1、Use of Subsea Wet-gas Flowmeters in Allocation Measurement SystemsAPI RECOMMENDED PRACTICE 85FIRST EDITION, AUGUST 2003REAFFIRMED, OCTOBER 2013Use of Subsea Wet-gas Flowmeters in Allocation Measurement SystemsUpstream SegmentAPI RECOMMENDED PRACTICE 85FIRST EDITION, AUGUST 2003REAFFIRMED, OCTOBER 20
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7、2) 682-8000. A catalog of API publications and materials is published annually and updated quar-terly by API, 1220 L Street, N.W., Washington, D.C. 20005, standardsapi.org.This document was produced under API standardization procedures that ensure appropri-ate notication and participation in the dev
8、elopmental process and is designated as an APIstandard. Questions concerning the interpretation of the content of this standard or com-ments and questions concerning the procedures under which this standard was developedshould be directed in writing to the standardization manager, American Petroleum
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10、neer-ing and operating practices. These standards are not intended to obviate the need for apply-ing sound engineering judgment regarding when and where these standards should beutilized. The formulation and publication of API standards is not intended in any way toinhibit anyone from using any othe
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13、ng Services, 1220 L Street, N.W., Washington, D.C. 20005.Copyright 2003 American Petroleum InstituteFOREWORDThis Recommended Practice is under the jurisdiction of the API Executive Committee onDrilling and Production Operations. It is intended to advise the user on various aspects of theuse of subse
14、a wet-gas owmeters in allocation measurement systems. Marinization, opera-tion, abnormal operation, and meter testing are important topics included here, but, foremost,this document proposes novel techniques to be used in the allocation of total production toindividual contributing streams.Deepwater
15、 oil and gas prospects often employ a form of development known as a subseatie-back. In these applications, wells are completed subsea, and production ows to hostfacilities for processing, generally in shallower waters, and then on to export markets. Inmany cases, the host infrastructure already exi
16、sts, although facilities modications may berequired. Certain of these developments require commingling ow from multiple wells, pos-sibly from multiple elds and an assortment of owners. In order to allocate production inthese cases, measurement of the full wellstream uids may be required.Add to this
17、the greater uncertainty of, and lack of recognized standards for, multi-phasemeasurement, then place the meters subsea in deep water, and one quickly enters unchartedwaters.Key to the use of multi-phase and wet-gas meters (subsea or topside) is the ability of anallocation system to account for the d
18、ifferential uncertainty of all the metering devices in thesystem. Even with established standards and practices, the process of reaching agreement onsingle-phase measurement allocation methodology involving multiple leases and owners isdifcult. It is important to understand that subsea wet-gas meter
19、s, or any metering system insuch a remote and isolated environment, are very likely to experience a higher level of uncer-tainty, and will probably be exposed to longer periods of undetected, uncorrected bias errorsthan conventional topside metering systems. When these systems are placed in a commin
20、-gled operation where they provide input for an allocation of production, the nancial risk tothe parties involved will be greater than is normally experienced with single-phase, accessi-ble measurement systems. This RP presupposes that these risks are recognized, and that theyhave been accepted by t
21、he affected parties.This RP presents a recommended allocation methodology that is technically defensibleand mathematically optimized to best t the application, and that equitably accommodatesvariances in the uncertainty level between meters in the system.API publications may be used by anyone desiri
22、ng to do so. Every effort has been made bythe Institute to assure the accuracy and reliability of the data contained in them; however, theInstitute makes no representation, warranty, or guarantee in connection with this publicationand hereby expressly disclaims any liability or responsibility for lo
23、ss or damage resultingfrom its use or for the violation of any federal, state, or municipal regulation with which thispublication may conict.Suggested revisions are invited and should be submitted to the standardization manager,American Petroleum Institute, 1220 L Street, N.W., Washington, D.C. 2000
24、5. As it isintended for this RP to be updated within approximately one year, comments on this editionwill be very much welcomed.iiiCONTENTSPage1 SCOPE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11.1 Wet Gas Denition a
25、nd Classications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11.2 Liquid Hydrocarbon Measurement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11.3 Scope Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
26、. . . . . . 12 REFERENCED PUBLICATIONS. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23 DEFINITIONS AND NOMENCLATURE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23.1 Denitions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
27、 . . . . . . . . . . . . . . . . . . . . . . 23.2 Nomenclature and Symbols. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44 SUBSEA METER CALIBRATION AND TESTING. . . . . . . . . . . . . . . . . . . . . . . . . . 44.1 General . . . . . . . . . . . . . . . . . . .
28、. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44.2 Testing Requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44.3 Flow Test Facilities . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
29、. . . . . . . . . 54.4 Calibration Test Program. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 64.5 Calibration Deliverables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 75 ALLOCATION METHODOLOGY. . . . . . . . . . .
30、. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 75.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 75.2 Principle . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
31、 . . . . . . 75.3 Validation of Performance and Applicability . . . . . . . . . . . . . . . . . . . . . . . . . . . . 85.4 Derivation of Allocation Factors and Allocated Quantities . . . . . . . . . . . . . . . . . 85.5 Application of the Allocation Equations . . . . . . . . . . . . . . . . . . . .
32、. . . . . . . . . . . 105.6 Perspective on Allocation: the Impact of Systematic Errors. . . . . . . . . . . . . . . . 106 INSTALLATION, OPERABILITY, PHYSICAL REQUIREMENTS. . . . . . . . . . . . 106.1 Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
33、 . . . . . . . . . 106.2 Normal Operating Conditions Over Field Life . . . . . . . . . . . . . . . . . . . . . . . . . . 116.3 Measurement Uncertainty Expected for Normal Operating Conditions . . . . . . 116.4 Design Considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
34、. . . . . . . . . . . 116.5 Installation Effects on Measurement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 136.6 Additional Testing on Measurement Systems. . . . . . . . . . . . . . . . . . . . . . . . . . . 146.7 Routine Verication . . . . . . . . . . . . . . . . . . . . .
35、. . . . . . . . . . . . . . . . . . . . . . . . . . 146.8 Operation Outside Calibrated Envelope . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 147 ABNORMAL OPERATIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 157.1 Contingency Plan. . . . .
36、. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 157.2 Detection of Abnormality (Normal-Abnormal Boundary Denition) . . . . . . . . 157.3 Investigation (Verication of Abnormality, Identication of Cause) . . . . . . . . . 167.4 Remedial Action. . . . . . . . . .
37、 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 167.5 If All Else Fails. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17vPage8 TEMPLATE FOR WET GAS PERMIT APPLICATION. . . . . . . . . . . . . . . . . . . . . . 17
38、8.1 Project Identication . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 178.2 Process Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 178.3 Measurement Devices . . . . . . . . . . . . . . . . . . .
39、 . . . . . . . . . . . . . . . . . . . . . . . . . . 178.4 Pre-installation Meter Test Plans. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 178.5 Operability Considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 179 BIBLIOGRAPHY .
40、. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18APPENDIX A UNCERTAINTY DETERMINATION AND THE APPLICATION OF EQUATIONS OF STATE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19APPENDIX B EVALUATING UNCERTAINTY . . . . . . .
41、 . . . . . . . . . . . . . . . . . . . . . . 23APPENDIX C WORKED EXAMPLE OF UNCERTAINTY-BASED ALLOCATION. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27APPENDIX D MONTHLY UNCERTAINTY DETERMINATION . . . . . . . . . . . . . . . 29APPENDIX E UNCERTAINTY-BASE
42、D ALLOCATIONDERIVATION OF OPTIMAL FACTORS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31APPENDIX F WET GAS METER TECHNOLOGY. . . . . . . . . . . . . . . . . . . . . . . . . . . 33Figures1 Commingling nProduction Streams Qito Form Stream Qz. . . . . . . . . . . . . . . . .
43、 . 9A.1 Schematic of Fluid for PVT Analysis. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19A.2 Illustration of Fluid Phase Change Between Subsea and Topside . . . . . . . . . . . . . 21B.1 Typical Flow Calibration Results . . . . . . . . . . . . . . . . . . . . . . . . . . .
44、. . . . . . . . . . . 24B.2 Uncertainty Curve Resulting from Flow Calibration of B.1 . . . . . . . . . . . . . . . . . 25D.1 Illustration of Combining Time-slice Production Data . . . . . . . . . . . . . . . . . . . 29F.1 Two-phase Flow Map Showing Approximate Locations of Various Flow Regimes with
45、Respect to Liquid and Gas Flow Velocities for Horizontal Flow. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34F.2 Gas Over-reading by Venturi Meter as a Function of Lockhart-Martinelli Parameter. . . . . . . . . . . . . . . . . . . . . . . . .
46、 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35F.3 Pressure Effect on Murdock Correlation (de Leeuw, Bibl. 3) . . . . . . . . . . . . . . . . 36vi1Use of Subsea Wet-gas Flowmeters in Allocation Measurement Systems1 Scope1.1 WET GAS DEFINITION AND CLASSIFICATIONSDening wet gasis n
47、ot an easy task. Historically mul-tiphase ow where gas volume fractions (GVF) haveexceeded 90% or 95% has been called wet gas. However,GVF is based on volumetric ow rates at actual conditions inthe pipe, and doesnt account for relative differences in thegas and liquid densities. Since many successfu
48、l devices usedfor wet gas measurement employ differential methods that arestrongly affected by the densities of the gas and liquid relativeto one another, the Lockhart-Martinelli parameter is often uti-lized in dening the boundary between wet gas and othermultiphase ow. The Lockhart-Martinelli param
49、eter isdened aswhere Qland Qgare the liquid and gas mass ow rates, andand are the densities of liquid and gas at meter conditions.Since mass ow is volumetric ow multiplied by density, wecan also dene the Lockhart-Martinelli parameter of the wetgas ow in terms of actual volumetric ow rates and .Based on experience gained in ow loop tests, it has beensuggested that when the Lockhart-Martinelli parameter for auid remains below about 0.35, its behavior is such that manycommon methods employed for wet gas ow measurementwork as they have been designed. A
