CN102493787A - Method for analyzing and preventing eruption disaster caused by hydrate thermal decomposition - Google Patents

Abstract

The invention relates to a method for analyzing and preventing eruption disaster caused by hydrate thermal decomposition. From relevant thermodynamics and geographic factors, through a statics equilibrium condition when the eruption disaster is caused by the hydrate thermal decomposition, a critical relation of the hydrate decomposition range and the pore pressure and soil layer mechanical strength characteristics is established, and through the obtained critical relation, an evaluation condition for causing the eruption disaster to happen by the hydrate thermal decomposition in an actual stratum is obtained, and a preventive measure is provided.

Description

The analysis of the eruption disaster that the hydrate thermal decomposition causes with prevent and treat method

Technical field

What the present invention relates to is marine petroleum exploitation engineering safety technology, specifically, be the eruption disaster that causes about hydrate thermal decomposition under the soil layer analysis with prevent and treat method, choose the purpose that suitable mining type and suitable recovery well are arranged to reach.

Background technology

The physical process that hydrate thermal decomposition eruption destroys is that as shown in Figure 1, thermal source provides heat to the hydrate deposit layer, makes hydrate thermal decomposition and decomposition region outwards expand.When hydrate thermal decomposition zone reaches critical radius R _CriThe time, the hole gas pressure overcomes gravity and the soil strength of the top soil body and destroys the decomposition region overlying strata and erupt.When eruption took place, the destruction of top, the decomposition region soil body had the forms of expression such as cracking, circular hole be outstanding, and the characteristic dimension of destruction is r; Corresponding to the hole gas pressure in the decomposition region under the heat source temperature is p _g, the soil strength of the top soil body is τ _f, the height of the supreme clad surface of thermal source is h, the mean specific gravity of last earthing body does

, seawater is pressed or atmospheric pressure is p ₀

In the prior art, thermal decomposition causes that threshold analysis and preventive action that eruption destroys also belong to blank for hydrate.

Summary of the invention

Therefore, the present invention's analysis of proposing the eruption disaster that a kind of new hydrate thermal decomposition causes with prevent and treat method.

Be to realize above-mentioned purpose, the technical scheme that the present invention takes is: the analysis of the eruption disaster that a kind of hydrate thermal decomposition causes with prevent and treat method, it is characterized in that,

The analysis of the eruption disaster that 1) thermal decomposition causes to hydrate comprises as follows:

1. the extensive diagnostic of hydrate thermal decomposition zone radius

The thermal source place at first reaches the hydrate phase balance temperature in the hydrate deposit layer; Undergo phase transition, form decomposition region and undecomposed zone, its interface is called the phase transformation front; The decomposition region consists of: water, gas, soil skeleton, and undecomposed zone consists of: hydrate, soil skeleton; Along with the rising of temperature, the decomposition region is constantly expanded, and the temperature of decomposition region depends on the averag density ρ of decomposition region ₁, avergae specific heat C ₁, evenly heat coefficient of conductivity K ₁, heating-up temperature T _h, initial temperature T ₀, latent heat of phase change Δ H, temperature T balances each other _e, ρ ₁=ε ₀ρ _g+ (1-ε ₀) ρ _s, C ₁=ε ₀C _g+ (1-ε ₀) C _s, K ₁=ε ₀K _g+ (1-ε ₀) K _sThe temperature in undecomposed zone depends on the averag density ρ in undecomposed zone ₂, avergae specific heat C ₂, evenly heat coefficient of conductivity K ₂, ρ ₂=ε ₀ρ _h+ (1-ε ₀) ρ _s, C ₂=ε ₀C _h+ (1-ε ₀) C _s, K ₂=ε ₀K _h+ (1-ε ₀) K _s, wherein: ε ₀Content for hydrate; ρ _hBe hydrate density, ρ _sBe soil skeleton density, ρ _gGas density, C _hBe hydrate specific heat, C _sBe soil skeleton specific heat, C _gBe the specific heats of gases, K _hBe the hydrate coefficient of heat conduction, K _sBe the soil skeleton coefficient of heat conduction, K _gBe the gas coefficient of heat conduction;

Suppose that each regional conduction of heat physical parameter is average, and latent heat of phase change is constant, writes out two calorifics expression formulas in the zone and be:

Decomposition region:

Undecomposed zone:

Solving equation (1) obtains

Wherein, ξ _eBe to depend on each component thermal parameters of hydrate deposit layer, by relational expression $\frac{{4\mathrm{\θ}}_h{K}_2}{{\mathrm{\ρ}}_h\mathrm{\Δ}{\mathrm{H\ϵ}}_0{\mathrm{\κ}}_1}\left(\frac{{\mathrm{\κ}}_1}{{\mathrm{\κ}}_2}\frac{{\mathrm{\υ}}_e\·\mathrm{Exp}(-4\frac{{\mathrm{\κ}}_1}{{\mathrm{\κ}}_2}{\mathrm{\ξ}}_e)}{\sqrt{{\mathrm{\π\; \ξ}}_e^{\′}}\·(\mathrm{Erf}\left(2\sqrt{\frac{{\mathrm{\κ}}_1}{{\mathrm{\κ}}_2}{\mathrm{\ξ}}_e}\right)-1)}\right)-\frac{{4\mathrm{\θ}}_h{K}_1}{{\mathrm{\ρ}}_h{\mathrm{\Δ\; H\ϵ}}_0{\mathrm{\κ}}_1}\left(\frac{({\mathrm{\υ}}_e-1)\·\mathrm{Exp}(-4{\mathrm{\ξ}}_e)}{2\sqrt{{\mathrm{\π\; \ξ}}_e}\·\mathrm{Erf}\left(2\sqrt{{\mathrm{\ξ}}_e}\right)}\right)=1$ Confirm, wherein, υ _e=T _e-T ₀, θ _h=T _h-T ₀, T ₁Be average temperature in the decomposition region, T ₂Be average temperature in the undecomposed zone, X _eBe the position of phase transformation front, t is the time, and κ is a thermal diffusion coefficient, has

The position X of decomposition region radius R and hydrate phase change front _eCorrespondence, therefore

Can remember and do:

$R=\sqrt{{\mathrm{\ξ}}_e{\mathrm{\κ}}_{1}t}---\left(2\right)$

2. the critical eruption analysis of hydrate thermal decomposition

When the decomposition of hydrate zone radius reaches a threshold, be designated as Gas pressure will be broken through overlying strata and erupt, and erupt pairing hydrate thermal decomposition zone radius R _CriWith the characteristic dimension r that destroys by following parameter determining: hole gas pressure p _g, top atmospheric pressure P ₀, the mean specific gravity of last earthing body

The soil strength τ of top, decomposition region _f, the height h of the supreme clad surface of thermal source; Therefore, decomposition region critical radius R _CriWith the characteristic dimension that destroys be that r can be write as respectively:

$\left\{\begin{array}{c}{R}_{\mathrm{cir}}=f(h,\stackrel{\‾}{\mathrm{\ρ}}g,p_g,{\mathrm{\τ}}_f,p_0)\\ r=s(h,\stackrel{\‾}{\mathrm{\ρ}}g,p_g,{\mathrm{\τ}}_f,p_0)\end{array}\right.---\left(3\right)$

Choose

and h as unit, formula (3) can turn to the dimensionless relation:

$\left\{\begin{array}{c}\frac{R_{\mathrm{cir}}}{h}=f(\frac{p_g-{\mathrm{<figure-callout\; id="0"\; label="p"\; filenames="HDA0000114260060000012.png"\; state="\{\{state\}\}">p</figure-callout>}}_0}{\stackrel{\&OverBar;}{\mathrm{\&rho;}}\mathrm{gh}},\frac{{\mathrm{\&tau;}}_f}{\stackrel{\&OverBar;}{\mathrm{\&rho;}}\mathrm{gh}})\\ \frac{r}{h}=s(\frac{p_g-{\mathrm{<figure-callout\; id="0"\; label="p"\; filenames="HDA0000114260060000012.png"\; state="\{\{state\}\}">p</figure-callout>}}_0}{\stackrel{\&OverBar;}{\mathrm{\&rho;}}\mathrm{gh}},\frac{{\mathrm{\&tau;}}_f}{\stackrel{\&OverBar;}{\mathrm{\&rho;}}\mathrm{gh}})\end{array}\right.---\left(4\right)$

Known

and

erupt the statics Analysis of critical condition; Then can judge whether and to erupt; If erupt, then can confirm the characteristic radius

in decomposition of hydrate zone and the characteristic dimension

that destroys

2) control of the eruption disaster that causes of hydrate thermal decomposition comprises as follows:

According to the analysis of step 1), prevent and treat from following aspect:

1. in the hydrate Development Engineering, control thermal source heating-up temperature, the efficiency of heating surface and heat time heating time, and the expansion of prediction decomposition region radius, confirm the development of the hole gas pressure of decomposition region, make that pore pressure is not enough to overlying strata is damaged;

2. mechanics parameter, hole and the fissured structure of on-the-spot sedimentary deposit that obtains and overlying strata, hydrate laterally, vertically on the synthetic and distributed basis; Choose suitable mining type and recovery well method for arranging, and sedimentary deposit or overlying strata weakness zone are carried out consolidation process.

Especially, break through overlying strata, the characteristic radius in decomposition of hydrate zone for gas eruption with the circular hole form

The characteristic dimension that destroys Be circle, suppose that two radiuses are linearly proportional, i.e. R _Cri=α r, α are empirical coefficients of being confirmed by actual formation; If the intensity of gas pressure and earth pillar gravity and earth pillar and sedimentary deposit satisfied the statics balance condition when supposition destroyed, make h _c=h-R _Cri=h-α r can obtain:

$\mathrm{\&pi;}\&CenterDot;{(\mathrm{\&alpha;}\&CenterDot;R_{\mathrm{cri}})}^2\&CenterDot;\stackrel{\&OverBar;}{\mathrm{\&rho;}}\&CenterDot;g\&CenterDot;h_c+2\mathrm{\&pi;}\&CenterDot;\mathrm{\&alpha;}\&CenterDot;R_{\mathrm{cri}}\&CenterDot;h_c\&CenterDot;{\mathrm{\&tau;}}_f=(p_g-p_0)\&CenterDot;\mathrm{\&pi;}\&CenterDot;{(\mathrm{\&alpha;}\&CenterDot;R_{\mathrm{cri}})}^2---\left(5\right)$

Arrangement obtains:

$\frac{p_g-{\mathrm{<figure-callout\; id="0"\; label="p"\; filenames="HDA0000114260060000012.png"\; state="\{\{state\}\}">p</figure-callout>}}_0}{\stackrel{\&OverBar;}{\mathrm{\&rho;}}\&CenterDot;g\&CenterDot;h_c}-\frac{2}{\mathrm{\&alpha;}\&CenterDot;R_{\mathrm{cri}}}\&CenterDot;\frac{{\mathrm{\&tau;}}_f}{\stackrel{\&OverBar;}{\mathrm{\&rho;}}\&CenterDot;g}=1---\left(6\right)$

Formula (6) has provided critical radius and the gravity of last earthing body and the functional relation of intensity of decomposition of hydrate; Known these two parameters; Then the size of critical radius can be confirmed, again with the critical radius substitution formula of finding the solution (2), can confirm to erupt the crash time of generation.

The present invention is owing to take above technical scheme; Its beneficial effect is: the statics balance condition when causing that through the hydrate thermal decomposition eruption destroys; Set up the critical relation formula of decomposition of hydrate scope and hole pressure, soil layer mechanical strength characteristics; Through the above-mentioned critical relation formula that obtains, can obtain hydrate thermal decomposition in the actual formation and cause the evaluation condition that the eruption disaster takes place and preventive action are provided.

Description of drawings

Fig. 1 is that hydrate thermal decomposition eruption destroys the evolution sketch map;

Fig. 2 is a hydrate phase change front evolution sketch map;

Fig. 3 is that sketch map is divided in decomposition of hydrate and undecomposed zone.

The specific embodiment

Introduce technical scheme of the present invention in detail below in conjunction with accompanying drawing.

The analysis of the eruption disaster that 1, thermal decomposition causes to hydrate:

Based on Fig. 1, learnt the physical process that hydrate thermal decomposition eruption destroys, so the eruption disaster analysis that thermal decomposition causes for hydrate also should be started with from these relevant parameters.We can be divided into the eruption destructive process " expansion in hydrate thermal decomposition zone " and " the critical eruption of hydrate thermal decomposition " two stages.

The I stage: the extensive diagnostic of hydrate thermal decomposition zone radius

The thermal source place at first reaches the hydrate phase balance temperature T in the sedimentary deposit _eAbsorb enough heats until hydrate and undergo phase transition, generate gas and water, begin to form the interface in decomposition region and undecomposed zone; It is the phase transformation front; This moment, the position of hydrate phase change front was x=0 (x representes with the thermal source center to be the coordinate of hydrate phase change front on the one dimension coordinate axes of initial point), then decomposed front and passed forward gradually, be i.e. (t ₁, x ₁) corresponding to t ₁Temperature is T constantly _eThe position, at t ₁Constantly, greater than x ₁The position be undecomposed zone, less than x ₁The zone be the decomposition region, that is to say x ₁For the position of phase transformation front, as shown in Figure 2.

Therefore, during the hydrate thermal decomposition, inside is divided into decomposition region and undecomposed regional two zones, and the decomposition region constituent is: water, gas, soil skeleton; Undecomposed regional constituent is: hydrate, soil skeleton.Temperature T in the sedimentary deposit depends on the averag density ρ of decomposition region ₁, avergae specific heat C ₁, evenly heat coefficient of conductivity K ₁, heating-up temperature T _h, initial temperature T ₀, latent heat of phase change Δ H, temperature T balances each other _e, and the averag density ρ of undecomposed area region ₂, avergae specific heat C ₂, evenly heat coefficient of conductivity K ₂, as shown in Figure 3.

For the decomposition region, the averag density ρ in the zone of definition mixed phase ₁, avergae specific heat C ₁, evenly heat coefficient of conductivity K ₁Be respectively: ρ ₁=ε ₀ρ _g+ (1-ε ₀) ρ _s, C ₁=ε ₀C _g+ (1-ε ₀) C _s, K ₁=ε ₀K _g+ (1-ε ₀) K _sFor undecomposed area region, the averag density ρ in the zone of definition mixed phase ₂, avergae specific heat C ₂, evenly heat coefficient of conductivity K ₂Be respectively: ρ ₂=ε ₀ρ _h+ (1-ε ₀) ρ _s, C ₂=ε ₀C _h+ (1-ε ₀) C _s, K ₂=ε ₀K _h+ (1-ε ₀) K _sWherein, ε ₀Content for hydrate; Under identify h, s, g represent hydrate phase, soil skeleton, gas phase respectively; ρ _hBe hydrate density; ρ _sBe soil skeleton density; ρ _gGas density; C _hBe hydrate specific heat; C _sBe soil skeleton specific heat; C _gBe the specific heats of gases; K _hBe the hydrate coefficient of heat conduction; K _sBe the soil skeleton coefficient of heat conduction; K _gBe the gas coefficient of heat conduction.

Because hydrate thermal decomposition evolution comprises conduction of heat and two physical effects of phase transformation in the sedimentary deposit; Suppose that each regional conduction of heat physical parameter is average; And latent heat of phase change (usually; Latent heat is the function of temperature) be constant, can write out the mathematic(al) representation of the hydrate deposit layer thermal decomposition in two zones of a phase transformation front:

Decomposition region:

Undecomposed zone:

Solving equation (1) can obtain

Wherein, ξ _eBe to depend on each component thermal parameters of hydrate deposit layer, by relational expression $\frac{{4\mathrm{\&theta;}}_h{K}_2}{{\mathrm{\&rho;}}_h\mathrm{\&Delta;}{\mathrm{H\&epsiv;}}_0{\mathrm{\&kappa;}}_1}\left(\frac{{\mathrm{\&kappa;}}_1}{{\mathrm{\&kappa;}}_2}\frac{{\mathrm{\&upsi;}}_e\&CenterDot;\mathrm{Exp}(-4\frac{{\mathrm{\&kappa;}}_1}{{\mathrm{\&kappa;}}_2}{\mathrm{\&xi;}}_e)}{\sqrt{{\mathrm{\&pi;\; \&xi;}}_e^{\&prime;}}\&CenterDot;(\mathrm{Erf}\left(2\sqrt{\frac{{\mathrm{\&kappa;}}_1}{{\mathrm{\&kappa;}}_2}{\mathrm{\&xi;}}_e}\right)-1)}\right)-\frac{{4\mathrm{\&theta;}}_h{K}_1}{{\mathrm{\&rho;}}_h{\mathrm{\&Delta;\; H\&epsiv;}}_0{\mathrm{\&kappa;}}_1}\left(\frac{({\mathrm{\&upsi;}}_e-1)\&CenterDot;\mathrm{Exp}(-4{\mathrm{\&xi;}}_e)}{2\sqrt{{\mathrm{\&pi;\; \&xi;}}_e}\&CenterDot;\mathrm{Erf}\left(2\sqrt{{\mathrm{\&xi;}}_e}\right)}\right)=1$ Find the solution.Wherein, υ _e=T _e-T ₀, θ _h=T _h-T ₀, T ₁Be average temperature in the decomposition region, T ₂Be average temperature in the undecomposed zone, X _eBe the position of phase transformation front, t is a time parameter, and κ is a thermal diffusion coefficient, has in resolver and undecomposed zone

With

The position X of decomposition of hydrate zone radius R and hydrate phase change front _eTherefore correspondence has:

$R=\sqrt{{\mathrm{\&xi;}}_e{\mathrm{\&kappa;}}_{1}t}---\left(2\right)$

The II stage: the critical eruption analysis of hydrate thermal decomposition

When the decomposition of hydrate zone radius reaches a threshold; Promptly when

, gas pressure can be broken through overlying strata and erupt.Erupt pairing hydrate thermal decomposition zone radius R _CriWith the characteristic dimension r that destroys by following parameter determining: load: hole gas pressure p _g, top atmospheric pressure ρ ₀Material property: the mean specific gravity that goes up the earthing body

The soil strength τ of top, decomposition region _fGeometry: the height h of the supreme clad surface of thermal source.

Therefore, decomposition region radius critical radius R _CriTo be that r can be write as functional form respectively following with the characteristic dimension that destroys:

$\left\{\begin{array}{c}{R}_{\mathrm{cir}}=f(h,\stackrel{\&OverBar;}{\mathrm{\&rho;}}g,p_g,{\mathrm{\&tau;}}_f,p_0)\\ r=s(h,\stackrel{\&OverBar;}{\mathrm{\&rho;}}g,p_g,{\mathrm{\&tau;}}_f,p_0)\end{array}\right.---\left(3\right)$

Two expression formulas represent to erupt the average severe of height, overlying strata, hole gas pressure, top, decomposition region soil strength, the specific function relation of top atmospheric pressure of characteristic dimension and the supreme clad surface of thermal source of decomposition of hydrate zone critical radius and the destruction of destruction, the dependence of the regional critical radius of sign decomposition of hydrate and destructive characteristics yardstick and these basic parameters respectively in the formula (3).

Choose and h as unit, formula (3) can turn to the dimensionless relation:

$\left\{\begin{array}{c}\frac{R_{\mathrm{cir}}}{h}=f(\frac{p_g-{\mathrm{<figure-callout\; id="0"\; label="p"\; filenames="HDA0000114260060000012.png"\; state="\{\{state\}\}">p</figure-callout>}}_0}{\stackrel{\&OverBar;}{\mathrm{\&rho;}}\mathrm{gh}},\frac{{\mathrm{\&tau;}}_f}{\stackrel{\&OverBar;}{\mathrm{\&rho;}}\mathrm{gh}})\\ \frac{r}{h}=s(\frac{p_g-{\mathrm{<figure-callout\; id="0"\; label="p"\; filenames="HDA0000114260060000012.png"\; state="\{\{state\}\}">p</figure-callout>}}_0}{\stackrel{\&OverBar;}{\mathrm{\&rho;}}\mathrm{gh}},\frac{{\mathrm{\&tau;}}_f}{\stackrel{\&OverBar;}{\mathrm{\&rho;}}\mathrm{gh}})\end{array}\right.---\left(4\right)$

Known

and erupt the statics Analysis of critical condition, then can judge whether to erupt.If erupt, can confirm that then they have also determined the characteristic dimension

that destroys to the regional characteristic radius of decomposition of hydrate equally

Especially; Break through overlying strata for gas eruption with the circular hole form, the characteristic dimension

that decomposition of hydrate characteristic radius during eruption

destroys also is circle hole radius.Suppose that two radiuses are linearly proportional, i.e. R _Cri=α r (α depends on the layout of direction anyhow etc. of laterally vertically synthetic and distribution, recovery well of hole and fissured structure, the hydrate of overlying strata, an empirical coefficient of being confirmed by actual formation).

Decomposition of hydrate makes the interior soil body (as shown in Figure 1) of characteristic size r scope reach eruption and destroys under the critical condition; This power of gas pressure can compound resolver, equilibrium water on gravity and the resistance that intensity forms of earthing body, if the intensity of gas pressure and earth pillar gravity and earth pillar and sedimentary deposit satisfies the statics balance condition when supposition destroys.

Make h _c=h-R _Cri=h-α r can obtain:

$\mathrm{\&pi;}\&CenterDot;{(\mathrm{\&alpha;}\&CenterDot;R_{\mathrm{cri}})}^2\&CenterDot;\stackrel{\&OverBar;}{\mathrm{\&rho;}}\&CenterDot;g\&CenterDot;h_c+2\mathrm{\&pi;}\&CenterDot;\mathrm{\&alpha;}\&CenterDot;R_{\mathrm{cri}}\&CenterDot;h_c\&CenterDot;{\mathrm{\&tau;}}_f=(p_g-p_0)\&CenterDot;\mathrm{\&pi;}\&CenterDot;{(\mathrm{\&alpha;}\&CenterDot;R_{\mathrm{cri}})}^2---\left(5\right)$

Arrangement obtains:

$\frac{p_g-{\mathrm{<figure-callout\; id="0"\; label="p"\; filenames="HDA0000114260060000012.png"\; state="\{\{state\}\}">p</figure-callout>}}_0}{\stackrel{\&OverBar;}{\mathrm{\&rho;}}\&CenterDot;g\&CenterDot;h_c}-\frac{2}{\mathrm{\&alpha;}\&CenterDot;R_{\mathrm{cri}}}\&CenterDot;\frac{{\mathrm{\&tau;}}_f}{\stackrel{\&OverBar;}{\mathrm{\&rho;}}\&CenterDot;g}=1---\left(6\right)$

Formula (6) has provided critical radius and the gravity of last earthing body and the functional relation of intensity of decomposition of hydrate.Known these two parameters, then the size of critical radius can be confirmed.With the critical radius substitution formula of finding the solution (2), can confirm to erupt the crash time of generation again.

The control of the eruption disaster that 2, thermal decomposition causes to hydrate:

Can know by formula (6); The critical radius of the decomposition of hydrate of eruption disaster depends on pressure reduction

and two dimensionless numbers of overlying strata intensity

; And can when decomposition of hydrate radius

reaches this critical radius and reach this critical radius confirm, therefore need to strengthen preventing and treating from these two aspects by formula (2).

(1) for pressure reduction; It is confirmed by degree of heat and decomposition region radius; Thereby in the hydrate Development Engineering, control thermal source heating-up temperature, the efficiency of heating surface and heat time heating time etc.; And the expansion of prediction decomposition region radius, confirm the hole gas pressure development of decomposition region, make that pore pressure is not enough to overlying strata is damaged;

(2) for overlying strata intensity; On the bases such as laterally vertically synthetic and distribution of mechanics parameter (elastic constants, intensity etc.), hole and the fissured structure of on-the-spot sedimentary deposit that obtains in the future and overlying strata, hydrate; Choose suitable mining type and recovery well method for arranging, and sedimentary deposit or overlying strata weakness zone are carried out consolidation process (cement injection, carbon dioxide hydrate displacement methane hydrate etc.);

(3) preceding two kinds of methods adopt simultaneously, promptly will in the hydrate Development Engineering, control thermal source heating-up temperature, the efficiency of heating surface and heat time heating time, and choose suitable mining type and recovery well method for arranging, and sedimentary deposit or overlying strata weakness zone are carried out consolidation process.

Claims (2)

1. The analysis of the eruption disaster that causes of a hydrate thermal decomposition with prevent and treat method, it is characterized in that 1) analysis of the eruption disaster that thermal decomposition causes to hydrate comprises as follows:

   1. the extensive diagnostic of hydrate thermal decomposition zone radius

   The thermal source place at first reaches the hydrate phase balance temperature in the hydrate deposit layer; Undergo phase transition, form decomposition region and undecomposed zone, its interface is called the phase transformation front; The decomposition region consists of: water, gas, soil skeleton, and undecomposed zone consists of: hydrate, soil skeleton; Along with the rising of temperature, the decomposition region is constantly expanded, and the temperature of decomposition region depends on the averag density ρ of decomposition region ₁, avergae specific heat C ₁, evenly heat coefficient of conductivity K ₁, heating-up temperature T _h, initial temperature T ₀, latent heat of phase change Δ H, temperature T balances each other _e, ρ ₁=ε ₀ρ _g+ (1-ε ₀) ρ _s, C ₁=ε ₀C _g+ (1-ε ₀) C _s, K ₁=ε ₀K _g+ (1-ε ₀) K _sThe temperature in undecomposed zone depends on the averag density ρ in undecomposed zone ₂, avergae specific heat C ₂, evenly heat coefficient of conductivity K ₂, ρ ₂=ε ₀ρ _h+ (1-ε ₀) ρ _s, C ₂=ε ₀C _h+ (1-ε ₀) C _s, K ₂=ε ₀K _h+ (1-ε ₀) K _s, wherein: ε ₀Content for hydrate; ρ _hBe hydrate density, ρ _sBe soil skeleton density, ρ _gGas density, C _hBe hydrate specific heat, C _sBe soil skeleton specific heat, C _gBe the specific heats of gases, K _hBe the hydrate coefficient of heat conduction, K _sBe the soil skeleton coefficient of heat conduction, K _gBe the gas coefficient of heat conduction;

   Suppose that each regional conduction of heat physical parameter is average, and latent heat of phase change is constant, writes out two calorifics expression formulas in the zone and be:

   Decomposition region:

   

   Undecomposed zone:

   

   Solving equation (1) obtains

   

   Wherein, ξ _eBe to depend on each component thermal parameters of hydrate deposit layer, by relational expression $\frac{{4\mathrm{\&theta;}}_h{K}_2}{{\mathrm{\&rho;}}_h\mathrm{\&Delta;}{\mathrm{H\&epsiv;}}_0{\mathrm{\&kappa;}}_1}\left(\frac{{\mathrm{\&kappa;}}_1}{{\mathrm{\&kappa;}}_2}\frac{{\mathrm{\&upsi;}}_e\&CenterDot;\mathrm{Exp}(-4\frac{{\mathrm{\&kappa;}}_1}{{\mathrm{\&kappa;}}_2}{\mathrm{\&xi;}}_e)}{\sqrt{{\mathrm{\&pi;\; \&xi;}}_e^{\&prime;}}\&CenterDot;(\mathrm{Erf}\left(2\sqrt{\frac{{\mathrm{\&kappa;}}_1}{{\mathrm{\&kappa;}}_2}{\mathrm{\&xi;}}_e}\right)-1)}\right)-\frac{{4\mathrm{\&theta;}}_h{K}_1}{{\mathrm{\&rho;}}_h{\mathrm{\&Delta;\; H\&epsiv;}}_0{\mathrm{\&kappa;}}_1}\left(\frac{({\mathrm{\&upsi;}}_e-1)\&CenterDot;\mathrm{Exp}(-4{\mathrm{\&xi;}}_e)}{2\sqrt{{\mathrm{\&pi;\; \&xi;}}_e}\&CenterDot;\mathrm{Erf}\left(2\sqrt{{\mathrm{\&xi;}}_e}\right)}\right)=1$ Confirm, wherein, υ _e=T _e-T ₀, θ _h=T _h-T ₀, T ₁Be average temperature in the decomposition region, T ₂Be average temperature in the undecomposed zone, X _eBe the position of phase transformation front, t is the time, and κ is a thermal diffusion coefficient, has

   

   

   The position X of decomposition region radius R and hydrate phase change front _eCorrespondence, therefore

   

   Can remember and do:

   $R=\sqrt{{\mathrm{\&xi;}}_e{\mathrm{\&kappa;}}_{1}t}---\left(2\right)$

   2. the critical eruption analysis of hydrate thermal decomposition

   When the decomposition of hydrate zone radius reaches a threshold, be designated as

   

   Gas pressure will be broken through overlying strata and erupt, and erupt pairing hydrate thermal decomposition zone radius R _CriWith the characteristic dimension r that destroys by following parameter determining: hole gas pressure p _g, top atmospheric pressure p ₀, the mean specific gravity of last earthing body The soil strength τ of top, decomposition region _f, the height h of the supreme clad surface of thermal source; Therefore, decomposition region critical radius R _CriWith the characteristic dimension that destroys be that r can be write as respectively:

   $\left\{\begin{array}{c}{R}_{\mathrm{cir}}=f(h,\stackrel{\&OverBar;}{\mathrm{\&rho;}}g,p_g,{\mathrm{\&tau;}}_f,p_0)\\ r=s(h,\stackrel{\&OverBar;}{\mathrm{\&rho;}}g,p_g,{\mathrm{\&tau;}}_f,p_0)\end{array}\right.---\left(3\right)$

   Choose

   

   and h as unit, formula (3) can turn to the dimensionless relation:

   $\left\{\begin{array}{c}\frac{R_{\mathrm{cir}}}{h}=f(\frac{p_g-p_0}{\stackrel{\&OverBar;}{\mathrm{\&rho;}}\mathrm{gh}},\frac{{\mathrm{\&tau;}}_f}{\stackrel{\&OverBar;}{\mathrm{\&rho;}}\mathrm{gh}})\\ \frac{r}{h}=s(\frac{p_g-p_0}{\stackrel{\&OverBar;}{\mathrm{\&rho;}}\mathrm{gh}},\frac{{\mathrm{\&tau;}}_f}{\stackrel{\&OverBar;}{\mathrm{\&rho;}}\mathrm{gh}})\end{array}\right.---\left(4\right)$

   Known

   

   and

   

   erupt the statics Analysis of critical condition; Then can judge whether and to erupt; If erupt, then can confirm the characteristic radius

   

   in decomposition of hydrate zone and the characteristic dimension that destroys

   2) control of the eruption disaster that causes of hydrate thermal decomposition comprises as follows:

   According to the analysis of step 1), prevent and treat from following aspect:

   1. in the hydrate Development Engineering, control thermal source heating-up temperature, the efficiency of heating surface and heat time heating time, and the expansion of prediction decomposition region radius, confirm the development of the hole gas pressure of decomposition region, make that pore pressure is not enough to overlying strata is damaged;

   2. mechanics parameter, hole and the fissured structure of on-the-spot sedimentary deposit that obtains and overlying strata, hydrate laterally, vertically on the synthetic and distributed basis; Choose suitable mining type and recovery well method for arranging, and sedimentary deposit or overlying strata weakness zone are carried out consolidation process.
2. 2. the analysis of the eruption disaster that hydrate thermal decomposition as claimed in claim 1 causes with prevent and treat method, it is characterized in that, break through overlying strata, the characteristic radius in decomposition of hydrate zone for gas eruption with the circular hole form

   

   The characteristic dimension that destroys Be circle, suppose that two radiuses are linearly proportional, i.e. R _Cri=α r, α are empirical coefficients of being confirmed by actual formation; If the intensity of gas pressure and earth pillar gravity and earth pillar and sedimentary deposit satisfied the statics balance condition when supposition destroyed, make h _c=h-R _Cri=h-α r can obtain:

   $\mathrm{\&pi;}\&CenterDot;{(\mathrm{\&alpha;}\&CenterDot;R_{\mathrm{cri}})}^2\&CenterDot;\stackrel{\&OverBar;}{\mathrm{\&rho;}}\&CenterDot;g\&CenterDot;h_c+2\mathrm{\&pi;}\&CenterDot;\mathrm{\&alpha;}\&CenterDot;R_{\mathrm{cri}}\&CenterDot;h_c\&CenterDot;{\mathrm{\&tau;}}_f=(p_g-p_0)\&CenterDot;\mathrm{\&pi;}\&CenterDot;{(\mathrm{\&alpha;}\&CenterDot;R_{\mathrm{cri}})}^2---\left(5\right)$

   Arrangement obtains:

   $\frac{p_g-p_0}{\stackrel{\&OverBar;}{\mathrm{\&rho;}}\&CenterDot;g\&CenterDot;h_c}-\frac{2}{\mathrm{\&alpha;}\&CenterDot;R_{\mathrm{cri}}}\&CenterDot;\frac{{\mathrm{\&tau;}}_f}{\stackrel{\&OverBar;}{\mathrm{\&rho;}}\&CenterDot;g}=1---\left(6\right)$

   Formula (6) has provided critical radius and the gravity of last earthing body and the functional relation of intensity of decomposition of hydrate; Known these two parameters; Then the size of critical radius can be confirmed, again with the critical radius substitution formula of finding the solution (2), can confirm to erupt the crash time of generation.

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