frequently posted against values in kilograms per cubicmetre (kg/m3) or in degrees API. However, this propertyalone is an uncertain indication of quality and must be cor-related with other properties.

The relative density (specific gravity) or density of acrude oil may also be reported in analyses. Relative densityis the ratio of the mass of a given volume of liquid at a spe-cific temperature to the mass of an equal volume of purewater at the same or a different temperature. Both referencetemperatures must be explicitly stated. Density is simply themass of liquid per unit volume at 15C, with the standardunit of measurement being kg/m3.

9



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Measurement by HydrometerAPI gravity, or density or relative density, can be determinedeasily using one of two hydrometer methods [ASTM D287:Test Method for API Gravity of Crude Petroleum and Petro-leum Products (Hydrometer Method), or ASTM D1298: TestMethod for Density, Relative Density (Specific Gravity), orAPI Gravity of Crude Petroleum and Liquid Petroleum Prod-ucts by Hydrometer Method]. A third hydrometer method(ASTM D6822: Test Method for Density, Relative Density,and API Gravity of Crude Petroleum and Liquid PetroleumProducts by Thermohydrometer Method) is more applicableto field applications in which limited laboratory facilities areavailable.

Measurement by Digital Density AnalyzerMany laboratories are now using an instrumental method(ASTM D5002: Test Method for Density and Relative Densityof Crude Oils by Digital Density Analyzer) rather than thehydrometer methods. This method requires a considerablysmaller sample than the hydrometer methods.

Density or API gravity as determined by the hydrometermethods is most accurate at or near the standard tempera-ture of 15.56C (60F). The results of all four of the testmethods will be affected by the presence of air or gas bub-bles and sediment and water and by the loss of light compo-nents. For volatile crude oils [i.e., those with a Reid vaporpressure (RVP) of >50 kPa] it is preferable to use a variablevolume (floating piston) sample container to minimize lossof light components. In the absence of this apparatus,extreme care must be taken to minimize losses, including thetransfer of the sample to a chilled container after sampling.It is also preferable to mix the sample in its original closedcontainer to minimize loss of light components.

For crude oils having a pour point greater than 10C, ora cloud point or wax appearance temperature (WAT) greaterthan 15C, the sample should be warmed to 9C above thepour point, or 3C above the cloud point or WAT, beforemixing. As discussed in a subsequent chapter, IP389 determi-nation of WAT of middle distillate fuels by differential ther-mal analysis (DTA) or differential scanning calorimetry(DSC) will provide an indication of the WAT.

BITUMEN AND EXTRA-HEAVY CRUDE OILSThe presence of water, solids, and air bubblesall of which canbe difficult to remove from these materials before analysismakes accurate determination of their density more difficult

than for lighter crude oils. Sediment and water do not readilysettle out, and air bubbles are not easily seen.

Pycnometers are suitable for measurement of density ofthese materials. ASTM D1480: Test Method for Density andRelative Density (Specific Gravity) of Viscous Materials byBingham Pycnometer describes two procedures for the mea-surement of the density of materials that are fluid at thedesired test temperature. In addition to ASTM D5002, ASTMD4052: Test Method for Density and Relative Density ofLiquids by Digital Density Meter has also been used fordetermining density of bitumens and heavy crude oils. Inusing digital density meters, air bubbles can result in unsta-ble readings, and heating the sample before analysis canhelp to eliminate them.

Determination of the density of semi-solid and solidbituminous materials and materials having a density greaterthan 1.00 (API



These older techniques have now largely been replacedby two instrumental methods: ASTM D2622: Test Method forSulfur in Petroleum Products by X-Ray Spectrometry andASTM D4294: Test Method for Sulfur in Petroleum Productsby Energy-Dispersive X-Ray Fluorescence Spectroscopy.

A fundamental assumption in ASTM D2622 is that thesample and standard matrices are well matched. When the ele-mental composition of the sample differs significantly fromthat of the standard, errors in the sulfur determination canresult. For crude oils, this matrix mismatch is usually theresult of differences in the carbon-hydrogen ratio. Presence ofinterfering heteroatomic species is less likely to be a contribut-ing factor. This test method provides rapid and precisemeasurement of total sulfur with a minimum of sample prep-aration. However, the equipment tends to be more expensivethan for alternative test methods, such as ASTM D4294.

In the round-robin studies used to develop precisiondata for ASTM D2622 and ASTM D4294, the highest level ofsulfur in a sample was 4.6 mass percent. Samples containingmore than 5.0 mass percent should be diluted to bring thesulfur concentration of the diluted material within the scopeof the test method. However, samples that are diluted canhave higher errors than nondiluted samples.

As with ASTM D2622, a fundamental assumption inASTM D4294 is that the sample and standard matrices arewell matched. Moreover, spectral interferences may arisefrom the presence of silicon, calcium, and halideselementscommonly present in the inorganic sediment inherently pres-ent in crude oils. In modern instruments, these may be com-pensated for with the use of built-in software. ASTM D4294also provides rapid and precise measurement of total sulfurwith a minimum of sample preparation, and the instrumenta-tion is less costly than that for ASTM D2622. Of the twomethods, ASTM D4294 has slightly better repeatability andreproducibility and is also adaptable to field applications.

Sediment, water, and waxes commonly present in crudeoil samples can settle onto the Mylar film sealing the testcell and interfere in sulfur determination by both of the X-raymethods. Before analysis, water and particulates should beremoved from the sample by centrifugation or settling, butcare must be taken that sample integrity is not compromised.

ASTM D7343 Optimization, Sample Handling, Calibra-tion, and Validation of X-ray Fluorescence SpectrometryMethods for Elemental Analysis of Petroleum Products andLubricants provides information relating to sampling, cali-bration, and validation of X-ray fluorescence instrumentsapplicable to determination of sulfur by ASTM D2622 andD4294. This practice includes sampling issues such as theselection of storage vessels, transportation, and subsampling.Treatment, assembly, and handling of technique-specificsample holders and cups are also included. Technique-specific requirements during analytical measurement andvalidation of measurement are described.

Hydrogen Sulfide and Thiols or MercaptansHydrogen sulfide (H2S) is a highly toxic and corrosive gasthat occurs naturally in some but not all crude oils. H2S canbe formed by thermal decomposition of elemental sulfur andthiols, and even crude oils that do not contain the compoundnaturally may produce the gas on heating or during distilla-tion. Reservoir souring by H2S may occur from reductionof bisulfite chemicals used as oxygen scavengers, thermaldecomposition of sulfur compounds, or dissolution of iron

sulfide. H2S is also known to be produced by action of sul-fate-reducing bacteria (SRB) in storage tanks, in the legs ofoffshore production platforms used for storage, and in thedead legs of pipelines. Studies have shown that the H2S pres-ent in some crude oil reservoirs has unequivocally resultedfrom SRB activity [41]. Sulfate reduction in the reservoir bySRB introduced with water used for enhanced oil recovery isnow widely accepted as the most significant mechanism con-tributing to formation of H2S in crude oils [42].

In analyses, it is important to report H2S as dissolved(existent; that which is naturally present) or evolved (poten-tial; that which results from decomposition of sulfur com-pounds on heating or distillation). Elemental sulfur andmany thiols will decompose when heated and form H2S.

Thiols or mercaptans are considerably more prevalentin crude oils than H2S. They are the least stable sulfur com-pounds and many decompose on heating to form H2S. Thisreaction can begin at less than 100C, with maximum evolu-tion at approximately 200C [43]. Thiols may be distributedacross a wide boiling range, extending from the lightest frac-tion well into vacuum gas oil, and can give rise to evolutionof H2S across much the same boiling range. Free sulfur isknown to occur in crude oils and it will also decompose onheating to form H2S.

These components are commonly determined by nona-queous potentiometric titration with silver nitrate (UOP 163:Hydrogen Sulfide and Mercaptan Sulfur in Liquid Hydrocar-bons by Potentiometric Titration). The presence of free sul-fur in samples complicates interpretation of the titrationcurves. A newer test method developed specifically for fueloils may prove applicable to crude oils with further testing(IP 570 Determination of Hydrogen Sulfide in Fuel OilsRapid Liquid Phase Extraction Method). The test method isautomatic, suitable for laboratory or field use, and providesresults in approximately 15 min. Crude oils were not includedin the interlaboratory study that developed the methods preci-sion data, and a new round robin will need to be conducted toobtain these.

H2S is very volatile and highly reactive, and unless pre-cautions are taken in the collection and preservation of sam-ples, results will not be representative (Appendix 1). A testkit has been developed that is very useful for rapidly deter-mining H2S concentration in liquid samples in the field [44].This kit has an accuracy of approximately 20 % for H2S. Acommonly used field technique for determining H2S concen-tration in head space gases is the so-called Drager tube,keeping in mind that concentration in the head space can-not be equated to liquid concentration. This is especiallyapplicable to marine cargoes as reported in the InternationalSafety Guide for Oil Tankers and Terminals. It is importantto distinguish between concentrations of H2S in the atmos-phere, expressed in ppmv, and concentrations in liquidpetroleum expressed in ppmw. For example, a crude oil con-taining 70 ppmw H2S has been shown to give rise to a con-centration of 7,000 ppmv in the gas stream [45].

WATER AND SEDIMENTThe water and sediment content of crude oil results princi-pally from production and transportation practices. Water,with its dissolved salts, may occur as easily removable sus-pended droplets or as an emulsion. The sediment dispersedin crude oil may be comprised of inorganic minerals fromthe production horizon or from drilling fluids, as well as

CHAPTER 3 n INSPECTION ASSAYS 11




scale and rust from pipelines and tanks used for oil trans-portation and storage. Usually water is present in far greateramounts than sediment, but, collectively, it is unusual forthem to exceed 1 % (v/v) of the crude oil on a deliveredbasis. Water and sediment can foul heaters, distillation tow-ers, and exchangers and can contribute to corrosion and todeleterious product quality. Also, water and sediment areprincipal components of the sludge that accumulates in stor-age tanks and must be disposed of periodically in an envi-ronmentally acceptable manner.

Further, water bottoms in storage tanks can promotemicrobiological activity and, if the system is anaerobic, pro-duction of corrosive acids and H2S can result. This is notusually a problem with crude oils because stocks are nor-mally rotated on a regular basis. Nevertheless, anaerobicdegradation of crude oil stocks and production of H2S hasbeen known to happen, and the operator must be aware ofthe potential for this occurring and the analyst must takethis into consideration in evaluating results.

Knowledge of the water and sediment content is alsoimportant in accurately determining net volumes of crudeoil in sales, taxation, exchanges, and custody transfers. Whena significant amount of free water is present in a marinecargo, identification of its probable source should be amajor consideration. Guidelines that include basic sampling,testing, and analytical procedures and interpretation andpresentation of results for this process have been publishedby API in their Manual of Petroleum Measurement Stand-ards [46].

Several test methods exist for the determination ofwater and sediment in crude oil. Some of these are specificto water alone, others to sediment alone, and one other to acombination of sediment and water.

WaterTechniques for measuring water content are heating underreflux conditions with a water immiscible solvent that distillsas an azeotrope with the water (ASTM D4006: Test Methodfor Water in Crude Oil by Distillation), potentiometric titra-tion (ASTM D4377: Test Method for Water in Crude Oils byPotentiometric Karl Fischer Titration), or the more generallypreferred coulometric titration (ASTM D4928: Test Methodfor Water in Crude Oils by Coulometric Karl Fischer Titra-tion). The latter two Karl Fischer methods include a homoge-nization step designed to redisperse any water that hasseparated from the crude oil while the sample has beenstored. Because the two Karl Fischer methods are quite simi-lar, it has been proposed that they be combined into a singlemethod with two partsone for potentiometric titration andthe second for coulometric titration. Water may also bedetermined by centrifugation, as discussed in the followingsubsection on water and sediment.

The precision of the distillation method, especially atlow levels, can be affected by water droplets adhering to sur-faces in the apparatus and therefore not settling into thewater trap to be measured. To minimize the problem, allapparatus must be chemically cleaned at least daily to removesurface films and debris, which hinder free drainage of waterin the test apparatus. At the conclusion of the distillation, thecondenser and trap should be carefully inspected for waterdroplets adhering to surfaces. These should then be carefullydislodged using a tetrafluoroethylene (TFE) pick or scraperand transferred to the water layer.

For both of the Karl Fischer methods, thiols and sul-fides (S and H2S) are known to interfere, but at levels ofless than 500 lg/g (ppm) the interference from these com-pounds is insignificant except at low water levels (



percent sediment by 2.0 and multiply by the relative densityof the crude oil according to the following equation:

Sv S2:0 3 relative density of oil 2

where:Sv = the sediment content of the sample as a percentage by

volume andS = the sediment content of the sample as a percentage by

mass.This calculation is for convenience only, and the preci-

sion and bias have not been established.Excessive reuse of thimbles in ASTM D473 is to be

avoided because, over time, the pores become clogged withinorganic material resulting in falsely high results. Also, theuse of toluene in laboratories is coming under increasingscrutiny by safety and health groups, and a future ban on itsuse is not inconceivable. No alternative solvent has beenidentified to date, although some laboratories are known touse Varsol and aviation turbine (jet) fuel in lieu of toluene.

Sediment and WaterCentrifugal separation of the water and sediment [ASTMD4007: Test Method for Water and Sediment in Crude Oil bythe Centrifuge Method (Laboratory Procedure)] is rapid andrelatively inexpensive, but the amount of water detected isalmost invariably lower than the actual water content. This canresult from inaccuracy in reading the interface between oiland water and emulsified water not being totally separated.

ASTM D96: Test Method for Water and Sediment inCrude Oil by Centrifuge Method (Field Procedure) covers thedetermination of sediment and water in crude oil duringfield custody transfers. This method may not always providethe most accurate results, but it is considered the most prac-tical method for field determination of sediment and water.The method is still widely used although it was withdrawnwith no replacement by ASTM in 2000. A technically equiva-lent version of the method is available as Chapter 10.4 in theAPI Manual of Petroleum Measurement Standards.

For all of the methods for sediment and water determi-nation, sample homogenization is critically important andanalyses must be conducted immediately after mixing to pre-clude settling. Loss of light ends will also affect results, andcare must be exercised during mixing so that the tempera-ture does not rise more than 10C.

SALT CONTENTThe salt content of crude oil is highly variable and, as withwater and sediment, results principally from production prac-tices used in the field and, to a lesser extent, from its handlingaboard tankers bringing it to terminals. The bulk of the saltpresent will be dissolved in coexisting free and emulsifiedwater and can be removed in desalters, but small amounts ofsalt may be dissolved in the crude oil itself and present as acrystalline solid. Salt may be derived from reservoir or forma-tion waters or from other waters used in secondary recoveryoperations. Aboard tankers, nonsegregated ballast water ofvarying salinity may also be a source of salt contamination.

Salt in crude oil may be deleterious in several ways.Even in small concentrations, salts will accumulate in distil-lation towers, heaters, and exchangers, leading to foulingthat requires expensive cleanup. More importantly, duringflash vaporization of crude oil, certain metallic salts,

especially magnesium chloride, can be hydrolyzed to hydro-chloric

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