GODAGER, Øivind (Asnesasen 17, Sandefjor, N-3222, NO)
COPSEY, Timothy, Graham (Kilburn & Strode LLP, 20 Red Lion Street, London WC1R 4PJ, GB)
| Claims A transducer assembly, comprising: four or more crystal controlled oscillators ( 19, 20, 21 , 22), four or more thickness shear mode crystal quartz resonators (2, 3, 4, 5), wherein each oscillator is controlled by the associated resonator, a first and second quartz resonator are a pressure (2) and a reference (3) resonator, configured together as a pressure sensor providing a frequency output (8), a third crystal resonator (4) is a temperature resonator, configured as a temperature sensor providing frequency output (9), and a fourth crystal resonator (5) is a temperature sensor. Apparatus as claimed in claim 1 , in which the resonators (2, 3) are individually mounted or are mounted together in a holder (6). Apparatus as claimed in claim 2, in which the holder (6) has an inert hydraulic fluid fill which houses the pressure resonator (2) and is exposed to applied pressure through process isolating bellows ( 15). Apparatus as claimed in any preceding claim, in which the two resonators (2, 3) are mounted in the same holder (6) for the improvement of the thermal response characteristics of the transducer assembly. Apparatus as claimed in any preceding claim, in which the temperature resonator (4) and the reference resonator (3) can be individual units or mounted in the same housing or holder (6). Apparatus as claimed in claim 5, in which the two resonators (3,4) are mounted in the same holder (6) for the improvement of the thermal response characteristics of the transducer assembly. Apparatus as claimed in any preceding claim, in which the fourth resonator (5) is a second temperature sensor and is part of the same holder (6) as resonators (3, 4), or is part of a different holder (7). Apparatus as claimed in claim 7, in which the two resonator temperature sensors (4, 5) have the same temperature to frequency characteristics. Apparatus as claimed in claim7 or claim 8, in which an output (29) of resonator temperature sensor (5) is mixed with an output (28) of resonator temperature sensor (4) deriving a dynamic thermal device with output (10). Apparatus as claimed in any one of claims 7 to 9, in which the resonator temperature sensors (4, 5) are individual units and mounted in different holders (6, 7) or are mounted in a common or same holder (6) providing characteristic thermal time constants (1 1 , 12) respectively. Apparatus as claimed in claim 10, in which the said thermal time constants ( 1 1 , 12) are di fferent. 12. Apparatus as claimed in any one of claims 7 to 1 1 , in which the mixing or other type signal processing combining the two independent resonator temperature sensors (4, 5) produces an output signal ( 10), having response that is dynamic and related to the temperature difference between them. 13. Apparatus as claimed in claim 12, in which said response is characterized by the temperature change, the thermal time constants (1 1 , 12), and the physical properties of the resonator temperature sensors (4, 5). 14. Apparatus as claimed in claim 12 or claim 13, in which said responses is related to the physical properties of the transducer housing ( 1 ), the environment, as well as the physical properties of the latter. 15. Apparatus as claimed in any one of claims 12 to 14, in which the said difference in temperature is used together with the temperature sensor output (9) and inputs to dynamic feed-forward correction systems ( 13, 14). 16. Apparatus as claimed in claim 15, in which said correction system ( 13) is used to provide dynamic correction of the transducer pressure determination 17. Apparatus as claimed in claim 15 or claim 16, in which the said correction system ( 14) is used to provide dynamic correction of the transducer temperature determination 18. Apparatus as claimed in any one of claims 15 to 17, in which said feed-forward correction (13) will improve the thermal response of the transducer pressure determination as the dynamics of output signal ( 10) is a true and real measure of the transducer thermal stability and can be effectively used to predict when and how much correction action is needed to eliminate gross pressure offsets during gradients Apparatus as claimed in any one of claims 1 5 to 17, in which said feed-forward correction ( 14) will improve the thermal response of the transducer temperature determination as dynamics of output signal (10) is a true and real measure of the transducer thermal stability and be effectively used to predict when and how much correction action is needed to eliminate gross temperature offsets during gradients Apparatus as claimed in any one of claims 15 to 19, in which the feed-forward correction ( 13, 14) applies a method derived to suppress the offsets induced by implementing a thermal diffusion model inverting the thermal response of the respective transducer sensor, and in which the diffusion model, which is a function of the temperature level and the gradient, improves the phase response of the measurement and speeds up the transducer performance to monitor the correct pressure and temperature. Apparatus as claimed in claim 1 , in which the first and second quartz unit are a pressure (2) and a reference (3) resonator, configured together as a pressure sensor providing a frequency output (8), and the third and fourth crystal resonator are respectively a temperature (4) and a reference resonator (5), configured as a temperature sensor providing frequency output (9). 22. Apparatus as claimed in claim 21 , in which the pressure (2) and reference (3) resonators are individually or mounted in the same holder (6). 23. Apparatus as claimed in claim 22, in which the holder (6) has an inert hydraulic fluid filling the housing around the pressure resonator (2), and the resonator is exposed to applied pressure through process isolating bellows ( 15). 24. Apparatus as claimed in any one of claims 21 to 23, in which the two resonators (2, 3) are mounted in the same holder (6) for the improvement of the thermal response characteristics of the transducer assembly. 25. Apparatus as claimed in any one of claims 21 to 24, in which the temperature (4) and reference (5) resonators can be individual units or mounted in the same holder (7). 26. Apparatus as claimed in claim 25, in which said resonators (4, 5) are a temperature sensor and part of the same holder (6) as resonators (2, 3). 27. Apparatus as claimed in claim 25, in which the two resonators (4, 5) are mounted in holder (6, 7), both for the improvement of the thermal response characteristics of the transducer assembly. 28. Apparatus as claimed in any one of claims 25 to 27, in which the two reference resonators (3, 5) have the same temperature to frequency characteristics. 29. Apparatus as claimed in claim 28, in which an output (27) of the resonator reference (3) is mixed with an output (29) of resonator reference (5) deriving a dynamic thermal device with output ( 10). Apparatus as claimed in any one of claims 21 to 29, in which each of the resonator references (3, 5) is an individual unit and mounted in different holders (6, 7) respectively, and providing their own characteristic thermal time constant ( 1 1 , 12). Apparatus as claimed in any one of claims 21 to 29, in which each of the resonator references (3, 5) is an individual unit and mounted in the same holder, providing their own characteristic thermal time constant ( 1 1, 12). Apparatus as claimed in claim 30 or claim 3 1 , in which the said thermal time constants ( 1 1 , 12) are different. Apparatus as claimed in any of claims 21 to 32, in which the combination of the two independent reference resonators (3, 5) produces a output signal (10) having a response that is dynamic and related to the temperature difference between them. Apparatus as claimed in claim 33, in which the said response is characterized by the temperature change, the thermal time constants ( 1 1 , 12), and the physical properties of the resonator references (3, 5). 35. Apparatus as claimed in claim 33 or claim 34, in which said response is also related to the physical properties of the transducer housing ( 1 ), the environment and the physical properties of the latter. 36. Apparatus as claimed in any one of claims 33 to 35, in which the said difference in temperature is used together with the temperature sensor output (9) and inputs to dynamic feed-forward correction systems ( 13, 14). 37. Apparatus as claimed in claim 36, in which said correction system ( 13) is used to provide dynamic correction of the transducer pressure determination. 38. Apparatus as claimed in claim 36 or claim 37, in which said correction system ( 14) is used to provide dynamic correction of the transducer temperature determination. 39. Apparatus as claimed in any one of claims 36 to 38, in which said feed-forward correction ( 13) will improve the thermal response of the transducer pressure determination as the dynamics of signal ( 1 0) is a true and real measure of the transducer thermal stability and be effectively used to predict when and how much corrective action to be added in order to avoid gross pressure offsets during gradients. 40. Apparatus as claimed in any one of claims 36 to 39, in which said feed- forward correction ( 14) will improve the thermal response of the transducer temperature determination as the dynamics of signal ( 10) is a true and real measure of the transducer thermal stability and be effectively used to predict when and how much corrective action to be added in order to avoid gross temperature offsets during gradients. Apparatus as claimed in any one of claims 36 to 40, in which the feed-forward correction ( 13, 14) is a method derived to suppress the offsets induced by implementing a thermal diffusion model inverting the thermal response of the respective transducer, and in which the diffusion model, which is a function of the temperature level and the gradient, is added to improve the phase response of the measurement and speed up the transducer performance to monitor correct pressure and temperature |
Assembly with Dynamic Correction
Background of the invention
The invention relates in general to a pressure measuring device and more particularly to a quartz crystal pressure and temperature transducer assembly having improved error correction when subjected to pressure and temperature gradients.
In nearly all phases of oil and gas exploration and production, it is essential to have accurate knowledge of both pressure and temperature at a given or specific location in a reservoir or borehole. For example, during a production phase, reservoir management engineers currently take advantage of monitored pressure and temperature in a well and use it for their indicative and model relationship to map the reservoir and understand its complexity in order to optimize performance as well as their assets. Instruments used for this kind of surveying or permanently monitoring application, generally include a high accuracy pressure sensor device.
In prior art systems, quartz pressure and/or temperature transducers consist of precision quartz resonators and are known to be very accurate for pressure and temperature determinations. However, their make and method of thermally compensating is based on stable and static wellbore conditions where the temperature is uniform throughout the transducer. For example, US523 1880 discloses a pressure transducer assembly suitable for downhole use and it is based on crystal quartz resonators and associated electronics to drive and process the signals. US5471 882 is an improvement on the pressure transducer level as the inherent quartz pressure and temperature resonators have been given a matched thermal response to temperature changes. However, the aforementioned transducers only provide static temperature compensation and are good representation of prior art quartz pressure transducers used for borehole applications. US5231880 and US5471882 provide no form of dynamic temperature compensation of their pressure and temperature determination as they provide no means of management for the heat-balance within the transducers. This limits their effectiveness as they do not predict the correct pressure and temperature of the environment to which they are exposed if the conditions are unstable and subject to change, and they can therefore produce gross offset in the pressure and temperature determination.
Typically, an oilwell will have a relatively warm fluid production from reservoir to surface. As the production flow rises to the surface, energy will be lost by means of heat transfer in the well. Moreover, since the production media in the tubing is the warmer medium, a radial heat flow will appear through the wellbore conduits and out to the surrounding formation. In turn, the colder the formation gets the more heat is lost. In a permanent pressure monitor application, the placement of the quartz pressure transducer is typically somewhere at the outer boundaries of the wellbore conduit. As heat is lost to the surroundings, the loss creates cylindrical isothermal temperature surfaces as heat progress outwards through the wellbore conduits to the formation. In turn, this makes the location of the transducer significant and dependent on a temperature gradient, and the ongoing monitoring application would require the involvement of dynamic compensation techniques in order to provide accurate and reliable pressure and temperature determinations.
Generally, the thermal heat balance of a Quartz Pressure Transducer in a borehole or oil- gas well will be affected by one or more of the following parameters: flow rate changes; fluid or gas composition changes within the production or injection tubing; fluid or gas composition changes in the annular volumes of the wellbore; direct pressure changes in the reservoir or induced at the surface; or any combination of the above. Furthermore, pressure changes in the well will cause temperature change within the transducer due to adiabatic effects within the transducer oil-fill as well as the quartz resonator pressure sensor itself. Moreover, the main concern is the fidelity or faithfulness of the transducer response as in use it exhibits a continuous rate of change in temperature induced by the well production and load as well as the physical properties of the environment. In real well pressure/temperature monitoring applications, the prior art quartz transducers such as given in US523 1 880, US5471882, US4802370, US3561832 and US3355949 provide static temperature compensation only, and they do not compensate for all the variations which results from the implications considered above. To be more effective, the application requires a Quartz Pressure and Temperature Transducer to be dynamic and be adaptable to the changes.
To provide accurate measurements using crystal quartz sensor technology in temperature gradient environments, some knowledge and measurement of the thermal stability of the system and the quartz transducer is required. Thermal response belongs, fundamentally, in the realm of transient heat transfer. The rate of response of the quartz resonator pressure and temperature sensors clearly depends on the physical properties of the transducer embodiment, the physical properties of its environment as well as the dynamical properties of its environment. Amplifying on this, and the fact that physical properties normally change with temperature, it follows that the response time of the transducer will vary with the temperature level. Therefore, this invention confines attention to make certain necessary modifications to the traditional transducer design as well as the concept of how to temperature compensate its outputs. This is achieved by implementing a dynamic feed-forward compensation technique that is directly driven by the temperature level and the rate of change in temperature that the transducer exhibits.
To manage this task a mathematical thermal model describing the temperature behaviour of the transducer quartz pressure and temperature resonators is derived. The model is based on a theorem of heat and energy-balance which defines that heat will not be lost but can be moved, accumulated and/or energy transfer only and is used for dynamic compensation means. Further, the transducer is provided with sensors to measure the temperature level as well as the temperature gradient. In turn, the temperature level and rate sensor outputs are inputs to the thermal models and provide means of dynamic feed-forward correction to the output of the quartz resonator temperature and pressure sensors. Furthermore, due to the feed-forward technique, it makes the inherent transducer embodiment to become a fast and accurate temperature compensated pressure and temperature transducer and not only a temperature compensated pressure transducer as in the prior art systems.
It is therefore an object of the present invention to predict how much corrective action a change in temperature will require to correct output data. This has been greatly improved by the thermal management and signal processing of the transducer embodiments of this invention. The Quartz Pressure and Temperature Transducer Assemblies have a split thermal configuration that includes two individual quartz resonator temperature sensors. This is a unique feature in that a mixing of the two temperature sensors is a direct measure of the temperature gradient or heat balance of the transducer sensors. In turn, the output is dynamic and controls how much and when corrective action is required by the feed-forward correction system in order to minimize the offsets of the transducer pressure and temperature determinations.
Summary of the invention
The present invention relates in general to a pressure and temperature measuring device and in more particularly a Quartz Pressure and Temperature Transducer Assembly with Dynamic Correction intended for use in nonstatic environments. To measure pressure and temperature the transducer provides a crystal quartz sensor set consisting of one pressure, two temperature, and one reference resonator. All four crystals vibrate in the thickness sheer mode and have their own oscillator that provides a frequency output. The quartz resonator pressure sensor is sensing the pressure of the media to which the transducer is exposed and the output is both pressure and temperature sensitive.
The two quartz resonator temperature sensors are temperature sensitive only and have the same temperature vs. frequency characteristics. The function of the first quartz resonator temperature sensor is two-fold. The first function is to measure the temperature to which the transducer is exposed, and the second is to compensate or correct the static temperature level effects of the quartz resonator pressure sensor. The function of the second quartz resonator temperature sensor is to provide means of dynamic correction of the transducer pressure and temperature determination. More particularly, the output of the second temperature resonator is mixed with the first, providing a means of "differential temperature" measurement. The product of the two is a dynamic measure, directly representing the transducer response to temperature, and utilizes the usage and the fact that the second resonator temperature sensor is configured to have a faster response to temperature change than the first. Amplifying on this, it follows that the differential temperature measurement derived is a footprint of the sensor response as it possesses a dynamic output that varies with the mass velocity of its environment. By dynamic means, this is an ideal input to use in a feed-forward correction system to provide a fast and accurate pressure and temperature measurements under nonstatic conditions.
Finally, the quartz resonator reference is used to process the signals of the pressure and temperature resonators and is typically made in a "SC" type cut, which possess very little temperature sensitivity. The "SC" (Sensitivity Cut) is a doubly rotated crystal quartz cut which results in the property that the resonator frequency varies little with wide variations in temperature. The quartz resonator reference is the "timebase" of the transducer and is used internally as time- and signal reference to mix and to process the frequency signals from the pressure and temperature sensor oscillators.
More particularly, the present invention provides a thermal management consisting of two temperature sensors. Each temperature resonator is mounted to its own isothermal block, one having slightly more mass than the other. As one temperature resonator is given more mass than the other the sensors will apparently have different time constants. By mixing the frequency outputs of the two quartz temperature crystal resonators, the mixer will produce a frequency signal that is proportional to the temperature difference between the two sensors and the transducer environment. Amplifying on this, the mixer outputs "bring forward" a dynamic measurement representing the thermal gradient or stability of the Quartz Pressure and Temperature Transducer Assembly. This is the case whether the gradient is induced directly by temperature change of the environment, or caused by adiabatic effect within the transducer, due to pressure change. Thus, the dual time-constant configuration is unique as it exactly monitors the temperature response behaviour of the transducer embodiment. Together with the temperature level, the two thermal measurements enhance the fidelity to correct the gradient disturbance to the pressure and temperature determination of the transducer.
According to the present invention, there is provided a transducer assembly, comprising: four or more crystal controlled oscillators, four or more thickness shear mode crystal quartz resonators, wherein each oscillator is controlled by the associated resonator, a first and second quartz resonator are a pressure and a reference resonator, configured together as a pressure sensor providing a frequency output, a third crystal resonator is a temperature resonator, configured as a temperature sensor providing frequency output, and a fourth crystal resonator is a temperature sensor. Preferred and optional features of the invention will be clear from the accompanying claims and from the detailed description of two illustrative embodiments which follow.
Brief description of the drawings
The above description and other features of the present invention will be more fully understood from the reading of the ensuing description of the preferred embodiments given with reference to the appended drawings. Figures la, 2a, 3a, ... etc refer to a first embodiment of the present invention and figures 1 b, 2b, 3b, . . . etc refer to a second embodiment. Figures l a and l b are schematics showing the outline of the Pressure and Temperature Transducer Assembly with its main components;
Figures 2a and 2b are another set of schematics representation of the transducer showing its configuration and signal flow; Figures 3a and 3b are supplementary schematics to Figure 2a and 2b which, in block diagram form only, show the transducer configuration and signal routing;
Figures 4a and 4b are schematics showing the primary signal routing and preprocessing of the raw resonator sensor signals;
Figures 5a and 5b are schematics showing the full processing of the pressure determination of the transducer including the dynamic and static temperature corrections;
Figures 6a and 6b are schematics showing the full processing chart for the transducer temperature determination and include the dynamic and static temperature corrections; Figures 7a and 7b are schematics of a production and an injection well respectively showing the heat and heat-flow distribution due to the process system and earth heat distribution;
Figures 8a and 8b are schematics showing the typical radial heat flow and temperature distribution from a producing oil/gas well to the formation of an application of the invention providing an annular mounted Pressure and Temperature Transducer Assembly;
Figures 9a and 9b is same as Figures 8a and 8b but for a tubular mounted Pressure and Temperature Transducer Assembly; and
Figures 10, 1 1 , and 12 are schematics showing magnified and more detailed picture of the 1 and 2- dimensional radial heatflow or heat exchange between a warm production fluid and a colder formation. Heat transfer creates isothermal surfaces throughout the wellbore conduits. These schematics are illustrating the heat distribution as well as the temperature gradient a permanent Pressure and Temperature Transducer Assembly as of this invention will see in the actual mounting location.
Detailed description of the embodiments of the transducer according to the invention
Two embodiments of the present invention will be described in context of pressure and temperature being the primary parameters to be measured and to which the transducer 1 is responsive. Figures are included to show the configuration of the two embodiments of transducer 1.
Figure l a shows a first embodiment of the present invention. Section 6 is a thermal block housing the main pressure and temperature measuring portion of the transducer 1 , while section 7 is the secondary thermal block housing the gradient temperature sensor 5.
Crystals 3 and 4 are shown as being enclosed in the same environment and protected from pressure by being enclosed in an atmosphere where the pressure remains constant at all time. They are, however, subject to the effects of temperature and temperature change. The temperature change is function of one or more of the temperature level, the physical properties of the thermal block 6 and the crystals 2, 3, and 4 as configured, and characterized by thermal time constant 1 1 (see figures 2a and 3a). Crystal 2 is mounted in substantially the same environment as crystals 3 and 4 but it is mounted in such a manner that it is subject to both temperature and pressure. Further, the pressure sensor crystal 2 is placed in a chamber that is part of and enclosed by thermal block 6, and which is filled with an inert oil- fill. In turn, the oil-fill is pressurized through process isolating bellows 15 of which its exterior is exposed to the environment of transducer 1. Temperature gradient crystal sensor 5 is housed in thermal block 7 and being enclosed in the same atmosphere as crystal 3 and 4, which is being protected from pressure. Temperature gradient sensor 5 is subject to temperature and temperature change. As with crystals 3 and 4, the temperature change is function of temperature level, the physical properties of thermal block 7 and the crystal 5 as configured and characterized by thermal time constant 12. All crystals referenced are made in thickness shear mode.
Now, referring to the second embodiment, of the invention as shown in figure l b of the drawings, like reference numerals will be used for the same features. Section 6 is the thermal block housing the pressure measuring portion, while thermal block 7 is the temperature measuring housing of the transducer 1. Crystals 2 and 3 are shown as being enclosed in the same thermal block and environment. However, crystal 3 is protected from pressure by being enclosed in an atmosphere where the pressure remains constant at all time. They are, however, subject to the effects of temperature and temperature change as they are part of the same thermal block 6. The temperature change is function of the temperature level, the physical properties of the thermal block 6 and the crystals 2 and 3 as configured, and characterized by thermal time constant 1 1 (see figures 2b and 3b). Crystal 2 is mounted in substantially the same environment as crystals 3 but it is mounted in such a manner that it is subject to both temperature and pressure. Further, the pressure sensor crystal 2 is placed in a chamber that is part of and enclosed by thermal block 6, and which is filled with an inert oil-fill. In turn, the oil-fill is pressurized through process isolating bellows 15 of which its exterior is exposed to the environment of transducer 1 . Any temperature gradient or difference within this transducer embodiment 1 , is monitored by the two reference resonators 3 and 5. As reference resonators 3 and 5 are housed in different thermal blocks 6 and 7, any temperature change or difference between the two will be detected. As previously described, the temperature change is function of the temperature level, the physical properties of thermal blocks 6 and 7 as characterized by thermal time constants 1 1 and 12 respectively. As with the crystals of the first embodiment described above, all crystals of this embodiment are also made in thickness shear mode.
Figures 2a and 2b are supplementary schematic outline drawings of the two preferred embodiments of transducer 1 , and illustrate more detailed signal routing from the crystals 2, 3, 4, and 5.
Figure 3a is a supplementary schematic to Figure 2a and shows the transducer 1 sensor configuration as an illustrated functional block diagram of the first embodiment of the present invention. For temperature measurement, temperature crystal 4 has a relatively large temperature coefficient with respect to reference crystal 3. Temperature crystal 5 has the same temperature to frequency characteristics as temperature crystal 4. Temperature crystal 5 is controlling the frequency of oscillator 22. Temperature crystal 4 is controlling the output of oscillator 21. The reference crystal 3 is controlling the frequency output of oscillator 20. Finally, the pressure crystal 2 is controlling the output of oscillator 19.
The outputs 26 and 27 of oscillators 19 and 20 are fed to mixer 23 which produces the difference frequency between the respective oscillators 19 and 20. The said difference frequency 8 is fed into the frequency counter 16. The output of the frequency counter 8 is in turn fed to a computer 17 that process the information from the pressure sensor signal 8. The output signal 8 is called the Pressure Signal and is a function of the applied pressure and temperature of transducer 1 . Furthermore, the output 27 of oscillator 20 is fed directly to the frequency counter 16 and function as timebase or reference time for the processing of the input frequency signals 8, 9, and 10.
In a similar manner, the frequency output 28 of temperature oscillator 21 is fed to mixer 24 and mixed with the reference oscillator 27. The output difference between frequency inputs 27 and 28, produce a beat-frequency or product 9 which is input to the frequency counter 16. The mixer output 9 is named the Temperature Signal and is function of the temperature level of the transducer 1.
Temperature crystal 5 is controlling the frequency of oscillator 22. In turn, the output of oscillator 22 is fed to frequency mixer 25 and mixed with the frequency output 28 of the temperature oscillator 21. Mixer 25 produces a frequency output 10 and is named the "Delta Temperature" signal. For the purpose of the rate and magnitude of signal 10, the two temperature crystals 4 and 5 have the same temperature sensitivity but are attached to and are part of two independent thermal blocks 6 and 7. Thermal blocks 6 and 7 are configured to have equal or different response to temperature and temperature changes over time, which difference is characterized by the thermal time constants 1 1 and 12. Changes in temperature of the two thermal bodies 6 and 7 will change the output of each of the crystals and consequently indicate any change and/or difference in temperature between the two bodies. Thus, the differential temperature between the bodies 6 and 7 will produce a change in frequency output 10 of mixer 25 and be counted and processed by the frequency counter 16 and the computer 17 respectively.
In order to prevent ambiguous readings, it is suggested that the differential temperature measurement is designed so that there are no convergence points over the range of use. Thus, it is practical to select the two temperature crystals 4 and 5 so that they have the same temperature to frequencies sensitivity but have sufficient difference in nominal frequency so that the frequency of the two never converge (become equal) over the temperature and differential temperature range of use. For example, if the maximum differential temperature expected within the transducer 1 is 20°C, one would select the nominal frequency of temperature crystal 5 so that it converges at a point 25 to 30°C below the nominal frequency of temperature crystal 4.
Although, temperature crystals 4 and 5 are illustrated as having a positive temperature coefficient, it is within the scope of this invention to provide two crystals that have a negative temperature coefficient, as long as they do not possess ambiguous frequency-temperature characteristics.
Crystal resonator 2 is mounted in the same environment 5 as crystal resonator 3 and 4 but is separated therefrom. Whereas crystal resonators 3 and 4 are housed so as to be free from the effects of change in pressure, crystal resonator 2 is housed inside a fluid filled section subject to both temperature and pressure changes. Furthermore, any changes of temperature within the pressurized system caused by adiabatic effects will transfer to the thermal block 5 and be picked up by temperature resonator 4.
Figure 3b is a supplementary schematic to Figure 2b and shows the transducer 1 sensor configuration as an illustrated functional block diagram of the second embodiment of the present invention.
For temperature measurement, temperature crystal 4 has a relatively large temperature coefficient with respect to reference crystal 5 and is controlling the frequency output of oscillator 21 . In turn, reference crystal 5 has the same temperature to frequency characteristics as reference crystal 3, and is controlling the frequency output of oscillator 20. Finally, pressure crystal 2 has a pressure and temperature sensitivity and is controlling the output of oscillator 19.
The output 26 and 27 of oscillators 19 and 20 is fed to mixer 23 which produces the difference frequency between the respective oscillators 19 and 20. The said difference frequency 8 is fed into the frequency counter 16. The output of the frequency counter 16 is in turn fed to a processor 1 7 that process the information from the pressure sensor signal 8. The output signal 8 is called the Pressure Signal and is function of the applied pressure and temperature of transducer 1. Furthermore, the output 27 of oscillator 20 is fed directly to the frequency counter 16 and function as timebase or reference time for the processing of the input frequency signals 8, 9, and 10.
In a similar manner to the description above, the frequency output 28 of temperature oscillator 21 is fed to mixer 24 and mixed with the reference oscillator 29. The output difference between frequency inputs 28 and 29, produce a beat-frequency or product 9 which is input to the frequency counter 16. The mixer output 9 is named the Temperature Signal, and is function of the temperature level of the transducer 1.
Reference crystal 5 is controlling the frequency of oscillator 22. In turn, the output of oscillator 22 is fed to frequency mixer 25 and mixed with the frequency output 28 of the reference oscillator 20. Mixer 25 produce a frequency output 10 and named the "Delta Temperature" or Delta-R signal. For the purpose of the invention, the two reference crystals 3 and 5 have the same temperature sensitivity but are attached and part of two independent thermal blocks 6 and 7. Thermal blocks 6 and 7 are configured to have equal or different response to temperature change and the difference between the two is characterized by their thermal time constants 1 1 and 12. Changes in temperature of the two thermal bodies 6 and 7 will induce a change in output. Thus, temperature change and difference in temperature between the bodies 6 and 7, will produce a change in frequency output 10 and be counted and processed by the frequency counter 16 and processor 17 respectively.
In order to prevent ambiguous readings, it is suggested that the differential temperature measurement is designed so that there are no convergence points over the range of use. Thus, it is practical to select the two reference crystals 3 and 5 so that they have the same temperature to frequencies sensitivity but have sufficient difference in nominal frequency so that the frequency of the two never converge (become equal) over the temperature and differential temperature range of use. For example, if the maximum differential temperature expected within the transducer 1 is 20°C, one would select the nominal frequency of reference crystal 5 so that it converges at a point 25 to 30°C below the nominal frequency of reference crystal 3.
Although, reference crystals 3 and 5 are illustrated as having a positive temperature coefficient, it is within the scope of this invention to provide two crystals that have a negative temperature coefficient cut as long as they not possess ambiguous frequency-temperature characteristics.
Crystal resonator 2 is mounted in the same environment or thermal block 6 as crystal resonator 3. Crystal resonator sets 4 and 5 are separated therefrom, and are placed in their own thermal block 7. However, all crystals are mounted inside transducer housing 1 and are exposed to the same temperature environment. Nevertheless, crystal resonators 3, 4, and 5 are mounted to be free from the effects of change in pressure, while, crystal resonator 2 housed inside a fluid filled section of thermal block 6 and subject to both temperature and pressure changes of the transducer 1 environment. Furthermore, any changes of temperature within the pressurized system caused by adiabatic effects will transfer to the thermal block 6 and induce temperature change and difference between the two thermal bodies 6 and 7. In turn, an output change of 10 will be derived by mixer 25 in response to the gradient condition. Now referring to Figure 4a, crystal resonator 2 is cut in thickness shear mode and is both temperature and pressure sensitive. Crystal resonator 3 is oriented and cut in a manner to be as little temperature sensitive over the temperature range as possible. However, the reference resonator 3 possesses some temperature-frequency characteristics, but these are small compared to those of crystal resonators 2, 4, and 5. Hence, when crystal resonator 2 is subjected to pressure, there will be an output 8 of mixer 23 equal to the difference in frequency between crystal resonators 2 and 3. The signal 8, F p , will be a function of pressure and temperature and the reference of the transducer. The signal described is called F P (P,R) and is input to the frequency counter 16.
In the same manner, temperature resonator 4 is part of the same environment as crystal resonators 2 and 3 but is made in a cut that is very sensitive to temperature. By these means an outstanding frequency-temperature response is provided when compared to resonators 2 and 3. Hence, when resonator 4 is subjected to the temperature, there will be an output 9 F T | of mixer 24 that will equal the difference in frequency between the crystal resonators 3 and 4. The signal or beat-frequency 9, or F-n, will be a function of the temperature T] of thermal block 6 and the reference R of the transducer 1 . The signal and its function is expressed as F T (Ti,R).
Finally, crystal resonator 5 is made in the same cut and sensitivity to temperature as crystal resonator 4. However, crystal resonator 5 is attached to thermal block 7 and is configured to a have different time constant to temperature change than crystal resonator 4. Crystal resonator 5 is mounted in the same transducer environment 1 as crystal resonator 4 but is separated by thermal response means as the two thermal blocks 6 and 7 are configured to have different thermal time constants 1 1 and 12. Crystal resonators 4 and 5 are free from the effects of changes in pressure. However, crystal resonator 4 will pick up pressure-induced temperature changes, e.g., within thermal block 6, due to adiabatic effects of the pressure sensing fluid and crystal exposure.
Upon a temperature change, the two crystal resonators will possess different thermal response characteristics as the time constant of thermal block 6 is different from that of thermal block 7. The sensor resonator with the faster thermal response time will "race" or phase-lead the longer as there will be an intermediate or transient period while the temperature changes, where there will be an apparent temperature difference between the two during the thermal gradient period. Consequently, as the resonator output signals 28 and 29 are mixed by mixer 25, there will be a change in output signal 10 every time there is a temperature change or temperature difference between the two crystal resonators. Moreover, there will be an output 10 of mixer 25 equal to the difference in frequency between the crystal resonators and will be proportional to the difference in temperature between the two. For processing means, the output 10 of mixer 25 is called the "ΔΤ" and expressed as function F(Ti,T 2 ). The ΔΤ signal is a measure of the thermal stability of transducer assembly 1 . In turn, the ΔΤ is used for dynamic correction of the transducer 1 pressure and temperature determination.
Now referring to Figure 4b, crystal resonator 2 is cut in thickness shear mode and is both temperature and pressure sensitive. Crystal resonators 3 and 5 are oriented and cut in a manner to be as little temperature sensitive over the temperature range as possible. However, the reference resonators 3 and 5 possess some temperature-frequency characteristics, but these are small compared to those of crystal resonators 2 and 4. Hence, when crystal resonator 2 is subjected to pressure, there will be an output 8 of mixer 23 equal to the difference in frequency between crystal resonator 2 and 3. The signal 8, F p , will be a function of pressure/temperature and the reference # 1 of the transducer. The signal described is called F p (P,¾i) and is input to the frequency counter 16.
In the same manner, temperature resonator 4 is part of the same environment as reference resonator 5 but made in a cut that is very sensitive to temperature. By these means, temperature resonator 4 provides an outstanding frequency- temperature response, compared to resonators 2, 3 and 5. Hence, when resonator 4 is subjected to the temperature, there will be an output 9, named F T , of mixer 24 that will equal the difference in frequency between the crystal resonator 5 and 4. The signal or beat- frequency 9, will be a function of the temperature T 2 of thermal block 7. The signal and its function is expressed as F(T,R# 2 ).
Finally, crystal resonator 5 is made in the same cut and sensitivity to temperature as crystal resonator 3. However, crystal resonator 5 is attached to thermal block 7 and is configured to a have different time constant to temperature change than crystal resonator 3. Crystal resonator 5 is mounted in the same transducer 1 environment as crystal resonator 3 but is separated by thermal response means as the two thermal blocks 6 and 7, are configured to have different thermal time constants 1 1 and 12. Crystal resonators 3 and 5 are free from the effects of changes in pressure. However, crystal resonator 3 will pick up pressure-induced temperature changes, e.g., within thermal block 6, due to adiabatic effects of the pressure sensing fluid and crystal exposure. Upon temperature change, the two reference crystal resonators will possess different thermal response characteristics as the time constant of thermal block 6 is different from that of thermal block 7. Thus, the reference resonator having the faster thermal response or time constant, will "race" or phase-lead the one with the longer time constant. Consequently, there will be an apparent temperature difference between the two during thermal gradient periods that induce a change in output signal 10. The output change will be equal to the difference in frequency between the reference crystal resonator 3 and 5, and be proportional to the difference in temperature (i.e., between the two). For processing means, the output 10 of mixer 25 is called the ΔΤ/AR and expressed as function F(R # ! ,R #2 ). The ΔΤ signal is a measure of the thermal stability of transducer assembly 1 . In turn, the ΔΤ is used for dynamic correction of the transducer 1 pressure and temperature determination.
Figures 5a and 5b are the signal processing charts for the pressure determination of the two illustrated embodiments of transducer 1. Output of mixer 23, 24, and 25 are all fed into a Dynamic Block 13 that produces a corrective signal "e" to output 8 of the crystal resonator 2. Within the dynamic block 13, pressure mixer output 8 is mixed with the corrective frequency output "e" of the dynamic temperature correction model. The dynamic block 13 is made so that it processes no corrective output "e" at static temperature conditions. By these means, the nature of dynamic block 13 is such that it provides no corrective effect to the transducer 1 pressure determination when the temperature of the transducer is in steady state and there is no difference in temperature between the two internal thermal bodies 6 and 7. Correspondingly, if there is a temperature change or difference in temperature between thermal bodies 6 and 7, the dynamics of the block 13 will produce an output "e", equal to the anticipated frequency offset of crystal resonator 2 caused by the temperature change or difference. By dynamics means, the corrected signal 30 is a multivariate function of which diffusivity coefficients are biased by the pressure and temperature levels 8 and 9, and being proportional to the temperature change or difference monitored by output 10. The thermally corrected signal 30 is named F p - and fed to the Static Block 32 for traditional temperature correction and linearization means. For those skilled in the art, it should be recognized that to achieve the optimum accuracy of the transducer 1 pressure determination it might be preferable to make sets of different values for the dynamic and static coefficients dedicated each transducer manufactured. In turn, the coefficients that are derived typically depend on what temperature and pressure ranges that are expected to be encountered. Both corrections and models, i.e., dynamic block 13 and static block 32, are not physical hardware functions but are implemented in software, and included as a signal processing tasks of processor 17. However, they are both thermal correction models which account for the thermal dynamics of the transducer 1 crystal resonators.
Figures 6a and 6b are the signal processing charts for the temperature determinations of the two illustrated embodiments of transducer 1. Output of mixer 24 and 25 are all feed into a Dynamic Block 14 that produces a corrective signal "e" to output 9 of the crystal resonator 4. Within the dynamic block 14, temperature mixer output 9 is mixed with the corrective frequency output "e" of the dynamic temperature correction model. The difference in frequency between the two equals output signal 3 1 , which in turn is thermally corrected. As with dynamic correction block 13, the nature of the dynamic block 14 is such that it provides no corrective effect on the transducer 1 temperature determination as the temperature of the transducer is at steady state and there is no difference in temperature between the two thermal bodies 6 and 7.
Conversely, if there is a temperature change or difference in temperature between the thermal bodies, the dynamics of the block 14 will produce an output "e", equal to the anticipated frequency offset of crystal resonator 4 caused by the temperature change or difference in progress. The corrected temperature signal 31 is multivariate function and its diffusivity coefficients are biased by the temperature level 9. In turn, the block output is proportional to the temperature difference and function of output 10. The thermally corrected signal 31 is named F r and fed to the Static Block 33 for traditional linearization means.
For those skilled in the art, it should be recognized that to achieve the optimum accuracy of the transducer 1 temperature determination it might be preferable to make sets of different values for the dynamic and static coefficients dedicated each transducer manufactured, and are depending upon what temperature ranges that are expected to be encountered. Both correction models, i.e., the dynamic block 14 and static block 33, are not physical hardware functions but are implemented in software, and included as a signal processing tasks of processor 17. However, they are both thermal correction models which account for the thermal dynamics of the transducer 1 crystal resonators. For the purpose of the invention, Figures 7a and 7b illustrate different service type wells. Figure 7a shows a production type well and figure 7b shows an injection type well. Both wells' production tubing is used to transport a process media consisting of gas, fluid or combination. In both applications illustrated the process media contribute to heat transfer by convection and conduction. As within any thermal application heat is transferred from a hot environment to a cold. Thus, heat will flow and transfer in the two applications as illustrated creating a two-dimensional (axial and radial) cross sectional temperature profile.
Figures 8a, 8b, 9a, and 9b shows in greater detail the transducer 1 location as mounted to the well completion. In figures 8a and 8b the transducer is attached to the wall of the wellbore casing and in figures 9a and 9b it is attached to the tubing or completion. Figures 8 and 9 show the well in cross-sectional view and illustrate the radii temperature profile as induced by heat transfer.
Referring to figures 10, 1 1 , and 12, these figures show a more detailed view of the wellbore temperature profile in respect to the transducer 1 and its mounting. Figure 10 shows the envisioned temperature profile induced by heat conduction from the production media through the wellbore conduits. Figure 1 1 shows the one-dimensional heat conduction in a well with a permanent pressure and temperature transducer installed. Figure 12 shows the heat flow in the quartz pressure and temperature transducer, with an assumption that temperature t 3 is greater than temperature t 4 . The figures are made for the purpose of this invention to illustrate the need for dynamic temperature correction means as the transducer 1 mounting location is by definition inside a thermal gradient zone. Moreover, due to process load changes, the illustrated temperature profile will fluctuate and induce thermal gradients within the transducer 1. The temperature profile within transducer 1 is illustrated by the lines of heat-flow 36 and isothermals 37 (see figure 12) in the direction of heat drop or transfer through the transducer cross-section. Due to heat transfer from the well to the surrounding formation, the transducer 1 is held at high t 3 (38) at one side and low t 4 (39) where the heat exit. Again, this is to illustrate the need for dynamic temperature correction of the transducer 1 pressure and temperature determination as required by gradient environment and location.
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