CN105092785A - Polymer injection well injection capacity evaluation method considering polymer viscoelasticity - Google Patents

Abstract

The invention relates to a polymer injection well injection capacity evaluation method considering polymer viscoelasticity, wherein the method includes the following steps: 1) establishing an effective shearing rate model during seepage of a polymer solution in a rock porous medium; 2) establishing a polymer solution viscoelasticity apparent viscosity model; 3) providing establishing conditions of a polymer injection well polymer injection driving capacity evaluation model; 4) establishing a single-oil-layer polymer injection well geological model, and providing model parameters; 5) establishing a polymer injection well flow control equation, an oil layer seepage control equation and a polymer injection well and oil layer contact surface continuity equation; 6) listing boundary conditions of a polymer injection well and an oil layer; 7) establishing an equation group by the effective shearing rate model, the viscoelasticity apparent viscosity model, the polymer injection well flow control equation, the oil layer seepage control equation and the polymer injection well and oil layer contact surface continuity equation, and solving the equation group under different polymer injection well injection pressures; and 8) according to the solved results, calculating the injection volume and the injection intensity, and evaluating the injection capacity of the polymer injection well by the injecting intensity.

Description

A kind of injection well injectability evaluation method considering polymer viscoelastic

Technical field

The present invention relates to a kind of injection well injectability evaluation method, particularly relate to and a kind ofly use polymer flooding to develop oil fields to consider the injection well injectability evaluation method of polymer viscoelastic in process.

Background technology

At present, polymer flooding has become the major technique that land oilfields in high water cut period improves recovery ratio, also becomes the important means that offshore oilfield improves recovery ratio simultaneously.In polymer flooding heavy industrialization application process, expose some technical matterss gradually, a wherein outstanding problem is: injection well Severe blockage, injection pressure is caused sharply to rise unreasonably, cause injectability degradation, injection well cannot complete injection allocation by injection allocation ratio, even stops note.Therefore, how to assess injection well injection pressure and injectability exactly, be one of key issue affecting polymer flooding development effectiveness and whole economic efficiency, particularly important in the enforcement that guarantee testing in Bohai heavy oil fields premature polymerization thing drives.

The polymer solution being applied to polymer flooding belongs to non-Newtonian fluid, and oil reservoir belongs to rock porous medium, when studying the rheological behaviour of non-Newtonian fluid in porous medium, generally non-Newtonian fluid is assumed to power rate fluid.But research in recent years finds, polymer solution shows complicated rheological behaviour when flowing in subsurface rock porous medium, along with the increase of flow rate, carry out from Newtonian fluid to shear thinning again to the transformation of shear thickening rheological behaviour, namely not only show viscous effect, also show certain elastic effect.But not yet find the injection well injectability evaluation method considering polymer solution Viscoelastic effect in prior art, cause to make accurate evaluation to the injection pressure of injection well and injectability.

Summary of the invention

For the problems referred to above, the object of this invention is to provide a kind of injection well injectability evaluation method considering polymer viscoelastic, can quick and precisely evaluate injection well injectability, instruct injection well Water injection rate, prevent reservoir choke and stop the problems such as note.

For achieving the above object, the present invention takes following technical scheme: a kind of injection well injectability evaluation method considering polymer viscoelastic, and it comprises the following steps:

1) the effective shear rate model of polymer solution in rock porous medium during seepage flow is set up;

2) polymer solution viscoelasticity apparent viscosity model is set up;

3) set up the condition of injection well polymer flooding injectability evaluation model is provided;

4) according to step 3) the model set up the condition that provides, set up the individual reservoir injection well geologic model for evaluating injection well injectability, and provide its model parameter;

5) according to step 3) the model set up the condition that provides and step 4) the individual reservoir injection well geologic model that provides, set up the Fluid Control Equation of injection well, the osmotic control equation of oil reservoir and injection well and oil reservoir surface of contact continuity equation;

6) according to step 3) the model set up the condition that provides and step 4) the individual reservoir injection well geologic model that provides, list the boundary condition of injection well and oil reservoir;

7) by step 4) model parameter that provides substitutes into step 1) and step 2) in effective shear rate model of obtaining and polymer solution viscoelasticity apparent viscosity model, by step 6) injection well and oil reservoir boundary condition substitute into step 5) in injection well Fluid Control Equation, oil reservoir osmotic control equation and the injection well set up and oil reservoir surface of contact continuity equation, be unified into vertical system of equations, under different injection well injection pressures, solve the flowing velocity u of injection well interpolymer solution _wellwith the percolation flow velocity u of oil reservoir interpolymer solution _res;

8) according to step 7) solving result, calculating injection rate IR Q and inject intensity q, evaluating the injectability of injection well by injecting intensity q; Inject intensity q larger, represent that the injectability of injection well is stronger.

Described step 1) in effective shear rate model be:

In formula, for the effective shear rate of polymer solution in rock porous medium during seepage flow; C is the effective shear rate constant of polymer solution, relevant with factor of porosity to the permeability of rock porous medium, gets 1; n ₁for polymer solution shear Thinning Index; u _resfor the percolation flow velocity of polymer solution in rock porous medium; K is rock porous medium permeability; k _rwfor polymer solution relative permeability; S _wfor polymer solution saturation degree; for rock porous medium factor of porosity.

Described step 2) in polymer solution viscoelasticity apparent viscosity model comprise shear thinning apparent viscosity μ when polymer solution flows in injection well _{app, well}with polymer flow through rock porous medium time viscoelasticity apparent viscosity μ _{app, res}, wherein:

${\mathrm{\μ}}_{app,well}={\mathrm{\μ}}_{\mathrm{\∞}}+({\mathrm{\μ}}_0-{\mathrm{\μ}}_{\mathrm{\∞}}){(1+{\left({\mathrm{\λ}}_1\stackrel{\·}{\mathrm{\γ}}\right)}^{\mathrm{\α}})}^{(n_1-1)/\mathrm{\α}}$

${\mathrm{\μ}}_{app,res}={\mathrm{\μ}}_{\mathrm{\∞}}+({\mathrm{\μ}}_0-{\mathrm{\μ}}_{\mathrm{\∞}}){(1+{\left({\mathrm{\λ}}_1{\stackrel{\·}{\mathrm{\γ}}}_{eff}\right)}^{\mathrm{\α}})}^{(n_1-1)/\mathrm{\α}}+{\mathrm{\μ}}_{max}(1-e^{\{-{\left({\mathrm{\τ}}_r{\mathrm{\λ}}_2{\stackrel{\·}{\mathrm{\γ}}}_{eff}\right)}^{n_2-1}\}})$

In formula, μ _∞for polymer solution high shear viscosity; μ ₀for polymer solution zero-shear viscosity; λ ₁, λ ₂be respectively polymer solution shear desaturation constant and shear thickening constant; for polymer solution shear speed; α is empirical constant, generally gets 2; n ₂for polymer solution shear thickening index; μ _maxfor the mxm. of shear degradation generation prepolymer solution viscosity; τ _rfor injecting the slack time of fluid; E is natural logarithm.

Described step 3) in model set up the condition specifically comprise:

1. the viscoelastic effect of polymer solution is considered;

2. being coupled of flowing and seepage flow in oil reservoir in injection well pit shaft is considered;

3. oil reservoir homogeneous, uniform thickness, isotropy is supposed;

4. open hole completion, injection well is hydrodynamic force completely penetrating well, ignores skin effect;

5. injection well bottom end closure, ignores the centripetal stream of sphere of injection well bottom;

6. suppose that in oil reservoir, seepage flow is planar radial steady flow, flow process ignores the impact of gravity and capillary force;

7. suppose that in flowing and oil reservoir, seepage flow is single-phase flow in pit shaft, the moisture and polymkeric substance two kinds of components of polymer solution fluid, and water and polymkeric substance complete miscibility;

8. suppose that the polymer solution injected is micro-compressible fluid;

9. the reservoir permeability ignored caused by the Adsorption And Retention of polymkeric substance on rock porous medium surface declines;

10. the degraded of polymkeric substance in rock porous medium during seepage flow is ignored;

assuming that pit shaft in flowing and oil reservoir in flow event be isothermal process.

Described step 4) in the individual reservoir injection well geologic model set up be the circular oil reservoir of horizontal homogeneous uniform thickness, the injection well bottom through oil reservoir is drilled with in circular oil reservoir center, by injection well inlet end level pressure injection of polymer solution, injection well bottom end closure, oil reservoir is rock porous medium, close up and down, outer boundary is constant-pressure boundary; The model parameter of described individual reservoir injection well geologic model is: injection well radius R _w, Oil reservoir radius R _e, core intersection h, injection well injection pressure P _w, oil reservoir terminal pressure P _e, reservoir permeability k.

Described step 5) in set up injection well interpolymer solution Fluid Control Equation be:

$\mathrm{\ρ}({\stackrel{\→}{u}}_{well}\·\▿{\stackrel{\→}{u}}_{well})=\▿\·\{p_{well}+{\mathrm{\μ}}_{app,well}(\▿{\stackrel{\→}{u}}_{well}+{(\▿{\stackrel{\→}{u}}_{well})}^T)\}$

Oil reservoir interpolymer fluid flow governing equation is:

$\▿\·{\stackrel{\→}{u}}_{res}=0;{\stackrel{\→}{u}}_{res}=-\frac{k}{{\mathrm{\μ}}_{app,res}}\▿\·p_{res}$

Injection well and oil reservoir surface of contact continuity equation are:

p _well＝p _res(r＝R _w,0≤z≤h)

u _well＝u _res(r＝R _w,0≤z≤h)

Above-mentioned various in, ρ is polymer solution density, u _wellfor the flowing velocity of injection well interpolymer solution, u _resfor the percolation flow velocity of oil reservoir interpolymer solution, p _wellfor injection well interpolymer solution pressure, p _resfor oil reservoir interpolymer solution pressure, T is polymer solution temperature.

Described step 6) in the injection well boundary condition that obtains be:

p _well＝P _w(z＝h,0≤r≤R _w)

u _well＝0(z＝0,0≤r≤R _w)

Oil reservoir boundary condition is:

p _res＝P _e(r＝R _e,0≤z≤h)

u _res＝0(z＝h,R _w≤r≤R _e)

u _res＝0(z＝0,R _w≤r≤R _e)。

Described step 8) in the computing formula of injection rate IR Q be:

Q＝πR _w ²u _well(z＝h,0≤r≤R _w)

The computing formula injecting intensity q is:

$q=\frac{Q}{P_w}.$

Adopt analysis of finite element method solve described step 7) in system of equations.

The polymer solution injected is polyacrylamide solution.

The present invention is owing to taking above technical scheme, it has the following advantages: 1, the present invention proposes a kind of injection well injectability evaluation method considering polymer viscoelastic, by introducing the viscoelastic computing formula of quantification characterize polymers, and flow in the injection well that is coupled and seepage flow condition in oil reservoir porous medium, set up individual layer oil reservoir injection well injectability evaluation model, realize the accurate quantitative analysis evaluation to injection well injectability, thus instruct the Water injection rate of injection well in oilfield development process, prevent reservoir choke and stop the problems such as note; 2, the present invention adopts analysis of finite element method to solve injection well injectability evaluation model, realizes quick and precisely evaluating injection well injectability, make the practicality of the technology of the present invention method and operability stronger.

Accompanying drawing explanation

Fig. 1 is the plan structure schematic diagram of individual layer geological model of oil accumulation of the present invention;

Fig. 2 is the sectional structure schematic diagram of individual layer geological model of oil accumulation of the present invention;

Fig. 3 is the structure for amplifying schematic diagram in A portion in Fig. 2.

Embodiment

Below in conjunction with drawings and Examples, the present invention is described in detail.

A kind of injection well injectability evaluation method considering polymer viscoelastic of the present invention, comprises the following steps:

1) the effective shear rate model of polymer solution in rock porous medium during seepage flow is set up:

In formula, for the effective shear rate of polymer solution in rock porous medium during seepage flow; C is the effective shear rate constant of polymer solution, and relevant with factor of porosity to the permeability of rock porous medium, the present embodiment gets 1; n ₁for polymer solution shear Thinning Index; u _resfor the percolation flow velocity of polymer solution in rock porous medium; K is rock porous medium permeability; k _rwfor polymer solution relative permeability; S _wfor polymer solution saturation degree; for rock porous medium factor of porosity.

2) polymer solution viscoelasticity apparent viscosity model is set up:

Shear thinning apparent viscosity μ when polymer solution apparent viscosity can be divided into polymer solution to flow in injection well by situation _{app, well}with polymer flow through rock porous medium time viscoelasticity apparent viscosity μ _{app, res}, be characterized by respectively:

${\mathrm{\μ}}_{app,well}={\mathrm{\μ}}_{\mathrm{\∞}}+({\mathrm{\μ}}_0-{\mathrm{\μ}}_{\mathrm{\∞}}){(1+{\left({\mathrm{\λ}}_1\stackrel{\·}{\mathrm{\γ}}\right)}^{\mathrm{\α}})}^{(n_1-1)/\mathrm{\α}}---\left(2\right)$

${\mathrm{\μ}}_{app,res}={\mathrm{\μ}}_{\mathrm{\∞}}+({\mathrm{\μ}}_0-{\mathrm{\μ}}_{\mathrm{\∞}}){(1+{\left({\mathrm{\λ}}_1{\stackrel{\·}{\mathrm{\γ}}}_{eff}\right)}^{\mathrm{\α}})}^{(n_1-1)/\mathrm{\α}}+{\mathrm{\μ}}_{\max }(1-e^{\{-{\left({\mathrm{\τ}}_r{\mathrm{\λ}}_2{\stackrel{\·}{\mathrm{\γ}}}_{eff}\right)}^{n_2-1}\}})---\left(3\right)$

In formula, μ _∞for polymer solution high shear viscosity; μ ₀for polymer solution zero-shear viscosity; λ ₁, λ ₂be respectively polymer solution shear desaturation constant and shear thickening constant; for polymer solution shear speed; α is empirical constant, generally gets 2; n ₂for polymer solution shear thickening index; μ _maxfor the mxm. of shear degradation generation prepolymer solution viscosity; τ _rfor injecting the slack time of fluid; E is natural logarithm.

3) provide the set up the condition of injection well polymer flooding injectability evaluation model, specifically comprise:

1. the viscoelastic effect of polymer solution is considered;

2. being coupled of flowing and seepage flow in oil reservoir in injection well pit shaft is considered;

3. oil reservoir homogeneous, uniform thickness, isotropy is supposed;

4. open hole completion, injection well is hydrodynamic force completely penetrating well, ignores skin effect;

5. injection well bottom end closure, ignores the centripetal stream of sphere of injection well bottom;

6. suppose that in oil reservoir, seepage flow is planar radial steady flow, flow process ignores the impact of gravity and capillary force;

7. suppose that in flowing and oil reservoir, seepage flow is single-phase flow in pit shaft, the moisture and polymkeric substance two kinds of components of polymer solution fluid, and water and polymkeric substance complete miscibility;

8. suppose that the polymer solution injected is micro-compressible fluid;

9. the reservoir permeability ignored caused by the Adsorption And Retention of polymkeric substance on rock porous medium surface declines;

10. the degraded of polymkeric substance in rock porous medium during seepage flow is ignored;

assuming that pit shaft in flowing and oil reservoir in flow event be isothermal process.

4) according to step 3) model set up the condition, set up the individual reservoir injection well geologic model for evaluating injection well injectability, and provide its model parameter:

As shown in FIG. 1 to 3, from model set up the condition, individual reservoir injection well geologic model is the circular oil reservoir 2 of horizontal homogeneous uniform thickness, the injection well 1 bottom through oil reservoir 2 is drilled with in circular oil reservoir 2 center, by injection well 1 inlet end level pressure injection of polymer solution, injection well 1 bottom end closure, oil reservoir 2 is rock porous medium, close up and down, outer boundary is constant-pressure boundary; Be true origin with injection well 1 wellbore bottom center (being also oil reservoir 2 bottom centre), radial distance r points to outer, height z by initial point and point to injection well 1 entrance by initial point and set up cylindrical-coordinate system (due to oil reservoir 2 isotropy, user's parallactic angle is not needed in modeling, therefore omit), then individual reservoir injection well geologic model is take r=0 as the circular reservoir model of radial symmetry axis, setting model parameter: injection well 1 radius R _w, oil reservoir 2 radius R _e, oil reservoir 2 thickness h, injection well 1 injection pressure P _w, oil reservoir 2 terminal pressure P _e, oil reservoir 2 permeability k.

5) Fluid Control Equation of injection well 1, the osmotic control equation of oil reservoir 2 and injection well 1 and oil reservoir 2 surface of contact continuity equation is set up.

According to step 3) the model set up the condition that provides and step 4) the individual reservoir injection well geologic model that provides is known, the flowing of injection well 1 interpolymer solution is controlled by Navier-Stokes (Neville-Stokes) equation, the only generation shear thinning behavior and polymer solution flows in injection well 1, its apparent viscosity is determined by shear thinning model, and namely the apparent viscosity of injection well 1 interpolymer solution is shear thinning apparent viscosity μ _{app, well}; Oil reservoir 2 is rock porous medium, the seepage flow of rock porous medium interpolymer solution is controlled by Darcy's law, and the apparent viscosity of polymer solution in rock porous medium during seepage flow is determined by viscoelasticity apparent viscosity model, namely the apparent viscosity of oil reservoir 2 interpolymer solution is viscoelasticity apparent viscosity μ _{app, res}; Meanwhile, the surface of contact of injection well 1 sidewall and oil reservoir 2 should meet the condition of continuity.Can draw according to above-mentioned conclusion:

Injection well 1 interpolymer solution Fluid Control Equation:

$\mathrm{\ρ}({\stackrel{\→}{u}}_{well}\·\▿{\stackrel{\→}{u}}_{well})=\▿\·\{p_{well}+{\mathrm{\μ}}_{app,well}(\▿{\stackrel{\→}{u}}_{well}+{(\▿{\stackrel{\→}{u}}_{well})}^T)\}---\left(4\right)$

Oil reservoir 2 interpolymer fluid flow governing equation:

$\▿\·{\stackrel{\→}{u}}_{res}=0;{\stackrel{\→}{u}}_{res}=-\frac{k}{{\mathrm{\μ}}_{app,res}}\▿\·p_{res}---\left(5\right)$

Injection well 1 and oil reservoir 2 surface of contact continuity equation:

p _well＝p _res(r＝R _w,0≤z≤h)(6)

u _well＝u _res(r＝R _w,0≤z≤h)(7)

Above-mentioned various in, ρ is polymer solution density, u _wellfor the flowing velocity of injection well 1 interpolymer solution, u _resfor the percolation flow velocity of oil reservoir 2 interpolymer solution, p _wellfor injection well 1 interpolymer solution pressure, p _resfor oil reservoir 2 interpolymer solution pressure, T is polymer solution temperature.

6) according to step 3) the model set up the condition that provides and step 4) the individual reservoir injection well geologic model that provides, list injection well 1 boundary condition and oil reservoir 2 boundary condition.

As shown in Figure 3, geologic model take r=0 as axis of symmetry, injection well 1 inlet end level pressure injection of polymer solution, injection well 1 bottom end closure, then injection well 1 boundary condition is:

p _well＝P _w(z＝h,0≤r≤R _w)(8)

u _well＝0(z＝0,0≤r≤R _w)(9)

Oil reservoir about 2 is closed boundary, and outer boundary is constant-pressure boundary, then oil reservoir 2 boundary condition is:

p _res＝P _e(r＝R _e,0≤z≤h)(10)

u _res＝0(z＝h,R _w≤r≤R _e)(11)

u _res＝0(z＝0,R _w≤r≤R _e)(12)

7) model parameter and boundary condition are substituted into step 2) formula that provides and step 5) in the equation set up, simultaneous solution system of equations.

Polymer Solution Property parameter and reservoir geology parameter are substituted in formula (1), (2), (3), by step 6) boundary condition (8) ~ (12) substitute in equation (4) ~ (7), be unified into vertical system of equations, comprise equation (1) ~ (7); At different injection well 1 injection pressure P _wunder solve the flowing velocity u of injection well 1 interpolymer solution _wellwith the percolation flow velocity u of oil reservoir 2 interpolymer solution _res.

8) according to step 7) solving result, calculating injection rate IR Q and inject intensity q, evaluating the injectability of injection well by injecting intensity q.

Be less than the condition of formation rock parting pressure in injection pressure under, namely injection well injectability can be injected intensity q to represent by the injection rate IR under unit pressure reduction, and injecting intensity q can by injection rate IR Q and injection pressure P _wrelation obtain.

Wherein, the computing formula of injection rate IR Q is:

Q＝πR _w ²u _well(z＝h,0≤r≤R _w)(13)

The computing formula injecting intensity q is:

$q=\frac{Q}{P_w}---\left(14\right)$

Inject intensity q larger, then represent that the injectability of injection well is stronger.

In above-described embodiment, step 7) in solving equation group analysis of finite element method can be adopted to solve.Because polymer solution is non-Newtonian fluid, polymer solution apparent viscosity is the nonlinear function of shear rate, considers the viscoelastic effect of polymer solution simultaneously, and the analytical expression solving injectability will be more difficult; And according to setting up the mathematical model of individual reservoir injection well geologic model, adopt analysis of finite element method to solve, the different injection pressure P of injection well 1 can be obtained fast _wthe flowing velocity u of lower injection well 1 interpolymer solution _wellwith the percolation flow velocity u of oil reservoir 2 interpolymer solution _resnumerical solution, thus obtain injection rate IR Q and injection pressure P _wrelation, and then obtain inject intensity q.

In above-described embodiment, the polymer solution of injection is polyacrylamide (HydrolyzedPolyacryamide, abbreviation HPAM) solution.

The present invention not only can be widely used in oil-field development research field, can also to be widely used in other research field relevant with seepage flow or as a reference, such as Groundwater movement research etc.

The various embodiments described above are only for illustration of the present invention; wherein the structure of each parts, setting position and connected mode etc. thereof all can change to some extent; every equivalents of carrying out on the basis of technical solution of the present invention and improvement, all should not get rid of outside protection scope of the present invention.

Claims (10)

1. consider an injection well injectability evaluation method for polymer viscoelastic, it comprises the following steps:

1) the effective shear rate model of polymer solution in rock porous medium during seepage flow is set up;

2) polymer solution viscoelasticity apparent viscosity model is set up;

3) set up the condition of injection well polymer flooding injectability evaluation model is provided;

4) according to step 3) the model set up the condition that provides, set up the individual reservoir injection well geologic model for evaluating injection well injectability, and provide its model parameter;

5) according to step 3) the model set up the condition that provides and step 4) the individual reservoir injection well geologic model that provides, set up the Fluid Control Equation of injection well, the osmotic control equation of oil reservoir and injection well and oil reservoir surface of contact continuity equation;

6) according to step 3) the model set up the condition that provides and step 4) the individual reservoir injection well geologic model that provides, list the boundary condition of injection well and oil reservoir;

7) by step 4) model parameter that provides substitutes into step 1) and step 2) in effective shear rate model of obtaining and polymer solution viscoelasticity apparent viscosity model, by step 6) injection well and oil reservoir boundary condition substitute into step 5) in injection well Fluid Control Equation, oil reservoir osmotic control equation and the injection well set up and oil reservoir surface of contact continuity equation, be unified into vertical system of equations, under different injection well injection pressures, solve the flowing velocity u of injection well interpolymer solution _wellwith the percolation flow velocity u of oil reservoir interpolymer solution _res;

8) according to step 7) solving result, calculating injection rate IR Q and inject intensity q, evaluating the injectability of injection well by injecting intensity q; Inject intensity q larger, represent that the injectability of injection well is stronger.

2. a kind of injection well injectability evaluation method considering polymer viscoelastic as claimed in claim 1, is characterized in that, described step 1) in effective shear rate model be:

In formula, for the effective shear rate of polymer solution in rock porous medium during seepage flow; C is the effective shear rate constant of polymer solution, relevant with factor of porosity to the permeability of rock porous medium, gets 1; n ₁for polymer solution shear Thinning Index; u _resfor the percolation flow velocity of polymer solution in rock porous medium; K is rock porous medium permeability; k _rwfor polymer solution relative permeability; S _wfor polymer solution saturation degree; for rock porous medium factor of porosity.

3. a kind of injection well injectability evaluation method considering polymer viscoelastic as claimed in claim 2, it is characterized in that, described step 2) in polymer solution viscoelasticity apparent viscosity model comprise shear thinning apparent viscosity μ when polymer solution flows in injection well _{app, well}with polymer flow through rock porous medium time viscoelasticity apparent viscosity μ _{app, res}, wherein:

${\mathrm{\μ}}_{app,well}={\mathrm{\μ}}_{\mathrm{\∞}}+({\mathrm{\μ}}_0-{\mathrm{\μ}}_{\mathrm{\∞}}){(1+{\left({\mathrm{\λ}}_1\stackrel{\·}{\mathrm{\γ}}\right)}^{\mathrm{\α}})}^{(n_1-1)/\mathrm{\α}}$

${\mathrm{\μ}}_{app,res}={\mathrm{\μ}}_{\mathrm{\∞}}+({\mathrm{\μ}}_0-{\mathrm{\μ}}_{\mathrm{\∞}}){(1+{\left({\mathrm{\λ}}_1{\stackrel{\·}{\mathrm{\γ}}}_{eff}\right)}^{\mathrm{\α}})}^{(n_1-1)/\mathrm{\α}}+{\mathrm{\μ}}_{max}\left(1-e^{\left\{-{\left({\mathrm{\τ}}_r{\mathrm{\λ}}_2{\stackrel{\·}{\mathrm{\γ}}}_{eff}\right)}^{n_2-1}\right\}}\right)$

In formula, μ _∞for polymer solution high shear viscosity; μ ₀for polymer solution zero-shear viscosity; λ ₁, λ ₂be respectively polymer solution shear desaturation constant and shear thickening constant; for polymer solution shear speed; α is empirical constant, generally gets 2; n ₂for polymer solution shear thickening index; μ _maxfor the mxm. of shear degradation generation prepolymer solution viscosity; τ _rfor injecting the slack time of fluid; E is natural logarithm.

4. a kind of injection well injectability evaluation method considering polymer viscoelastic as claimed in claim 1, is characterized in that, described step 3) in model set up the condition specifically comprise:

1. the viscoelastic effect of polymer solution is considered;

2. being coupled of flowing and seepage flow in oil reservoir in injection well pit shaft is considered;

3. oil reservoir homogeneous, uniform thickness, isotropy is supposed;

4. open hole completion, injection well is hydrodynamic force completely penetrating well, ignores skin effect;

5. injection well bottom end closure, ignores the centripetal stream of sphere of injection well bottom;

6. suppose that in oil reservoir, seepage flow is planar radial steady flow, flow process ignores the impact of gravity and capillary force;

7. suppose that in flowing and oil reservoir, seepage flow is single-phase flow in pit shaft, the moisture and polymkeric substance two kinds of components of polymer solution fluid, and water and polymkeric substance complete miscibility;

8. suppose that the polymer solution injected is micro-compressible fluid;

9. the reservoir permeability ignored caused by the Adsorption And Retention of polymkeric substance on rock porous medium surface declines;

10. the degraded of polymkeric substance in rock porous medium during seepage flow is ignored;

assuming that pit shaft in flowing and oil reservoir in flow event be isothermal process.

5. a kind of injection well injectability evaluation method considering polymer viscoelastic as claimed in claim 3, it is characterized in that, described step 4) in the individual reservoir injection well geologic model set up be the circular oil reservoir of horizontal homogeneous uniform thickness, the injection well bottom through oil reservoir is drilled with in circular oil reservoir center, by injection well inlet end level pressure injection of polymer solution, injection well bottom end closure, oil reservoir is rock porous medium, close up and down, outer boundary is constant-pressure boundary; The model parameter of described individual reservoir injection well geologic model is: injection well radius R _w, Oil reservoir radius R _e, core intersection h, injection well injection pressure P _w, oil reservoir terminal pressure P _e, reservoir permeability k.

6. a kind of injection well injectability evaluation method considering polymer viscoelastic as claimed in claim 5, is characterized in that, described step 5) in set up injection well interpolymer solution Fluid Control Equation be:

$\mathrm{\ρ}({\stackrel{\→}{u}}_{well}\·\▿{\stackrel{\→}{u}}_{well})=\▿\·\{p_{well}+{\mathrm{\μ}}_{app,well}(\▿{\stackrel{\→}{u}}_{well}+{\left(\▿{\stackrel{\→}{u}}_{well}\right)}^T)\}$

Oil reservoir interpolymer fluid flow governing equation is:

$\▿\·{\stackrel{\→}{u}}_{res}=0;{\stackrel{\→}{u}}_{res}=-\frac{k}{{\mathrm{\μ}}_{app,res}}\▿\·p_{res}$

Injection well and oil reservoir surface of contact continuity equation are:

p _well＝p _res(r＝R _w,0≤z≤h)

u _well＝u _res(r＝R _w,0≤z≤h)

Above-mentioned various in, ρ is polymer solution density, u _wellfor the flowing velocity of injection well interpolymer solution, u _resfor the percolation flow velocity of oil reservoir interpolymer solution, p _wellfor injection well interpolymer solution pressure, p _resfor oil reservoir interpolymer solution pressure, T is polymer solution temperature.

7. a kind of injection well injectability evaluation method considering polymer viscoelastic as claimed in claim 6, is characterized in that, described step 6) in the injection well boundary condition that obtains be:

p _well＝P _w(z＝h,0≤r≤R _w)

u _well＝0(z＝0,0≤r≤R _w)

Oil reservoir boundary condition is:

p _res＝P _e(r＝R _e,0≤z≤h)

u _res＝0(z＝h,R _w≤r≤R _e)

u _res＝0(z＝0,R _w≤r≤R _e)。

8. a kind of injection well injectability evaluation method considering polymer viscoelastic as claimed in claim 7, is characterized in that, described step 8) in the computing formula of injection rate IR Q be:

Q＝πR _w ²u _well(z＝h,0≤r≤R _w)

The computing formula injecting intensity q is:

$q=\frac{Q}{P_w}.$

9. a kind of injection well injectability evaluation method considering polymer viscoelastic as claimed in claim 1, is characterized in that, adopt analysis of finite element method solve described step 7) in system of equations.

10. a kind of injection well injectability evaluation method considering polymer viscoelastic as claimed in claim 1, it is characterized in that, the polymer solution of injection is polyacrylamide solution.