GB2479741A

GB2479741A - Permittivity measurements of pipe deposits

Info

Publication number: GB2479741A
Application number: GB1006554A
Authority: GB
Inventors: Jan Kocbach; Kjetil Folgero
Original assignee: Tecom Analytical Systems; TeCom AS
Current assignee: Tecom Analytical Systems; TeCom AS
Priority date: 2010-04-19
Filing date: 2010-04-19
Publication date: 2011-10-26
Also published as: GB201006554D0

Abstract

An inline measuring apparatus operable to measure hydrate, wax, scale or formation water film 150 which builds up on an inside surface of a vvall 100 of a pipe for guiding fluid 130, includes an electronics unit coupled to a sensor arrangement 20 disposed in a spatially extensive manner into the wall 100 of the pipe for sensing the growth 150. The electronics unit in cooperation with the sensor arrangement 20 is operable to perform a series of dielectric measurements at a plurality of interrogating frequencies for determining the nature and spatial extent of the growth 150. The sensor may comprise electrodes 110, or a waveguide, transmission line or resonator to measure permittivity and/or dielectric spectroscopy. The sensor may be circumferential or axial with the pipe.

Description

INLINE MEASURING APPARATUS AND METHOD

Field of the invention

The present invention relates to inline measuring apparatus for detecting hydrate formation and for assuring flow, for example to apparatus for sensing hydrate formation within pipes, namely close to walls of the pipes, which could potentially obstruct flow. Moreover, the present invention concerns methods of detecting hydrate formation and assuring flow.

Furthermore, the present invention also concerns software recorded on data storage media, wherein the software is executable on computing hardware for use when implementing these methods. Additionally, the invention relates to apparatus and associated methods of detecting growth of wax and/or scale.

Background of the invention

Problems related to crystallization and/or deposition of wax, hydrate and scale during production and transportation of hydrocarbons are potentially capable of causing considerable economic losses to petroleum industries. These losses arise through the cost of chemicals, reduced production, equipment failure, and so on. Flow assurance is thus becoming an increasing challenge as depth and step-out distance to new oil and gas fields are increasing in order to exploit more marginal fossU fuel reserves.

Gas hydrates are ice-like structures which form when water molecules assemble themselves into a cage' around a small organic molecule, for example around molecules present in oil and natural gas. Hydrates exhibit complex behaviour which represents a problem, given a large number of micro-and macro-scale phenomena involved in the process of hydrate formation, such as nucleation, crystal growth, agglomeration, break-up, entrainment and deposition along pipelines in transient multiphase flow conditions. Two distinct processes are observed in pipelines. A first process occurs at a pipeline wall with the formation of a hydrate layer (coat) as the pipeline wall is a coldest point in a system including the pipeline, providing an excellent nucleation and growth site. A second process is the formation and 5Q transport of hydrate particles in a bulk of a flow.

* ** .** * * Current methods of preventing formation of hydrate, wax and scale may include various :. approaches, and combinations including: (i) applying chemicals, for example using hydrate inhibitors such as methanol, glycol and/or new polymers injected at an upstream end of a pipeline, and wax inhibitors; *.: (ii) applying mechanical devices to remove or dislodge deposits, for example pigging of the pipeline; (iii) by applying temperature changes, for example by circulating hot fluid, by applying electrical heating to the pipeline, and by applying insulation to the pipeline and an associated subsea Xmas-tree; and (iv) by lowering an operating pressure to the pipeline, if feasible, at a constant temperature.

Hydrate inhibitor injection is today a main method of preventing formation of hydrate in transport pipelines during operation of an oil and/or gas field.

A most common way to monitor gas hydrate formation in pipelines involves using non-localized methods utilizing pVT (p = pressure, V = volume, I = temperature) measurements.

In the pVT-methods, a phenomenon that gas hydrates can only form within a special pressure and temperature region (namely a stability zone") is exploited in order to monitor the pipeline. Gas hydrate inhibitors are injected based on: (a) the calculated/measured hydrate stability zone; (b) worst case scenarios for pressure and temperature conditions; (c) water occurrence; and (d) the inhibitor loss to any non-aqueous phases present.

In many cases, high safety margins are used to account for uncertainties associated in measuring the above factors, as limited localized monitoring solutions are available along the pipeline. This results in a high consumption of inhibitor liquid, frequent pigging to avoid blocking of pipelines, in addition to the environmental challenges associated with such operations. Due to high inhibitor dosage requirement, a significant increase in capital expenditure and operational expenditure can arise, in particular at high water cut conditions.

Also, despite all these efforts, hydrates do form that can have considerable economic and safety impacts.

Some localized methods of monitoring hydrate formation along pipelines have been suggested. In a published US patent application no. 2007/0276169, a method of measuring a degree of inhibition of hydrate formation ma fluid is described, namely to find a liability to gas 3Q hydrate formation in the fluid. In the same patent application (see also a published scientific * paper Tohidi 2009: Tohidi, Bahman, Antonin Chapoy, and Jinhai Yang. 2009; "Developing a Hydrate-Monitoring System", SPE Projects Facilities & Construction 4, no. 1 (3). ****

* doi:10.2118/125130-PA, **.

http://www.onepetro.orQ/mslib/servletJonepetroprevjew?id=SPE-1251 30-PA&socSPE) a measurement of the dielectric constant for water history has also been suggested as a method of early warning of hydrate formation. A published US patent application no. 2007/0224692 describes an electromagnetic-based method of measuring water and hydrate content in production fluids. The method is based on measuring a complex permittivity in the fluid at two or more frequencies. These methods are all based on bulk measurements, and are not applicable to detecting very thin hydrate coatings at an inner wall of a pipe.

To our knowledge, the principle of on-line detecting and monitoring formation of gas hydrates in pipelines using permittivity measurements for plural frequencies was first suggested and published by Jakobsen and Folger� (one of the inventors of the present invention) in 1996 [Jakobsen 1996: Jakobsen, T. "Clathrate hydrates studied by means of time-domain dielectric spectroscopy," Dr. Scient. Thesis, University of Bergen, 1996. ISBN 82-7406-016- 4], [Folger� 1996: Folger�, Kjetil. "Coaxial sensors for broad-band complex permittivity measurements of petroleum fluids," Dr.Scient. Thesis, University of Bergen, 1996. ISBN 82- 994032-1 -9] [Jakobsen 1997: Jakobsen, T., and K. Folger�. "Dielectric measurements of gas hydrate formation in water-in-oil emulsions using open-ended coaxial probes". Measurement Science and Technology 8, no. 9 (1997): 1006-1015]. In these publications, it was shown that hydrate formation close to a wall of a sample cell could be monitored using permittivity measurements with an open-ended coaxial probe. A Norwegian patent no. 312169 describes the use of a similar permittivity sensor to monitor water fraction in thin liquid layers.

However, this sensor topology applies a point measurement, namely it is only sensitive to the fluid properties in a small spatial region around the probe. This is a drawback, on account of a single point measurement giving a measurement volume which is so limited such that it may not be representative for an actual hydrate deposition. It is possible to overcome this limitation by using a significant number of point measurement sensors. However, such an approach would be costly on account of each of these sensors requiring a separate electronics unit in order to measure at all points simultaneously. Moreover, the precision of an open-ended coaxial probe is limited, and cannot be controlled independently of the probe's sensitivity depth.

A published US patent application no. 2008/0041163 describes a method of detecting particles in a fluid; the method involves passing an ultrasonic signal through the fluid. This method is applicable for identifying gas hydrate nucleation, but it is however not suitable for * S*S.I * detecting thin hydrate coatings. *.* * ****

A published US patent no. 5756898 describes an acoustic method of measuring an effective internal diameter of a pipe containing flowing fluids. The patent application describes a *3 manner in which this method can be applied for measuring hydrate layer thickness or scale/wax deposition. Moreover, a published US patent no. 6470749 describes another method of measuring a build-up of deposits on an inner surface of a pipeline containing flowing fluid, this method using pulsed ultrasonic Doppler measurements. Further acoustic methods for measuring deposit build-up on insides of pipe walls involve use of a guided acoustic wave sensor as described in US patent no. 6568271, and a similar principle is described in a published US patent no. 6513385. However, these acoustic methods do not provide a required sensitivity for detecting very thin layers of coating for the case of non- uniform layers with varying bonding between pipe and layer; thus, detection of thin non-uniform coatings associated with hydrate formation is not possible using acoustic methods for providing warnings.

Summary of the invention

The present invention seeks to provide an inline measuring apparatus for detecting hydrate formation and for assuring flow, for example for sensing hydrate formation within pipes, namely close to walls of the pipes. Moreover, the present invention seeks to provide an inline measuring apparatus for detecting scale and/or wax deposition.

According to a first aspect of the present invention, there is provided an inline measuring apparatus as claimed in appended claim 1: there is provided an inline measuring apparatus for measuring hydrate, wax and/or scale presence on an inside surface of a wall of a pipe for guiding fluid in operation, characterized in that the apparatus includes an electronics unit coupled to a sensor arrangement disposed in a spatially extensive manner into the wall of the pipe for sensing the hydrate, wax and/or scale; and the electronics unit in cooperation with the sensor arrangement is operable to perform a series of dielectric measurements at a plurality of interrogating frequencies for determining a nature and spatial extent of the hydrate, wax andlor scale.

*.. The invention is of advantage in that it provides a more reliable approach for determining Q hydrate, wax and/or scale by coupling interrogating radiation efficiently into spatial regions of * ** *** * the pipe whereat such hydrate, wax and/or scale is likely to form in operation. * ****

* Optionally, the inline measuring apparatus is implemented so that the sensor arrangement is disposed in an axial and/or circumferential manner on an inside surface of the wall of the pipe. ** S * * * * **

Optionally, the inline measuring apparatus is implemented such that the sensor arrangement is disposed in a multisegment path on an inside surface of the wall of the pipe.

Optionally, the inline measuring apparatus is implemented so that the sensor arrangement includes at least one of: a coplanar waveguide, a hollow or filled waveguide, a coaxial cable, a microstrip line, a planar transmission line resonator, a dipole transmission line resonator.

Optionally, the inline measuring apparatus is implemented such that the sensor arrangement consists of several sensors with mutually different sensing properties.

Optionally, the inline measuring apparatus is implemented such that the electronics unit is operable to perform time domain reflectometry (TDR) for making a permittivity measurement.

Optionally, the inline measuring apparatus is implemented such that the electronics unit is operable to perform a swept or stepped measurement at a plurality of frequencies from the sensor arrangement.

Optionally, the inline measuring apparatus is implemented such that measurables of the apparatus are reflection coefficients and/or transmission coefficients and/or impedance or a combination of these. Optionally, the inline measuring apparatus is implemented so that an interrogating output from the electronics unit is terminated in a matched load. Optionally, the inline measuring apparatus is implemented such that the sensor arrangement includes a 1-port device terminated in a short circuit. Optionally, the inline measuring apparatus is implemented such that the sensor arrangement includes a 1-port device terminated in an open circuit.

Optionally, the inline measuring apparatus is implemented so that the measurements derived from the sensor arrangement are combined with measurements using another type of sensor principle. More optionally, the inline measuring apparatus is implemented such that the other sensor principle provides a temperature measurement. More optionally, the inline measuring * .**.* * apparatus is implemented such that the other sensor principle is a capacitive or inductive sensor. More optionally, the inline measuring apparatus is implemented such that the other **** * sensor principle provides a bulk measurement of the permittivity. More optionally, the inline *eS measuring apparatus is implemented such that the other sensor principle is an ultrasound measurement. More optionally, the inline measuring apparatus is implemented such that the *:*. other sensor principle is an optical measurement.

Optionally, the inline measuring apparatus is implemented such that the sensor arrangement includes at least one of: a planar transmission line resonator or a dipole transmission line resonator, wherein a hydrate, wax and/or scale content in a measurement volume of the sensor arrangement is determined from a measured resonance frequency and/or a resonance Q-factor.

Optionally, the inline measuring apparatus is implemented such that the sensor arrangement includes at least one sensor which is operable to function as a reference sensor which has a material with known material properties throughout its measurement range.

Optionally, the inline measuring apparatus is implemented such that the sensor arrangement includes an interfacing dielectric material in communication with a layer of hydrate, wax and/or scale formed in operation on an inside surface of the wall of the pipe, the dielectric material exhibiting a similar wettability to an inside surface of the wall of the pipe so that the hydrate, wax and/or scale forms in a representative manner on the dielectric material.

Optionally, the inline measuring apparatus is implemented such that the dielectric material is a ceramic and/or a polymer plastics material.

According to a second aspect of the invention, there is provided a method of measuring hydrate, wax and/or scale presence on an inside surface of a wall of a pipe for guiding fluid in operation, characterized in that the method includes: (a) using an electronics unit of an apparatus coupled to a sensor arrangement disposed in a spatially extensive manner into the wall of the pipe to interrogate the sensor arrangement for sensing formation of a layer of hydrate, wax and/or scale; and (b) using the electronics unit operating in cooperation with the sensor arrangement to perform a series of dielectric measurements at a plurality of interrogating frequencies for determining a nature and spatial extent of the layer of hydrate, wax and/or scale. S...

Q Optionally, the method includes: * .. .** * (c) performing the measurements at a plurality of frequencies using the sensor arrangement including a plurality of sensors exhibiting mutually different spatial ** * measurement characteristics in relation to the layer of hydrate, wax and/or scale to create a matrix of measurement values; and (d) solving a series of simultaneous equations in the electronics unit using the values in the matrix to determine a nature and/or extent of the layer of hydrate, wax and/or scale.

Optionally, the method is applied to measure the presence and/or amount of formation water within the pipe.

According to a thirds aspect of the invention, there is provided a software product recorded on a data storage medium, wherein the product is executable on computing hardware for implementing a method pursuant to the second aspect of the invention.

According to a fourth aspect of the invention, there is provided an inline measuring apparatus for measuring the presence and/or amount of formation water on an inside surface of a wall of a pipe for guiding fluid in operation, characterized in that the apparatus includes an electronics unit coupled to a sensor arrangement disposed in a spatially extensive manner into the wall of the pipe for sensing the formation water; and the electronics unit in cooperation with the sensor arrangement is operable to perform a series of dielectric measurements at a plurality of interrogating frequencies for determining the presence and/or amount of the formation water.

Thus, the present invention concerns an apparatus which employs complex permittivity measurements within a measurement volume close to the pipe wall to detect thin layers on hydrate, scale and/or wax deposits. It will be appreciated that features of the invention are susceptible to being combined in various combinations without departing from the scope of the invention.

Description of the diagrams

Embodiments of the present invention will now be described, by way of example only, with reference to the following diagrams wherein: FIG. 1A and lB are illustrations of an inline measuring instrument, namely "apparatus", for measuring hydrate, wax and/or scale formation within a pipeline or pipe, S ****.

* wherein FIG. 1A is a circumferential implementation and FIG. lB is an axial implementation; **** FIG. 2 is an illustration of a dielectric response characteristic during measurement by the instrument of FIG. 1A and FIG. I B during hydrate formation; FIG. 3A to FIG. 3F are examples of implementations of a sensor arrangement of the S.'.; instrument of FIG. lAand FIG. IB; FIG. 4 is a set of graphs showing changes of real (Real(g)) and imaginary (Imag(c)) components of relative permittivity for separate phases of oil (0), water (W) and hydrate (H), of a water/oil mixture (W/O) and of a hydrate/water/oil mixture (HJW/O) as a function of frequency (I); FIG. 5 is a graph of a variance in reflected time signal as a function of time for executing a measurement of hydrate layer thickness; and FIG. 6 is a graph of effective relative permittivity of a co-planar waveguide terminated by a hydrate layer backed by gas: there are several curves illustrating an effect on measurement of changing a spacing width w of the waveguide.

In the accompanying diagrams, an underlined number is employed to represent an item over which the underlined number is positioned or an item to which the underlined number is adjacent. A non-underlined number relates to an item identified by a line linking the non-underlined number to the item. When a number is non-underlined and accompanied by an associated arrow, the non-underlined number is used to identify a general item at which the arrow is pointing.

Description of embodiments of the invention

In overview, the present invention concerns apparatus which use complex permittivity measurements within a measurement volume close to a wall of a pipe wall to detect thin layers of hydrate, scale and/or wax deposits. Equipment based on complex permittivity measurements are in use in other fields, for example as described in: (I) US patent application no. 2009/152624 which pertains to use of a coplanar waveguide for non-invasive measurement on living tissue; and (ii) US patent no. 5223796 which pertains to measuring dielectric properties of a material, but their application to detecting hydrate, wax and/or scale deposition is not known.

The present invention relates to a method and apparatus for measuring deposits of gas hydrates on an inside region of a pipe, and is applicable for providing early warning of 9 hydrate formation along pipelines. From a viewpoint of known technology, it is perceived in * ** * ** * relation to the present invention that there is a need for monitoring solutions for early warning of hydrate formation along pipelines. Known systems for monitoring hydrate formation are * not able to detect the very thin layers of hydrates deposited on the pipe wall early in the build-up process with high accuracy. The present invention is thus focused towards a *3 problem which is not adequately addressed by known measurement systems. * .* ** * * ** * **

The present invention involves measuring a complex permittivity in a measurement volume close to a wall of a pipe using an electromagnetic sensor or a plurality of electromagnetic sensors, from which a hydrate fraction within the measurement volume is calculated. This measurement approach makes it possible to detect very thin coatings of hydrate. Moreover, this measurement approach is of advantage compared to prior art in that only a region which is a coldest point in a system is considered, namely a point providing an excellent nucleation and growth site for hydrates. Compared with previously proposed techniques using open-ended probes, the present invention uses a line measurement instead of a point measurement. This line measurement ensures that a larger area is monitored using single sensor, providing a more representative measurement of hydrate formation. In addition, the sensitivity of apparatus pursuant to the present invention can be enhanced by adjusting the length of the sensor, and in this manner the precision in measured hydrate fraction can be controlled independently of the sensor's sensitivity depth. Moreover, to make sure that the hydrate growth probability is the same for the area directly in front of the sensor as for the rest of the pipe wall, a thin layer may be attached at the front of the sensor, covering either all of the sensor or part of the sensor, the layer having the same wettability (i.e. the same properties with respect to hydrate growth) as the pipe wall; for example, the layer has similar hydrophobic or hydrophilic properties relative to an inside surface of the pipe wall. This layer comprises a material which must be electrically isolating; optionally, the material is added using a sputtering technique. It is to be borne in mind that the complex permittivity includes the dielectric constant, the dielectric losses and the conductivity, and that the measurements include conductivity measurements and dielectric spectroscopy. Such spectroscopy is optionally executed using spot or swept frequency measurements; alternatively, pulse measurements can be employed wherein response signals to pulse excitation are analysed.

In FIG. 1A, there is shown an inline measuring apparatus for performing permittivity measurements, for example over a range of frequencies in a manner of spectral measurement, optionally implemented using pulse excitation techniques; the instrument is indicated generally by 10. One example installation of the instrument 10, referred to also as being an "apparatus", is in a spool-piece in a pipeline 40 as shown in FIG. 1A. The instrument 10 includes a sensor arrangement 20 disposed in a circumferential manner around a portion of the pipeline 40. An alternative disposition of the sensor arrangement 20 : is axially along the pipeline 40 as illustrated in FIG. lB. Thus, the sensor arrangement 20 may be placed either in parallel with the pipeline 40 or perpendicular to the pipeline 40 as illustrated in FIG. 1A and FIG. lB. Optionally, the sensor arrangement 20 is implemented * both parallel in an elongate manner with the pipeline 40, and also perpendicular in an elongate manner with the pipeline 40. The sensor arrangement 20 optionally includes a plurality of sensors, for example disposed in a mutually coupled configuration to be interrogated by a common signal applied thereto. Alternatively, the sensor arrangement 20 includes a single spatially extensive sensor. Moreover, the sensor arrangement 20 is coupled to an electronics unit 30 which generates an electromagnetic signal, and computes a permittivity of a sample volume within the pipeline 40 based upon reflection and/or transmission coefficients and/or impedance associated with a signal received at the sensor arrangement 20 from the fluid within the pipeline 40. A sample volume in which the sensor measures permittivity can be modified by changing geometries and materials used for fabricating the sensor 20. As aforementioned, the sensor 20 may include an interfacing layer presented to an interior of the pipeline 40, the layer having a similar wettability in respect of hydrates to a remainder of an inner surface of the pipeline 40.

The instrument 10 employs, as a basis for its operation, a characteristic that the complex permittivity spectra are significantly different for the different fluids which may be part of the multiphase fluid present within the pipeline 40 when in use. As an example, the real (Real(c)) and imaginary (Imag(c)) parts of the relative permittivity of conductive water (W), oil (0), hydrate (H), a water/oil mixture (W/0) and a hydrate/water/oil mixture (H/W/0) as a function of frequency (t) are shown in FIG 4. It is observed that there are significant differences in the complex permittivities of the fluids in question. In particular, there are frequency dependencies in the permittivity of hydrate which are exploited in the apparatus 10 in order to distinguish variations in permittivity due to hydrate formation from variations in permittivity due to other causes, for example inhibitors, temperature/pressure changes and so forth. In FIG 4. it is to be observed how this frequency dependency in the permittivity of hydrate influences the permittivity of a water/oil mixture by comparing the permittivity spectrum of the water/oil mixture with the corresponding spectrum for the water/oil/hydrate mixture. Thus, when the amount of hydrate changes in the measurement volume within the sensitivity range of the sensor arrangement 20, the permittivity is correspondingly changed. Based on the measured permittivity in a plurality of frequencies, it is thus possible to calculate the hydrate fraction in the measurement volume. * *** * ,, *. *

: An example of a measurement of the change in measured permittivity during hydrate generation for a single frequency is shown in a graph of FIG. 2. The graph includes an abscissa axis denoting passing of time in hours from left to right, and an ordinate axis denoting a measure of relative permittivity. A significant variation in perniittivity is observed when the hydrate fraction within the measurement volume starts to increase around 3 hours ::.:1 into measurements presented in FIG. 2; the hydrate formation occurs from a mixture of cyclopentane, water and a surfactant (Span 80). The measurements were made for an interrogation signal having a frequency of I GHz. Hydrate formation can occur very suddenly when conditions allow, for example within a few minutes or less.

The present invention encompasses several different methods of measuring the complex permittivity of fluids present in the pipeline 40. One of these several methods concerns time domain refiectometry (TDR), namely using a time domain approach. TDR is based on measuring a step response or an impulse response of the medium under test included within the pipeline 40. Another method is using a frequency domain approach in which an oscillator circuit generates a high frequency oscillating signal, which is transmitted to the sensor arrangement 20; the oscillator is beneficially swept or stepped within a frequency range and corresponding permittivity characteristic of the fluids present in the pipeline 40 are computed for each of the swept or stepped frequencies.

In addition to detecting and providing early warning of hydrate deposits, the instrument 10 is susceptible to being used in several other technical applications: (i) for detecting formation water; when formation water is produced, the water fraction and the salinity of the water in the fluid film close to a wall of the pipeline 40 will be increased; the instrument 10 is capable of performing such measurements; (ii) for detecting and providing early warning regarding the formation of deposits of wax and scale on the wall of the pipeline 40; such scale can, for example, include sulphate and carbonate materials; such scale and wax deposits can be measured in similar fashion to hydrate deposits; and (iii) for measuring a water content in a fluid film forming along the wall of the pipeline 40.

The electronics unit 30 is beneficially adjusted to be able to measure formation of a film of formation water onto an inside wall of the pipeline 40.

The instrument 10 is capable of being implemented in several different embodiments which will now be described with reference to FIG. 3A to FIG. 3F.

In FIG. 3A, there is illustrated the sensor arrangement 20 implemented as a co-planar *0** * waveguide sensor incorporated into a recess in a wall 100 of a pipeline 40. The sensor "S.

* arrangement 20 is illustrated disposed axially along the wall 100; optionally the sensor : arrangement 20 is implemented in a circumferential manner. The sensor arrangement 20 S..

includes a configuration of electrodes IIOA, IIOB, hOC backed by a dielectric material mount 120. An interface layer 115 is included between the electrodes IIOA, IIOB, hOC and an interior region of the pipeline 40. The electrodes IIOA, hOC are beneficially : grounded/Earthed and the electrode IOOB is actively driven during measurements performed * .* by the instrument 10. The electrodes IIOA, IIOB, hOC couple efficiently to a film 150 potentially forming onto an inside surface of the pipeline 40; the film 150 is, for example, a collection of hydrate particles forming on account of conditions suitable for hydrate formation pertaining within the pipeline 40. The pipeline 40 conveys, for example, in operation a gas as illustrated. The electrodes IIOA, IIOB, hOC in combination with their dielectric material mount form a co-planar waveguide which is strongly coupled locally to the film 150 when present. Moreover, the electrodes IIOA, IIOB, hOC can be formed as longitudinal and/or circumferential strips, otherwise as discrete electrode islands. The electrodes IIOA, 11DB, hOC are beneficially coupled to the electronics unit 30. Although the electronics unit is shown in FIG. 1 attached to a side of the pipeline 40, it will be appreciated that the electronics unit 30 can be mounted remotely from the pipeline 40 if required, for example due to potential high temperature operation of the pipeline 40.

Referring to FIG. 3B, the sensor arrangement 20 is implemented as a hollow or filled waveguide 200 formed into the wall 100 of the pipeline 40 as illustrated. FIG. 3B is a cross-section view across a section of the pipeline 40. Microwave energy propagating in the waveguide 200 is coupled to the film 150 via a small aperture 210 provided on an inside surface of the waIl 100. The waveguide 200 can be implemented as an elongate axial or circumferential structure, or alternatively implemented as an interlinked series of microwave waveguide chambers. The waveguide 200 is coupled to the electronics unit 30. Optionally, the aperture 210 can be provided with a window having similar wettability to a remainder of the pipeline 40. Optionally, the waveguide can be implemented with an inner conductor, such that it operates as a leaky coaxial cable.

Referring to FIG. 3C, an implementation of the sensor arrangement 20 is shown in plan view looking from a centre of the pipeline 40 towards the wall 100. The sensor arrangement 20 includes a co-planar waveguide resonator 250 surrounded by ground or shielding electrodes 260 separated by a region of substrate dielectric 270. The resonator 250, namely functioning as a transmission line, is operable to guide microwave energy therealong which couples into the film 150 formed onto an inside surface of the wall 100. The sensor arrangement 20 of FIG. 3C is disposed circumferentially and/or axially around the pipeline 40. Moreover, the resonator 250 functioning as a transmission line is beneficially insulated from the ground or shielding electrodes 260 by way of a dielectric material region 270 exhibiting low loss at microwave frequencies, for example by using a ceramic or polymer plastics material in the region 270. The transmission line resonator 250 is coupled to the electronics unit 30. Each transmission line resonator 250 is an elongate conductor having a first end, for example an * end 255B1 of a resonator 250B, and a second end, for example an end 255B1 of the *: * resonator 250B. The transmission lines 250A, 250B, 250C couple interrogating radiation at their ends by capacitive and/or radiative coupling. Optionally, the sensor arrangement 20 of FIG. 3C is passivated in a thin layer of a dielectric material having a similar wettability to an interior surface of the pipeline 40.

Referring to FIG. 3D, the sensor arrangement 20 is implemented as a microstrip resonator 300 disposed in close proximity to a feed transmission line 310. FIG. 3D is a plan view from a central axis of the pipeline 40 looking towards an inside of the wall 100. Microwave signals from the electronics unit 30 are capable of propagating along the feed transmission line 310 and coupling into the resonator 300 housed within the wall 100 of the pipeline 40 and thereby coupling efficiently into the film 150. The resonator 300 includes an inner hollow volume as illustrated. Optionally, the resonator 300 is mechanically supported on an intervening dielectric material 320, for example a ceramic material or a plastics polymer material. The resonator 300 is beneficially disposed in an axial row and/or a circumferential row in the wall of the pipeline 40.

Referring to FIG. 3E, the sensor arrangement 20 is implemented as one or more stub resonators 400 fed from a feed transmission line 410 coupled to the electronics unit 30. FIG. 3E is a plan view from a central axis of the pipeline 40 looking towards an inside of the wall 100. The one or more stub resonators 400 are operable to couple into the aforementioned film 150 potentially formed in operation onto an inside surface of the wall 100 of the pipeline 40. The one or more stub resonators 400 are beneficially disposed in an axial and/or circumferential manner in one or more recesses machined into the inside surface of the pipeline 40. Fig. 3F provides an illustration of a further implementation of the sensor arrangement 20 as a dipole resonator 420 with open or shorted ends; the dipole resonator 420 is also known as a parallel coupled microstrip resonator. One or more of the dipole resonators 420 are beneficially coupled to the, electronics unit 30 and are disposed in an axial, circumferential and/or spiral helical arrangement within the wall 100 of the pipeline 40.

The one or more stub resonators 400 and their associated feed transmission line 410 are beneficially formed on a dielectric substrate 415. Moreover, the resonators 420 are *i'' **30 beneficially covered in a thin interfacing layer (not shown) facing into the pipeline 40, the thin :" interfacing layer having similar wettability characteristics in comparison to an inside-facing surface of the wall 100 of the pipeline 40; hydrate, wax and scale deposition onto the thin : layer is thus representative of similar deposit on onto the wall 100. For the sensor arrangement 20 shown in FIG. 3A to 3F, the thin layer interfacing facing to an interior of the 3 pipeline 40 beneficially has a thickness in a range of 20 pin to 2 mm. -14-

Thus, in one embodiment of the invention, the sensor arrangement 20 is a coplanar waveguide as shown in FIG. 3A. In another embodiment of the invention, the sensor arrangement 20 is a leaky waveguide as shown in FIG. 3B. Alternatively, the sensor arrangement 20 employs various forms of microwave resonator as illustrated in FIG. 3C to FIG. 3F. Measurables may be either the reflection coefficient, the transmission coefficient or both. The measurements are generally made for a plurality of frequencies or for a frequency band, but may in some embodiments also be made for only a single frequency. Yet alternatively, temporal pulse techniques are employed for determining the reflection coefficient, the transmission coefficient or both. In another implementation of the instrument 10, resonator methods are used to calculate the dielectric constant and dielectric losses for a single frequency or a plurality of frequencies with higher accuracy. In this case the dielectric constant and the dielectric losses are calculated based on measured resonance frequency and Q-factor.

The sensor arrangement 20 sensitivity range is scalable by changing some of the design parameters for the sensor arrangement 20. For an example embodiment of a coplanar waveguide sensor employed for implementing the sensor arrangement 20, the sensor sensitivity range can be scaled by changing a spacing between the conductors and/or exchanging the substrate material to a material with a different permittivity. An example, coplanar waveguide sensor has a substrate height of 50 mm, an electrode width of 2 mm, a gap width w of 1 mm, and substrate relative permittivity of 2.1. As an example of scaling of the sensitivity range, the effect on the sensitivity range of this coplanar waveguide sensor by changing the gap width w between the conductors in FIG. 3A is illustrated in FIG. 6.

Increasing the gap width w decreases the effective permittivity measured, giving effectively a change in sensitivity range. Note that a transformer section of coplanar waveguide is necessary to get from a 50 Ohm system to the coplanar waveguide sensor. For an example case of a leaky waveguide, for example as illustrated in FIG. 3B, the sensitivity range can be modified by changing the aperture size. Similarly, there are other design parameters which can be changed for the other configurations. In order to increase the accuracy in the S..' *....30 measurements and correct for temperature variations, a reference sensor covered with a medium with known permittivity and thickness larger than the sensors sensitivity range can be used as a component part of the sensor arrangement 20. S.

Furthermore, to determine accurately the film thickness of a deposit layer 150, a configuration consisting of two or more sensors with different sensitivity ranges can be used, * for example a combination of sensors of types as illustrated in FIG. 1 to FIG. 3F. For the case with two sensors, and where the thickness of the deposit layer 150 is smaller than the sensitivity depth of the sensor 20 with largest sensitivity depth, the layer thickness may be determined using a set of two simultaneous equations with two unknown parameters. These simultaneous equations can be solved in the electronics unit 30 on computing hardware.

The thin deposited layer 150 may in some cases consist of only hydrate as discussed above.

In other cases, the deposit layer 150 consists of a mixture of hydrate, water and hydrocarbons. In addition, the multiphase flow behind the deposited layer 150 as seen from the sensor arrangement 20, may also contain hydrate in addition to water, hydrocarbons and other fluids that can be present in a multiphase flow through the pipeline 40. The multiple-sensor configuration including two or more different types of sensors for implementing the sensor arrangement 20 with different sensitivity ranges utilized is applicable also for this case, making it possible to determine a hydrate fraction in the thin deposited layer 150 in addition to calculating the thickness of the deposited layer 150.

It is also possible to determine the thickness of a deposit layer 150 using a single sensor for implementing the sensor arrangement 20 pursuant to the present invention. In this case, the variation of the time signal is studied, see FIG. 5, and these time series are investigated statistically. The measured permittivity when an oil-water-gas is flowing in a pipeline 40 will show fluctuations with time as the fluid passing the sensor arrangement 20 will not be homogeneous. The sensitivity of the sensor arrangement 20 described in this invention decreases exponentially with the distance from the pipeline waIl 100. If a hydrate layer 150 is deposited on the pipeline waIl 100, the measured permittivity fluctuations will decrease.

Thus, the measured variation in the permittivity c is a function of a thickness of the layer 150, and a reduction in permittivity fluctuation is an early warning that a hydrate layer 150 is building up. In FIG. 5, a screenshot from a computer program for measurement of hydrate deposit layers using this method is shown. Time series with 1601 measurement points are measured over a time period of 0.8 seconds, and these time series are analyzed statistically using histograms and a variance as a function of time is computed. This method is used in order to determine a hydrate fraction in the measurement volume of the sensor arrangement *.* 0 20. When the hydrate fraction in the measurement volume is increased, the variance :: decreases. It has been observed that the variance may change with a factor of 1000 and the kurtosis may change with a factor of 100 000.

The apparatus 10 described in the foregoing beneficially includes a temperature sensor * 3 coupled to the electronics unit 30 for measuring a temperature of the sensing region of the sensors arrangement 20; the temperature measurement is beneficially used for increasing an accuracy of measurement of the apparatus 10 when predicting formation of a layer on the sensor arrangement 20. Optionally, the electronics unit 30 is also provided with a signal indicative of a pressure within the pipeline 40 in a vicinity of the sensor arrangement 20. The electronics unit 30 is beneficially provided with signals from other types of sensor principle,

for example:

(i) capacitive and/or inductive principle, for example a bulk measurement of permittivity of contents of the pipeline 40; and/or (ii) ultrasonic principle, for example for performing bulk ultrasonic measurement of contents within the pipeline 40; and/or (iii) optical principle, for example for performing bulk optical measurement of contents within the pipeline 40.

Modifications to embodiments of the invention described in the foregoing are possible without departing from the scope of the invention as defined by the accompanying claims.

Expressions such as "including", "comprising", "incorporating", "consisting of, "have", "is" used to describe and claim the present invention are intended to be construed in a non-exclusive manner, namely allowing for items, components or elements not explicitly described also to be present. Reference to the singular is also to be construed to relate to the plural.

Numerals included within parentheses in the accompanying claims are intended to assist understanding of the claims and should not be construed in any way to limit subject matter claimed by these claims. * *..t

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* .Is I. * . *I.* d's*I

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S a. * * * *S I * * . * .5

Claims

CLAIMS1. An inline measuring apparatus (10) for measuring hydrate, wax and/or scale presence (150) on an inside surface of a wall (100) of a pipe (40) for guiding fluid in operation, characterized in that the apparatus (10) includes an electronics unit (30) coupled to a sensor arrangement (20) disposed in a spatially extensive manner into the wall (100) of the pipe (40) for sensing the hydrate, wax and/or scale (150); and the electronics unit (30) in cooperation with the sensor arrangement (20) is operable to perform a series of dielectric measurements at a plurality of interrogating frequencies for determining a nature and spatial extent of the hydrate, wax and/or scale (150).
2. An inline measuring apparatus (10) as claimed in claim 1, wherein the sensor arrangement (20) is disposed in an axial and/or circumferential manner on an inside surface of the wall (100) of the pipe (40).
3. An inline measuring apparatus (10) as claimed in claim 1 or 2, wherein the sensor arrangement (20) is disposed in an multisegment path on an inside surface of the wall (100) of the pipe (40).
4. An inline measuring apparatus (10) as claimed in claim 1, 2 or 3, wherein the sensor arrangement (20) includes at least one of: a coplanar waveguide (110), a hollow or filled waveguide (200), a microstrip line, a planar transmission line resonator (250, 300, 400), a dipole transmission line resonator (420).

*.,,30
5. An inUne measuring apparatus (10) as claimed in claim 1, 2, 3 or 4, in which the sensor arrangement (20) consists of several sensors with mutually different sensing properties.
6. An inline measuring apparatus (10) as claimed in any one of the preceding claims, * 5 wherein the electronics unit (30) is operable to perform time domain reflectometry (TOR) for * . . * making a permittivity measurement (150). *. * *S SI
7. An inline measuring apparatus (10) as claimed in any one of claims 1 to 5, wherein the electronics unit (30) is operable to perform a swept or stepped measurement at a plurality of frequencies from the sensor arrangement (20).
8. An inline measuring apparatus (10) as claimed in any one of the preceding claims, wherein measurables of the apparatus (10) are reflection coefficients and/or transmission coefficients and/or impedance or a combination of these.
9 An inline measuring apparatus (10) as claimed in any one of the preceding claims, wherein an interrogating output from the electronics unit is terminated in a matched load.
10. An inline measuring apparatus (10) as claimed in any one of the preceding claims, wherein the sensor arrangement (20) includes a i-port device terminated in a short circuit.
11. An inline measuring apparatus (10) as claimed in claim 1, 2 or 3, in which the sensor arrangement (20) includes a 1-port device terminated in an open circuit.
12. An inline measuring apparatus (10) as claimed in any one of the preceding claims, wherein the measurements derived from the sensor arrangement (20) are combined with measurements using another type of sensor principle.
13. An inline measuring apparatus (10) as claimed in claim 12, wherein the other sensor principle provides a temperature measurement.
14. An inline measuring apparatus (10) as claimed in claim 12, wherein the other sensor principle is a capacitive or inductive sensor.
15. An inline measuring apparatus (10) as claimed in claim 12, wherein the other sensor principle provides a bulk measurement of the permittivity.
16. An inline measuring apparatus (10) as claimed in claim 12, wherein the other sensor principle is an ultrasound measurement. *1**
17. An inline measuring apparatus (10) as claimed in claim 12, wherein the other sensor principle is an optical measurement. * .1 S * * S. -19-
18. An inline measuring apparatus (10) as claimed in any one of the preceding claims, wherein the sensor arrangement (20) includes at least one of: a planar transmission line resonator (250, 300, 400), a leaky waveguide resonator, a dipole transmission line resonator (420), wherein a hydrate, wax and/or scale content in a measurement volume of the sensor arrangement (20) is determined from a measured resonance frequency and/or a resonance Q-factor.
19. An inline measuring apparatus (10) as claimed in any one of the preceding claims, wherein said sensor arrangement (20) includes at least one sensor which is operable to function as a reference sensor which has a material with known material properties throughout its measurement range.
20. An inline measuring apparatus (10) as claimed in any one of the preceding claims, wherein said sensor arrangement (20) includes an interfacing dielectric material (115) in communication with a layer of hydrate, wax and/or scale (150) formed in operation on an inside surface of the wall (100) of the pipe (40), the dielectric material (115) exhibiting a similar wettability to an inside surface of the wall (100) of the pipe (40) so that the hydrate, wax and/or scale (150) forms in a representative manner on the dielectric material (115).
21. An inline measuring apparatus (10) as claimed in claim 20, wherein the dielectric material (115) is a ceramic and/or a polymer plastics material.
22. A method of measuring hydrate, wax and/or scale presence (150) on an inside surface of a wall (100) of a pipe (40) for guiding fluid in operation, characterized in that the method includes: (a) using an electronics unit (30) of an apparatus (10) coupled to a sensor arrangement (20) disposed in a spatially extensive manner into the wall (100) of the pipe (40) to interrogate the sensor arrangement (20) for sensing formation of a layer of hydrate, wax and/or scale (150); and S... . . . . . 30 (b) using the electronics unit (30) operating in cooperation with the sensor arrangement (20) to perform a series of dielectric measurements at a plurality of interrogating frequencies for determining a nature and spatial extent of the layer of hydrate, wax and/or scale (150).S *.*S
23. A method as claimed in claim 22, including: *5 (c) performing the measurements at a plurality of frequencies using the sensor ** * *. .: arrangement (20) including a plurality of sensors exhibiting mutually different spatial -20 -measurement characteristics in relation to the layer of hydrate, wax and/or scale (150) to create a matrix of measurement values; and (d) solving a series of simultaneous equations in the electronics unit (30) using the values in the matrix to determine a nature and/or extent of the layer of hydrate, wax and/or scale (150).
24. A method as claimed in claim 22 or 23 applied to measure the presence and/or amount of formation water within the pipe (40).
25. A software product recorded on a data storage medium, wherein the product is executable on computing hardware (30) for implementing a method as claimed in claim 22, 23 or 24.
26. An inline measuring apparatus (10) for measuring the presence and/or amount of formation water on an inside surface of a wall (100) of a pipe (40) for guiding fluid in operation, characterized in that the apparatus (10) includes an electronics unit (30) coupled to a sensor arrangement (20) disposed in a spatially extensive manner into the wall (100) of the pipe (40) for sensing the formation water; and the electronics unit (30) in cooperation with the sensor arrangement (20) is operable to perform a series of dielectric measurements at a plurality of interrogating frequencies for determining the presence and/or amount of the formation water (150). *** I. S. *SSS * * * S * .*Amendments to the claims have been filed as followsCLAIMS1. An inline measuring apparatus (10) for measuring hydrate, wax and/or scale presence (150) on an inside surface of a wall (100) of a pipe (40) for guiding fluid in operation, characterized in that the apparatus (10) includes an electronics unit (30) coupled to a sensor arrangement (20) disposed in a spatially extensive manner into the wall (100) of the pipe (40) for sensing the hydrate, wax and/or scale (150); the electronics unit (30) in cooperation with the sensor arrangement (20) is operable to perform a series of dielectric measurements at a plurality of interrogating frequencies for determining a nature and spatial extent of the hydrate, wax and/or scale (150), and the sensor arrangement (20) consists of several sensors with mutually different sensing properties.2. An inline measuring apparatus (10) as claimed in claim 1, wherein the sensor arrangement (20) is disposed in an axial and/or circumferential manner on an inside surface of the wall (100) of the pipe (40). I.. * **:*s. 3. An inline measuring apparatus (10) as claimed in claim 1 or 2, wherein the sensor arrangement (20) is disposed in an multisegment path on an inside surface of the wall (100) S. S S* * .. of the pipe (40).** SS** * S * ** 4. An inline measuring apparatus (10) as claimed in claim 1, 2 or 3, wherein the sensor arrangement (20) includes at least one of: a coplanar waveguide (110), a hollow or filled waveguide (200), a microstrip line, a planar transmission line resonator (250, 300, 400), a dipole transmission line resonator (420).5. An inline measuring apparatus (10) as claimed in any one of the preceding claims, wherein the electronics unit (30) is operable to perform time domain reflectometry (TDR) for making a permittivity measurement (150).6. An inline measuring apparatus (10) as claimed in any one of claim 1, wherein the electronics unit (30) is operable to perform a swept or stepped measurement at a plurality of frequencies from the sensor arrangement (20).7. An inline measuring apparatus (10) as claimed in any one of the preceding claims, wherein measurables of the apparatus (10) are reflection coefficients and/or transmission coefficients and/or impedance or a combination of these.8 An inline measuring apparatus (10) as claimed in any one of the preceding claims, wherein an interrogating output from the electronics unit is terminated in a matched load.9. An inline measuring apparatus (10) as claimed in any one of the preceding claims, wherein the sensor arrangement (20) includes a 1-port device terminated in a short circuit.10. An inline measuring apparatus (10) as claimed in claim 1, 2 or 3, in which the sensor arrangement (20) includes a 1-port device terminated in an open circuit.11. An inline measuring apparatus (10) as claimed in any one of the preceding claims, wherein the measurements derived from the sensor arrangement (20) are combined with measurements using another type of sensor principle.12, An inline measuring apparatus (10) as claimed in claim 11, wherein the other sensor principle provides a temperature measurement.S* S'S.. * S13. An inline measuring apparatus (10) as claimed in claim 11, wherein the other sensor *..: principle is a capacitive or inductive sensor.**.*** * . * * 14. An inline measuring apparatus (10) as claimed in claim 11, wherein the other sensor principle provides a bulk measurement of the permittivity. I.. * 3015. An inline measuring apparatus (10) as claimed in claim 11, wherein the other sensor principle is an ultrasound measurement.16. An inline measuring apparatus (10) as claimed in claim 11, wherein the other sensor principle is an optical measurement.17. An inline measuring apparatus (10) as claimed in any one of the preceding claims, wherein the sensor arrangement (20) includes at least one of: a planar transmission line resonator (250, 300, 400), a leaky waveguide resonator, a dipole transmission line resonator (420), wherein a hydrate, wax and/or scale content in a measurement volume of the sensor arrangement (20) is determined from a measured resonance frequency and/or a resonance Q-factor.18. An inline measuring apparatus (10) as claimed in any one of the preceding claims, wherein said sensor arrangement (20) includes at least one sensor which is operable to function as a reference sensor which has a material with known material properties throughout its measurement range.19. An inline measuring apparatus (10) as claimed in any one of the preceding claims, wherein said sensor arrangement (20) includes an interfacing dielectric material (115) in communication with a layer of hydrate, wax and/or scale (150) formed in operation on an inside surface of the wall (100) of the pipe (40), the dielectric material (115) exhibiting a similar wettability to an inside surface of the wall (100) of the pipe (40) so that the hydrate, wax and/or scale (150) forms in a representative manner on the dielectric material (115).20. An inline measuring apparatus (10) as claimed in claim 19, wherein the dielectric material (115) is a ceramic and/or a polymer plastics material.21. A method of measuring hydrate, wax and/or scale presence (150) on an inside surface of a wall (100) of a pipe (40) for guiding fluid in operation, characterized in that the method includes: (a) using an electronics unit (30) of an apparatus (10) coupled to a sensor arrangement (20) disposed in a spatially extensive manner into the wall (100) of the pipe (40) to * *, interrogate the sensor arrangement (20) for sensing formation of a layer of hydrate, wax and/or scale (150); and (b) using the electronics unit (30) operating in cooperation with the sensor arrangement (20) to perform a series of dielectric measurements at a plurality of interrogating frequencies for determining a nature and spatial extent of the layer of hydrate, wax andlor scale (150); and (c) performing the measurements at a plurality of frequencies using the sensor arrangement (20) including a plurality of sensors exhibiting mutually different spatial measurement characteristics in relation to the layer of hydrate, wax and/or scale (150) to create a matrix of measurement values; and (d) solving a series of simultaneous equations in the electronics unit (30) using the values in the matrix to determine a nature and/or extent of the layer of hydrate, wax and/or scale (150).22. A method as claimed in claim 21 applied to measure the presence and/or amount of formation water within the pipe (40).23. A software product recorded on a data storage medium, wherein the product is executable on computing hardware (30) for implementing a method as claimed in claim 21 or 22.24. An inline measuring apparatus (10) for measuring the presence and/or amount of formation water on an inside surface of a wall (100) of a pipe (40) for guiding fluid in operation, characterized in that the apparatus (10) includes an electronics unit (30) coupled to a sensor arrangement (20) disposed in a spatially extensive manner into the wall (100) of the pipe (40) for sensing the formation water; the electronics unit (30) in cooperation with the sensor arrangement (20) is operable to perform a series of dielectric measurements at a plurality of interrogating frequencies for determining the presence and/or amount of the formation water (150); and * . ***.the sensor arrangement (20) consists of several sensors with mutually different sensing properties. S. * S* * S.Sa..... * * * ** * S * * 5IS S.. 30