CN116029149B - Fracturing design method for fracture-cavity carbonate oil reservoir with one well and multiple targets - Google Patents
Fracturing design method for fracture-cavity carbonate oil reservoir with one well and multiple targets Download PDFInfo
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Abstract
The invention discloses a fracturing design method for one well and multiple targets of a fracture-cavity carbonate reservoir, which comprises the following steps: step S10, stratum parameters and engineering parameters are obtained, wherein the stratum parameters comprise oil reservoir data, fracturing well shaft parameters and natural crack seam information, and the engineering parameters comprise fracturing well completion information and fracturing construction parameters; step S20, a non-uniform reservoir non-planar three-dimensional crack extension model considering crack initiation, steering and extension of a near-well perforation of a crack is established according to the stratum parameters and engineering parameters; and step S30, determining the influence of the shaft azimuth and construction parameters on the crack initiation and propagation rule and the crack space communication range under the condition of the horizontal well crack-hole complex medium according to the non-planar three-dimensional crack propagation model of the non-uniform reservoir layer established in the step S20 so as to determine the effect of acid fracturing cracks communicating with the crack hole body under different conditions.
Description
Technical Field
The invention belongs to the technical field of oil and gas field development, and particularly relates to a fracturing design method for one-well multi-target fracture-cavity carbonate oil reservoirs.
Background
Carbonate reservoirs are widely distributed in China, have huge reserves and are indispensable oil and gas exploration and development objects. The Tarim basin Oregano carbonate reservoir has been explored and developed for nearly twenty years, and has made remarkable progress in the development technology of carbonate fracture-cavity reservoir reservoirs. Because of the characteristics of low permeability of the carbonate hydrocarbon reservoir matrix and extremely strong transverse and longitudinal heterogeneity, the conventional flooding well pattern is adopted to develop low yield and poor economic benefit. The large fracture-cavity development of the oil reservoir is realized, oil gas is mainly stored in the fracture-cavity, and the artificial fracture is communicated with the fracture-cavity through the acidizing and fracturing transformation of the reservoir, so that the technology is a key technology for developing the fracture-cavity type carbonate oil reservoir.
The fracture-cavity type carbonate reservoir also develops the research and application of the horizontal well staged multi-cluster fracturing theory by referring to the thought of large-scale fracturing transformation of shale gas. However, the horizontal well staged multi-cluster fracturing generally only forms 'transverse cuts' with the fracture faces perpendicular to the well bore, and hydraulic fractures are difficult to communicate with the fracture cavity bodies at special positions, so that the number of acid fracturing fractures communicated with the fracture cavities is small. However, researches on crack propagation laws suitable for 'one-well multi-target' fracturing of carbonate reservoirs at present are still fresh, and theoretical basis is lacking in accurately designing azimuth arrangement, construction parameters and the like of horizontal well shafts.
Disclosure of Invention
Therefore, the present invention is to provide a fracturing design method for one-well multi-target fracture-cavity carbonate reservoirs, which aims to solve the above problems.
In order to achieve the above object, the present invention provides a fracturing design method for a fracture-cavity carbonate reservoir with one well and multiple targets, comprising:
step S10, stratum parameters and engineering parameters are obtained, wherein the stratum parameters comprise oil reservoir data, fracturing well shaft parameters and natural crack seam information, and the engineering parameters comprise fracturing well completion information and fracturing construction parameters;
step S20, a non-uniform reservoir non-planar three-dimensional crack extension model considering crack initiation, steering and extension of a near-well perforation of a crack is established according to the stratum parameters and engineering parameters;
step S30, determining the influence of shaft azimuth and construction parameters on crack initiation and propagation rules and crack space communication ranges under the condition of a horizontal well crack-hole complex medium according to the non-planar three-dimensional crack propagation model of the non-uniform reservoir layer established in the step S20 so as to determine the effect of acid fracturing crack communication crack-hole bodies under different conditions;
and S40, determining the crack extension condition by combining construction pressure analysis and distributed optical fiber strain monitoring, correcting the non-planar three-dimensional crack extension model of the non-uniform reservoir, and simulating and analyzing the multi-target fracturing transformation effect of one well.
Preferably, in the fracturing design method for a fracture-cavity carbonate reservoir with one well and multiple targets, the fracturing well wellbore parameters in the step S10 include a casing inner diameter, a casing inner wall roughness, and a fracturing segment length;
the natural fracture information comprises natural fracture density and size;
the fracturing completion information comprises perforation positions, cluster intervals, cluster numbers and perforation parameters;
the fracturing construction parameters include construction displacement, and fluid viscosity.
Preferably, in the fracture design method for a fracture-cavity carbonate reservoir with one well and multiple targets, the establishing of the non-planar three-dimensional fracture propagation model of the heterogeneous reservoir in step S20 includes establishing a particle motion equation, establishing a force displacement relationship, establishing a fluid flow equation, and establishing a fracture propagation standard.
Preferably, in the fracture design method for fracture-cavity carbonate reservoir one-well multi-target, the method for establishing the particle motion equation comprises the following steps:
the motion of a single particle is determined by the resultant force and moment acting on the particle, and the linear equation of motion is:
according to the speed at the time t+Deltat, the calculation formula of the acceleration of the particles at the time t is as follows:
the translational degree of freedom of the node is calculated by adopting a linear momentum balance equation and a displacement velocity relation:
the rotational equation of motion of the particles is:
wherein the angular velocity ω of the component i at time t i The calculation formula of the center difference equation is as follows:
m is the mass of the particle;
a is the acceleration of the particle, a t Acceleration of the particles at time t;
Δt is the time step;
v i (t) the velocity of particle i at time t;
∑F i is the sum of all forces acting on the particle;
m is moment;
Σmi is the sum of all moments acting on the particles;
r is the radius of the particles;
i is a component;
ω i （t+△t） is the angular velocity of component i at time t + [ delta ] t.
Preferably, in the fracturing design method for one-well multi-target of a fracture-cavity carbonate reservoir, the method for establishing the force displacement relationship comprises the following steps:
the positional formula for calculating the contact point of the particles includes:
wherein ,xi [D] Is the location of the particle contact point;
x i [A] 、x i [B] 、x i [C] the center positions of the particles A, B, C, respectively;
R [A] 、R [B] 、R [C] the radius of the particles A, B, C, respectively;
U n is the relative displacement in the normal vector direction;
d is the distance between the particles and the wall surface;
n i is a unit normal vector;
the contact force of the two contact units is as follows:
wherein ,
is the contact force of the contact unit;
F i N is the normal contact force of particle i;
F i S is the shear contact force of particle i;
v i N and vi S The velocities of the particle element i in the normal direction and in the shearing direction, respectively;
k N and kS The normal stiffness and shear stiffness of the particles, respectively;
Δt is the time step.
Preferably, in the fracture design method for fracture-cavity carbonate reservoir one-well multi-target, the step of establishing a fluid flow equation includes:
the flow rate along the pipeline from particle a to particle B in the rock matrix can be written according to the lubrication theory formula:
the pressure increase for a time step Δt can be calculated as:
wherein, beta is a calibration parameter;
k r is the relative permeability;
a is the fracture pore size;
μ is the viscosity of the fracturing fluid;
p A and pB Fluid pressure for particle a and particle B, respectively;
Z A and ZB The heights of particle a and particle B, respectively;
ρ w is the density of the fracturing fluid;
g is gravity acceleration;
Δp is the pressure increase;
q is the sum of all flows connected to the fluid unit;
v is node volume;
K f is the bulk modulus of the fluid.
Preferably, in the fracture design method for one-well multi-target fracture-cavity carbonate reservoir, the method for establishing the fracture propagation standard comprises the following steps:
the crack propagation stress intensity factor criterion is based on J integral, and the J integral can be expressed as:
the stress intensity factor based on J integral is obtained:
and (3) obtaining a crack propagation stress intensity factor criterion based on J integral:
wherein V is the region including the fracture front;
s is a crack surface;
r is half length of a crack;
w is the strain energy density;
n is a normal unit;
f is the volume force;
t is the traction force;
σ is the cauchy stress tensor;
u is a displacement vector;
x i ，x i c coordinates of an arbitrary point and a region center point, respectively;
K I is a stress intensity factor;
e is Young's modulus of the rock;
K IC is the toughness of the rock.
Preferably, in the fracturing design method for one-well multi-target of a fracture-cavity carbonate reservoir, the step S30 includes:
step S301, based on the non-planar three-dimensional fracture expansion model of the non-uniform reservoir established in the step S20, taking a communication fracture hole as a target on the premise of ensuring the stability of a shaft and a stratum, designing a numerical simulation scheme according to stratum parameters and engineering parameters, performing numerical simulation, and drawing a fracturing fracture expansion morphological diagram under different conditions;
step S302, determining the influence of the shaft azimuth and the construction parameters on crack expansion and crack hole communication effects based on the result of numerical simulation;
step S303, the number of the fracture communication karst cave bodies and the fracture cave body modification ratio are improved to serve as evaluation indexes, and the azimuth and construction parameters of the horizontal well shaft are optimized, wherein the established index fracture cave body modification ratio is defined as the ratio of the number of the natural fractures connected with the periphery of a certain karst cave to the total number of the natural fractures connected with the periphery of the karst cave through the fracture hydraulic fracture.
The invention has the following beneficial effects:
aiming at a fracture-cavity type carbonate reservoir with low permeability and extremely strong transverse and longitudinal heterogeneity, the invention provides a method for optimizing the arrangement azimuth and construction parameters of a 'one-well multi-target' fracturing shaft aiming at the fracture-cavity type carbonate reservoir. The method comprises the steps of obtaining stratum parameters and engineering parameters, wherein the stratum parameters comprise oil reservoir data, fracturing well shaft parameters and natural crack seam information, and the engineering parameters comprise fracturing completion information and fracturing construction parameters; establishing a non-planar three-dimensional fracture propagation model of the non-uniform reservoir taking into account fracture near-well perforation initiation, diversion and propagation according to the stratum parameters and engineering parameters; determining the influence of shaft azimuth and construction parameters on crack initiation and propagation rules and crack space communication ranges under the condition of a horizontal well crack-hole complex medium according to the non-planar three-dimensional crack propagation model of the non-uniform reservoir established in the step S20 so as to determine the effect of acid fracturing cracks in communication with a crack hole body under different conditions; and finally, combining construction pressure analysis and distributed optical fiber strain monitoring to determine crack extension conditions, correcting a non-planar three-dimensional crack extension model of the heterogeneous reservoir, simulating and analyzing a one-well multi-target fracturing modification effect, realizing the well shaft azimuth arrangement and the accurate design of construction parameters of the one-well multi-target fracturing of the target fracture-cavity type carbonate reservoir, realizing the optimal communication space multi-set fracture-cavity of the one-well multi-target type reservoir, and providing support for the efficient development of the type of reservoir.
Further, according to the method, a non-uniform reservoir non-planar three-dimensional crack expansion model is constructed according to the detailed geological and engineering data of the target block, the influence of a well shaft azimuth and construction parameters on a crack initiation and expansion rule and a crack space communication range under the condition of a horizontal well crack-hole complex medium is obtained through numerical simulation analysis, then the number of the communication karst cave bodies of the fracturing cracks and the fracture cave body modification ratio are improved to serve as evaluation indexes, and the well shaft azimuth and the construction parameters of the horizontal well are optimized.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings that are needed in the description of the embodiments or the prior art will be briefly described, and it is obvious that the drawings in the description below are some embodiments of the present invention, and other drawings can be obtained according to the drawings without inventive effort for a person skilled in the art.
FIG. 1 is a schematic diagram of a fracture-cave carbonate reservoir "one-well multi-target" fracturing physical model provided by the invention;
FIG. 2 is a schematic illustration of the "one well multi-target" fracture propagation of a fracture-cave carbonate reservoir of the present invention;
FIG. 3 is a schematic diagram showing the transformation ratio of a "one-well multi-target" fracture hole as a function of azimuth of a well bore;
FIG. 4 is a schematic diagram of the variation of the "one well multi-target" fracture hole modification ratio with the viscosity of the fracturing fluid.
The achievement of the objects, functional features and advantages of the present invention will be further described with reference to the accompanying drawings, in conjunction with the embodiments.
Detailed Description
In the embodiment of the invention, the term "and/or" describes the association relation of the association objects, which means that three relations can exist, for example, a and/or B can be expressed as follows: a exists alone, A and B exist together, and B exists alone. The character "/" generally indicates that the context-dependent object is an "or" relationship.
It should be noted that the terms "first," "second," and the like in the description and the claims of the present invention and the above figures are used for distinguishing between similar objects and not necessarily for describing a particular sequential or chronological order.
The term "plurality" in embodiments of the present invention means two or more, and other adjectives are similar.
For the purpose of making the objects, technical solutions and advantages of the embodiments of the present invention more apparent, the embodiments of the present invention will be described in detail below with reference to the accompanying drawings. However, it will be understood by those of ordinary skill in the art that in various embodiments of the present invention, numerous specific details are set forth in order to provide a thorough understanding of the present invention. However, the claimed technical solution of the present invention can be realized without these technical details and various changes and modifications based on the following embodiments. The following embodiments are divided for convenience of description, and should not be construed as limiting the specific implementation of the present invention, and the embodiments can be mutually combined and referred to without contradiction.
The invention provides a fracturing design method for one well and multiple targets of a fracture-cavity carbonate oil reservoir, which comprises the following steps of:
step S10, stratum parameters and engineering parameters are obtained, wherein the stratum parameters comprise oil reservoir data, fracturing well shaft parameters and natural crack seam information, and the engineering parameters comprise fracturing well completion information and fracturing construction parameters;
specifically, the fracturing well shaft parameters comprise the inner diameter of the casing, the roughness of the inner wall of the casing and the length of a fracturing section; the natural fracture information comprises natural fracture density and size; the fracture completion information includes perforation location, cluster spacing, cluster number, and perforation parameters (e.g., number of perforations per cluster, perforation diameter, etc.); the fracturing construction parameters include construction displacement, and fluid viscosity.
The oil reservoir data comprise reservoir thickness, porosity, permeability, rock Young modulus, poisson's ratio, fracture toughness, fluid loss coefficient, horizontal main stress distribution and the like, logging data, seismic data, fracture-cavity space distribution positions and the like;
taking a fracture-cavity type carbonate reservoir horizontal well as an example, the formation parameters and engineering parameters are shown in tables 1 to 4.
TABLE 1 geological parameters
| Parameters (parameters) | Numerical value |
| Model size/ |
50×40×25 |
| Horizontal maximum principal stress/MPa | 120 |
| Horizontal minimum principal stress/MPa | 100 |
| Vertical stress/MPa | 140 |
| Young's modulus/GPa | 36 |
| Poisson's ratio | 0.22 |
| Compressive Strength/MPa | 224.7 |
| Porosity/% | 3 |
| permeability/mD | 2 |
| Matrix pore pressure/ |
60 |
TABLE 2 engineering parameters
| Parameters (parameters) | Numerical value |
| Viscosity of fracturing fluid, mPas | To be optimized |
| Construction displacement, m 3 /min | To be optimized |
| Diameter of eyelet, mm | 12 |
| Number of perforations per |
16 |
| Injection time, min | To be optimized |
| Abrasion coefficient, dimensionless | 0.8 |
TABLE 3 wellbore orientation parameters
| Parameters (parameters) | Numerical value |
| Azimuth angle | To be optimized |
| Vertical distance from karst cave body, m | To be optimized |
| Transverse distance from karst cave body, m | To be optimized |
TABLE 4 Natural fracture parameters
| Parameters (parameters) | Numerical value |
| Size, m | （2-4）×2 |
| Coefficient of friction | 0.1 |
| Density, bar/m | 0.15 |
It should be noted that, a physical model of fracturing of a certain fracture-cavity type carbonate reservoir horizontal well may be established according to the parameters in step S10. FIG. 1 is a schematic diagram of a "one well multi-target" fracturing physical model of a horizontal well of a cave type carbonate.
Step S20, a non-uniform reservoir non-planar three-dimensional crack extension model considering crack initiation, steering and extension of a near-well perforation of a crack is established according to the stratum parameters and engineering parameters;
specifically, establishing a non-uniform reservoir non-planar three-dimensional fracture propagation model in S20 includes establishing a particle motion equation, establishing a force displacement relationship, establishing a fluid flow equation, and establishing a fracture propagation criteria.
(1) Establishing a particle motion equation
Specifically, the method for establishing the particle motion equation comprises the following steps:
since the position and contact force of the particles determine the movement of the particles, the movement of the individual particles is determined by the resultant forces and moments acting on the particles, and the linear equation of movement is:
according to the speed at the time t+Deltat, the calculation formula of the acceleration of the particles at the time t is as follows:
the lattice, as used herein, is a quasi-random combination of particle nodes contacted by nonlinear springs, and the translational degrees of freedom of the nodes are calculated using a linear momentum balance equation and displacement velocity relationship:
the rotational equation of motion of the particles is:
wherein the angular velocity ω of the component i at time t i The calculation formula of the center difference equation is as follows:
m is the mass of the particle;
a is the acceleration of the particle, a t Acceleration of the particles at time t;
Δt is the time step;
v i (t) the velocity of particle i at time t;
∑F i is the sum of all forces acting on the particle;
m is moment;
Σmi is the sum of all moments acting on the particles;
r is the radius of the particles;
i is a component;
ω i （t+△t） is the angular velocity of component i at time t + [ delta ] t.
(2) Establishing force displacement relation
The method for establishing the force displacement relationship comprises the following steps:
since the constitutive properties of a material are represented by different contact types between particles, the positional formula for calculating the contact point of a particle includes:
wherein ,xi [D] Is the location of the particle contact point;
x i [A] 、x i [B] 、x i [C] the center positions of the particles A, B, C, respectively;
R [A] 、R [B] 、R [C] the radius of the particles A, B, C, respectively;
U n is the relative displacement in the normal vector direction;
d is the distance between the particles and the wall surface;
n i is a unit normal vector;
the contact force of the two contact units is as follows:
wherein ,
is the contact force of the contact unit;
F i N is the normal contact force of particle i;
F i S is the shear contact force of particle i;
v i N and vi S The velocities of the particle element i in the normal direction and in the shearing direction, respectively;
k N and kS The normal stiffness and shear stiffness of the particles, respectively;
Δt is the time step.
Establishing fluid flow equations
The fluid flow model consists of the fluid flow in the rock matrix and the hydraulic fracture between which fluid can be exchanged. The rock matrix flow uses pore pressure stored in matrix model springs, which model takes into account fluid seepage in hydraulic fracturing into the surrounding rock matrix. Fluid flow in hydraulic fracturing is geometrically established by a flow model consisting of fluid nodes and a network of pipes.
The step of establishing a fluid flow equation includes:
the flow rate along the pipeline from particle a to particle B in the rock matrix can be written according to the lubrication theory formula:
the pressure increase for a time step Δt can be calculated as:
wherein, beta is a calibration parameter;
k r is the relative permeability;
a is the fracture pore size;
μ is the viscosity of the fracturing fluid;
p A and pB Fluid pressure for particle a and particle B, respectively;
Z A and ZB The heights of particle a and particle B, respectively;
ρ w is the density of the fracturing fluid;
g is gravity acceleration;
Δp is the pressure increase;
q is the sum of all flows connected to the fluid unit;
v is node volume;
K f is the bulk modulus of the fluid.
(4) Establishing a crack propagation standard
The method for establishing the crack extension standard comprises the following steps:
the crack propagation stress intensity factor criterion is based on J integral, and the J integral can be expressed as:
the stress intensity factor based on J integral is obtained:
and (3) obtaining a crack propagation stress intensity factor criterion based on J integral:
wherein V is the region including the fracture front;
s is a crack surface;
r is half length of a crack;
w is the strain energy density;
n is a normal unit;
f is the volume force;
t is the traction force;
σ is the cauchy stress tensor;
u is a displacement vector;
x i ，x i c coordinates of an arbitrary point and a region center point, respectively;
K I is a stress intensity factor;
e is Young's modulus of the rock;
K IC is the toughness of the rock.
Step S30, determining the influence of shaft azimuth and construction parameters on crack initiation and propagation rules and crack space communication ranges under the condition of a horizontal well crack-hole complex medium according to the non-planar three-dimensional crack propagation model of the non-uniform reservoir layer established in the step S20 so as to determine the effect of acid fracturing crack communication crack-hole bodies under different conditions;
in specific implementation, the step S30 includes:
step S301, based on the non-planar three-dimensional fracture expansion model of the non-uniform reservoir established in the step S20, taking a communication fracture hole as a target on the premise of ensuring the stability of a shaft and a stratum, designing a numerical simulation scheme according to stratum parameters and engineering parameters, performing numerical simulation, and drawing a fracturing fracture expansion morphological diagram under different conditions;
step S302, determining the influence of the shaft azimuth and the construction parameters on crack expansion and crack hole communication effects based on the result of numerical simulation;
in step S303, the number m of fracture communication karst cave bodies and the fracture cave body modification ratio n of the fracture hydraulic fracture communication karst cave are used as evaluation indexes, and the azimuth of the horizontal well shaft (such as the shaft azimuth, the shaft and karst cave body transverse distance and the shaft and karst cave body vertical distance) and the construction parameters (such as the fracturing fluid displacement, viscosity and injection time) are optimized, wherein the established index fracture cave body modification ratio is defined as the ratio of the number of natural fractures connected around a karst cave to the total number of natural fractures connected around the karst cave through the fracture hydraulic fracture communication karst cave.
Based on step S30, the influence of the shaft orientation and construction parameters on the crack initiation and expansion rule and the crack space communication range of the horizontal well under the condition of complex medium of the seam-hole is researched, and the shaft arrangement orientation and construction parameters are optimized. Example results are shown in fig. 2 to 4. Fig. 2 is a schematic diagram of expansion of a fracture-cavity type carbonate reservoir "one-well multi-target" fracture crack, fig. 3 is a schematic diagram of modification proportion of the one-well multi-target "fracture crack with azimuth change of a shaft, and fig. 4 is a schematic diagram of modification proportion of the" one-well multi-target "fracture crack with viscosity change of fracturing fluid. According to fig. 2 to 4, different shaft arrangement orientations and construction parameters are changed, changes of crack morphology, communication karst cave body number and a fracture cave body modification proportion are analyzed, the karst cave body number and the fracture cave body modification proportion are improved to serve as evaluation indexes, and the target block 'one-well multi-target' fracturing shaft arrangement orientations and construction parameters are optimized.
And S40, combining construction pressure analysis and distributed optical fiber strain monitoring to determine crack extension conditions, correcting the non-planar three-dimensional crack extension model of the non-uniform reservoir established in the step S20, and performing simulation analysis on the 'one-well multi-target' fracturing modification effect.
It will be apparent that the embodiments described above are merely some, but not all, embodiments of the invention. Based on the embodiments of the present invention, those skilled in the art may make other different changes or modifications without making any creative effort, which shall fall within the protection scope of the present invention.
Claims (6)
1. A fracture design method for a fracture-cavity carbonate reservoir with multiple targets in one well, comprising:
step S10, stratum parameters and engineering parameters are obtained, wherein the stratum parameters comprise oil reservoir data, fracturing well shaft parameters and natural crack seam information, and the engineering parameters comprise fracturing well completion information and fracturing construction parameters;
step S20, according to the stratum parameters and engineering parameters, a non-planar three-dimensional fracture expansion model of the non-uniform reservoir is established, wherein the non-planar three-dimensional fracture expansion model of the non-uniform reservoir is considered in the steps S20, and the non-planar three-dimensional fracture expansion model of the non-uniform reservoir comprises the steps of establishing a particle motion equation, establishing a force displacement relation, establishing a fluid flow equation and establishing a fracture expansion standard;
step S30, determining the influence of shaft azimuth and construction parameters on crack initiation and propagation rules and crack space communication ranges under the condition of a horizontal well crack-hole complex medium according to the non-planar three-dimensional crack propagation model of the non-uniform reservoir layer established in the step S20 so as to determine the effect of acid fracturing crack communication crack-hole bodies under different conditions;
step S40, combining construction pressure analysis and distributed optical fiber strain monitoring to determine crack extension conditions, correcting a non-planar three-dimensional crack extension model of the non-uniform reservoir, and simulating and analyzing a multi-target fracturing transformation effect of one well;
wherein, the step S30 includes:
step S301, based on the non-planar three-dimensional fracture expansion model of the non-uniform reservoir established in the step S20, taking a communication fracture hole as a target on the premise of ensuring the stability of a shaft and a stratum, designing a numerical simulation scheme according to stratum parameters and engineering parameters, performing numerical simulation, and drawing a fracturing fracture expansion morphological diagram under different conditions;
step S302, determining the influence of the shaft azimuth and the construction parameters on crack expansion and crack hole communication effects based on the result of numerical simulation;
step S303, the number of the fracture communication karst cave bodies and the fracture cave body modification ratio are improved to serve as evaluation indexes, and the azimuth and construction parameters of the horizontal well shaft are optimized, wherein the established index fracture cave body modification ratio is defined as the ratio of the number of the natural fractures connected with the periphery of a certain karst cave to the total number of the natural fractures connected with the periphery of the karst cave through the fracture hydraulic fracture.
2. The fracture-cave carbonate reservoir one-well multi-target fracturing design method of claim 1, wherein the fracturing well wellbore parameters in step S10 comprise casing inside diameter, casing inside wall roughness, and fracturing segment length;
the natural fracture information comprises natural fracture density and size;
the fracturing completion information comprises perforation positions, cluster intervals, cluster numbers and perforation parameters;
the fracturing construction parameters include construction displacement, and fluid viscosity.
3. The fracture-cave type carbonate reservoir one-well multi-target fracturing design method according to claim 1, wherein the method for establishing a particle motion equation comprises:
the motion of a single particle is determined by the resultant force and moment acting on the particle, and the linear equation of motion is:
according to the speed at the time t+Deltat, the calculation formula of the acceleration of the particles at the time t is as follows:
the translational degree of freedom of the node is calculated by adopting a linear momentum balance equation and a displacement velocity relation:
the rotational equation of motion of the particles is:
wherein the components are
At->
Angular velocity ω of time i The calculation formula of the center difference equation is as follows:
m is the mass of the particle;
a is the acceleration of the particle, a t Acceleration of the particles at time t;
Δt is the time step;
v i (t) particles
At->
Speed of time;
∑F i is the sum of all forces acting on the particle;
m is moment;
Σmi is the sum of all moments acting on the particles;
r is the radius of the particles;
i is a component;
ω i （t+△t） is the angular velocity of component i at time t + [ delta ] t.
4. The fracture-cave type carbonate reservoir one-well multi-target method for designing a fracture of claim 1, wherein the method for establishing the force-displacement relationship comprises:
the positional formula for calculating the contact point of the particles includes:
wherein ,xi [D] Is the location of the particle contact point;
x i [A] 、x i [C] the center positions of the particles A, C, respectively;
R [A] 、R [B] 、R [C] the radius of the particles A, B, C, respectively;
U n is a normal vector squareRelative displacement in the direction;
d is the distance between the particles and the wall surface;
n i is a unit normal vector;
the contact force of the two contact units is as follows:
wherein ,
is the contact force of the contact unit;
F i N is the normal contact force of particle i;
F i S is the shear contact force of particle i;
v i N and vi S The velocities of the particle element i in the normal direction and in the shearing direction, respectively;
k N and kS The normal stiffness and shear stiffness of the particles, respectively;
Δt is the time step.
5. The fracture-cave type carbonate reservoir one-well multi-target fracturing design method of claim 1, wherein the step of establishing a fluid flow equation comprises:
the flow rate along the pipeline from particle a to particle B in the rock matrix can be written according to the lubrication theory formula:
the pressure increase for a time step Δt can be calculated as:
wherein, beta is a calibration parameter;
k r is the relative permeability;
a is the fracture pore size;
μ is the viscosity of the fracturing fluid;
p A and pB Fluid pressure for particle a and particle B, respectively;
Z A and ZB The heights of particle a and particle B, respectively;
ρ w is the density of the fracturing fluid;
g is gravity acceleration;
Δp is the pressure increase;
q is the sum of all flows connected to the fluid unit;
v is node volume;
K f is the bulk modulus of the fluid.
6. The fracture design method for a one-well multi-target fracture-cavity carbonate reservoir of claim 1, wherein the method of establishing fracture propagation criteria comprises:
the crack propagation stress intensity factor criterion is based on J integral, and the J integral can be expressed as:
the stress intensity factor based on J integral is obtained:
and (3) obtaining a crack propagation stress intensity factor criterion based on J integral:
wherein V is the region including the fracture front;
s is a crack surface;
r is half length of a crack;
w is the strain energy density;
n is a normal unit;
f is the volume force;
t is the traction force;
σ is the cauchy stress tensor;
u is a displacement vector;
x i ，x i c coordinates of an arbitrary point and a region center point, respectively;
K I is a stress intensity factor;
e is Young's modulus of the rock;
K IC is the toughness of the rock.
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