Patent Publication Number: US-2022220686-A1

Title: Hydrostatically compensated device for ground penetration resistance measurements

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     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. 
    
    
     BACKGROUND 
     Technical Field 
     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. 
     Discussion of the Background 
     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  FIGS. 1 and 2 .  FIG. 1  shows the entire tool  10  having a large robust member  14  that holds in its tip  16 , a secondary probe  18 . The secondary probe  18  holds, as shown in  FIG. 2 , a miniature pressure sensor  20 . The large robust member  14  holds a pressure chamber  38  filled with oil  55 , through a connecting tube  54 . The connecting tube  54  communicates with a pump (not shown) located at the surface. The pump supplies the oil under pressure to force the probe member  18  to enter into the soil, when the primary probe  14  lands on the ocean bottom. A rod  60  extends from the probe member  18  into the pressure chamber  38  and guides the probe member  18  into the soil. 
     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 cm 2  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 &lt;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  FIGS. 1 and 2 , it has a standard cone partially compensated for the water column. However, this device is not reliable at high-water depths. Over the past number of years, different solutions have been proposed. For example, full-flow penetrometers that are partially water-compensated, have an external reduction of their shaft, which make them internally hydrostatically stressed. Further, such devices have a specially designed notch and strain gauge that can read the penetration forces rather than the impact of the water pressure on the cone. However, even these devices do not fully remove the negative influence of the hydrostatic water pressure on the measurements. 
     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. 
     BRIEF SUMMARY OF THE INVENTION 
     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. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       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: 
         FIGS. 1 and 2  illustrate a conventional push cone device; 
         FIG. 3  illustrates a push cone device that has a balanced hydrostatic water pressure tip resistance module; 
         FIG. 4  illustrates a detail of the hydrostatically balanced tip resistance module; 
         FIG. 5  illustrates a detail of a tip of the tip resistance module; 
         FIG. 6  illustrates the push cone device when pushed into the ground; 
         FIGS. 7A and 7B  illustrate various ways for deploying the push cone device into the ground; 
         FIGS. 8A, 8B and 8C  illustrate various parameters measured with the push cone device when deployed into the ground; and 
         FIG. 9  is a flowchart of a method for measuring a penetration resistance with the novel push cone device. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     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  FIG. 3 , the novel push cone device  300  has a body  302  that defines an internal housing  304 , which is sealed from the ambient environment, so that seawater cannot enter. The internal housing  304  may be configured to host a processor  306 , a memory  308  for storing data recorded by the various sensors associated with the device  300 , an optional power source  310 , for example, a battery, and sensor electronics  312 . The sensor electronics  312 , for example, analog-to-digital converters, amplifiers, etc., may be configured to provide support for a temperature sensor, a water pressure sensor, an electrical conductivity sensor, a soil sampler, or other sensors. The sensor electronics are electrically connected to the power source  310  and is configured to process the data collected from the various sensors. An additional body  320  may be connected to the main body  302  and may be configured to have a corresponding internal chamber  322 . One or more of the elements  306 ,  308 ,  310 , and  312  may be stored in this secondary internal chamber  322 . A communication passage  324  may be formed between the main internal chamber  304  and the secondary internal chamber  322  so that one or more wires may extend from one chamber to the other. The secondary internal chamber  322  is also sealed from the ambient environment. The additional body  320  may be attached to a coupler  326  that can be connected to a cable (tether)  328  from a mother vessel, as discussed later. The tether may be used to move the device  300  up and down and also to transmit electrical power and data from the device to the mother vessel and vice versa. 
     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  FIG. 4  and includes a tip  352  that is configured to have a pointed surface  353  that directly contacts the sediment  400  or ocean bottom to be measured.  FIG. 4  shows the tip  352  being partially embedded into the sediment  400  and partially being surrounded by the ocean water  410 . The pointed surface  353  may be inclined relative to the vertical axis Y with an angle between 5 and 65 degrees. An area of the pointed surface may be between 5 and 20 cm 2 . 
     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  352 A 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  FIG. 4 , there is a first water passage  362  that connects the sides  360 A and  360 B of the core  360  to a bottom  360 C of the core  360 . The first water passage  362  terminates with ports  362 A and  362 B at the side walls  360 A and  360 B of the core  360 . The first water passage  362  also communicates with a differential pressure sensor  370 . The differential pressure sensor  370  can be located in the sensing module  340  or even in the main body  302 . The first water passage  362  is provided with filters  364  on each of the sides  360 A and  360 B to prevent particulates from the sediment  400  to enter inside the core  360 . The first water passage  362  has a third port  362 C that fluidly communicates with an annular water chamber  365 , formed between a bottom part of the core  360  and a top annular surface  352 B of the tip  352 . The various surfaces of the tip  352  are more clearly illustrated in  FIG. 5 . Note that the tip  352  also has a central top surface  352 C, which faces an oil chamber  366 , which is filled with oil  367 , as illustrated in  FIG. 4 . The oil chamber  366  is defined by the central top surface  352 C of the core  352 , and side walls of the core  360 , as illustrated in  FIG. 4 . The oil chamber  366  fluidly communicates with the second oil passage  368  and also with the differential pressure sensor  370 . 
     In this way, the hydrostatic water pressure acts through port  362 A and first water passage  362  on the top annular surface  352 B 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  352 B 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 . 
       FIG. 6  shows the tip  352  being more embedded into the sediment  400  and less enclosed by the water  410 . Because of the resistance exhibited by the sediment  400 , the tip  352  has moved upward, toward the core  360 , which resulted in the formation of an annular chamber  600  between the interior of the sleeve  356  and the lower side of the tip shoulder  352 A. In addition, the upward movement of the tip  352  while the core  360  and the sleeve  354  remain fixed, resulted in the decrease in volume of the oil chamber  366  and also the decrease in volume of the annular water chamber  365 , as also illustrated in  FIG. 6 . 
     The device  300  can be deployed to the ocean bottom following various approaches. Two of these approaches are discussed with regard to  FIGS. 7A and 7B .  FIG. 7A  shows a configuration  700  in which a mother vessel  702  takes the device  300  to a desired location relative to the ocean bottom. The vessel  702  has a winch  704  or equivalent device for metering a cable  706  into the water  701 . Cable  706  may include a first element for providing resistance, and a second element for providing power and data exchange to the device  300 . However, the second element is optional. A weight  708  is added to the cable  706  for driving the device  300  into the ocean bottom  710 . The device  300  is shown in  FIG. 7A  approaching the ocean bottom  710 . The sensing module  340  and the tip resistance module  350  are also visible in this figure. 
     A second approach for delivering the device  300  to the ocean bottom  710  is illustrated in  FIG. 7B . In this configuration, a driving structure  730  is placed around the device  300  and is lowered to the ocean bottom  710  with the cable  706 . Once on the ocean bottom  710 , a driving mechanism  740  (for example, a moving weight or a piston) is activated by a controller  703  located on the vessel  702 , for pushing the device  300  into the ocean bottom. As the device  300  is entering the sediment associated with the ocean bottom  710 , the hydrostatic water pressure is fully balanced on the tip resistance module  350 , and the differential pressure sensor  370  is capable to measure the pressure associated with the penetration resistance experienced by the tip of the resistance module  352 . The data associated with these pressures is either stored in the local memory  308  of the device  300 , for later analysis, or is transmitted in real time to the controller  703  of the vessel  702 , through the cable  706 . Additional data is also stored in the local memory or transmitted to the vessel, for example, data associated with the temperature of the water, pressure, electrical conductivity, radioactivity, pH, etc. 
     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  FIGS. 8A, 8B and 8C . Each figure plots the data for a given location and each figure shows the temperature  800 , the electrical conductivity (EC)  802 , and the penetration resistance  804 . The axes for this data are shown on the top of each figure, as the X axes. The Y axis plots the depth of the tip  352  where the data is measured, where the depth is expressed in meters below sea level (mbsl). While the temperature at each location was substantially constant over approximately 3 meters of data collection, the EC and penetration resistance increased with the increase in depth, as expected. 
     A method for collecting this data is now discussed with regard to  FIG. 9 . The method includes a step  900  of lowering the push cone device  300  to the ocean bottom, a step  902  of self-balancing the hydrostatic water pressure acting on a tip  352  of the push cone device  300  so that a net pressure on the tip  352  is negligible (the term negligible is understood in this application as meaning less than 10% of the current hydrostatic water pressure where the measurement is taking place), a step  904  of pushing the tip  352  into the ground, and a step  906  of measuring with a differential pressure sensor  370  the pressure associated with a penetration resistance generated by the ground against the tip. The differential pressure sensor  370  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. 
     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.