Longitudinal wave velocity measurement apparatus and method for drilling shallow gas formations in deep water

Abstract

The application provides a longitudinal wave velocity measuring device and method for drilling a shallow gas containing formation in deep water, wherein the device comprises a reaction kettle, a controllable pressure tight gas bag, a confining pressure control system and an acoustic wave testing system. A simulated seabed formation is laid in the reaction kettle, and the simulated seabed formation comprises a normal formation and a shallow gas formation. Experimental soil is encapsulated in the controllable pressure tight gas bag to simulate the shallow gas formation. Valves, gas pressurizing equipment and liquid pressurizing equipment are arranged on the controllable pressure tight gas bag, and the confining pressure control system is arranged around the reaction kettle. The acoustic wave testing system is arranged on the reaction kettle and the controllable pressure tight gas bag respectively. The measuring device and method provided by the application can measure the propagation velocity of longitudinal waves in the normal formation and the shallow gas bag with different pressure levels, realize the measurement of the longitudinal wave velocity of the different pressure shallow gas containing formation in the laboratory, establish the quantitative relationship between the shallow gas pressure and the longitudinal wave velocity, and lay a foundation for the quantitative identification of the deep water shallow gas pressure.

Description

Technical Field

[0001] This invention relates to the field of drilling engineering technology, and more specifically to a device and method for measuring longitudinal wave velocity in deep-water drilling formations containing shallow gas. Background Technology

[0002] Shallow gas typically refers to overpressured gas accumulated within 800 meters below the seabed in the deep sea. It is generally difficult to extract as a resource and is widely distributed in shallow strata of the deep seabed. Due to its difficulty in prediction, shallow burial, high pressure, rapid eruption velocity, and limited well control methods, it can easily lead to major operational accidents such as well blowouts and platform sinking. Therefore, the identification of shallow gas is of great significance for ensuring the safety of drilling projects. Shallow gas exists primarily in the form of gas in the formation, altering the physical properties of the rocks and forming a multiphase high-pressure mixture composed of caprock, mud, sand, fluids, and gases. This significantly changes the propagation velocity of P-waves. Typically, the P-wave velocity in shallow gas-bearing strata is 800–1000 m / s, which is 20%–50% lower than the propagation velocity in normal strata. Therefore, identifying shallow gas by analyzing changes in P-wave velocity in seismic data is currently the most effective method. However, current shallow gas identification mainly relies on qualitative identification of features such as "gas chimneys," "bright spot reflections," and "blank zones" in three-dimensional high-precision seismic profiles. It lacks a quantitative identification method for shallow gas pressure, which is of utmost concern in drilling operations. It is impossible to establish the relationship between shallow gas pressure and P-wave velocity in the laboratory. Once a suspected risk is detected, the well site must be moved to avoid it, which increases the difficulty of operation and the cost of avoidance.

[0003] Existing testing devices cannot quantitatively control the pressure of shallow gas and shallow water flow, nor can they establish the relationship between shallow gas overpressure and longitudinal wave velocity under different confining pressures (i.e., shallow gas burial depth). Summary of the Invention

[0004] The technical problem to be solved by the present invention is to overcome the shortcomings of the prior art and provide a device and method for measuring the longitudinal wave velocity in shallow gas-bearing formations in deep water drilling. This device and method simulate shallow gas-bearing formations with different pressures and establish a quantitative relationship between the longitudinal wave velocity and the shallow gas pressure, which is of great significance for the identification of shallow gas in deep water drilling.

[0005] To solve the above-mentioned technical problems, the technical solution proposed by this invention is as follows:

[0006] A device for measuring the longitudinal wave velocity in deep-water drilling formations containing shallow gas includes a reaction vessel, a pressure-controlled sealed airbag, a confining pressure control system, and an acoustic wave testing system. The reaction vessel is lined with simulated seafloor formations, including normal formations and shallow gas-bearing formations. The pressure-controlled sealed airbag contains experimental soil to simulate shallow gas-bearing formations. The pressure-controlled sealed airbag is equipped with valves, gas pressurization equipment, and liquid pressurization equipment. The confining pressure control system is arranged around the reaction vessel. The acoustic wave testing system is positioned on both the reaction vessel and the pressure-controlled sealed airbag.

[0007] The present invention relates to a device for measuring the P-wave velocity in deep-water drilling formations containing shallow gas. This device uses a high-pressure, low-temperature, sealed reactor to simulate the deep-water working environment. It applies confining pressure to simulate different working water depths and overlying rock pressures. Saturated sand-clay mixture is laid inside the reactor to simulate seabed formations, and a controllable-pressure sealed airbag capable of quantitatively filling with gas and water is implanted within it to simulate shallow gas. The pressure inside the controllable-pressure sealed airbag is adjusted to simulate abnormally high shallow gas pressure. An acoustic wave testing system is used to measure the propagation velocity of P-waves in normal formations and in airbags containing shallow gas at different pressure levels. This enables laboratory measurement of the P-wave velocity in shallow gas-containing formations at different pressures, establishing a quantitative relationship between shallow gas pressure and P-wave velocity, and laying the foundation for the quantitative identification of shallow gas pressure in deep water.

[0008] The above technical solution can be further improved as described below.

[0009] In a preferred embodiment of the longitudinal wave velocity measuring device for deep-water drilling formations containing shallow gas according to the present invention, the sealing boundary of the pressure-controlled sealed airbag is made of neoprene rubber.

[0010] Using the above-mentioned material as the sealing boundary material of the controllable pressure sealed airbag is particularly suitable for manufacturing components of acoustic testing instruments because the longitudinal wave propagates slowly in the rubber material, and the rubber material has good sound transmission performance and strong pressure resistance. It is easy to identify the acoustic signal of the longitudinal wave passing through the medium inside the sealed airbag.

[0011] Furthermore, in a preferred embodiment, both the top and bottom of the reaction vessel and the controllable pressure sealed airbag are provided with metal top rods for fixing the acoustic wave testing system.

[0012] During the experiment, the metal push rod allows the acoustic testing system to be placed in close contact with both ends of the reaction vessel and the controllable pressure sealed airbag.

[0013] Specifically, in a preferred embodiment, the gas booster device includes a high-pressure gas flow meter.

[0014] The gas pressurization device with the above-mentioned structure facilitates the injection of gas into the sealed airbag to pressurize it, simulating the overpressure environment of shallow air, and can accurately control the pressure inside the sealed airbag in real time.

[0015] Specifically, in a preferred embodiment, the acoustic wave testing system includes an acoustic wave transmitter, an acoustic wave receiver, and a data acquisition card. The acoustic wave transmitter includes a single-pulse transmitting card for transmitting ultrasonic signals. The acoustic wave transmitter and receiver are respectively positioned at opposite ends of the reaction vessel and the pressure-controlled sealed airbag. The data acquisition card is used to convert the ultrasonic signals received by the acoustic wave receiver into digital waveforms and record them.

[0016] The above-described acoustic wave testing system is easy to place on the reactor and the controllable pressure sealed airbag, and can measure the acoustic wave characteristics of the entire formation and the shallow gas formation. The ultrasonic signal is emitted by the acoustic wave transmitter, passes through the entire formation and the shallow gas formation to be tested, and is received by the acoustic wave receiver. The signal is then converted into a digital waveform by the data acquisition card and recorded.

[0017] Furthermore, in a preferred embodiment, the acoustic wave testing system further includes a processing module for receiving digital waveform curve data recorded by the data acquisition card and adding a preset reduction coefficient interpolation correction to the high-frequency sound velocity measurement results.

[0018] Since indoor acoustic characteristic testing experiments primarily use ultrasound, with emission frequencies typically ranging from 200 to 500 kHz, while the acoustic waves used in actual seismic exploration are low-frequency, usually operating below 2 kHz, different frequencies of sound waves may exhibit varying propagation velocities and attenuation rates within sediments—a phenomenon known as dispersion. Based on the sound velocity dispersion predictions from the Biot-Stoll model, the sound velocity in seabed sediments increases by approximately 1% to 3.5% with increasing frequency. This increase is relatively small; therefore, the digitized waveform data recorded by the data acquisition card needs to be input into the data processing software to add appropriate reduction coefficients for interpolation correction of the high-frequency sound velocity measurements, ensuring the accuracy of the sound velocity measurements.

[0019] Specifically, in a preferred embodiment, both the acoustic wave transmitter and the acoustic wave receiver are made of piezoelectric composite material.

[0020] The acoustic transmitter and receiver are made of piezoelectric composite material, which has excellent pressure resistance and waterproof sealing performance, making it particularly suitable for measuring longitudinal wave velocity in deep-water drilling formations containing shallow gas.

[0021] The second aspect of the present invention provides a method for measuring the longitudinal wave velocity of shallow gas-bearing formations in deep-water drilling, implemented using the aforementioned measuring device, comprising the following steps: S01, laying a simulated seafloor formation inside a reactor and arranging an implantable, controllable-pressure sealed airbag inside the reactor; S02, lowering the temperature inside the reactor to a preset temperature, the preset temperature being the temperature of the deep-sea seabed; S03, arranging a confining pressure control system around the reactor; and arranging an acoustic wave testing system on the reactor and the controllable-pressure sealed airbag; S04, applying a confining pressure within a preset range to the reactor using the confining pressure control system to simulate different operating water depths and overlying rock pressures, and then using a gas pressurization device to inject gas into the controllable-pressure sealed airbag to pressurize it to a preset pressure range to simulate shallow gas overpressure conditions; S05, using the acoustic wave measurement system to test the longitudinal wave velocity of shallow gas under different confining pressures and shallow gas overpressure conditions.

[0022] Clearly, by employing the aforementioned measurement device, and simulating shallow gas-bearing strata using a high-pressure reactor and an implanted, controllable, sealed airbag, the pressure levels of shallow gas and the confining pressure of the seabed strata can be realistically simulated, significantly improving the accuracy of the test. This allows for the quantitative measurement of the relationship between shallow gas pressure and P-wave velocity in the laboratory, providing an important foundation for the quantitative identification of shallow gas pressure in the deep seabed.

[0023] The above technical solution can be further improved as described below.

[0024] According to a preferred embodiment of the method for measuring longitudinal wave velocity in deep-water drilling formations containing shallow gas strata, step S01 of the present invention includes the following sub-steps: S011, firstly, select the experimental soil, which is then exposed to the sun, crushed, and sieved. S012, add the selected soil sample into the reaction vessel, adding water for every 0.2m of soil sample added. After the water covers the soil sample, vibrate it with a vibrator for a preset time. Then, place a heavy object on the soil sample surface to apply pressure and allow it to stand for a preset time. S013, after spreading the soil to half its height in the reaction vessel, place a controllable pressure sealed airbag on the soil layer, fill the controllable pressure sealed airbag with soil, seal the valve, fix the acoustic wave detection system on the controllable pressure sealed airbag, and continue filling the soil until the reaction vessel is completely filled. S014, allow it to stand for a preset time.

[0025] Furthermore, in a preferred embodiment, the measurement method of the present invention further includes step S015: after the configuration is completed, the soil sample is taken out and tested for dry density, moisture content, plastic limit, liquid limit, plasticity index and other indicators of the configured soil sample through a constant temperature drying oven, a photoelectric liquid limit and plastic limit combined tester and a strain-controlled direct shear tester, so that its main parameters are the same as those of the actual deep seabed soil.

[0026] By using remolded soil to simulate seabed soil, and by controlling the particle size, dry density, moisture content of the sand used in the test, as well as the physical properties of the clay such as plastic limit, liquid limit, and plasticity index, the soil conditions of the deep seabed can be made to be close to those of the deep seabed, which can greatly ensure the accuracy of the test results.

[0027] Compared with existing technologies, the advantages of this invention are: it can measure the propagation speed of P-waves in normal formations and shallow gas bladders of different pressure levels, realize the measurement of P-wave velocity in shallow gas-bearing formations at different pressures in the laboratory, establish a quantitative relationship between shallow gas pressure and P-wave velocity, and lay the foundation for the quantitative identification of shallow gas pressure in deep water. Attached Figure Description

[0028] The invention will now be described in more detail with reference to embodiments and the accompanying drawings.

[0029] Figure 1 The schematic diagram illustrates the frame structure and principle of the measuring device of Embodiment 1 of the present invention;

[0030] Figure 2 The schematic diagram shows the frame structure of the controllable pressure sealed airbag in Embodiment 1 of the present invention;

[0031] Figure 3 The schematic diagram illustrates the frame structure of the acoustic wave testing system in Embodiment 1 of the present invention;

[0032] Figure 4 The diagram illustrates the relationship between shallow air pressure and longitudinal wave velocity under different confining pressures in Embodiment 2 of the present invention. Detailed Implementation

[0033] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments, but this does not limit the scope of protection of the present invention.

[0034] Figure 1 The schematic diagram illustrates the frame structure and principle of the measuring device 10 of Embodiment 1 of the present invention. Figure 2 The schematic diagram shows the frame structure of the controllable pressure sealed airbag 2 in Embodiment 1 of the present invention. Figure 3 The schematic diagram illustrates the framework structure and principle of the acoustic wave testing system 4 in Embodiment 1 of the present invention. Figure 4 The diagram illustrates the relationship between shallow air pressure and longitudinal wave velocity under different confining pressures in Embodiment 2 of the present invention.

[0035] Example 1

[0036] like Figure 1 and Figure 2As shown, the P-wave velocity measuring device 10 for deep-water drilling in shallow gas-bearing formations according to an embodiment of the present invention includes a reaction vessel 1, a pressure-controlled sealed airbag 2, a confining pressure control system 3, and an acoustic wave testing system 4. The reaction vessel 1 is filled with a simulated seafloor formation 5, which includes a normal formation 51 and a shallow gas-bearing formation 52. The pressure-controlled sealed airbag 2 is encapsulated with experimental soil to simulate the shallow gas-bearing formation 52. The pressure-controlled sealed airbag 2 is equipped with a valve 21, a gas pressurization device 22, and a liquid pressurization device 23. The confining pressure control system 3 is arranged around the reaction vessel 1. The acoustic wave testing system 4 is arranged on both the reaction vessel 1 and the pressure-controlled sealed airbag 2.

[0037] The P-wave velocity measurement device for deep-water drilling formations containing shallow gas, according to embodiments of the present invention, simulates the deep-water operating environment using a high-pressure, low-temperature, sealed reactor. It simulates different operating water depths and overlying rock pressures by applying confining pressure. Saturated sand-clay mixture is laid inside the reactor to simulate seafloor formations, and a controllable-pressure sealed airbag capable of quantitatively filling with gas and water is implanted within it to simulate shallow gas. The pressure inside the controllable-pressure sealed airbag is adjusted to simulate abnormally high shallow gas pressure. An acoustic wave testing system is used to measure the propagation velocity of P-waves in normal formations and in airbags containing shallow gas at different pressure levels. This enables laboratory measurement of P-wave velocities in formations containing shallow gas at different pressures, establishing a quantitative relationship between shallow gas pressure and P-wave velocity, and laying the foundation for the quantitative identification of shallow gas pressure in deep water.

[0038] Specifically, in this embodiment, the high-pressure reactor 1 is a barrel-shaped container with an inner diameter of 0.5m, a height of 1.5m, and an effective volume of 129.5L. Its maximum static pressure is 30MPa. The temperature of reactor 1 is controlled by a low-temperature constant-temperature water bath, with a temperature control range of -10℃ to 30℃, simulating the temperature environment of the seabed. The confining pressure control system 3 can apply a maximum confining pressure of 20MPa to simulate different operating water depths and overlying rock pressures. Reconstituted soil is used to simulate seabed soil. By controlling the particle size distribution, dry density, and moisture content of the experimental sand, as well as the plastic limit, liquid limit, and plasticity index of the clay, the soil conditions are made close to those of the deep seabed.

[0039] Specifically, in this embodiment, the implantable pressure-controlled closed-circuit airbag 2 is a cylindrical sealed envelope with dimensions of Ф0.5m × 0.3m. Specifically, in this embodiment, the envelope boundary of the pressure-controlled closed-circuit airbag 2 is made of neoprene rubber. Using this material as the envelope boundary material of the pressure-controlled closed-circuit airbag is advantageous because longitudinal waves propagate slowly in rubber materials, and rubber materials possess good sound transmission properties and strong pressure resistance, making them particularly suitable for manufacturing components of acoustic testing instruments. This facilitates the identification of acoustic signals from longitudinal waves passing through the medium inside the closed-circuit airbag.

[0040] like Figure 3As shown, specifically in this embodiment, the acoustic wave testing system 4 includes an acoustic wave transmitter 41, an acoustic wave receiver 42, and a data acquisition card 43. The acoustic wave transmitter 41 includes a single-pulse transmitting card 411 for emitting ultrasonic signals. The acoustic wave transmitter 41 and the acoustic wave receiver 42 are respectively arranged at both ends of the reaction vessel 1 and the controlled-pressure sealed airbag 2. The data acquisition card 43 is used to convert the ultrasonic signals received by the acoustic wave receiver 42 into digital waveforms and record them. This acoustic wave testing system with the above-described structure is easy to arrange on the reaction vessel and the controlled-pressure sealed airbag, and can measure the acoustic characteristics of all formations and shallow gas formations. The ultrasonic signal is emitted by the acoustic wave transmitter, passes through all formations and the shallow gas formation to be tested, is received by the acoustic wave receiver, and is converted into a digital waveform by the CompuSope 14100 data acquisition card and recorded in the computer. Since the acquisition card is a dual-channel digital card with a high digitization rate of 50MS / s and a digital transmission rate of up to 80MB / s, given its high digitization rate and high digital transmission rate, it is considered that its error in waveform acquisition and speed discrimination can be ignored.

[0041] like Figure 3 As shown, in this embodiment, the acoustic wave testing system 4 further includes a processing module 44, used to receive the digitized waveform curve data recorded by the data acquisition card 43 and add a preset reduction coefficient interpolation correction to the high-frequency sound velocity measurement results. Since indoor acoustic wave characteristic testing experiments primarily use ultrasound, the sound wave emission frequency is typically between 200 and 500 kHz. However, the sound waves used in actual seismic exploration are low-frequency sound waves, usually operating at frequencies below 2 kHz. Therefore, different frequencies of sound waves may exhibit different propagation speeds and sound attenuation in sediments, i.e., dispersion. The sound velocity dispersion results predicted based on the Biot-Stoll model, compared with those from the most representative in-situ measurement of seabed sediments in the northern Gulf of Mexico SAX99 experiment (Williams et al., 2002) and in-situ acoustic measurements of low-to-medium frequency (300Hz–34kHz) seabed sediments in my country, show that the sound velocity in seabed sediments increases by about 1%–3.5% with increasing frequency. This increase is relatively small. Therefore, it is necessary to input the digitized waveform data recorded by the data acquisition card into the data processing software and add corresponding reduction coefficients for interpolation correction to the high-frequency sound velocity measurement results to ensure the accuracy of the sound velocity measurement results. Preferably, the processing module 44 includes analysis and processing software.

[0042] like Figure 1As shown, specifically in this embodiment, a total of three sets of acoustic wave transmitters 41 and acoustic wave receivers 42 are provided. Two sets are installed on the top and bottom of the reactor 1 to measure the acoustic characteristics of all formations, and the remaining set is installed on the top and bottom of the implanted pressure-controlled sealed airbag 2 to measure the acoustic characteristics of shallow gas formations. Both the acoustic wave transmitters 41 and acoustic wave receivers 42 are made of piezoelectric composite materials. The use of piezoelectric composite materials in the acoustic wave transmitters and receivers provides excellent pressure resistance and waterproof sealing performance, making them particularly suitable for measuring the P-wave velocity in deep-water drilling formations containing shallow gas. The P-wave acoustic wave transmitters 41 and 42 operate at frequencies of 200kHz and 500kHz, respectively, and employ dual-channel simultaneous measurement to acquire the waveforms of both P-waves and S-waves.

[0043] Furthermore, in this embodiment, metal rods are provided at the top and bottom of both the reactor 1 and the controllable pressure sealed airbag 2 to fix the acoustic wave testing system. During the experiment, the metal rods allow the transmitting transducer and the receiving transducer to be tightly attached to both ends of the reactor and the airbag. The ultrasonic signal is emitted by the transmitting probe and received by the receiving probe after passing through the shallow gas layer to be tested.

[0044] Specifically, in a preferred embodiment, the gas pressurization device includes a high-pressure gas flow meter. This gas pressurization device, with its aforementioned structure, facilitates the injection of gas into a sealed gas bladder to simulate the overpressure environment of shallow gas, and enables real-time and precise control of the pressure within the sealed gas bladder. Specifically, sand-clay mixtures of different porosities and densities are compacted, sealed, and implanted into a high-pressure, low-temperature reactor. The seal is equipped with a valve connecting to the interior of the reactor. Opening the valve allows the pressure and temperature environment of the gas bladder to match that of the reactor. Closing the valve allows the high-pressure gas flow meter to inject gas into the sealed seal to simulate the overpressure environment of shallow gas. The high-pressure gas flow meter has a pressurization range of 0–10 MPa, a flow rate of 0–2000 mL / min, and a control accuracy of 0.2% FS.

[0045] Example 2

[0046] The method for measuring P-wave velocity in deep-water drilling formations containing shallow gas, according to an embodiment of the present invention, is implemented using the aforementioned measuring device 10 and includes the following steps: S01, simulating seabed formations is laid inside a reactor, and an implanted pressure-controlled sealed airbag is arranged inside the reactor. After fixing the acoustic transducers on the reactor and the airbag, the reactor lid is closed. S02, the temperature inside the reactor is lowered to 4°C (seabed temperature) using a low-temperature constant-temperature water bath. S03, a confining pressure control system is arranged around the reactor, and an acoustic testing system is arranged on the reactor and the pressure-controlled sealed airbag. S04. Using a confining pressure control system, apply a confining pressure within the range of 2–20 MPa to the reactor to simulate different operating water depths and overlying rock pressures, preferably 10–16 MPa. After the confining pressure is applied, use a high-pressure gas flow meter to inject gas into the controllable pressure sealed airbag to increase the pressure. The injected gas pressure level is 0.5 MPa–10 MPa to simulate shallow gas overpressure conditions. S05. Using an acoustic wave measurement system, test the longitudinal wave velocity of shallow gas under different confining pressures and shallow gas overpressure conditions. The test results are as follows: Figure 4 As shown.

[0047] Clearly, by employing the aforementioned measurement device, and simulating shallow gas-bearing strata using a high-pressure reactor and an implanted, controllable, sealed airbag, the pressure levels of shallow gas and the confining pressure of the seabed strata can be realistically simulated, significantly improving the accuracy of the test. This allows for the quantitative measurement of the relationship between shallow gas pressure and P-wave velocity in the laboratory, providing an important foundation for the quantitative identification of shallow gas pressure in the deep seabed.

[0048] According to an embodiment of the present invention, the method for measuring longitudinal wave velocity in deep-water drilling formations containing shallow gas, in a preferred embodiment, step S01 specifically includes the following sub-steps: S011, firstly, the experimental soil is initially selected, and then subjected to sun exposure, crushing, and sieving. S012, the initially selected soil sample is added to a high-pressure low-temperature reactor. To ensure the simulation of saturated soil, water is added every 0.2m of soil sample added. After the water covers the soil sample, it is vibrated with a vibrator for 10 minutes. Then, a large heavy object is placed on the soil sample surface for pressurization and static settling. After pressurization and static settling for 2 hours, the next layer of soil sample is placed. S013, after the soil is laid to half the height of the reactor, a controllable pressure sealed airbag is placed on the soil layer. After filling the controllable pressure sealed airbag with soil, the valve is sealed. The acoustic wave detection system on the controllable pressure sealed airbag is fixed, and soil is continued to be filled until the reactor is completely filled. S014. Allow the soil to stand for approximately 48 hours. During this period, the soil undergoes drainage and consolidation. Throughout the standing time, apply appropriate weights to the soil sample to simulate a pressure environment. S015. After preparation, remove the soil sample and test its dry density, moisture content, and the plastic limit, liquid limit, and plasticity index of the clay using a constant temperature drying oven, a photoelectric liquid limit and plastic limit tester, and a strain-controlled direct shear tester. Ensure that the main parameters are within 5% of the actual deep-sea seabed soil.

[0049] By using remolded soil to simulate seabed soil, and by controlling the particle size, dry density, moisture content of the sand used in the test, as well as the physical properties of the clay such as plastic limit, liquid limit, and plasticity index, the soil conditions of the deep seabed can be made to be close to those of the deep seabed, which can greatly ensure the accuracy of the test results.

[0050] As can be seen from the above embodiments, the P-wave velocity measuring device and method for deep-water drilling formations containing shallow gas, as disclosed in this invention, can measure the propagation velocity of P-waves in normal formations and in shallow gas bladders of different pressure levels. It realizes the measurement of P-wave velocities in shallow gas-containing formations at different pressures in the laboratory, establishes a quantitative relationship between shallow gas pressure and P-wave velocity, and lays the foundation for the quantitative identification of shallow gas pressure in deep water.

[0051] Although the invention has been described with reference to preferred embodiments, various modifications can be made and components can be replaced with equivalents without departing from the scope of the invention. In particular, the technical features mentioned in the various embodiments can be combined in any manner as long as there is no structural conflict. The invention is not limited to the specific embodiments disclosed herein, but includes all technical solutions falling within the scope of the claims.

Claims

1. A device for measuring compressional wave velocity in a shallow gas formation drilled in deep water, comprising: This includes a reaction vessel, a controllable pressure sealed airbag, a confining pressure control system, and an acoustic testing system; among which, The reactor is lined with a simulated seafloor stratum, which includes a normal stratum and a shallow gas stratum. The controllable pressure sealed airbag is filled with experimental soil to simulate the shallow gas formation. The controllable pressure sealed airbag is equipped with valves, gas pressurization equipment and liquid pressurization equipment; The confining pressure control system is arranged around the reactor; The acoustic wave testing system is respectively arranged on the reaction vessel and the controllable pressure sealed airbag, and the acoustic wave testing system includes an acoustic wave transmitter, an acoustic wave receiver, and a data acquisition card; wherein... The acoustic transmitter includes a single-pulse transmitting card for transmitting ultrasonic signals; The acoustic wave transmitter and the acoustic wave receiver are respectively arranged at both ends of the reaction vessel and the controllable pressure sealed airbag; The data acquisition card is used to convert the ultrasonic signals received by the acoustic receiver into digital waveforms and record them; The controllable pressure sealed airbag is placed inside the reactor. The normal ground layer is laid below and above the controllable pressure sealed airbag. The sound wave transmitters are all located on one side of the controllable pressure sealed airbag, and the sound wave receivers are all located on the other side of the controllable pressure sealed airbag. The acoustic wave testing system includes three sets of acoustic wave transmitters and receivers. Two sets are installed on the top and bottom of the reactor to measure the acoustic characteristics of all formations, and the remaining set is installed on the top and bottom of the implantable controllable pressure sealed airbag to measure the acoustic characteristics of shallow gas formations.

2. The apparatus for measuring compressional wave velocity in deep water drilling gas- bearing shallow formations of claim 1, wherein, The sealing boundary of the controllable pressure airbag is made of neoprene rubber.

3. The P-wave velocity measuring device for deep-water drilling formations containing shallow gas as described in claim 1 or 2, characterized in that, The top and bottom of both the reaction vessel and the controllable pressure sealed airbag are equipped with metal top rods for fixing the acoustic wave testing system.

4. The P-wave velocity measuring device for deep-water drilling in shallow gas-bearing formations according to claim 1 or 2, characterized in that, The gas booster device includes a high-pressure gas flow meter.

5. The P-wave velocity measuring device for deep-water drilling in shallow gas-bearing formations according to claim 1 or 2, characterized in that, The acoustic wave testing system also includes a processing module for receiving the digitized waveform curve data recorded by the data acquisition card and adding a preset reduction coefficient interpolation correction to the high-frequency sound velocity measurement results.

6. The P-wave velocity measuring device for deep-water drilling in shallow gas-bearing formations according to claim 1 or 2, characterized in that, Both the acoustic wave transmitter and the acoustic wave receiver are made of piezoelectric composite material.

7. A method for measuring P-wave velocity in deep-water drilling formations containing shallow gas, implemented using the measuring device described in any one of claims 1 to 6, characterized in that, Includes the following steps: S01. Lay a simulated seabed stratum inside the reactor and place an implantable, controllable, sealed airbag inside the reactor. S02. Reduce the temperature inside the reactor to the preset temperature, which is the temperature of the deep seabed. S03. Install a confining pressure control system around the reactor; install an acoustic wave testing system on the reactor and the controllable pressure sealed airbag; S04. Using the confining pressure control system, apply confining pressure within a preset range to the reactor to simulate different operating water depths and overlying rock pressures. Then, use a gas pressurization device to inject gas into the controllable pressure sealed airbag to pressurize it to the preset pressure range to simulate shallow gas overpressure conditions. S05. The longitudinal wave velocity of shallow air under different confining pressures and shallow air overpressure conditions was tested using an acoustic wave testing system.

8. The method for measuring P-wave velocity in deep-water drilling formations containing shallow gas, as described in claim 7, is characterized in that... Step S01 includes the following sub-steps: S011. First, the soil for the experiment is initially selected, and then exposed to the sun, crushed and sieved. S012. Add the pre-selected soil sample into the reactor. Add water for every 0.2m of soil sample added. After the water covers the soil sample, use a vibrator to vibrate it. After the preset vibration time, use a heavy object to pressurize and let it stand for the preset time. S013. After laying the soil to half the height inside the reactor, place the controllable pressure sealed airbag on the soil layer, fill the controllable pressure sealed airbag with soil, seal the valve, fix the acoustic wave testing system on the controllable pressure sealed airbag, and continue to fill the soil until the reactor is completely filled. S014. Preset storage time.

9. The method for measuring P-wave velocity in deep-water drilling formations containing shallow gas as described in claim 8, characterized in that, The process also includes step S015: After the soil sample is prepared, it is taken out and tested for dry density, moisture content, plastic limit, liquid limit, and plasticity index of the prepared soil sample using a constant temperature drying oven, a photoelectric liquid limit and plastic limit combined tester, and a strain-controlled direct shear tester, so that its parameters are the same as those of the actual deep-sea seabed soil.

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