Method for characterizing interlayer vertical seepage characteristics

Abstract

The invention discloses an interlayer vertical seepage characteristic characterization method. The method comprises the following steps: establishing an interlayer interlayer model of a research area; assigning conductivity values to grids with different attributes of the interlayer model to form a vertical conductivity model, and performing interlayer vertical seepage characteristic characterization of the research area by using the vertical conductivity model; the problems that the vertical streaming phenomenon exists between different unit layers in the composite sand body, and in the current geological modeling process, the influence of vertical streaming is not represented, so that the difference between a numerical simulation result and the actual oil layer production condition is large are effectively solved. According to the characterization method disclosed by the invention, the size of the interlayer vertical seepage capacity can be represented, fine research on interlayer and intra-layer vertical seepage characteristics is realized, and further accurate understanding on oil layer remaining oil and interlayer development interference influence is realized.

Description

Technical Field

[0001] The present disclosure relates to the technical field of oilfield development, and in particular to a method for characterizing layered sandstone reservoirs in an oil reservoir. Background Art

[0002] In reservoirs with complex sand bodies and numerous commingled production wells, vertical crossflow between individual layers can lead to significant errors if only the injection / production volume and remaining oil of each individual layer are analyzed without considering this phenomenon. Practice has shown that interlayer flow capacity significantly influences numerical modeling and remaining oil analysis, further impacting the understanding of reservoir development results. Therefore, detailed research on interlayer crossflow capacity is necessary. Failure to accurately describe this capacity can lead to significant errors in understanding individual layer production status and remaining oil, further impacting decisions about further development.

[0003] Currently, when performing 3D geological modeling, numerical simulation software systems assume that interlayer crossflow capacity exists between individual layers, as does the lateral crossflow capacity. However, in later simulations, vertical crossflow capacity is characterized by modified vertical connectivity, disconnection, and semi-connectivity based on empirical experience in areas with interlayered structures. However, laboratory test results show that interlayers with different lithologies have different vertical seepage capacities, and different types of sandstone have varying vertical and horizontal permeabilities. Therefore, it is not possible to accurately characterize the differences in seepage between different locations and layers between wells. Summary of the Invention

[0004] In view of this, the present disclosure provides a method for characterizing the characteristics of interlayer vertical seepage to solve the problem that vertical cross-flow exists between different unit layers within a composite sand body. However, in the current geological modeling process, the influence of this vertical cross-flow is not characterized, resulting in a large difference between the numerical simulation results and the actual oil layer production conditions.

[0005] The technical conception process of the method disclosed in the present invention is that after the formation is stratified by single layer, a formation system of reservoir and non-reservoir layers is formed. An interlayer of at least 0.2 meters is developed between independent oil layers, which is generally an impermeable layer of mudstone or calcareous rock and does not have a seepage effect. In the area where composite sand bodies are developed, there are low-permeability or ultra-low-permeability layers between high-permeability reservoirs, that is, interlayer interlayers, with a thickness of 0-0.4 meters. The results of core research show that the interlayer lithology is mudstone, calcareous rock, silty mudstone, muddy siltstone, muddy fine sandstone and other lithologies, with a vertical permeability between 0-2.0 millidarcy; under normal circumstances, if the permeability is higher than 0.1 millidarcy, it has seepage capacity. Therefore, a part of the interlayer has a seepage-blocking effect, and a part of the interlayer has permeability. Therefore, during the development of the oil layer, due to changes in pressure and other conditions, cross-flow will occur between the layers.

[0006] Characterizing the vertical conductivity of interlayer intercalations involves two steps: determining the development of intercalations in unknown areas between wells and determining their distribution. Through 3D geological modeling, a grid system is established according to modeling rules. Intercalations are treated as a new reservoir type and grid interpolation and prediction are performed to form an interlayer intercalation model. Grid calculations are then used to determine the thickness and properties of the intercalations. By assigning values ​​to grids with different properties in the intercalation model (based on core measurements), a vertical conductivity model is constructed. This allows for characterization of the seepage conditions between sand bodies.

[0007] In summary, the overall inventive concept of the disclosed method is to characterize the vertical seepage characteristics of interlayers by predicting interlayers between wells and establishing a vertical conductivity model based on the interlayers.

[0008] To solve the above technical problems, the present disclosure provides a technical solution, which is the method for characterizing interlayer vertical seepage characteristics, comprising: Establish an interlayer model for the study area; The grids of different properties of the sandwich model are assigned conductivity values ​​to form a vertical conductivity model, and the vertical conductivity model is used to characterize the interlayer vertical seepage characteristics of the study area.

[0009] In the present disclosure and possible embodiments, the method of establishing an interlayer model of a study area includes: When performing sedimentary unit layer modeling on the study area, the interlayer model is established according to the oil layer sand body modeling method for the interlayer.

[0010] In the present disclosure and possible embodiments, the method of assigning conductivity values ​​to grids of different attributes of the sandwich model includes: Based on the interlayer model, the interlayer thickness and lithology type are determined through grid attribute analysis; The conductivity value is assigned according to the interlayer thickness and the lithology type.

[0011] In the present disclosure and possible embodiments, the conductivity value is determined by a core chamber test.

[0012] In the present disclosure and possible embodiments, the thickness of the interlayer and the lithology type are determined by calculating the depth difference between the bottom of the sandstone above the boundary and the top of the sandstone below the boundary within the unit or reservoir.

[0013] The present disclosure has the following beneficial effects: The method for characterizing the characteristics of interlayer vertical seepage disclosed in the present invention uses modeling to predict the properties of interlayer interlayers based on the development characteristics of interlayer interlayers above the well. By assigning values ​​to different attribute grids, the magnitude of the interlayer vertical seepage capacity is characterized, thereby achieving a detailed study of the vertical seepage characteristics between and within layers, and further realizing a precise understanding of the remaining oil in the oil layer and the impact of interlayer development interference. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] The above and other objects, features and advantages of the present disclosure will become more apparent through the following description of the embodiments of the present disclosure with reference to the accompanying drawings, in which: Figure 1 is a flow chart of a method for characterizing interlayer vertical seepage characteristics according to an embodiment of the present disclosure; Figure 2 The single layer and interlayer of the embodiment of the present disclosure; Figure 3 Schematic diagram of the interlayer depth difference between Sa III 1+2 and Sa III 3 layers, and between Sa III 4+5 and Sa III 6+7 layers in the embodiment of the present disclosure. DETAILED DESCRIPTION

[0015] The present disclosure is described below based on embodiments, but it is worth noting that the present disclosure is not limited to these embodiments. In the detailed description of the present disclosure below, some specific details are described in detail. However, for the parts not described in detail, those skilled in the art can also fully understand the present disclosure.

[0016] At the same time, unless the context clearly requires otherwise, words such as "include", "comprising" and the like throughout the specification and claims should be interpreted as inclusive rather than exclusive or exhaustive; that is, as "including but not limited to".

[0017] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below with reference to the accompanying drawings and by listing embodiments and application examples.

[0018] The embodiment of the present disclosure takes the Sa III 1-7 oil layer in the test area as an example to specifically illustrate the process of characterizing the interlayer vertical seepage characteristics thereof using the method of the present invention.

[0019] In summary, we first conducted intra-layer boundary demarcation and grid system design based on the sandbody's development characteristics. This led to structural modeling of the composite sandbody's individual subdivisions, providing a suitable geometric framework for interlayer characterization studies. Then, based on facies-controlled attribute modeling, we optimized the grid parameter coarsening method to ensure the characterization accuracy of the coarsened model. Finally, by calculating the model's longitudinal conductivity, we investigated the longitudinal connectivity between various parts within the layer, thereby providing a high-quality static foundation model suitable for intralayer simulations.

[0020] Figure 1 is a flow chart of a method for characterizing interlayer vertical seepage characteristics according to an embodiment of the present disclosure; Figure 1 As shown, the specific steps of the interlayer vertical seepage characteristic characterization method are as follows: Step S10: Establish a grid system for the study area. The specific establishment process is as follows: 1. Demarcation of intra-layer boundaries Based on the Petrel modeling software, under the control of sedimentary unit boundaries, the intra-layer boundaries were calibrated according to the rhythmic characteristics of the sand bodies in individual wells, the distribution characteristics of porosity and permeability parameters, the distribution of interlayers, and the waterlogging characteristics.

[0021] The thickness values ​​of each part of each well after subdivision are calculated by using the unit boundary, and the thickness interpolation method is used to establish the thickness change trend surface. For example, for the Sa III 1-7 oil layer in the test area, it is subdivided into five units: Sa III 1+2, 31, 32, 4+5, and 6+7. Each unit is a single layer (such as Figure 2 Under the control of the top surface of Sa III 1+2 unit and the bottom surface of Sa III 6+7 unit, the stratigraphic plane of each unit and each part was established using the thickness variation trend surface.

[0022] 2. Fine grid system division The modeling grid system was optimized based on the actual conditions of the block and the accuracy requirements of the results. To ensure that there were no fewer than three grid cells between two wells in the numerical simulation (to satisfy the calculation of the interwell pressure gradient field), the horizontal grid size was set to 15m × 15m based on the well spacing of the block. To ensure that thin and poorly defined layers were not lost, the vertical grid size was 0.1m based on the thickness interpretation standards of the well logging curves. The grid lines were rotated 19° counterclockwise based on the provenance direction and well pattern azimuth. To ensure that the work area became a relatively complete and independent injection-production system, the 28# fault was designated as the southwestern boundary of the work area. A three-dimensional spatial grid system was established for the model, completing the structural modeling.

[0023] 3. Mesh coarsening According to the aforementioned three-dimensional space grid system, the total number of model grids reaches tens of millions, and the numerical simulation model cannot run, so the fine model grid needs to be coarsened.

[0024] Mesh coarsening first requires designing a mesh framework for the coarsening model to reduce the total number of meshes in the model. This means replacing the fine meshes in the fine model with a series of equivalent coarse meshes. The following principles are used to construct coarsening: First, the total number of model grids is limited by the software computing speed and hardware memory size, so try to keep it below one million.

[0025] Second, the plane grid system of the coarsening model must be consistent with the plane grid system of the fine model. Based on practical experience, if the plane grid system (model boundaries and grid size) changes before and after coarsening, it will cause mesh deformation near faults and displacement of the grid where well points are located, reducing model accuracy.

[0026] Third, vertical grids are coarsened primarily based on the research object. Generally, multiple grids within a unit (sublayer) are coarsened into a single grid. Based on actual needs, this study required studying oil-water flow within a layer, so each unit was coarsened into two or three grids along the layer boundaries (two grids for Sa III 1+2, and four grids for Sa III 31, 32, 4+5, and 6+7).

[0027] According to the above idea of ​​coarsening, the total number of model grids after coarsening is 88×85×11=82280.

[0028] Step S20: Establishing the interlayer model of the research area Specifically, when modeling sedimentary units, lithologic models are created for oil layers and interlayers according to their lithologic properties. Interlayers, previously considered only as layers, are now defined as a layered stratum type, and interlayer models are then created using the oil layer sandbody modeling method.

[0029] For the study area of ​​this embodiment, the specific establishment process is as follows: In the 3D lithologic model, different attribute codes were assigned to different lithologic types. Reservoir modeling was divided into four lithologic types: 1. Channel sand, 2. Main sheet sand, 3. Non-main sheet sand, and 4. Off-surface sand. Interlayer modeling was divided into five lithologic types, with attribute codes: 5. Mudstone (also known as pinchout), 6. Sandstone interlayer (including channel sand, main sheet sand, and non-main sheet sand), 7. Effective interlayer (including channel sand, main sheet sand, and non-main sheet sand), 8. Interlayers with different flooding levels, and 9. Interlayers with different permeabilities. These settings were loaded into the Petrel modeling software. The reservoir modeling is controlled by the distribution map of four types of sand bodies. The grid with wells is based on the wells. The inter-well grid is assigned according to the trend of different types of sandstone distribution (phase belt map). The interlayer modeling adopts the same method, which is divided into five interlayer types for inter-well grid attribute interpolation to establish the grid attribute model. By analyzing the grid between the upper and lower oil layers, the depth difference between the upper sandstone bottom and the lower sandstone top of the unit (or reservoir) stratification boundary is calculated to determine the thickness and attribute type of the interlayer, such as Figure 3 Show.

[0030] Step S30: assigning conductivity values ​​to grids with different attributes in the sandwich model to form a vertical conductivity model, as follows: First, the lithologic model was used to calculate the depth difference between the upper sandstone base and the lower sandstone top of each grid cell. Next, the lithologic type and thickness of the grid cells at the boundary were determined based on grid thickness and phase values. Different attributes were assigned based on interlayer type. Based on core measurements and actual fitting, the vertical permeability coefficients of mudstone interlayers were assigned values ​​of 0, 0.03 for silty mudstone interlayers, 0.1 for argillaceous siltstone interlayers, and 0.05 for calcareous siltstone interlayers. Finally, a vertical conductivity model was formed based on the coarsened model to characterize the connectivity of interlayer sand bodies. During the numerical simulation, the interlayer vertical permeability multiplication factor was determined based on the attribute volume.

[0031] To validate the effectiveness of the proposed method, a vertical conductivity model was added to the attribute volume data and numerical simulations were performed. The initial fitting accuracy improved by 5.4 percentage points compared to the model without vertical conductivity characterization, as shown in Table 1. Analysis indicates that the reduced vertical fluid flow in the grid slows convergence, but at the same time, it better reflects the actual reservoir conditions, thereby improving fitting accuracy.

[0032] Table 1 Simulation statistics of interlayer seepage capacity of Sa III 1-7 oil layer in the test area The above-described embodiments are merely examples of implementation methods of the present disclosure, and their descriptions are relatively specific and detailed. However, they should not be construed as limiting the scope of the present invention. It should be noted that a person skilled in the art may make various modifications, equivalent substitutions, and improvements without departing from the scope of the present disclosure, and these modifications are all within the scope of protection of the present disclosure. Therefore, the scope of protection of the present invention shall be based on the appended claims.

Claims

1. A method for characterizing interlayer vertical seepage characteristics, characterized in that: include: Establish an interlayer model for the study area; The grids of different properties of the sandwich model are assigned conductivity values ​​to form a vertical conductivity model, and the vertical seepage characteristics between layers of the study area are characterized using the vertical conductivity model.

2. The method for characterizing interlayer vertical seepage characteristics according to claim 1, characterized in that: The method for establishing the interlayer model of the research area includes: When performing sedimentary unit layer modeling on the study area, the interlayer model is established according to the oil layer sand body modeling method for the interlayer.

3. The method for characterizing interlayer vertical seepage characteristics according to claim 1 or 2, characterized in that: The method of assigning conductivity values ​​to grids of different attributes of the sandwich model comprises: Based on the interlayer model, the interlayer thickness and lithology type are determined through grid attribute analysis; The conductivity value is assigned according to the interlayer thickness and the lithology type.

4. The method for characterizing interlayer vertical seepage characteristics according to claim 3, characterized in that: The conductivity values ​​are determined by core chamber tests.

5. The method for characterizing interlayer vertical seepage characteristics according to claim 4, characterized in that: The thickness of the interlayer and the lithology type are determined by calculating the depth difference between the bottom of the sandstone above the stratification boundary and the top of the sandstone below the boundary within the unit or reservoir.

6. The method for characterizing interlayer vertical seepage characteristics according to claim 1, 2, 4 or 5, characterized in that: The interlayer model of the study area was established based on Petrel modeling software.

7. The method for characterizing interlayer vertical seepage characteristics according to claim 6, characterized in that: Establishing an interlayer model of the study area based on the study area grid system; The establishment of the grid system in the study area includes the process of demarcating the boundaries within the layer; The method for calibrating the intra-layer boundary is to calibrate the intra-layer boundary according to the rhythmic characteristics of the sand body of a single well, the distribution characteristics of porosity and permeability parameters, the distribution of interlayers and the flooding characteristics under the control of the sedimentary unit boundary.

Images