WO2015058811A1

WO2015058811A1 - Methods and apparatus for determining contents of production equipment

Info

Publication number: WO2015058811A1
Application number: PCT/EP2013/072417
Authority: WO
Inventors: Lene Amundsen
Original assignee: Statoil Petroleum As
Priority date: 2013-10-25
Filing date: 2013-10-25
Publication date: 2015-04-30

Abstract

There are described methods and associated apparatus for determining the contents of production equipment containing at least one product from a well. In certain embodiments, the production equipment is heated, and during the heating, the temperature and time is measured, the temperature being measured at at least one temperature sensor located adjacent to the production equipment. A characteristic of the contents of the equipment,for example the thickness of a wax deposit, can be determined from either or both of the measured temperature and time associated with said heating. In some embodiments, the wall of the production equipment is a source of the heat for providing a heat pulse.

Description

Methods and apparatus for determining contents of production equipment

Technical field The present invention relates to determining of contents of production equipment, such as for example pipes or separator equipment for containing fluid from a well. In certain embodiments, the invention relates to determining or monitoring the thickness of waxy material deposited on a wall of the equipment. Background

Fluids may be conveyed using conduits, conveniently as a multiphase flow, in which more than one fluid is present at the same time. In oil and gas production, fluid products from a well may be conveyed in a multiphase flow. This is advantageous because where more than one fluid is to be transported only one pipeline is needed. This is particularly advantageous in environments that are difficult to reach, such as sea beds and harsh climates, as the use of only one pipeline greatly reduces capital costs. Further downstream, the multiphase flow is received through a separator which separates the fluids of the multiphase flow before they are carried onward for further processing into a petroleum product.

It is useful for purposes of flow assurance to determine and/or characterise the contents of the flow space inside such pipelines. Such contents may include fluids and material deposits.

For example, it is useful to determine what fluids are present and the distribution of such fluids, and to determine the presence and thickness of any deposits which may have formed on pipe surfaces. The different fluids of a multiphase flow have different flow characteristics governed by their differing viscosities and densities. This makes it difficult to characterize multiphase flow. It is important to be able to characterize this as the flow characteristics describe the flow conditions. In turn, this is important for process control. For example, in pipe equipment one may wish to avoid excessive liquid accumulation. In separator equipment, one may wish to avoid contamination of the separator output (e.g. water into oil or oil into water). The flow of fluid can be affected by deposits. The flow characteristics may also indicate whether plugging of the flow or corrosion and erosion of pipeline and other equipment is likely. Plugging can occur by the formation of waxy deposits inside a pipeline or separator. In order to convey fluids in a multiphase flow safely, and with proper control, it is imperative to have a good knowledge about the flow characteristics. One of the more important flow characteristics is the phase distribution (sometimes termed flow regime).

It may be useful to monitor the contents inside pipes over time. For example, it may be useful to monitor the development of a deposit on a surface inside the equipment. In such a case, the thickness of a deposit may be monitored, so that if necessary it can be removed.

Flow characteristics are typically determined using empirical equations that have been tested using laboratory experiments. However, these equations are limited as they cannot take account of all of the variables that may be present in a working multiphase flow system, such as inclination of equipment, variations in flow rate and so on. Furthermore, as the test rigs used to verify the empirical equations have significantly smaller diameters than the equipment actually used in production, the validity of the models for the full scale production equipment is unknown. Multiphase flow can also be predicted theoretically using models and equations but these suffer similar limitations to using empirical models. Other techniques for determining flow characteristics involve using flow rates or using heat sources and associated probes. However, flow rate techniques may be inaccurate or invasive and therefore expensive and disruptive.

Flow regime and contents of production equipment has also been determined by applying a pulse of heat to the equipment based on using the measured decay in temperature after the heat pulse has been applied to determine contents [i.e. during cooling of the equipment] (see: Hoffmann, R., L. Amundsen, and R. SchGller, 201 1 , Online monitoring of wax deposition in subs-sea pipelines, Meas. Sci. Technol. 22, doi:10-1088/0957-0233/22/7/075701 ; and Hoffmann, R., L. Amundsen, R. Schulkes, R. B. SchGller, 2012, Measuring phase distribution using external thermal excitation, Flow Meas. Inst., 26, 55-62, doi: 10.1016/j.flowmeasinst.2012.04.008). The arrangements used for providing the heat pulse are based on heat sources provided adjacent to the equipment whereby heat is transferred from those sources to the equipment, e.g. pipe walls, by dissipation of heat. For example, an annulus may be formed around the wall of the pipe and filled with hot fluid. Heat from the hot fluid is then transferred to the wall.

Summary of the invention

The inventors have now recognised several improvements that go against the previously taught approaches to the use of heat pulses for determining contents of production equipment.

Various aspects of the invention are set out in the claims as appended hereto. Each feature disclosed or illustrated in the present specification may be incorporated in the invention, whether alone or in any appropriate combination with any other feature disclosed or illustrated herein.

The invention provides numerous advantages as will be apparent from the description, drawings and claims.

Description and drawings

There will now be described, by way of example only, embodiments of the invention with reference to the accompanying drawings, in which:

Figure 1 is a side cross-sectional representation of production equipment adapted to be supplied with an electrical current, according to an embodiment of the invention; Figure 2 is an end-on cross-sectional representation of the production equipment of Figure 1 showing further detail;

Figure 3 is a representation of an arrangement including a computer device for determining contents of the production equipment of Figures 1 and 2; Figure 4 is a graph showing temperature before, during and after the provision of a heat pulse to the production equipment;

Figure 5A is a graph showing decay in temperature during cooling of the production equipment in the presence of a deposit of different thicknesses;

Figure 5B is a graph showing an increase in temperature during heating of the production equipment to a target temperature for the deposits of Figure 5A;

Figure 5C is a graph showing an increase in temperature during heating of the production equipment for a target period of time for the deposits of Figure 5A;

Figure 6 is a graph of time constants obtained from the temperature decay for different temperature sensors;

Figure 7 is finite element model for use in determining contents of production equipment, according to an embodiment of the invention; Figure 8 is a flow chart showing steps of a method for determining contents of production equipment, according to an embodiment of the invention;

Figure 9 is an arrangement for determining the presence of a deposit using a single sensor according to an embodiment of the invention; and

Figure 10 is a representation of production equipment having an induction coil provided around the pipe to generate electrical currents in the production equipment, according to an embodiment of the invention. Referring to Figure 1 , there is illustrated production equipment 1 comprising a wall 2. The wall is arranged to be a source of heat. In Figure 1 , the production equipment 1 is provided with electrical connectors +, - for supplying the wall with an electrical current from an electrical power supply. The wall conducts electrical currents whilst providing a degree of electrical resistance to the flow of current. Heat is then generated in the wall in which the current flows, in the material of the wall. The wall may be formed of metal such as steel or the like. The particular material may be selected according to the required resistive / heat-generative performance.

The production equipment 1 in this example is a tubular separator. In other variants, the equipment may be a pipe section. In some variants, heating of the wall could alternatively be provided by a heat source provided externally of the production equipment and heat transferred to the wall, for example by using tubes or an annulus surrounding the wall 2 filled with hot fluid. Referring to Figure 2, the internal arrangement of the production equipment 1 can be seen in more detail. The production equipment 1 has a space 31 defined therein for receiving a multiphase flow. The space 31 is provided inside the wall 2, and is defined by an inner wall surface. A plurality of temperature sensors 4, 5, 6, 7, 8 are also disposed around the production equipment 1 . To ensure good contact between the temperature sensors and the wall 30 of the production equipment 1 , grooves may be introduced to an outer surface of the wall. Each groove is used to house a temperature sensor.

Referring to Figure 3, there is illustrated a system for determining contents of production equipment, in particular for characterizing multiphase flow. As can be seen, the wall 2 is connected to an electrical power supply 20 used for providing an electrical current in the material of the wall, for heating the production equipment.

The temperature sensors are connected to a computer device 9 using an In/Out device 10. The In/Out device 10 is used for sending instructions to and for receiving data from the temperature sensors. The processor 1 1 is used for analyzing measurements taken from the temperature sensors. It will be appreciated that the processor functions may be implemented using different processors, but for the sake of clarity only one processor 1 1 is shown.

Similarly, the power supply 20 is connected to the computer device 9 using the In/Out device 10. The In/Out device 10 is used for sending instructions to the power supply apparatus 20, for example to control a switch to selectively deliver the electrical current to the production equipment. The In/Out device 10 is further used for receiving data from the power supply 20, for example to provide status information or the like. The processor 1 1 is also used for generating instructions to be sent to the power supply apparatus 20 to control the supply of power to the wall of the production equipment.

In this exemplary embodiment, a display 12 is also provided for allowing a user to see the results of the analysis of information from the temperature sensors. A computer readable medium in the form of a memory 13 is also provided. The memory 13 can be used for storing collected data, pre-programmed instructions for the power supply apparatus 20 and temperature sensors 4,5,6,7,8, and a database 14 of thermal responses and Prandtl numbers for a variety of fluids and fluid mixtures under different conditions. The memory 13 may also be used to store a program 15 that includes instructions to be executed by the processor.

Note that Figure 3 illustrates a controller in the form of a computer device 9 connected to a single item of production equipment 1 . It will be appreciated that a single computer device 9 may be connected to a plurality of items of production equipment, or to control a plurality of wall sections at different points on one or more items of production equipment in order to determine contents and characterize multiphase flow in different items of production equipment or at different points on the same production equipment. When it is required in some way to determine contents or characterize the flow of the multiphase fluid, the processor 1 1 sends an instruction to the electrical power supply 20 to supply a current to the wall of the production equipment, typically as a heat pulse for a limited period of time. When the wall is supplied with a current, it begins to heat up due to the electrical resistance of the wall material. The heat generated in the wall is conducted through the wall and heats up the contents of the production equipment. The fluid in this example comprises output from a subsurface well.

While the supply of the electrical current is being provided, the temperature of the walls of the production equipment 1 starts to rise, the heat being dissipated into the fluid contained inside the production equipment. The rate at which the temperature rises is dependent, among other things, upon the nature of the fluid or contents adjacent to the wall of the production equipment 1 , and in particular on the heat transfer coefficient between the inner wall of the production equipment 1 and the fluid adjacent to the inner wall surface. If the wall has a waxy layer deposited on its inside surface, this also affects the heat transfer coefficient between the wall and the fluid adjacent to the wall. Such wax may precipitate out from the fluid, upon cooling of the fluid as it progresses from the well. For example, in the case of a subsea pipeline, the temperature of seawater in the environment surrounding the production equipment can cause cooling of the fluid being transported inside the production equipment and produce wax. The heat pulse is generally provided so that the wax deposited is not removed, so that the build-up of wax can be characterised and monitored.

The temperature of the walls is measured using the temperature sensors. The measurement signal of interest is the transient temperature response associated with heating the wall of the production equipment. The measurement time for one heat pulse is determined by the thermal mass that needs to be warmed up. This mass includes the separator pipe wall (with any deposit).

If a significant deposit of wax is determined to be present on an inside surface of the production equipment wall it may be desirable to remove the wax deposit. This may be done by supplying power and heating the wall for a sufficient period of time that the wax is melted at the contact with the wall and released in solidified form into the flow of fluid inside the production equipment. When heat is not supplied for a sufficient period of time, the wax deposit will remain in situ as may be the case for routine heat pulses to determine fluid contents or distribution.

The heat transfer coefficient depends on the Prandtl, P_r, number, which reflects the fluid's thermal properties. The Prandtl numbers for typically transported fluids (oil, gas, water) differ enough to show a significant difference in the measured thermal response. In particular, the measured temperatures during the heating phase can be sufficiently different to distinguish between the different fluids.

The Prandtl number is dimensionless, as it is a ratio of momentum diffusivity to thermal diffiusivity, and can be defined by:

where v is kinematic viscosity, a is thermal diffusivity, μ is dynamic viscosity, k is thermal conductivity, cp is specific heat, and p is density. A low Pr usually indicates that conductive transfer is a dominant mechanism of heat transfer, and heat diffuses quickly, whereas a high Pr usually indicates that convective heat transfer is a dominant mechanism of heat transfer, and heat diffuses less quickly. It can be seen from Figure 2 that in multiphase flow, a high density fluid is likely to be adjacent to the lower temperature sensors 7, 8 whereas a lower density fluid will be flowing adjacent to the higher temperature sensors 4, 5. This type of flow is termed stratified flow. The invention can be applied to other types of flow, but stratified flow is used as an example. Figure 4 shows an example thermal response from temperature sensor 4 and temperature sensor 8 in an example in which the production equipment 1 is transporting oil and water in stratified flow and will therefore be different. This may be a representative response for heat generation in a wall portion for a period of 10-30 seconds. In this example, owing to the differing densities of the two fluids, temperature sensor 4 is adjacent to oil in the production equipment 1 , and temperature sensor 8 is adjacent to water in the production equipment 1. The temperature at the sensor 4 adjacent to the oil rises more quickly, reaches a higher value, and decays more quickly than the temperature at the sensor 8 adjacent to the water. This information can be used to assist in characterizing multiphase flow, or at least in determining which phases are present and at what points in the conduit.

With reference to Figures 5A to 5C, temperature-time relationships at different deposit conditions are shown. Figure 5A is similar to Figure 4, in that it shows the temperature decay associated with deposits of different thicknesses, namely wax deposits with a thickness of 1 .0, 0.5, and 0.1 mm, after the active heating phase has ceased. There is a contrasting decay, depending on the thickness. As can be seen, a more slowly decaying temperature response is measured where there are thicker deposits.

Referring additionally to Figures 5B and 5C, it can also be seen, importantly, that the temperature development during heating also differs significantly depending upon the thickness of the deposit. The respective curves in Figures 5B and 5C show the temperature development in the presence of a wax deposit with a thickness of 1 .0, 0.5, and 0.1 mm, all other conditions being the same. Thicker deposits provide a greater insulation effect, whereby heat dissipates less easily from the wall. Consequently, the temperature measured at the wall increases more quickly where there are thicker deposits.

Figures 5B and 5C also show how the heating can be performed in practice. In Figure 5B, a target peak temperature is pre-determined, for example set in the memory of the computer control device. This is the temperature to be achieved in the wall. The power supply is controlled to heat the wall to reach the target peak temperature. The time to achieve the temperature is measured, and this can vary depending on the contents of the equipment. As can be seen in this example, it takes longer to reach the target temperature for a thinner deposit. Thus, in one variant, the measured time to reach a certain temperature can be used to determine the presence or thickness of the deposit.

In Figure 5C, the converse is shown. A suitable target heating time period is pre- determined, for example set in the memory of the control device. This is the time period over which heating is to take place, e.g. applying current to actively generate heat in the pipe wall. The temperature achieved in that time period is measured. As can be seen, a higher temperature is reached in that period where the deposits are thicker. Thus, in another variant, the temperature after a certain heating time period can be used to determine the presence or thickness of the deposit.

The supply current may also be predetermined and may be set to an appropriate value to facilitate distinguishing different contents, using the technique in Figures 5B or 5C above.

Temperature curves such as those of Figure 4 and Figures 5A to 5C can be obtained at each temperature sensor and used for determining flow regime. For example, the measured temperatures, times and/or curves may be compared with reference temperature, times and/or curves, for example as may be previously determined for different types of contents of fluids and/or deposits.

The temperature response during the heating, e.g. to reach the target temperature or target time period, by application of the heat pulse may be used to determine the flow regime. The actual temperature values, time, or parameters of the curve relating the temperature with respect to time may be used. For example, a parameter can be extracted from the measured temperature response at each sensor for the heating phase. The parameter could be a gradient or curvature of the measured temperatures with respect to time during heating, or other parameter characterising the response during the heating.

In Figure 4, it can be seen that a curve is fitted to the measured temperatures. A parameter of the fitted curve such as the gradient or curvature of the fitted curve, or the actual temperature or time values of the curve, may be used and compared with corresponding reference parameters or values for particular types of contents for example obtained from reference curves, at one or more sensors, and used to determine the flow regime

The flow regime can be determined from the temperature measurements during heating, as described above, without using the response of the decay in temperature after the heat pulse. However, the temperature response after the heat pulse, i.e. decay in temperature may also be used. In this case, a parameter in the form of a time constant can be extracted from the temperature response of each sensor from the change in temperature after application of the heat pulse. A logarithmic decrease in temperature occurs shortly after the maximum temperature has been measured, as demonstrated in Figure 4. Rather than measuring the time it takes to reach a certain temperature level, which would only use one temperature measurement point and may in general introduce a great deal of uncertainty (although in specific cases a single measurement value can be sufficient), determining the time constant from the logarithmic decrease in temperature uses a large series of points and smoothes out corresponding errors. Similar benefits are associated with using the fitted curves of the rising response.

From the rising temperature response during the heating, an independent determination of contents can be obtained. When combining this determination with data from the decaying response, a more accurate determination of the contents of the production equipment may be possible.

In particular, the determination of contents such as wax thickness from the heating period response (during attainment of target period or temperature), and from the decay response (after heating has ceased and current supply switched off), can be compared with each other and used detect changes in the condition of the equipment or faults in the system and equipment more generally.

If the phases expected in the production equipment are already known (in this case pure oil and pure water with no dispersion) then the flow regime can easily be determined. The time constant and/or gradient parameters can be used to determine one or more parameters of the fluid, such as the type of fluid flowing in proximity to the temperature sensor. Turning to Figure 6, an example time constant for each sensor 4, 5, 6, 7, 8 is shown. It can be seen that the time constant over a significant period of time for each temperature sensor 4, 5, 6 is around the same, whereas the time constant for temperature sensors 7 and 8 are similar to each other but different to the time constants of temperature sensors 4, 5 and 6. This clearly indicates a stratified flow with one fluid phase in the production equipment 1 up to at least the level at which temperature sensor 7 is located, and another fluid phase in the production equipment 1 above the level at which temperature sensor 7 is located.

The parameters and/or time constant extracted from the rising and decaying parts of the temperature response can be used to characterize fluid flow, as it is affected by both the fluid properties and the flow velocity. For example, the parameters and/or time constant can be measured for single-phase flow (for each of the used fluids in turn) at different flow velocities. This can be used to generate a look-up table of parameters and/or time constants as a function of the type of fluid and the flow velocity. A measurement from a multiphase flow can be subsequently looked-up in the table (the flow velocity has to be measured in parallel) to determine the phase distribution. This may be done manually or using a computer to give an indication of fluid flow.

If a reliable model of fluid flow within the measurement geometry is available, then the heat transfer coefficient can be calculated from the measurement result. The heat transfer coefficient depends on the Prandtl number and the Reynolds number. The Reynolds number is known, and so the Prandtl number can be determined. The Prandtl number can then be compared with the known Prandtl numbers of the expected fluids in the production equipment. Note that the material properties such as the Prandtl number are also dependent on the bulk temperature in the production equipment, so temperature needs to be known (either measured or simulated) and the material parameters need to be adjusted according to the current temperature.

If the phase distribution is not already known, for example, one phase may be a dispersion of oil in water, and another phase may be oil, then the parameters and/or time constant measured at each sensor is compared with a parameter and/or time constant previously measured for a known fluid that the production equipment is likely to contain. The parameters [e.g. gradient, curvature or other parameter based on rising response] and/or time constant can vary according to the nature of the fluid, the flow rate of the fluid and the temperature of the fluid.

In this way, the characteristics of the fluid in proximity to each of the temperature sensors can be determined and a picture can be built of the location within the production equipment 1 that phases can be found. It will be appreciated that providing more temperature sensors located at different points around the production equipment 1 will result in a more accurate picture of phase distribution in the multiphase fluid flow within the production equipment 1.

In order to get even more information to characterize the multiphase fluid flow, it is possible to calculate the Prandtl number of the fluid using the measured temperature response using a Finite Element Method (FEM) representation of the geometry, as shown in Figure 7. Comparing the calculated Prandtl number with previously measured Prandtl numbers of the various fluids (e.g. oil/water dispersions at various water cuts) can be used to give an even more detailed picture of the phase distribution.

The simplified FEM model illustrated in Figure 7 shows the wall of the production equipment 1 . The cooling chamber 2 in this model is considered to be insulated from ambient temperature, and U_f|_Ui_d may be obtained for oil, water, or a mixture of fluids. Note that Figure 7 illustrates a very simple geometry, and more complex geometries may be modelled. For example, a layer of wax deposits on the production equipment wall may be modelled.

Turning now to Figure 8, there is a flow diagram illustrating the steps according to an embodiment of the invention. The following numbering corresponds to that of Figure8: 51 . A pulse of heat is applied in the wall of the production equipment carrying multiphase fluid flow.

52. The temperature is measured at several temperature sensors disposed in proximity to the production equipment during the heating. A heating curve constant is obtained for each sensor using the increase in temperature.

53. The temperature at each temperature sensor is used to determine fluid parameters, such as the nature of the fluid or thickness of deposit, in proximity to each temperature sensor. This may require comparing the temperature with previously obtained data for known fluids under known conditions.

54. If no further information is required then the process ends. S5. If further information is required, then the Prandtl number of the fluid in proximity to each temperature sensor is calculated using FEM.

S6. The Prandtl number calculated at each temperature sensor is compared with Prandtl numbers for known fluids.

Although use of a heating curve parameter or time constant from the temperature response is used in the embodiments described above, it can nevertheless be possible to derive a phase distribution in other ways. For example, instead of the time constant, a temperature value at a certain point in time during the heating of the heat pulse and/or during temperature decay after the heat pulse has been applied, can be compared with modelled responses for different fluids and used to give an indication of the fluid in proximity to the sensor. The known or modelled responses could be stored in a database and looked-up automatically. In some embodiments, the thickness, presence and/or type of content of the conduit in the form of a waxy layer deposited on the inside of the separator wall may be determined, since the heat transfer coefficient depends upon the thickness of such a layer. In order to determine whether a deposit is present or its thickness, the temperature response may be compared with known or modelled responses for walls with waxy layers of different thicknesses. Alternatively, the temperature response from a sensor where it is unknown whether a waxy deposit is present may be compared with an earlier temperature response for the same sensor, from an earlier application of a heat pulse of differences in responses may be used to infer that a waxy deposit is present. For example, in a multiphase flow comprising an oil/gas stratified flow, it may be assumed that a given point (in this example at the lowest point in a pipe or separator) will always be in oil. All of the changes seen in the temperature response from the temperature sensor at this lowest point will then be due to a build-up or removal of deposit. Another example, in the case of oil/water stratified flow, could similarly use the response from the temperature sensor at the highest point in the pipe/separator to detect a change or presence of a deposit in proximity to the sensor.

Although we have referred above in particular to production equipment in the form of a separator, application of the invention to other types of production equipment can also be advantageous.

In some embodiments, a single temperature sensor can be used for determining a multiphase fluid characteristic. Such an embodiment is shown in Figure 9, where there is provided production equipment 1 , in the form of a section of pipe, through which a multiphase flow is transported. This also shows a waxy layer 203 that has been deposited from a multiphase flow on the inside surface of the equipment 1. A single temperature sensor 204 is provided on the wall of the production equipment for measuring a temperature during heating by a heat pulse. The thermal response can be used to determine a thickness of deposit or a phase distribution as explained above. Where a single temperature sensor is used, this provides information on fluid or deposit parameters in proximity to that particular sensor only. This may be sufficient where there is a uniform deposit and/or uniform flow regime.

The invention can be used to monitor multiphase flow within production equipment such as a pipeline or separator. Some types of flow can be destructive or damaging to a pipeline, and monitoring the multiphase flow can highlight any types of flow known to be damaging. This allows remedial action to be taken before flow becomes too damaging. In other embodiments, temperature sensors can be provided and responses measured along the length of a pipe section. Measurements from different positions along the length can be used to provide a profile of temperature measurements along the pipe section. This may be particularly useful in the case of a subsea pipeline which may be susceptible to wax deposits because the temperature of the fluid inside the pipe tends to drop with distance away from the well resulting such that deposits may be present to a varying extent at different distances from the well. In such embodiments, a plurality of temperature sensors may be provided on a fibre optic cable which may be installed along the pipe in thermal contact with the pipe.

The production equipment in the embodiments described above is supplied with an electrical current which flows in the material of the pipe wall and causes the generation of heat in the pipe wall. When the production equipment is provided under water, e.g. on the sea bed, it can be convenient to supply the current from an electrical power supply which may also be used in other operations or for powering other equipment. It may simplify the heating arrangement and heat transfer model, and electrical power supply might be simultaneously available with other operations.

In some subsea systems, it is proposed to use direct electrical heating (DEH) of a section of pipeline. DEH involves supplying an electrical current in the wall of the section of pipeline, such that it heats up and can keep the contents in the pipeline warm. The pipeline can be insulated to help the heating. Such a system is typically used to remove or prevent hydrates forming in the pipeline and causing a blockage. In particular, such a system may be applied to keep the contents of the pipeline warm during the start-up or re-start of the fluid transport of well fluid through the pipeline after a down period. When the pipeline is flowing and carrying warm well fluid at full flow, the DEH of the pipeline section may be switched off. The power supply for such a DEH system may be applied to generate heating in the production equipment of the invention. The production equipment, may in certain embodiments, take the form of a section of the pipeline, for example the section to which the DEH system is applied, or of another section of pipe either downstream or upstream with the current being supplied via the wall of the pipeline section to which the DEH system is applied.

The techniques described above may also be applied with a system of generating a cold flow for long-distance transport of fluid subsea from a well to a downstream facility. Thus, the heating can be delivered to produce a pulse as described for determining flow regime or contents in the pipe. At appropriate times, the heating can be applied for a longer period of time, so that wax deposited adjacent to the inner wall of the pipe or production equipment melts and is released in the form of solid particles of stabilised wax into the flow through the equipment.

In this way, a combined subsea system, e.g. using a common electrical supply or common pipeline sections or equipment, can be provided for providing heat pulse generation for determining contents or flow regime together with either or both of DEH for hydrate inhibition, and heating for wax release for cold flow. This can give cost savings.

Figure 10 shows an alternative embodiment, in which the production equipment is provided with an induction coil 310 around the wall 2, and currents are produced in the material of the pipe wall by supplying a current through the coil. The currents produced in the pipe wall generate heat in the pipe wall. Thus, the pipe is induced to generate heat. This type of heat source can be used instead of the direct electrical connection to the pipe, in any of the embodiments described above. It should be noted that term "fluid" in relation to a fluid of a multiphase flow, includes fluids in the form of a gas or a liquid or mixed fluids, such as an emulsion or the like, for example an oil-in-water emulsion. It also includes stratified fluids.

It will be appreciated that although the above has been described in terms of heating the production equipment, other examples could be performed with a converse arrangement, in that production equipment is cooled instead of heated, resulting in a reduction in temperature of the pipe. This may be applied by a pulse of cold fluid applied around an outside of the production equipment, in an annular chamber, in place of the current based heat generation in the equipment. The pulse is applied over a certain target time period or until a certain temperature is reached, with time and temperature being measured. After cooling has been performed, an increase in temperature of the wall of the production equipment is measured at the temperature sensors due to heating of the wall due to the contents of the production equipment being relatively warm. The temperature reduction behavior during cooling, and the subsequent increase in temperature after cooling is stopped is dependent on the thermal mass. The contents at the various sensors can be determined, compared and used to distinguish and determine different contents using the same measurements during cooling, rather than during heating, and performing the determination from those measurements in the same manner as that described above for the heating. Likewise, the increase in temperature after the pulse, can be used e.g. to extract a time constant, and used to determine the contents in the same way as for the heating.

Various modifications may be made to the above-described embodiments without departing from the scope of the present invention as defined in the appended claims. For example, while the examples given above apply to a pipeline and separator, the invention may be used to characterize the contents of any type of conduit of production equipment for use in oil and gas production. In particular, the production equipment may be a subsea pipe section.

Claims

CLAIMS:

1 . A method of determining the contents of production equipment containing at least one product from a well, the method comprising the steps of:

(a) heating the production equipment;

(b) during said heating, measuring either or both of:

at least one temperature at at least one temperature sensor located adjacent to the production equipment; and

at least one time of said heating;

(c) determining at least one characteristic of the contents of the equipment from either or both of the measured temperature and time associated with said heating.

2. A method as claimed in claim 1 , wherein step (c) is performed using a parameter obtained from an increase in the measured temperature.

3. A method as claimed in claim 1 or 2 which further comprises fitting a linear or non-linear curve to the measured temperature, and wherein step (c) is performed using a curve parameter from the fitted curve.

4. A method as claimed in claim 2 or 3, wherein the curve parameter is a gradient.

5. A method as claimed in any of claims 2 to 4, wherein the curve parameter is compared with a previously determined reference parameter.

6. A method as claimed in any preceding claim, wherein step (c) is performed by comparing the measured temperature with at least one previously determined reference temperature.

7. A method as claimed in any preceding claim, which further comprises providing a thermal response using the measured temperature, wherein the thermal response comprises a response parameter obtained from the measured temperature, and step (c) is performed using the thermal response.

8. A method as claimed in claim 7, wherein the step (c) is performed by comparing the thermal response with previously determined thermal responses.

9. A method as claimed in any preceding claim, wherein step (c) is performed without requiring to use measured temperatures during cooling of the production equipment.

10. A method as claimed in any preceding claim, which further comprises using the measured temperature or thermal response to determine a Prandtl number of a fluid in proximity to at least one temperature sensor of a plurality of temperature sensors.

1 1 . A method as claimed in claim 10, which further comprises comparing the determined Prandtl number with Prandtl numbers previously measured for known fluids in order to further characterize the content.

12. A method as claimed in any preceding claim, wherein the determined characteristic comprises the thickness of a wax deposit on the wall, and the method further comprises:

performing a comparison between the determined deposit thickness and a reference parameter to determine whether to remove the deposit; and

heating the wall to release the deposit from the wall when removal is determined upon performing the comparison, to produce a cold flow.

13. Apparatus for determining contents of production equipment containing at least one product from a well the apparatus comprising:

at least one temperature sensor adapted to be fitted adjacent to a wall portion of the equipment;

heating means for heating said wall portion;

a processor for measuring either or both of: at least one temperature during the heating of the wall portion from the or each temperature sensor, and at least one time of said heating ;

wherein the processor is adapted to determine a characteristic of said contents based on either or both of said measured temperature and time of said heating.

14. A computer device for determining contents of production equipment containing at least one product from a well, the computer device comprising: an in/out device for receiving, from at least one temperature sensor adjacent to the equipment, data indicative of at least one temperature of the contents in proximity to the or each temperature sensor during heating of the wall portion, and/or receiving data indicative of at least one time of said heating;

a processor arranged to determine a characteristic of the contents based on either or both of the measured temperature at the or each temperature sensor, and the time of said heating.

15. A computer program, comprising computer readable code which, when run on a computer device, causes the computer device to behave as a computer device as claimed in claim 14.

16. A computer program product comprising a computer readable medium and a computer program according to claim 15, wherein the computer program is stored on the computer readable medium.

17. A method of determining contents of production equipment containing at least one product from a well, the method comprising:

(a) providing a pulse of heat at a wall of the production equipment, said wall being the source of said heat;

(b) measuring the temperature at at least one temperature sensor located adjacent to the production equipment;

(c) providing a thermal response using the measured temperature, the thermal response comprising a time constant obtained from a decline in the measured temperature after the pulse of heat has been provided; and

(d) using the measured thermal response to determine a characteristic of the contents of the production equipment at the or each sensor.

18. A method as claimed in claim 17, wherein step (a) is performed by generating an electrical current in the material of the wall.

19. A method as claimed in claim 18, wherein step (a) includes supplying the electrical current from a Direct Electrical Heating (DEH) power supply.

20. A method as claimed in claim 18, wherein step (a) includes inducing heat in the wall using electrical induction means adjacent said wall.

21 . A method as claimed in any preceding claim, which further comprises:

using the determined characteristic to determine the thickness of a wax deposit on the wall;

heating the wall to remove the deposit when removal is determined upon performing the comparison.

22. A method as claimed in any preceding claim, wherein the time constant is compared with time constants previously measured for known fluids in order to characterize the contents.

23. A method as claimed in any preceding claim, which further comprises using the measured temperature to determine a Prandtl number of a fluid contained in the production equipment in proximity to at least one temperature sensor of the plurality of temperature sensors.

24. A method as claimed in claim 6, which further comprises comparing the determined Prandtl number with Prandtl numbers previously measured for known fluids in order to further characterize the contents.

25. Apparatus for determining contents of production equipment containing at least one product from a well, the apparatus comprising:

a heat source capable of providing a pulse of heat in a wall of the production equipment, said wall being the source of said heat;

a processor for measuring the temperature after the pulse of heat has been applied and providing a thermal response using the measured temperature from the or each temperature sensor, the thermal response comprising a time constant obtained from a decline in the measured temperature after the pulse of heat has been provided; wherein the processor is adapted to determine a characteristic of said contents based on said thermal response at the or each temperature sensor.

26. A computer device for determining multiphase flow characteristics inside production equipment containing at least two fluids, the computer device comprising: an in/out device for receiving, from a plurality of temperature sensors in proximity to the production equipment, data indicative of a thermal response of a fluid in proximity to the or each temperature sensor in response to a pulse of heat, provided in the wall of the production equipment, the wall being the source of said heat;

a processor for calculating, for the or each temperature sensor, a time constant obtained from a decline in the measured temperature after the pulse of heat has been provided;

wherein the processor is arranged to determine a characteristic of the contents of the production equipment in proximity to each of the temperature sensors using the or each calculated time constant.

27. A computer program, comprising computer readable code which, when run on a computer device, causes the computer device to behave as a computer device as claimed in claim 26.

28. A computer program product comprising a computer readable medium and a computer program according to claim 27, wherein the computer program is stored on the computer readable medium.

29. A method as claimed in any preceding claim, wherein the production equipment is selected from either or both of:

(i) a pipe section; and

(ii) a separator or separator tank.

30. A method as claimed in any preceding claim, wherein said product from the well comprises any one or more, in any combination, of:

(i) multiphase fluid;

(ii) hydrocarbon production fluid;

(iii) multiphase fluid flow;

(iv) a deposit derived from said fluid.

31 . A method as claimed in any preceding claim, wherein said characteristic of the contents comprises any one or more, in any combination, of:

(i) a distribution of the contents;

(ii) the presence of a deposit;

(iii) the deposit thickness; and

(iv) flow regime.

32. A method of determining the contents of production equipment containing at least one product from a well, the method comprising the steps of:

(a) cooling the production equipment;

(b) during said cooling, measuring either or both of at least one temperature at at least one temperature sensor located adjacent to the production equipment; and at least one time of said cooling; and

(c) determining a characteristic of the contents of the equipment from either or both of the measured temperature and time associated with said cooling.

33. A method as claimed in claim 32, wherein step (c) is performed using a parameter obtained from a decrease in the measured temperature.

34. A method as claimed in claim 32 or 33 which further comprises fitting a linear or non-linear curve to the measured temperature, and wherein step (c) is performed using a curve parameter from the fitted curve.

35. A method as claimed in claim 33 or 34, wherein the curve parameter is a gradient.

36. A method as claimed in any of claims 33 to 35, wherein the curve parameter is compared with a previously determined reference parameter.

37. A method as claimed in any preceding claim, wherein step (c) is performed by comparing the measured temperature with at least one previously determined reference temperature.

38. A method as claimed in any preceding claim, which further comprises providing a thermal response using the measured temperature, wherein the thermal response comprises a response parameter obtained from the measured temperature, and step (c) is performed using the thermal response.

39. A method as claimed in claim 38, wherein the step (c) is performed by comparing the thermal response with previously determined thermal responses.

40. A method as claimed in any preceding claim, wherein step (c) is performed without requiring to use measured temperatures during subsequent heating of the production equipment.

41 . A method as claimed in any preceding claim, which further comprises using the measured temperature or thermal response to determine a Prandtl number of a fluid in proximity to at least one temperature sensor of a plurality of temperature sensors.

42. A method as claimed in claim 41 , which further comprises comparing the determined Prandtl number with Prandtl numbers previously measured for known fluids in order to further characterize the content.

43. Apparatus for determining contents of production equipment containing at least one product from a well the apparatus comprising:

cooling means for cooling said wall portion;

a processor for measuring either or both of at least one temperature during the cooling of the wall portion from the or each temperature sensor, and at least one time of said cooling;

wherein the processor is adapted to determine a characteristic of said contents based on either or both of said measured temperature from the or each temperature sensor, and the time of said cooling.

44. A computer device for determining contents of production equipment containing at least one product from a well, the computer device comprising: an in/out device for receiving, from at least one temperature sensor adjacent to the equipment, data indicative of at least one temperature of the contents during in proximity to the or each temperature sensor during cooling of the wall portion, and/or receiving at least one time of said cooling; and

a processor arranged to determine a characteristic of the contents based on either or both of the measured temperature at the or each temperature sensor, and the time of said cooling.

45. A computer program, comprising computer readable code which, when run on a computer device, causes the computer device to behave as a computer device as claimed in claim 44.

46. A computer program product comprising a computer readable medium and a computer program according to claim 45, wherein the computer program is stored on the computer readable medium.

47. A method as claimed in any of claims 34 to 46, wherein the production equipment is selected from either or both of: