CN110827166A - Method for adjusting optimal steam injection speed in steam drive exploitation of heavy oil reservoir - Google Patents

Method for adjusting optimal steam injection speed in steam drive exploitation of heavy oil reservoir Download PDF

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CN110827166A
CN110827166A CN201911199882.8A CN201911199882A CN110827166A CN 110827166 A CN110827166 A CN 110827166A CN 201911199882 A CN201911199882 A CN 201911199882A CN 110827166 A CN110827166 A CN 110827166A
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王鹏鲲
黄小亮
田杰
戚志林
严文德
钱银
李赛男
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Chongqing University of Science and Technology
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Abstract

The invention discloses a method for adjusting the optimal steam injection speed of steam drive mining 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 cavityi(ii) a Fourthly, calculating the optimal average dryness X in the steam cavityo(ii) a Fifthly, judging whether the current steam injection speed i is the optimal steam injection speed or not, and when X is reachedo＝XiWhen the current steam injection speed i is the optimal steam injection speed, when X iso＞XiIn time, the current steam injection speed i to X is reducedo＝XiWhen X is presento＜XiIn time, the current steam injection speed i is increased to Xo＝Xi. By adopting the scheme, the optimal steam injection well is reversely deduced and determined in a mode of determining the optimal average dryness of the steam cavity of the heating areaSpeed, provide the best steam-drive oil recovery scheme, make full use of steam thermal efficiency, be favorable to improving oil reservoir development effect to reach the economic benefits of steam-drive oil recovery.

Description

Method for adjusting optimal steam injection speed in steam drive exploitation of heavy oil reservoir
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, thereby heating and displacing the crude oil toward 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 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 cavityi；
S4, calculating the optimal average dryness X in the steam cavityo；
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 speedo＝XiWhen the current steam injection speed i is the optimal steam injection speed, when X iso＞XiIn time, the current steam injection speed i to X is reducedo＝XiWhen X is presento＜XiIn time, the current steam injection speed i is increased to Xo＝Xi。
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 washing multiple N at the distance r is Nw+NsIn which N iswFor the time t at which the steam chamber extends to rsIs correspondingly provided withFlushing multiple of, NsIs a time tsThen continuously injecting steam, and generating scouring multiple N by expanding steam cavitysSaid
Figure BDA0002295599280000021
Wherein t is the cumulative injection time, s; i.e. isInjecting cold water equivalent rate for steam, g/s; rhowIs hot water density, kg/m3(ii) a Rho is the density of the water phase in the steam cavity, kg/m3(ii) a h is the oil layer thickness, m; r is the radius from the steam injection well shaft, m;
Figure BDA0002295599280000031
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 cavityoIs a specific value n0；
S4.2, passing number n0Respectively 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 layer0；
S4.4, assuming that the optimal average dryness of the steam cavity is a numerical value n1And n is1>n0；
S4.5, repeating the steps S4.2 and S4.3 to calculate the radius r of the invalid injection region1；
S4.6 when r0>r1When it is, then the value n0For the optimal average dryness of the steam cavity, when r0≤r1Then the process returns to step S4.4 to approach n in sequenceiAnd r isi>r1When n is greater than niThe 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
Figure BDA0002295599280000032
Wherein the content of the first and second substances,
Figure BDA0002295599280000034
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 isThe change relation of the temperature of the hot water area along with the heating radius is
Figure BDA0002295599280000041
Wherein T isiIs the original temperature of the oil layer, K; t issIs the steam injection temperature, K; r iswIs the heating radius of the hot water area, m; r issIs the heating radius of the steam cavity, m; lambda [ alpha ]eThe thermal conductivity of the top layer and the bottom layer is W/(m.K); mRIs the thermal capacity of the oil layer, J/(m)3·K),αsIs the top and bottom layer thermal diffusivity, m2/s；LvIs latent heat of vaporization, J/g; h issThe injection temperature corresponds to the enthalpy of hot water, J/g; h iswThe 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 S4.10Equal to 0. And the approximation is carried out according to the minimum value, so that the optimal average dryness of the steam cavity can be obtained through the minimum times in the subsequent approximation process, 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 the 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-steam 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 which mainly comprise oil deposit basic parameters, steam injection well and oil production well position parameters, steam injection related parameters and the like, wherein 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, and current or established steam injection well position parametersThe steam injection speed i, the injection temperature, the latent heat of vaporization, the saturated steam density, the bottom water density and the like; step three, calculating the average dryness X in the steam cavity according to the collected datai(ii) a In step four, X is calculated in step threeiValue calculation of optimal average dryness X in steam cavityo(ii) a In step five, X in step four is usedoAnd X in step threeiThe values are compared to judge whether the current or established steam injection speed i is reasonable, namely the optimal steam injection speed, and the current or established steam injection speed i can be adjusted according to the comparison result to reach the optimal steam injection speed, namely when X is reachedo＝XiWhen the current or the set steam injection speed i is the optimal steam injection speed, when X iso＞XiWhen the current or the set steam injection speed i to X is reducedo＝XiWhen X is presento＜XiWhile increasing the current or predetermined steam injection speed i to Xo＝XiI.e. so long as X iso＝XiAnd 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, a steam cavity and a hot water area, wherein the temperature of the steam cavity is equal to the temperature of the injected steam everywhere, the dryness fraction is lost in the steam transfer process, and the temperature of the steam in the hot water area is lost, 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 of the steam driving process, and is closer to the actual displacement production situation, and in addition, the pressure, the injection temperature and the dryness fraction of the steam in the model are kept unchanged when the steam is injected to the bottom of the shaft.
Considering that the change of the cold water equivalent retained in the section at the distance r from the steam injection well shaft is weak compared with the increase of the injected steam in the steam cavity, it is assumed that the cold water equivalent 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 maintained during the modeling processUnder the premise of the same, the total washing multiple N at the distance r is obtained as Nw+NsIn which N iswFor the time t at which the steam chamber extends to rsCorresponding flushing multiple, NsIs a time tsThen continuously injecting steam, and generating scouring multiple N by expanding steam cavitysAnd is and
Figure BDA0002295599280000061
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:
Figure BDA0002295599280000062
according to the conservation of mass equation, the scouring quantity of the section at the distance r from the shaft is as follows:
Wp＝Wi-Wz(2)
meanwhile, the volume of the water phase passing through the section r in an accumulated mode is as follows:
Figure BDA0002295599280000063
for the injection well, according to the Buckley-Leveret equation, there are:
Figure BDA0002295599280000064
then there are:
Figure BDA0002295599280000066
for a fixed radius r from the wellbore, due to SwIntegration of the separation variables across Buckley-Leveret equation, related only to injection time tThe following can be obtained:
Figure BDA0002295599280000067
substituting the formula (7) into the formula (3) to obtain:
Figure BDA0002295599280000068
and (3) performing fractional integration on the formula (8) to obtain:
Figure BDA0002295599280000071
substituting equation (9) into equation (1) yields:
Figure BDA0002295599280000072
according to the relation between the water content and the oil saturation:
Figure BDA0002295599280000073
for heavy oil reservoirs, the viscosity of crude oil corresponding to different temperatures is different, and according to the relationship between the viscosity of the crude oil and the temperature:
lgμo＝10C-DlgT(12)
meanwhile, the relative permeability ratio of oil and water phases can be expressed as a function of water saturation:
Figure BDA0002295599280000074
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 temperatureiThe right shift quantity of the oil-water relative permeability curve is delta S along with the increase of unit temperaturewThen, there are:
Figure BDA0002295599280000075
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 temperaturewAs a function of reservoir temperature T. It is assumed here that the variation is a linear relationship, namely:
ΔSw＝m(T-Ti) (15)
substituting equation (15) into equation (14) yields:
Figure BDA0002295599280000081
substituting the formula (12) and the formula (16) into the formula (11) to obtain:
Figure BDA0002295599280000082
assuming that the temperature field of the hot water region varies linearly in the radial direction, the variation of the heating temperature of the hot water region with the radius can be expressed as:
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):
Figure BDA0002295599280000085
Figure BDA0002295599280000086
Figure BDA0002295599280000087
Figure BDA0002295599280000089
average dryness in the steam cavity is xi(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:
Figure BDA00022955992800000810
substituting equation (19) and equation (20) into equation (18) yields the temperature T at a distance r from the wellbore as a function of injection time T:
Figure BDA0002295599280000091
the water content f of the hot water area can be obtained by substituting the formula (21) into the formula (17)wThe 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):
Figure BDA0002295599280000093
substituting the formula (23) into the formula (6) to obtain the water saturation S of the hot water areawVariation with injection time t:
Figure BDA0002295599280000094
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 rsCorresponding washing multiple NwPlus the flush factor N generated by the continued expansion of the steam chamber afters. I.e. r is rsSubstituting into the formula (20) to calculate t ═ tsThen r is further reduceds、tsSubstituting into equation (25) to calculate N ═ NwAnd considering the density of steam and hot water at r under dryness as follows:
Figure BDA0002295599280000101
the flush factor at this time for the steam chamber to expand through the section at r is:
Figure BDA0002295599280000102
the total flushing factor at distance r can be derived as follows: N-Nw+Ns(28)
Description of the symbols: n is the washing multiple, m3/m3；WpFor the amount of flushing through the cross-section, m3(ii) a r is the radius from the shaft, m; h is the oil layer thickness, m;
Figure BDA0002295599280000103
is the oil layer porosity, decimal; wiFor injecting the steam with the equivalent amount of cold water, m3；WzIs the retention between the wellbore and the cross section at a distance r from the radius of the wellbore, m3；isInjecting cold water equivalent rate for steam, g/s; f. ofw(Sw) The corresponding water content and decimal fraction under a certain water saturation; t is toTime, s, for the injection front to reach the section at r; t is the cumulative injection time, s; f'w(Sw) Is the water cut rate of rise; swfThe steam flooding front edge water saturation is decimal; f. ofw(Swf) The water content of the front edge of the steam cavity corresponds to the saturated water content; f. ofw'(Swf) The derivative of the water content corresponding to the water saturation of the front edge of the steam cavity; swThe water saturation and decimal of the section r from the time t to the shaft is shown; mu.swViscosity of water, mPa · s; mu.soCrude oil viscosity, mPa · s; koEffective permeability of the oil phase, D; kwEffective permeability of the aqueous phase, D; t is the oil layer temperature, K; t isiIs 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 issIs the steam injection temperature, K; r issIs the steam cavity radius, m; r iswIs the radius of the hot water zone, m; h issThe injection temperature corresponds to the enthalpy of hot water, J/g; h iswThe original temperature of the oil layer corresponds to the enthalpy of hot water, J/g; mRIs the thermal capacity of the oil layer, J/(m)3·K)；αsIs the top and bottom layer thermal diffusivity, m2/s；λeThe 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 isvIs latent heat of vaporization, J/g; rho is the density of the water phase in the steam cavity, kg/m3；ρsIs steam density, kg/m3；ρwIs hot water density, kg/m3(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 speedoIn the process, a method of hypothesis approximation is mainly adopted, and the method mainly comprises the following steps:
first, assume the optimal average dryness X of the vapor chamberoIs a specific value n0(ii) a Second pass value n0Respectively 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 layer0In this step, the flush multiple 50 can be directly used as a boundary, that is, the region with the flush multiple distribution greater than 50 is an invalid injection region, and the given boundary can 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 n1And n is1>n0(ii) a The fifth step uses the value n1Repeating the second step and the third step to calculate a new invalid injection radius r1(ii) a Sixthly, comparing and verifying when r is0>r1When it is, then the value n0For optimal average dryness of the steam chamber, when r0≤r1Then returning to the fourth step, re-assuming that one is larger than n0Number n of2、n3A, c, up to niAnd using niCalculating the invalid injection region in the fifth step to obtain a value riAnd r isiJust greater than r1Then the value n can be determinediNamely the optimal average dryness of the steam cavity, namely the average dryness of the steam cavity corresponding to the maximum radius of the invalid injection area is the optimal value, so that in the approaching process, a smaller approaching step length can be set through calculation software to ensure riJust greater than r1Without exceeding too much.
Calculating the average dryness X in the steam cavity in this applicationiThe process of the method comprises the following steps that the well distance between the steam injection well and the oil production well is known to be L, when the steam injection well injects steam for a period of time, the front edge of a hot water area reaches the oil production well, the temperature of produced liquid begins to rise, the temperature of the produced liquid continuously rises along with the extension of the steam injection time, and when steam is produced at the bottom of the oil production well, the front edge of a steam cavity can be judged to reach the oil production wellAt this time, it can be considered that the heating radius r of the steam cavity is L according to the production dynamics (the analysis idea here is to calculate the corresponding heating radius according to the different produced fluid temperature combination formula 18-20 of the production well, that is, the temperature at the position where r is L is known, then calculate the heating radius of the corresponding steam cavity and hot water region according to the formula, and the heating radius r is not necessarily L in the actual production), and substitute the related parameters collected in the earlier stage into the formulas (18), (19) and (20) to calculate the average dryness X in the steam cavityiIn the presence of XiAnd XoAnd 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 oil deposit parameters and steam injection parameters
Obtaining C (8.4791), D (3.218) and a correlation coefficient R (0.9998) after the crude oil viscosity-temperature relation regression curve of the block is obtained; regression of the initial reservoir temperature lower phase permeability curve of the block to obtain ai9655131 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 interval between the block well groups is 60m, the flash evaporation phenomenon occurs in the production well when the production reaches 400d, the temperature of the production fluid in the production well is 110 ℃, and the flash evaporation phenomenon is substituted into a relevant parameter meterThe radius r of the steam cavity at the moment is calculateds42 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
Figure BDA0002295599280000131
The results show that the analysis result of each steam injection speed shows that the development effect of the block can be effectively increased by a larger steam injection speed, the development effect is better when the steam injection speed is 120t/d, at the moment, the average dryness of the steam cavity is basically equal to the optimal average dryness of the steam cavity, and the comparison of the cumulative oil-steam ratio curve (fig. 3, wherein the abscissa is cumulative production time and the ordinate is the steam-oil ratio) under each steam injection speed shows that the cumulative oil-steam ratio is highest when the steam injection speed is 120t/d during 400d production, the economic benefit is the best, and the calculation result shows that the accuracy of the method for determining the optimal steam injection speed is higher.
In addition, by utilizing the method for calculating the average dryness 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 of the steam cavity0Equal 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 those skilled in the art can make various similar representations without departing from the spirit and scope of the present invention.

Claims (7)

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, 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 cavityi；
S4, calculating the optimal average dryness X in the steam cavityo；
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 speedo＝XiWhen the current steam injection speed i is the optimal steam injection speed, when X iso＞XiIn time, the current steam injection speed i to X is reducedo＝XiWhen X is presento＜XiIn time, the current steam injection speed i is increased to Xo＝Xi。
2. The method for adjusting the optimal steam injection speed for the steam drive recovery of the heavy oil reservoir according to claim 1, which is characterized in that: 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.
3. The method for adjusting the optimal steam injection speed for the steam drive recovery of the heavy oil reservoir according to claim 2, wherein 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 washing multiple N at the distance r is Nw+NsIn which N iswFor the time t at which the steam chamber extends to rsCorresponding flushing multiple, NsIs a time tsThen continuously injecting steam, and generating scouring multiple N by expanding steam cavitysSaid
Figure FDA0002295599270000011
Wherein t is the cumulative injection time, s; i.e. isInjecting cold water equivalent rate for steam, g/s; rhowIs hot water density, kg/m3(ii) a Rho is the density of the water phase in the steam cavity, kg/m3(ii) a h is the oil layer thickness, m; r is the radius from the steam injection well shaft, m;the oil layer porosity.
4. The method for adjusting the optimal steam injection speed for steam drive recovery of the heavy oil reservoir according to claim 1, wherein the step S4 comprises the following steps:
s4.1, assuming optimal average dryness X of the steam cavityoIs a specific value n0；
S4.2, passing number n0Respectively 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 layer0；
S4.4, assuming that the optimal average dryness of the steam cavity is a numerical value n1And n is1>n0；
S4.5, repeating the steps S4.2 and S4.3 to calculate the radius r of the invalid injection region1；
S4.6 when r0>r1When it is, then the value n0For the optimal average dryness of the steam cavity, when r0≤r1Then the process returns to step S4.4 to approach n in sequenceiAnd r isi>r1When n is greater than niThe optimal average dryness of the steam cavity.
5. The method for adjusting the optimal steam injection speed for the steam drive recovery of the heavy oil reservoir according to claim 4, wherein 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,
Figure FDA0002295599270000022
Figure FDA0002295599270000023
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 isThe change relation of the temperature of the hot water area along with the heating radius is
Wherein T isiIs the original temperature of the oil layer, K; t issIs the steam injection temperature, K; r iswIs the heating radius of the hot water area, m; r issIs the heating radius of the steam cavity, m; lambda [ alpha ]eThe thermal conductivity of the top layer and the bottom layer is W/(m.K); mRIs the thermal capacity of the oil layer, J/(m)3·K),αsIs the top and bottom layer thermal diffusivity, m2/s；LvIs latent heat of vaporization, J/g; h issThe injection temperature corresponds to the enthalpy of hot water, J/g; h iswThe original temperature of the oil layer corresponds to the enthalpy of hot water, J/g.
6. The method for adjusting the optimal steam injection speed for the steam drive recovery of the heavy oil reservoir according to claim 4 or 5, wherein 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.
7. The method for adjusting the optimal steam injection speed for the steam drive recovery of the heavy oil reservoir according to claim 4 or 5, wherein the method comprises the following steps: n in said step S4.10Equal to 0.
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