Cone penetrometer tool and method for measuring thermal conductivity of soil

Abstract

A thermal conductivity tool includes a housing having a penetrator cone on one longitudinal end. A thermal core is disposed in the housing at a selected distance from the penetrator cone. The thermal core comprises a core body having a plurality of circumferentially spaced apart longitudinal bores therein. Each of the bores has a heating element or a temperature sensor, wherein the heating elements and the temperature sensors are circumferentially symmetric about a longitudinal axis of the thermal core. A thermal system defined by the thermal conductivity tool and surrounding media having a plurality of different known thermal conductivities is predetermined by simulation or empirical measurement.

Description

CONE PENETROMETER TOOL AND METHOD FOR MEASURINGTHERMAL CONDUCTIVITY OF SOILBACKGROUND

[0001] This disclosure relates to the field of cone penetrometer tools used to determine properties of soils, particularly on the bottom of a body of water. More particularly, the present disclosure relates to cone penetrometers used to measure thermal conductivity of water bottom soils and sediments.

[0002] Probes such as cone penetrometers are urged into soil or sediments on the bottom of a body of water using various apparatus. Sensors on or in the penetrometer probe may include pressure, temperature and electrical resistivity sensors, among other sensors, to enable determining relevant properties of the soil or sediment. Such properties are known to include thermal conductivity, particularly where it is intended to install heat generating structures such as fluid pipelines.

[0003] International Application Publication No. WO 2023 / 201123 A2 discloses a thermal conductivity probe. In one implementation, the disclosed thermal conductivity probe includes at least one heating element, at least one thermal insulator, and at least one thermistor thermally isolated from the at least one heating element by the at least one thermal insulator. Specific implementations of the foregoing probe include a plurality of thermistors thermally isolated from the at least one heating element. The plurality of thermistors can include a first thermistor thermally isolated from the heating element by a thermal insulator and a second thermistor thermally isolated from the first thermistor by another thermal insulator. Further, the plurality of thermistors can include a third thermistor thermally isolated from the heating element by a thermal insulator and a fourth thermistor thermally isolated from the third thermistor by another thermal insulator. Alternatively, the plurality of thermistors can include thermistors thermally isolated from the heating element by thermal insulation and other thermistors thermally isolated from the heating element by a further thermal insulator.

[0004] A particular limitation to the thermal probe disclosed in the WO ‘ 123 publication is the limited longitudinal extent of the heating element and the thermistor sensors. Accordingly, measurements made by such probe may be subject to substantial error by reason of fluid that may be disposed in an annular space between the outer wall of the probe and any bore or opening created by impressing the probe into soil or sediment on the bottom of a body of water. Accordingly, there is a need for improved thermal conductivity probes for evaluating water bottom soil and sediment.SUMMARY

[0005] One aspect of the present disclosure relates to a thermal conductivity tool for measuring properties of soil or sediment, typically on the bottom of a body of water.

[0006] A thermal conductivity tool according to this aspect of the disclosure includes a housing having a penetrator cone on one longitudinal end. A thermal core is disposed in the housing at a selected distance from the penetrator cone. The thermal core comprises a core body having a plurality of circumferentially spaced apart longitudinal bores therein. Each of the bores has a heating element or a temperature sensor, wherein the heating elements and the temperature sensors are circumferentially symmetric about a longitudinal axis of the thermal core. A thermal system defined by the thermal conductivity tool and surrounding media having a plurality of different known themial conductivities is predetermined by simulation or empirical measurement.

[0007] In some implementations, the heating elements comprise electrical resistance heating elements.

[0008] In some implementations, the temperature sensors comprise thermistor sensors.

[0009] In some implementations, the thermal core comprises a through bore substantially coaxial with the longitudinal axis.

[0010] In some implementations, the thermal core comprises an outer diameter enabling contact with an inner wall of the housing.

[0011] In some implementations, the housing comprises a connector on an end opposed to the cone, the connector arranged to connect the housing to a conveyance.

[0012] In some implementations, the conveyance comprises coiled tubing.

[0013] Another aspect of the present disclosure relates to methods for determining thermal conductivity of soil or sediment. A method for determining thermal conductivity of soil or sediment according to this aspect of the disclosure includes moving a thermal conductivity measuring tool to a selected depth in the soil or sediment. The thermal conductivity tool comprises a housing having a penetrator cone on one longitudinal end a thermal core disposed in the housing at a selected distance from the penetrator core. The thermal core comprises a core body having a plurality of circumferentially spaced apart longitudinal bores therein, each of the bores having disposed therein a heating element or a temperature sensor, wherein the heating elements and the temperature sensors are circumferentially symmetric about a longitudinal axis of the thermal core. A model of a thermal system defined by the thermal conductivity tool and surrounding media have a plurality of different known thermal conductivities is predetermined by simulation or empirical measurement. A temperature is measured. The heating elements are switched on until a predetermined temperature increase is measured. The heating elements are switched off and temperature is measured until a selected time after the switching off. The thermal conductivity is determined by fitting the measured temperature to the model of the thermal system.

[0014] In some implementations, the measured temperature fitted to the model is obtained between a first time wherein a temperature gradient is negative for a predetermined time to a second time wherein a confidence of the fitting exceeds a predetermined value.

[0015] In some implementations, the predetermined temperature increase is at least 3 degrees Celsius (or degrees Kelvin).

[0016] Other aspects and possible advantages will be apparent from the description and claims that follow.BRIEF DESCRIPTION OF THE DRAWINGS

[0017] FIG. 1 shows an example implementation of a cone penetrometer tool according to the present disclosure.

[0018] FIG. 2 shows an oblique cut away view of a thermal probe part of the tool of FIG. 1.

[0019] FIG. 3 shows an oblique view of a thermal core part of the thermal probe shown in FIG. 2.

[0020] FIG. 4 shows a cross section of the thermal core of FIG. 3 to illustrate an example arrangement of heating elements and temperature sensors.

[0021] FIG. 5 shows a graph of simulated temperature measurements used to determine thermal conductivity according to the present disclosure.DETAILED DESCRIPTION

[0022] An example implementation of a cone penetrometer tool (hereinafter, “tool”) having thermal conductivity measuring devices is shown schematically at 10 in FIG. 1. The tool 10 may comprise a cone penetrator section 12 having at one longitudinal end a cone 12A for penetrating soils or sediments at the bottom of a body of water. The cone penetrator section 12 may comprise a pressure resistant housing (“cone penetrator section housing”) 14 within which may be disposed sensing devices (none shown separately) such as pressure, acoustic velocity and / or electrical resistivity sensors as are known to be used in cone penetrometer tools. It is to be understood that such devices need not be included in any particular implementation of a tool according to the present disclosure; the length of the cone penetrator section 12 may be chosen to provide substantial themial isolation between the cone 12A and temperature sensing devices to be explained further below.

[0023] The cone penetrator section housing 14 may comprise at its other longitudinal end a connector 18A for joining end to end a second pressure resistant housing (“thermal probe section housing”) 15 for a thermal probe section 11 of the tool 10. The adjoininglongitudinal end of the thermal probe section housing 15 may comprise a mating connector 18B to releasably, sealingly couple the thermal probe section housing 15 to the cone penetrator section housing 14. The opposed longitudinal end of the thermal probe section housing 15 may comprise a connector 16, such as a crimp on or roll on connector to couple the tool 10 to a conveyance such as a coiled tubing unit (not shown) of types known in the art for urging cone penetrometer tools into sediments or soils on the water bottom. A non-limiting example of such coiled tubing unit is described in US Pat. No. 10,392,880 issued to Boggess. The exact manner of conveyance of the tool 10 is not a limitation on the scope of the present disclosure. The second pressure resistant housing 15 may be made, for example and without limitation from high thermal conductivity, high strength material such as 4130 alloy steel.

[0024] A thermal probe core 20 having elements, to be described in more detail below disposed therein, may be disposed within the thermal probe section housing 15 at a selected longitudinal position and is in contact with the inner wall of the thermal probe section housing 15 at such position. In the present example implementation, the thermal probe core (“core”) 20 may be located such that a longitudinal spacing between the thermal probe core 20 and the cone 12A is about 22 to 28 inches in order to provide substantial thermal isolation between the thermal probe core 20 and the cone 12 A.

[0025] FIG. 2 shows an oblique, cut away view of the thermal probe section 11 to illustrate certain features of the themral probe core 20. The thermal probe core 20 may comprise (more detail shown and explained with reference to FIG. 3) a plurality of circumferentially spaced apart, longitudinally extending openings 13 for placement of heating elements and temperature sensors, and a centrally disposed longitudinal through bore used, for example, for electrical wiring feed through.

[0026] A cross section, oblique view of the thermal probe core 20 is shown in FIG. 3 to illustrate an example of placement of the longitudinally extending openings. A first plurality of circumferentially spaced apart, longitudinally extending openings 22 may be used for placement of heating elements (shown in FIG. 4). A second plurality of circumferentially spaced apart, longitudinally extending openings 26 may be used forplacement of temperature sensors (also shown in FIG. 4). A centrally located through bore 24 may be provided for pass through of, e.g., electrical cables and / or conduits where the cone penetrometer section (12 in FIG. 1) is instrumented. In the present example implementation, the openings 22, 26 may be circumferentially symmetrically arranged about the longitudinal axis A of the core 20 in order to simplify interpretation of temperature measurements made by the tool (10 in FIG. 1).

[0027] FIG. 4 shows a cross-sectional view of the core 20 to illustrate a possible arrangement of heating elements 32 and temperature sensors 30. The heating elements 32 may be electrical resistance heaters. The temperature sensors 30 may be temperature dependent resistance (e.g., thermistor) sensors. The heating elements 32 may have length and power rating in order to be able to elevate temperature of the thermal probe core 20 to at least 3 to 5° C above ambient temperature within a few seconds. Measurements of temperature (e.g., by measuring resistance of the temperature sensors 30) may be made and communicated to surface such as by a long electrical cable, or the measurements may be recorded locally within the tool (10 in FIG. 1) for a selected time interval after switching on the heating elements 32.

[0028] Although not shown in the drawing figures, it will be appreciated by those skilled in the art that necessary power and signal recording / communication devices may be disposed in the tool (10 in FIG. 1) in order to operate the heating elements 32 and make measurements using the temperature sensors 30 in order to perform methods to be explained in more detail below. Electrical power to operate the tool (10 in FIG. 1) may be provided by electrical cable (not shown) or by batteries (not shown) disposed within or proximate the tool (10 in FIG. 1).

[0029] Temperature decay as measured by the sensors in the tool 10 is a function of time t after a temperature increase caused by operating the heating elements 32. Eq. 1 is an approximation of a well-known solution to the 1 -dimensional heat equation, where 7b is the initial temperature, Ho / L is the heat release per unit of length, and k is the thermal conductivity. T is the measured temperature at time t. T (r,f), where r is the radial distanceinto soil or sediment, will asymptotically decrease toward 7b after a certain amount of time.

[0030] At sufficiently great time from switching off the heating elements 32, a term in the1 -dimensional heat equation related to radial distance, and density and heat capacity of the soil or sediment may be ignored, resulting in the following approximation for k.frc in Eq. 2 is a scale factor to account for heat transfer in any direction other than radially outwardly from the tool, frc is dependent on, among other factors, distance between the location of the temperature sensors 30 and the cone ( 12A in FIG. 1); the scale factor may be determined by, for example, modeling expected temperature measurements with respect to time made by the tool in response to various values of k, or by empirical measurement made by the tool in various, known k-value media (as representing various soils or sediments). When the scale factor frc is detemiined, it is then possible to extract k and To by fitting the temperature measurements made during an actual measurement procedure.

[0032] Eq. 2 allows for a direct calculation of thermal conductivity k. It is then only necessary to extract from temperature measurement data the value of T - To. The value of frc may be obtained through a calibration process which can use input from computer simulation of temperature in a tool / soil system. The foregoing process provides the system to reach thermal equilibrium by allowing a certain amount of time for the process to unfold. A temperature increase AT greater than about 3°C is typically enough to observe a meaningful process which will allow using Eq. 1 to determine k.

[0033] In operation, the heating elements 32 are switched on until the measured temperature in the thermal core (20 in FIG. 2) increases by a few degrees, e.g., in a rangeof 3 to 10 degrees C. Then, after the heating elements 32 are switched off, the heat energy transfer to the soil may be observed in the temperature measurements as a result of the temperature gradient created. There is no need to know the terminal temperature To for which the approximation applied to obtain Eq. 1 is valid. Previous strategies to calculate k are based on finding To. The present method is substantially correct for large enough values of t.

[0034] Perform a temperature measurement when the tool is moved to a chosen depth into the sediment or soil; the measured temperature may be referred to as Tfo. Then the heating elements 32 are switched on temperature measurements continue. The time at which the heating elements are switched on may be referred to as to.

[0035] When the temperature sensors 30 have detected a temperature increase greater than a predetermined increase, e.g., 3 to 10°C with respect to Tfo, the heating elements are switched off. This time may be referred to as ti. ti may be expected to be in a range of about 10 to 30 seconds using a tool configured as explained above.

[0036] Because there will be a temperature profile between the position of the heating elements 32 and the temperature sensors 30, the temperature measurements may still increase for a few seconds after the heating elements 32 have been turned off. The temperature gradient may be monitored from ti on until it is consistently negative for more than a predetermined time, e.g., 10 seconds. The time of such occurrence may be referred to as f and the measured temperature at such time as temperature Tfl' ).

[0037] T´fo is the beginning of the heat-transfer phase that will follow the model of the tool or the empirical calibration measurements explained above. After approximately 120 seconds a first fit (e.g., by χ2curve fitting) of temperature measurements to the model or the empirical calibration data may be performed using the temperature measurements starting at t´. The fitting process may be repeated at selected times, e.g., every 30 seconds, until the fit has reached a predetermined level of confidence, e.g., greater than 95%. At this point the resulting To and k values may be presented. The foregoing results may be deemed sufficient, or temperature measurements may continue until thermal equilibriumis reached. If thermal equilibrium is reached one can use the direct approach to calculate k from Eq. (1). Both results with their corresponding uncertainties may be presented.

[0038] An example of curve fitting temperature measurements to the tool model (or empirical calibration) is shown in FIG. 5 for simulated temperature data in a soil / tool system with a k value of 2.0 and an initial temperature To of 293.1°K. Temperature measurement once the tool is in place, Tfo, is shown at 41 ; once the foregoing temperature measurement is made, the heating elements (32 in FIG. 4) are switched on. Once a selected temperature increase above Tfo is measured, the heating elements are switched off as shown at 46. Temperature measurements continue until the temperature gradient is negative for a predetermined time, as can be identified between 46 and 44. The foregoing represents t' and the measured temperature at such time as temperature T´fo as explained above. At 44 the first attempt of χ2curve fitting can be performed.

[0039] A few strategies can help determine if a particular test is successful or if it should be repeated. y2 / ndf value of the fit or a more quantitative approach like the calculation of the confidence level. The fitted To needs to be lower than the initial test temperature between 46 and 44, Although not necessarily equal to the temperature prior to the use of the heating elements, as the cone may have heated due to friction during insertion into the sediments or soils, or may still carry some energy from a previous test. These differences will be very small and will have substantially no impact on the test. When a thermal element has not cooled down enough, the tool may communicate to surface the temperature of the heating element(s) and can thereby advise the tool operator.

[0040] In light of the principles and example implementations described and illustrated herein, it will be recognized that the example implementations can be modified in arrangement and detail without departing from such principles. The foregoing discussion has focused on specific implementations, but other configurations are also contemplated. In particular, even though expressions such as in “an implementation," or the like are used herein, these phrases are meant to generally reference implementation possibilities, and are not intended to limit the disclosure to particular implementation configurations. As used herein, these terms may reference the same or different implementations that arecombinable into other implementations. As a rule, any implementation referenced herein is freely combinable with any one or more of the other implementations referenced herein, and any number of features of different implementations are combinable with one another, unless indicated otherwise. Although only a few examples have been described in detail above, those skilled in the art will readily appreciate that many modifications are possible within the scope of the described examples. Accordingly, all such modifications are intended to be included within the scope of this disclosure as defined in the following claims.

Claims

AMENDED CLAIMS received by the International Bureau on 15 September 2025 (15.09.2025)1. Athermal conductivity tool, comprising: a housing having a penetrator cone on one longitudinal end; a thermal core disposed in the housing at a selected distance from the penetrator core, the thermal core comprising a core body having a plurality of circumferentially spaced apart longitudinal bores therein, each of the bores having disposed therein a heating element or a temperature sensor, wherein the heating elements and the temperature sensors are circumferentially symmetric about a longitudinal axis of the thermal core; and signal recording and communication devices arranged to operate the heating elements and the temperature sensors, the recording and communication devices further arranged to determine thermal conductivity of a medium surrounding the housing by comparing measured temperature with respect to time to a model of a thermal system defined by the thermal conductivity tool and a plurality of model surrounding media each having a different known thermal conductivity wherein a time-temperature relationship with respect to thermal conductivity is predetermined by simulation or empirical measurement.

2. The tool of claim 1 wherein the heating elements comprise electrical resistance heating elements.

3. The tool of claim 1 wherein the temperature sensors comprise thermistor sensors.

4. The tool of claim 1 wherein the thermal core comprises a through bore substantially coaxial with the longitudinal axis.

5. The tool of claim 1 wherein the thermal core comprises an outer diameter enabling contact with an inner wall of the housing.

6. The tool of claim 1 wherein the housing comprises a connector on an end opposed to the cone, the connector arranged to connect the housing to a conveyance.

7. The tool of claim 6 wherein the conveyance comprises coiled tubing.

8. A method for determining thermal conductivity of soil or sediment, comprising: moving a thermal conductivity measuring tool to a selected depth in the soil or sediment, the thermal conductivity tool comprising a housing having a penetrator cone on one longitudinal end a thermal core disposed in the housing at a selected distance from the penetrator core, the thermal core comprising a core body having a plurality of circumferentially spaced apart longitudinal bores therein, each of the bores having disposed therein a heating element or a temperature sensor, wherein the heating elements and the temperature sensors are circumferentially symmetric about a longitudinal axis of the thermal core; switching on the heating elements until a predetermined temperature increase is measured; switching off the heating elements; and measuring temperature until a selected time after the switching off; and determining the thermal conductivity by fitting the measured temperature with respect to time to a model of the a thermal system defined by the tool and media surrounding the tool, the model comprising a relationship of temperature with respect to time for a plurality of different model surrounding media each having a different known thermal conductivity.

9. The method of claim 8 wherein the measured temperature fitted to the model is obtained between a first time wherein a temperature gradient is negative for a predetermined time to a second time wherein a confidence of the fitting exceeds a predetermined value.

10. The method of claim 8 wherein the predetermined temperature increase is at least 3 degrees Celsius (or degrees Kelvin).

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