Measurement tool and method of use

(54) Title: MEASUREMENT TOOL AND METHOD OF USE (30) Unionist Priority: 27/09/2007 GB 0718851.9 (73) Holder (s): Precision Energy Services, INC (72) Inventor (s): Bryan William Kasperski, Margaret Cowsar Waid, Michael Andrew Yuratich (57) Summary: measurement tool and method of use. The present invention relates to a measurement tool and method of use, and in particular to a measurement tool for use in determining a parameter of a stationary or mobile fluid. The measurement tool was designed primarily for use in the borehole test. The measuring tool can measure the dielectric constant of a fluid inside a pipe or surrounding the tool. The pipe or wall between the tool and the fluid is electrically insulating. The tool has a pair of capacitor plates mounted adjacent to the pipe or wall, a signal generator that can apply an alternating electrical signal to at least one of the capacitor plates and a detector to measure a signal dependent on the electrical capacitance between the plates of the capacitor. The measuring tool can additionally measure the electrical resistivity of the fluid.

<img file="BRPI0804066A2_D0001.tif" />

<img file="BRPI0804066A2_D0002.tif" />

Descriptive Report of the Invention Patent for MEASURING TOOL AND METHOD OF USE.

FIELD OF THE INVENTION

The present invention relates to a measurement tool and method of use, and in particular to a measurement tool for use in determining a parameter of a stationary or mobile fluid. The measurement tool is designed for use in the borehole test and the following description will therefore refer primarily to such applications, but the invention is not limited to that.

BACKGROUND OF THE INVENTION

Measurement tools are in widespread use in borehole formation testing, for example, in boreholes drilled in the earth in order to test or recover underground oil and / or gas reserves. Some of these tools are carried by the drilling sequence and measurements are performed during the drilling operation of the borehole (so-called measurement applications while drilling (MWD) or registration while drilling (LWD)). Other measuring tools are used after the borehole has been drilled, the measuring tools being lowered into the borehole by a cable or conductor. In highly deviated wells, transportation can be aided by semi-rigid tubing or a drill pipe. Still other measuring tools are arranged in the vertical hole for extended periods of time with or without a connection cable and are referred to as permanent or recoverable gauges. These are generally for use in production after the exploration phase is complete.

Tools arranged using cable having one or more electrical conductors are generally referred to as electrical wire line tools. The present invention is more likely to be a part of an electric wire line tool, although its use in MWD / LWD or other applications in the vertical bore is hereby excluded.

A known power line tool is a formation test tool or depletion tool, which is used to extract a volume of fluid from a formation surrounding a borehole, the fluid being tested in order to assess likely productivity the oil or gas well.

It is a recognized problem in the operation of forming test tools that during the drilling hole drilling operation, the fluid within the formation can be contaminated with the boring fluid (or “mud) filtrate typically comprising liquid and other materials. In order to obtain valuable test results, it is of paramount importance that the forming fluid used for the analysis represents a virgin forming fluid with little or no contamination from the fluids used in the borehole drilling operation.

The boring fluid is generally divided into oil based mud (OBM) and water based mud (WBM). The pressure of the boring fluid is kept higher than that of the formation, and as a result, the boring fluid filters into the formation, the filtering fluid being known as filtered. Fine particles that cannot penetrate the formation are left behind in the borehole wall and prepared to form a filter mass (or mud). This is relatively impermeable and forms an outer layer substantially preventing further ingress of fluid. The filtrate displaces the virgin formation fluid from the vicinity of the borehole wall, until a stable invaded zone results. Depending on the virgin fluid, the type of mud and the composition and structure of the formation, different degrees and depth of invasion occur in the formation.

The forming fluid can naturally contain a large percentage of water, of some salinity. Water-based mud is predominantly water, but it does not need to have the same salinity. Although perfect oil-based mud has very little water, in practice, it can contain as much as 40% water. The filtrate can include water from other depths in the borehole that you mixed in the mud. DESCRIPTION OF THE PREVIOUS TECHNIQUE

Traditionally, operators wishing to extract a volume of fluid from a formation surrounding a borehole in order to assess the probable productivity of the well used the drill rod test, in which the formation fluid could flow or be pumped into the well. test surface. This practice became less desirable primarily because of the harmful environmental impact of the need to ignite excessive gas. Also, there is a difficulty in bringing the fluid to the surface of private wells, especially underwater wells. Furthermore, the pressure and temperature of the fluid change during its movement through the borehole to the surface and these changes in pressure and temperature can cause changes in the consistency of the fluid (i.e., the fluid can separate into oil, water and gas or otherwise change its material characteristics), which may invalidate the subsequent test.

To overcome the problems associated with flowing the forming fluid directly to the surface, forming testing tools have been developed that can undertake at least some of the tests in the vertical bore. Such a forming test tool is described in US patent 5,602,334, the tool including measuring tools capable of measuring selected parameters of the forming fluid in the vertical bore. This forming test tool also includes containers that can be filled with the forming fluid for transport to the surface for further testing if desired.

Of course, it is necessary for training test tools such as that of US patent 5,602,334 to be able to determine whether the fluid being pumped out of the formation is virgin forming fluid, or is contaminated forming fluid, so that the tests they are carried only in the virgin formation fluid, and only virgin formation fluid is collected in the containers. For present purposes, virgin means having as little contamination as possible, and certainly below some threshold of acceptability.

Many different parameters are desired to be tested in the vertical bore, some of which assist in determining whether the fluid is virgin or contaminated and others which assist the operator in assessing the likely productivity of the formation.

A parameter that can be measured in the vertical hole is the electrical resistivity of the fluid. This parameter is often used to determine whether the fluid is virgin or contaminated because the electrical resistivity of the oil is significantly different from that of water-based sludge. US patent application 2007/0018659 describes a measurement tool for use in a forming test tool, the tool measuring the resistivity of the forming fluid flowing through it.

In US patent application 2007/0018659, the resistivity of the forming fluid is tested when the fluid is flowing through a pipe, and this is a particularly desirable aspect of the measuring tools used in the forming testing tools where the pipe can be located. inside the training test tool. The pipe should preferably be substantially linear and free from restrictions, curves or voids that would induce pressure changes in the fluid, whose pressure changes may affect the consistency of the fluid and thus lead to a different test result than would be obtained with the fluid inside the formation.

Another parameter that can be measured at the vertical bore is pressure, typically as part of a release and formation pressure test that can be used to determine the mobility (permeability divided by viscosity) of a formation and therefore help to assess the likely productivity of training.

Yet another parameter is the chemical constituents of the fluid, which can be used to determine whether the forming fluid at one depth of the borehole is the same as that at another depth, any chemical difference between the forming fluids at different depths indicating that the formation is not contiguous and is, instead, composed of discrete reservoirs that will make oil and / or gas more difficult and costly to recover. The chemical difference can also be used to differentiate between virgin and filtered fluid.

The probable productivity of an oil and / or gas reservoir is a very valuable assessment for operators to make, as this determines the likely value of the reservoir for the operator. It is an objective of this invention to provide a measurement tool that can be used in a formation test tool and that is able to test more relevant parameters of the formation fluid and / or that is able to test the relevant parameters more accurately and reliably. , so that the operator can make a more accurate assessment of the productivity of a particular reservoir.

It is another objective of the present invention to assist in distinguishing the virgin formation fluid from the invasion (contamination) filtrate, recognizing that both water and oil components in the invaded zone are often a mixture of residual and filtered virgin fluid and that the virgin fluid in addition to the invaded zone there may be water or oil similar to that of the mud filtrate.

SUMMARY OF THE INVENTION

According to the first aspect of the invention, a measuring tool is provided to measure the dielectric constant of a fluid inside a pipe, the pipe being electrically insulating, the tool having:

a pair of capacitor plates mounted adjacent the pipe, a signal generator that can apply an alternating electrical signal to at least one of the capacitor plates and a detector to measure a signal dependent on the electrical capacitance between the capacitor plates.

By the proper arrangement of the capacitor plates, the measured signal will depend on the capacitance of the fluid inside the pipe and the capacitance of the fluid can be used to determine the fluid dielectric constant.

Preferably, the pair of capacitor plates is mounted outside the pipe, so that there is no direct contact between the plates and the fluid. The measured capacitance will therefore depend on the capacitance of the fluid and the capacitance of the pipe. The use of an insulated pipe with a high dielectric constant in an appropriate arrangement with the capacitor plates will result in the measured signal being dependent primarily on the capacitance of the fluid.

It has been recognized that the dielectric constant of virgin formation fluid predominantly of oil or gas is significantly different from the dielectric constant of water-based sludge. The dielectric constant of the virgin-forming fluid is also often measurably different from the oil-based sludge dielectric constant because of its different water content, so the present measurement tool can be used to assist in determining whether the fluid inside the pipe is contaminated or is virgin forming fluid suitable for further testing. Also, the dielectric constant of the virgin forming fluid can provide valuable information for the operator.

The capacitor plates can surround respective parts of the pipe so that capacitance is measured along the pipe. Alternatively, the capacitor plates can be mounted on opposite sides of the pipe, so that capacitance is measured through the pipe. In the modalities in which the pipe has a circular cross section, the capacitor plates can be annular or partially annular.

Desirably, the pipe dielectric constant is at least eight. The pipe, therefore, has a much higher dielectric constant than oil (which typically has a dielectric constant of approximately two) and is acceptable in relation to water (which has a dielectric constant ranging from approximately twenty to approximately eighty-one of according to factors such as temperature and contamination).

There can be three capacitor plates. The use of three capacitor plates can enhance the signal strength of the device and increase the volume of the measured fluid.

The three capacitor plates can be arranged along the length of the pipe, with the signal generator connected to the central driven capacitor plate and with the two other capacitor plates connected to the ground.

Preferably, the signal generator is connected to its capacitor board by a shielded signal conductor and the signal generator is connected to a metallic shield by a shield connector, the shield connector being connected to an operational amplifier configured as a voltage follower, so that the voltage at the shield connector is matched with that of the signal conductor. Ideally, the shield connector also surrounds the signal conductor for at least part of its length, in the form of a coaxial or shielded cable or the like. Because the voltages of the signal conductor and the shield connector are matched, the capacitance of the coaxial or shielded cable can be ignored, and the shield connector further protects the signal conductor against foreign electrical signals.

Preferably, at least the driven capacitor plate and the pipe are surrounded by one or more metal plates acting as a focusing plate, connected by means of a voltage follower at the same potential as the driven capacitor plate. The focusing plate (s) acts to reduce the desensitizing effects of the portions of the pipe dielectric material exposed between the capacitor plates. The focusing placard (s) also protects the capacitor plate (s) from foreign electrical signals.

Desirably, the focusing plate (s) is / are connected to the metal shield so that it (s) can share the same voltage follower. Desirably the signal generator and voltage follower circuits are on one end of the shielded conductor and the capacitor plates and the focusing plate (s) on the other end.

The signal that is measured can be the electrical voltage over, and the electrical current flowing through, the signal conductor, which together can be used to determine capacitance in a known way.

The frequency of the alternating signal is chosen to suit the application, it being understood that particular frequency ranges will be better suited to determine changes in the capacitance of particular fluids at particular temperatures. For a measurement tool for use in a training test tool, the currently preferred frequency is 16 kHz, although other frequencies are assumed to be suitable for particular configurations and devices.

According to a second aspect of the invention, a measuring tool is provided to measure the dielectric constant of a fluid, the measuring tool having a wall, the wall of the measuring tool being electrically insulating, the tool having:

a pair of capacitor plates mounted adjacent to the wall, a signal generator that can apply an alternating electrical signal to at least one of the capacitor plates and a detector to measure a signal dependent on the electrical capacitance between the capacitor plates.

The arrangement according to the first aspect of the invention, with the measuring tool located around a pipe within which the fluid is located, is inverted in the second aspect, so that the measuring tool is located inside a sensor element that is immersed in the fluid.

Thus, the inventors found that the invented tool can also be used in applications such as production logging, that is, determining the characteristics of the oil and gas fluid being produced by a well, perhaps during the life of the well, or at least for an extended period of time. Such continuous testing of a production well is used in smart wells, in which data regarding the production fluid is continuously or regularly evaluated.

In such applications, it may be preferable to use the invention according to its second aspect, that is, it may be more practical to immerse the measurement tool inside the fluid in the well, instead of trying to pass some or all of the fluid along the pipe measurement tool, which can unnecessarily restrict fluid flow.

Alternative, preferable and desirable aspects of the invention in its second aspect correspond with the alternative, preferable and desirable aspects of the invention in its first aspect.

According to the first aspect of the invention, a method of measuring the dielectric constant of a fluid within a pipe is also provided, the method comprising the steps of:

{i} provide an electrically insulating pipe and introduce the fluid into the pipe, {ii} mount a pair of capacitor plates adjacent to the pipe, {iii} connect a signal generator to at least one of the capacitor plates and apply an electrical signal alternating in said at least one of the capacitor plates, {iv} providing a detector to measure a signal dependent on the electrical capacitance between the capacitor plates and {v} using the signal measured by the detector to determine the fluid dielectric constant.

According to the second aspect of the invention there is provided a method of measuring the fluid dielectric constant, the method comprising the steps of:

{i} provide a measuring tool having an electrically insulating wall and a pair of capacitor plates mounted adjacent to the wall, {ii} connect a signal generator to at least one of the capacitor plates and apply an alternating electrical signal to said at least one of the capacitor plates, {iii} provide a detector to measure a signal dependent on the electrical capacitance between the capacitor plates, {iv} introduce the measurement tool into the fluid and {v} use the signal measured by the detector to determine the fluid dielectric constant.

The steps in the method need not be sequential and their order can be corrected if required and / or some of the steps can be simultaneous.

The measurement tool may also include an apparatus for determining a signal indicative of the electrical resistivity of the fluid. Electrical resistivity can be used to distinguish between filtrate and virgin-forming fluid due to their different salinities and hydrocarbon-water ratios, and can be used to obtain valuable information on its own. For example, if the virgin fluid is found to be water and not oil or gas, the operator can avoid producing it subsequently. Generally speaking, when water is the continuous phase, a resistivity reading can be obtained. When oil or gas is the continuous phase, a dielectric reading can be obtained. The measurements of the dielectric constant and resistivity are thus complementary. Furthermore, as the fluid flows from the formation, its composition may exhibit short-term fluctuations and these can be used as an additional differentiator and indicator of the transition from filtrate to virgin fluid.

Desirably, the measurement tool also includes: a first toroid surrounding a part of the pipe, a second toroid surrounding a part of the pipe, separated from the first toroid, a second signal generator connected to the first toroid to apply an alternating electric current to the coil of the first toroid, a second detector connected to the second toroid to determine the current flowing through the coil of the second toroid and a conductor of the return path connected to the fluid in the pipe on either side of the two toroids.

The conduction fluid in the pipe and the return path conductor together form a closed conduction circuit chained through the two toroids, thereby creating a coupled pair of transformers acting as a secondary resistive curve for the first toroid and a primary curve for the second toroid. The resistance is mainly due to the fluid as it can be arranged so that the return conductor is of relatively low resistance, such as the metal fabricator. For convenience, the metalwork of the tool that necessarily surrounds the toroids can be used as the conductor of the return path, although a connection with direct wiring (perhaps in addition to the metalwork of the tool) may be preferred in some applications.

The current flowing through the first toroid induces an electrical current to flow into the pipe and into the fluid within the pipe. Due to the fact that the pipe is an electrical insulator, the current induced in the pipe is very pe11 (

l smoothly or effectively zero. The current flowing in the fluid is directly dependent on the drive current and the resistivity of the fluid in the pipe.

Any current flowing within the fluid induces a current to flow within the coil of the second toroid, the induced current being directly dependent on the current flowing within the fluid. A comparison of current flows through the first toroid and the second toroid, therefore, will provide a direct measure of the resistivity of the fluid inside the pipe.

Reference is made above to a second signal generator to distinguish it from the first signal generator used in measuring the dielectric constant. Thus, it is recognized that the optimal frequency range of the alternating signal for measuring the dielectric constant will not necessarily be the same as the optimal frequency range for measuring resistivity. In

I certain applications, however, these ranges may overlap, in which case

The first signal generator and the second signal generator can be the same component. Similarly, the term second detector is used to distinguish it from the first detector used in measuring the dielectric constant, since these detectors, in most applications, will be different components.

It will be noted that it is desirable that the pipe containing the fluid (according to the first aspect of the invention) for both the measurement of the dielectric constant and the measurement of resistivity be the same pipe, and it is a benefit of the present invention that both of these measurements can be performed (perhaps continuously) on substantially the same volume of fluid, if desired. Thus, changes in material consistency or fluid constituents that affect both its dielectric constant and its electrical resistivity can be determined by measuring both of these parameters at substantially the same time, while changes in consistency and / or constituents that affecting only one of these parameters will be determined only by measuring that particular parameter. This will provide additional valuable information for operators about two unrelated measurement tools.

Thus, in its first aspect, the invention can provide a method of measuring the dielectric constant and electrical resistivity of a fluid inside a pipe, the method comprising the steps of:

{i} provide an electrically insulating pipe and introduce the fluid into the pipe, {ii} mount a pair of capacitor plates adjacent to the pipe, {iii} connect a first signal generator to at least one of the capacitor plates and apply a signal alternating electrical in said at least one of the capacitor plates, {iv} providing a first detector to measure a signal dependent on the electrical capacitance between the capacitor plates, {v} use the signal measured by the first detector to determine the fluid dielectric constant, {vi} locate a first toroid adjacent to one part of the pipe, {vii} locate a second toroid adjacent to another part of the pipe, {viii} connect a second signal generator to a coil of the first toroid and apply an alternating electric current to the coil of the first toroid, {ix} connect a second detector to a coil of the second toroid to measure the current flowing through the coil of the second toroid, {x} to provide a conductor of the return path connected to the fluid in the pipe on either side of the two toroids, {xi} use the current measured by the second detector to determine the electrical resistivity of the fluid.

In its second aspect, the invention can provide a method for measuring the dielectric constant and electrical resistivity of a fluid, the method comprising the steps of:

{i} provide a measuring tool having an electrically insulating wall and a pair of capacitor plates mounted adjacent to the wall, {ii} connect a signal generator to at least one of the capacitor plates and apply an alternating electrical signal to said at minus one of the capacitor plates, {iii} provide a detector to measure a signal dependent on the electrical capacitance between the capacitor plates, {iv} locate a first toroid adjacent to a part of the wall, {v} locate a second toroid adjacent to another part of the wall, {vi} connect a second signal generator to a coil of the first toroid and apply an alternating electric current to the coil of the first toroid, {vii} connect a second detector to a coil of the second toroid to measure the current flowing through the coil of the second toroid, {viii} providing a conductor of the return path to either side of the two toroids, {ix} introducing the measurement tool into the fluid, {x} use the signal measured by the detector to determine the fluid dielectric constant, {xi} use the current measured by the second detector to determine the electrical resistivity of the fluid.

The steps in the method need not be sequential and their order can be corrected if required and / or some of the steps can be simultaneous.

In preferred methods, the pair of capacitor plates is located between the two toroids and the dielectric constant and electrical resistivity are measured simultaneously or substantially simultaneously. This makes it possible for the two parameters to be measured on the same or substantially the same body of fluid, even if the fluid is flowing.

Õ alternating electrical signal and alternating electrical current could be of sine or square wave form, but this is not necessary for the performance of the invention, and any suitable alternating wave form can be used ·.

In the modalities according to the first aspect in which the same pipe is used for the measurement of both parameters, it must satisfy the separate requirements for each parameter, as indicated above. A ceramic pipe made of silicon nitride (Si₃N₄) has been found to have a dielectric constant and resistivity that match the requirements of the measurement tool, and a suitable material can be obtained from Ceradyne Inc., 3169 Red Hill Avenue, Costa Mesa, California 92626, USA, and sold under the trade name CERALLOY 147-31N. In addition, a pipe of this material having an internal cross-sectional diameter of approximately 6.4 mm (1/4 inches) and a wall thickness of 3.2 mm (1/8 inches) can withstand internal pressures greater than 1 , 7 x 10⁸ Pa (25,000 psi). Since these are the pressures typically found at borehole depths of approximately 10 km, it is possible to surround the pipe with air instead of requiring some incompressible material that could adversely affect the measurement of the die constant or resistivity, or make the more difficult and less reliable construction.

The measurement tool has additional benefits over the multi-flow forming test tools as described in US patent application 11 / 626,461 filed January 24, 2007. In this formation test tool, two (or more) flows of formation fluid are kept separate and are tested separately, and a measurement tool of the present invention could be arranged on each flow line and direct comparisons between the two fluids could be done as desired. In particular, a first flow of fluid can be the primary flow for measurement and sampling purposes and a second flow of fluid can be arranged to come from a different (but ideally adjacent) part of the formation to that of the first flow. For different fluid flows that leave formation at the same time, it is generally desirable to minimize any difference in the time in which the test is undertaken and ideally different fluid flows should be tested at exactly the same time so that the differences measured over time in the first and second fluid streams can be used as an indicator of the first fluid changing to virgin fluid (for example). It is possible to minimize (or eliminate) any differences in testing time using a multi-flow test tool such as that of US patent application 11 / 626.461 by arranging the pipes for different fluid flows situated side by side, and being of substantially identical lengths.

BRIEF DESCRIPTION OF THE PREFERRED EMBODIMENTS

The invention will now be described in more detail, by way of examples, with reference to the accompanying drawings, which show:

figure 1 is a longitudinal cross-section through the pipe of a measuring tool according to one embodiment of the first aspect of the invention, figure 2 is a schematic cross-section of the capacitance of the fluid and pipe when measured by the tool in figure 1, a figure 3 a representation like figure 2 showing the effect of a metallic focus plate, figure 4 is a cross section through a measurement tool according to the second aspect of the invention, figure 5 is a schematic cross-sectional representation of the fluid and pipe capacitance when measured in an alternative embodiment of the first aspect of the invention and figure 6 is a schematic representation like figure 5 showing the effect of a focusing plate.

DETAILED DESCRIPTION

According to the first aspect of the invention, the measuring tool 10 has a pipe 12. The pipe 12 is made of electrically insulating material. The pipe 12 is also substantially linear and has a substantially uniform cross section along its length, so that the pipe does not induce undesired pressure changes in a fluid flowing along it. The pipe ends are not shown, but in a known manner the ends are fitted with connectors through which the pipe can be connected with sealing in adjacent pipes or couplings. When used on a forming test tool, for example, pipe 12 can be connected to adjacent pipes within the body of the forming test tool, the adjacent pipes perhaps being parts of other measuring tools to measure other fluid parameters.

In this modality, the pipe has a circular cross section, with an external diameter of approximately 12.7 mm (approximately ¹/ 2 inch) and an internal diameter of approximately 6.4 mm (approximately Va inch).

Tool 10 also has three capacitor plates 14, 16, 18, the capacitor plates in this embodiment comprising conductive gloves surrounding respective parts of the barrel 12. In this embodiment, the plates of capacitor 14, 16 and 18 are of identical dimensions, but this it is not necessarily this way.

A signal generator 20 is connected to the central capacitor plate 16 by a signal conductor 22, whereby the signal generator 20 applies an alternating electrical signal to the capacitor plate 16. The capacitor plates 14 and 18 are connected to the ground, and the voltage that forms on the capacitor plate 16 and the current flowing over and out of the capacitor plate 16 during each cycle are directly dependent on the capacitance of the system.

A detector 24 is capable of measuring the voltage across the conductor of signal 22 (relative to ground) and also the current flowing along the conductor of signal 22 and can use these signals to determine the electrical capacitance of the system. The detector may incorporate a phase-sensitive detector to enhance the signal-to-noise ratio.

The capacitance of the system, namely, the capacitance between the capacitor plate 16 and the capacitor plates 14 and 18 is dependent on the dielectric constant of the material between them. In an arrangement like the one shown in figure 1, with the capacitor plates placed along the pipe, the electric field is generated between the confronting ends of the capacitor plates 16 and 14 and also between the confronting ends of the capacitor plates 16 and 18. Part of the electric field is located inside the wall of the pipe 12, part inside the fluid 26 inside the pipe 12 and part inside the material that surrounds the pipe and thus the capacitance of the system depends on the dielectric constant of the pipe, the fluid and the material that surrounds the pipe.

In this embodiment, the pipe 12 is made of silicon nitride which has a dielectric constant of approximately eight. Also, the pipe 12 is surrounded by air which has a dielectric constant of one. In this way, the capacitance of the system is highly dependent on the fluid dielectric constant 26 and changes in the fluid dielectric constant 26 caused by changes in the consistency or constituents of fluid 26 will cause a change in the system capacitance.

Tool 10 can be calibrated (by calculation or more typically with fluids 26 known at known temperatures), so that measurement tool 10 can determine the actual dielectric constant of fluid 26. This will allow measurement tool 26 to be used quantitatively , which will allow the operator to make detailed assessments of the fluid, including, for example, its chemical constituents. Alternatively, the tool can be used qualitatively to determine changes in material characteristics (for example, to identify the change from contaminated formation fluid to virgin formation fluid) whose determinations can be used by other measurement tools.

Capacitor plates 14, 16 and 18 are all surrounded by an electrically conductive sleeve 30, beneficially made of metal. The sleeve 30 is arranged close to the capacitor plates 14, 16, 18 and is referred to here as a focusing plate as long as its action is to focus or concentrate the electric field within the fluid 26 (see the detailed description below of figures 2 and 3 ). The focusing plate 30 also provides a shielding function preventing foreign electrical signals and the dielectric constant of the material outside the plate from affecting the load on the capacitor plates 14, 16, 18.

In order to allow the capacitance between the focusing plate 30 and the capacitor plate 16 to be ignored, the voltage of the focusing plate 30 is matched with that of the capacitor plate 16. This is accomplished by connecting the focusing plate 30 to the signal generator 20 by means of a shield connector 18 and an operational amplifier 34 configured as a voltage follower.

It will be understood that an operational amplifier 34 in the voltage follower mode provides the same voltage at its output as that at its input and since in this mode its input is connected to the signal generator 20, the voltage at the output and, therefore, the voltage on the shield connector 32 and the focusing plate 30, it equals that of the signal generator 20. At all times, therefore, the voltage on the focusing plate 30 equals that of the capacitor plate 16.

Also, at all times, the voltage of the shield connector 32 equals that of the signal conductor 22, making it possible for the signal conductor 22 and the shield connector 32 to be respective parts of a coaxial or shielded cable 36 for at least part of the its length, with the shield connector 32 forming the protection surrounding the signal conductor of the coaxial cable 36 in known manner. Again, because of their equalized voltages, the capacitance between the signal conductor 22 and the shield connector 32 can be ignored.

The frequency applied by the signal generator 20 can be adjusted as required and can be varied while using the measurement tool

10, if desired. The optimal frequency will depend on the application and may depend, for example, on the range of expected dielectric constants for fluid 26, and the other variable parameters such as fluid temperature 26. A suitable frequency for use in a practical training test tool has been verified to be 16 kHz.

This measuring tool 10 is not only capable of measuring the dielectric constant, but also the resistivity. Most importantly, the measuring tool 10 uses only one pipe 12 for the two measurements, so that the measurements can be substantially performed simultaneously on the same volume of fluid 26.

To perform a resistivity measurement on the fluid, the measuring tool 10 has a first toroid 40 surrounding a part of the barrel 12 and a second toroid 42 surrounding another part of the ca19 no 12, the toroids 40, 42 being separated along the barrel length. Toroids are conventionally formed, comprising an iron circuit (or other ferromagnetic material) surrounded by an electrical coil (not shown).

A second signal generator 44 is connected to the electrical coil 38 of the first toroid 40 and applies an alternating electric current to the electrical coil 38 (only part of the coil 38 is shown in figure 1). The passage of an electric current through the coil induces a magnetic field in the first toroid, which in turn induces an electric current to flow in any conductor located inside the first toroid. The pipe 12 is located inside the first toroid 40 and since the pipe 12 is an insulator, a current will be induced to flow into the fluid 26. Tool 10 includes a conductive return path comprising a pair of electrodes 46 and 48 connected by a conductor 50. The electrodes 46 and 48 are located inside the barrel 12, so that they directly contact the fluid 26. Preferably, electrodes 46, 48 are embedded in the wall of the barrel 12, so that they do not induce turbulence or any pressure changes in the fluid 26 when it flows past them.

It will be understood that the position of the toroids in relation to the rest of the tool does not matter and they can even be placed on either side of the focusing plate 30. The metal housing of the cell or tool can, in some modalities, provide part or all of the path return and this would avoid the requirement for a separate conductor 50 and reduce the complexity of the tool.

Desirably, the capacitor plates 14, 16, 18 and the focusing plate 30 are made of non-strongly magnetic materials so as not to increase the leakage flow of the toroids.

Any current flowing through fluid 26 between electrodes 48 and 46 will induce a current to flow around coil 54 of the second toroid 42 (only part of coil 54 is shown in figure 1). This current is detected by a second detector 52, the current flowing through the coil around the second toroid being directly related to the current flowing within the fluid and, therefore, directly related to the fluid resistivity 26. The detector may incorporate a phase-sensitive detector to enhance the signal-to-noise ratio.

The measurement tool 10 can be calibrated (again by calculating or experimenting with fluids of known resistivities) so that it can be used quantitatively or it can be used qualitatively to determine changes in fluid resistivity 26.

Figures 2 and 3 show representations of the tool to demonstrate the advantage of a metallic focuser plate such as 30. Specifically, the action of the focuser plate and the function of the pipe dielectric constant can be understood by reference to the simplified model of capacitance distribution in the cell as shown in figure 2. It will be understood that these capacitances, in reality, represent the distribution of electrical potential within the cell as can be calculated from the electromagnetic theory by someone versed in the technique. It will also be understood that the present invention is not dependent on the capacitance model.

A pipe 100 surrounds the fluid 101. The annular capacitance plate 102 is connected to the signal generator M at 108 and the annular capacitance plate 103 is connected to ground (the capacitance plates 102,103, therefore copying the capacitance plates 16, 14 or 16, 18 of figure 1). The capacitance of the fluid to be measured is that represented by the imaginary capacitor 104. This fluid capacitance is in parallel with the axial capacitance 106 of the pipe wall. There is also capacitance in radial series 105 due to the pipe wall and parasitic capacitance 107 outside the pipe between the electrodes. All capacitances other than 104 will affect the sensitivity and interpretation of the measurement;

In order to maximize the sensitivity to capacitance 104, it is desirable to maximize the capacitance in series 105, which can be obtained by maximizing the dielectric constant of the pipe material. On the other hand, this will increase the capacitance in parallel 106, which is undesirable.

Figure 3 demonstrates the effect of adding an annular focusing plate 110, the focusing plate 110 being kept at the same potential as the capacitor plate 102, preferably by a voltage follower as described in relation to the focusing plate 30 of figure 1. With the focusing plate 110 present, the axial capacitance 106 is replaced by a radial capacitance 106 'and the stray capacitance 107 is eliminated. The measurement is now only of the desired capacitance 104 in series with the radial capacitance 105. With a pipe material with a high dielectric constant, the measurement will be very sensitive to changes in the fluid dielectric constant.

Furthermore, it will be understood that the described focusing action requires only that the focusing plate 110 cover the dielectric material in the axial space between the capacitor plates 102 and 103. Similarly for the arrangement of figure 1, so that if the shielding function of plate 30 is not required, the focusing plate could be reduced to fill the axial space between plates 14 and 16 and the axial space between plates 16 and 18 , which would maximize the sensitivity to the fluid's capacitance as desired.

Figure 4 demonstrates the invention according to its second aspect, being verified that the dielectric measurement (and the resistivity) can be made outside the wall 112 of the measuring tool 110 when the capacitor plates (and preferably also the (s) focusing plate (s) are inside the wall 112 and the fluid 126 to be tested is outside the wall. Such a configuration has wide applicability in measuring the properties of the fluid in boreholes such as during production in the production recording tools and in the permanent arrangement as in an intelligent well.

The capacitor plate 116 of the embodiment of figure 4 performs the same function as the capacitor plate 16 in the embodiment of figure 1 and similarly for the capacitor plates 114 and 14, and also for the other components 130, 140, 142, 146 and 148 that perform the same functions as components 30, 40, 42, 46 and 48, respectively. Because of the similarity of many of the components of the Figure 4 modality to the components of the Figure 1 modality, it is believed that a knowledgeable person does not need a detailed description of Figure 4.

Although figure 4 shows only two capacitor plates 114 and 116, it will be understood that another modality could use three capacitors along the sensor element in an arrangement similar to the one in figure 1, with the signal generator (M in figure 4) being connected to the central capacitor and the other two capacitors being connected to the ground. Although figure 4 does not show the details of the M signal generator and related components, it will be understood that components identical or similar to the signal generator 20, signal conductor 22, detector 24, shield connector 32, operational amplifier 34 and perhaps also the coaxial cable 36 of the embodiment of figure 1 could be provided inside the measuring tool 110.

Figure 4 also shows the imaginary capacitance 104 of the fluid 126 that is desired to be measured, and also the imaginary series capacitance 105 using the same reference numerals as figures 2 and 3.

In the embodiment of figure 4, the wall 112 is tubular and the measuring tool 110 can be surrounded by the fluid 126. In alternative embodiments, the measuring tool is adapted to be located along the body of the fluid, for example, being mounted on the wall of a conduit for the fluid.

Figures 5 and 6 represent a measuring tool in which the capacitance plates 202, 203 are arranged through the pipe 212. Figure 5 corresponds with figure 2 and again is a generalized approximation of the actual distributed field structure in the cell. The capacitance between capacitor plates 202 and 203 is a measurement in series comprising the capacitance through the wall material 205 and the fluid capacitance 204. This capacitance is offset by the capacitance around the wall material 106 and external parasitic capacitance 107.

Figure 6 corresponds to figure 3 and shows the effect of a focusing plate 230. The focusing plate 230 is activated by the signal generator M to stay in the same potential as the plate of capacitor 202. This eliminates the effect of the external capacitance and by changing of the internal field greatly reduces the deviation capacitance 206 to a capacitance 206 'between · the focus plate 230 and the capacitor plate grounded 203. This results in a measurement closer to the simpler series structure of capacitances 205 and 204.

Figures 5 and 6 represent cross-sectional views through the measurement tool. The longitudinal length of the driven capacitor plate 202, (that is, the length in the direction along the longitudinal geometric axis of the tool) is chosen to suit the application. The longitudinal dimension of the focusing plate 230 is preferably greater than the longitudinal dimension of the driven capacitor plate 202.

Figure 6 shows a plate 230 that provides both focusing and shielding functions as in the modalities of figures 1, 3 and 4. The region 230a of plate 230 which is located between capacitor plates 202 and 203 provides the focusing action, while that the region 230b of the plate 230 that overlaps the driven capacitor plate 202 provides the shielding function. In addition, plate 230 extends beyond the edges of the driven capacitor plate 202 in the longitudinal direction.

It has been found to be beneficial that the grounded capacitor plate 203 extends longitudinally beyond the focusing plate 230 and the driven capacitor plate 202, and in particular that the grounded capacitor plate · 203 completely surrounds the measurement tool beyond the ends of the focusing plate 230. Thus, in the orientation of figure 6, the grounded capacitor plate 203 beneficially extends in and out of the paper beyond the driven capacitor plate 202 and the focusing plate 23.0 and surrounds the pipe 212 both above and below the focusing plate 230.

It will also be seen that the focusing plate 230 is scaled around the driven capacitor plate 202 so that its region 230a is closer to the pipe 212 between the capacitor plates 202 and 203. This has been found to improve the focusing action.

In a practical embodiment, the capacitor plates 202, 203 and the focus plate 230 are provided by a strip of flexible double-sided printed circuit board material, with the capacitor plate activated; 202, region 230a of focus plate 230 and capacitor plate grounded

203 being formed on one side of it (with the focus plate region 230a surrounding the driven capacitor plate 202 and the grounded capacitor plate 203 surrounding the focus plate region 230a). The shield region 230b of focuser plate 230 is formed on the other side of the printed circuit board and is connected to region 230a of focuser plate 230 via pathways through the plate. The flexible printed circuit board can be wound around the measuring tool with the capacitor plate activated 202, the region 230a of the focusing plate 230 and the capacitor plate grounded 203 preferably in contact with the pipe. The focus plate region 230b surrounds the driven capacitor plate 202 and is separated from the driven capacitor plate 202 by the substrate material of the printed circuit board.

Extending the grounded capacitor plate 203 beyond the longitudinal ends of the focusing plate 230 and passing the grounded capacitor plate 203 circumferentially around the pipe 212 provides a defined environment for the driven capacitor plate 202, within which the fluid capacitance is measured . This also helps to reduce or avoid any field distortion that could occur if the fluid being measured was conductive and was in contact with electrically conductive parts of the measurement tool housing.

It will be understood that the measuring tool represented by figures 5 and 6 uses capacitor plates 202, 203 mounted in radially spaced positions around the pipe 212 into which the fluid is introduced, so that this modality is in accordance with the first aspect of the invention. In another embodiment, a structure similar to the one in figure 4 could be provided, but with the capacitor plates mounted through the measurement tool for use according to the second aspect. Measuring tools on which the capacitor plates are mounted through the tool have been found to be more suitable in certain applications since they have a greater response variation to different fluids in the range of interest, that is, fluids with dielectric constants in the range of approximately two to approximately ten that are typical of vertical hole fluids in oil drilling applications.

Also, although figures 5 and 6 do not show toroids or other components for measuring the electrical resistivity of the fluid, it will be understood that such components could be provided. Alternatively, the radial arrangement of the two capacitors 202, 203 of figures 5 and 6 could replace the longitudinal arrangement of the three capacitors 14, 16 and 18 in figure 1, without altering the components of the electrical resistivity measurement. Furthermore, the signal generator 20, detector 24 and related components of the embodiment of figure 1 could be used with modalities in which the capacitor plates are arranged through the measurement tool.

It will also be understood that the invention will most often be used with fluid flowing along the pipe (or around the tool as applicable), but that measurements of the dielectric constant and electrical resistivity could also be taken in a stationary fluid if desired.