Embodiments of the subject matter disclosed herein generally relate to a system and method for measuring ground penetration resistance, and more particularly, to a device that can perform these types of measurement with a hydrostatically compensated tip.
The need for new energy sources has pushed oil and gas exploration to deeper waters, in what is known as offshore oil and gas exploration. To build the necessary oil infrastructure at these deep sea locations, for example, on the bottom of the ocean, which may be about 1,000 to 6,000 m deep, there is a growing need for high quality, in-situ testing, of the seabed soft sediments. The most common tool for characterization of these fine sediments is a cone that penetrates the ocean bottom and the test associated with it is called the cone penetration test (CPT). In addition, it is possible to use full-flow penetrometers such as the T-bar and Ball-cone.
A traditional tool to perform the CPT test is shown in
However, such a system is cumbersome and not reliable at high-water depths. A serious concern has risen during the last decades with respect to the test at the seabed at high-water depths because the standard push cones are not hydrostatically compensated for the water pressure. As the water depth at the testing location can get up to 6,000 meters, a standard cone having a surface of 10 cm2 would experience a force of 60 kN (6,000 kg). The soft sediments resistant force on the same cone at the seabed level can be as low as 0.01 kN (1 kg), which represents <0.02% with respect to the hydrostatic water pressure at that level. The current standard push cones cannot measure with such resolution and accuracy in the presence of the high hydrostatic water pressure. At the same time, as the penetrometer deepens in the sediment, the local water pressure will increase and result in less reliable readings.
Returning to the oil filled push cone shown in
Thus, there is a need for a new tool that is simple and is not negatively affected by the high hydrostatic water pressure at large measuring depths.
According to an embodiment, there is a push cone device for measuring a penetration resistance into ground. The device includes a body having an internal chamber, electronics located in the internal chamber, a sensing module attached to the body and configured to house one or more sensors, a tip resistance module attached to the sensing module and having a tip that is configured to be fully hydrostatically-balanced under water, and a differential pressure sensor that measures the penetration resistivity experienced by the tip resistance module.
According to another embodiment, there is a push cone device for measuring a penetration resistivity into ground. The device includes a body having an internal chamber that houses electronics, and a tip attached to the body and being configured to move relative to the body. The tip is configured to be pressure balanced under water.
According to yet another embodiment, there is a method for measuring a penetration resistance with a push cone device. The method includes a step of lowering the push cone device to the ocean bottom, a step of self-balancing a hydrostatic water pressure acting on a tip of the push cone device so that a net pressure on the tip is negligible, a step of pushing the tip into the ground, and a step of measuring with a differential pressure sensor a pressure associated with the penetration resistance generated by the ground against the tip. The differential pressure sensor is configured to be in fluid communication, at a first port, with an oil chamber located inside the push cone device and, at a second port, with a water passage also inside the push cone.
For a more complete understanding of the present invention, reference is now made to the following descriptions taken in conjunction with the accompanying drawings, in which:
The following description of the embodiments refers to the accompanying drawings. The same reference numbers in different drawings identify the same or similar elements. The following detailed description does not limit the invention. Instead, the scope of the invention is defined by the appended claims. The following embodiments are discussed, for simplicity, with regard to a system that uses a differential pressure transducer that factors out the influence of the hydrostatic pressure of the water. However, the embodiments to be discussed next are not limited to such a transducer, but may be used with other sensors that achieve the same result.
Reference throughout the specification to “one embodiment” or “an embodiment” means that a particular feature, structure or characteristic described in connection with an embodiment is included in at least one embodiment of the subject matter disclosed. Thus, the appearance of the phrases “in one embodiment” or “in an embodiment” in various places throughout the specification is not necessarily referring to the same embodiment. Further, the particular features, structures or characteristics may be combined in any suitable manner in one or more embodiments.
According to an embodiment, a stackable, modular, push cone device is configured to balance out the hydrostatic water pressure acting on the tip of the device and uses a differential pressure transducer to read a pressure acting on the tip of the device due to a resistance generated by the ground (soil) when the tip penetrates the ground. One or more advantages associated with this device are: (1) the tip of the pushing cone is fully compensated for the hydrostatic water pressure; (2) measurements performed with this device are not in the hydrostatically stressed shaft; and (3) more accurate and higher resolution measurements (for example, a resolution of +/−2.5 kPa of the penetration resistance under a 70 MPa of hydrostatic water pressure) can be obtained when compared to the current systems.
As illustrated in the embodiment of
The main body 302 is connected to a connector 314, which closes one end of the internal housing 304. One or more probes 330 are attached to the connector 314. A probe 330 may be configured as a tube that is connected to the connector 314 and is configured to collect a part of the ambient soil and/or water into which the device 300 is placed. Also connected to the connector 314 there is a sensing module 340 that is shaped as a tubular rod that extends past the connector 314 and the probes 330. The sensing module 340 is configured to receive one or more sensors 342 (only one shown for convenience). The sensor 342 can be one of temperature, pressure, electrical conductivity, chemical, biological, soil sampler, magnetic, radioactive, or any other sensor that is used when studying the ocean bottom. While the one or more sensors is located in the sensing module 340, part of the electronics supporting the sensor is located in the main or secondary bodies, as sensor electronics 312, as discussed above.
The sensing module 340 is designed to be reconfigurable so that any number of sensors, as desired by the operator of the device 300, can be added. In other words, the sensors can be added or removed from the sensing module as required by the operator. This means that the one or more sensors can be attached to or removed from the sensing module.
At the tip of the sensing module 340, there is a tip resistance module 350. The tip resistance module is illustrated in more detail in
The tip resistance module 350 also includes a sleeve 354 that is configured to partially enclose the tip 352. The sleeve 354 has a shoulder 356 that is configured to engage a corresponding shoulder 352A of the tip 352, so that the two elements are mechanically connected and one does not slide relative to the other one when the entire device is driven into the sediment 400. The tip resistance module 350 further includes a core 360, which extends along the vertical axis Y and connects the sensing module 340 to the sleeve 354 and tip 352. The core 360 may be made of metal and includes a few passages for allowing water and oil to move freely between desired locations of the device 300, as discussed later. The sleeve 354 is fixedly attached to the core 360. However, the tip 352 is slidably attached to the sleeve 354, so that the tip 352 can move vertically up and down between the sleeve 354 and the core 360.
More specifically, as illustrated in
In this way, the hydrostatic water pressure acts through port 362A and first water passage 362 on the top annular surface 352B of the tip 352, but also on the bottom pointed surface 353, reducing its effect on the tip 352. If the area A of the top annular surface 352B is sized to be equal with a horizontal projection area B of the bottom pointed surface 353, then the effect of the hydrostatic water pressure on the tip 352 is effectively cancelled. This means that the force exerted by the sediment 400 on the bottom pointed surface 353 is fully transmitted to the oil 367 in the oil chamber 366, and then the second oil channel 368 transmits this pressure to the differential pressure sensor 370. As the oil in the oil chamber 366 is also pressurized due to the hydrostatic pressure transmitted through the walls of the device and also due to the interaction between the tip 352 and the sediment 400, by subtracting in the differential pressure transducer 370 and thus the hydrostatic pressure, only the effect of the sediment on the tip can be measured, which is indicative of the penetration resistance.
Therefore, the device 300 discussed herein is capable to remove the hydrostatic water pressure from the measurement of the penetration resistance, which ensures that the small value of the penetration resistance is not obscured by the large value generated by the hydrostatic water pressure. Note that for this configuration, when the device 300 is lowered through the water toward the ocean bottom, but has not yet reached the ocean bottom, the pressures read by the differential pressure sensor 370, from the first water passage 362 and the second oil passage 368 are equal, which indicates that the hydrostatic water pressure is transmitted through the walls of the device to the oil in the oil chamber 366.
The device 300 can be deployed to the ocean bottom following various approaches. Two of these approaches are discussed with regard to
A second approach for delivering the device 300 to the ocean bottom 710 is illustrated in
One skilled in the art will understand that the device 300 may also be deployed in a well, onshore or offshore, for determining the penetration resistance at the bottom of the well. For this application, the drilling tools would be taken out of the well, the device 300 will be lowered into the well based on one of the approaches discussed above, then the device will be pushed into the bottom of the well and measurements will be performed, after which the device is taken out and the drilling tool is lowered back into the well and the drilling is resumed. Based on the penetration resistance measurements, the type of drill used may be changed before the drilling resumes. Other applications of the device 300 may be envisioned, for example, in relation to marine and fluvial ports, oil and gas recovery, mining, seabed survey, etc.
The temperature, electrical conductivity, and penetration resistance data was acquired with the device 300 for three different locations on the ocean floor and this data is illustrated in
A method for collecting this data is now discussed with regard to
The disclosed embodiments provide a hydrostatically-balanced push cone device for measuring a penetration resistance in the ocean bottom. It should be understood that this description is not intended to limit the invention. On the contrary, the embodiments are intended to cover alternatives, modifications and equivalents, which are included in the spirit and scope of the invention as defined by the appended claims. Further, in the detailed description of the embodiments, numerous specific details are set forth in order to provide a comprehensive understanding of the claimed invention. However, one skilled in the art would understand that various embodiments may be practiced without such specific details.
Although the features and elements of the present embodiments are described in the embodiments in particular combinations, each feature or element can be used alone without the other features and elements of the embodiments or in various combinations with or without other features and elements disclosed herein.
This written description uses examples of the subject matter disclosed to enable any person skilled in the art to practice the same, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the subject matter is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims.
This application claims priority to U.S. Provisional Patent Application No. 62/839,224, filed on Apr. 26, 2019, entitled “HYDROSTATICALLY COMPENSATED PROBE FOR SOIL PENETRATION RESISTANCE IN LABORATORY AND FIELD MEASUREMENTS,” the disclosure of which is incorporated herein by reference in its entirety.
Filing Document | Filing Date | Country | Kind |
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PCT/IB2020/052873 | 3/26/2020 | WO | 00 |
Number | Date | Country | |
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62839224 | Apr 2019 | US |