Discrete element-based splitting basin extension process simulation method
Technical Field
The invention belongs to the technical field of geological structure deformation simulation research, and particularly relates to a discrete element-based method for simulating a valley cracking basin stretching process.
Background
The rift valley basin is formed under the dynamic background of tensile stress, and a great deal of research is carried out on a formation evolution dynamic model of the rift valley basin by predecessors, so that the rift valley basin is a hot spot of oil and gas exploration at home and abroad at present. Through an experimental simulation method, it is necessary to explore the fault formation evolution process of the valley basin under different geological conditions. Moreover, studies have shown that basal lithology controls the pattern of tectonic development within the riflescent valley basin. In constructing a physical simulation, canvas is typically used to simulate a rigid substrate and a blanket to transmit tensile stresses to simulate a flexible substrate.
In the prior art, rigid substrates are mostly adopted for the simulation of the valley cracking basins, but in the nature, the tough substrates exist in the valley cracking basins, and the structural style of the tough substrates is obviously different from that of the valley cracking basins with the rigid substrates. For tough substrates in the valley basin, there is currently a lack of simulation studies.
The discrete element method treats the geologic body as a discrete unit, allows larger relative displacement among particles, can better simulate high deformation, is suitable for the research of discontinuous mechanical behaviors for simulating faults appearing in sedimentary strata and brittle deformation such as fault-related folds and the like, and is an important method for researching a structural deformation process and a deformation mechanism.
Disclosure of Invention
The invention aims to solve the technical problem of providing a discrete element-based method for simulating the stretching process of the valley cracking basin, which realizes the discrete element simulation of the stretching process of the valley cracking basin with a tough substrate and can be used for simulating the fracture evolution process of the valley cracking basin in different substrates.
In order to achieve the purpose of the invention, the following technical scheme is adopted in the application:
a discrete element-based method for simulating a valley cracking basin stretching process comprises the following steps:
1) and extracting stratum information of the area to be analyzed by observing the geology of the area to be analyzed and analyzing seismic data of the area, and inverting the structure evolution process. And carrying out inversion analysis on the seismic analysis graph obtained by analysis to obtain a historical stratigraphic distribution diagram before the valley cracking basin starts to extend, and finally obtaining the historical stratigraphic distribution condition of the area to be analyzed.
2) Constructing a discrete element initial model according to the stratum distribution condition obtained in the step 1): setting the radius of a first particle to be 60m, setting the radius of a second particle to be 80m, and randomly filling the first particle and the second particle into a rectangular box-shaped model with a given size according to a certain proportion, so that the particles are stacked at the bottom of the rectangular box-shaped model under the action of gravity to generate a first discrete element model.
3) And obtaining the mesoscopic parameters of the granular materials of each stratum in the discrete element initial model through a series of biaxial compression experimental tests.
4) Establishing a second discrete element model reflecting the geological characteristics of the area to be analyzed by giving the properties of the granular materials of each stratum according to the stratum distribution condition obtained in the step 1) and the microscopic properties of the granular materials of each stratum obtained in the step 3). The second discrete meta-model comprises a base divided into three parts: a first rigid substrate and a second rigid substrate on both sides and a flexible substrate in the middle. The rigid substrate is limited in particle displacement and rotation, while the flexible substrate is limited in particle displacement and rotation in the vertical direction, so that the particles of the flexible substrate can move freely in the horizontal direction. The toughness substrate and the rigid substrate are bonded, the tensile strength and the shear strength are 1e100 Pa, and the substrate is prevented from being bonded and disconnected.
The tough substrate is composed of mutually overlapped particles, and an initial overlapping rate cratio = | AO |/(rA + rO) is defined, namely the ratio of the circle center distance (| AO |) to the balance distance (rA + rO). When cratio ≦ 0.5, particle A is bonded to particle B across particle O, and in order to avoid the occurrence of the cross-particle bonding, a temporary radius scaling factor rext = r is definedtmp/rold. Temporarily changing the particle radius to r when a bond is createdtmp=roldRext. When cratio =0.4 and rext =0.4, the particle a is just bonded to the particle O after the temporary radius scaling is adopted, and the bonding is avoidedParticle a and particle B produced a bond.
5) Performing iterative operation on the second discrete element model established in the step 4) by adopting a discrete element calculation method to complete simulation of the evolution process of the basin extension structure of the region to be analyzed: setting boundary conditions based on the discrete element model which is obtained in the step 4) and reflects the geological characteristics of the area to be analyzed, fixing the boundaries at the two sides and the substrate, and enabling the boundaries at the two sides and the rigid substrate to be separated at a constant speed, namely giving displacement boundary conditions and simulating the horizontal stretching effect in reality; and adding isomorphic sedimentation to simulate a real geological event.
Further, the microscopic parameters of the particulate material include the following parameters: the radius of the particles, the density of the particles, the shear modulus of the particles, the poisson's ratio of the particles, the coefficient of friction of the particles, the bonding parameters between the particles, the local damping coefficient.
Further, the bonding parameters between the particles were set as follows: the Young modulus measuring amount is 2.0e8 Pa, the shear modulus is 2.0e8 Pa, the tensile strength is 0.0-4.0 e7 Pa, and the shear strength is 0.0-8.0 e7 Pa. The condition for generating the bonding is that | AO | - (rA + rO) ≦ tolerate, wherein tolerate takes 1 e-6.
Furthermore, a Hertz-Mindlin model is adopted as a contact model of the particle material, the radius of the particle is 60m and 80m, the density of the particle is 2500 km/m3, the shear modulus of the particle is 2.9e9 Pa, the Poisson ratio is 0.2, and the local damping coefficient is 0.4. The particle friction coefficient was set to 0.0 during the deposition phase and 0.3 during the extension phase.
The invention discloses a discrete element-based method for simulating a valley basin stretching process, which gives a tough substrate construction method by fully considering the original geological characteristics of a stratum in a geological history period, and establishes a discrete element model close to the geological history period; establishing an initial discrete element model by adopting a mode of randomly distributing particles with different sizes; simulating a certain stage, increasing deposition and denudation events, and researching the influence of general geological phenomena on the structural deformation of the area; according to the invention, a pre-existing fault is not required to be arranged, and the model is constructed by adopting discrete particles, so that the model has a particle structure similar to that of a real rock body; the physical simulation experiment constructed on a large scale is expensive and time-consuming, a part of the experiment can be supplemented and replaced by adopting discrete element simulation, and the data which is not easy to measure in the experiment can be obtained by the structural evolution process and structural deformation mechanism research method based on the discrete element simulation, so that the practical problems of the existing theory solution, such as the structural evolution process and the structural deformation mechanism, stress-strain distribution and the influence thereof on the reservoir property, and the like, are improved, and the theoretical support is provided for the oil-gas exploration work of the valley basin.
Drawings
FIG. 1 is a schematic diagram of the initial overlap ratio of the present invention;
FIG. 2 is a schematic diagram illustrating temporary radius scaling factor definition according to the present invention;
FIG. 3 is a schematic diagram of a substrate generation process in accordance with an embodiment of the present invention;
FIG. 4 is a schematic diagram of a rectangular box of a given size filled with particles randomly according to one embodiment of the present invention;
FIG. 5 is a schematic diagram of two-phase simultaneous structure deposition layers of the discrete element model during the stretching process according to an embodiment of the present invention.
Detailed Description
The following describes in detail a method for simulating a valley splitting basin stretching process based on discrete elements, which is provided by the present invention, with reference to the accompanying drawings. In the description of the present invention, it is to be understood that the terms "left side", "right side", "upper part", "lower part", "bottom", etc., indicate orientations or positional relationships based on those shown in the drawings, and are only for convenience of describing the present invention and simplifying the description, but do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, "first", "second", etc., do not represent an important degree of the component parts, and thus are not to be construed as limiting the present invention. The specific dimensions used in this example are only for illustrating the technical solution and do not limit the scope of protection of the invention.
A discrete element-based method for simulating a valley cracking basin stretching process comprises the following steps:
1) and extracting stratum information of the area to be analyzed by observing the geology of the area to be analyzed and analyzing seismic data of the area, and inverting the structure evolution process. And carrying out inversion analysis on the seismic analysis graph obtained by analysis to obtain a historical stratigraphic distribution diagram before the valley cracking basin starts to extend, and finally obtaining the historical stratigraphic distribution condition of the area to be analyzed.
2) Constructing a discrete element initial model according to the stratum distribution condition obtained in the step 1): setting the radius of the first particle to be 60m, the radius of the second particle to be 80m, and randomly filling the first particle and the second particle into a rectangular box-shaped model with a given size according to a certain proportion, wherein the proportion can be set as 1: 1. 2: 1. 3: 1, and as shown in fig. 4, are stacked on the bottom of the rectangular box-like model under the action of gravity to generate a first discrete element model.
3) And (3) obtaining the microscopic parameters of the granular materials of each stratum in the discrete element initial model through a series of biaxial compression experiment tests, and simulating the rock deformation of the actual stratum. The microscopic parameters of the particulate material include the following parameters: the radius of the particles, the density of the particles, the shear modulus of the particles, the poisson's ratio of the particles, the coefficient of friction of the particles, the inter-particle bonding parameters, and the like.
The bonding parameters between the particles were set as follows: the Young modulus measuring amount is 2.0e8 Pa, the shear modulus is 2.0e8 Pa, the tensile strength is 0.0-4.0 e7 Pa, and the shear strength is 0.0-8.0 e7 Pa. The condition for generating the bonding is that | AO | - (rA + rO) ≦ tolerate, wherein tolerate takes 1 e-6.
The contact model of the granule material adopts Hertz-Mindlin model, the radius of the granule is 60m and 80m, and the density of the granule is 2500 km/m3The elastic modulus of the particles was 2.9e9 Pa, the Poisson's ratio was 0.2, and the local damping coefficient was 0.4. The particle friction coefficient was set to 0.0 during the deposition phase and 0.3 during the extension phase.
4) Establishing a second discrete element model reflecting the geological characteristics of the area to be analyzed by giving the properties of the granular materials of each stratum according to the stratum distribution condition obtained in the step 1) and the microscopic properties of the granular materials of each stratum obtained in the step 3). As shown in fig. 3, the second discrete meta-model includes a substrate, two sides of the substrate are respectively a left wall and a right wall, and the substrate is divided into three parts: left side rigid base and right side of both sidesA side rigid substrate and a ductile substrate in the middle. The rigid substrate is limited in particle displacement and rotation, while the flexible substrate is limited in particle displacement and rotation in the vertical direction, so that the particles of the flexible substrate can move freely in the horizontal direction. The toughness substrate and the rigid substrate are bonded, the tensile strength and the shear strength are 1e100 Pa, and the substrate is prevented from being bonded and disconnected. In this example, the ductile base is composed of grains overlapped with each other, and an initial overlapping ratio cratio = | AO |/(rA + rO), i.e., a ratio of a circle center distance (| AO |) to an equilibrium distance (rA + rO) is defined. The general range of the initial superposition rate is set to be 0.0-1.0, and the radius scaling coefficient and the initial superposition rate have the same value. When cratio ≦ 0.5, as shown in FIG. 1, particle A is bonded to particle B across particle O, and in order to avoid the occurrence of cross-particle bonding, as shown in FIG. 2, a temporary radius scaling factor rext = r is definedtmp/rold. Temporarily changing the particle radius to r when a bond is createdtmp=roldRext. When cratio =0.4 and rext =0.4, the particle a is just bonded to the particle O after the temporary radius scaling is adopted, and the bonding between the particle a and the particle B is avoided.
5) Performing iterative operation on the second discrete element model established in the step 4) by adopting a discrete element calculation method to complete simulation of the evolution process of the basin extension structure of the region to be analyzed: setting boundary conditions based on the discrete element model which is obtained in the step 4) and reflects the geological characteristics of the area to be analyzed, fixing the boundaries at the two sides and the substrate, and enabling the boundaries at the two sides and the rigid substrate to be separated at a constant speed, namely giving displacement boundary conditions and simulating the horizontal stretching effect in reality; the isomorphic depositional is added to simulate a real geological event, as shown in figure 5. A typical simulation is shown in figure 5. Specifically, a horizontal velocity is applied to the left and right rigid bases and the left and right side walls, with the left and left rigid bases taking-2.0 m/s and the right and right rigid bases taking 2.0 m/s.
Based upon the foregoing description of the preferred embodiment of the invention, it should be apparent that the invention defined by the appended claims is not limited solely to the specific details set forth in the foregoing description, as many apparent variations thereof are possible without departing from the spirit or scope thereof.