CN109611067B - Numerical calculation method for effective acting distance of acid fracturing fluid of deep limestone reservoir - Google Patents
Numerical calculation method for effective acting distance of acid fracturing fluid of deep limestone reservoir Download PDFInfo
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Abstract
The invention discloses a numerical calculation method of an effective acting distance of acid fracturing fluid of a deep limestone reservoir, which comprises the following steps: (1) calculating the bottom hole temperature when the construction is finished; (2) calculating the length of a crack seam when construction is finished, dividing grid units in the direction of the seam length, and calculating the average seam width of each unit to obtain the acid liquor flow rate of each unit; (3) calculating the acid liquor temperature and the acid liquor concentration of each unit without considering the acid rock reaction heat by taking the bottom temperature as an initial condition; (4) calculating the acid rock molar reaction heat of each unit; (5) calculating the acid liquor temperature and the acid liquor concentration of each unit considering the acid rock reaction heat, establishing an acid liquor concentration distribution curve, defining 10% of the initial injection concentration of the acid liquor as the residual acid limit concentration, and taking the seam length corresponding to the residual acid limit concentration as the effective action distance of the acid liquor. The method considers the thermal effect of the acid liquor in the acid fracturing process, improves the accuracy of calculating the effective acting distance of the acid liquor, and has guiding significance on the acid fracturing design of the deep limestone reservoir.
Description
Technical Field
The invention relates to the field of petroleum engineering, in particular to a numerical calculation method for an effective acting distance of an acid liquid in an acid fracturing process of a deep limestone reservoir. And calculating the effective action distance of the acid liquor under the high-temperature condition by adopting a numerical calculation method, improving the accuracy of acid fracturing design of the deep limestone reservoir and realizing efficient acid fracturing modification of the deep limestone reservoir.
Background
The two-system deep carbonate rock reservoir in the western Sichuan region shows good exploration potential and becomes one of the most realistic successive strata series in the current stage of the Sichuan basin. The reservoir takes limestone and dolomite as main materials and has the characteristics of deep burial (>5000m), high temperature (>145 ℃) and the like. The development of the region is difficult to naturally obtain industrial oil and gas flow, and the acid fracturing technology is one of main yield increasing and improving means of a block reservoir (Qibao right, Zhao Zuo an, Hehong Gao and the like. the effectiveness of the reservoir is judged by applying a logging reservoir quality comprehensive evaluation index, namely, a second-fold Cyrtymenia group in the western region of Sichuan basin is taken as an example [ J ]. the natural gas industry, 2018,38(02): 25-32).
Acid fracturing (acid fracturing for short) means that acid liquor is squeezed into a reservoir under the condition that the fracture pressure of the reservoir or the closing pressure of a natural fracture is higher than the fracture pressure of the reservoir, a fracture is formed in the reservoir, meanwhile, the acid liquor and rock on the wall surface of the fracture are subjected to chemical reaction, the rock on the wall of the fracture is etched in a non-uniform mode, a groove-shaped or uneven etched fracture is formed, after construction is finished, the fracture is not closed completely, and finally an acid-etched fracture with a certain geometric size and flow conductivity is formed, so that the yield of an oil-. The effective action distance of the acid liquor is one of important indexes for evaluating the acid fracturing effect, and is mainly influenced by factors such as temperature, acid liquor concentration and the like. Among them, temperature is an important factor that affects the acid fracturing effect of limestone reservoirs (lugguan oil production engineering [ M ]. oil industry press, 2009).
The method for calculating the effective action distance of the acid liquor mainly focuses on the calculation of the limit concentration of the residual acid (Li Jianhui, Mulix, Zhao Shao, etc. A method for evaluating the effective action distance of the acid liquor based on the limit of the residual acid, CN105044288A [ P ] 2015), and the influence of the temperature change of the acid liquor on the acid fracturing transformation effect in the fracturing process is rarely comprehensively considered. Therefore, aiming at the characteristic of high reservoir temperature in the western Sichuan area, the change rule of the acid liquor temperature in the acid fracturing process is researched, the influence of the temperature on the acid fracturing effect (effective action distance of the acid liquor) is determined, and the method is of great importance to the design of reservoir acid fracturing modification in the western Sichuan area.
Disclosure of Invention
The invention aims to provide a numerical calculation method for the effective acting distance of acid liquor in acid fracturing of a deep limestone reservoir, which mainly researches the thermal effect (wellbore heat transfer, acid liquor flow heat exchange and acid rock reaction heat release) of the acid liquor in the acid fracturing process, adopts a numerical method to calculate the temperature and the concentration of the acid liquor considering the thermal effect, and finally determines the effective acting distance of the acid liquor based on the concentration of the acid liquor. The method is reliable in principle, is beneficial to calculating the temperature and the concentration of the acid liquor of the high-temperature stratum, improves the accuracy of calculating the effective acting distance of the acid liquor, and has guiding significance on the acid fracturing design of the deep limestone reservoir.
In order to achieve the above technical objects, the present invention provides the following technical solutions.
Firstly, establishing a shaft temperature field model to simulate the heat transfer of a shaft and calculating the bottom temperature; secondly, calculating the length and width of the acid fracturing fracture by adopting a PKN formula, and solving the acid liquid flow rate according to the fracture width distribution; thirdly, the temperature and the concentration of the acid liquor are solved according to the flow rate by taking the bottom temperature as an initial condition; then, calculating the acid rock reaction heat according to the temperature and the concentration of the acid liquor; and finally, calculating the temperature and the concentration of the acid liquor after the acid rock reaction heat is considered, establishing a relation curve of the acid liquor concentration and the crack length, and determining the effective action distance of the acid liquor.
The numerical calculation method of the effective acting distance of the acid fracturing fluid of the deep limestone reservoir sequentially comprises the following steps of:
(1) simulating a shaft temperature field by adopting an Eickmeier shaft temperature field model and calculating the bottom hole temperature at the end of construction (Wanghong, Zhang Shicheng. Hydraulic fracturing design numerical value calculation method [ M ]. Beijing: oil industry Press, 1998);
(2) calculating the length of a crack seam (Li Yingchuan. oil extraction engineering [ M ]. Beijing: oil industry Press, 2001) at the end of construction by adopting a PKN formula, dividing grid units in the direction of the length of the seam, calculating the average seam width of each unit, and calculating the acid liquor flow rate of each unit;
(3) taking the bottom hole temperature calculated in the step (1) as an initial condition, and calculating the acid liquid temperature and the acid liquid concentration of each unit without considering the acid rock reaction heat through the acid liquid flow rate calculated in the step (2);
(4) calculating the acid rock molar reaction heat of each unit according to the acid liquid temperature and concentration calculated in the step (3);
(5) and (4) substituting the acid rock molar reaction heat calculated in the step (4) into the step (3), calculating the acid liquor temperature and the acid liquor concentration of each unit considering the acid rock reaction heat, and establishing an acid liquor concentration distribution curve. And defining 10% of the initial injection concentration of the acid liquor as the limit concentration of the residual acid, and taking the length of a seam corresponding to the limit concentration of the residual acid as the effective acting distance of the acid liquor according to a distribution curve.
In the invention, in the step (1), an Eickmeier shaft temperature field model is adopted to simulate a shaft temperature field and calculate the bottom hole temperature when the construction is finished, and the process is as follows:
and establishing a target well shaft temperature field model and dividing grid units by adopting an Eickmeier shaft temperature field model modeling method. Taking the center of the oil pipe as an axis: in the radial direction, define riFor the mesh cell radius, N mesh cells are divided (i ═ 0,1,2, …, N). Wherein the model boundary points rNThe point is selected such that the temperature at the point is always equal to the formation temperature; in the vertical direction, if the target layer depth is H and the cell depth is Δ H, the vertical direction can be divided into M cells (j is 0,1,2 …, M), and the boundary point M is (H/Δ H). Defining the total construction time as tTTime step Δ t, time step n (n is 0,1,2 …, t)T). Calculating the temperature of the n time unit (i, j) by using the following formula in combination with the geological engineering parameters of the target well
Finally obtaining the bottom hole temperature at the end of construction
In the formula: q-discharge capacity of acid injection, m3/min；
ρiDensity of grid cell i, kg/m3；
Ci-the specific heat capacity of grid cell i, J/(kg ℃);
ΔHj-height, m, of grid cell j;
ri-the model radial grid radius, m;
λi-the thermal conductivity, W/(m. DEG C), of grid cell i;
Δ t-time step, min;
tT-total construction time, min;
n-time step, min;
In the invention, in the step (2), the length of the crack seam when the construction is finished is calculated by adopting a PKN formula, grid units are divided in the seam length direction, the average seam width of each unit is calculated, and then the acid liquor flow rate of each unit is calculated, wherein the process is as follows:
1) calculating the construction end, namely n-tTDefining x as the slit length direction and dividing grid units, and calculating the average slit width w corresponding to each unit:
in the formula: l is the length of the seam when the construction is finished, m;
c-acid fluid loss coefficient, m/min0.5；
μf-acid viscosity, Pa · min;
h-crack height, m;
E-Young's modulus of reservoir rock, Pa
Reservoir rock poisson ratio, dimensionless;
x-unit coordinate in the slot direction, m;
w is the average seam width of each unit at the end of construction, m.
2) Obtaining the flow velocity v of each unit acid liquid through the following formulax：
In the formula: v. ofl-the filtration rate of each unit, m/s;
vx-flow velocity in x-direction, m/s, for each cell.
The derivation process of equation (3) is as follows:
the acid continuity equation is:
assuming that the acid flow velocity in the fracture is considered as the average flow velocity, the pressure in the fracture is uniformly distributed, and the pressure gradient near the fracture axis (i.e. where y is 0) is 0, so there is vy|y＝00. In addition, the acid flow rate on the fracture wall is equal to the fluid loss rate, i.e.
Therefore, equation (3) can be derived by integrating equation (4) from the fracture axis (y ═ 0) to the fracture wall surface (y ═ w/2).
In the invention, in the step (3), the bottom hole temperature calculated in the step (1) is used as an initial condition, and the acid liquor temperature and the acid liquor concentration of each unit without considering the acid rock reaction heat are calculated through the acid liquor flow rate calculated in the step (2), and the process is as follows:
1) assuming that the crack inlet temperature is equal to the bottom temperature calculated in the step (1), considering the temperature of each unit in the crack length direction as an average temperature, and substituting the acid liquid flow rate solved in the step (2) into the following formula to solve the temperature of each unit acid liquid and the temperature of the wall surface of the crack:
wherein the convective heat transfer coefficient can be solved by the nuschelt criterion:
hT＝NNuKhf/w (7)
in the formula: t-average temperature of each unit acid solution, DEG C;
Tw-temperature of wall of crack of each unit, ° c;
hT-convective heat transfer coefficient, J/(m)2·min·℃)；
NNu-nuschelt number, dimensionless;
Khfthe thermal conductivity of the acid solution, J/(m.min. DEG C);
ρfreservoir rock density, kg/m3；
CfThe specific heat capacity of reservoir rock, J/(kg. DEG C.).
2) Assuming convective heat transfer h of acid liquorT(Tw-T) is mainly provided by formation heat transfer and acid rock reaction heat:
hT(Tw-T)＝q(tT)-kRCmΔrQm(Tw,p) (8)
in the formula: k is a radical ofRAcid rock reaction rate constant, (kg/m)3)-m·mol/(m2·s)；
C-acid solution concentration per unit, kg/m3；
ΔrQm(TwP) -Heat of acid rock molar reaction, kJ/mol;
m is the reaction grade number and has no dimension;
q(tT) -heat transfer from formation at end of construction，kJ。
Wherein the heat flow function formula is (Whitsitt, Dysart. the effect of temperature on simulation design [ J ]. SPE 2497,1970):
in the formula: mmaFormation rock volumetric heat capacity, J/m3·℃；
Khr-formation rock thermal conductivity, W/(m ℃);
Since the heat of acid rock reaction is a function of the acid solution temperature and concentration, the acid rock reaction heat (assuming that the value thereof is 0) is not considered in step (3), and the acid solution temperature in each unit without the heat of acid rock reaction can be determined by substituting formula (9) and formula (8) for formula (6).
The derivation process of equation (6) is as follows:
assuming a steady state acid temperature field. Each unit can establish an energy conservation equation:
in the same way as in the formula (5), the integral of the formula (10) from the crack axis (y is 0) to the crack wall surface (y is w/2):
since the fracture axis (y ═ 0) velocity gradient is 0, the temperature gradient is also 0. The cell temperatures are considered as average temperatures, and equation (11) is treated as an ordinary differential equation:
the convective heat transfer coefficient is characterized byThe parameter of heat exchange capacity between solid surfaces is defined as the ratio of the heat exchanged per unit area to the temperature difference between the fluid and the solid (flow flood, Von skies. chemical principle [ M)]Beijing: scientific Press 2001: 190). Thus, define hTAs convective heat transfer coefficient:
the formula (7) is a solution formula derived based on the Knoop number definition, and is hTAnother manifestation is. The formula (6) can be derived by substituting the formula (3) or the formula (13) for the formula (12).
3) Assuming that the concentration of each unit acid solution is an average concentration, substituting the acid solution flow rate solved in the step (2) into the following formula to obtain the concentration of each unit acid solution and the concentration of the wall surface of the crack:
in the formula: k is a radical ofg-convection mass transfer coefficient, m/min;
Cwacid concentration in kg/m for each unit fracture wall3；
Assuming that the acid solution on the fracture wall surface completely reacts with the rock on the fracture wall surface, the following steps are provided:
kg(C-Cw)＝kRCw m(15)
where, defined by the Sheword number, the convective mass transfer coefficient can be expressed as:
kg＝DeNSh/w (16)
acid rock reaction rate constant KRSolving from the Allunius formula (Leying-Chuan oil production engineering [ M ]]Beijing, oil industry Press, 2001):
in the formula: de-effective mass transfer coefficient of acid liquid hydrogen ions, m2/s；
Nsh-shewood number, dimensionless;
k0frequency factor, (kg/m)3)-m·mol/(m2·s)；
Ea-reaction activation energy, J/mol;
r-gas constant, 8.314J/(mol. cndot.).
Therefore, the temperature of each unit acid solution solved in the step 2) is substituted into the formula (17) to obtain KRThen, the acid solution concentration of each unit can be obtained by simultaneously solving equations (14) and (15).
The derivation of equation (14) is as follows:
the acid liquor concentration and substance balance equation is established in each unit:
in the same way as in the formula (5), the formula (18) is integrated from the crack axis (y is 0) to the crack wall surface (y is w/2):
since the fracture axis (y ═ 0) velocity gradient is 0, the concentration gradient is also 0. The unit concentrations are considered as average concentrations, and equation (19) is treated as an ordinary differential equation:
defined by convective mass transfer coefficient (liu gem, wanghao, wangzhong. heat and mass transfer [ M ]. southwest petroleum university, 2007):
the formula (16) is a solving formula derived based on the definition of the truncated number, and k isgAnother manifestation is. The formula (14) can be derived by substituting the formula (3) or the formula (21) into the formula (20). To sum up, the steps(3) The acid liquor temperature and concentration of each unit without considering the acid rock reaction heat can be obtained.
In the invention, in the step (4), the acid rock molar reaction heat of each unit is calculated by combining the acid liquor temperature and the acid liquor concentration calculated in the step (3), and the process is as follows:
1) considering the lithology of the reservoir in the target work area as limestone, look up the physical and chemical handbook (Sun brilliance, what is flat, Ma Guajing, etc.. physical and chemical practical handbook [ M)]Beijing, chemical industry Press 2016) to obtain the standard molar heat of reaction of each component in the reaction system, and calculate the molar heat of reaction of the reaction system
In the formula: upsilon isiThe stoichiometric coefficient of the component i in the reaction system has no dimension;
2) Combining the calculation result of the step 1), calculating the acid rock molar reaction heat delta under the high-temperature and high-pressure conditionsrHm(Tw,p)(GuoJ,Liu H,Zhu Y,et al.Effects of acid–rock reaction heat on fluid temperatureprofile in fracture during acid fracturing in carbonate reservoirs[J].Journalof petroleum science&engineering,2014,122:31-37)：
Wherein f isgIs free CO2Mole fraction：
In the formula: deltarHm(Tw) Temperature TwThe molar heat of reaction, kJ/mol;
p-formation pressure, MPa;
Cp,m(i, T) -the atmospheric molar heat capacity of component i at temperature T, J/(. degree.C.mol);
fg——CO2mole fraction, dimensionless;
Vco2——CO2molar volume, m3/mol；
VacidResidual acid volume, m3；
Sco2-CO in residual acid2Solubility, m3/m3。
ΔrHm(TwP) -temperature TwHeat of reaction molar at pressure p, kJ/mol.
3) In the acid rock reaction process, the reaction system is to CO2Do volume work. Therefore, the temperature, pressure and CO are taken into consideration2To obtain the acid rock molar reaction heat delta under the formation conditionrQm(Tw,p)：
In the invention, in the step (5), the acid rock molar reaction heat calculated in the step (4) is substituted into the step (3), and the acid liquor temperature and the acid liquor concentration of each unit taking the acid rock reaction heat into consideration are calculated, so as to establish an acid liquor concentration distribution curve. Defining 10% of the initial injection concentration of the acid liquor as the limit concentration of the residual acid, and taking the length of a seam corresponding to the limit concentration of the residual acid as the effective acting distance of the acid liquor according to a distribution curve, wherein the process is as follows:
1) substituting the acid rock molar reaction heat calculated in the step (4) into a formula (8) to calculate the reaction heat of each unit acid rock, calculating the acid liquor temperature and the acid liquor concentration of each unit taking the acid rock reaction heat into consideration in the step (3), and making an acid liquor concentration distribution curve of each unit in the seam length direction;
2) defining 10% of the initial injection concentration of the acid liquor as the residual acid limit concentration, referring to an acid liquor concentration distribution curve, and taking the length of a crack corresponding to the residual acid limit concentration as the effective action distance of the acid liquor.
Compared with the prior art, the invention provides a numerical calculation method for the effective action distance of acid liquor of a deep limestone reservoir. The method couples three thermal effects of wellbore heat transfer, acid liquor convective heat transfer and acid rock reaction heat in the calculation process: firstly, calculating the bottom temperature of the construction completion well through a shaft temperature field model; solving the flow velocity of each unit acid liquor in the seam length direction by utilizing the seam width calculated by a PKN formula, solving the temperature and the concentration of each unit acid liquor by using the flow velocity of the acid liquor with the bottom temperature as an initial condition, and realizing the coupling of heat transfer and convective heat transfer of a shaft; solving the acid rock reaction heat through the temperature and the concentration of each unit acid liquor, calculating the concentration of each unit acid liquor after coupling the acid rock reaction heat to obtain an acid liquor concentration distribution curve, and determining the effective action distance of the acid liquor. The method overcomes the limitation that the influence of various heat effects on the acid fracturing reconstruction effect in the fracturing process cannot be comprehensively considered in the conventional method.
Drawings
FIG. 1 is a schematic representation of a wellbore temperature field model meshing in accordance with the present invention.
FIG. 2 is a graph showing the simulation results of bottom hole temperature variations in the present invention.
FIG. 3 is the calculation result of the heat of acid rock reaction in the present invention.
Fig. 4 is a diagram showing the calculation result of the effective action distance of the acid solution in the present invention.
Detailed Description
The invention will be further described with reference to the drawings and examples of application, which are intended to illustrate and explain the invention without limiting its scope. The method comprises the following specific steps:
1. and (2) establishing an X-well shaft temperature field physical model and dividing grids (see figure 1) based on X-well acid pressure design basic parameters (table 1) of a certain exploratory well in the target work area, and calculating the dynamic bottom temperature in the construction process of the well by adopting the shaft temperature field model established in the step (1) to obtain the bottom temperature when the construction is finished. The model can be proven reliable by comparison with the measured bottom hole temperature curve (see fig. 2).
TABLE 1 basic parameters of the acid fracturing design section of the X well
2. And (3) calculating the temperature and concentration equation of the fracture acid liquid in the step (2) and the step (3) by adopting a numerical method by taking the bottom temperature at the end of construction as an initial condition to obtain the temperature and concentration of each unit acid liquid at the end of construction.
3. The heat of acid rock reaction of each unit is calculated based on the acid liquor temperature and concentration of each unit calculated in step 2 in the embodiment, as shown in fig. 3.
4. Substituting the reaction heat of each unit acid rock calculated in step 3 in the specific embodiment into step 2, calculating the acid liquor temperature and the acid liquor concentration considering the reaction heat of the acid rock to obtain a distribution curve of the concentration of each unit acid liquor in the joint length direction, and taking the joint length of the crack corresponding to the limit concentration of the residual acid as the effective acting distance of the acid liquor, as shown in fig. 4.
Claims (6)
1. The numerical calculation method of the effective acting distance of the acid fracturing fluid of the deep limestone reservoir sequentially comprises the following steps of:
(1) simulating a shaft temperature field by adopting an Eickmeier shaft temperature field model and calculating the bottom hole temperature when the construction is finished;
(2) calculating the length of a crack seam when the construction is finished by adopting a PKN formula, dividing grid units in the direction of the length of the crack, calculating the average seam width of each unit, and calculating the acid liquor flow rate of each unit;
(3) taking the bottom hole temperature calculated in the step (1) as an initial condition, and calculating the acid liquid temperature and the acid liquid concentration of each unit without considering the acid rock reaction heat through the acid liquid flow rate calculated in the step (2);
(4) calculating the acid rock molar reaction heat of each unit according to the acid liquid temperature and concentration calculated in the step (3);
(5) substituting the acid rock molar reaction heat calculated in the step (4) into the step (3), calculating the acid liquor temperature and the acid liquor concentration of each unit considering the acid rock reaction heat, establishing an acid liquor concentration distribution curve, defining 10% of the initial injection concentration of the acid liquor as the residual acid limit concentration, and taking the seam length corresponding to the residual acid limit concentration as the effective action distance of the acid liquor according to the distribution curve.
2. The method for calculating the effective acting distance of the acid fracturing fluid in the deep limestone reservoir according to claim 1, wherein the step (1) comprises the following steps:
establishing a target well shaft temperature field model and dividing grid units, taking the center of an oil pipe as an axis: in the radial direction, define riFor the mesh cell radius, N mesh cells (i ═ 0,1,2, …, N) are divided, with model boundary points rNThe point is selected such that the temperature at the point is always equal to the formation temperature; in the vertical direction, if the target layer depth is H and the cell depth is Δ H, the vertical direction can be divided into M cells (j is 0,1,2 …, M), and the boundary point M is (H/Δ H); defining the total construction time as tTTime step Δ t, time step n (n is 0,1,2 …, t)T) The temperature of the cell (i, j) at time n is calculated using the following equation
Finally obtaining the bottom hole temperature at the end of construction
In the formula: q-discharge capacity of acid injection, m3/min；
ρiDensity of grid cell i, kg/m3；
Ci-the specific heat capacity of grid cell i, J/(kg ℃);
ΔHj-height, m, of grid cell j;
ri-the model radial grid radius, m;
λi-the thermal conductivity, W/(m. DEG C), of grid cell i;
Δ t-time step, min;
tT-total construction time, min;
n-time step, min;
3. The method for calculating the effective acting distance of the acid fracturing fluid in the deep limestone reservoir according to claim 1, wherein the step (2) comprises the following steps:
calculating the end of construction, i.e. n-tTDefining x as the slit length direction and dividing grid units, and calculating the average slit width w corresponding to each unit:
in the formula: l is the length of the seam when the construction is finished, m;
c-acid fluid loss coefficient, m/min0.5；
μf-acid viscosity, Pa · min;
h-crack height, m;
E-Young's modulus of reservoir rock, Pa
Reservoir rock poisson ratio, dimensionless;
x-unit coordinate in the slot direction, m;
w is the average seam width of each unit at the end of construction, m;
thereby obtaining the flow velocity v of acid liquid in each unitx：
In the formula: v. ofl-the filtration rate of each unit, m/s;
vx-flow velocity in x-direction, m/s, for each cell.
4. The method for calculating the effective acting distance of the acid fracturing fluid in the deep limestone reservoir according to claim 1, wherein the step (3) is as follows:
let Δ be given that the fracture entrance temperature is equal to the bottom hole temperaturerQm(TwAnd p) is 0, and the acid liquid temperature and the fracture wall surface temperature of each unit without considering the acid rock reaction heat are calculated as follows:
hT＝NNuKhf/w
hT(Tw-T)＝q(tT)-kRCmΔrQm(Tw,p)
in the formula: t-average temperature of each unit acid solution, DEG C;
Tw-temperature of wall of crack of each unit, ° c;
hT-convective heat transfer coefficient, J/(m)2·min·℃)；
NNu-nuschelt number, dimensionless;
Khfthe thermal conductivity of the acid solution, J/(m.min. DEG C);
ρfreservoir rock density, kg/m3；
Cf-specific heat capacity of reservoir rock, J/(kg ℃);
kRacid rock reaction rate constant, (kg/m)3)-m·mol/(m2·s)；
C—Acid liquor concentration per unit, kg/m3；
ΔrQm(TwP) -Heat of acid rock molar reaction, kJ/mol;
m is the reaction grade number and has no dimension;
q(tT) -formation heat transfer at end of construction, kJ;
Mmaformation rock volumetric heat capacity, J/m3·℃；
Khr-formation rock thermal conductivity, W/(m ℃);
the concentration of each unit acid solution and the concentration of the wall surface of the crack are obtained by the following formula:
kg(C-Cw)＝kRCw m
kg＝DeNSh/w
in the formula: k is a radical ofg-convection mass transfer coefficient, m/min;
Cwacid concentration in kg/m for each unit fracture wall3；
De-effective mass transfer coefficient of acid liquid hydrogen ions, m2/s；
Nsh-shewood number, dimensionless;
k0frequency factor, (kg/m)3)-m·mol/(m2·s)；
Ea-reaction activation energy, J/mol;
r-gas constant, 8.314J/(mol. cndot.).
5. The method for calculating the effective acting distance of the acid fracturing fluid in the deep limestone reservoir according to claim 1, wherein the step (4) comprises the following steps:
firstly, calculating the molar reaction heat delta of the acid rock under the conditions of high temperature and high pressurerHm(Tw,p)：
In the formula: deltarHm(Tw) Temperature TwThe molar heat of reaction, kJ/mol;
p-formation pressure, MPa;
Cp,m(i, T) -the atmospheric molar heat capacity of component i at temperature T, J/(. degree.C.mol);
fg——CO2mole fraction, dimensionless;
Vco2——CO2molar volume, m3/mol；
VacidResidual acid volume, m3；
Sco2-CO in residual acid2Solubility, m3/m3；
ΔrHm(TwP) -temperature TwThe heat of reaction in moles at pressure p, kJ/mol;
thereby obtaining the molar reaction heat delta of the acid rock under the formation conditionrQm(Tw,p)：
6. The method for calculating the effective acting distance of the acid fracturing fluid in the deep limestone reservoir according to claim 1, wherein the step (5) is as follows:
1) calculating the temperature and the acid liquor concentration of each unit of acid liquor taking the acid rock reaction heat into consideration by the acid rock molar reaction heat calculated in the step (4) in the step (3), and drawing a distribution curve of the acid liquor concentration of each unit in the seam length direction;
2) defining 10% of the initial injection concentration of the acid liquid as the limit concentration of the residual acid, and taking the length of a crack corresponding to the limit concentration of the residual acid as the effective acting distance of the acid liquid.
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