CN102943620A - Pressure-controlled drilling method based on drilling annulus wellbore multi-phase flow computing - Google Patents

Abstract

The invention relates to a pressure-controlled drilling method based on drilling annulus wellbore multi-phase flow computing, which comprises the following steps: obtaining basic parameters for drilling wellbore multi-phase flow computing; determining the variety of fluid in wellbore annulus; considering multi-phase multi-component complex flow factors, and establishing a wellbore annulus internal multi-phase flow control equation group; establishing definite conditions for the multi-phase flow control equation group by combining with technical processes under pressure-controlled drilling different working conditions; carrying out grid division on the time and space domains obtained by multi-phase flow computing; carrying out numerical discretion; solving the wellhead back pressure required by pressure-controlled drilling; and adjusting the wellhead throttling valve based on the computed wellhead back pressure value to realize pressure-controlled drilling. Through the adoption of the method, pressure-controlled drilling can be continued under the condition that the drilling fluid contains gas; the method can be applied to the pressure-controlled drilling process of strata highly containing acidic gases; and the computation accuracy is high, the error is small, the control accuracy of pressure-controlled drilling is improved, and the application range is enlarged.

Description

Controlled pressure drilling method based on the calculating of drilling well annulus wellbore Multiphase Flow

Technical field

The invention belongs to the oil-gas field development field, particularly, relate to oil gas drilling wellbore pressure control, particularly a kind of controlled pressure boring method.

Background technology

Continuous expansion along with the oil-gas exploration scope, the formation condition that drilling well runs into becomes increasingly complex, leakage in the drilling engineering, bit freezing, cave-in down hole problem frequent occurrence, especially for fracture pressure and the pore pressure window is narrower in addition drain spray with the stratum of depositing, the frequent occurrence of down-hole accident increases nonproductive time greatly, has raised the cost of drillng operation.Simultaneously, three low (low resistance, low hole, hyposmosis) complex reservoir becomes the pith that resource is taken over, and these oil-gas reservoir low-resistances, low hole, hypotonic feature have such oil-gas reservoir to be difficult to the characteristics of finding and estimating.Thereby, how to prevent the generation of leakage in the bad ground, bit freezing, cave-in complex situations, drill safely and efficiently the bad ground of narrow Density Window, effectively reduce simultaneously in the drilling process drilling fluid to the injury of reservoir, become the hot technology of current drilling well industry and the key of increasing economic efficiency.In addition, contain H for height ₂S, CO ₂How the sour gas stratum of gas guarantees that drilling safety is the technical barrier of puzzlement drilling well circle always.Height contains H ₂S, CO ₂Sour gas special phase transformation law and flowing law are arranged in pit shaft, sour gas is in above-critical state in the depths, shaft bottom, and has very high solubility in water-base drilling fluid, so that the intrusion of sour gas has disguise; But when sour gas rose to upper wellbore, it was gaseous state that sour gas is known from experience phase transformation, and the gas that is dissolved in the drilling fluid also can discharge again, and violent expansion can appear in the volume of high acid gas-containing natural gas, and gas expansion has sudden.Disguise during the sour gas gas cut and sudden control to wellbore pressure are brought huge harm, and the controlled pressure drilling well can suppress the burst expansion of sour gas by applying in real time wellhead back pressure, and the circulating system of controlled pressure drilling sealing can be guaranteed H ₂The S toxic gas can not be diffused among the atmosphere.

The requirement of complex reservoir probing is satisfied in controlled pressure drilling well owing to can be good at, and has obtained worldwidely greatly developing and promoting.Present controlled pressure drilling technology depends on APWD (Annular Pressure While drilling)/PWD (Pressure While drilling) shaft bottom measuring apparatus and comes Real-time Obtaining bottom pressure numerical value, adjust in real time wellhead back pressure according to this numerical value, reach the purpose of controlled pressure drilling well.But the signal of APWD/PWD device for subsurface measuring relies on mud-pulse more, and signal can't normally reach ground when being mixed with gas in drilling fluid, and pressure control creeps into then and can't normally carry out.Simultaneously, APWD/PWD testing pressure down hole instrument is mostly monopolized by minority technical service company, only provides the high price service not sell product, has restricted to a certain extent the development of controlled pressure drilling technology.

Summary of the invention

In order to overcome the defective of prior art, the present invention proposes a kind of controlled pressure boring method that calculates based on the bored shaft Multiphase Flow; Calculate in real time bottom pressure and required wellhead back pressure is realized the controlled pressure drilling well by bored shaft Multiphase Flow computational methods, do not rely on APWD/PWD shaft bottom measuring apparatus and come Real-time Obtaining bottom pressure numerical value.

For achieving the above object, following technical proposals that the present invention adopts:

A kind of controlled pressure boring method that calculates based on the bored shaft Multiphase Flow is characterized in that:

(1), obtains the basic parameter that the bored shaft Multiphase Flow calculates.According to Drilling Design parameter and real-time controlled pressure drilling drilling parameter, obtain and calculate required master data, wherein the Drilling Design parameter comprises: the gas phase in casing programme, drilling assembly, formation data, the drilling fluid and liquid phase discharge capacity, drilling fluid density, drilling fluid viscosity, well depth, hole angle, azimuth; Real-time controlled pressure drilling drilling parameter comprises: current bit depth, current time wellhead back pressure.

(2), determine the kind of mineshaft annulus inner fluid.According to injecting drilling fluid liquid phase or gas phase, produced fluid oil, hydrocarbon gas, water, sour gas in the reservoir are determined the kind of mineshaft annulus inner fluid component.

(3), consider multi-phase multi-component Complex Flows factor, set up the Multiphase Flow governing equation group in the mineshaft annulus.For the difference of flow media in the annular space, set up respectively injected gas, liquid, stratum output oil, water, hydrocarbon gas, the continuity equation of sour gas, momentum conservation equation, energy conservation equation; In order to make the governing equation sealing also need set up subsidiary equation, mainly comprise: the solubility equation of the state equation of fluid, sour gas, fluid above-critical state are judged the slippage equation of equation, friction drag loss equation, formation temperature field equation, gas phase and solid phase, the geometric equation that flow pattern is judged equation, annular space runner.

(4) in conjunction with the activities under the different operating modes of controlled pressure drilling well, obtain the definite condition of annular space Multiphase Flow governing equation group.

The time of (5) Multiphase Flow being calculated and spatial domain are carried out Finite Difference Meshes and are divided.Wherein, spatial domain is whole mineshaft annulus, and time-domain is for implementing the whole process of controlled pressure drilling; The present invention dynamically selects space lattice length according to the gas rate of climb, and grid is the lower minister of well, and top is short.

(6) quantize the Multiphase Flow governing equation discrete.The present invention adopts 4 difference schemes to disperse, and discrete equation mainly comprises: the continuity equation of each phase, the equation of momentum and energy equation.

(7) find the solution the required wellhead back pressure of controlled pressure drilling well.Use finite-difference algorithm Multiphase Flow governing equation group to be carried out numerical solution, the required wellhead back pressure of controlled pressure drilling well.

(8) based on the wellhead back pressure value of calculating, regulate the well head choke valve, realize that pressure control creeps into.

The present invention has following remarkable result:

(1), method of the present invention carries out the controlled pressure drilling well, can in the situation that drilling fluid gassiness APWD/PWD shaft bottom measuring apparatus signal can't normal transmission, proceed the controlled pressure drilling well;

(2), method of the present invention can be carried out controlled pressure drilling, the cost of use of saving APWD/PWD shaft bottom measuring apparatus, minimizing drilling cost in without APWD/PWD shaft bottom measuring apparatus situation;

(3), because this method has been considered above-critical state and the dissolution characteristics of acidic components in the natural gas, so that the method can be applied to the controlled pressure drilling process on high acid gas-containing stratum;

(4), this method is considered multicomponent multi-phase complex mobility status in the pit shaft, more meet the actual flow process in the controlled pressure bored shaft, computational accuracy is high, and error is little, improve the control accuracy of controlled pressure drilling well, enlarged the range of application of controlled pressure drilling well.

Figure of description

Fig. 1 is the schematic flow sheet based on the controlled pressure boring method of bored shaft Multiphase Flow calculating;

Fig. 2 annular space Multiphase Flow computer memory time-domain Finite Difference Meshes is divided schematic diagram;

Fig. 3 controlled pressure drilling well n is the interior Multiphase Flow parametric solution step schematic diagram of pit shaft constantly;

Fig. 4 controlled pressure drilling well n+1 is required wellhead back pressure value solution procedure schematic diagram constantly.

The specific embodiment

Below in conjunction with accompanying drawing embodiment of the present invention are specifically described.Fig. 1 is the schematic flow sheet of the controlled pressure boring method that calculates based on bored shaft annular space Multiphase Flow of the present invention, and the controlled pressure boring method that calculates based on bored shaft annular space Multiphase Flow comprises following key step:

1, obtains the basic parameter that the bored shaft Multiphase Flow calculates

According to Drilling Design parameter and real-time controlled pressure drilling drilling parameter, obtain and calculate required master data, wherein the Drilling Design parameter comprises: the gas phase in casing programme, drilling assembly, formation data, the drilling fluid and liquid phase discharge capacity, drilling fluid density, drilling fluid viscosity, well depth, hole angle, azimuth; Real-time controlled pressure drilling drilling parameter comprises: current bit depth, current time wellhead back pressure.

2, determine the kind of mineshaft annulus inner fluid

Consider the situation of more complicated in the controlled pressure drilling in the present embodiment, the drilling fluid of injection is the gas-liquid two-phase fluid-mixing, and produced fluid is oil, water, hydrocarbon gas, sour gas in the reservoir, and wherein sour gas is carbon dioxide (CO ₂) and hydrogen sulfide (H ₂S).Therefore, the type of fluid in the mineshaft annulus is 8 kinds, is respectively: injected gas, injection liquid, landwaste, oil, water, hydrocarbon gas, CO ₂And H ₂S.

3, consider multi-phase multi-component Complex Flows factor, set up the Multiphase Flow governing equation group in the mineshaft annulus

Consider gas, the liquid of injection, the landwaste that the place, shaft bottom produces, the oil of output, gas, water in the stratum, and the phase transformation between oil/gas, the above-critical state in the high acid gas-containing deep-well flows, the dissolving in water-base drilling fluid and separate out multi-phase multi-component and flow, alternate slippage, on the basis of the coupling factor of stratum filtration and pit shaft Multiphase Flow, set up the governing equation group of Multiphase Flow system in the mineshaft annulus, comprise continuity equation, the equation of momentum, energy equation and the subsidiary equation of each phase.

For the one dimension Multiphase Flow in the mineshaft annulus, algoritic module calls relevant parameter, sets up continuity equation, the equation of momentum and the energy equation of each phase.Relevant parameter comprises: annular space sectional area A, inject gas phase discharge capacity q _Pg, inject drilling well liquid phase discharge capacity q _m, stratum output hydro carbons tolerance q _g, stratum output H ₂S tolerance q _Ss, stratum output CO ₂Tolerance q _Sc, stratum output oil mass q _o, the meltage q of hydrocarbon gas _Rg, H ₂The meltage q of S _Rs, CO ₂Meltage q _Rc, the amount of the separating out x of hydrocarbon gas _Rg, H ₂The amount of the separating out x of S _Rs, CO ₂The amount of separating out x _Rc, stratum output water yield q _w, shaft bottom landwaste output q _c, dissolved gas oil ratio R _s, crude oil volume fraction B _o, the density p of stratum output hydrocarbon gas under the mark condition _Gs, along the length s of pit shaft direction, hole angle α, hydrocarbon gas phase volume fraction E _g, H ₂S volume fraction E _Ss, CO ₂Volume fraction E _Sc, hydrocarbon gas dissolving phase volume fraction E _Rg, H ₂S dissolving phase volume fraction E _Rs, CO ₂Dissolving phase volume fraction E _Rc, landwaste volume fraction E _c, the volume fraction E of drilling well liquid phase _m, the volume fraction E of injection gas phase _Pg, the volume fraction E of stratum output oil _o, the volume fraction E of stratum output water _w, the speed V of hydrocarbon gas phase _g, H ₂The speed V of S _Ss, CO ₂Speed V _Sc, the speed V of hydrocarbon gas dissolving phase _Rg, H ₂The speed V of S dissolving phase _Rs, CO ₂The speed V of dissolving phase _Rc, the speed V of landwaste _c, the speed V of drilling well liquid phase _m, the speed V of injection gas phase _Pg, the speed V of stratum output oil _o, the speed V of stratum output water _w, the density p of hydrocarbon gas phase _g, H ₂The density p of S _g, CO ₂Density p _Sc, the density p of hydrocarbon gas dissolving phase _Rg, H ₂The density p of S dissolving phase _Rs, CO ₂The density p of dissolving phase _Rc, the density p of landwaste _c, the density p of drilling well liquid phase _m, the density p of injection gas phase _Pg, the density p of stratum output oil _o, the density p of stratum output water _w, frictional resistance pressure drop f _r, annular pressure P, gas phase hybrid density ρ _Ga, volume of gas mark E _Ga, the specific heat at constant pressure C of mist _Ga, density of liquid phase ρ _l, liquid phase volume mark E _l, liquid phase specific heat at constant pressure C _l, the mass flow w of mist _Ga, sleeve pipe external diameter r _Co, the temperature T of annular space inner fluid _a, formation thermal conductivity k _e, total thermal transmittance U in the pit shaft _a, transient state heat conduction function T _D, temperature T in the stratum _Ei, drill string inner fluid temperature T _t, drill string internal diameter r _Ti

(1), continuity equation

Inject the gas phase of drilling fluid

$\frac{\∂}{\∂t}\left({\mathrm{\ρ}}_{\mathrm{pg}}{E}_{\mathrm{pg}}A\right)+\frac{\∂}{\∂s}\left({\mathrm{\ρ}}_{\mathrm{pg}}{E}_{\mathrm{pg}}{V}_{\mathrm{pg}}A\right)=q_{\mathrm{pg}}$

Inject the liquid phase of drilling fluid

$\frac{d}{\mathrm{dt}}\left({\mathrm{AE}}_m{\mathrm{\ρ}}_m\right)+\frac{d}{\mathrm{ds}}\left({\mathrm{AE}}_m{\mathrm{\ρ}}_m{V}_m\right)=q_m$

Stratum output hydrocarbon gas phase

$\frac{\∂}{\∂t}({\mathrm{\ρ}}_g{E}_{g}A+\frac{{\mathrm{AR}}_s{\mathrm{\ρ}}_{\mathrm{gs}}{E}_o}{B_o})+\frac{\∂}{\∂s}({\mathrm{\ρ}}_g{E}_g{V}_{g}A+\frac{{\mathrm{AR}}_s{\mathrm{\ρ}}_{\mathrm{gs}}{E}_o{V}_o}{B_o})=q_g-q_{\mathrm{rg}}+x_{\mathrm{rg}}$

Stratum output oil phase

$\frac{\∂}{\∂t}({\mathrm{\ρ}}_o{E}_{o}A-\frac{{\mathrm{AR}}_s{\mathrm{\ρ}}_{\mathrm{gs}}{E}_o}{B_o})+\frac{\∂}{\∂s}({\mathrm{\ρ}}_o{E}_o{V}_{o}A-\frac{{\mathrm{AR}}_s{\mathrm{\ρ}}_{\mathrm{gs}}{E}_o{V}_o}{B_o})=q_o$

Stratum output H ₂S sour gas phase

$\frac{\∂}{\∂t}\left({\mathrm{\ρ}}_{\mathrm{ss}}{E}_{\mathrm{ss}}A\right)+\frac{\∂}{\∂s}\left({\mathrm{\ρ}}_{\mathrm{ss}}{E}_{\mathrm{ss}}{V}_{\mathrm{ss}}A\right)=q_{\mathrm{ss}}-q_{\mathrm{rs}}+x_{\mathrm{rs}}$

Stratum output CO ₂The sour gas phase

$\frac{\∂}{\∂t}\left({\mathrm{\ρ}}_{\mathrm{sc}}{E}_{\mathrm{sc}}A\right)+\frac{\∂}{\∂s}\left({\mathrm{\ρ}}_{\mathrm{sc}}{E}_{\mathrm{sc}}{V}_{\mathrm{sc}}A\right)=q_{\mathrm{sc}}-q_{\mathrm{rc}}+x_{\mathrm{rc}}$

Stratum output hydrocarbon gas dissolving phase

$\frac{\∂}{\∂t}\left({\mathrm{\ρ}}_{\mathrm{rg}}{E}_{\mathrm{rg}}A\right)+\frac{\∂}{\∂s}\left({\mathrm{\ρ}}_{\mathrm{rg}}{E}_{\mathrm{rg}}{V}_{\mathrm{rg}}A\right)=q_{\mathrm{rg}}-x_{\mathrm{rg}}$

Stratum output H ₂S sour gas dissolving phase

$\frac{\∂}{\∂t}\left({\mathrm{\ρ}}_{\mathrm{rs}}{E}_{\mathrm{rs}}A\right)+\frac{\∂}{\∂s}\left({\mathrm{\ρ}}_{\mathrm{rs}}{E}_{\mathrm{rs}}{V}_{\mathrm{rs}}A\right)=q_{\mathrm{rs}}-x_{\mathrm{rs}}$

Stratum output CO ₂Sour gas dissolving phase

$\frac{\∂}{\∂t}\left({\mathrm{\ρ}}_{\mathrm{rc}}{E}_{\mathrm{rc}}A\right)+\frac{\∂}{\∂s}\left({\mathrm{\ρ}}_{\mathrm{rc}}{E}_{\mathrm{rc}}{V}_{\mathrm{rc}}A\right)=q_{\mathrm{rc}}-x_{\mathrm{rc}}$

The landwaste phase

$\frac{d}{\mathrm{dt}}\left({\mathrm{AE}}_c{\mathrm{\ρ}}_c\right)+\frac{d}{\mathrm{ds}}\left({\mathrm{AE}}_c{\mathrm{\ρ}}_c{V}_c\right)=q_c$

Stratum output water

$\frac{d}{\mathrm{dt}}\left({\mathrm{AE}}_w{\mathrm{\ρ}}_w\right)+\frac{d}{\mathrm{ds}}\left({\mathrm{AE}}_w{\mathrm{\ρ}}_w{V}_w\right)=q_w$

Total volume fraction

E _rg+E _rs+E _rc+E _g+E _ss+E _sc+E _m+E _c＝1

(2), the equation of momentum:

$\frac{\∂}{\∂t}({\mathrm{AE}}_g{\mathrm{\ρ}}_g{V}_g+{\mathrm{AE}}_{\mathrm{ss}}{\mathrm{\ρ}}_{\mathrm{ss}}{V}_{\mathrm{ss}}+{\mathrm{AE}}_{\mathrm{sc}}{\mathrm{\ρ}}_{\mathrm{sc}}{V}_{\mathrm{sc}}+{\mathrm{AE}}_{\mathrm{rg}}{\mathrm{\ρ}}_{\mathrm{rg}}{V}_{\mathrm{rg}}+{\mathrm{AE}}_{\mathrm{rs}}{\mathrm{\ρ}}_{\mathrm{rs}}{V}_{\mathrm{rs}}+{\mathrm{AE}}_{\mathrm{rc}}{\mathrm{\ρ}}_{\mathrm{rc}}{V}_{\mathrm{rc}}$

$+A{E}_m{\mathrm{\ρ}}_m{V}_m+{\mathrm{AE}}_c{\mathrm{\ρ}}_c{V}_c)+\frac{\∂}{\∂s}({\mathrm{AE}}_g{\mathrm{\ρ}}_g{V}_g^2+{\mathrm{AE}}_{\mathrm{ss}}{\mathrm{\ρ}}_{\mathrm{ss}}{V}_{\mathrm{ss}}^2+{\mathrm{AE}}_{\mathrm{sc}}{\mathrm{\ρ}}_{\mathrm{sc}}{V}_{\mathrm{sc}}^2+{\mathrm{AE}}_{\mathrm{rg}}{\mathrm{\ρ}}_{\mathrm{rg}}{V}_{\mathrm{rg}}^2$ $\left(\right($

$+{\mathrm{AE}}_{\mathrm{rs}}{\mathrm{\ρ}}_{\mathrm{rs}}{V}_{\mathrm{rs}}^2+{\mathrm{AE}}_{\mathrm{rc}}{\mathrm{\ρ}}_{\mathrm{rc}}{V}_{\mathrm{rc}}^2+{\mathrm{AE}}_m{\mathrm{\ρ}}_m{V}_m^2+{\mathrm{AE}}_c{\mathrm{\ρ}}_c{V}_c^2)+\mathrm{Ag}\cos \mathrm{\α}(E_g{\mathrm{\ρ}}_g+E_{\mathrm{ss}}{\mathrm{\ρ}}_{\mathrm{ss}}+$

$E_{\mathrm{sc}}{\mathrm{\ρ}}_{\mathrm{sc}}+E_{\mathrm{rg}}{\mathrm{\ρ}}_{\mathrm{rg}}+E_{\mathrm{rs}}{\mathrm{\ρ}}_{\mathrm{rs}}+E_{\mathrm{rc}}{\mathrm{\ρ}}_{\mathrm{rc}}+E_m{\mathrm{\ρ}}_m+E_c{\mathrm{\ρ}}_c)+A\frac{\mathrm{dP}}{\mathrm{ds}}+A{\left|\frac{\mathrm{dP}}{\mathrm{ds}}\right|}_{\mathrm{fr}}=0$

3), energy equation

$\frac{\∂}{\∂t}[\left({\mathrm{\ρ}}_{\mathrm{ga}}{E}_{\mathrm{ga}}{C}_{\mathrm{ga}}{T}_a\right)+\left({\mathrm{\ρ}}_l{E}_l{C}_l{T}_a\right)]A-\frac{\∂}{\∂s}[\left(w_{\mathrm{ga}}{C}_{\mathrm{ga}}{T}_a\right)+\left(w_l{C}_l{T}_a\right)]$

$=\frac{2\mathrm{\π}\left(r_{\mathrm{co}}{U}_a{k}_e\right)}{k_e+r_{\mathrm{co}}{U}_a{T}_D}(T_{\mathrm{ei}}-T_a)-2{\mathrm{\πr}}_{\mathrm{ti}}{U}_t(T_a-T_t)$

(4), auxiliary ten thousand journeys

The present invention considers the phase transformation between oil/gas, above-critical state in the high acid gas-containing deep-well flows, gas in water-base drilling fluid dissolving and separate out, alternate slippage, the coupling of stratum filtration and pit shaft Multiphase Flow, and Multiphase Flow governing equation group confining factor, need a series of subsidiary equation, algoritic module to call relevant parameter and set up subsidiary equation.Relevant parameter comprises: fluid density ρ, fluid pressure P, fluid temperature (F.T.) T, fluidity type i, overcritical factor S, gas solubility R _g, dissolved gas oil ratio R _s, the density p of gas under the mark condition _Gs, gas critical pressure P _GPc, gas critical-temperature T _GTc, formation temperature T _e, surface temperature T _o, well depth h, geothermal gradient Δ T, gas slip speed V _Gr, gas density ρ _g, drilling fluid density ρ _m, drilling fluid viscosity μ _m, gas viscosity μ _g, circulation of drilling fluid passage equivalent diameter D _e, cuttings density ρ _c, solid phase subsidence velocity V _Cr, discrimination factor F _j, gas velocity V _g, gas volume fraction E _g, annular space runner geometric area Φ _A, the drill string inner diameter d _Tin, the drill string outside diameter d _Tout, mineshaft diameter r _w, stratum output hydro carbons tolerance q _g, stratum output H ₂S tolerance q _Ss, stratum output CO ₂Tolerance q _Sc, stratum output oil mass q _o, stratum output water yield q _w, shaft bottom landwaste output q _c, formation pore pressure P _p, reservoir thickness h _f, oil reservoir drainage radius r _e, oleic permeability k _o, oil phase viscosity μ _o, water phase permeability k _w, aqueous viscosity μ _w, gas phase permeability k _g, gaseous viscosity μ _g, hydro carbons gas molar fraction m _g, H ₂S molar fraction m _Gs, CO ₂Molar fraction m _GcRate of penetration V _RopConcrete subsidiary equation is as follows:

Fluid PVT equation: ρ=f (P, T, i, S)

Gas solubility equation: R _g=f (P, T, i, S)

Dissolved gas oil ratio equation: R _s=f (P, T, ρ _o, ρ _Gs)

Gas critical-temperature equation: T _GTc=f (P, T, i)

Gas critical pressure equation: P _GPc=f (P, T, i)

The fluid above-critical state is judged equation: S=f (P, T, i, T _GPc, T _GTc)

Formation temperature field equation: T _e=f (T ₀, h, Δ T)

Gas phase slippage velocity equation: V _Gr=f (P, T, ρ _g, ρ _m, μ _m, μ _g, D _e)

Solid phase settling rate equation: V _Cr=f (P, T, ρ _c, ρ _m, μ _m, D _e)

Discrimination equation: F _j=f (P, T, S, V _g, V _Gr, ρ _g, E _g)

Well absorbing boundary equation: Φ _A=Γ (h, d _Tin, d _Tout, r _w)

Formation oil yield equation: q _o=f (P, T, P _p, h _f, r _w, r _e, k _o, μ _o)

Formation water rate equation: q _w=f (P, T, P _p, h _f, r _w, r _e, k _w, μ _w)

Formation hydrocarbon gas yield equation: q _g=f (P, T, P _p, h _f, r _w, r _e, k _g, μ _g, m _g)

H ₂S gas yield equation: q _Ss=f (P, T, P _p, h _f, r _w, r _e, k _g, μ _g, m _Gs)

CO ₂Gas yield equation: q _Sc=f (P, T, P _p, h _f, r _w, r _e, k _g, μ _g, m _Gc)

Landwaste yield equation: q _c=f (A, V _Rop, ρ _c)

4, in conjunction with the activities under the different operating modes of controlled pressure drilling well, set up the definite condition of Multiphase Flow governing equation group

In conjunction with the activities under the different operating modes of controlled pressure drilling well, obtain primary condition and the fringe conditions of Multiphase Flow governing equation group.Algoritic module calls primary condition and the fringe conditions that relevant parameter is set up the Multiphase Flow equation group.Relevant parameter comprises: certain flow parameter X in the pit shaft, space nodes n, timing node t, last timing node t-1, drill string inlet temperature T _In, drill string inner fluid temperature T _t, annular space inner fluid temperature T _a, formation temperature T _e, surface temperature T ₀, well depth h, geothermal gradient Δ T, current well depth H, annular pressure P, controlled pressure drilling is set bottom pressure P _Bs, inject gas phase discharge capacity q _Pg, inject drilling well liquid phase discharge capacity q _m, stratum output hydro carbons tolerance q _g, stratum output H ₂S tolerance q _Ss, stratum output CO ₂Tolerance q _Sc, stratum output oil mass q _o, stratum output water yield q _w, shaft bottom landwaste output q _c, owing to rising/the lower interior mud flow rate q of the annular space that causes that bores _Mt

Primary condition:

It is that the primary condition of flow parameter is the parameter distribution in the whole pit shaft of its previous moment that thermal field under each operating mode and pressure field are found the solution, that is:

The solution of Temperature fringe conditions:

The fluid temperature of drill string entrance can directly be measured, that is: T _t(0, t)=T _In

Liquid and annulus fluid equate in the temperature at place, shaft bottom in the drill string, that is: T _t(H, t)=T _a(H, t)

The formation temperature field is known, that is: T _e=T ₀+ Δ Th

Pressure field is found the solution fringe conditions and is divided following several different operating modes:

The pressure control drilling condition:

$\left\{\begin{array}{c}P(H,t)=P_{\mathrm{bs}}\\ q_{\mathrm{pg}}(h,t)=q_{\mathrm{pg}}\\ q_m(h,t)=q_m\\ q_g(h,t)=q_g\\ q_{\mathrm{ss}}(h,t)=q_{\mathrm{ss}}\\ q_{\mathrm{sc}}(h,t)=q_{\mathrm{sc}}\\ q_o(h,t)=q_o\\ q_w(h,t)=q_w\\ q_c(H,t)=q_c\end{array}\right.$

Operating mode makes a trip:

$\left\{\begin{array}{c}P(H,t)=P_{\mathrm{bs}}\\ q_{\mathrm{pg}}(h,t)=0\\ q_m(h,t)=q_{\mathrm{mt}}\\ q_g(h,t)=0\\ q_{\mathrm{ss}}(h,t)=0\\ q_{\mathrm{sc}}(h,t)=0\\ q_o(h,t)=0\\ q_w(h,t)=0\\ q_c(H,t)=0\end{array}\right.$

Operating mode makes up a joint:

$\left\{\begin{array}{c}P(H,t)=P_{\mathrm{bs}}\\ q_{\mathrm{pg}}(h,t)=0\\ q_m(h,t)=0\\ q_g(h,t)=0\\ q_{\mathrm{ss}}(h,t)=0\\ q_{\mathrm{sc}}(h,t)=0\\ q_o(h,t)=0\\ q_w(h,t)=0\\ q_c(H,t)=0\end{array}\right.$

The time of 5, Multiphase Flow being calculated and spatial domain are carried out Finite Difference Meshes and are divided

Spatial domain is whole drill string and annular space node, and time-domain describes as an example of annular space example for implementing the whole process of controlled pressure drilling.The present invention dynamically selects space lattice length according to the gas rate of climb, and grid is not thin under the pit shaft, and upper grid is close.Long such as arbitrary space lattice: Δ S _j=S _J+1-S _j, time step adopts non-homogeneous form equally, follows the tracks of the multiphase flow forward position, according to gas rate of climb v _gAnd should the space lattice length Δ S of place _j, by formula Obtain time step Δ t, the grid of time and spatial domain is divided as shown in Figure 2.

6, quantize the Multiphase Flow governing equation discrete

Algoritic module calls multiphase flow governing equation group the cell of timing node i space nodes j is found the solution, and adopts 4 difference schemes to disperse.

Wherein, the continuity equation of the discrete form of continuity equation liquid phase in the drilling fluid describes as example, and its discrete form is:

${\left({\mathrm{\ρ}}_m{E}_m{V}_{m}A\right)}_{j+1}^{n+1}-{\left({\mathrm{\ρ}}_m{E}_m{V}_{m}A\right)}_j^{n+1}$

$=\frac{\mathrm{\Δs}}{2\mathrm{\Δt}}[{\left({\mathrm{\ρ}}_m{E}_{m}A\right)}_j^n+{\left({\mathrm{\ρ}}_m{E}_{m}A\right)}_{j+1}^n-{\left({\mathrm{\ρ}}_m{E}_{m}A\right)}_j^{n+1}-{\left({\mathrm{\ρ}}_m{E}_{m}A\right)}_{j+1}^{n+1}]$

The discrete form of the equation of momentum:

${\left(p\right)}_{j+1}^{n+1}-{\mathrm{\ρ}}_j^{n+1}$

$=\frac{\mathrm{\ΔS}}{2\mathrm{\Δt}}[({\mathrm{AE}}_g{\mathrm{\ρ}}_g{V}_g+{\mathrm{AE}}_{\mathrm{ss}}{\mathrm{\ρ}}_{\mathrm{ss}}{V}_{\mathrm{ss}}+{\mathrm{AE}}_{\mathrm{sc}}{\mathrm{\ρ}}_{\mathrm{sc}}{V}_{\mathrm{sc}}+{\mathrm{AE}}_{\mathrm{rg}}{\mathrm{\ρ}}_{\mathrm{rg}}{V}_{\mathrm{rg}}$

${+{\mathrm{AE}}_{\mathrm{rs}}{\mathrm{\ρ}}_{\mathrm{rs}}{V}_{\mathrm{rs}}+{\mathrm{AE}}_{\mathrm{rc}}{\mathrm{\ρ}}_{\mathrm{rc}}{V}_{\mathrm{rc}}+{\mathrm{AE}}_m{\mathrm{\ρ}}_m{V}_m+{\mathrm{AE}}_c{\mathrm{\ρ}}_c{V}_c)}_j^n$

$+({\mathrm{AE}}_g{\mathrm{\ρ}}_g{V}_g+{\mathrm{AE}}_{\mathrm{ss}}{\mathrm{\ρ}}_{\mathrm{ss}}{V}_{\mathrm{ss}}+{\mathrm{AE}}_{\mathrm{sc}}{\mathrm{\ρ}}_{\mathrm{sc}}{V}_{\mathrm{sc}}+{\mathrm{AE}}_{\mathrm{rg}}{\mathrm{\ρ}}_{\mathrm{rg}}{V}_{\mathrm{rg}}$

${+{\mathrm{AE}}_{\mathrm{rs}}{\mathrm{\ρ}}_{\mathrm{rs}}{V}_{\mathrm{rs}}+{\mathrm{AE}}_{\mathrm{rc}}{\mathrm{\ρ}}_{\mathrm{rc}}{V}_{\mathrm{rc}}+{\mathrm{AE}}_m{\mathrm{\ρ}}_m{V}_m+{\mathrm{AE}}_c{\mathrm{\ρ}}_c{V}_c)}_{j+1}^n$

$-({\mathrm{AE}}_g{\mathrm{\ρ}}_g{V}_g+{\mathrm{AE}}_{\mathrm{ss}}{\mathrm{\ρ}}_{\mathrm{ss}}{V}_{\mathrm{ss}}+{\mathrm{AE}}_{\mathrm{sc}}{\mathrm{\ρ}}_{\mathrm{sc}}{V}_{\mathrm{sc}}+{\mathrm{AE}}_{\mathrm{rg}}{\mathrm{\ρ}}_{\mathrm{rg}}{V}_{\mathrm{rg}}$

${+{\mathrm{AE}}_{\mathrm{rs}}{\mathrm{\ρ}}_{\mathrm{rs}}{V}_{\mathrm{rs}}+{\mathrm{AE}}_{\mathrm{rc}}{\mathrm{\ρ}}_{\mathrm{rc}}{V}_{\mathrm{rc}}+{\mathrm{AE}}_m{\mathrm{\ρ}}_m{V}_m+{\mathrm{AE}}_c{\mathrm{\ρ}}_c{V}_c)}_j^{n+1}$

$-({\mathrm{AE}}_g{\mathrm{\ρ}}_g{V}_g+{\mathrm{AE}}_{\mathrm{ss}}{\mathrm{\ρ}}_{\mathrm{ss}}{V}_{\mathrm{ss}}+{\mathrm{AE}}_{\mathrm{sc}}{\mathrm{\ρ}}_{\mathrm{sc}}{V}_{\mathrm{sc}}+{\mathrm{AE}}_{\mathrm{rg}}{\mathrm{\ρ}}_{\mathrm{rg}}{V}_{\mathrm{rg}}$

$+{{\mathrm{AE}}_{\mathrm{rs}}{\mathrm{\ρ}}_{\mathrm{rs}}{V}_{\mathrm{rs}}+{\mathrm{AE}}_{\mathrm{rc}}{\mathrm{\ρ}}_{\mathrm{rc}}{V}_{\mathrm{rc}}+{\mathrm{AE}}_m{\mathrm{\ρ}}_m{V}_m+{\mathrm{AE}}_c{\mathrm{\ρ}}_c{V}_c)}_{j+1}^{n+1}]$

$+\left[\right({\mathrm{AE}}_g{\mathrm{\ρ}}_g{V}_g^2+{\mathrm{AE}}_{\mathrm{ss}}{\mathrm{\ρ}}_{\mathrm{ss}}{V}_{\mathrm{ss}}^2+{\mathrm{AE}}_{\mathrm{sc}}{\mathrm{\ρ}}_{\mathrm{sc}}{V}_{\mathrm{sc}}^2+{\mathrm{AE}}_{\mathrm{rg}}{\mathrm{\ρ}}_{\mathrm{rg}}{V}_{\mathrm{rg}}^2$

${+{\mathrm{AE}}_{\mathrm{rs}}{\mathrm{\ρ}}_{\mathrm{rs}}{V}_{\mathrm{rs}}^2+{\mathrm{AE}}_{\mathrm{rc}}{\mathrm{\ρ}}_{\mathrm{rc}}{V}_{\mathrm{rc}}^2+{\mathrm{AE}}_m{\mathrm{\ρ}}_m{V}_m^2+{\mathrm{AE}}_c{\mathrm{\ρ}}_c{V}_c^2)}_j^{n+1}$

$-({\mathrm{AE}}_g{\mathrm{\ρ}}_g{V}_g^2+{\mathrm{AE}}_{\mathrm{ss}}{\mathrm{\ρ}}_{\mathrm{ss}}{V}_{\mathrm{ss}}^2+{\mathrm{AE}}_{\mathrm{sc}}{\mathrm{\ρ}}_{\mathrm{sc}}{V}_{\mathrm{sc}}^2+{\mathrm{AE}}_{\mathrm{rg}}{\mathrm{\ρ}}_{\mathrm{rg}}{V}_{\mathrm{rg}}^2$

${+{\mathrm{AE}}_{\mathrm{rs}}{\mathrm{\ρ}}_{\mathrm{rs}}{V}_{\mathrm{rs}}^2+{\mathrm{AE}}_{\mathrm{rc}}{\mathrm{\ρ}}_{\mathrm{rc}}{V}_{\mathrm{rc}}^2+{\mathrm{AE}}_m{\mathrm{\ρ}}_m{V}_m^2+{\mathrm{AE}}_c{\mathrm{\ρ}}_c{V}_c^2)}_{j+1}^{n+1}]$

$-\frac{\mathrm{\ΔS}}{2}\left[\right(\mathrm{Ag}\cos \mathrm{\α}(E_g{\mathrm{\ρ}}_g+E_{\mathrm{ss}}{\mathrm{\ρ}}_{\mathrm{ss}}+E_{\mathrm{sc}}{\mathrm{\ρ}}_{\mathrm{sc}}+E_{\mathrm{rg}}{\mathrm{\ρ}}_{\mathrm{rg}}$

${+E_{\mathrm{rs}}{\mathrm{\ρ}}_{\mathrm{rs}}+E_{\mathrm{sc}}{\mathrm{\ρ}}_{\mathrm{sc}}+E_m{\mathrm{\ρ}}_m+E_c{\mathrm{\ρ}}_c))}_j^{n+1}$

$+(\mathrm{Ag}\cos \mathrm{\α}(E_g{\mathrm{\ρ}}_g+E_{\mathrm{ss}}{\mathrm{\ρ}}_{\mathrm{ss}}+E_{\mathrm{sc}}{\mathrm{\ρ}}_{\mathrm{sc}}+E_{\mathrm{rg}}{\mathrm{\ρ}}_{\mathrm{rg}}$

${{+E}_{\mathrm{rs}}{\mathrm{\ρ}}_{\mathrm{rs}}+E_{\mathrm{sc}}{\mathrm{\ρ}}_{\mathrm{sc}}+E_m{\mathrm{\ρ}}_m+E_c{\mathrm{\ρ}}_c\left)\right)}_{j+1}^{n+1}]$

$-\frac{\mathrm{\ΔS}}{2}[A{{\left|\frac{\mathrm{dp}}{\mathrm{ds}}\right|}_{\mathrm{fr}}}_j^{n+1}+A{\left|\frac{{\mathrm{dF}}_r}{\mathrm{ds}}\right|}_{j+1}^{n+1}]$

The discrete form of energy equation:

${[\left(w_{\mathrm{ga}}{C}_{\mathrm{ga}}{T}_a\right)+\left(w_l{C}_l{T}_a\right)]}_{j+1}^{n+1}-{[\left(w_{\mathrm{ga}}{C}_{\mathrm{ga}}{T}_a\right)+\left(w_l{C}_l{T}_a\right)]}_j^{n+1}$

$=\frac{\mathrm{\Δs}}{2\mathrm{\Δt}}[{({\mathrm{\ρ}}_{\mathrm{ga}}{C}_{\mathrm{ga}}{T}_{a}A+{\mathrm{\ρ}}_l{C}_l{T}_{a}A)}_j^n+{({\mathrm{\ρ}}_{\mathrm{ga}}{C}_{\mathrm{ga}}{T}_{a}A+{\mathrm{\ρ}}_l{C}_l{T}_{a}A)}_{j+1}^n$

$-{({\mathrm{\ρ}}_{\mathrm{ga}}{C}_{\mathrm{ga}}{T}_{a}A+{\mathrm{\ρ}}_l{C}_l{T}_{a}A)}_j^{n+1}-{({\mathrm{\ρ}}_{\mathrm{ga}}{C}_{\mathrm{ga}}{T}_{a}A+{\mathrm{\ρ}}_l{C}_l{T}_{a}A)}_{j+1}^{n+1}]$

$+\frac{\mathrm{\Δs}}{2}\{{[\frac{{\mathrm{\πr}}_{\mathrm{co}}{U}_a{k}_e}{k_e+r_{\mathrm{co}}{U}_a{T}_D}(T_{\mathrm{ei}}-T_a)-{\mathrm{\πr}}_{\mathrm{ti}}{U}_t(T_a-T_t)]}_j^{n+1}+$

${[\frac{{\mathrm{\πr}}_{\mathrm{co}}{U}_a{k}_e}{k_e+r_{\mathrm{co}}{U}_a{T}_D}(T_{\mathrm{ei}}-T_a)-{\mathrm{\πr}}_{\mathrm{ti}}{U}_t(T_a-T_t)]}_{j+1}^{n+1}\}$

7, find the solution the required wellhead back pressure of controlled pressure drilling well

Can read the currency of (n constantly) wellhead back pressure of certain moment in the controlled pressure drilling process by the measureing equipment of wellhead back pressure

According to n moment wellhead back pressure value

Calculate constantly Multiphase Flow parameter in the pit shaft of n, and as the n+1 primary condition calculated of wellhead back pressure constantly; According to the controlled pressure drilling well next constantly standard value of (n+1 constantly) bottom pressure is determined in the requirement of bottom pressure

Standard value according to n+1 moment bottom pressure

Determine the wellhead back pressure value that n+1 is constantly required

Grid in the annular space is divided from top to bottom, and the shaft bottom node is designated as the j node, and it is as follows that the required wellhead back pressure of controlled pressure drilling calculates concrete steps:

The first step: the measureing equipment by wellhead back pressure reads n wellhead back pressure constantly in the controlled pressure drilling process

Second step: according to n moment wellhead back pressure

Calculate the constantly interior Multiphase Flow parameter of pit shaft of n, such as annular pressure, each phase velocity, each phase volume fraction, as the primary condition of constantly wellhead back pressure calculating of n+1, flow process is as shown in Figure 3.

(1) supposes n bottom pressure constantly

(2) calculate place, shaft bottom annular space inner fluid temperature

(3) in conjunction with the output of each phase in the stratum filtration equation solution stratum;

(4) judge the phase of gas and calculate the solubility that the shaft bottom is located by phase equilibrium equation;

(5) output and the solubility with stratum output gas phase compares, and determines that each phase gas is at the meltage in shaft bottom;

(6) locate speed, volume fraction, the density parameter of each phase according to continuity equation and Solving Equation of State shaft bottom this moment, and as the known parameters of next space nodes (j+1 node);

(7) suppose j+1 Nodes n pressure constantly

(8) calculate j+1 node n temperature constantly

(9) judge whether the j+1 node is positioned at payzone, and ask for the output of this moment each phase of stratum of this node;

(10) calculate the constantly phase of each phase of j+1 node n by phase equilibrium equation, and calculate the solubility of this each phase of node this moment;

(11) solubility of j+1 node and the solubility of j node are compared, judge the amount of separating out of two internodal dissolving gas phases;

(12) find the solution the constantly density of each phase of j+1 node n;

(13) find the solution each phase velocity, volume fraction parameter by continuity equation;

(14) find the solution j+1 node n pressure constantly by the equation of momentum

And with the hypothesis pressure

Compare, if error between the two within allowed band, then j+1 Nodes n pressure constantly is

Otherwise, return (6), reappraise j+1 node n pressure constantly, until meet the demands;

(15) with the j+1 node n that obtains each phase parameter constantly as known, continue the calculating of next node (j+2 node);

(16) repeating step (6)～(15) calculate wellhead back pressure to well head node j+M And with n known wellhead back pressure constantly

Relatively, if both in error range, the n that supposes of step (1) bottom pressure constantly then

Be current bottom pressure

Otherwise repeating step (1)～(15) are until satisfy condition.

The 3rd step: next constantly standard value of (n+1 constantly) bottom pressure is determined in the requirement of bottom pressure according to the controlled pressure drilling well

Require such as the X well that the shaft bottom is in under-voltage condition in the controlled pressure drilling process, and under-voltage value is Δ P, then the n+1 standard value of bottom pressure constantly

The 4th step: the Multiphase Flow parameter of calculating gained with second step is as primary condition, according to the n+1 standard value of bottom pressure constantly Determine the wellhead back pressure value that n+1 is constantly required

Flow process as shown in Figure 4.

(1) determines that n+1 bottom pressure constantly is standard value

(2) calculate constantly place, shaft bottom annular space inner fluid temperature of n+1

(3) in conjunction with the stratum filtration equation solution n+1 output of each phase in the stratum constantly;

(4) judge the phase of n+1 moment gas and calculate the solubility that the shaft bottom is located by phase equilibrium equation;

(5) output and the solubility with stratum output gas phase compares, and determines that n+1 each phase gas of the moment is at the meltage in shaft bottom;

(6) constantly locate speed, volume fraction, the density of each phase in the shaft bottom according to continuity equation and Solving Equation of State n+1, and as the known parameters of next space nodes (j+1 node);

(7) suppose j+1 Nodes n+1 pressure constantly

(8) calculate j+1 node n+1 temperature constantly

(9) judge whether the j+1 node is positioned at payzone, and ask for the constantly output of this each phase of node stratum of n+1;

(10) calculate j+1 node n+1 phase constantly by phase equilibrium equation, and calculate the solubility of this node this moment;

(11) solubility of j+1 node and the solubility of j node are compared, judge the amount of separating out of two internodal dissolving gas phases;

(12) find the solution the constantly density of each phase of j+1 node n+1;

(13) find the solution n+1 constantly each phase velocity, volume fraction by continuity equation;

(14) find the solution j+1 node n+1 pressure constantly by the equation of momentum

And with the hypothesis pressure

Compare, if error between the two within allowed band, then j+1 Nodes n+1 pressure constantly is

Otherwise, return (6), reappraise j+1 node n+1 pressure constantly, until meet the demands;

(15) with the j+1 node n+1 that obtains each phase parameter constantly as known, continue the calculating of next node (j+2 node);

(16) repeating step (6)～(15) calculate constantly required wellhead back pressure of n+1 to well head node j+M

8, based on calculating gained wellhead back pressure value, regulate throttle valve opening, reach required wellhead back pressure, realize real-time wellhead back pressure control.

Claims (10)

1. a controlled pressure boring method that calculates based on the bored shaft Multiphase Flow is characterized in that, step is as follows:

(1), obtains the basic parameter that the bored shaft Multiphase Flow calculates;

(2), determine the kind of mineshaft annulus inner fluid;

(3), consider multi-phase multi-component Complex Flows factor, set up the Multiphase Flow governing equation group in the mineshaft annulus;

(4), in conjunction with the activities under the different operating modes of controlled pressure drilling well, set up the definite condition of Multiphase Flow governing equation group;

The time of (5), Multiphase Flow being calculated and spatial domain are carried out grid and are divided;

(6), quantize the Multiphase Flow governing equation discrete;

(7), find the solution the required wellhead back pressure of controlled pressure drilling well;

(8), based on the wellhead back pressure value of calculating, regulate the well head choke valve, realize that pressure control creeps into.

2. the controlled pressure boring method that calculates based on the bored shaft Multiphase Flow according to claim 1, it is characterized in that: the basic parameter that described bored shaft Multiphase Flow calculates comprises: the discharge capacity of casing programme, drilling assembly, bit depth, formation data, hole angle, azimuth, injection drilling fluid gas phase and liquid phase, drilling fluid density, drilling fluid viscosity, current time wellhead back pressure.

3. the described controlled pressure boring method that calculates based on the bored shaft Multiphase Flow according to claim 1-2, it is characterized in that: the kind of described mineshaft annulus inner fluid comprises: the gas, liquid that injects drilling fluid, the landwaste that the place, shaft bottom produces, the oil of output, gas, water in the stratum, and the phase transformation gas of oil in migration process, the acidic components in the natural gas.

4. the described controlled pressure boring method that calculates based on the bored shaft Multiphase Flow according to claim 1-3, it is characterized in that: described consideration multi-phase multi-component Complex Flows factor refers to: the gas, liquid that injects drilling fluid, the landwaste that the place, shaft bottom produces, the oil of output, gas, water in the stratum, and the phase transformation between oil/gas, above-critical state in the high acid gas-containing deep-well flow and sour gas in water-base drilling fluid dissolving and separate out, alternate slippage, the coupling of stratum filtration and pit shaft Multiphase Flow.

5. the described controlled pressure boring method that calculates based on the bored shaft Multiphase Flow according to claim 1-4, it is characterized in that: the described Multiphase Flow governing equation group of setting up in the mineshaft annulus comprises: the continuity equation of each phase, momentum conservation equation, energy conservation equation and subsidiary equation in the annular space inner fluid.

6. the described controlled pressure boring method that calculates based on the bored shaft Multiphase Flow according to claim 1-5, it is characterized in that: the different operating modes of described controlled pressure drilling well comprise: the pressure control drilling condition, rise/lower driller's condition, operating mode makes up a joint; The definite condition of described Multiphase Flow governing equation group comprises: the primary condition of wellbore pressure field and solution of Temperature and fringe conditions.

7. the described controlled pressure boring method that calculates based on the bored shaft Multiphase Flow according to claim 1-6, it is characterized in that: the acidic components in the described natural gas comprise: hydrogen sulfide and carbon dioxide; The subsidiary equation of setting up comprises: the solubility equation of fluid state equation, sour gas, above-critical state are judged equation, stratum output equation, discrimination equation, slippage velocity equation, formation temperature field equation; The Multiphase Flow parameter comprises in the described pit shaft: the annular pressure at diverse location place, temperature, the volume fraction of each phase, the speed of each phase in the pit shaft.

8. the described controlled pressure boring method that calculates based on the bored shaft Multiphase Flow according to claim 1-7, it is characterized in that: the described time that Multiphase Flow is calculated and spatial domain are carried out grid and are divided and refer to: whole mineshaft annulus as spatial domain, will be implemented the whole process of controlled pressure drilling as time-domain; Dynamically select space lattice length according to the gas rate of climb, space lattice is dredged in wellbore bottom, and is close in upper wellbore; The non-homogeneous form of the same employing of time step is determined time step according to the gas rate of climb and this place's space lattice length.

9. the described controlled pressure boring method that calculates based on the bored shaft Multiphase Flow according to claim 1-8, it is characterized in that: described with Multiphase Flow governing equation discrete the referring to that quantize: as to adopt 4 difference schemes that continuity equation, the equation of momentum and energy equation are dispersed, obtain the discrete form of Multiphase Flow governing equation group finite difference.

10. the described controlled pressure boring method that calculates based on the bored shaft Multiphase Flow according to claim 1-9, it is characterized in that: the described step of finding the solution the required wellhead back pressure of controlled pressure drilling well comprises:

(1), the measureing equipment by wellhead back pressure reads the controlled pressure drilling process wellhead back pressure at current quarter;

(2), according to the wellhead back pressure value of current time, calculate Multiphase Flow parameter in the current time pit shaft, as next primary condition of calculating of wellhead back pressure constantly;

(3), according to the requirement of controlled pressure drilling well to bottom pressure, calculate next constantly standard value of bottom pressure;

(4), the pit shaft Multiphase Flow parameter calculated take current time is as primary condition, according to next standard value of bottom pressure constantly, calculates next constantly required wellhead back pressure value.

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