METHOD AND APPARATUS FOR NON-INTRUSIVE MONITORING OF MATERIALS TRANSPORTED THROUGH PIPELINES

FIELD OF THE INVENTION

The present invention relates to a method and apparatus for the non-intrusive monitoring of materials that are transported through a pipeline. In particular, the invention relates to a continuous, non-intrusive method for monitoring material passing through a pipeline that involves gauging the resistivity of the material immediately adjacent the inner wall of the pipeline at any moment in time. An apparatus is also proposed for use in such a method.

The present invention has particular, but not exclusive application in the monitoring of a pipeline transporting oil sand from a mine to a recovery plant. Reference will generally be made to this application of the invention, but it should be realised that the invention is not so limited and may be equally applicable in other fields where a material is being passed through a pipeline.

BACKGROUND TO THE INVENTION

As noted above, the present invention has particular application in monitoring of oil sand travelling through a pipeline. Effective oil recovery from oil sand deposits is somewhat dependent on the detection of the grade of the oil sand that is being transported from a mine into an oil recovery plant at any one time. Transport of the oil sand from mine to plant is frequently through pipelines. The material that is transported through the pipeline in this case is in the form of slurry. That is, a mixture of oil sand and water. The slurry generally moves though the pipeline with a velocity of more than 1m/s. Treatment of slurry containing no or a low amount of bitumen will have a negative impact on the overall efficiency of bitumen recovery. Therefore it is most desirable to have method for precise, reliable, real-time collection of information relating to the composition of the material that is entering the oil recovery plant.

At present pipeline monitoring is based on the observation of flow velocity, pressure and in some cases the propagation of guided elastic waves along the pipeline. From the dispersion properties of such waves, information about the material flowing through the pipeline can be deduced. Electrical resistivity has been proposed for monitoring conditions of the interior of large cylindrical rock grinding mills. Electrical conductivity measurement for monitoring of rock grinding mills initially considered the conductivity of material inside the mill using two electrical probes mounted within the mill shell. This method has shown some good results but the disadvantage of wear on the electrical probes and drift in measurements due to that wear. A similar method has been proposed in the field of multi-phase flow monitoring in the oil industry.

Typical electrical resistivity of bitumen-saturated sand is above 200 ohm-m, sometimes above 500 ohm-m, while that of unwanted materials without bitumen is generally in the range of from 20 to 30 ohm-m or less. Therefore, in the case of piping oil sands, there is a significant contrast in the inherent electrical resistivities of the materials that are transported through the pipelines.

SUMMARY OF THE INVENTION

According to one aspect of the invention there is provided a method of monitoring material travelling through a pipeline including gauging the resistivity of the material that is immediately adjacent at least one region of an interior wall of the pipeline.

The step of gauging the resistivity of the material may comprise measuring the resistivity of the material. For example this may be accomplished by passing a current over an external surface of the pipeline and obtaining a measure of the extent of current leakage from the pipeline into the material immediately adjacent the region of the interior wall of the pipeline.

As noted above, the method involves gauging resistivity of the material that is immediately adjacent at least one region of the interior wall of the pipeline. In order to obtain a more complete picture of the movement of the material within the pipeline, the method preferably includes gauging the resistivity of the material that is immediately adjacent a plurality of regions of the interior wall of the pipeline. For example, the method may include obtaining a measure of the extent of current leakage from the pipeline into the material immediately adjacent a plurality of regions of the interior wall of the pipeline.

The regions may be positioned adjacent to each other and extending around the circumference of the pipeline, for example extending equidistantly around the circumference of the pipeline. That is, the regions may be positioned in turn as one travels around the circumference of the pipeline.

In a certain embodiment, the extent of current leakage is measured in at least three regions of the pipeline. For example, there may be 4-8 regions, or 5-7 regions on the pipeline in respect of which current leakage is measured. It will be appreciated that many more regions may be investigated for current leakage into the material passing through the pipeline.

The step of obtaining a measure of the extent of current leakage may comprise measuring the voltage difference between spaced points on the external surface of the pipeline. The step may include measuring the voltage difference between two spaced points in each said region on the pipeline.

A measured voltage difference between two points on the pipeline indicates leakage of current into the material immediately adjacent the interior wall of the pipeline in that region.

The voltage that is applied, for example across two electrodes, causes a current to flow across the pipeline between the two electrodes. As will be known in the art, the pipeline will generally be made of steel which is highly conductive. Consequently, if there is no current leakage there will be very little drop in voltage across the electrodes. However, there may be some

voltage drop between points on the pipeline depending on the resistivity of the material or phase immediately adjacent the interior wall of the pipeline between the electrodes. That is, a material passing through the pipeline having a low resistivity can lead to current leakage into the material and thereby a measurable voltage difference between the electrodes.

By measuring the voltage difference between adjacent electrodes a picture of the resistivity in each of the regions around the pipeline can be built up. From that the nature of the material immediately adjacent the interior wall of the pipeline, and therefore the make-up of the material passing through the pipeline at any one time, can be deduced.

The current leakage into the material immediately adjacent the interior wall of the pipeline is greatest in a given region when low resistivity material, such as bitumen/oil depleted materials, clay rich materials and/or water is in contact with the interior wall of the pipeline. The current leakage into the phase immediately adjacent the interior wall of the pipeline is smallest when air is in contact with the interior wall of the pipeline. Further, the current leakage is at an intermediate level when bitumen or oil rich sand is in contact with the interior wall of the pipeline.

If the wall of the pipeline in question is not of consistent cross-section, there will be differences in electrical resistivity within the wall itself, albeit only very small differences. Even so, given that any leakage of current into the material that is passing through the pipeline will be relatively small, it is preferred that the method includes a preliminary step of determining the resistivity of the pipeline wall to provide a map of the resistivity of the pipeline itself. This will be dealt with in more detail below.

The current applied to the pipeline is preferably in the range of from 0.1 to 2.0 Amps. Although the current applied may be direct current, it is more preferred that the current be a low frequency alternating current. Preferably the frequency is in the range of from 1 to 5 Hz. High frequency AC may result in skin effect that may limit penetration depth. Direct current is preferably

avoided if possible due to electrode polarisation associated with DC measurements.

The method may further include sending the measured voltage drops between adjacent electrodes to a processor. If so, the voltage readings are preferably sent to the processor in real time. The electrodes may have means for transmitting the sensed voltage reading to the processor by wireless transmission, for example by telemetry equipment.

The step of determining the nature of the material that is in contact with the interior wall of the pipeline at any given time may be carried out using the processor. The processor may be a central processing unit, for example a microprocessor, which may be incorporated in a computer.

The step of determining the material that is in contact with a particular region of the interior wall of the pipeline at any given point in time may be carried out by comparing the voltage difference between adjacent electrodes with data in the processor. For example, a nil voltage drop may indicate that air is in contact with the interior wall at that point; a voltage drop of at least 10 to 100 microvolt may indicate that water and/or oil depleted sand is in contact with the interior wall at that point; and a voltage drop of an intermediate amount, say 1 to 10 microvolt may indicate that an oil rich sand is in contact with the interior wall at that point.

The method may further include using the processor to build up an image of the material passing through the pipeline based on the determination of what material is in contact with the interior wall of the pipeline in the regions being monitored by the electrodes.

The method advantageously enables the effective mapping of the material travelling through the pipeline at any one time. Over a period of time with repeated measurements at regular time intervals the method may include producing an image of the movement of the material within the pipeline in real time.

Thus, according to a particular aspect of the invention there is provided a method of determining the composition of a material travelling through a pipeline including: gauging the resistivities of phases of the material that are immediately adjacent regions of an interior wall of the pipeline; and interpreting the resistivities gauged to determine the phases that are immediately adjacent the regions of the interior wall of the pipeline.

DETAILED DESCRIPTION OF THE INVENTION

A more detailed description will now be provided with reference to the accompanying drawings. However, it should be realised that the following description is provided for exemplification only and should not be construed as limiting on the invention in any way. In the Figures:

Figure 1 illustrates a configuration for measurement of voltage leakage for mapping of the pipeline;

Figure 2 illustrates a configuration for measurement of voltage leakage for gauging the resistivities of material inside the pipeline; Figure 3 illustrates a graph of measured voltages between a set of electrodes;

Figure 4 illustrates a graph of measured voltages between a set of electrodes under different conditions;

Figure 5A illustrates a configuration for measurement of voltage leakage for the detection of water in a pipeline; and

Figure 5B illustrates a configuration for measurement of voltage leakage for the detection of water and oil in a pipeline.

Referring to Figure 1, electrical resistivity of different sections or regions around the perimeter of an empty pipeline 10 may vary. As such, it will generally be advantageous to map the resistivity of the pipeline 10 prior to implementing the method of the invention. This may be achieved by locating a number, for example 3, of potential electrodes at points M, N and M' on the outer surface of the pipeline 10 and passing a current between two current

electrodes located at points A and B on the outer surface of the pipeline 10. As the distance between the two points A and B, incorporating points M, N and M', is relatively small, the current will flow from point A through points M, N and M' to point B. From the measured current (I) and voltages (V1, V2), resistivity (or conductance) of the pipeline for each section M to N and N to M' can be calculated from Ohm's law:

Rmn=V1/l and Rnm'=V2/l

This procedure may be repeated to map the resistivity of the entire circumference of the pipeline 10. From this, subsequent measurements using the method of the invention may be suitably interpreted.

Furthermore, the process may be repeated at desired intervals, generally of weeks or months, to record any changes in the resistivity of the pipeline.

With reference to Figure 2, the step of gauging resistance of a material within the pipeline 10 includes measuring minute amounts of electrical current that leak from the pipeline wall into the material being transported through the pipeline 10, or includes measuring the consequence of such electrical leakage on the effective resistivity of the selected section of the pipeline 10 and the material in the immediate proximity to the tested part of the pipeline wall.

This involves placing the second current electrode at point B that is remote from the first current electrode located at point A. Generally the current electrodes are connected to the pipeline 10 at points A and B that are substantially at opposite sides of the pipeline 10. In such way electrical current (I) is stimulated travel partly through the pipeline interior, although the current (I) will continue to predominantly flow through the wall of pipeline 10.

Current that leaks into interior of the pipeline 10 can be determined from voltages measured between points M and N and between N and M' using potential electrodes located at those points, and previously determined resistivities of the pipeline 10 at sections MN and NM':

lch=(Vmn/Rmn) - (VnmVRnm ¹ )

For a uniform pipeline wall with known or assumed resistivity (Rmn=Rnm'=R), leakage current is given by:

lch=(Vmn-Vnm')/R

Electrical resistivity of the pipeline interior, corresponding to the centre point (N) between the potential electrodes, can be determined from equation:

R = K(Vn,~)/lch

Where:

K geometrical constant of electrode array.

Vn,~ voltage between electrode N and remote voltage reference electrode lch electrical current that travels into the interior of the pipeline at that location (N)

It is anticipated that the reference voltage (Vn,~) will not change significantly, therefore only the amount of current that leaks into the interior of the pipeline will govern the overall resistivity at a particular location.

Generally, quite a number of potential electrodes are fixed on the exterior of the pipeline 10, in the form of uniformly spaced array. Generally, the spacing between the potential electrodes at points M, N, M' and so on will be in the order of 0.05-0.2Om. Measurements from the potential electrodes at points M, N and M' can be transferred to a central processing or recording unit. Based on the measurements of injected current and recorded voltages from the array of potential electrodes, leakage current that travels into the interior of the pipeline, and therefore effective resistivity of the material in the pipeline alone and the collective resistivity of the material in the pipeline and pipeline wall, can be calculated in real time and correlated with other parameters. In such a

way, the composition of the material in the pipeline, and possibly the spatial and temporal variation in the composition of the material being transported through the pipeline, can be determined in real time. Pictorial representation of resistivity distribution within the interior of the pipeline can be obtained by applying a suitable tomography reconstruction algorithm.

The method of the invention has been validated through the series of measurements, the results of which are provided in the graphical illustrations in Figures 3 and 4. In that regard, a DC current with an amplitude of 1.5A was injected into a steel cylinder using two supply electrodes, A and B, located on the outer surface of the cylinder. The cylinder contained an amount of salty water. Potential differences (voltage), between potential electrodes (M, N and M') located on the outside of the cylinder were measured as a function of the level of salty water within the steel cylinder. For each level of water three tests were performed with using different positions for the current electrodes. All measurements were performed with constant current of 1.5A.

The measured voltages between the potential electrodes confirmed low resistivity, corresponding to the level of the water within the cylinder, at the position of electrodes 5 and 6.

With regard to Figure 4, the influence of a wet surface above the level of the salty water within the cylinder was tested by applying water to the internal wall of the cylinder. The results illustrated in the graph of Figure 4 confirm that the wet surface was not sufficient to prevent detection of the water level inside the cylinder at an applied current of 2.5A.

Again, the measured voltages between the potential electrodes confirmed low resistivity at the position of electrodes 5 and 6. This is irrespective of the nature of interior surface of the steel pipe above water level (wet or dry).

With regard to Figure 5A, there is shown a further configuration for determining the composition of a material travelling through a pipeline. In this

embodiment, the configuration is used to determine the presence of water in a pipeline.

Figure 5B illustrates a similar configuration to Figure 5A for determining the composition of a material travelling through a pipeline. In this embodiment, the configuration is used for determining the presence of water and oil in a pipeline.

In Figure 5A and Figure 5B, two examples of the present invention was conducted to illustrate that the method of the present invention can detect the presence of water (See Figure 5A) and oil and water (See Figure 5B). The examples of the present invention utilize an upstanding pipeline.

In both Figure 5A and Figure 5B, a DC current of 1.5A was injected between a first electrode and a second electrode. The first electrode is depicted as X as shown in both Figure 5A and Figure 5B, where the first electrode X is immersed in a liquid and the second electrode is attached to the exterior of the pipeline at position 1. Voltage was measured with three potential electrodes 2, 3, 4. After each measurement, all of the outside electrodes were stepped down the pipe.

In Figure 5A when the pipeline was only filled with water until position 10, the measurement taken, that is, difference in the voltage drops normalized with current (2 ^nd Order Differential Voltage) is plotted against the voltage electrode positions. It can be seen that the value of the measurement was relatively steady until the air water interface and then the value increased from about 0.5 x 10- ⁶ to 1.5 x 10 ^"6 (units V/A).

In Figure 5B, where the pipe was filled with water (from electrode positions 14 to 10) and oil (from electrode positions 10 to 5), it can be seen that in the transition between air and oil, the measurement value decreased from about 1 x 10 ^"6 to about 0 (units V/A). And in the transitions between oil and water, the measurement rapidly increased from 0 to 4.5 x 10 ^"6 (units V/A).

It is believed that these examples clearly demonstrate the ability of the method of the present invention to differentiate the presence of oil and water in a steel pipeline.

It will be appreciated that the foregoing description is has been given by way of illustrative example of the invention and that all such modifications and variations thereto as would be apparent to persons of skill in the art are deemed to fall within the broad scope and ambit of the invention as herein set forth.