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API RP 85:2003(2013) pdf download

API RP 85:2003(2013) pdf download.Use of Subsea Wet-gas Flowmeters in Allocation Measurement Systems.
In addition to Meter Calibration. Factory Acceptance Testing, and Meter Component Testmg. prior to actual operation of subsea meters, certain other testing must be done to insure correct lunction. Tipical of these tests are:
6.6.1 Systems Integration Test (SIT). Systems Integration Test is where two or more pieces which arc to be connected subsca are lit together on land to insure proper function prior to installation underwater. It is recommended br metering systems and their associated pipework.
6.6.2 Installation Demonstration. This can also be described as a “wet test:’ in which access and handling by ROV in tanks is demonstrated.
6.6.3 Software Testing. The operator should test all flow meter software to verify correct algorithm output against a variety of selected known inputs and outputs. Other aspects which need to be tested to assure quality arc the ability of all systems to recover from intcrrupLs (cg. power outage, computer lockup. etc.) and the ability of the operator to remotely download software “patches” or improvements.
Ii is essential that an active campaign of verification be an integral part of the routine operation of the Ileld production.
Prior to approval by regulatory authorities and partners to use wet gas meters subsca. the applicant must declare what will be done to verify the correct operation of the meters as an ongoing. routine procedure. In this Verification Plan, a number of variables will be identified. including the following.
6.7.1 ComparIson of Redundant Sensors. A source of information when erifying the performance of the measurement system is the collection of sensors which are used. Since at least one level of redundancy must be present. it will be useful to gather data on the readings observed on the sensors relative to one another.
In the case of dcepwater and harsh environments, it may prove cost effective to install additional transducers, which can be introduced into the measurement system by “software” methods.
6.7.2 Monthly System Balance Check. This is the test most likely to be used as the primary veritication tool. This first level of system auditing compares the Master Quantity with the sum of the Individual Theoreticai Quantities (see Section 5). The ditTerence between the two over a pre-debined period of time, called the System Balance, should lie within an error range defined by the uncertainties due to the subsea meters, to the reference nieters, and to the equation-of-state and transport methodologies used. It should be pcrftrmed on both the primary product (gas) and secondary products (liquids) to verify that measurement of both phases is within tolerance. More frequent balance checks are encouraged when used for diagnostic or other purposes.
Perhaps the most difficult part of the System Balance Check is the setting of thresholds and defining of criteria for declaring the system out of balance. This is challenging for two reasons. The first is that the elimination of systematic errors must have been done well, or these will tend to skew the imbalance analysis. The second is that dikrvnces in relative production levels through meters may tend to mask a failure. (i.e.. a hard failure in a minimal producer may be hard to detect), and may resemble a marginal failure in a high producer. For these reasons, it will be necessary to look at many parameters in combination with the System Balance to determinc the overall health of the system. More details on the System Balance Check are found in Section 7.
It must be noted that for secondary products, due to the very small volumes of liquids anticipated in developments which use wet gas flow motering. the overall inaccuracies for these components may be relatively high.
67.3 Sensor Zero and Offset Check at Shut-in. There will be occasions, scheduled and otherwise, when the individual wells will have their production shut in. Most governing and regulatory bodies require regular testing of well equipment. The operator should ensure that these regular tests are used to verify the zero-offset and calibration of the sensors as part of an agreed program of verification.
6.7.4 Other Recommended Diagnostics. What has been recommended here is potentially a small part of the overall diagnostic capability available to the user who tries to ascertain the performance of his measurement system and the devices which comprise it. Certain new technologies to he offered for wet gas measurement in the future may be able to completely diagnose their own performance through extensive diagnostic measurements and calculations. Where these are available, they should be identified in the application.


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