Abstract:
A method of providing information regarding erosion in an oil and/or a gas production system, which system includes at least one equipment/piping, the method including the steps of obtaining CFD results regarding hot spots in the equipment/piping from a CFD analysis of the equipment/piping for a range of pressures, flow rates and sand rates; and to, during production, obtaining data regarding erosion rates in a particular location in the system; and combining the data regarding erosion rates and CFD results to estimate and monitor sand erosion rates in the hot spots of the system. Further disclosed is a module performing the method steps as well as a computer program.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    The present application is a continuation of pending International patent application PCT/IB2010/003334 filed on Dec. 22, 2010 which designates the United States and claims priority from Norwegian patent application 20093580 filed on Dec. 22, 2009, the content of which is incorporated herein by reference. 
       FIELD OF THE INVENTION 
       [0002]    The present invention relates to production systems for fluids such as oil and gas, which could contain particles that cause erosion inside the system. 
       BACKGROUND OF THE INVENTION 
       [0003]    The modern off-shore production of oil and gas comprises complex production systems from the wells to platforms and also further to shore. Apart from oil and/or gas the systems also contain water, solid particles such as sand and other unwanted matter that negatively affects the function and life of the system. 
         [0004]    Sand and other abrasive materials are one major concern regarding the function and life of the system where erosion is a key problem. Thus, in a system/equipment geometry like a valve tree or a manifold there may be a number of critical points where erosion affects the system/equipment. Computational Fluid Dynamics (CFD) is one of the branches of fluid mechanics that uses numerical methods and algorithms to solve and analyze problems that involve fluid flows. Computers are used to perform the millions of calculations required to simulate the interaction of liquids and gases with surfaces defined by boundary conditions. Even with high-speed supercomputers only approximate solutions can be achieved. The fundamental basis of almost all CFD problems is the Navier-Stokes equations, which define any single-phase fluid flow. 
         [0005]    In order to try to handle the situation the production systems are often arranged with a number of sensors that provide information regarding the system, such as sand detectors that are capable of detecting the presence of sand, and erosion probes that can measure directly the erosion rate. Sensor placements are restricted to a few locations. Erosion hot spots may occur in other locations than the sensor placements. Further the accuracy of the sensors may be limited, providing inaccurate information about the condition of the system. 
         [0006]    Thus, in a complex production system there may be many erosion hot spots that are not monitored. Further erosion rates might also change based on measured sand rates and the actual flow pattern through these geometries. 
         [0007]    Some methods that utilize CFD analysis in order to find erosion, corrosion or wear have been developed. The document WO 2009/073495 A1 discloses a method where one or more computational fluid dynamics (CFD) simulations may be conducted based on the results of a comparison step. CFD simulations may provide velocity vectors corresponding with various portions of a well tool with high fluid flow rates. 
         [0008]    One evaluation may be to determine if exterior portions of a rotary drill with high fluid velocity correspond with areas of high abrasion, erosion and/or wear. Comparing an “as built” 3D data file with an associated after use 3D data file and an associated 3D design data file may show areas of abrasion, erosion and/or wear with a high degree of precision and accuracy. Such evaluations and comparisons may result in changing the location and/or orientation of one or more nozzles on rotary drill bits. 
         [0009]    The geometrical configuration and dimensions associated with blades and/or junk slots may also be changed. The design of associated cutting elements and other cutting structures may also be modified to minimize abrasion, erosion and/or wear. 
         [0010]    The document US 2008/0257782 A1 discloses a method that includes assessing corrosion in a refinery operation having a piping network. Assessing can include identifying in a petroleum sample a presence and an amount of a species determined to be potentially corrosive to equipment in a refinery. A corrosion risk presented by the presence, the amount, and the boiling point of the species is determined. The corrosion risk is evaluated in view of piping network information. 
         [0011]    A system for implementing the method is also provided. An advanced flow model is a computational fluid dynamics model. The information from a corrosion model and the advanced flow model is fed into a corrosion simulation model to predict the corrosion rate. The corrosion simulation model basis its prediction on the particular corrosive species, such as for example naphthenic acid and sulphur compositions. 
         [0012]    Document Andrews, J et al.: Production Enhancement From Sand Management Philosophy. A case study from Staifjord and Gullfaks. SPE European Formation Damage Conference, Scheveningen, Holland, 25-27 May 2005. SPE 94511 discloses a method of handling sand contained in piping networks in order to increase production and the reduce down-time due to erosion. The document discloses monitoring the sand production by sensors, preferably a dual acoustic sensor system, and by well samples collected from a sand trap during well testing. 
         [0013]    Production data such as well rates, pressures, choke positions and uptime is collected daily. This data is then used for calculating an erosion potential at various locations assuming a base sand load. The erosion potential can then be related to sand measurements such as from the above mentioned acoustic sensor system and well samples in order to distinguish wells with high or negligible sand erosion potential. 
         [0014]    It is mentioned in the document that an on-line monitoring is provided for an operator, but in reality, no information or data is processed during actual production and provided to the operator directly. On the contrary data collected and processed is related to off-line measurements and given to the operator on a day to day basis not instantly but well after occurrence. It is also to be noted that it is only an erosion potential that is obtained, no actual or current conditions on the production piping due to erosions. 
       SUMMARY OF THE INVENTION 
       [0015]    The aim of the present invention is to provide a method and a module for accurately determining erosion in oil and/or gas production systems. 
         [0016]    This aim is obtained by a method and a module according to the features of the independent patent claims. Preferable embodiments form the subject of the dependent patent claims. 
         [0017]    According to a main aspect of the invention, it is characterised by a method of providing information regarding erosion in an oil and/or a gas production system, which system comprises at least one equipment/piping, the method comprising the steps of: 
         [0018]    obtaining CFD results regarding hot spots in the equipment/piping from a CFD analysis of the equipment/piping for a range of pressures, flow rates and sand rates; and to, during production 
         [0019]    obtaining data regarding erosion rates in a particular location in the system; and 
         [0020]    combining said data regarding erosion rates and CFD results to estimate and monitor sand erosion rates in the hot spots of the system. 
         [0021]    According to another aspect of the invention also data regarding flow rates and pressures are obtained. 
         [0022]    According to yet another aspect of the invention, unadjusted, interpolated or extrapolated CFD data results are used for obtaining an erosion pattern depending on the obtained data. 
         [0023]    According to a further aspect of the invention, said obtained data regarding erosion rates is derived from previously obtained and stored data. 
         [0024]    According to yet a further aspect of the invention, said estimated sand erosion rates are correlated and adjusted against actual erosion results. 
         [0025]    According to another aspect of the invention, said data regarding erosion rates also is obtained from sensors arranged in said equipment/piping. 
         [0026]    Said sensors may include physical and/or virtual sensors. 
         [0027]    According to another aspect of the invention, said erosion rates are estimated instantaneously. Alternatively accumulated erosion rates are estimated. Future erosion rates can also be estimated. 
         [0028]    According to a further aspect of the invention, data from sensors comprise data from sand detectors, erosion probes, pressure sensors, flow sensor, temperature sensors. 
         [0029]    According to yet an aspect of the invention, data further is obtained from production management tools, simulation tools and/or soft sensor methods. 
         [0030]    According to yet another aspect of the invention, the method further comprises the step of correlating available data with analytical models based on models from said computational fluid dynamics of the actual geometry of said system. 
         [0031]    The present invention also comprises a module, an erosion adviser, that is capable of performing the method steps mentioned above, where preferably the method steps are comprised in a computer program that is run by the erosion adviser. 
         [0032]    The advantages with the present invention are several and there are several uses for the present invention. Some examples for are: 
         [0033]    the erosion adviser, preferably working on-line, can supervise the erosion in all the system and give warnings if the erosion is higher than an acceptable level. This level is set by the user. 
         [0034]    an operator wants to minimize erosion on equipment/piping. Using a look-ahead functionality of the erosion adviser, it is possible to see how the erosion changes with the production rates. The erosion adviser will in this way be an input to the production planning. 
         [0035]    for maintenance purposes, the adviser can take into account the production history of the field and tell the operator how much is eroded away and, for a certain production profile, how long time it will take before the equipment has to be changed because of erosion. The results from the adviser will probably be different from what the design base tells, as the adviser uses more realistic data than the design base, which must be a worst-case. 
         [0036]    a valve, such as a choke valve, erodes during its lifetime, and the flow capacity (Cv) changes. If sufficient CFD analysis has been done for the valve (choke), the erosion adviser can tell the current Cv of the choke and hence act as guidance for intervention frequency. 
         [0037]    These and other aspects of, and advantages with, the present invention will become apparent from the following detailed description of the invention and from the accompanying drawing. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0038]    In the following detailed description of the invention, reference will be made to the accompanying drawing, 
           [0039]      FIG. 1 , which schematically shows the structure of a module according to the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0040]    An embodiment of the present invention as shown schematically in  FIG. 1  comprises an erosion adviser or module capable of handling and running computer programs, which computer programs are provided with data that are either stored in memories of the module as well as external data provided via input means, where the external data may come from a plurality of different types of sensors, data from other modules, and data entered by a user via keyboards, touch panels and the like. 
         [0041]    The module may further comprise filters for filtering signals from sensors, A/D-converters for converting and sampling the signals and a micro processor. The micro processor comprises a central processing unit CPU performing the functions according to the present invention that will be described by way of example. The micro processor further comprises a data memory and a program memory. The result from the functions may be stored in appropriate memory means, displayed to a user via display means and/or transmitted via wired or wireless network connections to other suitable receivers of data and/or results of the processing unit. Data and information may also be transmitted to the module via network connections. 
         [0042]    A computer program for carrying out the method according to the present invention is stored in the program memory. It is to be understood that the computer program may also be run on a general purpose computer instead of a specially adapted computer. 
         [0043]    The module requires several different data depending on the functionality requirements of a user. This input data may comprise a list of equipment/piping names or geometry names that are included in the production system to be analyzed, a design base and equipment/piping geometry, i.e. on the first hand wall thickness and equipment/piping geometry, CFD analyses, sand rate measured by sensors, sand detector design data, sand particle size, flow and historical flow, pressure, temperature, valve (choke) capacity Cv, valve footprint, historical data and erosion probes etc. The sensors may be both physical (hard) sensors positioned in the equipment/piping as well as virtual (soft) sensors. The soft sensors, for example edpm or a virtual flowmeter, are algorithms capable of estimating quality indexes when no physical sensors are available due to e.g. mounting costs. They make use of secondary variables, easily measured in real time, such as pressure, temperature, flow rates etc. and a mathematical model that correlates these parameters and the variables that must be monitored. 
         [0044]    Further input data, as data files, may be stored in memory means in the module, which data contain information regarding the system to be analyzed and maybe also information regarding the current state of the system. These files may contain geometry of the equipments/piping and/or system, design base data, CFD analyses, sensor or OPC (OLE (Object linking and embedding) for Process Control) tag names, recorded or constructed system state and look-ahead scenario, see further description below. 
         [0045]    With this input data the module will have different functionalities: 
         [0000]    1) On-line functionality. A real time system that monitors and analyzes the current system during production. With this functionality, the system may work with any data collection system like Master Control Station from GE Oil &amp; Gas or modelling systems like edpm (eField Dynamic Production Management System) from SPT Group. Such systems are known to the person skilled in the art and will not be described in detail.
 
2) Off-line functionality.
 
a) Design case functionality. The worst case possible is always used when designing the system (equipment/piping). This functionality shows the worst case scenario.
 
b) Look ahead functionality. Starts with current situation or user defined case. It then calculates results of future erosion rates according to user input.
 
         [0046]    Thus the module is capable of estimating both instantaneous and accumulated erosion rates at all spots in the analyzed system, based on i.a. measured sand and erosion rates at the sensor locations and the actual flowing configuration. The module can further use future estimated production conditions to calculate future erosion rates, provide estimates on the changes in valve (choke) characteristics due to erosion and give advice on intervention strategies, correlate valve (choke) wear estimate to either measured or modelled valve (choke) characteristics as well as estimation of sand production rate based on monitoring erosion at erosion probes in correlation with CFD simulation. 
         [0047]    The erosion adviser is preferably based on detailed CFD modelling of entire valve trees (X-mas trees), jumpers, connectors and manifolds under a range of conditions, but may also use other erosion models like Tulsa® from University of Tulsa or Veritas® from Det Norske Veritas. It can function either as a standalone unit, or together with an on-line system. 
         [0048]    It is at present not possible to use CFD on-line in the system, due to computing power limitations, so it is the results of the CFD work for the geometry that are used by the module. For each geometry, several CFD scenarios will have to be performed, for a range of different parameters. 
         [0049]    Here follows two examples of how the adviser will perform a calculation. In the first example all parameters are fixed except the flow rate and no measurements from erosion probes are available. 
         [0050]    CFD results for the analyzed geometry are available for three different flow rates (result a, b and c). These flow rates cover the expected operational envelope for the field. 
         [0051]    All necessary information is read, either from set-up files, scenario files, system instrumentation or a modelling system. Also the actual production flow rate is obtained. 
         [0052]    If the actual production flow rate, i.e. the flow rate for which the module will calculate the erosion, is between the flow rate for a and b, the module will interpolate between the results a and b and get an erosion pattern for the actual flow rate. This step as well as the following are done during production, i.e. on-line. 
         [0053]    In this erosion pattern the module will find the maximum erosion value. 
         [0054]    The module then uses an experimentally verified erosion correlation to calculate the value for the maximum erosion. 
         [0055]    The module will then adjust the whole erosion pattern to fit the maximum erosion value calculated and will present this adjusted erosion pattern to the user together with the calculated value for the maximum erosion. 
         [0056]    In the second example the CFD results will be adjusted to the measurements of an erosion probe: 
         [0000]    1) CFD results are available for several different combinations of parameters, e.g. for variations of flow rate, sand particle size and sand rate.
 
2) All necessary information is read, either from set-up files, scenario files, system instrumentation or a modelling system. The data from the erosion probe is also read. This is done during production, i.e. on-line, as well as the following steps.
 
3) The module will now interpolate (or extrapolate if necessary) between the CFD results to get an erosion pattern for the actual values read from the different sensors (or from a modelling system).
 
4) The module then uses an experimentally verified erosion correlation to calculate the value for the maximum erosion.
 
5) The module will then adjust the whole erosion pattern from 3) to fit the maximum erosion value calculated.
 
6) The module will then from the new erosion pattern from 5) find the predicted erosion in the location of the erosion probe and compare this erosion with the data read from the erosion probe. The values in the erosion pattern will then be adjusted according to the findings in this comparison. E.g. if the erosion probe tells us that the erosion is only half of what was predicted by the CFD-results, the values in the erosion pattern can be divided by two (this is a simplification, an erosion correlation will probably be used for this).
 
7) The adjusted erosion pattern resulting from 6) will be presented, preferably directly to the user together with the value for the maximum erosion from this erosion pattern.
 
         [0057]    In the first example, the parameter flow rate is the one that varies. In reality most parameters in a system will vary: sand rate, sand particle size, flow rate, pressure and others. So the module will have to interpolate (or in some cases also extrapolate) between several CFD results. In fact, in many cases none of the parameters will be exactly the same as the CFD simulations have used. 
         [0058]    A short description of how the system can work with two varying parameters follows: 
         [0059]    Varying parameters are sand particle size and flow rate. For sand particle size three values have been studied, a, b and c. For the flow rate the three rates x, y and z has been studied. In this example we can have CFD results for the following combinations: ax, ay, az, bx, by, bz, cx, cy, cz. 
         [0060]    If the actual sand particle size is between a and b and the actual flow rate is between y and z, the module has to combine/interpolate the CFD results ay, az, by and bz to get the erosion pattern for actual values of the parameters. If more parameters vary, interpolation between even more CFD results has to be done. The algorithms and equations used will depend on the parameters that vary. 
         [0061]    When the module is working according to any of the three functionalities mentioned above (last paragraph of page 7), the output or returned/shown results may be: 
         [0000]    1) Erosion rate, which may be either or all of instantaneous erosion, accumulated erosion and look-ahead erosion.
 
2) Erosion amount, i.e. how many millimetres are, or will have been, eroded away.
 
3) Wall thickness left.
 
4) Choke Cv, i.e. flow capacity.
 
5) Production sand rate.
 
6) Service intervals, i.e. time to wall thickness limit or valve (choke) intervention.
 
         [0062]    The module or adviser can work on both one or more pieces of equipment/piping or a whole system. The adviser must have the geometry of the equipment/piping in the memory. When working with a whole system the adviser has to have a set of geometries stored in the memory. 
         [0063]    When a specific equipment/piping is analyzed the output could be presented as values for the worst hot spot and a visual presentation of the whole piece of equipment/piping. When a whole geometry or list of equipment/piping are analyzed the output could be presented as values for worst hot spot, a list of the worst hot spot for each equipment/piping and a visual presentation of the most eroded piece of equipment/piping. 
         [0064]    The module will have several ways to present the results. It will be a module that can be used separately with its own user interface, or it can be used together with other control or on-line systems. 
         [0065]    The module will have its own interface to the user, where it will be possible to make several choices, such as e.g. functionality (on-line, design case, look-ahead), set-up files, presentation form (graphical or not), which results should be presented. 
         [0066]    The results will be shown in this interface, as numerical data and graphically when that is possible. The graphical presentation will typically be a 2-D presentation of the equipment/piping analyzed where the degree of erosion is presented with different colours. The input to the graphical presentation will be the CFD results. The relevant cases will have to be analyzed and the results will have to be in the input files of the module. The module will then interpolate between CFD results to be able to present the results for the current situation. If the input data is outside the range for the CFD analysis, e.g. outside valid operation window, the user should be warned about this. The user may also be provided with recommended service intervals. 
         [0067]    It is also possible to present the results as 3-D graphics, but there are at present not many cases where this will add value for the user. In some cases, no CFD analyzes are available and the module will perform the analysis with the chosen erosion correlation. The result will not be presented graphically, only numerically. 
         [0068]    The module will in many cases be used together with other control or on-line systems. It will communicate with the connected system via wired or wireless networks through appropriate communication protocols. The module can be called from the other systems, get the input from them and send the results back. Which input the calling system will give to the module will vary from case to case. It should be possible to send over all the needed inputs, except geometry and CFD analyzes. The input the calling system does not provide, should be available from set-up files. 
         [0069]    The module is intended to be able of primarily working during production, i.e. on-line as described above, but it may also be used off-line. When used off-line the module loads the files with input data needed for doing the analysis from its memory means. Further, the module can also create such input files from current scenarios to be used off-line. All this information is stored in the history database. 
         [0070]    The methods according to the present invention may be implemented as software, hardware, or a combination thereof. A computer program product implementing the method or a part thereof comprises software or a computer program run on a general purpose or specially adapted computer, processor or microprocessor. The software includes computer program code elements or software code portions that make the computer perform the method. The program may be stored in whole or part, on, or in, one or more suitable computer readable media or data storage means such as a magnetic disk, CD-ROM or DVD disk, hard disk, magneto-optical memory storage means, in RAM or volatile memory, in ROM or flash memory, as firmware, or on a data server. Such a computer program product can also be supplied via a network, such as Internet. 
         [0071]    It is to be understood that the embodiments described above and shown in the drawing are to be regarded only as non-limiting examples of the invention. The invention may thus be modified in many ways within the scope of the patent claims.