WO2010014471A2 - Estimating worst case corrosion in a pipepline - Google Patents
Estimating worst case corrosion in a pipepline Download PDFInfo
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- WO2010014471A2 WO2010014471A2 PCT/US2009/051379 US2009051379W WO2010014471A2 WO 2010014471 A2 WO2010014471 A2 WO 2010014471A2 US 2009051379 W US2009051379 W US 2009051379W WO 2010014471 A2 WO2010014471 A2 WO 2010014471A2
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- Prior art keywords
- pipeline
- extreme value
- wall thickness
- sample
- measurements
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Classifications
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N29/00—Investigating or analysing materials by the use of ultrasonic, sonic or infrasonic waves; Visualisation of the interior of objects by transmitting ultrasonic or sonic waves through the object
- G01N29/04—Analysing solids
- G01N29/06—Visualisation of the interior, e.g. acoustic microscopy
- G01N29/0654—Imaging
- G01N29/0672—Imaging by acoustic tomography
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F17—STORING OR DISTRIBUTING GASES OR LIQUIDS
- F17D—PIPE-LINE SYSTEMS; PIPE-LINES
- F17D1/00—Pipe-line systems
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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
-
- 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
- F17D5/005—Protection or supervision of installations of gas pipelines, e.g. alarm
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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
- F17D5/02—Preventing, monitoring, or locating loss
- F17D5/06—Preventing, monitoring, or locating loss using electric or acoustic means
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
- G01B17/00—Measuring arrangements characterised by the use of infrasonic, sonic or ultrasonic vibrations
- G01B17/02—Measuring arrangements characterised by the use of infrasonic, sonic or ultrasonic vibrations for measuring thickness
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
- G01B21/00—Measuring arrangements or details thereof, where the measuring technique is not covered by the other groups of this subclass, unspecified or not relevant
- G01B21/02—Measuring arrangements or details thereof, where the measuring technique is not covered by the other groups of this subclass, unspecified or not relevant for measuring length, width, or thickness
- G01B21/08—Measuring arrangements or details thereof, where the measuring technique is not covered by the other groups of this subclass, unspecified or not relevant for measuring length, width, or thickness for measuring thickness
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N29/00—Investigating or analysing materials by the use of ultrasonic, sonic or infrasonic waves; Visualisation of the interior of objects by transmitting ultrasonic or sonic waves through the object
- G01N29/04—Analysing solids
- G01N29/043—Analysing solids in the interior, e.g. by shear waves
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N29/00—Investigating or analysing materials by the use of ultrasonic, sonic or infrasonic waves; Visualisation of the interior of objects by transmitting ultrasonic or sonic waves through the object
- G01N29/44—Processing the detected response signal, e.g. electronic circuits specially adapted therefor
- G01N29/4454—Signal recognition, e.g. specific values or portions, signal events, signatures
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N2291/00—Indexing codes associated with group G01N29/00
- G01N2291/26—Scanned objects
- G01N2291/263—Surfaces
- G01N2291/2634—Surfaces cylindrical from outside
Definitions
- This invention is in the field of pipeline inspection. In one of its aspects, the invention is directed to the evaluation of the worst case corrosion in a pipeline from sampled measurements.
- 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.
- RT and ultrasonic tomography (UT) measurements are either not done, or require excavation. As such, it is not practical to acquire RT and UT measurements at small intervals along the entire length of a pipeline. Rather, for these and other reasons, these measurement technologies are typically carried out by random or semi-random sampling of wall thickness along the pipeline.
- 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, from which the wall thickness can be inferred.
- ILI inspection can also be carried out using ultrasonic energy, as well-known in the art. As such, ILI can acquire measurements of wall thickness at small intervals along the entire length of a pipeline.
- ILI monitoring cannot be applied to all pipelines, because of factors such as construction, location, or geometry.
- 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 an extreme value of pipeline wall thickness loss can be determined from sample measurements.
- a library of measurement datasets acquired by a 100% inspection method, such as in-line inspection, for a subset of the pipelines is stored in a database.
- simulated sampling of these datasets is used to derive a discrimination function or equation set, by way of which a statistical distribution shape can be selected from sample statistics and other pipeline descriptors.
- Sampled wall thickness loss measurements from another pipeline are statistically characterized, and the sample statistics and other pipeline descriptors are applied to the discrimination function to select a statistical distribution shape for the sample set. The extreme value of maximum wall thickness loss is then determined from the selected statistical distribution shape, as fit to the sampled wall thickness loss measurements for the sampled pipeline.
- 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 derivation of a discriminant function from an in-line inspection calibrated measurement library, according to an embodiment of the invention.
- Figure 4 is a flow diagram illustrating the evaluation of sample sets with candidate statistical distributions in the process of Figure 3, according to an embodiment of the invention.
- Figures 5 a through 5d are plots illustrating the shape of examples of candidate statistical distributions, used in an example of an embodiment of the invention.
- Figure 5e illustrates an example of the evaluation of an extreme value quantile according to an embodiment of the invention.
- Figures 5f through 5i are plots illustrating the evaluation of extreme value quantiles of candidate statistical distributions according to an embodiment of the invention.
- Figure 5j illustrates an example of a conventional discriminant function.
- Figure 6 is a flow diagram illustrating the estimation of worst case corrosion for a pipeline for which sampled measurements of wall thickness loss have been acquired, 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, for example, 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 W, 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 W 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 W depicted in Fig. 1.
- each well W 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 W; 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 W, and forwards the gathered output to processing facility 6 via one of pipelines 5.
- processing facility 6 is coupled into an output pipeline 5, which in turn may couple into a larger-scale pipeline facility along with other processing facilities 6.
- pipeline 1 would connect into a larger pipeline system, along with many other wells W, drilling sites 2, pipelines 5, and processing facilities 6.
- Some pipeline systems include thousands of individual pipelines that are interconnected into an overall production and processing 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, pipeline age, pipeline type, overall length, numbers and angles of elbows and curvature, location (underground, above-ground, underwater, or extent of such placement), to name a few.
- parameters regarding the contents (i.e., liquids, gases, solids such as sand, scale, or others, or combinations of these fluids and solids) carried by the various pipelines 5 also can vary widely in composition, pressure, temperature, 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.
- wall loss i.e., wall thickness loss
- ILI in-line inspection
- a measurement tool such as the tool commonly referred to as a "pig”
- 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. Alternatively, the pig may be towed along the pipeline, if the pipeline is being measured while shutdown.
- 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
- 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; other types of measurement devices and mapping tools known by those skilled in the art are also suitable for use in connection with this embodiment of the invention.
- a sizeable number of pipelines 5 in a large-scale pipeline system are "unpiggable" (unpassable by pigs, or otherwise inaccessible to in-line inspection), 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 ultrasonic tomography
- RT radiography
- conventional 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. As such, sampled UT/RT wall thickness measurements are typically performed on a periodic scheduled basis, especially in large-scale pipeline systems.
- 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 extreme value of pipeline wall loss (worst case corrosion) of a pipeline.
- pipeline wall loss wast case corrosion
- 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, coprocessing circuitry, and the like. The particular construction and capability of central processing unit 15 is 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 2 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.
- 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.
- ILI in-line inspection
- 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.
- the particular memory resource or location in which the UT/RT measurements 18 are stored, or in which ILI library 20 resides, can be implemented in various locations accessible to evaluation system 10.
- these data may be stored in local memory resources within evaluation system 10, or in network-accessible memory resources as shown in Figure 2.
- these data sources can be distributed among multiple locations, as known in the art.
- 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 an estimate of the likely extreme wall loss value for 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. For example, 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.
- VBA Visual Basic Algorithm
- these computer- executable software instructions may 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.
- a quantile is the data value marking the boundaries between consecutive ones of q essentially equal-sized data subsets in the distribution.
- the extreme value will be derived as the data value at the 99 th percentile of the distribution. Extreme value generation therefore obviously depends strongly on the choice of the statistical distribution to be used.
- a desired result from embodiments of this invention, as practiced, is an estimate of the extreme value of wall thickness loss (worst case corrosion) of a pipeline based on sample measurements taken along that pipeline.
- wall thickness loss measurements along a pipeline do not reliably follow known statistical distributions. Indeed, it has been observed that the distribution of actual pipeline wall thickness loss measurements along a pipeline does not fit any one statistical distribution, but often appears as a mixture of distributions. In addition, this mixture of distributions is not necessarily constant from pipeline to pipeline, which is intuitive given the variation of pipelines in length, material, construction, composition of the fluid carried, frequency and number of supports and couplings and joints, and the like.
- statistics from those pipelines that have been measured along their length are used to derive a discriminant function by way of which an optimal distribution can be selected for a pipeline for which only sampled measurements are available. Once the distribution is selected for the sampled pipeline, then an extreme value can be estimated and the confidence intervals for that extreme value estimate can be derived.
- the candidate statistical distributions, from which the optimal distribution is selected are based on ILI measurements taken along the length of the reference pipelines.
- ILI measurements are especially useful in connection with this invention, because of the ability of ILI technology to obtain thickness measurements at small increments along the length of the pipeline being measured.
- ILI measurement can be considered to be virtually, if not literally, "100% inspection" of the wall thickness or wall thickness loss along the measured length of the pipeline. This high degree of coverage provides an accurate measure of the minimum wall thickness along that pipeline, which in turn enables the corresponding statistical distribution of ILI measurements to provide a reasonable extreme value estimate for a pipeline for which only sampled measurements are available, according to this embodiment of the invention.
- these candidate statistical distributions may be based on measurements acquired by technologies other than ILI, or by ILI measurements at less than virtually 100% coverage, so long as the measurement coverage of those reference pipelines substantially characterizes the relevant length of the pipeline to an extent that one can be highly confident (e.g., on the order of 99% confident) that the true largest possible wall thickness loss has been observed.
- Full measurement coverage obtained by in-line inspection of the reference pipelines is, of course, particularly useful in connection with this embodiment of the invention, as that approach will provide the highest degree of confidence in the extreme value measurement for the reference pipelines.
- ILI library 20 includes measurement data for each of those pipelines upon which in-line inspection (ILI) has been carried out, and also includes statistical information based on those measurements as well as other parameters regarding those pipelines themselves.
- the pipelines for which ILI measurements may be useful include those pipelines within the same system as the pipeline of interest for which an extreme value estimate is being made, and also pipelines in other systems that can be considered as possibly analogous.
- the properties of Monte Carlo samples, at various sample sizes, taken from these datasets of ILI measurements stored in ILI library 20, along with the other pipeline descriptors, will be used to derive a discriminant function for selecting a statistical distribution from sample statistics and other parameters for other pipelines, according to this embodiment of the invention.
- evaluation system 10 may itself build ILI library 20 and derive the discriminant function, or alternatively another computer system may build ILI library 20 and derive the discriminant function, with the discriminant function then communicated or otherwise made accessible to evaluation system 10.
- the particular computer system that carries out the processing illustrated in Figure 3 to derive the discriminant function is not of particular importance in connection with this invention.
- derivation of the discriminant function need only be done once, in advance of the operations to be carried out by evaluation system 10 in analyzing sampled measurements according to this embodiment of the invention. Additional ILI measurement datasets that are acquired can be processed and added into ILI library 20. In this event, the discriminant function can then be recalculated, to be further updated with the additional distributions and statistics from the new datasets.
- 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 deriving the discriminant function.
- the ILI measurements retrieved in process 22 are expressed in incremental lengths consistent with UT/RT sample measurements taken of other pipelines.
- 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.
- pipeline wall loss measurements vary among measurement technology. More specifically, it has been observed that a bias exists between ILI measurements and those obtained from UT/RT inspections (with UT and RT measurements observed to correspond well with one another).
- 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.
- the result of this regression provided the following relationship of maximum wall loss thickness UT max as measured by sampled ultrasonic tomography to the corresponding ILI maximum wall loss thickness as measured ILI max :
- calibration process 25 is performed over the ILI wall loss measurements for pipeline dataset k according to that function.
- the true extreme value of wall thickness loss measurement indicated by the converted and calibrated ILI measurements will be used in deriving the discriminant function, according to this embodiment of the invention. Accordingly, that extreme value is identified for dataset k, and stored in memory in a manner associated with dataset k, in process 26.
- certain parameters about the physical pipeline can be useful in deriving the discriminant function. Examples of these pipeline descriptors include the length of the pipeline, the diameter of the pipeline, whether a water phase is present in the fluid carried by the pipeline, whether an oil phase is present, and the like. These parameters are also stored in memory in association with dataset k, in process 26.
- Decision 27 determines whether additional ILI datasets remain to be converted and calibrated. If so (decision 27 is YES), dataset index k is incremented in process 29, and the next dataset k is retrieved (process 22), converted into the desired increments of pipeline length (process 24), calibrated to UT/RT measurements (process
- process 25 determines which of the ILI datasets are suitable for use in deriving extreme value estimators.
- the operative computer system determines which of the converted and calibrated datasets are suitable for use in extreme value estimation, by selecting those datasets that exhibit patterns, in their measurement values, that are similar to the sampled measurement values obtained by UT/RT from other pipelines that are to be investigated.
- the discriminant function used to select an optimal statistical distribution is not based on the fit of the statistical distribution over the entire distribution of measurements, but rather will be based on the accuracy of the statistical distribution in estimating the extreme value of worst case corrosion.
- the actual distribution of wall thickness loss measurements typically appears to be a mixture of distributions.
- process 28 eliminates those datasets for which the converted and calibrated ILI measurements do not meet a similarity criterion.
- An example of a similarity criterion useful in process 28 is a percentage threshold of non- zero wall loss measurements. For example, if more than 50% of the converted calibrated wall thickness loss measurements of a dataset are zero-valued, that dataset will be eliminated from the derivation of the discriminant function by process 28.
- Process 30 begins, as shown in Figure 4 with the random sampling of calibrated ILI wall loss measurements in pipeline dataset k, in process 32. These random samples correspond to wall thickness measurements (expressed, in this embodiment, as percentage of wall thickness loss) at random locations along the length of the pipeline.
- Each instance of process 32 samples the distribution of calibrated ILI measurements in pipeline dataset k to a specified sample size j; for best results, the sample size j will correspond generally to a range of possible sample sizes of UT/RT measurements for pipelines in the field.
- the method of this embodiment of the invention is most useful in connection with UT/RT measurement sample sizes ranging from about ten to about one thousand.
- process 32 may reduce the number of random samplings performed at higher sample sizes j, as these higher sample sizes will exhibit less variability among one another (and will thus give the same result).
- certain sample statistics that may prove useful in deriving the discriminant function are also calculated for this sample set, and stored in memory. These statistics include at least those statistics that will be useful in fitting various statistical distributions to the sample values ⁇ e.g., mean, median, standard deviation or variance), as well as other statistics that may assist the discriminant calculation ⁇ e.g., 75% quantile value, kurtosis, skewness, sample size, maximum sample value, etc.).
- the set of candidate statistical distributions to be evaluated for extreme value estimation in this embodiment of the invention, will be preselected. It has been observed, in connection with this invention, that statistical distributions that are characterizable by two parameters are best suited for worst case corrosion estimation, as opposed to three-parameter statistical distributions such as the Generalized Pareto Distribution and the Generalized Extreme Value (GEV) Distribution.
- Figures 5 a through 5d illustrate the shapes of some statistical distributions that are contemplated to be generally useful in connection with this embodiment of the invention. These statistical distributions include the Minimum Extreme Value Distribution, the Logisitic Distribution, the Maximum Extreme Value Distribution, and the Weibull Distribution, shown in Figures 5 a through 5d, respectively. For the description of this embodiment of the invention, these four statistical distributions will be the candidate statistical distributions.
- each of the candidate statistical distributions are evaluated for each of the sample sets. Referring again to Figure 4, this operation begins, for a given sample set (each sample set being considered individually, without regard to the ILI dataset to which it belongs except by way of reference to its true extreme value and any associated pipeline descriptors that were stored in process 26), in process 34. In this process 34, each candidate statistical distribution is fit to the sample set by way of the statistics calculated for that sample set in process 32.
- This fitting of the candidate statistical distributions to the sample sets is contemplated to be performed by conventional statistical or mathematical computer software, typically applying maximum-likelihood techniques, and executed by evaluation system 10 or such other computer system that is operating to derive the discriminant function; various conventional computer software programs for carrying out this function are well-known to those skilled in the art.
- This fitting is performed for each of the candidate statistical distributions for the current sample set, in process 34.
- each of the candidate statistical distributions are interrogated to obtain an estimate of the extreme maximum value of wall thickness loss.
- the evaluation of a distribution to obtain an extreme value amounts to an evaluation of the distribution at a specific quantile.
- the extreme value quantile is thus determined as:
- each candidate statistical distribution, in process 36 can be performed using conventional statistical computer software as known in the art.
- An example of such computer software that is particularly useful in this evaluation process 36 is the SPLIDA statistical software package developed by Dr. William Meeker of Iowa State University; the SPLIDA software package is implemented in the S-Plus statistical programming language, and follows the methodologies, described in Meeker and Escobar, Statistical Methods for Reliability Data (Wiley-Interscience, New York, 1998).
- Figure 5c illustrates an example of a result from the SPLIDA statistical software package in identifying the value at the extreme value quantile. In this example, the software package returns an extreme value estimate of 45% wall thickness loss, taken at the 99.995% quantile.
- FIG. 5e The confidence level distribution for this estimate is illustrated in Figure 5e, and shows that this extreme value ranges from 38% to 53% wall thickness loss, at a 95% confidence level.
- the extreme value quantile calculated for each candidate statistical distribution is compared to the true extreme value that was stored for this dataset k in process 26.
- This comparison of process 38 may be a simple arithmetic comparison of the most likely extreme value determined in process 36 with the true extreme value; alternatively, the confidence level about the calculated extreme value may be considered.
- Figures 5f through 5i illustrate examples of comparison process 38, for an example in which the true extreme value of wall thickness loss was 38% as measured by ILI (and calibrated to UT/RT).
- Figure 5f illustrates that the extreme value indicated by the Maximum Extreme Value distribution was 30%.
- Figure 5g illustrates that the extreme value indicated by the Logistic distribution was 26%.
- Figure 5h illustrates that the extreme value indicated by the Minimum Extreme Value distribution was 29%.
- Figure 5i illustrates that the extreme value indicated by the Weibull distribution was 40%, which of course is the closest of these four candidate distributions in this example. An identifier of the closest estimating candidate distribution is then stored in memory, along with the calculated sample statistics and pipeline descriptors associated with the ILI dataset k from which this sample set was taken, also in process 38.
- the number “N” is the sample size of the particular sample set.
- the pipeline descriptors of "Serv PW”, “Serv PO”, and “Serv O” indicate, respectively, whether the pipeline service includes produced water, produced oil (i.e., oil in the pipeline as pumped from the ground), and “oil” (i.e., oil in the pipeline from the outflow of a separator). Other statistics and pipeline descriptors in this table are self-explanatory.
- process 39 If additional sample sets remain to be analyzed (decision 37 is YES), the next sample set is selected (process 39) and evaluation processes 34, 36, 38 are repeated for the next sample set. Upon all sample sets being evaluated and the best candidate statistical distribution identified (decision 37 is NO), process 39 is complete, and the discriminant function can now be derived in process 40 ( Figure 3).
- the discriminant function will be derived in the form of a set of linear equations.
- a useful step is to initially identify any of the sample statistics stored for each dataset that tend to correlate with one another, so that but one of those correlating statistics are preferably removed from the discriminant function derivation. Otherwise, those correlating statistics would tend to be overemphasized in the resulting function. For example, in one example of this method, kurtosis correlated with skewness and was therefore dropped from the analysis.
- Figure 5j illustrates simplified illustration of this type of problem by way of a figure from the Afifi reference, for the example of a two-response set (Population I and Population II) with a single predictor variable x. It is the value of predictor x that determines whether a particular member ought to be assigned to Population I or Population II.
- the discriminant function in this example is simply the vertical line shown in Figure 5h between the two populations.
- the discriminant function will be more complex than the simple example shown in Figure 5j, both in the number of populations to be separated, and also in the number of predictor variables.
- modern computing capability is fully capable of deriving the appropriate discriminator function, as a set of linear equations, using conventional techniques. It has been observed, in connection with this invention, that some of the prediction behavior is nonlinear, and as such it is useful to evaluate both the linear and the quadratic behavior of all of the possible predictors.
- logarithms may be used to express some of the predictors, simplifying the equations.
- Table 1 An example of a resulting discriminant equation derived according to an example of this embodiment of the invention, for an example of 538 datasets considered from eighteen ILI pipelines, is shown in Table 1 :
- process 40 creates and stores a set of classification equations, one for each candidate statistical distribution.
- Table 2 An example of these classification equations is shown in Table 2:
- the discriminant function according to this embodiment of the invention is a set of linear equations, each linear equation associated with one of the candidate statistical distributions.
- the linear equation for each candidate distribution is the simple linear combination of each of the numbers in a column of Table 2 with the data values for the pipeline of the interest corresponding to the sample statistics or pipeline descriptor for each row.
- An additive constant is also included in each linear equation ("Constant") at the bottom of the table.
- S Minimum Extreme Value distribution
- FIG. 6 illustrates the overall operation of a method of analyzing UT/RT measurements to obtain an estimate of such an extreme value, 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 include an individual wall loss value for each of a number of samples acquired at locations along pipeline PUI, for example by way of ultrasonic tomography (UT) or radiography (RT), or some other measurement technology.
- 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 the length of pipeline PUI, the number of UT/RT samples acquired, the diameter of pipeline PUI, and other pipeline descriptors as will be applied to the discriminant function described above.
- evaluation system 10 Upon retrieval of the UT/RT measurement data for pipeline PUI, evaluation system 10 next calculates sample statistics based on the UT/RT sample measurements retrieved, in process 52. These sample statistics include those statistics that are factors in the discriminant function derived from the ILI datasets, as described above. It is contemplated that these sample statistics calculated in process 52 will generally include common statistics such as mean, median, standard deviation, skewness, and the like.
- evaluation system 10 accesses ILI library 20 to retrieve the discriminant function, in the form of a set of linear equations according to this embodiment of the invention. As described above, these linear equations that make up the discriminant function enable the selection of the most appropriate candidate statistical distribution for evaluating the extreme value of worst case corrosion for pipeline PUI.
- Process 56 is next executed by evaluation system 10 to apply the sample statistics and pipeline descriptors for pipeline PUI to the discriminant function retrieved in process 54.
- process 56 involves the evaluation of each of the linear equations with the sample statistics and pipeline identifiers for pipeline PUI, and a comparison of the evaluated result from each of those linear equations to identify the equation returning the largest- valued result.
- the candidate statistical distribution associated with the largest-valued result of the discrimination function evaluation is, according to this embodiment of the invention, the best one of the candidate statistical distributions for accurately predicting the extreme value of worst case corrosion for pipeline PUI.
- evaluation system 10 evaluates an estimate of the extreme quantile value for pipeline PUI, to provide an estimate of the worst case corrosion.
- Evaluation process 60 involves first fitting the selected statistical distribution to the sample UT/RT values for pipeline PUI, for example by evaluation system 10 executing conventional statistical computer software applying maximum-likelihood functions, as known to those skilled in the art. Once the distribution is fit to the sample data, this distribution is used to obtain an estimate of the extreme maximum value of wall thickness loss (worst case corrosion). As discussed above, in this embodiment of the invention, the extreme value evaluation amounts to an evaluation of the distribution at a specific quantile that is related to the overall length of pipeline PUI:
- evaluation system 10 also returns one or more confidence levels and their associated intervals about the calculated extreme value.
- the results returned from process 60 are similar to those discussed above relative to Figure 5e, in that the peak of the distribution of extreme values corresponds to the worst case corrosion, with an interval surrounding that peak identified at one or more confidence levels.
- the extreme value of worst case corrosion, and the confidence level and associated interval, are evaluated by a system user or by programmed operation of evaluation system 10 itself, in process 62, to determine whether the degree of precision with which the worst case corrosion is identified in process 60 is adequate for the analyst's purposes. If so, the process is complete and another pipeline under investigation can be similarly analyzed. If the worst case corrosion value is sufficiently high, in the opinion of an expert user or relative to a pre-programmed limit at evaluation system 10, other action such as performing additional statistical assessment of the sampled data already obtained for pipeline PUI, and perhaps acquiring new or additional sample data, can be performed to define the appropriate action to be taken in light of the worst case corrosion in pipeline PUI. The appropriate actions to be taken may also depend on the precision of the estimate at the desired confidence level, if the value of the worst case corrosion determined in process 60 is somewhat high.
- 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 estimate of worst case corrosion 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 and in-depth statistical analysis to ensure a suitable level of integrity, by focusing measurement and analytical resources where most needed.
Abstract
Description
Claims
Priority Applications (7)
Application Number | Priority Date | Filing Date | Title |
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EP09790717A EP2361382A2 (en) | 2008-08-01 | 2009-07-22 | Estimating worst case corrosion in a pipepline |
CN200980130738.7A CN102625911B (en) | 2008-08-01 | 2009-07-22 | Estimating worst case corrosion in a pipeline |
CA2730569A CA2730569A1 (en) | 2008-08-01 | 2009-07-22 | Estimating worst case corrosion in a pipeline |
EA201100274A EA201100274A1 (en) | 2008-08-01 | 2009-07-22 | METHOD AND SYSTEM FOR THE ESTIMATION OF PIPELINE INTEGRITY |
AU2009276891A AU2009276891B2 (en) | 2008-08-01 | 2009-07-22 | Estimating worst case corrosion in a pipepline |
BRPI0916855A BRPI0916855A2 (en) | 2008-08-01 | 2009-07-22 | pipe integrity estimation method, evaluation system and computer readable media |
EG2011010123A EG26277A (en) | 2008-08-01 | 2011-01-19 | Estimating worst case corrosion in a pipeline |
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US12/349,851 | 2009-01-07 |
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EP (1) | EP2361382A2 (en) |
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CA2730569A1 (en) | 2010-02-04 |
CN102625911B (en) | 2015-06-03 |
WO2010014471A3 (en) | 2012-10-26 |
AU2009276891A1 (en) | 2010-02-04 |
EP2361382A2 (en) | 2011-08-31 |
EG26277A (en) | 2013-06-11 |
CN102625911A (en) | 2012-08-01 |
US7941282B2 (en) | 2011-05-10 |
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