GB2597698A

GB2597698A - Fluid property sensor

Info

Publication number: GB2597698A
Application number: GB2011847.7A
Authority: GB
Inventors: Haughs James
Original assignee: Clear Solutions Holdings Ltd
Current assignee: Clear Solutions Holdings Ltd
Priority date: 2020-07-30
Filing date: 2020-07-30
Publication date: 2022-02-09
Also published as: WO2022023567A1; GB202011847D0

Abstract

Dosing apparatus 14 provides a dose of fluid to first pressure vessel 10. A pressurisation apparatus creates a pressure differential between the first pressure vessel and second pressure vessel 12. Valve 32 selectively prevents fluid flow between the pressure vessels. A flow of fluid is initiated from the first pressure vessel via passageway 22 to the second pressure vessel. Pressure data from pressure sensor 21 in the first pressure vessel is inputted into a fluid model that relates pressure data to rheological properties of the fluid. A rheological property is thereby determined. A rheological profile may be generated from the pressure data, and physical properties of the passageway and pressure vessels. The volumetric flow rate through the passageway, the shear stress applied to the fluid, the shear rate of the fluid, or the viscosity of the fluid may be used to determine the rheological profile and one or more pressure differentials.

Description

Fluid Property Sensor

Technical Field

The present invention relates to sensors for measuring properties of a fluid. More specifically, the invention relates to a system and a method for determining the rheological properties of a fluid.

Background

Many fluids for use in industrial processes (such as coolants, lubricants etc.) display at least some non-Newtonian character. Non-Newtonian fluids have fluid properties which vary depending on the forces and stresses applied thereto. A fluid is considered Newtonian if the fluid properties are proportional to the stresses applied thereto, in contrast with non-Newtonian fluids whose properties may demonstrate non-proportional increases or decreases in response to varying applied forces. Fluids which appear to decrease in viscosity when a shear force is applied thereto are considered to be shear-thinning or pseudoplasfic. Examples include whipped cream and some paints. Fluids which exhibit increasing viscosity in response to shear forces are said to be shear-thickening, or dilatant. A classic example of a shear-thickening fluid is corn starch in water, which appears almost solid when experiencing a high shear force.

Shear-thinning and thickening properties are often desirable in various industrial applications. For example, in the field of borehole drilling in the oil and gas industry, a drilling fluid engineer will be responsible for monitoring the physical properties of the drilling fluid to ensure it is able to effectively lubricate and cool the drill head, while transporting cuttings back to the surface for removal. Many drilling fluid additives are available which change the fluid properties to ensure that the fluid properties fall within a desired range.

As the drilling process progresses the composition of the drilling fluid is liable to change, whether due to fluid or additive loss, fluid ingress from surrounding rock formations, or due to the cuttings entraining or dissolving in the drilling fluid. The changing composition is known to cause changes in fluid properties, which can make the drilling fluid less effective. The drilling fluid engineer is thus responsible for 35704417-4 frequently adapting the drilling fluid composition to compensate for the ongoing fluctuations in the rheological properties of the fluid.

Existing methods for determining rheological properties of drilling fluids involve the use of complex and expensive mechanical and electro-mechanical devices. The high sensitivity of these devices means they require frequent recalibration and maintenance by skilled technicians, and thus are expensive to maintain.

The present invention seeks to resolve or ameliorate the above problems, or provide a useful alternative thereto.

Summary of Invention

According to a first aspect of the invention, there is provided a method for measuring a rheological property of a fluid. The method may comprise controlling a dosing apparatus to provide a dose of a fluid to be measured to a first pressure vessel. The method may comprise controlling a pressurisation apparatus to create a pressure differential between the first pressure vessel and a second pressure vessel. The method may comprise initiating flow of the fluid from the first pressure vessel to the second pressure vessel via a passageway. The method may comprise receiving pressure data from a pressure sensor located within the first pressure vessel. The method may comprise determining a rheological property of the fluid by inputting the pressure data into a fluid model that relates the pressure data to the rheology of the fluid.

The method is particularly advantageous, since it does not require use of delicate equipment and is able to provide a robust and reliable result more simply than conventional methods. Advantageously, the method may be carried out by an operator, or it may be semi or fully-automated.

Creating a pressure differential may comprise increasing the pressure in the first and/or second pressure vessel. Creating a pressure differential may comprise controlling the pressurisation apparatus to add a pressurised gas to one or both of the first and second pressure vessels. Gas pressurisation is simple, reliable and cheap. The pressurised gas may be compressed air or nitrogen gas. Nitrogen gas is particularly 35704417-4 desirable due to its low solubility in water and its low reactivity. In some embodiments, the second pressure vessel may be pressurised in addition to the first. Pressurising both pressure vessels may prevent or reduce the effects of dissolved gases in the fluid. For example, since gas solubility increases with pressure, it is possible for the pressurising gas to dissolve in the fluid sample in the first pressure vessel. When the valve is opened and the fluid sample is pushed into the second pressure vessel (which is at a lower pressure), the gas solubility may drop and cause out-gassing of the pressurising gas from the fluid sample. Since this may cause bubbles to form in the fluid sample, it can greatly affect the viscosity and rheological properties, and it is thus desirable to minimise the effects. In alternative embodiments, the pressure differential may be created using one or more mechanical means, such as a pneumatic or hydraulic piston. Such embodiments may be mechanically more complex, but may have reduced risk of out-gassing.

In some embodiments, initiating the flow of the pressurised fluid comprises opening a valve between the first and second pressure vessels. The valve may be provided in the passageway. Additionally or alternatively, the valve may be provided on the first or second pressure vessels.

The pressure sensor may be configured to continuously or repeatedly record the pressure when the fluid flows from the first to the second pressure vessel.

The method may further comprise receiving pressure data from a further pressure sensor located within the second pressure vessel. The further pressure sensor may be configured to continuously or repeatedly record the pressure when the fluid flows from the first to the second pressure vessel The method may comprise determining a pressure differential based on the pressure data from the first and second pressure sensors. The method may comprise continuously or repeatedly recording and/or determining the pressure differential when the fluid flows from the first to the second pressure vessel.

The method may comprise receiving temperature data from one or more temperature sensors. The method may comprise continuously or repeatedly recording the 35704417-4 temperature of fluid, first pressure vessel, second pressure vessel and/or the passageway.

In some embodiments, determining a rheological property of the fluid comprises generating a rheological profile for the fluid. Generating a rheological profile may comprise calculating or estimating a graph of shear stress vs shear rate for the fluid. The rheological profile may be calculated or estimated from the pressure data, measurable fluid properties such as temperature, volume and/or density, and the physical properties of the passageway and/or first and/or second pressure vessels.

Determining the rheological profile may comprise calculating or estimating, at one or more pressure differentials, one or more of: the volumetric flow rate through the passageway; the shear stress applied to the fluid; the shear rate of the fluid; and the viscosity of the fluid. Determining the rheological profile may comprise calculating or estimating the change in pressure differential over time. Determining the rheological profile may comprise calculating or estimating the fluid density.

The method may comprise repeating the process by controlling the pressurisation apparatus to create a pressure differential between the first pressure vessel and a second pressure vessel and initiating the flow of the pressurised fluid from the second pressure vessel to the first pressure vessel via the passageway. The method may comprise receiving further pressure data from the pressure sensor or sensors. The method may comprise determining the rheology of the fluid by inputting the pressure data into a fluid model that relates the pressure data to the rheology of the fluid.

Determining the rheology may comprise updating the rheological profile with the additional data. The method may comprise repeating the process multiple times until sufficient data has been generated.

The method may comprise repeating the process using a plurality of passageways, the passageways having different lengths and/or internal diameters. The passageways way be configured to provide differing shear conditions on a fluid passing therethrough. Using a plurality of passageways may allow for a broader range of shear conditions to be applied to the fluid during a series of tests.

35704417-4 The method may comprise emptying and/or cleaning the first and second pressure vessels.

According to a second aspect of the invention, there is provided a processor-readable medium comprising instructions that, when executed by one or more processors, cause the processors to perform a method as described herein.

According to a third aspect of the invention, there is provided a computer program comprising instructions that, when executed by a computer, cause the computer to perform a method as described herein.

According to a fourth aspect of the invention, there is provided a system for measuring a rheological property of a fluid. The system may comprise a first pressure vessel for receiving fluid to be measured. The system may comprise a second pressure vessel.

The system may comprise a passageway connecting the first and second pressure vessels. The system may comprise a valve for selectively preventing fluid flow between the first and second pressure vessels. The system may comprise a pressurisation apparatus configured to create a pressure differential between the first and second pressure vessels. The system may comprise a pressure sensor configured to measure the pressure within the first pressure vessel.

The passageway may be between 0.5 and 5m in length. Optionally, the passageway may have a length between lm to 4m, 1.5m to 3.5m, 2m to 3m, or 2.5m. The passageway may have an internal diameter of 0.1 to 5mm. Optionally, the passageway may have an internal diameter of 0.5 to 4mm, 1 to 3mm or 2mm. The internal diameter of the pipe may be configured such that it provides a high amount of sheer stress on the fluid sample when the fluid sample is passed therethrough. The passageway may be interchangeable. For example, the passageway may comprise end connectors for connecting corresponding connectors on the first and second pressure vessels. A range of passageways of differing lengths and/or internal diameters may be provided to allow for adaptation of the system depending on the fluid being measured.

In one series of embodiments, the system may comprise a plurality of passageways connecting the first and second pressure vessels, the passageways each having a different length and/or internal diameter. For example, the system may comprise a high 35704417-4 shear passageway and a low shear passageway. The system may comprise a valve configured to select which of the plurality of passageways the fluid will be directed through. Additionally or alternatively, the system may comprise a plurality of valves for controlling which of the passageways test fluid is directed along e.g. each passageway may comprise a valve. Such embodiments allow for the measurement process to be repeated under differing shear conditions due to the different passageway structures. Thus, the system may be able to measure a rheological property across a broader range of conditions and/or with greater accuracy.

The system may comprise a dosing apparatus configured to provide a dose of the fluid to be measured to the first pressure vessel. The dosing apparatus may be configured to supply a pre-determined dose of fluid e.g. by volume or weight. For example, the dosing apparatus may be configured to fill the first pressure vessel to between 30 to 70%, between 40 and 60%, 45 to 55% or to 50% full.

The first pressure vessel may comprise a first port for receiving fluid to be measured therethrough. The second pressure vessel may comprise a drain port for draining the system of fluid.

The system may comprise a cleaning apparatus for cleaning the first pressure vessel, second pressure vessel and/or the passageway. The cleaning apparatus may comprise a source of cleaning fluid e.g. water or disfilled/demineralised water. The dosing apparatus may be configured to supply the cleaning fluid to the first and/or second pressure vessel. The system may be configured to carry out a cleaning process comprising adding a cleaning fluid to the first and/or second pressure vessel, passing the cleaning fluid through the passageway under pressure, and draining the cleaning fluid from the first and second pressure vessels.

The pressurisation apparatus may comprise a source of pressurised gas. The pressurisation apparatus may comprise a conduit operatively connectable to a first gas port in at least the first pressure vessel for receiving said pressurised gas for pressurising the first pressure vessel. The pressurisation apparatus may comprise a further conduit operatively connectable to a second gas port in the second pressure vessel for receiving said pressurised gas for pressurising the second pressure vessel.

35704417-4 The system may comprise a further pressure sensor configured to measure the pressure within the second pressure vessel.

The system may comprise one or more temperature sensors. The one or more temperature sensors may be located in the first pressure vessel, second pressure vessel and/or the passageway.

The system may further comprising a controller comprising one or more processors; and a processor-readable medium storing instructions that, when executed by the one or more processors, cause the controller to perform a method as described herein.

Brief Description of the Ficiures

Embodiments will now be described, purely by way of example, with reference to the accompanying drawings, wherein like elements are indicated using like reference signs, and in which: Figure 1 is a schematic diagram of a system; Figure 2 is a flow diagram of a method for measuring a rheological property of a fluid; Figure 3 is a flow diagram of a method for measuring a rheological property of a fluid; and Figure 4 is a graph of pressure against time obtainable by the method of Figures 2 and 3.

Specific Description

Turning now to Figure 1, there is shown a schematic diagram of a system 1 for measuring a rheological property of a fluid The system 1 has a first pressure vessel 10 and a second pressure vessel 12. A dosing apparatus 14 is connected to the first pressure vessel 10 via inlet conduit 20. Fluid flow into the first pressure vessel 10 is controlled via solenoid valve 30 located in the inlet conduit 20. A passageway 22 with a second solenoid valve 32 connects the first and second pressure vessels 10, 12. The passageway 22 may be between 0.5 and 35704417-4 5m in length, and may have a pipe diameter of 0.1 to 5mm. The narrow passageway diameter thus provides a high shear stress to the fluid sample when it is being passed therethrough. The passageway 22 dimensions may be configured to provide a suitable level of shear to a fluid sample depending on the expected properties of the fluid. A range of sizes may be provided to allow for adaptability, or a range of pre-sized systems may be offered to user for varying applications. In further embodiments (not shown) multiple passageways 22 connecting the first and second pressure vessels 10, 12 are provided, having differing lengths and/or internal diameters. The second solenoid valve 32 is configured to direct the fluid down one of the passageways 22 at a time, or alternatively, each passageway 22 would be provided with its own solenoid valve to control flow down each passageway.

An outlet conduit 24 with a third solenoid valve 34 is connected to the second pressure vessel 12 and leads to a drain 16. Each of the first and second pressure vessels 10, 12 is provided with a pressure sensor 21, 23.

A pressurisation apparatus is provided and connected to the first and second pressure vessels 10, 12. The pressurisation apparatus is formed from a pressurised gas source 18 such as a high pressure pump or compressed gas cylinder. The pressurised gas source 18 is connected to a first gas conduit 27, which splits into a first channel 26 connected to the first pressure vessel 10 and a second channel 28 connected to the second pressure vessel 12. The first channel 26 has a first pneumatic valve 40 and a fourth solenoid valve 36. The second channel 28 has a second pneumatic valve 42 and a fifth solenoid valve 38. The fourth and fifth solenoid valves 36, 38 provide simple control of the addition of pressurised gas into the first and second pressure vessels 10, 12. The first and second pneumatic valves 40, 42 can be adjusted to control the flow rate of gas through the first and second channels 26, 28 and thus provide a simple mechanism for achieving a pressure differential between the first and second pressure vessels.

The system 1 also has a controller 11 such as an electronic controller or computer system. The controller 11 is connected to each of the solenoid valves 30, 32, 34, 36, and 38 and the pneumatic valves 40, 42 for operation thereof. The controller 11 is also connected to the first and second pressure sensors 21, 23 and is configured to receive 35704417-4 pressure data therefrom relating to the pressure within the first and second pressure vessels 10, 12.

The controller 11 may comprise one or processors operatively coupled to a memory (not shown in Figure 1). The memory may comprise instructions that, when executed by the one or more processors, cause the processor to perform any of the methods disclosed herein. The controller 11 is configured to receive pressure data from the first and second pressure sensors 21, 23, and to control the solenoid valves 30, 32, 34, 36, and 38 and the pneumatic valves 40, 42 in response to the pressure data. For example, the controller 11 may have one or more interfaces through which sensor data can be received from the pressure sensors 21, 23, and through which instructions and/or data can be sent to control the solenoid valves 30, 32, 34, 36, and 38 and the pneumatic valves 40, 42.

Turning now to Figure 2, a method 50 of determining a rheological property of a fluid will be described. The method 50 of Figure 2 can be performed by the controller 11 discussed above At the first block 52 a predetermined dose of a fluid sample is supplied to the first pressure vessel 10. The volume of the sample supplied will depend on a number of factors such as volume of the pressure vessels, intended pressures to be used, predicted or known fluid properties etc. The actual volume of fluid is less important than ensuring the volume is accurately known. The controller 11 may open the first solenoid valve 30 to allow the fluid to be supplied by the dosing apparatus 14.

A pressure differential is then created at block 54. A pressurised gas, such as compressed nitrogen, is supplied via the channels 26 and 28 to the first and second pressure vessels 10, 12, thereby pressurising the fluid sample in the first pressure vessel 10. The controller 11 adjusts the pneumatic valves 40, 42 to ensure that the pressure within the first pressure vessel 10 is greater than the second pressure vessel 12. The pressure in the first pressure vessel 10 may be, for example, from 25 to 200 psi (approx. 172 to 1379 kPa). The pressure in the second pressure vessel 12 can be varied by the controller 11 depending on the desired pressure differential.

35704417-4 The fluid flow is then initiated in block 56. This may comprise opening the second valve 32. Since a pressure differential has been created, the higher pressure within the first pressure vessel 10 will push the fluid sample through the passageway 22 to equalise the pressures between the first and second pressure vessels 10, 12. The pressure differential may be configured such that all of the fluid sample is driven into the second pressure vessel 12.

While the pressure is equalising between the first and second pressure vessels 10, 12, the pressure sensors 21, 23 send pressure data to the controller 11 in block 58. The pressure sensors 21, 23 may be configured to provide continuous pressure readings to the controller 11, or they may be configured to provide multiple discrete readings at regular intervals. An example of the pressure data obtainable is shown in Figure 4. As the fluid flows from the first pressure vessel 10 to the second pressure vessel 12, the pressure p1 in the first pressure vessel 10 drops. Simultaneously, the pressure p2 in the second pressure vessel 12 rises until equilibrium is reached between the two pressure vessels 10, 12. The pressure differential is the difference between p1 and p2 (i.e. p1,2 = p1 -p2). The system has reached equilibrium when p1,2 reaches zero. Figure 4 shows a fluid which is shear-thinning, since the pressure differential p1,2 decreases quickly at high pressure differentials (i.e. due to high volumetric flow and thus lower apparent viscosity) and decreases more slowly at lower pressure differentials, indicating an increase in viscosity and corresponding reduction in volumetric flow.

The pressure data is then inputted into a fluid model in block 60. The fluid model may be stored in the controller 11 or on a separate computer system (not shown in Figure 1). The fluid model relates pressure data, such as the absolute pressures of the first and second pressure vessels p1 & p2, the pressure differential p1,2, and rates of change thereof (e.g. Apl, Sp2, & ap1,2) to the rheological properties of a fluid, such as apparent viscosity (i.e. the shear stress divided by the shear rate). The fluid model may include a plurality of equations, where the equations relate an observed pressure change to a property of the fluid. Similar calculations are described in Chilton, RA and R Stainsby, 1998. "Pressure loss equations for laminar and turbulent non-Newtonian pipe flow', Journal of Hydraulic Engineering 124(5) pp. 522 ff, which is hereby incorporated by reference.

35704417-4 The fluid model can be generated through a calibration process, comprising a test process as described below carried out using fluids of known rheological properties. A large dataset can then be gathered and the known rheological properties correlated with the observed pressure changes to form a reference data set. This may include the use of a neural network, or a stochastic optimisation algorithm. The properties of a sample fluid can be estimated through comparison of the recorded pressure data during a test process with the reference data.

Subsequently the rheological properties of the fluid sample are determined in block 62.

Determining the rheological properties may include calculating the volumetric flow rate from the pressure and the observed change in pressure and rate thereof as the process is carried out. Since both pressure vessels 10, 12 are sealed, as the fluid is pushed from the first pressure vessel 10, the pressure within the first pressure vessel 10 will decrease. Similarly, the pressure within the second pressure vessel will increase until the pressure differential equilibrates. The volumetric flow can thus be calculated from the pressure change over time. The calculated volumetric flow rate, pressure differential, and rate of differential change can subsequently be used to derive the viscosity of the fluid, since more viscous fluids will take longer to pass through the passageway 22. Furthermore, since the shear rate applied to the non-Newtonian fluid will cause changes in the apparent viscosity, shear-thinning or shear-thickening fluids would exhibit non-linear changes in volumetric flow in relation to the applied pressure differential. Similarly, the volumetric flow rate and the geometry of the passageway 22 can be used to calculate the shear rate applied to the fluid. This allows for the viscosity at multiple shear rates to be calculated. The pressure loss in a pipe during laminar flow is a function of fluid density, the fluid rheological profile, volumetric flowrate and the pipe geometry and length. The pipe geometry and the fluid density are constant throughout the tests. By determining the volumetric flow rate from the pressure differential curves, the shear rate and shear stress can be calculated accordingly. The Herschel-Bulkley viscosity parameters comprises three separate coefficients (the consistency k, the flow index n, and the yield shear stress To), and thus multiple measurements at differing shear rates are required.

As the pressure differential reduces over time, the fluid velocity, volumetric flow rate and thus the shear rate applied to the fluid sample will reduce over time. The system can thus calculate the range of different shear stresses and shear rates over the time 35704417-4 of the process. A rheological profile of the fluid is thus generated and the viscosity can be derived. Further rheological parameters of the fluid can be calculated or estimate through a combination of simulation and the use of statistical inference, such as the Herschel-Bulkley viscosity parameters and/or the Bingham Plastic yield stress.

A feasibility check is performed in block 64. The controller 11 can compare the rheological properties or profile against existing results or predicted results in order to identify outlying or erroneous results. For example, the system could be used to repeatedly monitor a working fluid, such as a bore hole drilling fluid. For repeat monitoring, the system may retain the previous results, and thus be able to identify any results which represent significant or rapid changes in rheological properties. The system may provide an alert to an operator. Should the system detect a non-feasible result, the system is drained in block 66, and the process repeated with a new dose of sample fluid. The draining process of block 66 may be automatic, or it may require a user input in order to proceed, such that user oversight is required to confirm feasibility.

Non-feasible results may be determined as those with a change greater than a predetermined value, such as a percentage increase or decrease. It is expected to observe changes in viscosity due to the effects of shear-thinning or thickening, but a large change of viscosity at similar pressure differentials may indicate a blockage has occurred. The level of sensitivity may be adjustable by a user. Additionally or alternatively, the system may estimate rheological properties based on the fluid composition if known, and determine feasibility by comparing the observed rheological properties to those estimated from the composition, with large disparities being deemed erroneous and non-feasible. If the rheological properties are feasible, then the rheology of the fluid sample has been determined in block 68 and the process 50 ended.

Turning now to Figure 3, there is shown a further flow diagram for a process 70. The process 70 is substantially the same as process 50 of Figure 2 but with the additions described below. The method 70 of Figure 3 can be performed by the controller 11 discussed above.

After the pressure data has been inputted into the fluid model in block 60, the controller 11 carries out a check for whether the system has sufficient data in block 61.

35704417-4 If the system does not have sufficient data to determine the rheological properties, the system creates a new pressure differential in block 67, and the process is repeated. Preferably, the new pressure differential will be different to the previous or each of the previous test conditions in order to generate a larger data set. The repeat test may be carried out using a fresh dose of sample fluid, as described with reference to block 66.

Alternatively, since the fluid sample will be located within the second pressure vessel 12, the valve 32 can be closed and a pressure differential generated as described previously, but with a higher pressure in the second pressure vessel. In such systems, the location of the second valve 32 may be adapted or a further valve (not shown) may be provided in the passageway 22 to ensure comparable test conditions. Once the pressure differential is created, the valve 32 can be opened by the controller 11 and the pressure data recorded while the fluid is pushed through the passageway 22 back into the first pressure vessel 10. It will be understood that the same sample could be tested multiple times by generating pressure differentials and pushing the fluid back and forth between the first and second pressure vessels 10, 12 until a sufficient pressure data set is generated. Once the controller 11 has determined that sufficient data has been collected in block 61, the process continues as previously described.

Optionally, if the feasibility check in block 64 is negative, the process could create a new pressure differential in block 67 and repeat the testing as described above rather than draining the system and testing a new dose as described with reference to block 66 (Figure 2). In practice, a further check (not shown) may be implemented for whether to drain the system and restart, or whether to re-test the same sample.

The processes 50, 70 may be used in a system such as a stand-alone fluid sensor.

Equally, the processes 50, 70 can be carried out automatically by a controller 11 without user input. For example, the rheological data may feed into a larger automation system for constant or periodic fluid monitoring, such as for bore-hole drilling fluid monitoring.

The methods disclosed herein can be performed by instructions stored on a processor-readable medium. The processor-readable medium may be: a read-only memory (including a PROM, EPROM or EEPROM); random access memory; a flash memory; an electrical, electromagnetic or optical signal; a magnetic, optical or magneto-optical storage medium; one or more registers of a processor; or any other type of processor-35704417-4 readable medium. In alternative embodiments, the present disclosure can be implemented as control logic in hardware, firmware, software or any combination thereof. The apparatus may be implemented by dedicated hardware, such as one or more application-specific integrated circuits (ASICs) or appropriately connected discrete logic gates. A suitable hardware description language can be used to implement the method described herein with dedicated hardware.

It will be understood that the invention has been described above purely by way of example, and that modifications of detail can be made within the scope of the invention 35704417-4

Claims

CLAIMS: 1. A method for measuring a rheological property of a fluid, the method comprising: controlling a dosing apparatus to provide a dose of a fluid to be measured to a first pressure vessel; controlling a pressurisation apparatus to create a pressure differential between the first pressure vessel and a second pressure vessel; initiating flow of the fluid from the first pressure vessel to the second pressure vessel via a passageway; receiving pressure data from a pressure sensor located within the first pressure vessel, determining a rheological property of the fluid by inputting the pressure data into a fluid model that relates the pressure data to the rheological properties of the fluid.
2. The method according to claim 1, wherein creating a pressure differential comprises: controlling the pressurisation apparatus to add a pressurised gas to one or both of the first and second pressure vessels.
3. The method according to either preceding claim, wherein initiating the flow of the pressurised fluid comprises opening a valve between the first and second pressure vessels.
4. The method according to any one of the preceding claims, wherein the pressure sensor is configured to continuously or repeatedly record the pressure when the fluid flows from the first pressure vessel to the second pressure vessel.
5. The method according to any one of the preceding claims, further comprising receiving pressure data from a further pressure sensor located within the second pressure vessel, the further pressure sensor configured to continuously or repeatedly record the pressure when the fluid flows from the first pressure vessel to the second pressure vessel.
35704417-4 6 The method according to claim 5, comprising determining a pressure differential based on the pressure data from the first and second pressure sensors.
7. The method according to any one of the preceding claims, wherein determining a rheological property of the fluid comprises generating a rheological profile for the fluid derived from the pressure data and the physical properties of the passageway and/or first and/or second pressure vessels.
8. The method according to claim 7, wherein determining the rheological profile comprises determining, at one or more pressure differentials, one or more of: the volumetric flow rate through the passageway; the shear stress applied to the fluid; the shear rate of the fluid; and the viscosity of the fluid
9. A processor-readable medium comprising instructions that, when executed by one or more processors, cause the processors to perform a method in accordance with any one of claims 1 to 8.
10. A computer program comprising instructions that, when executed by a computer, cause the computer to perform a method in accordance with any one of claims 1 to 8.
11. A system for measuring a rheological property of a fluid, the system comprising: a first pressure vessel for receiving a fluid to be measured; a second pressure vessel; a passageway connecting the first and second pressure vessels, a valve for selectively preventing fluid flow between the first and second pressure vessels, a pressurisation apparatus configured to create a pressure differential between the first and second pressure vessels, and a pressure sensor configured to measure the pressure within the first pressure vessel 35704417-4
12. The system according to claim 11, wherein the system comprises a dosing apparatus configured to provide a dose of the fluid to be measured to the first pressure vessel.
13. The system according to claim 11 or 12, wherein the first pressure vessel comprises a first port for receiving the fluid to be measured therethrough.
14. The system according to any one of claims 11 to 13, wherein the second pressure vessel comprises a drain port for draining the system of fluid.
15. The system according to any one of the preceding claims, wherein the pressurisation apparatus comprises a source of pressurised gas and a conduit operatively connectable to a first gas port in the first pressure vessel, the first gas port configured to receive said pressurised gas for pressurising the first pressure vessel.
16. The system according to claim 15, wherein the pressurisation apparatus comprises a further conduit operatively connectable to a second gas port in the second pressure vessel, the second gas port for receiving said pressurised gas for pressurising the second pressure vessel.
17. The system according to any one of claims 11 to 16, comprising a further pressure sensor configured to measure the pressure within the second pressure vessel.
18. The system according to any one of claims 11 to 17, further comprising a controller comprising: one or more processors; and a processor-readable medium storing instructions that, when executed by the one or more processors, cause the controller to perform a method according to any one of claims 1 to 8.35704417-4