The invention relates to a scale indicator for a flowline for a fluid, more closely defined by a branch fluid line, arranged to carry a branch fluid stream, being provided with means arranged to provide and register a differential

temperature between a branch fluid stream through the branch fluid line and a main fluid stream. The invention also relates to a method of monitoring a scaling condition in a flowline .

In production wells for hydrocarbons, mineral scaling

constitutes a problem by the very fact of the scales

resulting in the flow capacity of pipes, ports, filters, perforations et cetera being reduced considerably as the scales build up. The type of scales that contributes to the greatest extent to the problem arises when injected seawater mixes with reservoir water. Barium ions (Ba ²⁺ ) dissolved in the formation water react with sulphate ions (S0 ₄ ^2~ ) dissolved in the seawater, forming barium sulphate (BaS0 ₄ ) .

The scale development is not always predictable, and there is a need to be able to improve the quality and the reliability of the monitoring of the wells, so that the necessary action can be taken before the development has gone too far.

From the state of the art it is known to make chemical analyses of the production water from the relevant well. These measuring results may indicate that scaling is in progress, but not whether this is happening in the reservoir, where the consequences are limited, or in the production equipment, where protection is necessary. The production progress may be used as an indicator of adverse scaling in production equipment. The drawback is still that the scaling downhole has already developed to a harmful level before it has been possible to take the necessary action, and

irreparable damage may already have been caused to the well.

The problems that have been described above for a well could also exist in other parts of a production system for

hydrocarbons. In the further description, unless something else is explicitly mentioned, the term "well" also includes other installations in which the build-up of scales or other types of precipitations can cause reduction in a flow

capacity .

By the terms "scale" and "scaling", other forms of clogging of fluid flow paths than the chemically conditional formation of solids mentioned are meant as well, for example

precipitation, formation of wax and ice, formation of

hydrates, sedimentation of solid particles and so on.

From EP 0622630 A2 a system and a method for optimizing the dosing of a scale inhibitor is known, wherein a heat transfer rate or heat transfer resistance sensor is connected through a contact surface, which is in contact with water in a water- circulation system, to a monitor, and a first temperature modulator is arranged near the contact surface to maintain a temperature which encourages scaling. Reading values for heat transfer rate or heat transfer resistance are used as an indicator of scaling to see whether the desired conditions for inhibiting scaling have been achieved, in order thereby to control the addition of the scale inhibitor. US 2008163700 Al , US 6880402 Bl and US 2003071988 Al disclose other examples of devices and methods of detecting scale on the internal walls of a pipe by the use of either thermal, acoustic or ultrasonic methods . The invention has for its object to remedy or reduce at least one of the drawbacks of the prior art, or at least provide a useful alternative to the prior art.

The object is achieved through features which are specified in the description below and in the claims that follow. Instrumentation which performs monitoring of the scale situation in one or more representative portions of a well has been provided. Recorded data are processed and the scale development at the portion or portions in which the

instruments are arranged can be illustrated in an appropriate manner to an operator who may take the necessary action.

The instrumentation is formed by a branch fluid line having been arranged at an appropriate portion of a well

installation, including at least one upstream inlet and at least one downstream outlet which are in fluid communication with a main fluid stream in such a way that a branch fluid stream may pass through the branch fluid line, the branch fluid stream passing from the main fluid stream, into the branch fluid line through the at least one upstream inlet, out of the branch fluid line through the at least one

downstream outlet and into the main fluid stream again. The smallest flow area of the branch fluid line is relatively small in relation to the cross section of the ordinary main flow path.

A heating element is arranged in the branch fluid line. Temperature sensors sense the temperature in the well flow at the branch fluid line and in the branch fluid stream in the partial fluid line. Thereby, a differential temperature between the main and partial flow paths may be determined.

When the fluid flow is running in a normal way, that is to say unobstructed by scales, in and out of the branch fluid line, the branch stream will experience some heating

determined by the flow rate, the thermal capacity of the fluid, the thermal conductivity of the branch fluid line and the thermal energy supplied. The flow rate in the branch flow path will generally be affected by the flow rate in the main flow path. For an installation with no scales, a definite differential temperature will thereby be known. As soon as the partial flow path begins to narrow, for example because of scaling, the flow rate through the partial fluid line will decrease, and the differential temperature will increase. For a certain well fluid viscosity and thermal capacity, a certain change in the differential temperature will represent a particular change in the flow rate through the branch fluid line, and the differential temperature will thereby be an indication of how large rate of scale is present in relation to a branch fluid line with no scale.

To encourage scaling at the scale indicator, scale-increasing means may expediently be provided at the inlet, typically one or more cooling means to lower the temperature of the

entering branch fluid stream in periods when there is no measuring, turbulence-enhancing means and the use of

materials enhancing scaling. The materials may be of a type and/or provided with a surface that is scale-enhancing in itself .

In a first aspect, the invention relates more specifically to a scale indicator for a flowline for a fluid, in which

a branch fluid line, which is arranged to carry a branch fluid stream, is provided with an inlet arranged upstream in a main fluid stream and an outlet arranged downstream in the main fluid stream;

one or more heating elements, which are arranged to supply the branch fluid stream with thermal energy, are arranged in the branch fluid line; and

a first temperature sensor is arranged in the branch fluid line, characterized by

a second temperature sensor being arranged in the flowline upstream of the outlet of the branch fluid line, the temperature sensor being connected in a signal communicating manner to a signal -processing unit arranged remotely from the branch fluid line.

The branch fluid line may be formed as a container, the inlet and outlet being arranged in end portions of the container.

The highest flow rate of the branch fluid stream may be substantially lower than the flow rate of the main fluid stream.

The branch fluid line may be formed out of a thermally insulating material .

At the inlet arranged upstream, turbulence-intensifying means may be arranged.

The branch fluid line may be provided with one or more cooling elements arranged to cool the inlet down.

At least a portion of the branch fluid line surrounding the inlet may be formed out of a material with scale-increasing properties. The material may be copper.

The material may have a rough surface.

In connection with the flowline, means arranged to record fluid characteristics taken from the group consisting of viscosity and thermal capacity may be arranged, the means being connected to the signal -processing unit.

In a second aspect, the invention relates more specifically to a method of monitoring a scaling condition in a flowline for a fluid, the method including the steps of:

carrying a branch fluid stream through a branch fluid line from an inlet arranged upstream in a main fluid stream to an outlet arranged downstream in the main fluid stream; supplying the branch fluid stream with thermal energy by means of a heating element which is arranged in the branch fluid line, characterized by the method including the further steps of :

monitoring a temperature difference between the

temperature of the main fluid stream upstream of the outlet from the branch fluid line and the temperature of the branch fluid stream, the differential temperature being the

difference between the second temperature and the first temperature; and

calculating, by means of a change in the temperature difference, a change in the flow rate of the partial fluid stream and thereby simulating the scaling condition of the flowline at the branch fluid line.

The temperature difference can be correlated with concurrent recordings of fluid characteristics taken from the group consisting of viscosity and thermal capacity.

In what follows is described an example of a preferred embodiment and method which is visualized in the accompanying drawing, in which: Figure 1 shows a longitudinal section through a scale indicator arranged in a flowline that forms a production tubing in a well .

In the drawing, the reference numeral 1 indicates an

underground structure including a borehole 11 which forms a well, from which a well fluid 12 is produced through a flowline 2. In a portion of the flowline 2, a scale indicator 3 is arranged, shown here in a pocket in a pipe section 21. From the scale indicator 3, several signal lines 4 extend to a signal processing unit 5 remote from the scale indicator 3, typically at a production control plant (not shown) at the surface. In the flowline 2, near the scale indicator 3, means 6 are arranged for measuring fluid characteristics, for example thermal capacity and viscosity, of the well fluid 12 flowing through the flowline 2.

The flowline 2 is provided, in a manner known per se, with means for controlling the influx of well fluid, shown

schematically in the figure as a perforated downhole section 22.

The scale indicator 3 is formed out of a partial fluid line 31 in the form of a container with a fluid inlet 311 arranged upstream in a first end portion 313 of the container 31 and an outlet 312 arranged downstream in a second end portion 314 of the container 31. The inlet 311 and the outlet 312 exhibit a flow area which provides a branch fluid stream F ₂ with a substantially lower flow rate than the flow rate of a main fluid stream F _x in the flowline 2. In the branch fluid line 31, a heating element 32 is arranged. In the branch fluid line 31, downstream of the heating element 32, a first temperature sensor 33 is arranged.

Near the branch fluid line 31, in the main fluid stream Fi , a second temperature sensor 34 is arranged.

To maintain an unrestricted main fluid flow path through the pipe section 21, the second temperature sensor 34 and a measuring instrument 6 for fluid characteristics are arranged in a pocket in the pipe section 21 as well. Thereby tools may be moved unobstructed through the pipe section 21.

Upstream of the inlet 311, means 35 that are arranged to provide a turbulent fluid flow towards the inlet 311 are arranged. The inlet 311 is surrounded by a cooling element 36.

The heating element 32, temperature sensors 33, 34, cooling element 36 and measuring instrument 6 for fluid

characteristics are connected to the signal -processing unit 5 via the signal lines 4.

When the branch fluid stream F ₂ is supplied with thermal energy by means of the heating element, a differential temperature ΔΤ between the branch fluid stream F ₂ and the main fluid stream Fx may be registered, the branch fluid stream F ₂ exhibiting a temperature T ₂ which is higher than the temperature T _x of the main fluid stream Fi . When the flow rate of the branch fluid stream F ₂ decreases because of the flow area in the scale indicator 3, for example in the inlet 311, being reduced in consequence of scaling, the heat supply to the partial fluid stream F ₂ will bring about a greater temperature rise than by a condition without scaling. An increase in the differential temperature ΔΤ may thereby be derived as an indication of scaling or risk of scaling in the flowline 2 or associated elements 22.

As the temperature increase is dependent on the thermal capacity of the well fluid 12, it is obvious to correct the differential temperature development with respect to possible changes in the well fluid composition. The flow rate through the scale indicator 3 is also affected by the viscosity of the well fluid 12, and it is obvious to correct the

differential temperature values with respect to changes in the viscosity of the well fluid 12.

In the case of most substances, for example sulphate salts, which are dominant in this field, cold surfaces and

turbulence will increase the tendency of scaling. Especially in periods with no monitoring of the differential temperature development, it is therefore usually beneficial to activate the cooling element 36 to increase the tendency of scaling, without the use of the cooling element 36 disturbing the differential temperature ΔΤ directly by its cooling effect on the partial fluid stream F ₂ .

By forming at least part of the first end portion 313, for example an annular portion surrounding the inlet 311, out of a material that increases the tendencies of scaling, the risk of scaling may be revealed sooner. It is known that copper has such properties. A rough material surface could also increase the tendencies of scaling, and it will be beneficial to form the inlet 311 with a rough surface on its side wall (s) .