阅读说明：本技术 一种储层改造方法 (Reservoir transformation method ) 是由 李海波 卢聪 于 2019-10-22 设计创作，主要内容包括：本发明公开了一种储层改造方法,包括以下步骤：获取待改造储层的基础参数；明确所述储层的改造目标,当所述储层为天然裂缝发育储层时,所述改造目标为疏通天然裂缝、解除钻井液伤害,所述储层通过网络裂缝酸化优化方法进行改造；当所述储层为天然裂缝欠发育储层时,所述改造目标为压开储层、增大泄流面积,所述储层通过超深高温气井酸压优化方法进行改造。本发明能够对天然裂缝发育储层以及天然裂缝欠发育储层进行改造,提升储层的单井产量。(The invention discloses a reservoir transformation method, which comprises the following steps: acquiring basic parameters of a reservoir to be modified; determining the modification target of the reservoir, wherein when the reservoir is a natural fracture development reservoir, the modification target is to dredge natural fractures and remove drilling fluid damage, and the reservoir is modified by a network fracture acidizing optimization method; and when the reservoir is a natural fracture underdeveloped reservoir, the modification target is to open the reservoir and increase the drainage area, and the reservoir is modified by an ultra-deep high-temperature gas well acid fracturing optimization method. The method can be used for improving the natural fracture development reservoir and the natural fracture underdeveloped reservoir and improving the single-well yield of the reservoir.)

1. A method of reservoir modification comprising the steps of:

acquiring basic parameters of a reservoir to be modified;

the goal of the reformation of the reservoir is defined,

when the reservoir is a natural fracture development reservoir, the modification aims to dredge natural fractures and remove drilling fluid damage, and the reservoir is modified by a network fracture acidizing optimization method;

and when the reservoir is a natural fracture underdeveloped reservoir, the modification target is to open the reservoir and increase the drainage area, and the reservoir is modified by an ultra-deep high-temperature gas well acid fracturing optimization method.

2. A reservoir reconstruction method as claimed in claim 1 wherein said base parameters are obtained by conducting laboratory experiments using cores, or a combination of cores and outcrops.

3. A reservoir reconstruction method as claimed in claim 2 wherein said base parameters include rock mineral composition, rock mechanics parameters, magnitude of ground stress, direction of ground stress, acid rock reaction rate.

4. A reservoir modification method as defined in claim 3, wherein the rock mineral composition is obtained by an X-ray diffraction experiment, and the core is subjected to an erosion rate experiment, and when the mineral composition of the core contains carbonate, and the average carbonate content is greater than 85% and the average erosion rate is greater than 90%, the core is subjected to an acid-rock reaction rate experiment, a drilling fluid damage and relief experiment, an acid penetration experiment, and an acid erosion fracture conductivity experiment.

5. A reservoir reconstruction method as claimed in claim 4 wherein hydrochloric acid or gelled acid is used for the erosion rate test, acid rock reaction rate test, drilling fluid damage and relief test, acid penetration test, acid erosion fracture conductivity test.

6. A reservoir reconstruction method as claimed in claim 3 wherein said petromechanical parameters include compressive strength, young's modulus, poisson's ratio, tensile strength, said compressive strength, young's modulus and poisson's ratio being obtained by experimental methods employing triaxial compression, said tensile strength being obtained by experimental methods employing brazilian splitting.

7. A reservoir reconstruction method as claimed in claim 1 wherein the network fracture acidizing optimization method requires that the natural fractures be propped open during the acidizing process and the net pressure in the fractures is increased to allow the acid fluid to be drained into the reservoir along the fractures, and a plurality of reticulated flow channels with flow conductivity are established in the formation by the reaction of the acid fluid with the primary and secondary mineral packings and external pollutants in the fractures.

8. A reservoir modification method as claimed in claim 7, wherein a 150 ℃ high temperature gelled acid system is used as the acid liquid for the network fracture acidizing optimization method.

9. A reservoir reconstruction method as claimed in claim 7 wherein said network fracture acidizing optimization method comprises: determining the depth of the crack to be unplugged; acquiring a ground stress parameter of a reservoir; defining the pressure condition required by the natural fracture to open; defining the lower limit and the upper limit of wellhead discharge capacity required by opening the natural fracture; calculating the effective acting distance of the acid liquid corresponding to the alternative discharge capacity; calculating the acidified epidermis coefficients under the different scales and the different discharge capacities; construction scale and displacement are preferred based on the skin factor.

10. The reservoir reconstruction method as claimed in claim 1, wherein the ultra-deep high temperature gas well acid fracturing optimization method is used for building a set of multi-field coupling acid fracturing models with temperature fields as cores by considering the influence of temperature on the acid fracturing of the ultra-deep high temperature gas well, so that the acid fracturing reconstruction optimization design of the reservoir is realized.

Technical Field

The invention relates to the technical field of oil and gas field development, in particular to a reservoir stratum transformation method.

Background

In order to increase the production of oil and gas wells or the injection of water into water wells, the reservoir is usually modified by taking a series of engineering measures on the reservoir. Reservoir transformation mainly aims at reservoir characteristics and production conditions, and researches economic and effective technical measures adapted to the reservoir transformation so as to improve the connectivity between a shaft and the reservoir and achieve the purposes of increasing production and increasing injection. Reservoir modification techniques are essential in the oil industry for the development of low-permeability, ultra-low-permeability oil and gas fields, and for contaminated medium-permeability and high-permeability oil and gas fields near the wellbore, in order to achieve industrial oil and gas flow.

The reservoir reconstruction technology mainly comprises the following steps: the fracturing technology which utilizes various different media, such as hydraulic fracturing technology, acid fracturing technology, foam fracturing technology, high-energy gas fracturing technology and the like, mainly aims at generating one or more fractures with certain flow conductivity in a compact reservoir so as to facilitate oil and gas to flow from the reservoir to a shaft; acidizing techniques that utilize a variety of different matrices, such as sandstone acidizing techniques, carbonate acidizing techniques, and the like, differ from fracturing primarily in that matrix acidizing techniques inject chemicals at pressures below the reservoir fracture pressure and thus do not create fractures. The principle of acidification, production increase and injection increase is that after the chemical blocking remover is injected into the stratum, certain substances in the reservoir are dissolved, and the permeability of the near wellbore zone is recovered and improved.

However, the properties of each reservoir are different, and the yield increase of different reservoir reconstruction technologies is also different, so that the definition of reconstruction target selection of each reservoir and the adaptation of the reconstruction target selection are the problems to be solved urgently at present.

Disclosure of Invention

In view of the above problems, the present invention aims to provide a reservoir reformation method that can define a reservoir reformation target according to reservoir basic parameters and select a reservoir reformation method suitable for the target.

The technical scheme of the invention is as follows:

a method of reservoir modification comprising the steps of: acquiring basic parameters of a reservoir to be modified; determining the modification target of the reservoir, wherein when the reservoir is a natural fracture development reservoir, the modification target is to dredge natural fractures and remove drilling fluid damage, and the reservoir is modified by a network fracture acidizing optimization method; and when the reservoir is a natural fracture underdeveloped reservoir, the modification target is to open the reservoir and increase the drainage area, and the reservoir is modified by an ultra-deep high-temperature gas well acid fracturing optimization method.

Preferably, the basic parameters are obtained by performing an indoor experiment in a mode of combining a rock core or a rock core and an outcrop.

Preferably, the basic parameters comprise rock mineral components, rock mechanical parameters, crustal stress magnitude, crustal stress direction and acid rock reaction rate.

Preferably, the rock mineral components are obtained through an X-ray diffraction experiment, the rock core is subjected to an erosion rate experiment, and when the mineral components of the rock core contain carbonate, the average carbonate content is greater than 85%, and the average erosion rate is greater than 90%, the rock core is subjected to an acid-rock reaction rate experiment, a drilling fluid damage and relieving experiment, an acid penetration experiment and an acid erosion fracture conductivity experiment.

Preferably, hydrochloric acid or gelled acid is adopted to perform the corrosion rate experiment, the acid rock reaction rate experiment, the drilling fluid damage and relief experiment, the acid penetration experiment and the acid corrosion crack flow conductivity experiment.

Preferably, the rock mechanical parameters include compressive strength, young modulus, poisson ratio and tensile strength, the compressive strength, young modulus and poisson ratio are obtained by adopting a triaxial compression test method, and the tensile strength is obtained by adopting a brazilian splitting test method.

Preferably, the network fracture acidizing optimization method requires that natural fractures are propped open in the acidizing process, the net pressure in the fractures is increased, acid liquor is filtered and enters a reservoir layer along the fractures, and a plurality of reticular flow channels with flow guiding capacity are established in the stratum by means of reaction of the acid liquor with primary and secondary filling minerals and external pollutants in the fractures.

Preferably, a 150 ℃ high-temperature resistant gelled acid system is adopted as the acid liquid of the network fracture acidizing optimization method.

Preferably, the network fracture acidizing optimization method comprises the following steps: determining the depth of the crack to be unplugged; acquiring a ground stress parameter of a reservoir; defining the pressure condition required by the natural fracture to open; defining the lower limit and the upper limit of wellhead discharge capacity required by opening the natural fracture; calculating the effective acting distance of the acid liquid corresponding to the alternative discharge capacity; calculating the acidified epidermis coefficients under the different scales and the different discharge capacities; construction scale and displacement are preferred based on the skin factor.

Preferably, the acid fracturing optimization method for the ultra-deep high-temperature gas well establishes a set of multi-field coupling acid fracturing model with a temperature field as a core by considering the influence of temperature on the acid fracturing of the ultra-deep high-temperature gas well, so that the acid fracturing modification optimization design of the reservoir is realized.

Compared with the prior art, the invention has the following advantages:

the invention defines the modification target of the reservoir by acquiring the basic parameters of the reservoir to be modified, and selects an adaptive modification method to ensure that the reservoir is suitable for different types of reservoirs. When the reservoir is a natural fracture development reservoir, the reservoir is modified by a network fracture acidizing optimization method, so that natural fractures are dredged, the damage of drilling fluid is relieved, and the yield of a single well is improved; when the reservoir is a natural fracture underdeveloped reservoir, the method is modified by an ultra-deep high-temperature gas well acid fracturing optimization method, the reservoir is pressed open, the drainage area is increased, and the single well yield is improved.

Drawings

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to these drawings without creative efforts.

FIG. 1 is a dimensionless equivalent wellbore radius chart;

FIG. 2 is a construction curve for optimal reconstruction of network fracture acidizing according to one embodiment;

FIG. 3 is a block diagram of a calculation of the heat of the acid rock molar reaction;

FIG. 4 is a schematic view of the distribution of the heat transfer medium in the center of the oil tube;

FIG. 5 is a schematic diagram showing the comparison between the temperature field calculation model of the present invention and the conventional water pressure model;

FIG. 6 is a block diagram of crack temperature field calculation at any time during acid fracturing construction;

FIG. 7 is a block diagram of a process for calculating an effective acid solution working distance;

FIG. 8 is a construction curve for the acid fracturing optimization modification of an ultra-deep high temperature gas well according to an embodiment.

Detailed Description

The invention is further illustrated with reference to the following figures and examples.

A method of reservoir modification comprising the steps of: acquiring basic parameters of a reservoir to be modified; determining the modification target of the reservoir, wherein when the reservoir is a natural fracture development reservoir, the modification target is to dredge natural fractures and remove drilling fluid damage, and the reservoir is modified by a network fracture acidizing optimization method; and when the reservoir is a natural fracture underdeveloped reservoir, the modification target is to open the reservoir and increase the drainage area, and the reservoir is modified by an ultra-deep high-temperature gas well acid fracturing optimization method.

In a specific embodiment, the basic parameters are obtained by performing an indoor experiment in a mode of combining a rock core or a rock core and an outcrop. The basic parameters comprise rock mineral components, rock mechanical parameters, crustal stress magnitude, crustal stress direction and acid rock reaction rate.

Optionally, the rock mineral components are obtained through an X-ray diffraction experiment, the rock core is subjected to an erosion rate experiment, and when the mineral components of the rock core contain carbonate, the average carbonate content is greater than 85%, and the average erosion rate is greater than 90%, the rock core is subjected to an acid-rock reaction rate experiment, a drilling fluid damage and release experiment, an acid penetration experiment, and an acid erosion fracture conductivity experiment.

Optionally, the corrosion rate experiment, the acid rock reaction rate experiment, the drilling fluid damage and relief experiment, the acid penetration experiment, and the acid corrosion fracture conductivity experiment are performed by using hydrochloric acid or gelled acid.

Wherein the rock mechanical parameters comprise compressive strength, Young modulus, Poisson's ratio and tensile strength.

Alternatively, the compressive strength, young's modulus and poisson's ratio are obtained by an experimental method using triaxial compression.

Alternatively, the tensile strength is obtained by using the brazilian split test method.

The network fracture acidizing optimization method requires that natural fractures are propped open in the acidizing process, net pressure in the fractures is increased, acid liquor is filtered and enters a reservoir layer along the fractures, and a plurality of reticular flow channels with flow guiding capacity are established in a stratum by the reaction of the acid liquor and primary and secondary filling minerals and external pollutants in the fractures.

In a specific embodiment, a 150 ℃ high-temperature resistant gelled acid system is adopted as the acid liquid of the network fracture acidizing optimization method.

The network fracture acidizing optimization method comprises the following steps: determining the depth of the crack to be unplugged; acquiring a ground stress parameter of a reservoir; defining the pressure condition required by the natural fracture to open; defining the lower limit and the upper limit of wellhead discharge capacity required by opening the natural fracture; calculating the effective acting distance of the acid liquid corresponding to the alternative discharge capacity; calculating the acidified epidermis coefficients under the different scales and the different discharge capacities; construction scale and displacement are preferred based on the skin factor.

In a specific embodiment, the pressure conditions required for the natural fracture to open are determined by:

p_f＞p_open＝σ_n (1)

in the formula:

p_ffluid pressure in the fracture, MPa;

p_openthe natural fracture opening pressure is MPa;

σ_nnormal stress on natural fracture surface, MPa;

in formula (1):

in the formula:

σ_His the horizontal maximum principal stress, MPa;

σ_his the horizontal minimum principal stress, MPa;

theta is the angle of approach, degree, of the natural fracture and the wellbore or hydraulic fracture;

whether the closed natural fracture can be opened under the condition of acid injection discharge capacity is judged by adopting the following physical model:

ΔV＝V_inj-V_out (3)

p_f＝P_i+ΔP (4)

in the formula:

Δ V is the volume change of the fluid in unit time, m³；

V_injInjection of fluid volume, m, per unit time³；

V_outVolume of fluid flowing in unit time, m³；

p_iInitial bottom hole pressure, MPa;

Δ P is the additional increase pressure, MPa;

in formula (3):

in the formula:

k is the perforation section permeability, mD;

h is the perforation section thickness, m;

r_fis the natural fracture length, m;

r_wis the borehole radius, m;

in the formulae (4) and (5):

in the formula:

V_wis the wellbore volume, m³；

C_wIs the acid liquid compression coefficient, MPa^-1；

The critical discharge capacity for opening the natural crack can be obtained according to the formulas (1) to (6);

if the pressure of the well head is limited, the well head pressure under different acid injection discharge volumes is determined, namely:

p_t＝p_f+p_F-p_h (7)

in the formula:

p_tthe wellhead pressure is MPa;

p_Ffriction resistance of acid liquid in a shaft is MPa;

p_hthe pressure of a liquid column in a shaft is MPa;

in a specific embodiment, the effective acid effect distance in the natural fracture is determined by the following method:

assuming that the natural fracture is a circular fracture around the wellbore, the fluid loss from the natural fracture wall is ignored. The effective action distance of the acid liquid in the natural fracture is focused, and an acidification model of the acid liquid with an experimental scale flowing linearly in the fracture-type rock sample is improved into an acidification model of the acid liquid flowing into the natural fracture radially under the condition of a shaft. Therefore, the acid liquor mass conservation equation, the mass transfer equation and the seam width dynamic change equation in the length direction of the natural fracture seam are as follows:

in the formula:

mu is acid liquid viscosity, mPa & s;

p is pressure, MPa;

w is the width of the crack, mm;

c is acid liquor concentration, mol/m 3;

K_gis the reaction rate constant, m/s;

beta is the dissolving power and has no dimension;

is the effective mass transfer coefficient of acid liquor, m²/s；

The initial conditions were:

the boundary conditions are as follows:

p_tthe wellhead pressure is MPa;

optionally, the finite difference method is used to numerically solve the established acid liquid flow reaction model formula (8) -formula (15).

In a specific embodiment, the network fracture acidized skin coefficient is determined by the following method:

1) calculation of the skin coefficient of the zone of contamination

In the formula:

r_dthe mud pollution radius, m;

K_dmean permeability of the contamination zone, mD;

in formula (16):

in the formula:

V_lossrepresents the amount of slurry leakage, m³；

Reservoir average porosity,%;

2) network fracture acidizing skin coefficient calculation

The final purpose of network fracture acidizing is to dredge a natural fracture network, thoroughly remove reservoir pollution and maximally reduce the skin coefficient, so that the establishment of an acidized skin coefficient prediction model is favorable for optimizing the acid injection discharge and the acid injection quantity.

Dimensionless parameter a is defined as:

in the formula:

r_efm is the effective acting distance of the acid solution;

after acidizing the fractured reservoir, the effective borehole radius is:

r_ew＝r_efr_wD(a) (19)

in the formula:

r_ewis the effective borehole radius, m;

r_wDrepresenting a dimensionless equivalent wellbore radius, dimensionless;

r_wDis a function of a, when a is determined, the dimensionless equivalent borehole radius r_wDThe determination may be made from a dimensionless equivalent borehole radius chart as shown in figure 1.

When the acidified zone is less than the contamination radius, the acidified skin factor is:

when the acidified zone is greater than the contamination radius, the acidified skin factor is:

in one specific example, the yield is 0.08X 10⁴m³D, performing network fracture acidizing optimization reconstruction on the well 1 to be reconstructed, wherein the basic parameters of the well 1 to be reconstructed are shown in a table 1:

table 1 basic parameters of a well 1 to be modified

Ground altitude, m	776.826	Elevation of heart tonifying, m	787.326
				Depth of completed well, m	7793.00 (oblique)	Position of finished drilling	Aspiration line
Position of plug surface, m	7450.00	Well completion method	Perforation completion
				Maximum well deviation, °	23.62	Depth of well at maximum well deviation, m	7050.00
Gas production wellhead	KQ78-140	Annular clear water pressure control, MPa	75.6

The density of the oil testing section is 1.88-2.11 g/cm³The drilling of the polysulfonate drilling fluid is shown in 2 gas invasion. The well log interpretation is shown in Table 2The well was 6 permeable layers, cumulative reservoir thickness 37.3m, average porosity 3.3%, where: class II reservoir 1.3m, average porosity 6.6%; class III reservoirs 36m, average porosity 3.2%, explain the relative development of pores and fractures.

TABLE 2 well logging interpretation of well to be modified 1

Using a 200.0m³The gel acid has a designed discharge capacity of 3.0-3.5 m³And (5) carrying out network fracture acidizing optimization modification at min. The construction parameter table is shown in table 3:

TABLE 3 construction parameter Table

The construction curve is shown in figure 2, the pump pressure is relatively stable in the construction process, obvious blockage removal characteristics are not shown, the pump stop pressure is 86.92MPa, the stratum acid absorption pressure gradient is 0.022MPa/m, and the pressure drop rate is 0.077 MPa/min. Well-opening liquid drainage of 200.7m³Pouring the mixture into a test pipeline, adopting a phi 5mm test pore plate, stabilizing the test time for 11: 30-17: 30, testing the average oil pressure for 43.3MPa, stabilizing the upper pressure for 0.24MPa, lowering the pressure for 0, stabilizing the upper temperature for 35.05 ℃, and obtaining the test yield of 0.12 multiplied by 10⁴m³/d。

According to the acid fracturing optimization method for the ultra-deep high-temperature gas well, the influence of temperature on the acid fracturing of the ultra-deep high-temperature gas well is considered, a set of multi-field coupling acid fracturing model with a temperature field as a core is established, and the acid fracturing modification optimization design of the reservoir is realized. The acid fracturing optimization method for the ultra-deep high-temperature gas well specifically comprises the following steps:

first, whether the reservoir can be subjected to acid fracturing is judged by the following method:

in the formula:

P_wh,maxthe highest treatment pressure at the bottom of the well, MPa;

P_t,maxallowing the highest construction pressure, MPa, for the oil pipe side;

P_c,maxallowing the highest construction pressure, MPa, for the oil pipe side;

P_t,injthe highest construction pressure of the oil pipe is MPa;

P_c,injthe highest construction pressure of the casing is MPa;

P_toolmaximum allowable pressure for the tool, MPa;

P_t,lthe pressure of a liquid column in the oil pipe is MPa;

P_c,lthe pressure of a liquid column in the sleeve is MPa;

P_pacthe maximum sealing resistance pressure of the packer is MPa;

in a specific embodiment, the construction adopts a 140MPa wellhead, and the oil pressure is controlled according to 125 MPa; the packer is a well completion packer with sealing pressure difference of 70 MPa; the control pressure of annular clear water is 75MPa, the low value of the operating pressure of the RDS valve at the upper part of the packer is 70MPa, and in order to avoid opening the RDS valve in the construction process, the balance pressure is controlled according to 60 MPa. The maximum allowable construction pressure of the bottom of the well is 190MPa, and the fracture pressure of the layer is 160-175 MPa, which is obtained by the parameter drive-in type (22), and the capacity of pressing open the reservoir layer is demonstrated.

Then, establishing a multi-field coupling acid fracturing model taking the temperature field as a core:

1. acid rock reaction heat calculation method

(1) Relationship between enthalpy of acid rock reaction and temperature

For the reaction of limestone with hydrochloric acid, the ion reaction equation is:

CaCO₃+2H⁺＝＝Ca²⁺+H₂O+CO₂↑ (23)

when T298.15K, the standard molar reaction enthalpy of the reaction is equal to the difference between the standard molar formation enthalpy of the product and the standard molar formation enthalpy of the reactant:

the standard molar enthalpy of formation for each of the substances in formula (24) is shown in table 4:

TABLE 4 values of thermodynamic parameters of related substances

Assuming that the temperature of the crack wall is T_wThe standard molar reaction enthalpy at this temperature is:

substituting the isobaric molar heat capacity values of the reactants and the products into formula (25) to obtain:

for acid fracturing of dolomite reservoirs, the main chemical reactions within the fracture are:

CaMg(CO₃)₂+4H⁺＝＝Ca²⁺+Mg²⁺+2H₂O+2CO₂↑ (27)

the standard molar reaction enthalpy at room temperature of chemical equation (27) can be obtained in the same manner:

and a temperature T_wStandard molar reaction enthalpy when:

(2) relationship between enthalpy of acid rock reaction and pressure

In the acid fracturing process, the pressure in the crack is up to dozens of megapascals, and the molar reaction enthalpy of the acid rock is different from that under normal pressure, so that the molar reaction enthalpy of the acid rock under the high-pressure condition needs to be calculated. From the formula (27):

for the reaction of hydrochloric acid with carbonate rock, except for the CO formed₂Some are in free state, others are in condensed state. The condensed matter has a small volume expansion coefficient, which is usually the caseWherein the subscript c represents condensed material and thus can be considered:

to highlight free CO₂The chemical reaction equation of limestone and hydrochloric acid can be written as:

CaCO₃(s)+2HCl(aq)＝＝CaCl₂(aq)+H₂O(l)+(1-f_g)·CO₂(aq)+f_g·CO₂(g)↑ (32)

in the formula (f)_gIs free CO₂Is defined as the fraction of CO which is in the free state when 1mol of reaction takes place₂The amount of substance(s) and CO formed₂The ratio of the amounts of the total substances. Then, combining equation (31) and equation (32), equation (30) can be:

the acid rock reaction is carried out in a solution, and the volume change of the condensed material before and after the reaction is not large, so that it is considered thatIt can be seen that the pressure in the acid fracturing process of carbonate rock mainly passes through free CO₂To influence the enthalpy of the acid rock reaction, formula (33) can be further refinedComprises the following steps:

for the reaction of dolomites with hydrochloric acid, CO₂Is 2, so formula (33) can be converted in the same way to:

V_CO2is CO₂Is a function of temperature and pressure. Free CO₂Mole fraction of f_gCan be calculated by the following formula:

in the formula:

V_acidis 1molCO₂Volume of residual acid produced upon generation, L;

S_CO2solubility of CO2 in the residual acid at the corresponding temperature and pressure, m³/m³。

The integral expressions on the right of the expressions (34) and (35) cannot be directly solved, and optionally, a complex simpson formula is adopted for solving:

the interval [1atm, p ] is divided into n equal parts, each part is delta p, and the formula of the product is shown in the specification according to the compound Simpson

The differential expression in expression (38) is simplified by a central difference method and then solved. Taking a proper temperature infinitesimal Δ T, the differential expression can be simplified as:

(3) heat of reaction of acid rock with reaction product CO₂In relation to (2)

The reaction of carbonate rock with hydrochloric acid has gaseous CO₂And (4) generating. Calculations show that these COs are generally the case₂Not all of which is dissolved in the residual acid, but a portion of which is liberated in the crack. This shows that the reaction system performs volume work on the environment during the acid rock reaction process. According to formula (39), consider CO₂The calculation formula of the acid rock reaction heat affected by the volume work is as follows:

is CO₂The stoichiometric coefficient of (1) is limestone and 2 is dolomite.

Taking into account temperature, pressure and CO₂Of volume work of (1), temperature T_wThe calculation formula of the molar reaction heat of the acid rock with the pressure p can be expressed as follows:

limestone:

dolomitic rock:

(4) acid rock mole reaction heat calculation program block diagram

The magnitude of the acid rock molar reaction heat depends on three input parameters: a block diagram of the temperature, pressure and initial concentration of the acid solution, and the calculation of the acid rock molar reaction heat is shown in fig. 3.

2. Wellbore unsteady state temperature field model

The heat transfer media are distributed in axial symmetry around the center of the oil pipe, as shown in fig. 4, and are assumed as follows: the tube string, the annulus and the stratum are isotropic on the same cross section; the liquid is incompressible and is injected into a shaft with constant discharge capacity; reaction between the acid liquor and the inner wall surface of the oil pipe is ignored; the stratums are distributed in a layered mode, and the thermophysical parameters of different lithological stratums are different; forced convection heat transfer is carried out in the oil pipe, and natural convection heat transfer is carried out in the annular space.

(1) Heat transfer model in oil pipe

According to a first law of thermodynamics of an unsteady system, the following parameters are obtained:

in the formula: e is the total energy per volume of fluid, J.

In the formula:

u is the internal energy per unit volume of fluid, J;

p ν is the flow energy per volume of fluid, J;

ν^2/2 is the kinetic energy of the fluid per unit volume, J;

E_kis the potential energy per volume of fluid, J.

Equation (44) describes the total energy change of the fluid, and the mechanical energy change can be expressed as:

in the formula: e.g. of the type_kIs the total mechanical energy per volume of fluid, J.

From the continuity equation, bringing equation (45) into equation (43) can be:

the internal and flow energies are expressed in terms of enthalpy, and it is generally believed that the rate of heat energy generated by the fluid absorbing viscous forces to perform work is approximately equal to the rate of viscous forces to perform work, so equation (46) can be rewritten as:

expression of equation (47) in enthalpy facilitates the description of the heat transfer process, while the first two terms can be expanded and combined as:

with the help of the continuity equation, equation (48) can be rewritten as:

according to the basic law of thermodynamics, enthalpy can be expressed as:

dh＝c_pdT-α_Jc_pdp (50)

meanwhile, the vertical heat conduction of the fluid is negligible. Therefore, in combination with formula (49), formula (48) can be rewritten as:

the satellite derivatives in equation (51) are rewritten to the partial derivatives form, which can be described for a one-dimensional flow process as:

the heat transfer model within the oil pipe can therefore be expressed as:

in the formula: q_mThe heat generated in unit length in the oil pipe is W/m;

r₁is the inner diameter of the oil pipe, m;

ρ₁fluid density, kg/m³；

v₁Is the fluid flow rate, m/s;

c₁is the specific heat capacity of the fluid, J/(kg DEG C);

T₁fluid temperature, deg.C;

p₁is pressure, MPa;

alpha J is the coke soup coefficient, DEG C/MPa;

T₂the temperature of the oil pipe wall is measured at DEG C;

h₁is the convective heat transfer coefficient of the inner wall of the oil pipe, W/(m)²·℃)。

(2) Tubing wall heat transfer model

The heat exchange of the tubing wall can be made up of two parts: oil pipe wall axial heat conduction is generated; radial convection heat exchange with the fluid in the oil pipe and the annular space. Therefore, from the principle of conservation of energy, one can derive:

in the formula:

T₃annulus fluid temperature, deg.C;

h₂is the convective heat transfer coefficient of the outer wall of the oil pipe, W/(m)²·℃)；

ρ₂Is the density of the oil pipe in kg/m³；

c₂The specific heat capacity of the oil pipe is J/(kg ℃);

λ₂is the heat conductivity coefficient of the oil pipe, W/(m DEG C);

r₂is the outer diameter of the oil pipe, m.

(3) Annular heat transfer model

The heat exchange generated by radial convection is mainly considered in the annulus, and can be expressed as:

in the formula:

T₄the casing wall temperature, deg.C;

h₃for convection exchange of the inner wall of the casingThermal coefficient, W/(m)²·℃)；

ρ₃Is annular fluid density, kg/m³；

c₃Specific heat capacity of annular fluid, J/(kg DEG C);

r₃is the inside diameter of the cannula, m.

(4) Composite layer heat transfer model

The heat transfer mode in the casing, the cement sheath and the stratum is pure heat conduction, so that the casing, the cement sheath and the stratum form a composite cylinder heat conduction system, and a two-dimensional heat conduction differential equation under a cylindrical coordinate can be derived by arranging an energy conservation equation:

at the sleeve inner wall interface, the heat of convection heat exchange between the sleeve wall and the annular fluid is equal to the heat conduction of the sleeve wall, namely:

the introduced heat and the led-out heat are equal at the casing wall, the cement sheath interface and the cement sheath and formation interface, namely:

wherein: the casing wall is when i is 4, the cement sheath is when i is 5, and the formation is when i is 6.

The temperature remains constant at the outer boundary of the formation, i.e.:

T_ou＝T_const (59)

in the formula:

T_ouis the temperature at the outer boundary of the formation, deg.C;

T_constis a constant temperature equal to the formation original temperature at that point, c.

And carrying out differential discretization on the control equation of the unsteady coupling model of the shaft based on the discrete grid division. And adopting an implicit difference format of performing intermediate difference on the space items and performing forward difference on the time items. In order to avoid the zigzag pressure distribution of the solution result, the model control equation is processed by adopting a staggered grid division method, namely, the speed node is arranged on the interface of the area grid, and other nodes are arranged at the center of the area grid.

In one specific example, the production zone of this example was hung down at 7460m depth, the manometer was lowered 7220m, and the gas reservoir temperature was 155.1 ℃. And (3) performing simulation calculation by using the model and a hydraulic fracturing shaft temperature field model (a hydraulic pressure model for short) which is commonly used at present. The calculation result is shown in fig. 5, and it can be seen that the bottom hole temperature calculated by the model of the invention is close to the measured temperature, and the bottom hole temperature error calculated by the hydraulic pressure model reaches 50 ℃ at most.

3. Acid fracturing fracture temperature field model

The entire construction time is divided into a plurality of time bins, and the fracture temperature field can be considered to be stable within each time bin. The crack is divided into a number of micro-elements along the length of the crack corresponding to each time micro-element, and the width of the crack can be regarded as constant as long as the length micro-element is sufficiently small. Then within each fracture infinitesimal, it is readily available according to the principle of conservation of energy:

boundary conditions:

x＝0，T＝T₀ (61)

in the formula:

Δ_rQ_m(T_wp) is the molar reaction heat of the acid rock corresponding to the temperature and pressure on the wall surface of the infinitesimal internal fracture;

c is acid liquor concentration.

The meaning of formula (63) is: heat flow q from the formation to the fracture wall_h(t) the heat generated by the acid rock reaction on the fracture wall surface is equal to the heat flow transferred by the fracture wall surface to the fluid in the fracture. Whitsitt and Dysart derived the heat transfer from the formation to the fracture as expressed by:

wherein:

v in formula (60)_xV and v_yAcid flow rates in the seam length and width directions, respectively, which satisfy the continuity equation:

boundary conditions:

within each fracture infinitesimal, the distribution of acid concentration satisfies the following material balance equation:

boundary conditions:

x＝0，C＝C₀ (69)

the fracture temperature field at any time in the acid fracturing construction process can be obtained according to the acid rock reaction heat calculation model and the fracture temperature field calculation model, and a calculation block diagram is shown in fig. 6.

And finally, solving the multi-field coupling acid fracturing model, and realizing the acid fracturing optimization modification of the ultra-deep high-temperature gas well of the reservoir to be modified according to the solution. During solving, the acid-etched fracture length is solved on the basis of acid liquid concentration distribution in the fracture, so that the acid-etched fracture geometric dimension calculation model must be coupled with the acid liquid flow reaction model for solving. According to the calculation process of the fracture temperature field, the fracture temperature field and the acid liquid concentration distribution in the fracture are calculated at the same time, so that the acid corrosion fracture geometric dimension calculation program is embedded with the fracture temperature field calculation program considering the acid rock reaction heat, and the effective acid corrosion fracture length can be obtained. A block diagram of a calculation process of the effective acid solution acting distance is shown in fig. 7.

In one specific example, the yield is 32.23X 10⁴m³D, performing acid fracturing optimization modification on the ultra-deep high-temperature gas well 2 to be modified, wherein basic parameters of the well 2 to be modified are shown in a table 5:

TABLE 5 basic parameters of the well 2 to be modified

The density of the oil testing section is 1.48-1.49 g/cm³The drilling of the polysulfonate drilling fluid is shown by 3 gas invasion. The log interpretation is shown in table 6, the well is a 3-zone gas formation, cumulative reservoir thickness 21.5m, and average porosity 3.8%, where: class II reservoir 1.9m, average porosity 6.8%; class III reservoir 19.6m, average porosity 3.5%. The rock core is compact, and erosion holes develop locally; imaging logging shows sporadic development of erosion holes and local development of low-angle cracks.

TABLE 6 well logging interpretation of well to be modified 2

Using 160.0m³The gel acid has a designed discharge capacity of 3.0-3.5 m³And performing acid fracturing optimization modification on the ultra-deep high-temperature gas well in min. The construction parameters table is shown in table 7:

TABLE 7 construction parameter Table

The construction curve is shown in FIG. 8, the discharge capacity is increased to 3.0m in the construction process³At/min, the pump pressure dropped rapidly from 100.3MPa to 93.1MPa, with a significant indication of fracturing the formation. At 4.1m³In the process of injecting gelled acid at the displacement of/min, the pump pressure is slowly and continuously reduced from 94.6MPa to 92.8MPa, which shows that the acid liquid plays a certain improvement role in a seepage passage of a reservoir. The pump stop pressure is 62.46MPa, the pressure gradient of acid absorption of the stratum is 0.0197MPa/m, and the pressure drop rate is 0.65 MPa/min. Well opening liquid discharge of 80.0m³Pouring the mixture into a test pipeline, adopting a phi 35mm test orifice plate, stabilizing the test time for 13: 40-16: 10, increasing the test oil pressure from 42.61 to 54.04MPa, stabilizing the casing pressure for 13.81MPa, stabilizing the upper pressure for 2.14MPa, pressing down for 0, stabilizing the upper temperature for 5.85 ℃, and obtaining the test yield of 41.86 multiplied by 10⁴m³/d。

In another embodiment, 300.0m is used³And the designed discharge capacity is 3.5-4.5 m³Acid solution pair yield of 31.03 multiplied by 10/min⁴m³D, performing acid fracturing optimization modification on the ultra-deep high-temperature gas well by using the well 3 to be modified, wherein the acid liquor is 60.0m³The self-generated acid pad liquid is mixed with 240.0m³Gelled acid composition, and the test yield is 36.88 multiplied by 10 after the modification is finished⁴m³/d。

Although the present invention has been described with reference to a preferred embodiment, it should be understood that various changes, substitutions and alterations can be made herein without departing from the spirit and scope of the invention as defined by the appended claims.