CN115186524A - Low-permeability long-fracture fracturing well group CO 2 Evaluation method for flooding critical gas injection parameters - Google Patents
Low-permeability long-fracture fracturing well group CO 2 Evaluation method for flooding critical gas injection parameters Download PDFInfo
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Abstract
The invention provides a low-permeability long-fracture fracturing well group CO 2 The evaluation method of the flooding critical gas injection parameter comprises the following steps: developing CO 2 Finely describing the oil reservoir characteristics of the gas injection well group; developing CO 2 Describing geomechanical parameters of the gas injection well group; establishing low permeability long fracture fracturing well group CO 2 A reservoir flooding matrix-fracturing fracture coupling numerical simulation model; performing long fracture fracturing well group CO 2 Simulating a displacement value, and evaluating the pressure change of the oil reservoir; developing long fracture fracturing well group CO 2 Evaluating the change of the ground stress field of the driving disturbance, and developing the long-crack fracturing well group CO 2 Determination of crack extension and evaluation of gas channeling and CO 2 And (4) leakage risk, and determining a critical gas injection parameter limit. The low-permeability long-crack fracturing well group CO 2 Evaluation method for flooding critical gas injection parameters combines low-permeability long-slit fracturing well characteristics and dynamic change of oil reservoir physical parameters to evaluate CO 2 Driving critical gas injection parameters, for increasing CO 2 Drives out hair and realizes CO 2 The scientific management of the reservoir oil displacement is of great significance.
Description
Technical Field
The invention relates to the technical field of oil reservoir development, in particular to a low-permeability long-crack fracturing well group CO 2 Evaluation method of flooding critical gas injection parameters.
Background
Low permeability reservoir CO 2 Flooding is an effective method for increasing the recovery of crude oil. CO 2 2 Can reach supercritical state under the conditions of temperature and pressure of deep low-permeability reservoir, and has the density of liquid, viscosity of gas and capacityThe low permeability reservoir is easy to inject to supplement the formation energy; with CO 2 Easy to mix with crude oil, so that the volume of the crude oil is expanded, the viscosity of the crude oil is reduced, and the oil displacement efficiency is greatly improved.
CO (carbon monoxide) transfer injection at later stage of low-permeability reservoir hydraulic fracturing well development 2 And the oil displacement can realize the conversion of development modes, and is beneficial to solving the development problem of 'no injection and no extraction'. But long fracture fracturing reservoir CO 2 Drive out existing fracturing crack and CO 2 Gas injection parameter coupling affects the problem. On one hand, the gas injection capacity of the large fracturing well is obviously higher than that of the conventional gas injection well, and the length and the azimuth of the fracture affect CO 2 Oil displacement effect; CO on the other hand 2 Gas injection parameters influence the stress state of a fracture, and too high gas injection parameters easily cause fracture expansion, so that CO is induced 2 Risk of gas channeling and leakage, which becomes a constraint on CO 2 Driving the technical bottleneck of the development effect.
Low permeability reservoir CO at present at home and abroad 2 The flooding research is mainly directed at CO 2 Mechanism of miscible injection, CO 2 The problem of improving the recovery ratio and the like is solved, and the method is lack of CO aiming at the long fracture fracturing well 2 A method for quantitatively evaluating flooding critical gas injection parameters.
In the application No.: CN201711128892.3, relates to a method for determining gas injection parameters of a carbon dioxide flooding layered gas injection well. The determination method comprises the following steps: establishing a single-tube layered gas injection mathematical model or a concentric double-tube layered gas injection mathematical model according to a carbon dioxide flooding layered gas injection process; solving the mathematical model by using a node system analysis method; the method comprises the steps of performing single-tube layered gas injection, namely drawing a single-layer gas nozzle outflow curve and a single-layer stratum inflow curve, and solving by using an iteration method to determine reasonable gas injection amount and gas injection pressure of each oil layer under different gas nozzle conditions; and (3) concentric double-pipe layered gas injection, wherein reasonable gas injection amount and gas injection pressure of each oil layer are determined by drawing a single-layer inflow curve, a total inflow curve and a ground pipeline outflow curve.
In the application No.: CN201910561096.1, relating to a two-dimensional CO of a low permeability reservoir 2 Non-miscible flooding mathematical simulation method. The method comprises the following steps: establishing two-dimensional CO for low permeability reservoir 2 A non-miscible flooding mathematical model; the low permeability reservoir two-dimensional CO 2 Processing parameters and boundary conditions required by the unmixed phase flooding solving process; the low permeability reservoir two-dimensional CO 2 Solving a non-miscible flooding mathematical model, wherein the mathematical model is solved by adopting a numerical method, namely, a hidden pressure apparent saturation method is adopted for solving; selecting a low permeability reservoir and obtaining geological parameters thereof, and adopting the two-dimensional CO of the low permeability reservoir 2 Calculating by a non-miscible flooding mathematical simulation method, and analyzing the result.
In the application No.: CN201510501873.5, relating to a method for determining CO 2 Process for displacing foam flow oil components and CO 2 Method for simulating flooding, in which CO is determined 2 The method for expelling the content of the foam flow oil component comprises the following steps: a parameter determination step, which is used for determining thermodynamic parameters, relative permeability and mole percentages of components and bubbles of the foam flow oil; and determining components, namely determining the content of each component and the content of bubbles based on a preset component model according to the parameters obtained in the parameter determining step.
The prior art is greatly different from the invention, and the technical problems which we want to solve are not solved, so we invent a novel low-permeability long-fracture fracturing well group CO 2 Evaluation method of flooding critical gas injection parameters.
Disclosure of Invention
The invention aims to provide a method for fully considering CO 2 CO in the process of gas injection 2 Coupling influence of gas injection parameters and fracturing fractures, and evaluation of CO in long fracture fracturing well group by combining dynamic change of physical parameters of oil reservoir 2 Gas injection potential, low permeability long crack fracturing well group CO for determining critical gas injection parameters 2 Evaluation method of flooding critical gas injection parameters.
The object of the invention can be achieved by the following technical measures: low-permeability long-fracture fracturing well group CO 2 Evaluating method of flooding critical gas injection parameters, namely CO of low-permeability long-crack fracturing well group 2 The evaluation method of the flooding critical gas injection parameter comprises the following steps:
step 1, developing CO 2 Finely describing the oil reservoir characteristics of the gas injection well group;
step 2, developing CO 2 Describing geomechanical parameters of the gas injection well group;
step 3, establishing a low-permeability long-fracture fracturing well group CO 2 A reservoir flooding matrix-fracturing fracture coupling numerical simulation model;
step 5, developing the long fracture fracturing well group CO 2 Evaluating the change of the driving disturbance ground stress field;
The object of the invention can also be achieved by the following technical measures:
in step 1, collecting structural data, drilling data, logging data, formation testing and production testing and core analysis testing data of a research area to which the long-fracture fracturing well group belongs, and determining basic parameters such as oil reservoir depth, temperature, pressure, porosity and permeability of a gas injection interval.
In step 2, the description of the geomechanical parameters comprises the rock mechanical parameters of the gas injection interval of the long-fracture fracturing well and the explanation and evaluation of the geostress logging, and the length and the direction of the fracture of the gas injection interval are determined.
In the step 2, determining rock mechanical strength parameters of Young modulus, poisson's ratio, tensile strength, cohesion and internal friction angle of the gas injection interval according to mechanical property test or well logging data explanation of the core of the gas injection interval of the long-fracture fracturing well; evaluating the crustal stress and the fracture pressure of a gas injection layer by using the fracturing construction data of the long-fracture fracturing well; and determining the length and the direction of the main fracture according to the microseism monitoring record of the fracturing well.
In step 2, determining the fracture pressure and the instantaneous pump-stopping pressure of the fracturing layer section of the well by using the fracturing construction data of the long-fracture fracturing well, and performing maximum horizontal stress and minimum horizontal stress interpretation on the fracturing layer section; further according to the logging information of the long-fracture fracturing well, carrying out layered crustal stress explanation to obtain CO 2 The gas driving and injection layer has large ground stress and rupture pressureIs small.
In step 3, according to the fracture morphology of the long fracture fracturing well obtained in step 2, a deterministic modeling method is adopted to establish a CO low-permeability long fracture fracturing well group 2 Reservoir flooding matrix-fracturing fracture coupling model; developing CO 2 Reservoir pressure change and CO 2 And (3) carrying out drive-induced ground stress field change coupling simulation evaluation.
In step 3, a low permeability long fracture fracturing well group CO is established 2 And (3) driving the reservoir matrix-fracturing fracture coupling numerical simulation model, wherein the length of the fracturing fracture in the model is consistent with that in the step (2), and the orientation of the fracturing fracture is consistent with that of the maximum horizontal ground stress.
In step 4, an initial CO is set 2 Gas injection parameters, utilizing the matrix-fracturing fracture coupling model established in the step 3, and carrying out numerical simulation analysis on CO under different parameters 2 The reservoir pressure of the gas injection well group changes.
In step 4, the reservoir pressure change is obtained by simultaneous solving of the following equation sets of the low permeability reservoir matrix seepage field and the hydraulic fracture internal seepage field and corresponding boundary conditions and initial conditions:
the low permeability reservoir matrix seepage field is described as:
the flow within the hydraulic fracture is described as:
wherein phi is the porosity of the low permeability reservoir; c w Is the matrix compressibility; k is the matrix permeability; mu is the fluid viscosity; ρ is the fluid density; u is the matrix skeleton deformation of the low permeability reservoir; f. of w Is a fluid source sink item; α is the Biot consolidation coefficient; t is time; z is the vertical depth; v is CO 2 The velocity of the fluid in admixture with the crude oil; c f Is the hydraulic fracture compressibility; k is a radical of f Is the crack permeability; d f Is the width of the crack;
derivation is conducted along the hydraulic fracture tangential direction; q f The flow exchange between the low-permeability reservoir matrix and the hydraulic fracture surface is realized; and n is the normal direction of the crack surface.
The equations (1) - (4) are solved by numerical calculation methods such as a finite difference method, a finite element method and the like.
In step 5, CO is developed according to the reservoir pressure change obtained in step 4 2 Analyzing the change of the driving and disturbing ground stress field; wherein CO is 2 The change of the displacement disturbance crustal stress field is obtained by simultaneous solving of a low-permeability reservoir matrix deformation equation and boundary conditions under the action of pore fluid pressure.
In step 5, the low permeability reservoir matrix deformation is described by the following formula:
wherein G is shear modulus; ν is the poisson ratio; α is the Biot coefficient; u. of i Is the formation displacement; f. of i Is physical strength; p is the reservoir pressure.
The boundary conditions are as follows:
wherein, σ' ij Is the effective stress of the rock formation; n is j Cosine of the direction of the normal outside the boundary;
T i (t) solving the boundary conditions of the known displacement and stress on the boundary respectively; delta ij Is a Kronecker symbol.
Equations (5) and (6) can be solved numerically by using a finite element method.
In step 6, according to the dynamic change data of the ground stress field of the well group obtained in the step 5, the rock fracture criterion of the low permeability reservoir is combined to develop the well group CO 2 Determination of crack extension and evaluation of gas channeling and CO 2 Risk of leakage; the low permeability reservoir rock fracture criteria include fracture tensile fracture and fracture shear fracture.
In step 6, the crack is tensile cracked at a maximum tensile critical stress F t As a test for CO 2 Drive induced fracture tensile failure criteria, i.e.
F t ＝σ 1 -f t0 (7)
Fracture shear failure at maximum shear failure stress F s As a test for CO 2 Drive induced fracture shear failure criteria, i.e.
Wherein σ 1 ，σ 3 Respectively obtaining a first main stress and a third main stress of a ground stress field in the step 5; reservoir pressure p, obtained in step 4; f. of t0 The tensile strength of the rock stratum,
And c is the cohesive force of the rock stratum and the internal friction angle of the rock stratum, and the internal friction angle is obtained in the step 2.
In step 6, if F is evaluated t Not less than 0 or F s If the gas injection parameter is more than or equal to 0, the long-seam fracturing well reaches the critical fracture condition and is easy to generate gas channeling and CO 2 Risk of leakage; the gas injection parameter corresponding to step 4 is determined as the critical gas injection parameter.
In step 6, if F is evaluated t Less than or equal to 0, indicating that the crack propagation condition is not reached, further increasing CO 2 Gas injection ginsengCounting; the flow returns to step 4; through cycle optimization, critical gas injection parameters are determined.
Low permeability long fracture fracturing well group CO in the invention 2 Evaluation method of flooding critical gas injection parameters fully considers CO 2 CO in the process of gas injection 2 Coupling influence of gas injection parameters and fracturing fractures, and evaluation of CO in long fracture fracturing well group by combining dynamic change of physical parameters of oil reservoir 2 Potential for insufflation, determining critical insufflation parameters. The low-permeability long-crack fracturing well group CO 2 The evaluation method of the flooding critical gas injection parameter establishes a matrix-fracture coupling model of the long fracture fracturing well on the basis of geological data, well logging data and fracturing micro-seismic monitoring data, and accurately and visually reflects CO by comprehensively utilizing field test and numerical simulation calculation 2 The gas drive has influence on the reservoir pressure and the ground stress field, the gas drive crack expansion judgment is carried out, the gas channeling and leakage risk are evaluated, the critical gas injection parameters are determined, and the application prospect is wide in the work of improving the low-permeability reservoir development effect and the like.
Drawings
FIG. 1 is a low permeability long fracture fracturing well group CO of the present invention 2 A flow diagram of one embodiment of a method for evaluating a flooding critical gas injection parameter;
FIG. 2 is a representation of a low permeability long fracture well set CO in an embodiment of the present invention 2 A schematic diagram of a reservoir flooding matrix-fracturing fracture coupling simulation model;
FIG. 3 shows a long fracture fracturing well CO in an embodiment of the invention 2 A schematic of reservoir pressure distribution;
FIG. 4 shows a long fracture fracturing well CO in an embodiment of the present invention 2 A schematic of the drive tensile fracture prediction evaluation;
FIG. 5 shows a long fracture fracturing well CO in an embodiment of the present invention 2 Schematic representation of drive shear fracture prediction evaluation.
Detailed Description
It is to be understood that the following detailed description is exemplary and is intended to provide further explanation of the invention as claimed. Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs.
It is noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of exemplary embodiments according to the invention. As used herein, the singular forms "a", "an" and "the" are intended to include the plural forms as well, and it should be understood that when the terms "comprises" and/or "comprising" are used in this specification, they specify the presence of the stated features, steps, operations, and/or combinations thereof, unless the context clearly indicates otherwise.
The low-permeability long-fracture fracturing well group CO of the invention 2 The evaluation method of the flooding critical gas injection parameter comprises the following steps:
step one, developing CO 2 Fine characterization of gas injection well group reservoir characteristics
Collecting structural data, drilling data, logging data, oil testing and production testing and core analysis testing data of a research area to which the long-fracture fracturing well group belongs, and determining basic parameters such as oil deposit depth, temperature, pressure, porosity and permeability of the gas injection interval.
Step two, developing CO 2 Description of geomechanical parameters of gas injection well group
The description of the geomechanical parameters comprises rock mechanical parameters of a gas injection interval of the long-fracture fracturing well, the interpretation and evaluation of the ground stress logging, and the length, the direction and the like of the fracturing fracture of the gas injection interval.
Determining rock mechanical strength parameters such as Young modulus, poisson ratio, tensile strength, cohesion, internal friction angle and the like of the gas injection interval according to the mechanical property test or well logging information explanation of the core of the gas injection interval of the long-fracture fracturing well; evaluating the ground stress and the fracture pressure of the gas injection layer by using the fracturing construction data of the long-fracture fracturing well; and determining the length and the direction of the main fracture according to the microseism monitoring record of the fracturing well.
Evaluating the ground stress and the fracture pressure of the gas injection layer by using the fracturing construction data of the long-fracture fracturing well; and determining the fracture pressure and the instantaneous pump-stopping pressure of the fracturing layer section of the well by using the fracturing construction data of the long-fracture fracturing well, and performing maximum horizontal stress and minimum horizontal stress interpretation on the fracturing layer section. Further root ofAccording to the logging information of the long fracture well, the layered crustal stress explanation is carried out, and CO can be obtained 2 The magnitude of the ground stress and the fracture pressure of the gas injection layer.
Step three, establishing a long-fracture fracturing well group CO 2 Oil displacement reservoir matrix-fracturing fracture coupling numerical simulation model
According to the fracture morphology (fracture length, fracture azimuth and the like) of the long fracture fracturing well obtained in the step two, a deterministic modeling method is adopted to establish a CO low-permeability long fracture fracturing well group 2 Reservoir flooding matrix-fracturing fracture coupling model; developing CO 2 Pressure change and CO in reservoir of reservoir oil displacement 2 And (3) carrying out drive-induced ground stress field change coupling simulation evaluation.
Establishing low-permeability long-fracture fracturing well group CO 2 And (3) driving the reservoir matrix-fracturing fracture coupling numerical simulation model, wherein the length of the fracturing fracture in the model is consistent with that in the second step, and the orientation of the fracturing fracture is consistent with that of the maximum horizontal ground stress.
Step four, fracturing well group CO with long cracks 2 Simulating the displacement value to evaluate the pressure change of oil reservoir
Setting initial CO 2 Gas injection parameters, a matrix-fracturing fracture coupling model established in the step three is utilized, and the CO under different parameters is analyzed in a numerical simulation mode 2 The reservoir pressure of the gas injection well group changes.
The reservoir pressure change can be obtained by simultaneous solving of the following equation sets of the low-permeability reservoir matrix seepage field and the hydraulic fracture internal seepage field and corresponding boundary conditions and initial conditions.
The low permeability reservoir matrix seepage field is described as:
the flow within the hydraulic fracture is described as:
wherein phi is the porosity of the low permeability reservoir; c w Is the matrix compressibility; k is the matrix permeability; mu is the fluid viscosity; ρ is the fluid density; u is the matrix framework deformation of the low permeability reservoir; f. of w Is a fluid source sink item; alpha is the Biot consolidation coefficient; t is time; z is the vertical depth; v is CO 2 The velocity of the fluid in mixture with the crude oil; c f Is the hydraulic fracture compressibility; k is a radical of formula f Is the crack permeability; d f Is the width of the crack;
the derivation is carried out along the hydraulic fracture tangential direction; q f The flow exchange between the low-permeability reservoir matrix and the hydraulic fracture surface is realized; and n is the normal direction of the crack surface.
The equations (1) - (4) can be solved by numerical calculation methods such as finite difference method and finite element method.
Step five, long-crack fracturing well group CO 2 Evaluation of driving disturbance ground stress field change
Further developing CO according to the reservoir pressure change obtained in the fourth step 2 And (4) analyzing the change of the driving disturbance ground stress field. Wherein said CO 2 The displacement disturbance crustal stress field change can be obtained by simultaneous solving of a low-permeability reservoir matrix deformation equation and boundary conditions under the action of pore fluid pressure.
In step 5, the low permeability reservoir matrix deformation is described by the following formula:
wherein G is shear modulus; ν is the poisson ratio; α is the Biot coefficient; u. of i Is the formation displacement; f. of i Is physical strength; p is the reservoir pressure.
The boundary conditions are as follows:
wherein, σ' ij Effective stress of the rock formation; n is j Cosine of the direction of the normal outside the boundary;
T i (t) solving the boundary conditions of the known displacement and stress on the boundary respectively; delta ij Is a Kronecker symbol.
Equations (5) and (6) can be solved numerically by using a finite element method.
Step six, long-crack fracturing well group CO 2 Determination of crack propagation and evaluation of gas channeling and CO 2 Risk of leakage
Further developing well group CO according to the well group ground stress field dynamic change data obtained in the fifth step and in combination with the low permeability reservoir rock fracture criterion 2 Determination of crack extension and evaluation of gas channeling and CO 2 The risk of leakage. Wherein the low permeability reservoir rock fracture criteria include fracture tensile fracture and fracture shear fracture.
The fracture tensile failure is at a maximum tensile critical stress F t As a test for CO 2 Drive induced fracture tensile failure criteria, i.e.
F t ＝σ 1 -f t0 (7)
Said fracture shear failure at maximum shear failure stress F s As a test for CO 2 Drive induced fracture shear failure criteria, i.e.
Wherein σ 1 ，σ 3 Respectively obtaining a first main stress and a third main stress of a ground stress field in the fifth step; the reservoir pressure p is obtained in the fourth step; f. of t0 Tensile strength of rock formation,
And c is the internal friction angle of the rock stratum, and the internal friction angle is obtained in the second step.
If the evaluation F t Not less than 0 or F s If the gas injection parameter is more than or equal to 0, the long fracture fracturing well reaches the critical fracture condition and is easy to generate gas channeling and CO 2 The risk of leakage. And determining the gas injection parameter corresponding to the fourth step as the critical gas injection parameter.
If the evaluation F t Less than or equal to 0 and F s If the crack propagation condition is less than or equal to 0, the crack propagation condition is not reached, and CO can be further increased 2 Gas injection parameters;
further returning to the step four, carrying out oil reservoir pressure evaluation after optimizing gas injection parameters;
further carrying out step five of evaluating CO 2 Driving and disturbing the change of the ground stress field;
further carrying out the sixth step of evaluating CO 2 Gas channeling and leakage risk elimination; through cycle optimization, critical gas injection parameters are determined.
In a specific embodiment 1 applying the invention, CO is injected by a long-crack fracturing well group of a low-permeability reservoir of a victory oil field 2 The method is used as an exemplary engineering research object and is shown in the accompanying drawings to be described in detail as follows.
FIG. 1 shows a low permeability long fracture fracturing well group CO of the present invention 2 And (3) a flow chart of an evaluation method of the flooding critical gas injection parameters.
Step one, developing CO 2 The parameters such as geological position, permeability and the like of the gas injection well group are described finely; collecting structural data, drilling data, logging data, oil testing and production data, production data and core analysis test data of a research area to which the long fracture fracturing well belongs, and determining the basic parameters of the oil deposit depth, temperature, pressure, porosity, permeability and the like of the gas injection interval as shown in table 1.
TABLE 1 Long fracture fracturing well group CO 2 Gas injection interval reservoir basic parameter table
And step two, carrying out geomechanical parameter description of the gas injection well group, including rock mechanical parameters, geostress logging interpretation and evaluation, and determining the length, the direction and the like of the fracture of the fracturing well.
According to the mechanical property test of the core of the gas injection interval of the long-fracture fracturing well, the mechanical strength parameters of rocks such as Young modulus, poisson's ratio, tensile strength, cohesion, internal friction angle and the like of the gas injection interval are determined as shown in the table 2.
TABLE 2 Long crack fracturing well CO 2 Gas injection layer rock mechanics parameter meter
Evaluating rock mechanical parameters of the well and explaining the ground stress of a gas injection layer by using basic data such as fracturing construction data, well logging interpretation data and the like of the long-fracture fracturing well; the maximum horizontal stress of 81.1MPa and the minimum horizontal stress of 75.0MPa in the gas injection layer interval are determined. And determining the fracture length and the fracture azimuth of the fracture well group according to the microseism monitoring record of the fracture well as shown in the table 3.
TABLE 3 Long fracture fracturing well group fracture parameter table
Step three, long crack fracturing well CO 2 Reservoir flooding matrix-fracturing fracture coupling numerical simulation model establishment
According to the fracture morphology (fracture length, main fracture orientation and the like) of the long-fracture fracturing well obtained in the step two, a deterministic modeling method is adopted to establish a CO (carbon monoxide) low-permeability long-fracture fracturing well group 2 Reservoir flooding matrix-fracturing fracture coupling model; developing CO 2 Reservoir pressure change and CO 2 Drive-induced ground stress field change couplingAnd (5) performing matched simulation evaluation.
FIG. 2 is a long fracture fracturing well CO established by finite element software COMSOL 2 The oil displacement matrix-fracturing fracture coupling simulation model has the advantages that the length and the direction of the fracture are consistent with the field data of the long-fracture fracturing well.
Step four, long-crack fracturing well group CO 2 Simulating the displacement value to evaluate the pressure change of oil reservoir
Developing CO of the low-permeability long-fracture fractured well by utilizing the oil reservoir matrix-fractured fracture coupling model established in the third step 2 And (5) evaluating reservoir flooding pressure. In the long fracture fracturing well group, two wells Z23-X416 and Z23-X417 are gas injection wells. Setting initial gas injection parameters of the two wells as 100t/d, and carrying out numerical simulation analysis on the oil reservoir pressure change of the low-permeability long-fracture fracturing near-well region under the gas injection parameters.
The reservoir pressure change of the low-permeability long-fracture fracturing well near-well region can be obtained by simultaneous solving of a low-permeability reservoir matrix seepage field and a hydraulic fracture internal seepage field equation set and corresponding boundary conditions and initial conditions.
The low permeability reservoir matrix seepage field is described as:
the flow within the hydraulic fracture is described as:
wherein phi is the porosity of the low permeability reservoir; c w Is the matrix compressibility; k is the matrix permeability; mu is fluid viscosity; ρ is the fluid density; u isDeformation of a matrix framework of the low-permeability reservoir; f. of w Is a fluid source sink item; alpha is the Biot consolidation coefficient; t is time; z is the vertical depth; v is CO 2 The velocity of the fluid in mixture with the crude oil; c f Is the hydraulic fracture compressibility; k is a radical of f Is the crack permeability; d f Is the width of the crack;
the derivation is carried out along the hydraulic fracture tangential direction; q f The flow exchange between the low-permeability reservoir matrix and the hydraulic fracture surface is realized; and n is the normal direction of the crack surface.
FIG. 3 shows the calculation of CO for a long fracture fractured well group according to the formulas (1) to (4) by using finite element software COMSOL 2 Reservoir pressure distribution.
Step five, long-crack fracturing well group CO 2 Evaluation of driving disturbance ground stress field change
Further developing CO according to the reservoir pressure change obtained in the fourth step 2 And (5) analyzing the change of the ground stress field of the driving disturbance. Wherein said CO 2 The displacement disturbance crustal stress field change can be obtained by simultaneous solving of a low permeability reservoir matrix skeleton deformation equation and boundary conditions under the action of pore fluid pressure.
The low permeability reservoir matrix framework deformation is described by the following formula:
wherein G is shear modulus; ν is the poisson ratio; α is the Biot coefficient; u. of i Is the formation displacement; f. of i Is physical strength; p is the reservoir pressure.
The boundary conditions are as follows:
wherein, σ' ij Effective stress of the rock formation; n is j Cosine of the direction of the normal outside the boundary;
T i (t) solving the boundary conditions of the known displacement and stress on the boundary respectively; delta ij Is a Kronecker symbol.
Equations (5) and (6) can be solved by finite element software COMSOL numerical calculation.
Step six, long-crack fracturing well group CO 2 Determination of crack extension and evaluation of gas channeling and CO 2 Risk of leakage
Further developing the CO of the long-fracture fracturing well according to the dynamic change data of the ground stress field of the long-fracture fracturing well obtained in the step five and by combining the rock fracture criterion of the low-permeability reservoir 2 Determination of crack extension and evaluation of gas channeling and CO 2 The risk of leakage. Wherein the low permeability reservoir rock fracture criteria include fracture tensile fracture and fracture shear fracture.
The fracture tensile failure is at a maximum tensile critical stress F t As a test for CO 2 Drive induced fracture tensile failure criteria, i.e.
F t ＝σ 1 -f t0 (7)
Said fracture shear failure at maximum shear failure stress F s As a test for CO 2 Shear fracture criteria of drive-induced fracture, i.e.
Wherein σ 1 ，σ 3 Respectively obtaining a first main stress and a third main stress of the ground stress field in the fifth step; the reservoir pressure p is obtained in the fourth step; f. of t0 The tensile strength of the rock stratum,
And c, obtaining the rock stratum cohesion and the rock stratum internal friction angle in the second step.
FIG. 4 shows a long fracture fracturing well CO 2 Drive-tension fracture prediction evaluation, and FIG. 5 shows a long fracture fracturing well CO 2 Evaluation of drive shear fracture prediction, tensile fracture criteria F t 0 or less, shear fracture standard F s Less than or equal to 0; indicating that the crack propagation condition has not been reached and further CO can be adjusted 2 And (3) gas injection parameters.
Further returning to the step four, carrying out oil reservoir pressure evaluation after optimizing gas injection parameters;
further carrying out step five of evaluating CO 2 Driving and disturbing the change of the ground stress field;
further carrying out the sixth step of evaluating CO 2 Gas channeling and leakage risk elimination; through cycle optimization, critical gas injection parameters are determined.
Table 4 shows the statistics of different CO 2 And judging the bottom pressure of the long fracture fracturing well and the induced fracture expansion under the flooding parameters, according to the calculation result, when the gas injection parameters reach 120t/d, the near fracture area reaches the fracture expansion judgment condition, and determining that 105t/d is used as the critical gas injection parameters.
TABLE 4 different CO 2 Evaluation table for downhole pressure induced fracture of driving parameter
In one embodiment 2 of the present invention, a low permeability long fracture frac well group CO in accordance with the present invention is used 2 The evaluation steps, the implementation principle, the beneficial effects and the like of the evaluation method of the flooding critical gas injection parameter are the same as those of the evaluation method of the embodiment 1, except that the initial gas injection parameters of the two wells are set to be 80t/d, and the numerical simulation analysis is performed on the reservoir pressure change of the low-permeability long-fracture fracturing near-well region under the gas injection parameters.
Table 5 shows the statistics of different CO 2 Judging the long fracture fracturing bottom hole pressure and the induced fracture expansion under the flooding parameters, simulating gas channeling and leakage risks under the gas injection displacement of 80t/d,90t/d and 100t/d according to the calculation result, and improving the gas injection displacement of a well head; however, when the discharge capacity is increased to 110t/d, the risk of gas channeling is high, and the CO at the well head needs to be reduced 2 And (4) injecting gas and discharging volume. According to the evaluation step cyclic optimization of the method, the critical gas injection parameter is determined to be 105t/d.
TABLE 5 different CO 2 Downhole pressure induction with flooding parametersCrack guide evaluation table
In one embodiment 3 of the invention, a low permeability long fracture frac well set CO is used in accordance with the invention 2 The evaluation steps, the implementation principle, the beneficial effects and the like of the other embodiment of the evaluation method of the flooding critical gas injection parameters are the same as those of the embodiment 1, except that the position of the Z23-X416 well gas injection zone section is adjusted to 3822.5-3828.8 m. According to CO in step 2 2 Geomechanical parameters of the gas injection well group are described, and the geomechanical parameters of the Z23-X416 well 3822.5-3828.8 m are shown in Table 6.
TABLE 6 rock mechanics parameters table for Z23-X416 well gas injection interval
And step two, carrying out geomechanical parameter description of the gas injection well group, including rock mechanical parameters, geostress logging interpretation and evaluation, and determining the length, the direction and the like of the fracture of the fracturing well.
Evaluating rock mechanical parameters of the well and explaining the ground stress of a gas injection layer by using basic data such as fracturing construction data, well logging interpretation data and the like of the long-fracture fracturing well; the maximum horizontal stress of 82.3MPa and the minimum horizontal stress of 75.7MPa in the gas injection layer interval are determined. And determining the fracture length and the fracture azimuth of the fracture well group according to the microseism monitoring record of the fracture well as shown in the table 7.
TABLE 7Z23-X416 well fracture parameters Table
Step three, long crack fracturing well CO 2 Reservoir flooding matrix-fracturing fracture coupling numerical simulation model establishment
Determining the fracture shape change (fracture length, main fracture and the like) of the Z23-X416 well obtained in the step twoThe method comprises the steps of establishing a Z23-X416 well gas injection zone section updated low-permeability long-fracture fracturing well group CO 2 Reservoir flooding matrix-fracturing fracture coupling model; developing CO 2 Reservoir pressure change and CO 2 And (3) carrying out drive-induced ground stress field change coupling simulation evaluation.
Step four, long-crack fracturing well group CO 2 Simulating drive value and evaluating pressure change of oil reservoir
Developing CO of the low-permeability long-fracture fractured well by utilizing the oil reservoir matrix-fractured fracture coupling model established in the third step 2 And (5) evaluating reservoir flooding pressure. In the long fracture fracturing well group, the Z23-X417 initial gas injection parameter is 100t/d, the Z23-X416 initial gas injection parameter is 110t/d, and the numerical simulation analysis is performed on the reservoir pressure change of the low permeability long fracture fracturing near-well area under the gas injection parameter.
Step five, long-crack fracturing well group CO 2 Evaluation of driving disturbance ground stress field change
Further developing CO according to the reservoir pressure change obtained in the fourth step 2 And (4) analyzing the change of the driving disturbance ground stress field.
Step six, evaluating CO 2 Risk of gas channeling and leakage; through cycle optimization, critical gas injection parameters are determined.
Further developing the CO of the long-fracture fracturing well according to the dynamic change data of the ground stress field of the long-fracture fracturing well obtained in the step five and by combining the rock fracture criterion of the low-permeability reservoir 2 Determination of crack extension and evaluation of gas channeling and CO 2 The risk of leakage.
Table 8 shows statistical Z23-X417 well bottom pressure and induced fracture propagation determinations, and based on the calculated results, 105t/d was determined as the critical gas injection parameter. Table 9 shows statistical Z23-X416 well bottom pressure and induced fracture propagation determinations, and based on the calculated results, 115t/d was determined as the critical gas injection parameter.
TABLE 8Z23-X417 well bottom pressure induced fracture assessment Table
TABLE 9Z23-X416 well bottom pressure induced fracture evaluation Table
Low-permeability long-fracture fracturing well group CO of the invention 2 The evaluation method of flooding critical gas injection parameters fully considers CO 2 The CO is evaluated by combining the coupling influence of gas injection parameters and fracturing fractures in the gas injection process and the dynamic change of the low-permeability long-fracture fracturing well characteristics and the physical parameters of an oil reservoir 2 Driving critical gas injection parameters, for increasing CO 2 Driving out hair and realizing CO 2 The scientific management of the reservoir oil displacement is of great significance.
Finally, it should be noted that: although the present invention has been described in detail with reference to the foregoing embodiments, it will be apparent to those skilled in the art that changes may be made in the embodiments and/or equivalents thereof without departing from the spirit and scope of the invention. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention. In addition to the technical features described in the specification, the technology is known to those skilled in the art.
Claims (15)
1. Low-permeability long-fracture fracturing well group CO 2 The evaluation method of the flooding critical gas injection parameters is characterized in that the low-permeability long-fracture fracturing well group CO 2 The evaluation method of the flooding critical gas injection parameter comprises the following steps:
step 1, developing CO 2 Finely describing the oil reservoir characteristics of the gas injection well group;
step 2, developing CO 2 Describing geomechanical parameters of the gas injection well group;
step 3, establishing a low-permeability long-fracture fracturing well group CO 2 A reservoir flooding matrix-fracturing fracture coupling numerical simulation model;
step 4, performing long-fracture fracturing well group CO 2 Simulating a displacement value, and evaluating the pressure change of the oil reservoir;
step 5, developing the long fracture fracturing wellGroup CO 2 Evaluating the change of the driving disturbance ground stress field;
step 6, developing long-seam fracturing well group CO 2 Determination of crack propagation and evaluation of gas channeling and CO 2 And (4) leakage risk, and determining a critical gas injection parameter limit.
2. The low-permeability long-fracture fracturing well group CO of claim 1 2 In the step 1, collecting structural data, drilling data, logging data, oil test and production test and core analysis test data of a research area to which a long-seam fracturing well group belongs, and determining basic parameters of oil deposit depth, temperature, pressure, porosity and permeability of an air injection interval.
3. The low-permeability long-fracture fracturing well group CO of claim 1 2 In the step 2, the description of geomechanical parameters comprises rock mechanical parameters of a gas injection interval of the long-fracture fracturing well and the interpretation and evaluation of ground stress logging, and the length and the direction of a fracture of the gas injection interval are determined.
4. The low-permeability long-fracture fracturing well group CO of claim 3 2 In the step 2, determining rock mechanical strength parameters of Young modulus, poisson's ratio, tensile strength, cohesion and internal friction angle of a gas injection interval according to mechanical property test or well logging data explanation of a core of the gas injection interval of the long-fracture fracturing well; evaluating the ground stress and the fracture pressure of the gas injection layer by using the fracturing construction data of the long-fracture fracturing well; and determining the length and the direction of the main fracture according to the microseism monitoring record of the fracturing well.
5. The low-permeability long-fracture fracturing well group CO of claim 3 2 In the step 2, determining the fracture pressure and instantaneous pump-stopping pressure of the fracturing layer section of the well by using the fracturing construction data of the long-fracture fracturing well, and performing maximum horizontal stress and minimum horizontal stress explanation on the fracturing layer section; further according to long seam pressureThe logging information of the fractured well is used for carrying out the explanation of the layered ground stress to obtain CO 2 The magnitude of the ground stress and the fracture pressure of the gas injection layer.
6. The low-permeability long-fracture fracturing well group CO of claim 1 2 In the step 3, according to the fracture morphology of the long-fracture fracturing well obtained in the step 2, a deterministic modeling method is adopted to establish a low-permeability long-fracture fracturing well group CO 2 Reservoir flooding matrix-fracturing fracture coupling model; developing CO 2 Reservoir pressure change and CO 2 And (4) performing drive induced ground stress field change coupling simulation evaluation.
7. The low-permeability long-fracture fracturing well group CO of claim 6 2 The evaluation method of flooding critical gas injection parameters comprises the step 3 of establishing low-permeability long-fracture fracturing well group CO 2 And (3) driving the reservoir matrix-fracturing fracture coupling numerical simulation model, wherein the length of the fracturing fracture in the model is consistent with that of the microseism monitoring fracture in the step (2), and the fracture azimuth is consistent with the maximum horizontal ground stress azimuth.
8. The low-permeability long-fracture fracturing well group CO of claim 1 2 The evaluation method of flooding critical gas injection parameters comprises the step 4 of setting initial CO 2 Gas injection parameters, namely, the matrix-fracturing fracture coupling model established in the step 3 is utilized to carry out numerical simulation analysis on CO under different parameters 2 The reservoir pressure of the gas injection well group changes.
9. The low-permeability long-fracture fracturing well group CO of claim 8 2 In step 4, the reservoir pressure change is obtained by simultaneous solution of the following equation sets of the low permeability reservoir matrix seepage field and the hydraulic fracture internal seepage field and corresponding boundary conditions and initial conditions:
the low permeability reservoir matrix seepage field is described as:
the flow within the hydraulic fracture is described as:
wherein phi is the porosity of the low permeability reservoir; c w Is the matrix compressibility; k is the matrix permeability; mu is fluid viscosity; ρ is the fluid density; u is the matrix skeleton deformation of the low permeability reservoir; f. of w Is a fluid source sink item; α is the Biot consolidation coefficient; t is time; z is the vertical depth; v is CO 2 The velocity of the fluid in mixture with the crude oil; c f Is the hydraulic fracture compressibility; k is a radical of f Is the crack permeability; d f Is the width of the crack;
the derivation is carried out along the hydraulic fracture tangential direction; q f The flow exchange between the low-permeability reservoir matrix and the hydraulic fracture surface is realized; n is the normal direction of the crack surface;
equations (1) to (4) are solved by numerical calculation methods such as a finite difference method and a finite element method.
10. The low-permeability long-fracture fracturing well group CO of claim 1 2 The evaluation method of flooding critical gas injection parameters comprises the step 5 of developing CO according to the reservoir pressure change obtained in the step 4 2 Analyzing the change of the driving and disturbing ground stress field; wherein CO is 2 Low permeability reservoir matrix deformation equation and boundary for flooding disturbance crustal stress field change by considering pore fluid pressure effectAnd (5) performing simultaneous solving and obtaining.
11. The low permeability long fracture frac well group CO of claim 10 2 In step 5, deformation of the low permeability reservoir matrix is described by the following formula:
wherein G is shear modulus; ν is the poisson ratio; α is the Biot coefficient; u. of i Is the formation displacement; f. of i Is physical strength; p is reservoir pressure;
the boundary conditions are as follows:
wherein σ ij ' is the effective stress of the formation; n is j Cosine of the direction of the normal outside the boundary;
T i (t) solving the boundary conditions of the known displacement and stress on the boundary respectively; delta ij Is a Kronecker symbol;
equations (5) and (6) are solved by numerical calculation using a finite element method.
12. The low permeability long fracture frac well group CO of claim 1 2 In step 6, according to the dynamic change data of the geostress field of the well group obtained in step 5, the rock fracture criterion of the low permeability reservoir is combined to develop the well group CO 2 Determination of crack extension and evaluation of gas channeling and CO 2 Risk of leakage; the low permeability reservoir rock fracture criteria include fracture tensile fracture and fracture shear fracture.
13. The low permeability long fracture of claim 12Well group CO 2 The evaluation method of flooding critical gas injection parameters comprises the step 6 of stretching and breaking the crack to obtain the maximum stretching critical stress F t As a test for CO 2 Drive induced fracture tensile failure criteria, i.e.
F t ＝σ 1 -f t0 (7)
Fracture shear fracture at maximum shear failure stress F s As a test for CO 2 Drive induced fracture shear failure criteria, i.e.
Wherein σ 1 ，σ 3 Respectively obtaining a first main stress and a third main stress of a ground stress field in the step 5; the reservoir pressure p is obtained in the step 4; f. of t0 The tensile strength of the rock stratum,
And c is the cohesive force of the rock stratum and the internal friction angle of the rock stratum, and the internal friction angle is obtained in the step 2.
14. The low permeability long fracture frac well group CO of claim 13 2 Evaluation of flooding parameters in step 6, if F is evaluated t Not less than 0 or F s If the gas injection parameter is more than or equal to 0, the long fracture fracturing well reaches the critical fracture condition and is easy to generate gas channeling and CO 2 Risk of leakage; the gas injection parameter corresponding to step 4 is determined as the critical gas injection parameter.
15. The low permeability long fracture fracturing well group CO of claim 14 2 Evaluation of flooding parameters in step 6, if F is evaluated t Less than or equal to 0 and F s If the crack propagation condition is not reached, the CO is further increased 2 Gas injection parameters; the flow returns to step 4; and determining critical gas injection parameters through cycle optimization.
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