阅读说明：本技术 一种水合物诱发海底失稳的原位实时监测装置及方法 (In-situ real-time monitoring device and method for hydrate induced seabed instability ) 是由 贾永刚 孙志文 郭秀军 刘涛 单红仙 范智涵 宋晓帅 薛凉 于 2020-06-29 设计创作，主要内容包括：本发明公开了一种水合物诱发海底失稳的原位实时监测装置及方法,属于海洋地质探测领域。本发明包括测试探杆,测试探杆上设置若干电极环和若干孔压传感器；测试探杆的底部为锥形头；测试探杆上部固定设置有配重、水声通讯机一、采集控制仓、电源仓以及吊环；采集控制仓内设有电阻率采集单元、孔压采集单元和下位机控制单元；电阻率采集单元分别与各电极环以及下位机控制单元通信连接；孔压采集单元分别与各孔压传感器以及下位机控制单元通信连接。电阻率计算得到的超孔隙水压力的变化与孔压传感器测量得到的超孔隙水压力的变化取最大值,根据该最大值判断海底失稳的可能性,进而对海底地质灾害进行监测预警。(The invention discloses an in-situ real-time monitoring device and method for hydrate-induced seabed instability, and belongs to the field of marine geological detection. The invention comprises a test probe rod, wherein a plurality of electrode rings and a plurality of pore pressure sensors are arranged on the test probe rod; the bottom of the test probe rod is a conical head; the upper part of the test probe rod is fixedly provided with a balance weight, an underwater acoustic communication machine I, an acquisition control bin, a power supply bin and a hanging ring; the acquisition control bin is internally provided with a resistivity acquisition unit, a pore pressure acquisition unit and a lower computer control unit; the resistivity acquisition unit is respectively in communication connection with each electrode ring and the lower computer control unit; the pore pressure acquisition unit is respectively in communication connection with each pore pressure sensor and the lower computer control unit. The maximum value of the change of the water pressure of the ultra-pore obtained by resistivity calculation and the change of the water pressure of the ultra-pore obtained by pore pressure sensor measurement is obtained, the possibility of seabed instability is judged according to the maximum value, and further the seabed geological disaster is monitored and early warned.)

1. The utility model provides an in situ real-time monitoring device of hydrate induced seabed unstability, includes test probe rod, its characterized in that: the test probe rod is provided with a plurality of electrode rings which are longitudinally distributed and a plurality of pore pressure sensors which are longitudinally distributed; the bottom of the test probe rod is a conical head; the upper part of the test probe rod is fixedly provided with a balance weight, an underwater acoustic communication machine I, an acquisition control bin, a power supply bin and a hanging ring; a resistivity acquisition unit, a pore pressure acquisition unit and a lower computer control unit are arranged in the acquisition control bin; the resistivity acquisition unit is respectively in communication connection with each electrode ring and the lower computer control unit; the pore pressure acquisition unit is respectively in communication connection with each pore pressure sensor and the lower computer control unit; and the lower computer control unit is in communication connection with the deck unit through a sea surface communication buoy.

2. The in-situ real-time monitoring device for hydrate-induced seafloor instability of claim 1, wherein: the sea surface communication buoy is provided with a buoy control unit and an underwater acoustic communication machine II; the underwater sound communication machine II is respectively in communication connection with the underwater sound communication machine I and the buoy control unit; the buoy control unit is in communication connection with the deck control unit through a Beidou satellite communication machine.

3. The in-situ real-time monitoring device for hydrate-induced seafloor instability of claim 1, wherein: the lower computer control unit is an FPGA chip which is connected with an ARM processor and supports SOPC.

4. The in-situ real-time monitoring device for hydrate-induced seafloor instability of claim 1, wherein: the buoy control unit is an FPGA chip which is connected with an ARM processor and supports SOPC.

5. An in-situ real-time hydrate induced seafloor instability monitoring device as claimed in any one of claims 1 to 4, wherein: at least 30 electrode rings are arranged; at least 6 pore pressure sensors are provided.

6. An in-situ real-time hydrate induced seafloor instability monitoring device as claimed in any one of claims 1 to 4, wherein: each electrode ring is arranged at the upper part of the test probe rod; each pore pressure sensor is arranged at the lower part of the test probe rod.

7. A method for real-time monitoring of hydrate-induced seafloor instability using the apparatus of claim 1, wherein:

1) calculating the saturation of the natural gas hydrate and the change of the water pressure of the excess pore according to the resistivity

Obtained according to the Archie's formula

R_w2＝R_w1(T₁+21.5)/(T₂+21.5)

Wherein a and m are Archie constants and phi is sediment porosity which can be obtained by sediment sampling determination, and R is₀Is the saturated water formation resistivity; r_w1、R_w2At a temperature of T₁、T₂Pore water resistivity at a certain salinity;

the hydrate saturation was calculated according to the following formula

In the formula, S_HIs the hydrate saturation; n is a saturation index, and n is 1.7 for unconsolidated formations; r_tThe resistivity obtained for the measurement;

the amount of water before decomposition is

In the formula, n_w0The amount of material that is water prior to hydrate decomposition; rho_w＝1g/cm³Is the density of water; m_wAmount of substance(s) water (18 g/mol), V_HIs the volume of hydrate; v_vIs the volume of the pores; s_HIs the hydrate saturation;

suppose that: 1m³Natural gas hydrate CH₄·nH₂Decomposition of O to N_gmol of gas and N_wmol of water, i.e. V_gm³Gas and V_wm³Of the amount of the substance of water after decomposition of natural gas hydrate of (1) is changed to

n_w＝n_w0+N_w

In the formula, n_wThe amount of material that is the total water after hydrate decomposition; n is a radical of_wThe amount of material that is added water after hydrate decomposition;

the amount of the substance of methane gas after hydrate decomposition is changed to

n_gi＝N_g-n_gs

n_gs＝n_w×s_g

In the formula, n_giConsidering the amount of methane gas species in the pores after methane dissolution for hydrate decomposition; n is a radical of_gThe amount of methane gas species in the pores for the purpose of hydrate decomposition without regard to methane dissolution; n is_gsThe amount of dissolved substances in water of methane gas generated after hydrate decomposition; s_gIs the solubility of methane gas;

according to the ideal state gas equation, i.e.

PV＝nRT

In the formula, P is the pressure of ideal gas; v is the volume of the ideal gas; n is the amount of species of the desired gas; r is the gas constant of an ideal gas; t is the thermodynamic temperature of the ideal gas; of methane gas under standard conditions

P_s＝1.013×10²kPa，T_s＝298.15K；

In the formula, P_sThe pressure of the gas in a standard state; v_sIs the volume of gas at standard conditions; t is_sIs the temperature of the gas in the standard state; p_aThe pressure of the gas after the hydrate is decomposed; v_aThe volume of gas after hydrate decomposition; t is_aIs the temperature of the gas after hydrate decomposition;

thus, the amount of change in volume before and after the decomposition of the hydrate, i.e., the amount of change in volume after the decomposition of the hydrate can be obtained

ΔV＝V_a+V_w-V_H

In the formula, Δ V is the change in volume after hydrate decomposition; v_HVolume of decomposed natural gas hydrates;

according to the definition of the soil compression modulus and the relation between the soil compression modulus and the elastic modulus and the Poisson ratio, the volume change and the effective stress change after the hydrate decomposition are established, namely

In the formula, E_sThe compression modulus of the soil body; sigma_zThe vertical effective stress of the soil body;_zeffective strain is vertical to the soil body; delta sigma_zThe change of the vertical effective stress of the soil body; delta_zThe change of the vertical effective strain of the soil body; v is the initial volume of hydrate; e is the elastic modulus of the soil body; mu is the Poisson's ratio of the soil body;

according to the principle of effective stress, the change of the excess pore water pressure Δ u is equal to the change of the effective stress, i.e. the change of the effective stress

Δu＝-Δσ_z

In the formula, delta u is the calculated change of the water pressure of the hyper-pores;

2) judging whether seabed instability is caused according to the calculated change of the excess pore water pressure and the tested excess pore water pressure

The method comprises the following steps:

when the hyperstatic excess pore water pressure is greater than the overlying effective stress, the seabed instability is caused, namely

max{Δu，Δu_m}＞σ_z＝ρgH

In the formula, rho is the density of the overlying sediments of the hydrate, and g is the gravity acceleration; h is the depth of the overlying deposit; Δ u_mThe change of the excess pore water pressure measured by the pore pressure sensor;

or the second method:

according to the rigid body limit balance method, assuming that the sliding surface is circular arc-shaped, the sliding body slides along the circular arc surface, and when the moment causing the sliding is larger than the moment resisting the sliding, i.e., K < 1, the submarine landslide, i.e., the sliding occurs

In the formula, K is a sliding safety coefficient; w_iα for gravity of overlying sediment_iIs the included angle between the vertical direction of the sliding slope surface and the normal direction; phi is a_iIs an internal friction angle; c. C_iIs cohesive force; l_iIs the length of the sliding slope surface; delta u is the calculated change in excess pore water pressure; Δ u_mThe change in excess pore water pressure measured for the pore pressure sensor.

Technical Field

The invention relates to the field of marine geological detection, in particular to an in-situ real-time monitoring device and method for hydrate-induced seabed instability.

Background

Natural gas hydrate is a novel unconventional alternative energy source, and is mostly located in shallow sediments of deep-water continental shelves. Decomposition of hydrate (1 m)³Decomposition of the natural hydrate solid yields approximately 164m³And methane gas of 0.8m³Water) can cause the increase of the pore water pressure of sediments, the effective stress is reduced, and seabed instability conditions such as seabed landslide and the like are easily induced, so that tsunami is caused, and the production and life safety of human beings is threatened.

At present, the exploitation of natural gas hydrate is very fierce globally, and the exploitation of perhydrate is carried out in the united states, japan and china, but the in-situ monitoring of hydrate exploitation is only limited to temperature, pressure, methane concentration and the like, and at present, no device and method specially used for in-situ monitoring of hydrate induced seabed instability exists.

Disclosure of Invention

In order to make up for the defects of the prior art, the invention provides an in-situ real-time monitoring device and method for hydrate-induced seabed instability.

The technical scheme of the invention is as follows:

an in-situ real-time monitoring device for hydrate induced seabed instability comprises a test probe rod, wherein a plurality of electrode rings which are longitudinally distributed and a plurality of pore pressure sensors which are longitudinally distributed are arranged on the test probe rod; the bottom of the test probe rod is a conical head; the upper part of the test probe rod is fixedly provided with a balance weight, an underwater acoustic communication machine I, an acquisition control bin, a power supply bin and a hanging ring; a resistivity acquisition unit, a pore pressure acquisition unit and a lower computer control unit are arranged in the acquisition control bin; the resistivity acquisition unit is respectively in communication connection with each electrode ring and the lower computer control unit; the pore pressure acquisition unit is respectively in communication connection with each pore pressure sensor and the lower computer control unit; and the lower computer control unit is in communication connection with the deck unit through a sea surface communication buoy.

As a preferred scheme, a buoy control unit and an underwater acoustic communication machine II are arranged on the sea surface communication buoy; the underwater sound communication machine II is respectively in communication connection with the underwater sound communication machine I and the buoy control unit; the buoy control unit is in communication connection with the deck control unit through a Beidou satellite communication machine.

Preferably, the lower computer control unit is an FPGA chip supporting SOPC and connected with an ARM processor.

As a preferred scheme, the buoy control unit is an FPGA chip which is connected with an ARM processor and supports SOPC.

Preferably, at least 30 electrode rings are provided; at least 6 pore pressure sensors are provided.

As a preferred scheme, each electrode ring is arranged at the upper part of the test probe rod; each pore pressure sensor is arranged at the lower part of the test probe rod.

The method for monitoring the hydrate induced seabed instability in real time by adopting the device comprises the following steps:

1) calculating the saturation of the natural gas hydrate and the change of the water pressure of the excess pore according to the resistivity

Obtained according to the Archie's formula

R_w2＝R_w1(T₁+21.5)/(T₂+21.5)

Wherein a and m are ArchieThe constant, phi, is the sediment porosity, and can be determined by sediment sampling, R₀Is the saturated water formation resistivity; r_w1、R_w2At a temperature of T₁、T₂Pore water resistivity at a certain salinity;

the hydrate saturation was calculated according to the following formula

In the formula, S_HIs the hydrate saturation; n is a saturation index, and n is 1.7 for unconsolidated formations; r_tThe resistivity obtained for the measurement;

the amount of water before decomposition is

In the formula, n_w0The amount of material that is water prior to hydrate decomposition; rho_w＝1g/cm³Is the density of water; m_wAmount of substance(s) water (18 g/mol), V_HIs the volume of hydrate; v_vIs the volume of the pores; s_HIs the hydrate saturation;

suppose that: 1m³Natural gas hydrate CH₄·nH₂Decomposition of O to N_gmol of gas and N_wmol of water, i.e. V_gm³Gas and V_wm³Of the amount of the substance of water after decomposition of natural gas hydrate of (1) is changed to

n_w＝n_w0+Nw

In the formula, n_wThe amount of material that is the total water after hydrate decomposition; n is a radical of_wThe amount of material that is added water after hydrate decomposition;

the amount of the substance of methane gas after hydrate decomposition is changed to

n_gi＝N_g-n_gs

n_gs＝n_w×s_g

In the formula, n_giFor hydrationThe amount of methane gas in the pores after dissolution of methane is taken into account after decomposition of the product; n is a radical of_gThe amount of methane gas species in the pores for the purpose of hydrate decomposition without regard to methane dissolution; n is_gsThe amount of dissolved substances in water of methane gas generated after hydrate decomposition; s_gIs the solubility of methane gas;

according to the ideal state gas equation, i.e.

PV＝nRT

In the formula, P is the pressure of ideal gas; v is the volume of the ideal gas; n is the amount of species of the desired gas; r is the gas constant of an ideal gas; t is the thermodynamic temperature of the ideal gas; of methane gas under standard conditions

P_s＝1.013×10²kPa，T_s＝298.15K；

In the formula, P_sThe pressure of the gas in a standard state; v_sIs the volume of gas at standard conditions; t is_sIs the temperature of the gas in the standard state; p_aThe pressure of the gas after the hydrate is decomposed; v_aThe volume of gas after hydrate decomposition; t is_aIs the temperature of the gas after hydrate decomposition;

thus, the amount of change in volume before and after the decomposition of the hydrate, i.e., the amount of change in volume after the decomposition of the hydrate can be obtained

ΔV＝V_a+V_w-V_H

In the formula, Δ V is the change in volume after hydrate decomposition; v_HVolume of decomposed natural gas hydrates;

according to the definition of the soil compression modulus and the relation between the soil compression modulus and the elastic modulus and the Poisson ratio, the volume change and the effective stress change after the hydrate decomposition are established, namely

In the formula, E_sThe compression modulus of the soil body; sigma_zThe vertical effective stress of the soil body;_zeffective strain is vertical to the soil body; delta sigma_zThe change of the vertical effective stress of the soil body; delta_zThe change of the vertical effective strain of the soil body; v is the initial volume of hydrate; e is the elastic modulus of the soil body; mu is the Poisson's ratio of the soil body;

according to the principle of effective stress, the change of the excess pore water pressure Δ u is equal to the change of the effective stress, i.e. the change of the effective stress

Δu＝-Δσ_z

In the formula, delta u is the calculated change of the water pressure of the hyper-pores;

2) judging whether seabed instability is caused according to the change of the excess pore water pressure and the tested excess pore water pressure

The method comprises the following steps:

when the hyperstatic excess pore water pressure is greater than the overlying effective stress, the seabed instability is caused, namely

max{Δu，Δu_m}＞σ_z＝ρgH

In the formula, rho is the density of the overlying sediments of the hydrate, and g is the gravity acceleration; h is the depth of the overlying deposit; Δ u_mThe change of the excess pore water pressure measured by the pore pressure sensor;

or the second method:

according to the rigid body limit balance method, assuming that the sliding surface is circular arc-shaped, the sliding body slides along the circular arc surface, and when the moment causing the sliding is larger than the moment resisting the sliding, i.e., K < 1, the submarine landslide, i.e., the sliding occurs

In the formula, K is a sliding safety coefficient; w_iα for gravity of overlying sediment_iIs the included angle between the vertical direction of the sliding slope surface and the normal direction; phi is a_iIs an internal friction angle; c. C_iIs cohesive force; l_iIs the length of the sliding slope surface; is measured by delta uCalculating the change of the water pressure of the excess pore; Δ u_mThe change of the excess pore water pressure measured by the pore pressure sensor; i is the ith bar calculated in the bar method.

The invention has the beneficial effects that:

1. the device can measure and obtain the resistivity of the submarine sediments, and the saturation of the hydrate is obtained through the resistivity inversion of the hydrate in the submarine sediments. The volume change before and after the hydrate decomposition can be obtained through inversion according to the saturation of the hydrate, and then the change of the water pressure of the super-pore is obtained.

Meanwhile, the device can measure and obtain the change of the excess pore water pressure of the seabed sediments.

The maximum value of the change of the water pressure of the ultra-pore obtained by resistivity calculation and the change of the water pressure of the ultra-pore obtained by pore pressure sensor measurement is obtained, the possibility of seabed instability is judged according to the maximum value, and further the seabed geological disaster is monitored and early warned.

Meanwhile, the change of the water pressure of the super-pore obtained by resistivity calculation and the change of the water pressure of the super-pore obtained by pore pressure sensor measurement can be verified mutually.

2. The device has a simplified structure, all equipment is concentrated on one rod, and the resistivity probe rod and the hole pressure probe rod are arranged on one rod, so that the device is more convenient to penetrate compared with more than two rods; adopt gravity injection, avoided hydraulic pressure injection the possibility that breaks down, single pole compares many poles and injects more easily simultaneously, and is with low costs, and accessible acoustics UNICOM carries out extensive network deployment and puts, monitors the early warning to the seabed unstability that arouses in the large tracts of land scope, and the practicality is strong.

Drawings

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to these drawings without creative efforts.

FIG. 1 is a schematic structural diagram of an in-situ real-time monitoring device for hydrate-induced seafloor instability of the present invention;

FIG. 2 is a schematic top view of the structure of FIG. 1;

FIG. 3 is a schematic view of the connection relationship between the lower machine and the floating ball;

FIG. 4 is a schematic structural diagram of a surface communication buoy;

FIG. 5 is a top view of FIG. 4;

FIG. 6 is a control block diagram of a surface communication buoy;

FIG. 7 is a block diagram of the lower computer control of the present invention.

Wherein, 1-battery chamber; 2-hoisting rings; 3, collecting a control bin; 4-underwater acoustic communicator I; 5-an electrode ring; 6-hole pressure probe rod; 7-a conical head; 8-pore pressure sensor; 9-resistivity probe; 10-counterweight of the lower machine; 11-a floating ball; 12-an underwater acoustic releaser; 13-floating ball counterweight; 14-a satellite communicator; 15-a protective frame; 16-underwater acoustic communicator II; 17-a buoy battery control cabin; 18-sea surface communication buoy; 19-solar panel.

Detailed Description