New method for modeling geologic genesis of fractured reservoirs

Abstract

The present application relates to the technical field of geological modeling, and is a new type of fractured reservoir geological genesis modeling method, which comprises the following steps: according to the difference between the reservoir space and the percolation channel, the fractured carbonate rock reservoir is divided into two categories of matrix and fracture, and step-by-step modeling is carried out; according to the difference in scale, the fractures are divided into two categories of large scale and small scale, and step-by-step modeling of different scale fracture models is established; during fracture modeling, different methods are used for classified modeling according to the difference in fracture scale; according to different scale fractures, fracture elements are counted, and the fracture porosity, permeability and saturation are classified and valued; the matrix model and the fracture model are equivalently combined, and a three-dimensional model is established. The present application establishes a three-dimensional geological model which accurately reflects the real distribution of underground fractures, and accurately depicts the three-dimensional spatial distribution characteristics of the matrix and fractures of the fractured carbonate rock oil and gas reservoir, and the result can reflect the real underground geological information.

Description

Technical Field

[0001] This invention relates to the field of geological modeling technology and is a novel method for modeling the geological genesis of fractured reservoirs. Background Technology

[0002] A certain oil and gas field has achieved significant breakthroughs in the exploration and development of Paleogene carbonate reservoirs in recent years. However, the Neogene carbonate reservoirs in this area are highly fractured, and the distribution of fractures has a significant impact on well productivity. Limited technical methods for modeling fractured carbonate reservoirs hinder oil and gas exploration and development, making it difficult to formulate efficient well network deployment plans. This severely restricts the progress and effectiveness of carbonate reservoir exploration and development in this area. Therefore, it is essential to develop a suitable three-dimensional geological modeling method for fractured carbonate reservoirs and establish a three-dimensional geological model with fracture characterization accuracy meeting the design requirements of the oil and gas field's development plan.

[0003] Currently, modeling fractured carbonate oil and gas reservoirs primarily employs a two-step fracture modeling approach based on a matrix model. For large-scale fractures, these are typically faults determined by seismic data; their location and morphology are largely predetermined and do not require random generation. Deterministic methods such as ant tracking can be used. For small- to medium-scale fractures, which form the main part of the reservoir fracture network, detailed information on each fracture segment is usually unavailable. However, statistical information and prior knowledge regarding their distribution density, orientation, length, aperture, and other aspects can be obtained. Using this information, geostatistical methods can be used to randomly generate a fracture network system composed of thousands of fracture segments, satisfying various prior statistical and cognitive requirements.

[0004] Meanwhile, Dan Lingling, Ma Chao, and Shi Changlin published a paper entitled "Study on Three-Dimensional Geological Modeling of Carbonate Reservoirs in Iraq M Oilfield with Dual Media" in the journal "Complex Oil and Gas Reservoirs" (Volume 11, Issue 2, June 2018). The main content is: based on the characteristics of fractured carbonate reservoirs in the Middle East, a modeling method is proposed that "on the basis of fracture parameter analysis, the relationship between fault distance and fracture development intensity is established, and the fracture development probability volume is used as a trend constraint". Specifically, it includes: (1) Grid division: based on the actual area and well spacing of the study area, considering the needs of later numerical simulation and the requirements of development well network deployment, the planar grid is determined to be 100m×100m. Through statistical analysis of the reservoir thickness in this area, it was found that there are many thin interlayers in the reservoir in this area, and the lateral distribution changes rapidly. In order to accurately simulate the vertical distribution of the reservoir, the vertical grid accuracy is determined to be 0.5m. (2) Structural model: the structure of the M oilfield is a fault anticline trending from north to south to east, with a total of 7 reverse faults. The faults develop along the two flanks of the anticline, and are basically consistent with the long axis of the anticline, mostly trending NW-SE. Using single-well layered data as control and the four structural layers of seismic interpretation as constraints, a structural model was established by inter-well kriging interpolation. (3) Lithofacies model: In order to accurately depict the spatial distribution of complex lithofacies in this area, corresponding lithofacies parameters were applied in this modeling process. First, lithofacies interpretation was performed on all single wells, and these were used as hard data inputs for lithofacies modeling. Based on the lithofacies data analysis, and constrained by comprehensive geological understanding, a sequential indicator simulation method was adopted to establish the lithofacies model of the oilfield. (4) Physical property model: The porosity of different lithofacies in each sublayer of the oilfield was normally transformed, and the permeability attribute was first logarithmically transformed and then normally transformed. The characteristic values ​​of the physical property data distribution were statistically analyzed and used to constrain the stochastic simulation. Based on the variogram analysis, the sequential Gaussian simulation method was used to predict the distribution of matrix porosity and permeability. (5) Fracture Modeling: The study area is close to an orogenic belt, with strong strata deformation and folding, resulting in a high degree of fracture development. Analysis of the main controlling factors of fracture development shows that the degree of fracture development is largely controlled by faults; the closer to the fault, the higher the degree of fracture development; while the farther away from the fault, the less developed the fracture. The fracture orientation is mostly parallel to the main controlling fault, with occasional vertical fault fractures. Based on this, the relationship between fault distance and fracture development intensity is established to obtain a three-dimensional data volume of fracture development probability. A fracture network model is established based on the parameters of the previous fracture characteristic analysis, and finally, a fracture attribute model is obtained. (6) Model Verification: Production wells show that production capacity is basically positively correlated with the permeability of the dual media. From the numerical simulation results, during the historical fitting stage, the relative error between the fitted reserves and geological reserves of each reserve unit in this oilfield is less than 3%, meeting the requirements for numerical simulation reserve fitting. In terms of production fitting, the main fitting of the oilfield's pressure, production, and other development indicators is performed. Through overall adjustment of the oilfield parameters, all indicators have achieved good fitting results.The oilfield has 17 producing wells. The pressure, daily oil production, daily fluid production and water cut of each well were fitted, and the fitting rate reached more than 90%.

[0005] Among the existing technologies, the available materials include: Zhang Lan (2011) et al. used imaging logging data and conventional logging data to zonate metamorphic buried hills, and combined fault distance function and seismic attribute prediction to carry out three-dimensional geological modeling of fractured reservoirs; Dan Lingling (2018) proposed a modeling method of "establishing a relationship between fault distance and fracture development intensity based on fracture parameter analysis, and using fracture development probability volume as a trend constraint"; Dong Shaoqun (2020) et al. used the method of coupling fractures at different scales to establish a three-dimensional geological model of tight sandstone fractured reservoirs.

[0006] The existing three-dimensional geological modeling methods and technologies for fractured carbonate reservoirs, represented by the aforementioned journal articles, can effectively establish three-dimensional geological models to guide early-stage oil and gas resource exploration and evaluation. However, once fractured carbonate oil and gas reservoirs enter the development phase, especially in the mid-to-late stages of development, the three-dimensional geological models established by these methods are insufficient to meet the technical requirements of well network deployment and development effect evaluation in development plans. Their main shortcomings are: while using seismic attributes as constraints and fault distance functions to control fracture intensity, they do not consider the important factor of varying fracture development intensity caused by changes in fault displacement at different fault locations. The simulated fracture results in areas with relatively weak tectonic activity, such as fault terminals and locations with smaller fault displacements, often differ significantly from the actual fracture development. Summary of the Invention

[0007] This invention provides a novel geological genesis modeling method for fractured reservoirs, which overcomes the shortcomings of the existing technologies. It can effectively solve the problem that the three-dimensional geological models established by existing methods are difficult to meet the technical requirements of well network deployment and development effect evaluation in fractured carbonate oil and gas reservoirs, especially in the middle and late stages of development.

[0008] The technical solution of this invention is achieved through the following measures: a novel method for modeling the geological genesis of fractured reservoirs, comprising the following steps:

[0009] Step A1: Based on the differences in reservoir space and seepage channels, fractured carbonate reservoirs are divided into two main categories: matrix and fractures, and modeled step by step.

[0010] Step A2: Based on the difference in scale, the cracks are divided into two categories: large-scale and medium-scale, and crack models of different scales are established step by step.

[0011] Step A3: When modeling cracks, different methods are used to classify and model them according to the differences in crack scale, and large-scale crack models and medium- and small-scale crack models are established.

[0012] Step A4: Based on cracks of different scales, statistically analyze crack elements and classify and assign values ​​to crack porosity, permeability, and saturation.

[0013] Step A5: Merge the matrix model and the fracture model into an equivalent three-dimensional model of porosity, permeability and saturation of fractured carbonate oil and gas reservoirs to meet the requirements of numerical simulation.

[0014] The following are further optimizations and / or improvements to the above-mentioned technical solution:

[0015] The above may also include step A6: calculating geological reserves based on static and dynamic methods, and correcting the three-dimensional geological model by combining historical fitting results, so that the established three-dimensional geological model is more consistent with the actual geological conditions.

[0016] In step A3 above, a large-scale fracture model can be established first. Then, based on the fractures identified from core data, conventional logging data, and imaging logging data, a medium- and small-scale fracture model can be established by combining the fault distance function with the fault displacement normalized and the seismic fracture prediction results to accurately depict the spatial distribution of fractures.

[0017] The modeling steps for the aforementioned large-scale fracture model may include: smoothing and filtering the seismic data, performing fracture prediction, filtering out non-fracture responses such as faults from the fracture prediction results to obtain the large-scale fracture data volume of the seismic prediction, using modeling software to automatically track and identify fractures using deterministic methods, establishing the original large-scale fracture model, and using human-computer interactive editing functions to classify and edit the large-scale fractures in combination with the regional stress analysis results to establish a large-scale fracture model that conforms to geological characteristics.

[0018] The modeling steps for the above-mentioned small-to-medium scale crack model may include:

[0019] The fault displacements at different locations of all faults were statistically analyzed, and the fault displacements were normalized to obtain the normalized fault displacement function for each fault.

[0020] Using the normalized fault displacement function of each fault as a constraint, a fault distance function based on fault displacement is established;

[0021] Based on outcrop, core, logging and testing data, we study fracture elements such as azimuth and dip angle, determine the fracture development stages and groups, and give the parameter ranges of azimuth, length and aperture of each group of fractures. We also study the distribution law of each group of fractures by combining the results of seismic fracture prediction and regional geostress analysis.

[0022] Using single-well fracture density data from imaging logging statistics as hard data, and employing fault distance function based on fault displacement statistics and seismic fracture prediction data as constraints, sequential Gaussian simulation is applied to simulate fracture density and establish a fracture density model that conforms to tectonic genesis.

[0023] Discrete crack mesh models for each group of cracks were established based on their orientation and length.

[0024] The specific steps involved in calibrating the above three-dimensional geological model are as follows:

[0025] Calculate the geological reserves of oil and gas reservoirs in a three-dimensional geological model of fractured carbonate rocks, and compare them with the proven reserves and other oil and gas reservoir geological research results to identify problems in the three-dimensional geological model, correct the model, and continue until the error between the model reserves and the geological research reserves results is within the allowable range.

[0026] The corrected three-dimensional geological model was exported for numerical simulation. The history of single wells and blocks was fitted, the problems of the three-dimensional geological model in history fitting were analyzed, the model was further modified, and finally a three-dimensional geological model of fractured carbonate rocks that matches the information of underground oil and gas reservoirs was established.

[0027] This invention provides an effective 3D geological modeling method for fractured carbonate reservoirs. Its core lies in fully considering the tectonic influence on fracture formation during small-to-medium scale fracture modeling. Based on detailed fracture characteristic analysis, single-well fracture statistical parameters are used as hard data. A 3D geological model that accurately reflects the true distribution of subsurface fractures is established using a fault distance function based on fault displacement normalization and a fracture prediction attribute volume as common constraints. This meets the needs of well location deployment, scheme design, and dynamic development analysis. This invention primarily addresses the complex spatial distribution and high simulation difficulty of fractures, especially small-to-medium scale fractures, in fractured carbonate reservoirs. Based on fracture characteristic analysis, single-well fracture data is used as hard data, and 3D geological modeling of fractured carbonate oil and gas reservoirs is achieved through the joint constraints of a fault distance function based on fault displacement normalization and a seismic attribute volume. This invention overcomes the problem in current fractured reservoir modeling that does not consider the control effect of different fault locations on fracture development, and establishes a 3D geological model that accurately reflects the true distribution of subsurface fractures. Compared with existing technologies, the implementation process of this invention requires a high level of expertise and is difficult to operate. Once it enters the market, it will be difficult for competitors to imitate and use. As a novel method for three-dimensional geological modeling of fractured reservoirs, this invention faces strong market competition. The three-dimensional geological model established according to this invention accurately depicts the matrix and three-dimensional spatial distribution characteristics of fractured carbonate oil and gas reservoirs. In particular, the depiction of fractures at fault terminals and locations with small fault displacements more closely matches the actual development of underground fractures, and the results reflect the true underground geological information. Attached Figure Description

[0028] Appendix Figure 1 This is a flowchart illustrating an embodiment of the present invention.

[0029] Appendix Figure 2 This is a schematic diagram of the process for large-scale three-dimensional geological modeling of fractures according to an embodiment of the present invention.

[0030] Appendix Figure 3 This is a schematic diagram of the process for three-dimensional geological modeling of small- and medium-scale fractures in an embodiment of the present invention. Detailed Implementation

[0031] The present invention is not limited to the following embodiments, and the specific implementation can be determined according to the technical solution of the present invention and the actual situation.

[0032] In this invention, for ease of description, the relative positional relationships of each component are described according to the layout of the accompanying drawings. For example, the positional relationships of front, back, top, bottom, left, right, etc., are determined according to the layout direction of the accompanying drawings.

[0033] The present invention will be further described below with reference to embodiments and accompanying drawings:

[0034] Example 1: As shown in the attached document Figure 1 , 2 As shown in Figure 3, this novel modeling method for the geological genesis of fractured reservoirs includes the following steps:

[0035] Step A1: Based on the differences in reservoir space and seepage channels, fractured carbonate reservoirs are divided into two main categories: matrix and fractures, and modeled step by step. This embodiment of the invention is based on existing data and classifies modeling into major categories based on fault modeling, structural modeling, stratigraphic modeling, and lithofacies modeling. According to the dual-medium structure of fractured carbonate reservoirs, modeling is generally divided into two main categories: matrix and fractures, and different methods are used for step-by-step modeling of each.

[0036] Step A2: Based on the difference in scale, the fractures are divided into two categories: large-scale and small-to-medium-scale, and fracture models of different scales are established step by step. In this embodiment of the invention, large-scale fractures refer to fractures with a large aperture and long extension that can be identified using seismic data; while fractures with relatively short extension distances and small apertures that can only be identified using outcrops, core samples, conventional logging, or imaging logging are called small-to-medium-scale fractures.

[0037] Step A3: During fracture modeling, different methods are used to classify and model fractures according to their scale, establishing large-scale fracture models and small-to-medium-scale fracture models. In Step A3, a large-scale fracture model is first established using deterministic modeling methods such as ant tracking based on seismic data; then, based on fractures identified from core data, conventional well logging, and imaging well logging, and combined with fault distance functions normalized to fault displacement and seismic fracture prediction results, a small-to-medium-scale fracture model is established to accurately depict the spatial distribution of fractures.

[0038] Step A4: Based on cracks of different scales, statistically analyze crack elements and classify and assign values ​​to crack porosity, permeability, saturation, etc.

[0039] Step A5: Merge the matrix model and the fracture model into an equivalent three-dimensional model of the porosity, permeability, and saturation of the fractured carbonate oil and gas reservoir to meet the requirements of numerical simulation.

[0040] Step A6: Due to the strong heterogeneity and complex fluid distribution of fractured carbonate reservoirs, after establishing a three-dimensional geological model, it is necessary to calculate the geological reserves using static and dynamic methods, and then correct the three-dimensional geological model by combining historical fitting results, so that the established three-dimensional geological model is more consistent with the actual geological conditions.

[0041] In this embodiment of the invention, the modeling steps of the large-scale fracture model are as follows: First, the seismic data is smoothed and filtered, and fracture prediction is carried out. Non-fracture responses such as faults are filtered out from the fracture prediction results to obtain the large-scale fracture data volume of the seismic prediction. The modeling software is used to automatically track and identify the fractures using a deterministic method to establish the original large-scale fracture model. Combined with the regional stress analysis results, the large-scale fractures are divided and edited using the human-computer interactive editing function to establish a large-scale fracture model that conforms to the geological characteristics.

[0042] In this embodiment of the invention, the modeling steps for the small-to-medium scale fracture model are as follows: first, the fault displacement S at different locations of all faults is statistically analyzed, and then... Normalize the fault distance S (where, The normalized fault displacement function is given for each sampling point on the fault (S_max is the maximum fault displacement in the work area, and S_min is the minimum fault displacement in the work area). To obtain the normalized fault displacement function for each fault, considering the consistency of structural features within a small area, a fault displacement-based fault distance function is established, constrained by the normalized fault displacement function. Based on outcrop, core, well logging, and testing data, fracture elements such as azimuth and dip are studied to determine the fracture development stages and groups. The range of values ​​for parameters such as azimuth, length, and aperture of each group of fractures is given. The distribution law of each group of fractures is studied by combining results from seismic fracture prediction and regional geostress analysis. Then, using single-well fracture density data from imaging logging statistics as hard data, and employing the fault displacement-based fault distance function and seismic fracture prediction data as constraints, sequential Gaussian simulation is applied to simulate fracture density and establish a fracture density model consistent with tectonic genesis. Finally, discrete fracture mesh models for each group of fractures are established based on their azimuth and length.

[0043] Step B8: Modeling small- to medium-scale fractures. First, calculate the fault displacement S at different locations on all faults, and then use... Normalize the fault distance S (where, The normalized fault displacement function is defined as follows: S_max is the maximum fault displacement within the work area, and S_min is the minimum fault displacement within the work area. This yields the normalized fault displacement function for each fault. Considering the consistency of structural features within a small area, a fault displacement-based fault distance function is established, constrained by the normalized fault displacement function. Based on outcrop, core, well logging, and testing data, fracture elements such as azimuth and dip are studied to determine the fracture development stages and groups. The range of values ​​for parameters such as azimuth, length, and aperture of each fracture group is given. The distribution patterns of each fracture group are studied by combining seismic fracture prediction and regional geostress analysis results. Then, using single-well fracture density data from imaging logging as hard data, and employing the fault displacement-based fault distance function and seismic fracture prediction data as constraints, sequential Gaussian simulation is applied to simulate fracture density and establish a fracture density model consistent with tectonic genesis. Finally, discrete fracture mesh models for each fracture group are established based on the azimuth and length of each group.

[0044] Step B9: Fracture Parameter Modeling. Based on the established discrete fracture network model and fracture aperture data, models for fracture porosity, fracture conductivity, and fracture permeability are established. The fracture permeability model is then modified based on production characteristics and well test fracture permeability interpretation results. Fracture saturation is established based on fracture saturation analysis and testing results. Below the oil-gas-water interface, values ​​are directly assigned as water layers to establish a fracture saturation model.

[0045] Step B10: Model Merging. The three-dimensional geological models established for the matrix and fractures are merged using equivalent merging calculation methods for each parameter, and an equivalent model is generated through grid calculation to establish a three-dimensional geological model of fractured carbonate oil and gas reservoirs.

[0046] Step B11, Model Calibration. Calibration is divided into two parts: static calibration and dynamic calibration. Specifically, the calibration of the 3D geological model includes the following steps: First, calculate the geological reserves of the fractured carbonate rock 3D geological model for oil and gas reservoirs, and compare it with the proven reserves and other oil and gas reservoir geological research results to identify problems in the 3D geological model. Correct the model until the error between the model reserves and the geological research reserves is within the allowable range. Then, export the corrected 3D geological model for numerical simulation, conduct history fitting for single wells and blocks, analyze the problems in the history fitting of the 3D geological model, further modify the model, and finally establish a fractured carbonate rock 3D geological model that matches the underground oil and gas reservoir information.

[0047] This invention has been applied to a fractured carbonate reservoir in an oil and gas field. The three-dimensional geological model established according to this invention accurately depicts the three-dimensional spatial distribution characteristics of the matrix and fractures in the fractured carbonate reservoir. In particular, the depiction of fractures at fault terminals and locations with small fault displacements more closely matches the actual development of underground fractures. The results reflect the true underground geological information and have played an important role in well location deployment, well trajectory optimization design, and drilling tracking in an oil and gas field in Iraq. Currently, 32 wells have been drilled, with 29 wells completed, achieving a 100% drilling success rate and a high-production rate of 72% for single-well testing.

[0048] The above technical features constitute the embodiments of the present invention, which have strong adaptability and implementation effect. Unnecessary technical features can be added or removed according to actual needs to meet the needs of different situations.

Claims

1. A novel method for modeling the geological genesis of fractured reservoirs, characterized in that... Includes the following steps: Step A1: Based on the differences in reservoir space and seepage channels, fractured carbonate reservoirs are divided into two main categories: matrix and fractures, and modeled step by step. Step A2: Based on the difference in scale, the cracks are divided into two categories: large-scale and medium-scale, and crack models of different scales are established step by step. Step A3: When modeling cracks, different methods are used to classify and model them according to the differences in crack scale, and large-scale crack models and medium- and small-scale crack models are established. Step A4: Based on cracks of different scales, statistically analyze crack elements and classify and assign values ​​to crack porosity, permeability, and saturation. Step A5: Merge the matrix model and the fracture model into an equivalent three-dimensional model of porosity, permeability and saturation of fractured carbonate oil and gas reservoir that meets the requirements of numerical simulation. The modeling steps for small- to medium-scale crack models include: The fault displacements at different locations of all faults were statistically analyzed, and the fault displacements were normalized to obtain the normalized fault displacement function for each fault. Using the normalized fault displacement function of each fault as a constraint, a fault distance function based on fault displacement is established; Based on outcrop, core, logging and testing data, we studied the azimuth and dip fracture elements, determined the fracture development stages and groups, and gave the parameter ranges of azimuth, length and aperture of each group of fractures. We also studied the distribution law of each group of fractures in combination with the results of seismic fracture prediction and regional geostress analysis. Using single-well fracture density data from imaging logging statistics as hard data, and employing fault distance function based on fault displacement statistics and seismic fracture prediction data as constraints, sequential Gaussian simulation is applied to simulate fracture density and establish a fracture density model that conforms to tectonic genesis. Discrete crack mesh models for each group of cracks were established based on their orientation and length. When modeling fracture saturation, values ​​below the oil-gas-water interface are directly assigned as water layers; when studying fracture distribution patterns, regional geostress analysis results are combined simultaneously; the model merging adopts the equivalent merging calculation method for each parameter, and an equivalent model is generated through grid calculation.

2. The novel fractured reservoir geological genesis modeling method according to claim 1, characterized in that... It also includes step A6, calculating geological reserves based on static and dynamic methods, and correcting the three-dimensional geological model by combining historical fitting results, so that the established three-dimensional geological model is more in line with the actual geological conditions. During the model calibration process, the fracture permeability model is modified based on production characteristics and well test fracture permeability interpretation results when modeling fracture parameters.

3. The novel fractured reservoir geological genesis modeling method according to claim 1 or 2, characterized in that... The modeling steps for a large-scale fracture model include: smoothing and filtering the seismic data, performing fracture prediction, filtering out non-fracture responses of the fault from the fracture prediction results to obtain the large-scale fracture data volume of the seismic prediction, using modeling software to automatically track and identify fractures using deterministic methods, establishing the original large-scale fracture model, and using human-computer interactive editing functions to classify and edit the large-scale fractures based on the regional stress analysis results to establish a large-scale fracture model that conforms to geological characteristics.

4. The novel fractured reservoir geological genesis modeling method according to claim 2, characterized in that... The specific steps involved in calibrating a three-dimensional geological model are as follows: Calculate the geological reserves of oil and gas reservoirs in a three-dimensional geological model of fractured carbonate rocks, compare the results with those from geological research, identify problems in the three-dimensional geological model, and revise the model until the error between the model reserves and the geological research reserves is within the allowable range. The corrected three-dimensional geological model was exported for numerical simulation. The history of single wells and blocks was fitted, the problems of the three-dimensional geological model in history fitting were analyzed, the model was further modified, and finally a three-dimensional geological model of fractured carbonate rocks that matches the information of underground oil and gas reservoirs was established.

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