CN-116717224-B - Fracturing productivity prediction method for complex fracture network of hypotonic tight reservoir

CN116717224BCN 116717224 BCN116717224 BCN 116717224BCN-116717224-B

Abstract

The invention provides a fracturing productivity prediction method for a complex fracture network of a low-permeability tight reservoir, which comprises the steps of obtaining a reservoir compressibility evaluation index based on a reservoir weak face influence index, a fracture space physical model, a fracture symbolization index and a stratum toughness index, obtaining a fracture closing point based on a well bottom pressure drop function, identifying main fracture fluid loss and natural fracture fluid loss at the moment of the fracture closing point, establishing a reservoir pressure fracture network seepage mathematical model according to reservoir DFIT test results, and establishing a fracturing well section complex fracture network numerical model according to the compressibility evaluation index and the natural fracture fluid loss. And finally, establishing a single well productivity prediction model after fracturing by taking the fracturing well section complex fracture network numerical model as a boundary condition. The invention fully utilizes the field and test data, lays a foundation for reasonable assumption of the fracture geometric model, and the established complex fracture network mathematical model is closer to reality, thereby having important significance for fracture evaluation and productivity prediction.

Inventors

WEI MINGQIANG
ZOU HAN
JING YADONG
DUAN YONGGANG
FANG QUANTANG
LI ZHENGLAN
REN KEYI
MA BENTENG
MENG LEI

Assignees

西南石油大学

Dates

Publication Date: 20260508
Application Date: 20230522

Claims (7)

1. A fracturing productivity prediction method for a complex fracture network of a hypotonic tight reservoir is characterized by comprising the following steps: s1, establishing a weak face influence index during reservoir fracturing based on the mechanical influence of the weak face of the reservoir; S2, establishing a crack space physical model based on the dynamic change of the crack width; s3, acquiring a crack symbolic index and a stratum toughness index; S4, obtaining a reservoir compressibility evaluation index based on the weak face influence index, the fracture space physical model, the fracture symbolism index and the stratum toughness index; S5, well bottom pressure drop based The function is used for acquiring a fracture closing point, so that the main fracture fluid loss when the fracture is closed after fracturing and the natural fracture fluid loss when the fracture is closed after fracturing are obtained; s6, establishing a reservoir fracture network seepage mathematical model based on reservoir DFIT test results; S7, establishing a complex fracture network numerical model of the fracturing well section according to the compressibility evaluation index and the natural fracture fluid loss; S8, acquiring the diversion capacity of the closed fracture, and establishing a one-dimensional flow continuity equation of fluid in the fracture along the length direction of the fracture; s9, based on a fracture network seepage mathematical model, the diversion capacity after fracture closure and a one-dimensional flow continuity equation, establishing a single well productivity prediction model after fracturing by taking a fracture well section complex fracture network numerical model as a boundary condition, and predicting single well productivity after fracturing through the single well productivity prediction model; the vulnerability impact index is calculated by the following formula: Wherein: The evaluation auxiliary function is represented, and independent variables of an evaluation target are arranged in brackets, so that the evaluation auxiliary function is dimensionless; E is the Young's modulus of the core taken out of any well section, ; 、 The maximum and minimum Young's modulus values of the fractured wells Duan Yanxin, ; Is that Normal direction of surface and maximum principal stress The included angle between the directions is , The face is a weak face present in the reservoir rock; For the reservoir rock Dan Ruomian to be cohesive, ; Taking out poisson ratio of the core for any well section, and having no dimension; 、 poisson ratio maximum value and minimum value of the fracturing well Duan Yanxin are respectively, and dimensionless; Is a weak influence index, and is dimensionless; the crack space physical model is as follows: The crack forms axisymmetric geometric figure along the length extending direction of the crack, and a certain initial moment before fracturing The geometric parameters of the seam are that the seam length is The seam width is To The solid line is the crack form at the moment, and after the fracturing for a period of time T, the moment is The geometric parameters of the crack are that the length of the crack is The seam width is To The dotted line is the form of the crack at the moment, and the change of the length of the crack in the fracturing is Variation of seam width The absolute value of the variation of the slit width is measured; according to the assumed conditions, a dynamic change equation of the seam width between the crack expansion and the minimum main stress is obtained, as follows: in the formula, Converting the reservoir fracture pressure near the well bore from logging data; 、 representing the maximum principal stress and the minimum principal stress respectively, which are obtained by core test, ; The coefficients are calculated for undetermining, and are determined by a pressure drop test process, and have no dimension.
2. The method of claim 1, wherein the fracture symbolism index and the formation toughness index are obtained by the following two equations: Wherein: is a crack symbolism index, and is dimensionless; For the measured well angle of the fractured well Duan Zhouxian, ; The uniaxial tensile strength of the rock body is measured by experiments, ; 、 The toughness factors of the rock stratum are respectively type I and type II, are measured by a rock core experiment, and have no dimension; 、、、、 selecting a proper value for substituting calculation according to the solving accuracy for the toughness fitting coefficient of the type I rock stratum, wherein the value range is-0.34-0.52; 、、 Selecting a proper value for substituting the type II stratum toughness fitting coefficient with the value range of-0.08-0.14 and the type I stratum toughness fitting coefficient into calculation; For confining pressure, triaxial rock mechanics experiments can be set to obtain values, ; Is a stratum toughness index, and is dimensionless.
3. The method according to claim 2, wherein the compressibility evaluation index is obtained by: EST is a compressibility evaluation index, the higher the value is, the easier the corresponding well section is fractured, and the dimensionless is realized; For the coefficient to be calculated, determining by a pressure drop testing process, and having no dimension; T represents the time of the fracturing operation, ; For confining pressure, triaxial rock mechanics experiments can be set to obtain values, ; The pumping pressure of the fracturing fluid is constantly pumped into the fracturing pump, ; R represents the distance from the borehole axis at a point in the near wellbore zone, ; For the radius of the borehole, 。
4. The method according to claim 1, characterized in that the crack closing point is obtained by: During the closing period of the crack after stopping the pump, the linear relation between the bottom hole pressure P and the G function is observed, and the calculation is performed Derivative of function Logarithmic derivative Solving according to the derivative relation The maximum point of the linear relation of the function is used as a crack closing datum point to draw A function plate; Introducing a fitting regression line passing through the origin point into the function chart, tangent the regression line to the derivative curve as much as possible, and initially taking the point deviating from the line as a crack closing point and combining the point with the derivative curve Comparing the most value points of the function linear relation, calibrating the expression of the fitting regression line, finally obtaining the representative crack closing point position, recording the corresponding fracturing time step of the point position Crack closing pressure P; Based on The function of the plate of the drawing is that, the main fracture fluid loss at the moment of fracture closing point after fracturing is calculated as follows: Based on The function of the plate of the drawing is that, the natural fracture fluid loss at the moment of fracture closing point after fracturing is calculated as follows: Wherein: Indicating the main fracture fluid loss at a certain moment, ; The ratio of the fracture fluid loss height to the fracture width is represented, and the fracture fluid loss height is dimensionless; representing the fluid loss coefficient of the main fracture, ; Indicating the fluid loss area of the main fracture, ; Indicating the natural fracture fluid loss at a certain moment, ; Represents the fluid loss coefficient of the natural fracture, ; Represents the fluid loss area of the natural fracture, 。
5. The method of claim 1, wherein the reservoir fracture network seepage mathematical model is: Wherein: 、 respectively represents the size of the large-scale rock pore gap and the rock matrix permeability, ; Indicating the effective viscosity of the fracturing fluid, ; The pumping pressure of the fracturing fluid is constantly pumped into the fracturing pump, ; The fracture pressure of the reservoir near the well bore is converted from the logging data, ; The porosity is indicated by the fact that, ; Represents the comprehensive elastic coefficient of the stratum, ; N represents the fluid state index of the fracturing fluid, and has no dimension; biot represents the magnitude of the elastic coefficient of the rock hole, and has no dimension; Represents the consistency coefficient of the fracturing fluid, ; X and y respectively represent two orthogonal decomposition sub-directions of the crack extension and expansion direction.
6. The method of claim 1, wherein the frac interval complex fracture numerical model is: the high-efficiency seam net extension model is as follows: The steering storage model is as follows: Wherein: The ratio of the average static pressure of the cracks to the pressure of the well bore is dimensionless; 、 the fitting pressure and the fitting pressure drop are respectively adopted, ; For the fracture radius at the point of fracture closure, ; To achieve a seam height at the seam closing point, ; The median length of the slit at the closing point of the slit, ; Injecting auxiliary calculation coefficients for the fracturing pump, wherein the value range is 0-1, and the fracturing pump is dimensionless; Indicating the natural fracture fluid loss at a certain moment, ; Is the fracturing time step; Indicating the main fracture fluid loss at a certain moment, ; EST is a compressibility evaluation index, the higher the value is, the easier the corresponding well section is to fracture, and the dimensionless is realized; The ratio of the fracture fluid loss height to the fracture width is represented, and the fracture fluid loss height is dimensionless; when the natural fracture fluid loss indication value is 40% -60%, the corresponding model is selected from the two complex fracture network numerical models of high-efficiency fracture network extension and steering storage to conduct fracturing well section research depending on the EST value of the compressibility evaluation index, and meanwhile PKN type, KGD type and Radial type auxiliary calculation parameters are selected according to the fracture simulation space corresponding to the well section.
7. The method of claim 1, wherein the single well capacity prediction model is: Wherein: the fracture conductivity at the initial moment is obtained by converting rock core experimental data, ; In order to achieve the density of the fracturing fluid, ; For the production capacity of a single well after fracturing, ; Is a mass exchange term between the rock matrix and the fracture, ; The porosity is indicated by the fact that, ; Indicating the effective viscosity of the fracturing fluid, ; The pumping pressure of the fracturing fluid is constantly pumped into the fracturing pump, ; The fracture pressure of the reservoir near the well bore is converted from the logging data, R represents the distance from a point in the near wellbore wall zone to the axis of the wellbore, ; For the radius of the borehole, ; Is fracturing fluid efficiency; The ratio of the fracture fluid loss height to the fracture width is represented, and the fracture fluid loss height is dimensionless; representing the fluid loss coefficient of the main fracture, ; Indicating the fluid loss area of the main fracture, ; Represents the fluid loss coefficient of the natural fracture, ; Represents the fluid loss area of the natural fracture, ; The fluid loss of the fracturing fluid is indicated, 。

Description

Fracturing productivity prediction method for complex fracture network of hypotonic tight reservoir Technical Field The invention relates to the technical field of oil and gas well production increase and oil and gas field development, in particular to a fracturing productivity prediction method for a complex fracture network of a low-permeability tight reservoir. Background As a guiding theory and a practical means of modern oil and gas yield improvement, the volume fracturing operation expands natural cracks, shears and slides the brittle rock layer, and the natural cracks and the artificial cracks are staggered. When the volume of the horizontal well is fractured, the fracturing fluid continuously pumped in can enable the artificial main fracture to generate a plurality of branch fractures, so that the natural fracture is communicated, a complex fracture network is formed, the contact area between an oil gas reservoir and a shaft is increased, the transformation volume of the oil gas reservoir is increased, the seepage capability of the oil gas reservoir is enhanced, and a complex fracture network is formed. At present, the post-pressing productivity evaluation method based on the geometric parameters of the cracks and the flow conductivity of the cracks is mainly evaluated by using a symmetrical double-wing crack model, and is not suitable for complex fracture networks formed after volume fracturing. Therefore, in order to improve the fracturing effect and the single well yield after fracturing, how to develop evaluation and explanation work for complex fracture network is of great significance. Disclosure of Invention In order to solve the problems, the invention provides a fracturing productivity prediction method for a complex fracture network of a hypotonic tight reservoir, which is based on the influence of a weak face, considers the communication seepage condition of a main fracture and a natural fracture and accurately describes various fracture parameters. Meanwhile, according to the level of the natural fracture fluid loss and the reservoir compressibility index, two complex fracture network numerical models of high-efficiency fracture network extension and steering storage are established and used for predicting the single well productivity after fracturing. According to the technical scheme, the fracturing productivity prediction method for the complex fracture network of the hypotonic tight reservoir is provided, because the hypotonic tight reservoir possibly has a weakness to influence the water conservancy fracture expansion rule, the mechanical influence of the weakness is considered first, the study of the fracture deformation and destruction mechanism of the rock of the hypotonic tight reservoir is developed, and a new reservoir compressibility evaluation method based on three fracture network influence indexes is established. And secondly, developing a target reservoir DFIT test, exploring a reservoir compressibility rule, and establishing a fracture network seepage mathematical model. In a key link, performing improved calculation on a traditional G function method to obtain a delta P-G function chart, determining a crack closing point, finally establishing a complex fracture network numerical model suitable for volume fracturing, calculating the crack flow conductivity according to the crack fluid loss condition, using the complex fracture network numerical model of a fractured well section as a boundary condition, establishing a single well productivity prediction model after fracturing, and predicting the single well productivity after fracturing. Specifically, the method comprises the following steps: s1, establishing a weak face influence index during reservoir fracturing based on the mechanical influence of the weak face of the reservoir; S2, establishing a crack space physical model based on the dynamic change of the crack width; s3, acquiring a crack symbolic index and a stratum toughness index; S4, obtaining a reservoir compressibility evaluation index based on the weak face influence index, the fracture space physical model, the fracture symbolism index and the stratum toughness index; S5, acquiring a crack closing point based on a well bottom pressure drop delta P-G function, so as to obtain main crack fluid loss when the crack is closed after fracturing and natural crack fluid loss when the crack is closed after fracturing; s6, establishing a reservoir fracture network seepage mathematical model based on reservoir DFIT test results; S7, establishing a complex fracture network numerical model of the fracturing well section according to the compressibility evaluation index and the natural fracture fluid loss; S8, acquiring the diversion capacity of the closed fracture, and establishing a one-dimensional flow continuity equation of fluid in the fracture along the length direction of the fracture; s9, based on the fracture network seepage mathematical model, the diversion capa