WO2010002659A2 - Rapid data-based data adequacy procedure for pipepline integrity assessment - Google Patents
Rapid data-based data adequacy procedure for pipepline integrity assessment Download PDFInfo
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- WO2010002659A2 WO2010002659A2 PCT/US2009/048441 US2009048441W WO2010002659A2 WO 2010002659 A2 WO2010002659 A2 WO 2010002659A2 US 2009048441 W US2009048441 W US 2009048441W WO 2010002659 A2 WO2010002659 A2 WO 2010002659A2
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- pipeline
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- wall thickness
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F17—STORING OR DISTRIBUTING GASES OR LIQUIDS
- F17D—PIPE-LINE SYSTEMS; PIPE-LINES
- F17D5/00—Protection or supervision of installations
Definitions
- This invention is in the field of pipeline inspection, and is more specifically directed to the evaluation of the amount of pipeline inspection that is necessary to ensure pipeline integrity.
- Maintaining the integrity of pipelines is a fundamental function in maintaining the economic success and minimizing the environmental impact of modern oil and gas production fields and systems.
- pipeline integrity is also of concern in other applications, including factory piping systems, municipal water and sewer systems, and the like. Similar concerns exist in the context of other applications, such as production casing of oil and gas wells.
- corrosion and ablation of pipeline material from the fluids flowing through the pipeline, will reduce the thickness of pipeline walls over time. In order to prevent pipeline failure, it is of course important to monitor the extent to which pipeline wall thickness has been reduced, so that timely repairs can be made.
- ILI in-line inspection
- a vehicle commonly referred to as a “pig” travels in the interior of the pipeline along its length, propelled by the production fluid itself or otherwise towed through the pipeline.
- the pig includes transducers that indirectly measure the wall thickness of the pipeline repeatedly along the pipeline length as the pig travels.
- Measurement technologies used in ILI include magnetic flux leakage techniques that measure the extent to which a magnetic field can be induced into the pipeline wall is measured, from which the wall thickness can be inferred.
- ILI inspection can also be carried out using ultrasonic energy, as well-known in the art. Unfortunately, ILI monitoring cannot be applied to all pipelines, because of their construction or geometry. Sampled measurements must therefore be used on a substantial number of pipelines in modern production fields and pipeline systems.
- a known approach to the characterization of pipeline integrity applies sample thickness measurements to a predictive model of the pipeline.
- Known models apply parameters such as properties of the fluid carried by the pipeline, pressure, temperature, flow rate, and the like, such that a minimum wall thickness can be calculated given sample measurements of the wall thickness.
- the accuracy of such computer simulations in characterizing the minimum wall thickness depends on the accuracy with which the model corresponds to the true behavior of the pipeline. And, in turn, the accuracy of the model depends on the accuracy of the assumptions underlying the model to the actual pipeline. But in practice, as known in the art, real-world pipelines vary widely from one another in corrosion behavior, due to structural and environmental variations that are not contemplated by the model or its underlying assumptions. As more complicated models are derived to include the effects of these variations, the resulting computations will of course also become more complicated.
- ILI in-line inspection
- the present invention may be implemented into a computerized method, an evaluation system programmed to perform the method, and a computer program stored in a computer readable medium, by way of which sample coverage of external pipeline wall thickness measurements can be determined to achieve a desired statistical confidence level.
- a library of measurement data acquired by a 100% inspection method, such as in-line inspection, for a subset of the pipelines is stored in a database. These library data are arranged into distributions of measurements for each pipeline, for example by percentage deciles of pipeline wall thickness loss.
- Monte Carlo sampling is performed for each of a plurality of sample coverages. The results of each sampling are evaluated to associate a sample coverage with a confidence level for identifying an extreme value of wall loss.
- the distribution of the sampled wall thickness measurements is compared with the distributions of similar pipelines in the 100% inspection library.
- the sample coverage required for a given confidence level for a given conclusion is then determined from the Monte Carlo results for the one or more most similar pipelines in the library to the pipeline under investigation. If indicated by the results, new samples may be obtained from the pipeline to increase the sample coverage and thus satisfy the requirement for a given confidence level.
- Figure 1 is a schematic diagram of an example of a production field in connection with which the preferred embodiment of the invention may be used.
- Figure 2 is an electrical diagram, in block form, of an evaluation system programmed to carry out an embodiment of the invention.
- Figure 3 is a flow diagram illustrating the generation of an in-line inspection calibrated measurement library, according to an embodiment of the invention.
- Figure 4 is a flow diagram illustrating the generation of calibrated distributions in the process of Figure 3, according to an embodiment of the invention.
- Figure 5 is a flow diagram illustrating the evaluation of the adequacy of the number of sampled measurements of wall thickness loss for a pipeline under investigation, according to an embodiment of the invention.
- Figure 6 is a flow diagram illustrating the selection of a test set of similar in-line inspected pipelines and the selection of subsets of statistical distribution of measurements in those pipelines, in the process of Figure 5 according to an embodiment of the invention.
- the present invention will be described in connection with its embodiments, including its preferred embodiment, in connection with a method and system for monitoring and evaluating pipeline integrity in a production field and system for oil and gas.
- this invention can also provide important benefit in other applications, including the monitoring and evaluating of production casing integrity in oil and gas wells, and the monitoring and evaluating of pipeline integrity in other applications such as water and sewer systems, natural gas distribution systems on the customer side, and factory piping systems, to name a few. Accordingly, it is to be understood that the following description is provided by way of example only, and is not intended to limit the true scope of this invention as claimed.
- FIG. 1 an example of an oil and gas production field, including surface facilities, in connection with which an embodiment of the invention may be utilized, is illustrated in a simplified block form.
- the production field includes many wells 4, deployed at various locations within the field, from which oil and gas products are to be produced in the conventional manner. While a number of wells 4 are illustrated in Fig. 1, it is contemplated that modern production fields in connection with which the present invention may be utilized will include many more wells than those wells 4 depicted in Fig. 1.
- each well 4 is connected to an associated one of multiple drill sites 2 in its locale by way of a pipeline 5.
- eight drill sites 2 0 through 2 7 are illustrated in Fig.
- Each drill site 2 may support many wells 4; for example drill site 2 3 is illustrated in Fig. 1 as supporting forty-two wells 4 0 through 4 4 i .
- Each drill site 2 gathers the output from its associated wells 4, and forwards the gathered output to central processing facility 6 via one of pipelines 5.
- central processing facility 6 is coupled into an output pipeline 5, which in turn may couple into a larger-scale pipeline facility along with other central processing facilities 6.
- the pipeline system partially shown in Figure 1 connects into the Trans- Alaska Pipeline System, along with many other wells 4, drilling sites 2, pipelines 5, and processing facilities 6.
- Thousands of individual pipelines are interconnected in the overall production and processing system connecting into the Trans-Alaska Pipeline System.
- the pipeline system illustrated in Figure 1 can represent a miniscule portion of an overall production pipeline system.
- pipelines 5 vary widely from one another in construction and geometry, in parameters including diameter, nominal wall thickness, overall length, numbers and angles of elbows and curvature, location (underground, above-ground, or extent of either placement), to name a few.
- parameters regarding the fluid carried by the various pipelines 5 also can vary widely in composition, pressure, flow rate, and the like. These variations among pipeline construction, geometry, contents, and nominal operating condition affect the extent and nature of corrosion and ablation of the pipeline walls, as known in the art.
- wall loss i.e., wall thickness loss
- ILI involves the insertion of a measurement tool, commonly referred to as a "pig", into the pipeline.
- Conventional measurement pigs are generally cylindrical bodies that include navigational or positional systems to monitor the location of the pig in the pipeline, along with instrumentation for measuring pipeline wall thickness as the pig travels along the pipeline propelled by the production fluid.
- the pig may be towed along the pipeline, if the pipeline is being measured while shutdown.
- Conventional ILI pigs measure loss of pipeline wall thickness using the technologies of magnetic flux leakage (MFL), ultrasonic tomography, electrostatic induction and the like.
- MFL magnetic flux leakage
- ultrasonic tomography ultrasonic tomography
- electrostatic induction electrostatic induction
- Examples of conventional ILI pigs suitable for obtaining ILI measurements include the CPIG MFLCAL ILI instruments available from Baker Hughes Pipeline Management Group, and the HIRES metal loss mapping tools available from Rosen Inspection Technologies.
- a sizeable number of pipelines 5 in a large-scale pipeline system are "unpiggable", in that those pipelines cannot be inspected by way of ILI for one or more various reasons.
- access to the pipeline may be restricted, valves or other impassable fittings may impede the travel of a pig through the pipeline, or a given pipeline may have varying diameter along its length such that a pig cannot snugly engage the pipeline walls as it travels.
- the operator of the production field must also monitor these unpiggable pipelines for loss of wall thickness.
- UT/RT measurements are typically obtained as the average of wall thickness measurements over some incremental distance (e.g., one foot) along the length of the pipeline.
- Conventional sampled UT/RT wall thickness measurements involve a substantial amount of labor, such as removing insulation or coatings from the pipeline, and physically traveling between sample locations.
- sampled UT/RT wall thickness measurements are typically performed on a periodic scheduled basis, especially in large-scale pipeline systems. For pipeline systems in a hostile climate, such as northern Alaska, such pipeline wall thickness measurements are preferably obtained in summer months, because some locations along some pipelines may require special precautions to be safely accessible in winter.
- Figure 2 illustrates the construction of evaluation system 10 according to an example of an embodiment of the invention, as realized by way of a computer system.
- Evaluation system 10 performs the operations described in this specification to determine the adequacy of sample coverage for a pipeline to determine the extreme value of pipeline wall loss.
- the particular architecture and construction of a computer system useful in connection with this invention can vary widely.
- evaluation system 10 may be realized by a computer based on a single physical computer, or alternatively by a computer system implemented in a distributed manner over multiple physical computers. Accordingly, the generalized architecture illustrated in Figure 2 is provided merely by way of example.
- evaluation system 10 includes central processing unit 15, coupled to system bus BUS. Also coupled to system bus BUS is input/output interface 11 , which refers to those interface resources by way of which peripheral functions P (e.g., keyboard, mouse, display, etc.) interface with the other constituents of evaluation system 10.
- Central processing unit 15 refers to the data processing capability of evaluation system 10, and as such may be implemented by one or more CPU cores, co-processing circuitry, and the like. The particular construction and capability of central processing unit 15 is preferably selected according to the application needs of evaluation system 10, such needs including, at a minimum, the carrying out of the functions described in this specification, and also including such other functions as may be desired to be executed by computer system.
- data memory 12 and program memory 14 are also coupled to system bus BUS, and provide memory resources of the desired type useful for their particular functions.
- Data memory 12 stores input data and the results of processing executed by central processing unit 15, while program memory 14 stores the computer instructions to be executed by central processing unit 15 in carrying out those functions.
- this memory arrangement is only an example, it being understood that data memory 12 and program memory 14 can be combined into a single memory resource, or distributed in whole or in part outside of the particular computer system shown in Figure 1 as implementing evaluation system 10.
- data memory 12 will be realized, at least in part, by high-speed random-access memory in close temporal proximity to central processing unit 15.
- Program memory 14 may be realized by mass storage or random access memory resources in the conventional manner, or alternatively may be accessible over network interface 16 (i.e., if central processing unit 15 is executing a web-based or other remote application).
- Network interface 16 is a conventional interface or adapter by way of which evaluation system 10 accesses network resources on a network.
- the network resources to which evaluation system 10 has access via network interface 16 can include those resources on a local area network, as well as those accessible through a wide-area network such as an intranet, a virtual private network, or over the Internet.
- sources of data processed by evaluation system 10 are available over such networks, via network interface 16.
- ILI library 20 stores measurements acquired by in-line inspection (ILI) for selected pipelines in the overall production field or pipeline system; ILI library 20 may reside on a local area network, or alternatively be accessible via the Internet or some other wider area network. It is contemplated that ILI library 20 may also be accessible to other computers associated with the operator of the particular pipeline system.
- measurement inputs 18 acquired by sampled ultrasonic or radiography (UT/RT) for other pipelines in the production field or pipeline system are stored in a memory resource accessible to evaluation system 10, either locally or via network interface 16.
- UT/RT measurements 18 are stored, or in which ILI library 20 resides, can be implemented in various locations accessible to evaluation system 10. For example, these data may be stored in local memory resources within evaluation system 10, or in network-accessible memory resources as shown in Figure 2. In addition, these data sources can be distributed among multiple locations, as known in the art. Further in the alternative, the measurements corresponding to UT/RT measurements 18 and to ILI library 20 may be input into evaluation system 10, for example by way of an embedded data file in a message or other communications stream. It is contemplated that those skilled in the art will be readily able to implement the storage and retrieval of UT/RT measurements 18 and ILI library 20 in a suitable manner for each particular application.
- program memory 14 stores computer instructions executable by central processing unit 15 to carry out the functions described in this specification, by way of which UT/RT measurements 18 for a given pipeline are analyzed to determine whether a sufficient number of measurements have been acquired to attain a particular confidence level for a particular conclusion regarding an extreme value measurement of that pipeline.
- These computer instructions may be in the form of one or more executable programs, or in the form of source code or higher-level code from which one or more executable programs are derived, assembled, interpreted or compiled. Any one of a number of computer languages or protocols may be used, depending on the manner in which the desired operations are to be carried out.
- these computer instructions may be written in a conventional high level language, either as a conventional linear computer program or arranged for execution in an object- oriented manner.
- These instructions may also be embedded within a higher-level application.
- an embodiment of the invention has been realized as an executable within the ACCESS database application using Visual Basic Algorithm (VBA) instructions to provide output in the form of an EXCEL spreadsheet, which is beneficial because of the relatively low level of user training that is required. It is contemplated that those skilled in the art having reference to this description will be readily able to realize, without undue experimentation, this embodiment of the invention in a suitable manner for the desired installations.
- VBA Visual Basic Algorithm
- these computer-executable software instructions may, according to the preferred embodiment of the invention, be resident elsewhere on the local area network or wide area network, accessible to evaluation system 10 via its network interface 16 (for example in the form of a web-based application), or these software instructions may be communicated to evaluation system 10 by way of encoded information on an electromagnetic carrier signal via some other interface or input/output device.
- ILI library 20 includes measurement data for each of those pipelines in the system upon which in-line inspection (ILI) has been carried out, and also statistical information based on those measurements.
- the pipelines and datasets for which ILI measurements have been made, processed, and stored in ILI library 20 will serve as "reference pipelines" for determining the statistical validity of conclusions to be drawn from the sampled measurement of other pipelines, according to this embodiment of the invention.
- reference pipelines for determining the statistical validity of conclusions to be drawn from the sampled measurement of other pipelines, according to this embodiment of the invention.
- evaluation system 10 may itself build ILI library 20, or alternatively another computer system may build ILI library 20.
- the particular computer system that carries out the processing illustrated in Figure 3 to build ILI library 20 is not of particular importance in connection with this invention.
- the building of ILI library 20 need only be done once, in advance of the operations to be carried out by evaluation system 10 in analyzing the sufficiency of sampled measurements according to this embodiment of the invention; if additional ILI measurement datasets are acquired for pipelines in the production field or pipeline system, these additional ILI measurements can be processed and added into ILI library 20, without recalculation of the distributions and statistics already in ILI library 20.
- process 22 the in-line inspection data for a pipeline are retrieved.
- the in-line inspection dataset k retrieved in process 22 includes measurements taken along the entire length of a pipeline, at a spacing determined by the particular ILI technology and system used to acquire the data. These data may be retrieved in process 22 from a memory resource or over a network, or otherwise received by the operative computer system involved in building ILI library 20.
- the operative computer system generates a distribution of wall loss thickness measurements for the pipeline from dataset k retrieved in process 22.
- Figure 4 illustrates process 24 in more detail, according to this embodiment of the invention.
- the ILI measurement data are converted into measurements at a unit length corresponding to the unit length of sampled measurements.
- the length of interest for a sampled UT/RT measurement may be a one-foot interval along the length of a pipeline. It is likely that ILI measurements do not correspond to one-foot intervals, but instead present data more finely ⁇ i.e., effectively continuous) than the sampled UT/RT measurements.
- the operative computer system converts the ILI measurement data into the desired unit of measurement (e.g., percent wall loss) at the unit length of interest (e.g., one-foot lengths) corresponding to the UT/RT measurements carried out by the measurement operator.
- This conversion can be carried out by conventional techniques, for example by selecting and storing the maximum wall loss measurement within each of the desired intervals.
- a useful calibration function can be derived by comparing only those measurements of relatively high (e.g., >20%) wall loss among the various technologies. This truncation of the measurements can provide a useful calibration function. Accurate calibration renders the ILI measurements useful in characterizing the distribution of the UT/RT measurements according to this embodiment of the invention, as will be described below.
- a calibration of ILI wall loss measurements to UT wall loss measurements has been performed from a regression of maximum wall loss values for several pipelines, as detected by ILI measurements, with maximum wall loss values for those same pipelines as detected by UT sampling.
- This regression used only those ILI values greater than 20% wall loss, and excluded obvious exceptions.
- this regression does not require the ILI measurement to be at the same physical location along the pipeline as a corresponding UT (or RT) measurement.
- calibration process 42 is performed over the ILI wall loss measurements for pipeline dataset k according to that function.
- the operative computer system arranges the calibrated ILI readings from process 42 into categories of wall loss, in a manner similar to a histogram.
- questions of interest from the sampled UT/RT measurements include i) whether a pipeline for which no UT/RT measurement exceeds 30% may in fact have a location at which wall loss exceeds 30%; and ii) whether a pipeline for which no UT/RT measurement exceeds 50% in fact has any location at which wall loss exceeds 50%.
- a useful arrangement of measurements produced by process 44 indicates the percentage or fraction of calibrated ILI readings in pipeline dataset k over the entire length of pipeline that fall within each decile interval of wall loss (e.g., ⁇ 10% wall loss, between 10% wall loss and 20% wall loss, between 20% and 30% wall loss, etc.).
- An example of such an arrangement, for a hypothetical pipeline for which calibrated ILI measurements have been derived, can be expressed in tabular form, which is convenient for storing in a conventional database:
- the hypothetical pipeline is 32377 feet long, and thus has 32377 ILI measurements in one-foot intervals along its length. It is also useful to retain some indication of the date at which the ILI measurements are obtained for each pipeline.
- calibration process 42 precedes the arrangement of the readings into a distribution in process 44.
- a distribution of the ILI measurements can be generated prior to calibration, and the distribution then calibrated according to a calibration function, if desired. In any event, the generation of a calibrated distribution of ILI measurements over the pipeline from its dataset k is performed in process 24.
- the maximum wall loss detected by ILI for pipeline k is useful to identify the maximum wall loss detected by ILI for pipeline k, as calibrated to a UT/RT reading.
- knowledge of the maximum wall loss enables a determination of the sample coverage required to provide a desired level of confidence that the highest sampled wall loss is within 10% of the true maximum wall loss.
- the calibrated ILI measurements for pipeline k generated in process 24 are interrogated by the operative computer system to identify this maximum reading, in process 26.
- ILI library 20 also includes the statistical behavior of random samples taken of these calibrated wall loss measurements for each pipeline. This behavior is determined, according to this embodiment of the invention, beginning with process 28, in which a Monte Carlo simulated sampling is performed to randomly sample the calibrated ILI wall loss measurements in pipeline dataset k that were obtained along the length of the pipeline.
- the distribution of calibrated ILI measurements may be idealized ⁇ e.g., all readings between 10% and 20% are considered to be 15%) within the intervals, and the idealized distribution is sampled, if desired.
- each instance of process 28 samples the distribution of calibrated ILI measurements in pipeline dataset k to a specified sample coverage level ofy ' %.
- a first instance of process 28 may randomly sample 0.1% of the calibrated ILI measurements.
- the sample measurements acquired in this random sampling are then evaluated according to particular questions of interest in the statistical analysis.
- the randomly sampled measurements may be evaluated to determine whether any measurements exceed 30% wall loss, whether any measurements exceed 50% wall loss, and whether any measurements are within 10% of the maximum wall loss reading over the pipeline (as identified in process 26). The results of this evaluation are then stored in memory.
- This Monte Carlo simulated sampling of the calibrated ILI measurements, at j% coverage, is repeated n times in process 28, with n being a relatively large number ⁇ e.g., on the order of thousands, for example ten thousand samples), and the results recorded for each sample.
- Decision 29 is performed to determine whether additional coverage levels are also to be analyzed; if so (decision 29 is YES), the coverage level j% is adjusted to the next sample coverage in process 30, and process 28 and decision 29 are repeated for this new adjusted coverage level j%.
- the sample coverage may be adjusted by 0.1%, at least up to a certain sample coverage level, at which point the step size may be larger.
- a maximum sample coverage can be determined based on the practical limit of UT/RT measurement coverage in the field (e.g., 7% or 10% coverage may be the maximum practical limit, for reasons of cost).
- process 32 is then performed to identify the sample coverage required for various confidence levels. These various confidence levels reflect upon the particular conclusions that are to be drawn from the eventual UT/RT sample testing of other pipelines. For example, the analysis may be interested in the following questions for a pipeline that has been sampled using UT or RT wall loss measurement technology:
- the distribution of calibrated ILI measurements generated in process 24 from pipeline dataset k, and also the sample coverage results to obtain the desired confidence levels for selected maximum measurement thresholds generated in process 32 for that pipeline, are stored in ILI library 20 in association with pipeline dataset k.
- Decision 35 determines whether additional datasets remain to be added to ILI library 20. These additional datasets may be measurements of other pipelines in the field or system, or additional ILI datasets for any of the same pipelines that were acquired at different times. If so (decision 35 is YES), index k is incremented to point to a next dataset to be processed, that ILI measurement dataset is retrieved in process 22, and the process is repeated.
- ILI library 20 If multiple ILI datasets for the same pipelines are available, the processed results from each of these datasets are stored in ILI library 20, as the statistical behavior of the wall loss measurements may change over times. As will be apparent from the following description, these additional ILI datasets for the same pipeline are individually considered, for purposes of this embodiment of the invention. If no additional datasets remain to be processed (decision 35 is NO), ILI library 20 is complete. Of course, if ILI measurement data is later obtained for other pipelines in the system, or if new ILI measurement data is later obtained for pipelines that are already characterized in ILI library 20, ILI library 20 may be updated to include results from such additional ILI monitoring.
- ILI library 20 includes, for each analyzed pipeline dataset, an indication of the distribution of wall loss thickness over its length as measured by ILI, and if necessary, as calibrated to a sampling measurement technology. These distributions of wall loss measurements are not theoretical or assumed distributions, but rather are based entirely on actual measurements.
- ILI library 20 includes, for each analyzed pipeline dataset, statistics regarding sampling of its wall loss measurement distribution based on a Monte Carlo simulation of such sampling. These statistics include the numbers of samples ⁇ i.e., sample coverage) necessary to determine whether a certain level of wall loss is present, to one or more confidence levels.
- the distribution and statistics stored in ILI library 20 for these pipelines will be used, by analogy, to evaluate the effectiveness of sample measurements taken of other pipelines in the pipeline system, according to this embodiment as will now be described.
- FIG. 5 illustrates the overall operation of a method of analyzing UT/RT measurements for sufficiency in determining whether an extreme value measurement has been obtained by sampling, according to this embodiment of the invention. It is contemplated that this process will be carried out by evaluation system 10, an example of which is described above relative to Figure 3, which may be a workstation operated by a human analyst determining the sufficiency of the UT/RT sample coverage for one or more pipelines. As mentioned above in connection with that description of evaluation system 10, it is also contemplated that the computational resources and components carrying out this process may be deployed in various ways, including by way of a web application or other distributed approach.
- pipeline PUI the analysis of UT/RT measurements for a particular pipeline under investigation
- this pipeline referred to herein as "pipeline PUI”
- Pipeline PUI is typically an "unpiggable" pipeline, for which only sampled measurements of wall loss have been obtained.
- the retrieved data for pipeline PUI preferably include the number of UT/RT samples acquired, as well as an individual wall loss value for each of the samples.
- sample UT/RT measurements may be pre-processed so as to be expressed as a figure of wall thickness loss (e.g., percentage wall loss).
- each UT/RT sample is considered as the maximum percentage wall loss detected over a relatively small interval (e.g., one foot) of the length of pipeline PUI, although other measurements may also be taken or used.
- the sample interval of the UT/RT measurements should match the interval to which the ILI measurement data were transformed (process 40 of Figure 4).
- the data retrieved in process 50 should also include an overall length of pipeline PUI, so that the sample coverage for that pipeline PUI is known.
- the next task in the method according to this embodiment of the invention is to identify one or more pipelines for which data are stored in ILI library 20 that have a distribution of wall loss measurements that are most similar to the distribution of UT/RT sample results. In this way, an estimate of the full distribution of wall loss measurements along the entire length of pipeline PUI can be made, and the effectiveness of the UT/RT sample coverage can be statistically determined using this estimated distribution.
- this identification of similar ILI pipelines to the sampled pipeline PUI begins with process 51, in which evaluation system 10 categorizes the sampled measurements for pipeline PUI into "bins", in a manner analogous to a histogram of the wall loss measurements.
- the wall loss measurements may be binned into deciles of the percentage wall loss (e.g., from 10 to 20% wall loss; from 20 to 30% wall loss, etc.).
- computer system categorizes pipeline PUI according to the maximum wall loss measurement value detected within its UT/RT samples.
- evaluation system 10 accesses ILI library 20 to select a
- test set of pipelines for which ILI measurement data are available and that have been processed, as described above, to have calibrated distributions of their measurements and also sampling statistics associated with those distributions.
- Process 54 identifies those ILI pipeline data sets (referred to herein as "ILI pipelines") that are similar, in a somewhat coarse sense according to the categorization of process 52, to pipeline PUI under investigation.
- process 56 determines the relative populations of measurements in a subset of the bins in the distributions of the ILI pipeline datasets in the test set, and the relative populations of a subset of the bins in the distribution of UT/RT measurements for pipeline PUI itself.
- Figure 6 illustrates a particular implementation of processes 52, 54, 56, by way of example, to more clearly describe the operation of this embodiment of this invention. It is to be understood, of course, that the specific bins, limits, etc., as well as the manner in which the selections of processes 52, 54, 56 are made, may vary widely from those in this example of Figure 6.
- categorization of pipeline PUI in process 52 is based on identification of the maximum wall loss sample value acquired for pipeline PUI and retrieved in process 50.
- a minimum threshold of wall loss may be enforced (not shown in Figure 6); for example, pipeline PUI may only be considered according to this method if its maximum wall loss measurement exceeds 10% wall loss, and if this 10% threshold is exceeded by three or more measurements.
- process 52 categorizes pipeline PUI into one of three possible categories of maximum wall loss: i) maximum sample wall loss less than 30%; ii) maximum sample wall loss between 30% and 50%; and iii) maximum sample wall loss greater than 50%.
- This categorization determines the manner in which the test set of ILI pipeline datasets is defined in process 54, and also the manner in which the bin populations in the measurement distributions are compared in process 56.
- process 54 is carried out by evaluation system 10 retrieving calibrated distributions for the ILI pipeline datasets in ILI library
- the calibrated distributions stored in ILI library 20 and retrieved in process 54 include calibrated distributions for separate pipelines, but may also include multiple calibrated distributions for some pipelines acquired over time (e.g., from annual inspections over the years).
- the calibrated distributions stored in ILI library 20 and retrieved in process 54 include calibrated distributions for separate pipelines, but may also include multiple calibrated distributions for some pipelines acquired over time (e.g., from annual inspections over the years).
- pipeline PUI on the retrieved calibrated distributions
- the categorization of pipeline PUI performed in process 52 also determines the manner in which the subsets of bins to be compared are defined in process 56. Because, in this example, pipeline PUI may fall into three categories, three different paths are defined through processes 54, 56, as shown in Figure 6.
- process 54a derives a test set of ILI pipelines as those ILI pipelines that have a calibrated maximum wall loss measurement that exceeds 30%; all ILI pipelines that have a maximum calibrated wall loss measurement of less than 30% are excluded from the test set.
- This definition of the test set in process 54 is made because the analysis of this method is intended, in this example, to determine whether sufficient UT/RT samples have been acquired for pipeline PUI to determine that the maximum wall loss does not exceed 30% (question (1) above).
- test set is defined in process 54a as those ILI pipeline datasets
- process 74a generates the relative populations of measurements within a subset of the bins of the distribution for each of these ILI pipeline datasets in this test set, for comparison with sampled pipeline PUI.
- the relative population of measurements within decile wall loss ranges below 30% for pipeline PUI will be compared against the same relative populations for each of the ILI pipeline datasets in the test set.
- evaluation system 10 determines, for each ILI pipeline in the test set identified in process 54a, the fraction of its calibrated ILI measurements that are between 10% and 20% wall loss, and the fraction that are between 20% and 30% wall loss, as percentages of the number of calibrated ILI measurements that are between 10% and 30% for that pipeline in the test set.
- the measurement values below 10% and above 30% are disregarded in process 74a.
- only the percentage of measurements between 10% and 20% wall loss, and the percentage that are between 20% and 30%, are considered, with these two bin populations adding up to 100%.
- this hypothetical pipeline would be within the test set selected in process 54a, as it has at least one wall loss reading above 30%.
- process 74a the subset of bins in this distribution considered in process 74a will be:
- process 76a the bins in the distribution of UT/RT sample readings for pipeline PUI are similarly truncated into a subset, expressed as a relative percentage of measured sample values between 10 and 20% wall loss, and between 20% and 30% wall loss (the sum of the two populations adding to 100%). It is possible, in this situation, that the number of sample values between 20% and 30% will be zero for pipeline PUI; that situation is unlikely for members of the test set of ILI pipeline datasets, considering that each pipeline in that test set has at least one reading above 30%. As will be described below in connection with process 58, the relative populations of the bins for pipeline PUI derived in process 76a will be compared against the relative populations of the bins for the ILI pipeline datasets in the test set derived in process 74a.
- process 54b defines the test set of ILI pipeline datasets as those that have maximum wall loss readings above 50%. This is because the question of interest for this category of sampled pipelines is question (2) above, namely whether the number of current sample values is sufficient, to a desired confidence interval, to determine whether pipeline PUI has or does not have a maximum wall loss exceeding 50%.
- each pipeline in the test set is processed by computer system to derive a subset of four bins in this example: namely the percentages of calibrated ILI measurements from 10 to 20% wall loss, from 20 to 30% wall loss, from 30 to 40% wall loss, and from 40 to 50% wall loss.
- the percentages of these four bins for each ILI pipeline dataset in the test set will add up to 100%.
- the example of the ILI pipeline dataset discussed above relative to process 74a would fall within the test set selected in process 54b, and the populations in its subset of bins produced by process 74b would be:
- each ILI pipeline dataset in the test set is similarly processed by evaluation system 10 in process 74b.
- process 76b the relative populations of sample values obtained for pipeline PUI by UT/RT in the subset of distribution bins are derived, for comparison in process 58 with the distribution subsets for the ILI pipeline datasets in the test set produced in process 74b.
- test set of ILI pipelines selected in process 54c is the same test set selected in process 54b, namely those ILI pipeline datasets with a maximum calibrated ILI measurement of greater than 50% wall loss.
- each ILI pipeline dataset in this test set is processed by evaluation system 10 to produce relative populations in a subset of bins for that pipeline. In this case, five bins are considered, specifically the four bins produced in process 74b plus a fifth bin for the relative percentage of readings exceeding 50% wall loss.
- the measurements for the ILI pipeline dataset of below 10% wall loss are discarded for purposes of process 74c, and thus the relative percentages in these five bins add up to 100%.
- the relative populations of sample values obtained for pipeline PUI are similarly considered in five bins, ignoring the sample values of 10% wall loss and below.
- the distribution subset for pipeline PUI can then be compared with the distribution subset of each of the ILI pipeline datasets in the test set, in process 58.
- the intervals of 10% (10 to 20% wall loss, 20 to 30% wall loss, etc.) may instead be set to intervals of 5%.
- the lowest threshold wall loss, below which the measurements and sample values are discarded in process 56 may vary from 10%; indeed, process 56 need not have such a lower threshold but may use all data (including a bin of, for example, 0 to 10% wall loss).
- the number of categories into which a pipeline PUI may be categorized may also vary. It is contemplated that the particular approach followed for a pipeline system may be determined by trial and error, with the eventual design of processes 54, 56 being specific for that system.
- process 58 carried out by evaluation system 10 examines the relative population of each bin generated for pipeline PUI with the relative populations in the same bins generated for each of the ILI pipeline datasets in the test set. It is useful for process 58 to return some figure of merit, reflecting a numerical measure of similarity, to facilitate the ranking of ILI pipeline datasets in the test set according to the similarity of their measurement distribution to that of pipeline PUI.
- evaluation system 10 performs comparison 58 for each ILI pipeline dataset in the test set, by calculating the difference between the percentage of readings in each bin for pipeline PUI with the percentage of calibrated measurements in that bin for the ILI pipeline dataset, squaring that difference for each bin, and adding the squared differences to produce a comparison value for that ILI pipeline dataset.
- a pipeline PUI within the second category maximum reading between 30% and 50% wall loss
- process 76b of: the squared difference values with the hypothetical ILI pipeline above would return (rounded to integers):
- this calculation of a figure of merit (e.g., sum of squares of bin-by-bin differences) is performed by system computer 10 for pipeline PUI against each of the ILI pipeline datasets in the test set, using the relative bin populations generated in process 56.
- the result of comparison process 58 is then evaluated in process 60, to determine one or more ILI pipeline datasets in the test set with the most similar distributions (i.e., distribution subsets) to that of pipeline PUI.
- process 60 is performed by evaluation system 10 interrogating and ranking the figure of merit (e.g., sum of squares of bin-by-bin differences) derived in process 58.
- the ILI pipeline datasets in the test set with the three lowest figure of merit values may be selected as the most similar ILI datasets, based on this comparison of the measurement distributions processed in the manner described above.
- one or more ILI pipeline datasets are selected as having measurement distributions, over their entire length, that are most similar to the distribution of sample values acquired by UT/RT for pipeline PUI under analysis.
- the one or more most similar ILI pipeline datasets selected in process 60 provide an estimate of the sampling behavior of pipeline PUI. Statistical analysis of the sufficiency of the UT/RT samples already acquired can now be made.
- system computer 10 identifies the sample coverage required for the desired result, based on the Monte Carlo statistics stored in ILI library 20 for the most similar one or more ILI pipeline datasets selected in process 60. As described above in connection with process 32 in Figure 3, each ILI pipeline dataset has had various sample coverage levels defined, based on Monte Carlo simulation, for various confidence levels and various result "questions" (e.g., "What is the sample coverage required to ensure, to a 95% confidence level, that a wall loss measurement of >50% will be sampled?").
- the sample coverage identified in process 62 is determined by the statistics produced for that ILI pipeline dataset in process 32 and stored in ILI library 20.
- multiple most similar ILI pipeline datasets e.g., three
- the number of ILI pipeline datasets selected in process 60 could be determined in a data dependent fashion, for example by considering the closeness of the f ⁇ gures-of-merit from process 58 in determining the number of ILI pipeline datasets to select in process 60.
- Process 62 identifies the sample coverage for pipeline PUI from some combination of the statistics stored in ILI library 20 for these multiple most similar ILI pipeline datasets. For example, a simple arithmetic average of the statistics may be used. Alternatively, a weighted average of these statistics may be derived. Other alternative combinations of these statistics can be readily derived by those skilled in the art having reference to this specification. In any event, the result of process 62 is to provide sample coverages, or levels of inspection, that are required to validly draw conclusions to specified confidence levels.
- system computer 10 can now evaluate decision 63 to determine whether the UT/RT sampling performed upon pipeline PUI is adequate to draw the conclusion desired by the human analyst. It is contemplated that the human analyst will indicate or select one or more potential conclusions for evaluation in decision 63. This evaluation simply compares the actual UT/RT sample coverage for the pipeline PUI with the combined statistics for sample coverage determined in process 62, to determine whether that UT/RT sample coverage is adequate to draw the selected conclusions.
- the human analyst can therefore conclude that, if hypothetical pipeline PUI in fact had any location at which wall loss exceeded 50%, the UT/RT sample coverage of 4.3% would have detected that condition at least 95% of the time; in other words, the analysis can conclude with 95% confidence that the sampled hypothetical pipeline PUI does not have any location with greater than 50% wall loss. Also in this case, the human analyst can also conclude, with 95% confidence, that the maximum sampled wall loss value obtained by UT/RT for hypothetical pipeline PUI is within 10% of the true maximum wall loss present in that pipeline.
- the result of decision 63 can be used to direct further action. If the sample coverage for the sampled pipeline PUI is sufficient to draw the desired conclusion (decision 63 is YES), then the result can be accepted (process 64). The appropriate action to store or log the results of this analysis for this pipeline PUI can then be taken in the usual manner for the particular pipeline system. If, however, the sample coverage for pipeline PUI is not adequate for drawing the desired conclusion (decision 63 is NO), the human analyst can then notify the appropriate personnel to obtain a new set of UT/RT sample measurements from that pipeline (process 66).
- the behavior exhibited by pipeline PUI in its UT/RT sample measurements indicate that a higher level of sampling is required, based on the experience gained from ILI measurements on pipelines with similar apparent behavior.
- the entire process may then be repeated using the entire new set of UT/RT sample measurements. This is because the additional samples may affect the entire distribution of the UT/RT sample measurements, such that different ILI pipeline distributions may now be most similar to the pipeline PUI; in other words, the additional sample measurements may alter the shape of the distribution, rather than merely add to the existing distribution.
- Important benefits in the monitoring of pipeline integrity in a large scale pipeline system can be obtained according to this invention.
- the operator can obtain a realistic level of confidence from sampled pipeline wall thickness loss measurements through the use of this invention, without relying on unsupportable assumptions about the statistical distribution of wall loss along the pipeline, and without relying on fluid and material models with unrealistic or unsupportable underlying assumptions.
- the operator of the production field or pipeline system can more efficiently perform the necessary monitoring to ensure a suitable level of integrity, by focusing measurement resources where most needed..
Abstract
Description
Claims
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BRPI0914648A BRPI0914648A2 (en) | 2008-06-30 | 2009-06-24 | method of assessing the sufficiency of various pipe integrity measurements, assessment system for assessing pipe wall thickness measurements, and computer readable media |
CN200980125411.0A CN102077197B (en) | 2008-06-30 | 2009-06-24 | Rapid data-based data adequacy procedure for pipepline integrity assessment |
EP09774110A EP2304602A2 (en) | 2008-06-30 | 2009-06-24 | Rapid data-based data adequacy procedure for pipepline integrity assessment |
CA2729157A CA2729157A1 (en) | 2008-06-30 | 2009-06-24 | Rapid data-based data adequacy procedure for pipepline integrity assessment |
EA201100121A EA021550B1 (en) | 2008-06-30 | 2009-06-24 | Method and system for evaluating pipeline integrity and computer-readable medium |
AU2009264938A AU2009264938B2 (en) | 2008-06-30 | 2009-06-24 | Rapid data-based data adequacy procedure for pipeline integrity assessment |
EG2010122116A EG26363A (en) | 2008-06-30 | 2010-12-14 | Rapid data-based data adequacy procedure for pipepline integrity assessment |
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US12/164,971 US9182081B2 (en) | 2008-06-30 | 2008-06-30 | Rapid data-based data adequacy procedure for pipeline integrity assessment |
US12/164,971 | 2008-06-30 |
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US (1) | US9182081B2 (en) |
EP (1) | EP2304602A2 (en) |
CN (1) | CN102077197B (en) |
AU (1) | AU2009264938B2 (en) |
BR (1) | BRPI0914648A2 (en) |
CA (1) | CA2729157A1 (en) |
EA (1) | EA021550B1 (en) |
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US9182081B2 (en) | 2015-11-10 |
CA2729157A1 (en) | 2010-01-07 |
WO2010002659A3 (en) | 2012-11-22 |
EA021550B1 (en) | 2015-07-30 |
EG26363A (en) | 2013-09-01 |
EP2304602A2 (en) | 2011-04-06 |
CN102077197A (en) | 2011-05-25 |
AU2009264938A1 (en) | 2010-01-07 |
US20090326865A1 (en) | 2009-12-31 |
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