CN101701955A - Experimental device and experimental method for simulating obvious stratum damage resulted from hydrate decomposition - Google Patents

Abstract

The invention discloses an experimental device for simulating obvious stratum damage resulted from the hydrate decomposition, comprising a model box with a top cover. A flow meter, a pore pressure meter, a temperature sensor, a heat source, monitoring equipment and a data acquiring and processing system are arranged in the model box. The invention also provides an experimental method for measuring the phase-change heat conduction at the periphery of the cylindrical hydrate deposit heat source and a method for analyzing the experimental result.

Description

Outstanding device and the experimental technique that destroys in the stratum that a kind of simulating hydrate decomposition causes

Technical field

The present invention relates to the decomposition of hydrate field, especially the experimental provision and the method for the stratum crash simulation that causes of decomposition of hydrate.

Background technology

Gas hydrate are under suitably high pressure and suitably low temperature conditions, the cage type crystalline compounds that the class of being made up of water and rock gas is iced.Gas hydrate extensively are distributed in the deepwater environment of continent, ocean and some interior lakes, are a kind of important potential resourcess.

Along with the minimizing of world's oil gas allowable exploitation and the increase of consumption, the urgency of deep sea hydrate exploitation is remarkable day by day.States such as the U.S., Japan, Canada have carried out the work of aspects such as a large amount of phase balance conditions, method of exploration, and have carried out pilot production.

Oil-gas mining, hydrate exploitation or natural conditions variation can cause decomposition of hydrate in the hydrate deposit layer.Decomposition of hydrate makes the rock soil medium in the sedimentary deposit lose splicing on the one hand, can change the structure of sedimentary deposit on the other hand, generates gas and can increase pore pressure again, thereby the intensity of this sedimentary deposit is reduced.The reduction of hydrate deposit layer intensity can cause multiple serious disaster, as because the destruction of works in sea that the well head surrounding soil large deformation that causes of decomposition of hydrate causes or the sea bed, as platform topple, oil gas well breaking-up etc.This disaster will produce serious harm to works in the sea bed, but the research of aspects such as its controlled variable and evolutionary process is also lacked very much.It is documented that the norwegian continental shelf edge is 2500～3200 cubic kilometers of sediments owing to slip altogether in the submarine slide (Storegga) that decomposition of hydrate takes place, is the submarine slide of the maximum found so far.A large amount of geologic examinations is that water temperature increases at that time with the reason that the analysis showed that this landslide of generation, and decomposition has taken place hydrate.The rapid decomposition of hydrate will cause multiple failure modes such as wide-spread decline, and may cause tsunami.

At present in the world for the achievement in research of this problem seldom, therefore field data still less must obtain the rule of seepage flow and thermal diffusion in the basic parameter, decomposable process of hydrate sediment at first by experiment, and the intensity etc. on stratum after the decomposition of hydrate.

And obtain condition, principal character and the phenomenon of the ground damage layer that hydrate causes by experiment, for engineering design provides foundation.

Summary of the invention

Decomposition of hydrate may cause the disaster that outstanding eruption destroys in the sediment, this experimental provision is mainly used in the thermal decomposition of simulation sediment hydrate, and under the condition that decomposition generation gas can not be discharged rapidly, the evolution rule of sedimentary deposit internal pressure temperature and decomposition of hydrate forward's propelling rule, the outstanding eruption that gases at high pressure cause after the exploration decomposition of hydrate destroys the disaster appraisal procedure.

The outstanding test unit that destroys in the stratum that a kind of simulating hydrate decomposition causes: comprise, have the model casing of top cover, sealing around the model casing can be resisted hydrate and be formed and the needed pressure of simulated formation stress; Top cover can move up and down, and the position of external force is provided in the time of need providing greater than 1 atmospheric pressure as experiment, and exhaust is used when top cover preformed hole confession decomposes experiment; The limit wall of model casing scribbles insulating moulding coating, makes the limit wall and the external world have heat insulating function; The sediment layer is set to form hydrate formation in the model casing bottom, sediment layer top be not for containing the cap rock of hydrate, and the cap rock top is the antifreezing liquid layer of simulated seawater layer, and the water layer top is mobilizable model casing top cover; Also be provided with flowmeter, hole pressure meter, temperature sensor, thermal source, watch-dog, collection and data handling system in the model casing; Flowmeter is mainly used in controls the water yield or the tolerance that enters in the sedimentary deposit hole, is about to the saturation degree quantification of water or gas, satisfies the test demand; The hole presses meter to be used to measure the pressure of layout points, vertically arranges the pressure field in the pressure meter real time record sedimentary deposit of some holes; Temperature sensor is used for the temperature field in the real time record sedimentary deposit; Thermal source is used to satisfy the heating condition of constant temperature or firm power; Watch-dog is used for remote live record decomposition of hydrate forward's propelling, the outstanding process of variation, gas that the potpourri after the decomposition of hydrate is given prominence to the front and back cover surface, guarantees safety and writes down accurately; Collection and data handling system are used to gather and handle the data of real time record.

Further, described model casing is shaped as rectangular parallelepiped or right cylinder.

Further, described model casing top cover is made according to the different choice different materials of experiment condition: adopt pmma material when forming the tetrahydrofuran hydrate sediment; Form the methane hydrate sediment, adopt high-strength stainless steel material.

The outstanding test method of destroying in the stratum that a kind of simulating hydrate decomposition causes may further comprise the steps:

(1) insert experiment soil in model casing, layering hits tight and makes it possess certain dry density, forms the sedimentary deposit that does not contain hydrate, and puts layout thermal source, temperature sensor and hole at the experiment desired location and press meter.According to the difference of experiment demand, the overlayer of sedimentary deposit top capping varying strength;

(2) a certain amount of water is penetrated in the sedimentary deposit by inlet, when forming the tetrahydrofuran hydrate sediment, in advance tetrahydrofuran is become solution with the water proportioning, infiltrate sedimentary deposit uniformly; When forming methane hydrate formation, then continue the methane source of the gas connected and make it infiltrate the stratum, the pressure of needs when at this moment applying the vertical load that equates with air pressure hydrate formation being provided at the cover plate top.Then system is put into constant temperature oven.

(3) provide low temperature by temperature control box, form the hydrate sediment of certain saturation degree through 2-3 days times;

(4) after hydrate sediment forms, close source of the gas, and with inner residual gas discharging, apply pressure to the confined pressure condition that provides experiment to need in water layer and the stratum by top cover by external force, open all measuring equipments, and set certain thermal source condition, carry out decomposition of hydrate test in the sediment, and the variation of each parameter of real time record.

(5) test proceeds to the generation of outstanding disaster, writes down this decomposition of hydrate leading edge, pressure field distribution, temperature field distribution, ejection soil amount and tolerance constantly, and observes the mode of giving prominence to and interrelated geometrical parameters.

The outstanding test result analysis method of destroying in the stratum that a kind of simulating hydrate decomposition causes, at first distribute according to experiment measuring decomposition of hydrate leading edge, pressure field and temperature field, determine the geometric configuration and the pressure of the distribution of decomposition of hydrate potpourri in sedimentary deposit, according to sedimentary deposit and tectal mechanical property and geometric parameter, determine to take place outstanding critical condition, damage envelope and the spray volume that destroys again; Wherein, critical condition is:

$p_g\≥A\frac{2v}{1-v}(p_c+{\mathrm{\ρ}}_m\mathrm{gz})/[\frac{1}{{(\frac{h}{R}-\frac{z}{R})}^3}+\frac{3+4v}{{(\frac{h}{R}+\frac{z}{R})}^3}-\frac{6\frac{z}{R}}{{(\frac{h}{R}+\frac{z}{R})}^4}]---\left(1\right)$

p _cBe atmospheric pressure, ρ _mBe soil body density, g is that gravity quickens, and z is a vertical coordinate, and v is a Poisson ratio, and h is a depth of cover, and R is a decomposition of hydrate district characteristic length, p _gBe emergent pressure,

Damage envelope L is:

In the formula:

Angle of internal friction for cap rock.Coefficient B is wherein determined by formula (2) inverting according to experimental data;

Spray volume Q is determined by following formula:

$Q=C{\left(\frac{p_g}{p_c}\right)}^{\mathrm{\α}}{\left(\frac{h}{R}\right)}^{\mathrm{\β}}---\left(3\right)$

α, β, C are constant coefficient, are determined by formula (3) inverting according to experimental data.

Description of drawings

Fig. 1 is the cross section front view of experimental provision among the present invention;

Fig. 2 is the side cross-sectional view of experimental provision among the present invention;

Fig. 3 is the pressure and temperature in the stratum that records of an experiment;

Pressure and temperature in the in addition stratum that Fig. 4 records for another experiment.

Embodiment

As shown in Figure 1, 2, model casing 9 is shaped as rectangular parallelepiped or right cylinder, sealing all around can be resisted hydrate and be formed and the needed pressure of simulated formation stress, top cover 2 can move up and down the position that external force is provided in the time of need providing greater than 1 atmospheric pressure as experiment, and exhaust is used when top cover 2 preformed hole confessions decompose experiment.Different choice different materials according to experiment condition is made: can adopt pmma material to be convenient to Direct observation if form the tetrahydrofuran hydrate sediment; If form the methane hydrate sediment, need to adopt high-strength stainless steel material.The limit wall of model casing scribbles insulating moulding coating, make limit wall and extraneous heat insulating function, in the model casing bottom is that sediment layer 16 is to form hydrate formation, sediment layer 16 top are not for containing the cap rock 10 of hydrate, cap rock 10 tops are the antifreezing liquid layer 3 of simulated seawater layer, antifreeze liquid layer top is mobilizable model casing top cover 2, and vertical external force puts on and provides stratum and hydrate to form needed pressure condition on the top cover.Flowmeter 11 is mainly used in control and enters the water yield or tolerance in the sedimentary deposit hole by inlet, is about to the saturation degree quantification of water or gas, satisfies the test demand; The hole presses meter 5 to be used to measure the pressure of layout points, vertically arranges the pressure field in the pressure meter 5 real time record sedimentary deposits of some holes; Temperature sensor 15 is used for the temperature field in the real time record sedimentary deposit; Thermal source 6 is used to satisfy the heating condition of constant temperature or firm power; Watch-dog 7 be used for potpourri (water, gas, soil particle) after remote live record decomposition of hydrate forward's the propelling, decomposition of hydrate outstanding before and after variation, the outstanding process of cover surface, guarantee safety and record accurately; Collection and data handling system 1 are used to gather and handle the data of real time record.

Experimental procedure:

As shown in Figure 1, 2:

1. insert experiment soil in model casing 9, layering hits tight and makes it possess certain dry density, and this density is according to the situation value in actual area, seabed.Form the sedimentary deposit that does not contain hydrate, and put layout thermal source 6, temperature sensor 15 and hole at the experiment desired location and press meter 5, according to symmetry, thermal source 6 is placed on the middle of bottom hydrate layer.Because model is symmetrical, temperature sensor 15 all arranges with the spacing that is not less than 2cm in the upper and lower, and on one side transducer arrangements on the upper strata, on one side transducer arrangements in lower floor, avoid the interference of sensor like this, can measure the distribution of whole temperature field again the soil body; The hole is pressed meter 5 to arrange and correspondingly with temperature sensor 6 is arranged and be close to, and is convenient to data analysis.According to the difference of experiment demand, the overlayer of sedimentary deposit top capping varying strength and thickness, for example: for simulation cap rock 10 is raised outstanding then situation, it is high (greater than 10 that the intensity of cap rock is wanted ⁸Pa) and be fragility; As simulate partially perforation and destroy situation, then depth of cover has half of following hydrate layer thickness at least, and the low position of local strength is arranged, and intensity is less than 10 ⁶Pa, the cap rock intensity of other positions is greater than 10 ⁷Pa;

2. a certain amount of water is penetrated in the sedimentary deposit by inlet 13,, in advance tetrahydrofuran is become solution with the water proportioning, infiltrate sedimentary deposit uniformly if form the tetrahydrofuran hydrate sediment; As form methane hydrate formation, then after water infiltrates fully, continue methane to be connected and made it infiltrate the stratum pressure of needs when at this moment applying the vertical load that equates with air pressure hydrate formation being provided at the cover plate top.Then system is put into constant temperature oven 8;

3. provide low temperature by temperature control box, form the hydrate sediment of certain saturation degree through 2-3 days times;

4. after hydrate sediment forms, close source of the gas, and, apply pressure to the confined pressure that the stratum is provided in water layer and the stratum by external force by top cover, as simulate 3000 meters stratum under water, then add confined pressure 30MPa inner residual gas discharging.Open all measuring equipments, and set certain thermal source condition, even thermal source condition heating arrangement such as heating rod are exported the temperature of setting as 100 °, 200 °, 300 ° etc., or the power such as the 100W of output setting, 500W, 1000W etc., determining of size is mainly definite according to the actual conditions of research, carry out decomposition of hydrate test in the sediment, and the variation of each parameter of real time record, as temperature, hole pressure etc.;

5. test proceeds to the generation of the outstanding disaster of eruption, write down this decomposition of hydrate leading edge, pore pressure field distribution, temperature field distribution, ejection soil amount and tolerance constantly, and observation is given prominence to mode and measured interrelated geometrical parameters.

The test result analysis method:

By the model test that this experimental provision is carried out, find under decomposition of hydrate and the gas discharge condition fast the outstanding criterion of decomposition of hydrate eruption in the sediment.Shown in Fig. 3,4, at first distribute according to experiment measuring decomposition of hydrate leading edge, pressure field and temperature field, determine the geometric configuration and the pressure of the distribution of decomposition of hydrate district in sedimentary deposit, according to sedimentary deposit and tectal mechanical property (rigidity, intensity) and geometric parameter (thickness etc.), determine to take place outstanding critical condition, damage envelope and the spray volume that destroys again.

Critical condition is determined:

$p_g\≥A\frac{2v}{1-v}(p_c+{\mathrm{\ρ}}_m\mathrm{gz})/[\frac{1}{{(\frac{h}{R}-\frac{z}{R})}^3}+\frac{3+4v}{{(\frac{h}{R}+\frac{z}{R})}^3}-\frac{6\frac{z}{R}}{{(\frac{h}{R}+\frac{z}{R})}^4}]$

p _cBe atmospheric pressure, ρ _mBe soil body density, g is that gravity quickens, and z is a vertical coordinate, and v is a Poisson ratio, and h is a depth of cover, and R is a decomposition of hydrate district characteristic length, p _gBe emergent pressure, determine coefficient A in the following formula, just obtain the application of formula of critical failure condition by experimental data.

Damage envelope L is determined by following formula:

Angle of internal friction for cap rock.Coefficient B is wherein determined by the following formula inverting according to experimental data.

Spray volume Q is determined by following formula:

$Q=C{\left(\frac{p_g}{p_c}\right)}^{\mathrm{\α}}{\left(\frac{h}{R}\right)}^{\mathrm{\β}}$

α, β, C are constant coefficient, are determined by the following formula inverting according to experimental data.

Claims (5)

1. the outstanding test unit that destroys in stratum that causes of a simulating hydrate decomposition: comprise, have the model casing of top cover, sealing around the model casing can be resisted hydrate and be formed and the needed pressure of simulated formation stress; Top cover can move up and down, and the position of external force is provided in the time of need providing greater than 1 atmospheric pressure as experiment, and exhaust is used when top cover preformed hole confession decomposes experiment; The limit wall of model casing scribbles insulating moulding coating, makes the limit wall and the external world have heat insulating function; The sediment layer is set to form hydrate formation in the model casing bottom, sediment layer top be not for containing the cap rock of hydrate, and the cap rock top is the antifreezing liquid layer of simulated seawater layer, and the water layer top is mobilizable model casing top cover; Also be provided with flowmeter, hole pressure meter, temperature sensor, thermal source, watch-dog, collection and data handling system in the model casing; Flowmeter is mainly used in controls the water yield or the tolerance that enters in the sedimentary deposit hole, is about to the saturation degree quantification of water or gas, satisfies the test demand; The hole presses meter to be used to measure the pressure of layout points, vertically arranges the pressure field in the pressure meter real time record sedimentary deposit of some holes; Temperature sensor is used for the temperature field in the real time record sedimentary deposit; Thermal source is used to satisfy the heating condition of constant temperature or firm power; Watch-dog is used for remote live record decomposition of hydrate forward's propelling, the outstanding process of variation, gas that the potpourri after the decomposition of hydrate is given prominence to the front and back cover surface, guarantees safety and writes down accurately; Collection and data handling system are used to gather and handle the data of real time record.

2. according to the experimental provision described in the claim 1, it is characterized by, described model casing is shaped as rectangular parallelepiped or right cylinder.

3. according to the experimental provision described in the claim 1, it is characterized by, described model casing top cover is made according to the different choice different materials of experiment condition: adopt pmma material when forming the tetrahydrofuran hydrate sediment; Form the methane hydrate sediment, adopt high-strength stainless steel material.

4. the outstanding test method of destroying in stratum that causes of a simulating hydrate decomposition may further comprise the steps:

(1) insert experiment soil in model casing, layering hits tight and makes it possess certain dry density, forms the sedimentary deposit that does not contain hydrate, and puts layout thermal source, temperature sensor and hole at the experiment desired location and press meter; According to the difference of experiment demand, the overlayer of sedimentary deposit top capping varying strength;

(2) a certain amount of water is penetrated in the sedimentary deposit by inlet, when forming the tetrahydrofuran hydrate sediment, in advance tetrahydrofuran is become solution with the water proportioning, infiltrate sedimentary deposit uniformly; When forming methane hydrate formation, then continue the methane source of the gas connected and make it infiltrate the stratum, the pressure of needs when at this moment applying the vertical load that equates with air pressure hydrate formation being provided at the cover plate top; Then system is put into constant temperature oven.

(3) provide low temperature by temperature control box, form the hydrate sediment of certain saturation degree through 2-3 days times;

(4) after hydrate sediment forms, close source of the gas, and with inner residual gas discharging, apply pressure to the confined pressure condition that provides experiment to need in water layer and the stratum by top cover by external force, open all measuring equipments, and set certain thermal source condition, carry out decomposition of hydrate test in the sediment, and the variation of each parameter of real time record;

(5) test proceeds to the generation of outstanding disaster, writes down this decomposition of hydrate leading edge, pressure field distribution, temperature field distribution, ejection soil amount and tolerance constantly, and observes the mode of giving prominence to and interrelated geometrical parameters.

5. the outstanding test result analysis method of destroying in stratum that causes of a simulating hydrate decomposition, at first distribute according to experiment measuring decomposition of hydrate leading edge, pressure field and temperature field, determine the geometric configuration and the pressure of the distribution of decomposition of hydrate potpourri in sedimentary deposit, according to sedimentary deposit and tectal mechanical property and geometric parameter, determine to take place outstanding critical condition, damage envelope and the spray volume that destroys again; Wherein, critical condition is:

$p_g\≥A\frac{2v}{1-v}(p_c+{\mathrm{\ρ}}_m\mathrm{gz})/[\frac{1}{{(\frac{h}{R}-\frac{z}{R})}^3}+\frac{3+4v}{{(\frac{h}{R}+\frac{z}{R})}^3}-\frac{6\frac{z}{R}}{{(\frac{h}{R}+\frac{z}{R})}^4}]---\left(1\right)$

p _cBe atmospheric pressure, ρ _mBe soil body density, g is that gravity quickens, and z is a vertical coordinate, and v is a Poisson ratio, and h is a depth of cover, and R is a decomposition of hydrate district characteristic length, p _gBe emergent pressure,

Damage envelope L is:

In the formula:

Angle of internal friction for cap rock; Coefficient B is wherein determined by formula (2) inverting according to experimental data;

Spray volume Q is determined by following formula:

$Q=C{\left(\frac{p_g}{p_c}\right)}^{\mathrm{\α}}{\left(\frac{h}{R}\right)}^{\mathrm{\β}}---\left(3\right)$

α, β, C are constant coefficient, are determined by formula (3) inverting according to experimental data.

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