CN104504192B - A kind of simulation method of nano particle shutoff shale pore throat - Google Patents

Abstract

The invention discloses a kind of simulation method of nano particle shutoff shale pore throat, based on shale pore structure characteristic, the analogue simulation size of setting shale and boundary condition; The starting condition of setting nano particle each stressed and speed in drilling fluid; According to particle and drilling fluid properties, set up and set particle contacts and motion model; Application discrete element method solves nano-granular system and the process with the particle contacts in shale surface and hole, collision, deposition and migration, analogue simulation goes out shale hole shutoff situation and plugged zone pore texture etc., and announcement shutoff rule and shutoff microprocess are with machine-processed.

Description

A kind of simulation method of nano particle shutoff shale pore throat

Technical field

The present invention relates to the analogue simulation research method of nano particle shutoff shale pore throat, belong to the anti-unstability of the petroleum drilling completion borehole wall, reservoir protection and leak stopping leak proof technology field.

Background technology

Water-base drilling fluid probing shale bed key is effectively to reduce drilling fluid aqueous phase irruptive rock layer, and this is the Pinch technology concerning shale gas economic development.Current drilling fluid blocks water, precipitation is invaded the Strategic Measures taked and mainly contained following methods: 1. Chemical Inhibition Method by adding shale control agent and the water suction of expansion-resisting agent prevention shale, dehydration and expanding in drilling fluid; 2. chemical plugging by adding chemical membrane agent in drilling fluid, forms one deck impermeable film or selectivity semi-permeable diaphragm block water and enter shale hole at the borehole wall; 3. physics shutoff by adding with the particle of pore throat diameter adaptation, elastic granule or forming foam etc. in drilling fluid, and borehole wall physics plugged zone blocks water, precipitation is invaded to utilize the elastic granule of the particle of grating or scalable expansion or foam blocking shale pore throat to be formed.

Particle shutoff precipitation is invaded from the middle of last century, and Chinese scholars has carried out great many of experiments and study mechanism, defines 1/3 outer mud cake rule, shields multiple theory of granulartities such as blocking up temporarily, ideal filling, d90 are regular.

Relevant nano particle shutoff shale pore throat, current existing data document is all adopt the strategy process of experiment to carry out the research of shutoff mechanism, shutoff rule and system formulation.Texas, USA university Austin shale laboratory is according to shale pore throat characteristics of diameters, introduce SiO2 nano particle shutoff shale pore throat precipitation to invade, define the efficient anti-unstability experimental technique of nano particle shutoff shale pore throat, and applied for the United States Patent (USP) (No.2009/0314549,2011/EP2315911) of shutoff experimental technique.At present, for such research, there are no relevant numerical simulation or simulation study method report.

Summary of the invention

The invention provides a kind of analogue simulation research method of nano particle shutoff shale pore throat, simulation discloses microprocess and the mechanism of nano particle shutoff shale pore throat, draws rule and the plugged zone density (porosity) of nano particle shutoff shale pore throat.

The technical solution used in the present invention is as follows:

A simulation method for nano particle shutoff shale pore throat, comprises the steps:

Step (1) characterizes shale, and experiment test multi-point statistic obtain all kinds of characterisitic parameters of shale body, carry out the simplification of pore texture body feature form, provide agent structure feature;

Step (2) setting nano particle is the soft ball with viscosity, elasticity, plasticity, with contact force-displacement model, describe the contact between particle and particle, between particle and the borehole wall, employing normal direction, tangential vibrations and tangential frost-heaves, rolling movement equation describe contact model; Based on the equation of motion that Newton second law is set up, and equation solution is carried out to the equation of motion;

Step (3) is according to shale particle diameter composition, consolidation strength, three stress states, elastic modulus, Poisson ratio, setting shale composition particle ball and rock frame stress state, generate a rectangular parallelepiped or different uneven surface annular cylinder or different uneven surface oval ring cylinder border, press particle diameter composition stochastic generation shale body particle swarm again, under stress state, contact compacting be full of whole rectangular parallelepiped or different uneven surface annular cylinder or different uneven surface oval ring cylinder; According to testing the shale body architectural feature drawn, in shale analogue body, deleting the particle in pore texture shape, forming shale body opening gap structure;

Step (4) utilizes the middle borehole wall rock mass border of contact model, the equation of motion and step (3) in step (2), particle characteristics and speed starting condition is given to shutoff nano particle group, apply the effect of all kinds of acting force and fluid, setting stops strategy, calculate the equation of motion by step during setting and judge particle contacts, adopting different iterative algorithm to carry out the simulation of shutoff shale pore throat.

Shale sign is carried out by SEM imaging or Micro-CT, high-pressure mercury, triaxial stress, sreen analysis Physical Experiment means in step (1).

Characterisitic parameter described in step (1) comprises pore character radius, connectedness, tortuosity, factor of porosity, intensity, particle diameter composition.

In step (2), self-defined sticky, elastic and plastic properties contact force-displacement model is shown in formula (1), (2).

F _c＝F _v(v _ij)+F _e(δ，v _ij)+F _p(δ，v _ij)(1)

In formula, F _cfor interparticle contact power; F _v(v _ij) be liquid film acting force; F _e(δ, v _ij) be particle elastic deformation stage acting force; F _p(δ, v _ij) be particulate plastic deformation stage acting force; δ is interparticle contact deflection, v _ijfor particles collision relative velocity.

$\begin{array}{c}{F}_v\left(v_{\mathrm{ij}}\right)=c_f{v}_{\mathrm{ij}}^0...r_c\&le;r_{\mathrm{ij}}<r_c+b_{\text{ij}}\\ F_e(\mathrm{\&delta;},v_{\mathrm{ij}})=c_e{v_{\mathrm{ij}}}^{\&prime;}+k_e\mathrm{\&delta;}...r_c-{\mathrm{\&delta;}}_y\&le;r_{\mathrm{ij}}<r_c\\ F_p(\mathrm{\&delta;},v_{\mathrm{ij}})=c_p{v}_{\mathrm{ij}}^{\&prime;\&prime;}+l_p(\mathrm{\&delta;}-{\mathrm{\&delta;}}_y)...r_{\mathrm{ij}}<r_c-{\mathrm{\&delta;}}_y\end{array}---\left(2\right)$

In formula, c _ffor the lubrication ratio of damping of particle surface attachment liquid film; r _ijbe the centre distance of two particles; r _cequal the radius sum of two particles; b _ijit is the drilling fluid liquid film width sum of two particle surface absorption; c _efor collision deformation elastic stage ratio of damping; c _pfor collision deformation plastic stage ratio of damping; v _ij', v ' ' _ijbe respectively particles collision attachment liquid film starts time of contact, particle bulk starts time of contact, particle starts to occur speed of related movement between particle corresponding to plasticity moment; k _efor Elastic contact stiffness; k _pfor plastic contact coefficient; δ is interparticle contact deflection; δ _yfor deflection when particle reaches yield stress.

The equation of motion that step (2) is set up is shown in formula (3), (4):

$m\frac{d^2\stackrel{\&RightArrow;}{\mathrm{\&Delta;}}}{{\mathrm{dt}}^2}=\stackrel{\&RightArrow;}{G}+{\stackrel{\&RightArrow;}{F}}_f+{\stackrel{\&RightArrow;}{F}}_{\mathrm{\&Delta;p}}+{\stackrel{\&RightArrow;}{F}}_D+{\stackrel{\&RightArrow;}{F}}_R+{\stackrel{\&RightArrow;}{F}}_L+\stackrel{\&RightArrow;}{F}+{\stackrel{\&RightArrow;}{F}}_V+{\stackrel{\&RightArrow;}{F}}_e+{\stackrel{\&RightArrow;}{F}}_{\mathrm{vn}}+{\stackrel{\&RightArrow;}{F}}_{\mathrm{Lub}}\text{+}{\stackrel{\&RightArrow;}{F}}_c+{\stackrel{\&RightArrow;}{F}}_B---\left(3\right)$

$I\frac{d\stackrel{\&RightArrow;}{w}}{\mathrm{dt}}=\left|\mathrm{\&Sigma;}{\stackrel{\&RightArrow;}{F}}_{\mathrm{ct}}\right|r_p---\left(4\right)$

In formula, m is granular mass; Δ is intergranular relative displacement; G is gravity; F _ffor buoyancy; F _{Δ p}for axial pressure gradient produces pulling force; F _dfor drag; F _rfor drill string rotating side direction lifting force; F _lfor the lifting force that the upper and lower pressure reduction difference of particle produces; F is drilling well difference force; F _vfor Van der Waals force; F _efor electrostatic force; F _vufor liquid bridge power; F _lubfor lubricating capacity; F _bfor the surging force that thermal motion causes; F _cfor in collision process, act on the contact force on particle; F _ctfor tangential contact force component; r _pfor particle radius; I is particle moment of inertia; W is particle velocity of rotation.

In step (4), physical simulation mode is as follows:

(4-1) on the rectangular parallelepiped that generates in the step (3) (or different uneven surface annular cylinder or different uneven surface oval ring cylinder) shale face, shutoff particle swarm is generated by nano particle proportioning and domain size distribution, motive power is applied to all nanosphere body particles, and under the effect of various power, between particle and particle, particle and shale wall contact-impact, the interaction force of generation;

(4-2) select certain particle contacts evaluation algorithm to judge interparticle contact and particle and borehole wall Contact, to determine between particle and the various physical quantitys of relation and count particles between particle and the borehole wall;

(4-3) carry out equation of motion judgement, count particles speed and position, upgrade particle (discrete element) each physical quantity;

(4-4) adopt certain iterative algorithm to carry out step particle shutoff form when loop iteration calculates next, particle at the acting in conjunction retrofilling pore throat of motive power, and is piled up till stablizing gradually.

Acting force described in step (4-1) comprises drilling well difference force, gravity, buoyancy, lifting force, drag, pulling force that axial pressure gradient produces, Van der Waals force, liquid bridge power, electrostatic force, lubricating capacity, contact force and thermal motion cause between particle surging force.

Method/tangential component that step (4-2) physical quantity is made a concerted effort suffered by method/tangential relative displacement, rotation angle, particle.

The present invention has following excellent results:

(1) traditional experiment is replaced with analogue simulation, define new shutoff research method, contribute to eliminating the length of experimental study to shale core sample, the requirement of thickness, high sealing (more than nanoscale) condition of experimental study requirement can be avoided simultaneously.

(2) (can be obtained by experimental study) except can obtaining macroscopical plugging effect, also can reflect and disclose the important parameter (shutoff experiment cannot obtain) that the plugging effect such as microscopic void size, distribution, connectedness of the microprocess of shutoff, mechanism and plugged zone is closely related shutoff mechanism from micro-scale aspect and fall water-invasion mechanism;

(3) shale hole changes greatly, and true core has uniqueness, and only namely obtain discarded after shutoff experiment, analogue simulation can repeat to realize shutoff experiment; Nano particle can be realized mate with any shutoff of shale pore throat, comprehensive characterization nano particle shutoff shale pore throat matching grating;

(4) can be analogue simulation and directly replace experimental study supplying method, can save shale core from the necessary expense use getting out, seal and make experiment original place state a series of process of little rock core, use manpower and material resources sparingly cost;

(5) method therefor of the present invention has versatility, is applicable to many-sided all kinds of shutoff problems such as the reservoir protection in petroleum engineering field, wellbore stability, leak-proof leak-stopping.

Accompanying drawing explanation

Fig. 1 is that conditions setting is to simulate shale body 100nm × 200nm space.

Fig. 2 (a) figure represents the shale formation of shale body granular cementation compacting original state.

After Fig. 2 (b) figure represents and forms pore texture, simulation has the shale formation of certain factor of porosity.

Fig. 3 (a)-Fig. 3 (d) represents the motion conditions of four moment shutoff particles before and after t1, t2, t3, t4 respectively.

Fig. 4 (a)-Fig. 4 (i) represents the shutoff result sectional view of variable grain grating respectively.

Fig. 5 (a)-Fig. 5 (b) is for D50 rule, the schematic diagram of the shutoff fore-and-aft survey circle of drafting.

Fig. 6 is the closely knit rule figure of shutoff of variable grain grating.

Embodiment

Below in conjunction with embodiment, the invention will be further described, but be not limited thereto.

The simulation method of nano particle shutoff shale pore throat of the present invention is, based on shale pore structure characteristic, and the analogue simulation size of setting shale and boundary condition; The starting condition of setting nano particle each stressed and speed in drilling fluid; According to particle and drilling fluid properties, set up and set particle contacts and motion model; Application discrete element method solves nano-granular system and the process with the particle contacts in shale surface and hole, collision, deposition and migration, analogue simulation goes out shale hole shutoff situation and plugged zone pore texture etc., and announcement shutoff rule and shutoff microprocess are with machine-processed.

Term illustrates: discrete element method (DEM) is a kind of description and the mechanical characteristic of Analysis of Complex discrete system (Micromechanics, mechanics of granular media and particle system) and the method for value solving of the characteristics of motion.

Simulation implementation environment is the PFC2D software environment of Itasca company.

Embodiment 1:

(1) conditions setting

First generate AB, BC, CD, DA, EF five border, road, five borders, road define the space (simulation shale body 100nm × 200nm space) of two 10:5 ratios.As shown in Figure 1, conditions setting to simulate shale body 100nm × 200nm space, i.e. ABFE region, and EFCD represents annular space region, is the zone of action of nano particle; Leftward space is as borehole wall region (shale simulation region), and rightward space is as annular space region.

Present case simulation has shale formation and the migration of nano particle in Nano grade shale pore throat of certain factor of porosity, and for the ease of observing, model is amplified 10 by present case ⁸doubly to Macrovision.Wherein, the basic mechanical parameter of the shale body component particles of generation and original state, in table 1.

Table 1 shale component basic parameter

(2) shale section generation strategy

Associative list 1 shale component basic parameter, under software environment, generate shale body component particles and be filled in shale simulation region, till being filled with in shale simulation region, its structure is as shown in accompanying drawing 2 (a).

Be dominant according to data in literature shale 10nm ~ 20nm pore throat quantity, shale pore throat diameter is set to definite value 15nm, software environment is given a definition shale pore texture, then the particle of predefined pore throat character is deleted, simulation shale pore throat, obtains the shale pore texture as shown in accompanying drawing 2 (b).

(3) nanometer shutoff particles generation

Based on grain composition principle, present case adopts D10-D90 different gradation rule, and for D90, grating principle is that the grain diameter that shutoff particulate accumulation volume accounts for 90% is less than the maximum pore throat diameter of reservoir.Present case is based on the shale pore throat diameter of the 15nm of setting, the nano particle being equipped with 10nm, 20nm, 30nm tri-kinds of sizes carries out shutoff simulation, particle overall volume involved by each grating of D10-D90 is identical, scheme outfit is carried out according to the cumulative volume mark being less than shale hole and shouting the particle of diameter (15nm), outfit scheme is as shown in table 2, the basic parameter of nano particle in associative list 3, generates nanometer shutoff particle, and gives attribute shown in nano particle table 3 under software environment.

Table 2 shutoff particle basic scheme

The basic parameter of table 3 nano particle

(4) shutoff simulation

First in simulation region, shutoff particle is set perpendicular to the rotational speed of the speed on shale borehole wall direction and borehole axis direction, particle and various stressed as starting condition; Secondly, based on the drilling fluid basic parameter shown in table 4, apply fluid matasomatism.Shutoff simulation is carried out under software environment, set self-defined interparticle contact power-displacement model, the movement of particles equation (solving the equation of motion with central difference method) of foundation, NBS particle contacts determination methods judge particle contacts, the contact under the acting in conjunction of starting condition and drilling fluid of each particle, collision, deposition and migration, dynamic relaxation is adopted to carry out step particle shutoff form when loop iteration calculates next, until stable or till reaching and stopping strategy.The process of the contact of each particle, collision, deposition and migration can be monitored under software environment, not shutoff section in the same time can be obtained thus, shown in accompanying drawing 3.

Table 4 drilling fluid basic parameter

Drilling fluid density/kg/m 3	Drilling fluid viscosity/mPas	Drilling fluid flow velocity/m.s -1	Acceleration of gravity/m.s -2
				1.3×10 3	35	0.64	9.81

(5) shutoff stops strategy

In particle shutoff process, partial particulate enters pore throat, is filled in pore throat inside, forms internal filter cake; Partial particulate is formed in pore throat port and builds bridge, and meets together with particle that crag stopped by crag, finally forms outer plugged zone (outer mud cake).

When meeting the following conditions, shutoff simulation stops: 1. follow the trail of particle speed under software environment, when all shutoff particle speeds converge to 0, terminator; 2. the intergranular out-of-balance force of shutoff process reaches default value, and the ratio of the average out-of-balance force of this example is less than 0.5%, stops analogue simulation; 3. simulation reaches the time step preset, and this example 2000000 Walk (needs guarantee that simulation reaches steady state (SS)), stops analogue simulation.

(6) the shutoff simulation of variable grain grating

Based on the grain composition simulated experiment scheme (D10-D90) that present case is different, the shutoff sectional view of final formation 9 kinds of modeling schemes is as shown in accompanying drawing 4 (a)-Fig. 4 (i).Fig. 4 (a) represents d10, Fig. 4 (b) represents d20, Fig. 4 (c) % represents d30, Fig. 4 (d) represents d40, Fig. 4 (e) represents d50, and Fig. 4 (f) represents d60, and Fig. 4 (g) represents d70, Fig. 4 (h) represents d80, and Fig. 4 (i) represents d90.

(7) the shutoff simulation packing evaluation of variable grain grating

From the result sectional view of variable grain grating, the plugging effect difference of variable grain grating is obvious.Present case adopts packing to analyze plugging effect.

Based on the formula measuring circular hole porosity under software environment, obtain the formula of packing, as shown in formula (5):

$d=\frac{A_p}{A}---\left(5\right)$

In formula, d-packing, A _pthe area of particle total in-measurement circle scope, the area of A-measurement circle.

In present case, carry out analysis mode effect from two kinds of packings, namely nano particle fills the packing of the packing of pore throat (internal filter cake) and the plugged zone accumulation body (outer mud cake) of formation.

(i) particles filled pore throat packing

For particles filled pore throat packing, first the difference of the forward and backward factor of porosity of shutoff is obtained based on the measurement circle of (accompanying drawing for D50 rule) label 1-6 as shown in Figure 5, get all difference averages, as the packing (being expressed as a percentage) in shutoff pore throat, the packing of contrast 9 kinds of grain compositions, can universal law be obtained, as shown in table 5.

Table 5 variable grain grating fills pore throat packing

(ii) the outer mud cake accumulation body packing of particle

For the outer mud cake accumulation body packing of particle, based on the shutoff front and rear gaps porosity of the measurement circle of the such as label 7-12 shown in accompanying drawing (5), average is got to all differences, obtain the average packing (percentage represents) of outer mud cake, the average packing of contrast 9 kinds of grain compositions, can universal law be obtained, as shown in table 6.

The outer mud cake packing of table 6 variable grain grating

Above two kinds of packings are depicted as scatter diagram, and shown in accompanying drawing 6 (a), (b), horizontal ordinate representative is less than the number percent of the particle of pore throat diameter, and ordinate represents shutoff packing (percentage represents).From accompanying drawing 6 (a), by D10 to D90, in pore throat, packing enlarges markedly gradually; The packing of the known outer mud cake of accompanying drawing 6 (b) presents the trend of increase with the increase of cumulative volume mark shared by granule.

Dimension, under variable grain grating condition, shared by plugging effect and granule, cumulative volume number percent is in increasing progressively relation, and the nano particle shutoff shale pore throat that present case is carried out is consistent with d90 shutoff rule, and analog result is correct.

Application simulation analogy method of the present invention studies nano particle shutoff shale pore throat, except can obtaining macroscopical plugging effect (experimental study can obtain), emphasis reflects the important parameter (current laboratory facilities cannot obtain) that the plugging effect such as microscopic void size, distribution, connectedness of the microprocess of shutoff, mechanism and plugged zone is closely related, eliminate experimental study to the length thickness requirement of shale core sample simultaneously, also can ensure the repetitive operation studied, save core, airtight preservation experimental cost etc.

By reference to the accompanying drawings the specific embodiment of the present invention is described although above-mentioned; but not limiting the scope of the invention; one of ordinary skill in the art should be understood that; on the basis of technical scheme of the present invention, those skilled in the art do not need to pay various amendment or distortion that creative work can make still within protection scope of the present invention.

Claims (5)

1. a simulation method for nano particle shutoff shale pore throat, comprises the steps, it is characterized in that:

Step (1) characterizes shale, and experiment test multi-point statistic obtain all kinds of characterisitic parameters of shale body, carry out the simplification of pore texture body feature form, provide agent structure feature;

Step (2) setting nano particle is the soft ball with viscosity, elasticity, plasticity, with contact force-displacement model, describe the contact between particle and particle, between particle and the borehole wall, employing normal direction, tangential vibrations and tangential frost-heaves, rolling movement equation describe contact model; Based on the equation of motion that Newton second law is set up, and equation solution is carried out to the equation of motion;

Step (3) is according to shale particle diameter composition, consolidation strength, three stress states, elastic modulus, Poisson ratio, setting shale composition particle ball and rock frame stress state, generate a rectangular parallelepiped or different uneven surface annular cylinder or different uneven surface oval ring cylinder border, press particle diameter composition stochastic generation shale body particle swarm again, under stress state, contact compacting be full of whole rectangular parallelepiped or different uneven surface annular cylinder or different uneven surface oval ring cylinder; According to testing the shale body architectural feature drawn, in shale analogue body, deleting the particle in pore texture shape, forming shale body opening gap structure;

Step (4) utilizes the middle borehole wall rock mass border of contact model, the equation of motion and step (3) in step (2), particle characteristics and speed starting condition is given to shutoff nano particle group, apply the effect of all kinds of acting force and fluid, setting stops strategy, calculate the equation of motion by step during setting and judge particle contacts, adopting different iterative algorithm to carry out the simulation of shutoff shale pore throat;

In step (2), self-defined sticky, elastic and plastic properties contact force-displacement model, is shown in formula (1), (2);

F _c＝F _v(v _ij)+F _e(δ，v _ij)+F _p(δ，v _ij)(1)

In formula, F _cfor interparticle contact power; F _v(v _ij) be liquid film acting force; F _e(δ, v _ij) be particle elastic deformation stage acting force; F _p(δ, v _ij) be particulate plastic deformation stage acting force; δ is interparticle contact deflection, v _ijfor particles collision relative velocity;

$F_v\left(v_{ij}\right)=c_f{v}_{ijc}^0..............................r_c\&le;r_{ij}<r_c+b_{ij}$

F _e(δ,v _ij)＝c _ev _ij′+k _eδ.................r _c-δ _y≤r _ij＜r _c(2)

F _p(δ,v _ij)＝c _pv″ _ij+k _p(δ-δ _y).......r _ij＜r _c-δ _y

In formula, c _ffor the lubrication ratio of damping of particle surface attachment liquid film; r _ijbe the centre distance of two particles; r _cequal the radius sum of two particles; b _ijit is the drilling fluid liquid film width sum of two particle surface absorption; c _efor collision deformation elastic stage ratio of damping; c _pfor collision deformation plastic stage ratio of damping; v _ij', v " _ijbe respectively particles collision attachment liquid film starts time of contact, particle bulk starts time of contact, particle starts to occur speed of related movement between particle corresponding to plasticity moment; k _efor Elastic contact stiffness; k _pfor plastic contact coefficient; δ is interparticle contact deflection; δ _yfor deflection when particle reaches yield stress;

The equation of motion that step (2) is set up is shown in formula (3), (4);

$m\frac{d^2\stackrel{\&RightArrow;}{\mathrm{\&Delta;}}}{{\mathrm{dt}}^2}=\stackrel{\&RightArrow;}{G}+{\stackrel{\&RightArrow;}{F}}_f+{\stackrel{\&RightArrow;}{F}}_{\mathrm{\&Delta;}p}+{\stackrel{\&RightArrow;}{F}}_D+{\stackrel{\&RightArrow;}{F}}_R+{\stackrel{\&RightArrow;}{F}}_L+\stackrel{\&RightArrow;}{F}+{\stackrel{\&RightArrow;}{F}}_V+{\stackrel{\&RightArrow;}{F}}_e+{\stackrel{\&RightArrow;}{F}}_{vn}+{\stackrel{\&RightArrow;}{F}}_{Lub}+{\stackrel{\&RightArrow;}{F}}_c+{\stackrel{\&RightArrow;}{F}}_B---\left(3\right)$

$I\frac{d\stackrel{\&RightArrow;}{w}}{dt}=\left|\mathrm{\&Sigma;}{\stackrel{\&RightArrow;}{F}}_{ct}\right|r_p---\left(4\right)$

In formula, m is granular mass; Δ is intergranular relative displacement; G is gravity; F _ffor buoyancy; F _{Δ p}for axial pressure gradient produces pulling force; F _dfor drag; F _rfor drill string rotating side direction lifting force; F _lfor the lifting force that the upper and lower pressure reduction difference of particle produces; F is drilling well difference force; F _vfor Van der Waals force; F _efor electrostatic force; F _vufor liquid bridge power; F _lubfor lubricating capacity; F _bfor the surging force that thermal motion causes; F _cfor in collision process, act on the contact force on particle; F _ctfor tangential contact force component; r _pfor particle radius; I is particle moment of inertia; W is particle velocity of rotation;

In step (4), physical simulation mode is as follows:

(4-1) on the rectangular parallelepiped shale generated in the step (3) or different uneven surface annular cylinder or border, different uneven surface oval ring cylinder face, shutoff particle swarm is generated by nano particle proportioning and domain size distribution, motive power is applied to all nanosphere body particles, and under the effect of various power, between particle and particle, particle and shale wall contact-impact, the interaction force of generation;

(4-2) select that certain particle contacts evaluation algorithm judges between particle, particle and wall Contact, to determine between particle and the various physical quantitys of relation and count particles between particle and the borehole wall;

(4-3) equation of motion judgement is carried out, count particles speed and each physical quantity of location updating particle;

(4-4) adopt certain iterative algorithm to carry out step particle shutoff form when loop iteration calculates next, particle at the acting in conjunction retrofilling pore throat of motive power, and is piled up till stablizing gradually.

2. the simulation method of nano particle shutoff shale pore throat as claimed in claim 1, it is characterized in that, in described step (1), carry out shale sign by SEM imaging or Micro-CT, high-pressure mercury, triaxial stress and sreen analysis Physical Experiment means.

3. the simulation method of nano particle shutoff shale pore throat as claimed in claim 1, it is characterized in that, the characterisitic parameter described in step (1) comprises pore character radius, connectedness, tortuosity, factor of porosity, intensity, particle diameter.

4. the simulation method of nano particle shutoff shale pore throat as claimed in claim 1, it is characterized in that, the acting force described in step (4-1) comprises drilling well difference force, gravity, buoyancy, lifting force, drag, pulling force that axial pressure gradient produces, Van der Waals force, liquid bridge power, electrostatic force, lubricating capacity, contact force and thermal motion cause between particle surging force.

5. the simulation method of nano particle shutoff shale pore throat as claimed in claim 1, is characterized in that, the various physical quantitys described in step (4-2) comprise the method/tangential component of making a concerted effort suffered by method/tangential relative displacement, rotation angle, particle.