CN110827166B - Method for adjusting optimal steam injection speed in steam drive exploitation of heavy oil reservoir - Google Patents
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- 238000010793 Steam injection (oil industry) Methods 0.000 title claims abstract description 107
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Abstract
The invention discloses a method for adjusting the optimal steam injection speed in the steam drive exploitation of a heavy oil reservoir, which comprises the following steps of constructing a scouring multiple distribution model; secondly, collecting basic parameters; thirdly, calculating the average dryness X in the steam cavity i (ii) a Fourthly, calculating the optimal average dryness X in the steam cavity o (ii) a Fifthly, judging whether the current steam injection speed i is the optimal steam injection speed or not, and when X is reached o ＝X i When the current steam injection speed i is the optimal steam injection speed, when X is o ＞X i In time, the current steam injection speed i to X is reduced o ＝X i When X is present o ＜X i In time, the current steam injection speed i is increased to X o ＝X i . By adopting the scheme, the optimal steam injection speed of the steam injection well is reversely deduced and determined by determining the average dryness of the optimal steam cavity of the heating area, the optimal steam-drive oil extraction scheme is provided, the steam thermal efficiency is fully utilized, and the oil reservoir development effect and the economic benefit of the steam-drive oil extraction are favorably improved.
Description
Technical Field
The invention relates to the technical field of oil extraction processes, in particular to a method for adjusting the optimal steam injection speed for steam drive mining of a heavy oil reservoir.
Background
Heavy oil occupies an important proportion in oil and gas resources in the world, and steam flooding is one of the most common technologies for developing heavy oil reservoirs. During steam flooding, steam and hot water continually scour the reservoir, heating and displacing the crude oil towards the production well. Because the temperature, the oil-water viscosity and the specific volume of steam and water at different positions are greatly different, the flushing degree of the steam and hot water at different positions is different.
According to the concept of scouring multiple, the volume of water phase passing through the unit pore volume is accumulated so as to describe the displacement effect of steam and hot water at different positions. The change of the scouring multiple is closely related to the steam injection speed, the scouring multiple in the reservoir can be effectively increased by the larger steam injection speed, the steam channeling and other problems can be caused by the overlarge steam injection speed, and meanwhile, the dryness in the steam cavity is higher when the steam injection speed is higher, so that the heating efficiency of the injected steam on the oil layer is reduced; too small steam injection speed can result in slow production effect, heat loss of the top layer and the bottom layer is serious, a steam cavity cannot be formed, the development effect of steam flooding is further reduced, the steam flooding development effect can be the best only through the optimal steam injection speed, and the better development effect and the higher economic benefit are ensured.
Disclosure of Invention
In view of the above, the invention provides a method for adjusting the optimal steam injection speed for steam drive mining of a heavy oil reservoir, which can quickly assist in determining the optimal steam injection speed and improve block development effect and economic benefit.
The technical scheme is as follows:
the method for adjusting the optimal steam injection speed for the steam drive exploitation of the heavy oil reservoir is characterized by comprising the following steps of:
s1, constructing a washing multiple distribution model;
s2, collecting basic parameters, wherein the basic parameters comprise current steam injection speed i, a steam injection well and a production well spacing, injection temperature, bottom hole dryness, vaporization latent heat, oil layer heat capacity, heat conductivity and diffusion coefficient of a top layer and a bottom layer, oil layer thickness, original formation temperature, original formation oil saturation, oil layer porosity, saturated steam density and water density;
s3, calculating the average dryness x in the steam cavity i ；
S4, calculating the optimal average dryness in the steam cavityx o ；
S5, judging whether the current steam injection speed i is the optimal steam injection speed or not, and when x is the optimal steam injection speed o ＝x i When the current steam injection speed i is the optimal steam injection speed, when x is o ＞x i When the current steam injection speed is reduced from i to x o ＝x i When x is o ＜x i Then, the current steam injection speed i to x is increased o ＝x i 。
By adopting the scheme, the concept of the optimal average dryness in the steam cavity is introduced, and the steam thermal efficiency can be ensured to be higher while the steam cavity is ensured to have a larger scouring multiple only when the steam cavity is in the optimal average dryness, so that a reference standard is provided for determining the optimal steam injection speed.
Preferably, the method comprises the following steps: in the step S1, the steam injection heating area is divided into a steam cavity and a hot water area, wherein the temperature of the steam cavity is equal to the temperature of the injected steam, and the temperature of the hot water area decreases from the front edge of the steam cavity in the direction close to the oil layer. The method of assuming the partition is adopted, which is helpful for simplifying the washing multiple model of the steam injection heating area, is convenient for understanding, and has excellent auxiliary research value.
Preferably, the method comprises the following steps: in step S1, assuming that the equivalent of cold water retained in the cross section at a distance r from the steam injection well wellbore remains unchanged between the steam injection well and the oil recovery well wellbore, the total flushing multiple N at the distance r is equal to N w +N s In which N is w For the time t at which the steam chamber extends to r s Corresponding flushing factor, N s Is a time t s Then continuously injecting steam, and generating scouring multiple N by expanding steam cavity s Said
Wherein t is the cumulative injection time, s; i all right angle s Injecting cold water equivalent rate for steam, g/s; rho w Is hot water density, kg/m 3 (ii) a Rho is the density of the water phase in the steam cavity, kg/m 3 (ii) a h is the thickness of the oil layer,m; r is the radius m from the shaft of the steam injection well;
is the oil layer porosity, decimal.
By adopting the scheme, the calculation model of the scouring multiple generated by the steam in the hot water area is further simplified, the calculation difficulty of the total scouring multiple is reduced, the calculation result is relatively closer to the actual situation, and the method has good field implementation and popularization significance.
Preferably, the method comprises the following steps: step S4 includes the following steps:
s4.1, assuming optimal average dryness x of the steam cavity o Is a specific value n 0 ；
S4.2, passing number n 0 Respectively calculating the distribution of the steam cavity and the distribution of the hot water area;
s4.3, calculating the radius r of an invalid injection area in the oil layer 0 ；
S4.4, assuming the optimal average dryness of the steam cavity as a numerical value n 1 And n is 1 >n 0 ；
S4.5, repeating the steps S4.2 and S4.3 to calculate the radius r of the invalid injection region 1 ；
S4.6 when r 0 >r 1 When it is, then the value n 0 For the optimal average dryness of the steam cavity, when r 0 ≤r 1 Then the process returns to step S4.4 to approach n in sequence i And r is i >r 1 When n is greater than n i The optimal average dryness of the steam cavity.
By adopting the scheme, the radius of the invalid injection area is used as a reference critical point, and the optimal average dryness in the steam cavity is calculated by a sequential approximation method, so that the accuracy and the reliability of the calculation result of the optimal average dryness in the steam cavity are favorably ensured.
Preferably, the method comprises the following steps: the steam cavity distribution comprises a steam cavity heating radius
Wherein the content of the first and second substances,
the hot water area distribution comprises a hot water area heating radius and a relation that the temperature of the hot water area changes along with the radius, wherein the hot water area heating radius is
The change relation of the temperature of the hot water zone along with the heating radius is
Wherein T is i Is the original temperature of the oil layer, K; t is s Is the steam injection temperature, K; r is w Is the heating radius of the hot water area, m; r is s M is the heating radius of the steam cavity; lambda [ alpha ] e The thermal conductivity of the top layer and the bottom layer is W/(m.K); m R Is the thermal capacity of the oil layer, J/(m) 3 ·K),α s Is the top and bottom layer thermal diffusivity, m 2 /s；L v Is latent heat of vaporization, J/g; h is s The injection temperature corresponds to the enthalpy of hot water, J/g; h is a total of w The original temperature of the oil layer corresponds to the enthalpy of hot water, J/g.
By adopting the scheme, the loss of the temperature in the hot water area is fully considered, the temperature loss is quantitatively analyzed, and the accuracy of the calculation result is improved.
Preferably, the method comprises the following steps: in the step S4.3, the area with the flushing multiple greater than 50 in the oil layer is the invalid injection area. By adopting the scheme, 50 is directly taken as a boundary, the radius of the invalid injection region can be rapidly calculated, the calculation efficiency is improved, and the numerical value can be subjected to back-stepping verification through later-stage calculation to verify the accuracy of the numerical value.
Preferably, the method comprises the following steps: n in said step S4.1 0 Equal to 0. The approximation is carried out with the minimum value, so that the subsequent approximation process can pass through the minimum number of timesThe optimal average dryness of the steam cavity can be obtained by counting, and the operation efficiency is improved.
Compared with the prior art, the invention has the beneficial effects that:
by adopting the method for adjusting the optimal steam injection speed in the steam drive exploitation of the heavy oil reservoir, the optimal steam injection speed of the steam injection well is reversely deduced and determined in a mode of determining the average dryness of the optimal steam cavity of the heating area, the optimal steam drive oil extraction scheme is provided, the steam thermal efficiency is fully utilized, and the oil reservoir exploitation effect and the economic benefit of steam drive oil extraction are favorably improved.
Drawings
FIG. 1 is a flow chart of the present invention;
FIG. 2 is a graph showing the relationship between the washing factor and the saturation of water and oil in the examples;
FIG. 3 is a graph of the cumulative oil-to-gas ratio of different steam injection speeds in the embodiment of the present application.
Detailed Description
The present invention will be further described with reference to the following examples and the accompanying drawings.
Referring to fig. 1 to 3, the present application mainly provides a method for adjusting an optimal steam injection speed in steam drive recovery of a heavy oil reservoir, which mainly includes the following steps, namely, a first step of constructing a scouring multiple distribution model, namely, determining a scouring multiple calculation formula at a distance r from a well shaft of a steam injection well; collecting basic parameters, wherein the basic parameters mainly comprise oil deposit basic parameters, steam injection well and oil production well position parameters, steam injection related parameters and the like, and the oil deposit basic parameters mainly comprise bottom hole dryness, oil layer heat capacity, oil layer thickness, top and bottom layer heat conductivity coefficient and diffusion coefficient, original stratum oil saturation and oil layer porosity, well spacing between injection and production wells, current or established steam injection speed i, injection temperature, latent heat of vaporization, saturated steam density, bottom hole water density and the like of the steam injection well; step three, calculating the average dryness x in the steam cavity according to the collected data i (ii) a In step four, x is calculated in step three i Value calculation of optimal average dryness x in steam cavity o (ii) a In step five, x in step four is determined o And x in step three i The values are compared to determineCutting off whether the current or set steam injection speed i is reasonable or not, namely whether the current or set steam injection speed i is the optimal steam injection speed or not, and adjusting the current or set steam injection speed i according to the comparison result to enable the current or set steam injection speed i to reach the optimal steam injection speed, namely when x is the optimal steam injection speed o ＝x i When the current or the set steam injection speed i is the optimal steam injection speed, when x is o ＞x i When the current or the set steam injection speed i to x is reduced o ＝x i When x is o ＜x i While increasing the current or predetermined steam injection speed i to x o ＝x i I.e. as long as x is caused o ＝x i And the steam injection speed i with the established condition is the optimal steam injection speed of the steam injection well, and the first step and the second step are not separated in sequence in the actual application process.
It should be noted that, in the present application, when the washout multiple distribution model is constructed, the injection heating area is divided into two relatively independent areas, namely, the steam cavity and the hot water area, wherein the temperature of the steam cavity is equal to the temperature of the injected steam everywhere, the steam loss in the steam transfer process is the dryness, and the steam loss in the hot water area is the temperature, namely, the temperature of the hot water area decreases from the front edge of the steam cavity along the direction close to the oil layer, so that the zonal modeling is helpful for better understanding the steam driving process, and is closer to the actual displacement production situation.
Considering that the equivalent of cold water retained in a cross section at a distance r from a steam injection well shaft in a steam cavity is slightly changed compared with the increase of injected steam, the equivalent of cold water retained in the cross section at the distance r from the steam injection well shaft is kept unchanged between the steam injection well and a production well shaft in the process of constructing a model, and on the premise, the total scouring multiple N at the distance r is obtained w +N s In which N is w For the time t at which the steam chamber extends to r s Corresponding flushing factor, N s Is a time t s Then continuously injecting steam, and generating scouring multiple N by expanding steam cavity s And is and
the construction of the distribution model of the total washing multiple N is as follows:
according to the definition of the washing multiple, the washing multiple at the position r away from the steam injection well shaft at the time t is as follows:
according to the conservation of mass equation, the scouring quantity of the section at the distance r from the shaft is as follows:
W p ＝W i -W z (2)
meanwhile, the volume of the water phase passing through the section r in an accumulated mode is as follows:
for the injection well, according to the Buckley-Leveret equation, there are:
then there are:
for a fixed radius r from the wellbore, due to S w Only with respect to the injection time t, the integration of the separate variables at both ends of the Buckley-Leveret equation can be found:
substituting the formula (7) into the formula (3) to obtain:
and (3) performing fractional integration on the formula (8) to obtain:
substituting equation (9) into equation (1) yields:
according to the relation between the water content and the oil saturation:
for heavy oil reservoirs, the viscosities of the corresponding crude oils at different temperatures are different, and according to the relationship between the viscosities of the crude oils and the temperatures:
lgμ o ＝10 C-DlgT (12)
meanwhile, the relative permeability ratio of oil and water phases can be expressed as a function of water saturation:
among these, it is considered that the coefficient A, B is such that the increase in temperature increases the hydrophilicity of the reservoir rock, and the oil-water relative permeability curve shifts to the right as a whole with the morphology thereof substantially unchanged, and therefore the B value remains unchanged. The assumption is that the coefficient A is calculated according to the relative permeability of oil and water at the original oil reservoir temperature i The right shift quantity of the oil-water relative permeability curve is delta S along with the increase of unit temperature w Then, there are:
the measured oil-water phase permeability of different oil fields is different along with the right shift rule of the temperature, and S can be obtained by fitting the oil-water phase permeability curve corresponding to each temperature w As a function of reservoir temperature T. It is assumed here that the variation is a linear relationship, namely:
△S w ＝m(T-T i ) (15)
substituting equation (15) into equation (14) yields:
substituting the formula (12) and the formula (16) into the formula (11) to obtain:
assuming that the temperature field of the hot water region varies linearly in the radial direction, the relationship between the heating temperature of the hot water region and the variation of the radius can be expressed as follows:
according to the correction of the Marx-Langenheim model, the heating radius of the hot water area is obtained as follows:
the heating radius of the hot water area and the temperature of the hot water area change with the radius jointly form a hot water area distribution structure.
In equation (19):
average dryness in the steam cavity is x i (unknowns), since the vapor chamber heat is provided by the latent heat of vaporization of the injected vapor, according to the Marx-Langenheim model, the vapor chamber heating radius is:
substituting equations (19) and (20) into equation (18) yields the relationship between the temperature T at the distance r from the wellbore and the injection time T:
the water content f of the hot water area can be obtained by substituting the formula (21) into the formula (17) w The rule of change along with the distance r from the steam injection well shaft is as follows:
the derivation can be found across equation (22):
substitution of equation (23)The water saturation S of the hot water area can be obtained by the formula (6) w Variation with injection time t:
substituting the formula (22), the formula (23) and the formula (24) into the formula (10) can obtain the change relation of the hot water zone flushing multiple along with the injection time t:
and (3) calculating the water saturation and the washing multiple of the heating area at the position r away from the steam injection well shaft by using a formula (24) and a formula (25).
For the steam cavity, since the equivalent of cold water retained in the section at a distance r from the steam injection well shaft is constant between the steam injection well and the oil production well shaft as the former assumption, the washing multiple at r should be equal to the time t for the steam cavity to expand to r s Corresponding flushing multiple N w Plus the flush factor N generated by the continued expansion of the steam chamber after s . I.e. r is r s Substituting into the formula (20) to calculate t ═ t s Then r is added s 、t s Substituting into equation (25) to calculate N ═ N w And considering the density of steam and hot water at r under dryness as follows:
the flush factor at this time for the steam chamber to expand through the section at r is:
the total flushing factor at distance r can be derived as follows: N-N w +N s (28)
Description of the symbols: n is the washing multiple of the water flow,m 3 /m 3 ；W p for the amount of flushing through the cross-section, m 3 (ii) a r is the radius from the shaft, m; h is the oil layer thickness, m;
is the oil layer porosity, decimal; w i For injecting the steam with the equivalent amount of cold water, m 3 ；W z Is the hold up between the wellbore and the cross-section at radius r from the wellbore, m 3 ；i s Injecting cold water equivalent rate for steam, g/s; f. of w (S w ) The corresponding water content and decimal fraction under a certain water saturation; to is the time, s, for the injection front to reach the cross section at r; t is the cumulative injection time, s; f' w (S w ) Is the water cut rate of rise; s. the wf The steam flooding front edge water saturation is decimal; f. of w (S wf ) The water content of the front edge of the steam cavity corresponds to the saturated water content; f. of w '(S wf ) The derivative of the water content corresponding to the water saturation of the front edge of the steam cavity; s w The water saturation and decimal of the section r from the time t to the shaft is shown; mu.s w Viscosity of water, mPa · s; mu.s o Crude oil viscosity, mPa · s; k is o Effective permeability of the oil phase, D; k is w Effective permeability of the aqueous phase, D; t is the oil layer temperature, K; t is i The original temperature of the oil layer, K; m is the coefficient of variation of the phase permeation curve with temperature, and has no dimension; t is s Is the steam injection temperature, K; r is s Is the steam cavity radius, m; r is w Is the radius of the hot water zone, m; h is s The injection temperature corresponds to the enthalpy of hot water, J/g; h is w The original temperature of the oil layer corresponds to the enthalpy of hot water, J/g; m is a group of R Is the thermal capacity of the oil layer, J/(m) 3 ·K)；α s Is the top and bottom layer thermal diffusivity, m 2 /s；λ e The thermal conductivity of the top layer and the bottom layer is W/(m.K); x is the dryness of steam injected into the bottom of the well, and the decimal number; l is v Is latent heat of vaporization, J/g; rho is the density of the water phase in the steam cavity, kg/m 3 ；ρ s Is steam density, kg/m 3 ；ρ w Is hot water density, kg/m 3 (ii) a C. D is a constant and can be obtained by fitting a relation curve of the viscosity and the temperature of the crude oil.
In the application, the optimal average dryness x in the steam cavity is calculated by determining the optimal steam injection speed o In the process, a method of hypothesis approximation is mainly adopted, and the method mainly comprises the following steps:
in the first step, the optimal average dryness xo of the steam cavity is assumed to be a specific value n 0 (ii) a Second pass value n 0 Respectively calculating the distribution of a steam cavity and the distribution of a hot water area, wherein the distribution of the steam cavity is calculated by adopting a formula (20), the heating radius of the hot water area in the distribution of the hot water area is calculated by adopting a formula (19), and the relation of the temperature of the hot water area along with the change of the radius is calculated by adopting a formula (18); thirdly, calculating the radius r of an invalid injection area in the oil layer 0 In this step, the flush multiple 50 may be directly used as a boundary, that is, the region with the flush multiple distribution greater than 50 is the invalid injection region, and the given boundary may be verified by back-stepping according to the calculation result.
The fourth step assumes again that the optimal average dryness of a steam chamber is a specific value n 1 And n is 1 >n 0 (ii) a The fifth step uses the value n 1 Repeating the second step and the third step to calculate a new invalid injection radius r 1 (ii) a Sixthly, comparing and verifying when r is 0 >r 1 When it is, then the value n 0 For optimal average dryness of the steam chamber, when r 0 ≤r 1 Then returning to the fourth step, assuming again that one is greater than n 0 Number n of 2 、n 3 A, c, up to n i And using n i Calculating the invalid injection region in the fifth step to obtain a value r i And r is i Just greater than r 1 Then the value n can be determined i Namely the optimal average dryness of the steam cavity, namely the average dryness of the steam cavity corresponding to the maximum radius of the ineffective injection area is an optimal value, so that in the approaching process, a smaller approaching step length can be set through calculation software to ensure r i Just greater than r 1 Without exceeding too much.
Calculating the average dryness x in the steam cavity in this application i Is carried out by knowing the well spacing between the steam injection well and the production well as L, when the steam injection well is injected into a sectionAfter the time, the front edge of the hot water area reaches the oil production well, the temperature of the produced liquid begins to rise at the moment, and along with the prolonging of the steam injection time, the temperature of the produced liquid continuously rises, when steam is produced at the bottom of the oil production well, the front edge of the steam cavity can be judged to reach the oil production well, at the moment, the heating radius r of the steam cavity can be considered to be L according to the production dynamics (the analysis idea here is that the corresponding heating radius can be calculated according to the different produced liquid temperature combination formulas 18-20 of the oil production well, namely the temperature at the position where r is known to be L, then the heating radius of the corresponding steam cavity and the hot water area can be calculated according to the formulas, the heating radius r is not necessarily L in the actual production), the related parameters collected in the early stage are substituted into the formulas (18), (19) and (20), and the average dryness x in the steam cavity can be calculated i In the presence of a compound of formula (I) in which x is obtained i And x o And then comparison can be carried out to determine the optimal steam injection speed.
In the following, a certain block of a certain oil field is used for example analysis and calculation, the block is a typical shallow and thin layer heavy oil reservoir, a steam huff and puff mode is adopted in the early development stage, after the steam huff and puff is finished and the well is shut down for a period of time, the test steam flooding is carried out, the average temperature of the stratum is 47 ℃, and the average oil saturation is 60%. The basic reservoir parameters and steam injection parameters in the test area are shown in table 1.
TABLE 1 basic reservoir parameters and steam injection parameters
Obtaining C-8.4791, D-3.218 and a correlation coefficient R-0.9998 after the regression curve of the viscosity-temperature relationship of the crude oil in the block is obtained; regression of the initial reservoir temperature lower phase permeability curve of the block to obtain a i 9655131 and 29.929, and the correlation coefficient R is 0.9973.
Substituting the related parameters into a washing multiple calculation model, calculating the washing multiple and the change relation of the water saturation by using MATLAB software, wherein the result is shown in figure 2, and as can be seen from figure 2, when the washing multiple is below 20, the water saturation is sensitive to the change along with the washing multiple; when the flushing multiple is more than 50, the influence of continuously increasing the flushing multiple on the water saturation is small, and the fact that the boundary of the invalid injection area when the flushing multiple is 50 is matched with the actual situation is proved.
The well spacing of the block well group is 60m, the production well has flash evaporation phenomenon when the production reaches 400d, the liquid production temperature of the production well is 110 ℃, and the relevant parameters are substituted to calculate the radius r of the steam cavity at the moment s 42 m. Substituting the data into the equations (19) and (20) can calculate the average dryness of the steam cavity to be 0.171, obtaining the optimal dryness of the steam cavity under the injection parameter to be 0.215 by optimizing the optimal dryness of the steam cavity, increasing the steam injection speed, establishing a geological model by using the relevant data of the well group, performing historical fitting, determining the optimal steam injection speed to be 120t/d by multiple calculations, then calculating the result of the steam injection speed to be 150t/d by using the model, and comparing the calculation results of different steam injection speeds (90t/d, 120t/d and 150t/d), wherein the results are shown in table 2:
TABLE 2 statistics of data relating to different steam injection speeds
According to results, analysis results of all steam injection speeds show that the development effect of the block can be effectively improved by a larger steam injection speed, the development effect is better when the steam injection speed is 120t/d, the average dryness of the steam cavity is basically equal to the optimal average dryness of the steam cavity at the moment, and comparison of an accumulated oil-steam ratio curve (shown in figure 3, wherein the abscissa is accumulated production time, and the ordinate is a steam-oil ratio) under all steam injection speeds shows that the accumulated oil-steam ratio is the highest when the steam injection speed is 120t/d during 400d production, the economic benefit is the best, and calculation results show that the accuracy of the method for determining the optimal steam injection speed is higher.
In addition, by using the calculation method of the average dryness fraction of the steam cavity, the calculation of the multiple oil field blocks can be carried out, and n which can be assumed in the first step is used for calculating the optimal average dryness fraction of the steam cavity 0 Equal to 0, the calculation efficiency can be effectively saved.
The method is based on the thermodynamics and thermal conductivity principle, when the steam injection speed is high, the heat transfer efficiency of injected steam is low, the average dryness in the steam cavity is high, when the steam injection speed is low, the heat transfer of the injected steam to an oil layer and the heat loss rate of a top and bottom cover layer are high, the average dryness in the steam cavity is low, the optimal average dryness in the steam cavity can be rapidly determined according to the average dryness, the optimal steam injection speed is reversely pushed through the optimal average dryness, and the method has excellent guiding significance for field production.
Finally, it should be noted that the above-mentioned description is only a preferred embodiment of the present invention, and that those skilled in the art can make various similar representations without departing from the spirit and scope of the present invention.
Claims (2)
1. A method for adjusting the optimal steam injection speed in the steam drive exploitation of a heavy oil reservoir is characterized by comprising the following steps: the method comprises the following steps:
s1, constructing a washing multiple distribution model;
s2, collecting basic parameters including current steam injection speed i, well distance between a steam injection well and a production well, injection temperature, bottom hole dryness, vaporization latent heat, oil layer heat capacity, heat conductivity and diffusion coefficient of a top layer and a bottom layer, oil layer thickness, original formation temperature, oil saturation of an original formation, oil layer porosity, saturated steam density and water density;
s3, calculating the average dryness x in the steam cavity i ；
S4, calculating the optimal average dryness x in the steam cavity o ；
S5, judging whether the current steam injection speed i is the optimal steam injection speed or not, and when x is the optimal steam injection speed o ＝x i When the current steam injection speed i is the optimal steam injection speed, when x is o ＞x i When the current steam injection speed is reduced from i to x o ＝x i When x is o ＜x i Then, the current steam injection speed i to x is increased o ＝x i ；
Wherein, in the step S1, the steam injection heating area is divided into a steam cavity and a hot water area, wherein the temperature of the steam cavity is equal to the temperature of the injected steam, and the temperature of the hot water area is from the front edge of the steam cavityThe flushing time is gradually reduced along the direction close to the oil layer, and the equivalent of cold water retained in the section at the distance r from the steam injection well shaft between the steam injection well and the oil production well shaft is kept unchanged, so that the total flushing multiple N at the distance r is N w +N s In which N is w For the time t at which the steam chamber extends to r s Corresponding flushing multiple, N s Is a time t s Then continuously injecting steam, and generating scouring multiple N by expanding steam cavity s Said
Wherein, step S4 includes the following steps:
s4.1, assuming optimal average dryness x of the steam cavity o Is a specific number n 0;
s4.2, respectively calculating the distribution of the steam cavity and the distribution of the hot water area through the value n 0;
s4.3, calculating the radius r0 of an invalid injection area in the oil layer, wherein the area with the flushing multiple being more than 50 in the oil layer is the invalid injection area;
s4.4, assuming that the optimal average dryness of the steam cavity is n1, and n1> n 0;
s4.5, repeating the steps S4.2 and S4.3 to calculate the radius r1 of the invalid injection region;
s4.6, when r0>r1, the value n0 is the optimal average dryness of the steam cavity, and when r0 is not more than r1, the step S4.4 is returned, and the steps are sequentially approached to n i And r is i >r1 is n i The optimal average dryness of the steam cavity is obtained;
the steam cavity distribution comprises a steam cavity heating radius
Wherein the content of the first and second substances,
the hot water area distribution comprises a hot water area heating radius and a relation that the temperature of the hot water area changes along with the radius, wherein the hot water area heating radius is
The change relation of the temperature of the hot water zone along with the heating radius is
Wherein t is the cumulative injection time, s; i.e. i s Injecting cold water into the steam at an equivalent rate of g/s; rho w Is hot water density, kg/m 3 (ii) a Rho is the density of the water phase in the steam cavity, kg/m 3 (ii) a h is the oil layer thickness, m; r is the radius from the steam injection well shaft, m;
oil layer porosity; t is i Is the original temperature of the oil layer, K; t is a unit of s Is the steam injection temperature, K; r is w Is the heating radius of the hot water area, m; rs is the heating radius of the steam cavity, m; lambda [ alpha ] e The thermal conductivity of the top layer and the bottom layer is W/(m.K); m R Is the thermal capacity of the oil layer, J/(m) 3 ·K),α s Is the top and bottom layer thermal diffusivity, m 2 /s；L v Is latent heat of vaporization, J/g; h is s The injection temperature corresponds to the enthalpy of hot water, J/g; h is w The original temperature of an oil layer corresponds to the enthalpy of hot water, J/g, and x is the dryness and decimal number of steam injected into a well bottom; x is the number of i Is the average dryness in the steam cavity.
2. The method for adjusting the optimal steam injection speed for steam drive exploitation of the heavy oil reservoir according to claim 1, wherein the method comprises the following steps: n0 is equal to 0 in said step S4.1.
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