Method for making comprehensive comparison chart of porous low-permeability sandstone reservoir

Abstract

The present invention relates to a method for making a comprehensive comparison map of a porous low-permeability sandstone reservoir, including: selecting a number of profiles parallel and transverse to the sediment source according to the sedimentary background to obtain the backbone profiles for sand body comparison, using spectral analysis technology to extract spectral characteristics from the original logging curves, realizing the identification of sequence boundaries to avoid the influence of human factors, carrying out stratigraphic division and correlation, and then building a sequence stratigraphic framework; under the sequence stratigraphic framework, carrying out sand body comparison according to sedimentary cycles and sand body development stages; classifying and comparing the target sandstone reservoir sections according to the physical properties, microscopic reservoir characteristics and productivity of the target sandstone reservoir sections; checking the comparison relationships of the types of the sandstone reservoir sections, selecting the comparison relationships or explanatory conclusions of the parts with abrupt comparison or sharp changes for correction, and completing comparison mapping to quickly locate the sweet spot reservoirs and the laws of heterogeneity.

Description

Technical Field

[0001] The present invention relates to the field of geological technologies for oilfield exploration and development. Specifically, it relates to an apparatus and method for making a comprehensive comparison map of a pore-type low-permeability sandstone reservoir. Background Art

[0002] With the progress of oil and gas exploration and development technologies and the deepening of exploitation degree, newly discovered and undeveloped oilfields in China in recent years mainly consist of low-permeability and ultra-low-permeability oil and gas reservoirs, accounting for about 67% - 72% of the discovered reserves. The heterogeneity of low-permeability reservoirs is an important factor affecting the development effect of oil layers and the distribution of remaining oil. Reservoir correlation is of great significance for studying the heterogeneity characteristics and distribution patterns of low-permeability oil reservoirs, improving the water injection and gas injection development effects of heterogeneous reservoirs in low-permeability oil reservoirs, and enhancing the efficient and economic development of low-permeability oil reservoirs.

[0003] During the oilfield development process, within the same low-permeability oil and gas reservoir, the dynamic change of oil and gas movement is relatively small, and oil and gas usually preferentially choose the flow path with less movement resistance within the heterogeneous flow path layer. The flow path layer generally refers to a permeable formation with developed pores, fractures, or holes and other basic spaces for migration. The matrix permeability of pore-type and fracture-type low-permeability oil and gas reservoirs is very low. Fracture-type low-permeability oil and gas reservoirs mainly rely on the communication of natural fracture systems as the flow path layer for oil and gas migration, while pore-type low-permeability oil and gas reservoirs need to implement fracturing transformation to establish artificial fractures to communicate with relatively sweet spots to improve the oilfield development benefit.

[0004] In order to accurately locate the position and distribution law of the preferential flow path layer for oil and gas migration (relative to the sweet spot reservoir), and verify the rationality and accuracy of the physical property interpretation of low-permeability sandstone reservoirs, it is necessary to develop a mapping method for comprehensive comparison of low-permeability sandstone reservoirs, so as to achieve a simple and intuitive classification comparison of the reservoir capacity and flow path quality of the reservoir section, determine the scale and distribution of high-quality reserves, provide a reference for the development plan and injection-production well pattern deployment, and further improve the development effect of low-permeability oil reservoirs.

[0005] Regarding the research on the distribution law, connectivity, etc. of the reservoir section, major domestic oil and gas fields and universities and research institutes have done a lot of research work, but there is no example of comprehensively comparing the reservoir quality and physical property quality and selecting and marking the preferential flow path layer on the cross-section. Summary of the Invention

[0006] Aiming at the above problems, the purpose of the present invention is to provide a mapping method for comparing the reservoir quality and flow path capacity of low-permeability sandstone reservoirs on the cross-section, which can simply and clearly display the quality differences of reservoirs and the distribution law of reservoirs with different reservoir capacities at different stages of oilfield development.

[0007] To achieve the above purpose, the present invention adopts the following technical solutions:

[0008] A method for making a comprehensive comparison map of a porous low-permeability sandstone reservoir, comprising:

[0009] Select a number of profiles parallel and transverse to the sediment source according to the sedimentary background to obtain the backbone profiles for sand body comparison. Use spectral analysis technology to extract spectral features from the original logging curves, realize the identification of sequence boundaries by avoiding the influence of human factors, conduct stratigraphic division and correlation, and then build a sequence stratigraphic framework;

[0010] Under the sequence stratigraphic framework, conduct sand body comparison according to the sedimentary cycle and the development stages of sand bodies;

[0011] According to the physical properties, microscopic reservoir characteristics and productivity of the target sandstone reservoir section, conduct classification and comparison of the types of sandstone reservoirs in the target sandstone reservoir section;

[0012] According to the classification and comparison of sandstone reservoir types, conduct differential color / pattern filling for the target sandstone reservoir section, and display the reservoir quality from good to poor according to the rule of changing from warm color to cold color or from simple pattern to complex pattern; and

[0013] Conduct a comparison check on the types of sandstone reservoir sections, select the comparison relationships or explanatory conclusions of the parts with abrupt comparison or sharp changes, and make corrections and complete the comparison mapping.

[0014] Due to the adoption of the above technical solutions, the present invention has the following advantages:

[0015] 1. The present invention proposes a method for making a comprehensive comparison map of a porous low-permeability sandstone reservoir section, which simply and clearly shows the change trend and transitional relationship of reservoir quality in the sand body, and provides convenient conditions for quickly locking the distribution area of sweet spot reservoirs for fracturing transformation;

[0016] 2. Through the classification and comprehensive comparison display of well-connected sand bodies, some wells with unreasonable permeability interpretations can be quickly found, thereby improving the accuracy of reserve calculation;

[0017] 3. By fully combining the sedimentary background and well data, the migration trajectory of the main sedimentary sand body can be roughly judged according to the law that the physical properties of the main part of the sand body are better and the physical properties of the edge of the sand body are relatively worse.

[0018] In summary, the present invention is applicable to the production of comprehensive comparison maps of porous low-permeability sandstone reservoirs, and is also applicable to conventional sandstone reservoirs for application in the exploration and development of sandstone-type oil reservoirs. Description of the Drawings

[0019] By reading the detailed description of the implementation modes below, various other advantages and benefits will become clear to those of ordinary skill in the art. The drawings are only for the purpose of showing the selected implementation modes and are not considered as a limitation of the present invention. Throughout the drawings, the same reference numerals are used to represent the same components. In the drawings:

[0020] Figure 1 is a schematic flow chart of a method for physical property contrast mapping of a matrix-type low-permeability sandstone reservoir section disclosed in some embodiments of the present invention;

[0021] Figure 2 is a schematic diagram of formation contrast analysis carried out by applying CycloLog software based on sedimentary cycle characteristics in some embodiments of the present invention;

[0022] Figure 3 is a schematic diagram of intelligent sand layer contrast analysis carried out by applying Shiwen software in some embodiments of the present invention;

[0023] Figure 4A and Figure 4B is a comparison chart before and after permeability adjustment in some embodiments of the present invention; and

[0024] Figure 5 is a physical property contrast profile of a low-permeability sandstone reservoir section in some embodiments of the present invention, and the comparison chart can show the migration process of the sedimentary main body. Detailed implementation modes

[0025] The exemplary embodiments of the present invention will be described in more detail below with reference to the drawings. Although the exemplary embodiments of the present invention are shown in the drawings, it should be understood that the present invention can be implemented in various forms and should not be limited by the embodiments set forth herein. On the contrary, these embodiments are provided so that the present invention can be more thoroughly understood and the scope of the present invention can be completely conveyed to those skilled in the art.

[0026] According to some embodiments of the present application, a method for making a comprehensive contrast map of a pore-type low-permeability sandstone reservoir is provided. This solution is only applicable to the study of pore-type low-permeability oil and gas reservoirs with underdeveloped natural fracture systems, and can characterize the distribution of low-permeability heterogeneous reservoirs in a simple and clear manner, including the following steps:

[0027] S1: Conduct formation division and contrast to establish a sequence stratigraphic framework. First, select several profiles parallel and transverse to the sediment source (the long axis direction of the sediment body) according to the sedimentary background to obtain the backbone profiles for sand body contrast. Use spectral analysis technology to extract spectral characteristics from the original logging curves through CycloLog software to achieve the identification of sequence boundaries that avoid the influence of human factors, and then build a sequence stratigraphic framework.

[0028] S2: Under the sequence stratigraphic framework, conduct sand body correlation work according to sedimentary cycles and the development stages of sand bodies.

[0029] S3: According to research needs, divide and correlate the target reservoir section according to the physical properties, microscopic reservoir characteristics, productivity or other comprehensive evaluation methods of the sandstone reservoir section;

[0030] S4: Fill the target reservoir section with different colors / patterns according to the classification results. Generally, the reservoir quality is displayed from good to poor, following the rule of changing from warm colors to cold colors or from simple patterns to complex patterns.

[0031] S5: Conduct classification and correlation inspection work on the sandstone reservoir section, select the correlation relationships or interpretation conclusions of the parts with abrupt correlation or sharp changes (significantly inconsistent with geological understanding) for correction, and complete the correlation mapping.

[0032] In the above technical solution, the sand body correlation work is a relatively basic research process in the industry. Generally, it follows the principle of "cyclic correlation and hierarchical control", and is carried out step by step from large to small on the basis of well-seismic calibration. The present invention mainly uses the spectral analysis method of logging curves to identify sequence boundaries, and further includes the following steps:

[0033] S11: Selection of sensitive logging curves: Select the curves and parameters mainly affected by the sedimentary environment to achieve the effect that the logging curves show consistent cyclic characteristics with the cyclic changes of the sedimentary environment.

[0034] S12: Reconstruction of INPEFA curves, and application of the inflection point technology of INPEFA curves to identify sequence boundaries of different orders. Well-seismic calibration determines the long-term cycle division scheme.

[0035] S13: Select parameters to perform trapezoidal band-pass filtering on the INPEFA curves, and conduct cycle division on the target well section.

[0036] Furthermore, flatten the sequence boundary, divide the development stages of sand bodies according to core information, logging facies and sedimentary sequence combinations, and laterally connect the sand bodies of the same stage to complete the sand body correlation work.

[0037] The present invention mainly uses the Shiwen software, and according to the intelligent layer connection based on curve similarity and the curve automatic interpolation correlation method, the specific steps are as follows:

[0038] S21: Select the stratigraphic mode to connect the strata → switch to the sand body mode → automatically / manually connect the sand bodies → select one-key curve fitting.

[0039] S22: Edit the layer connection according to sedimentary understanding and actual needs using the edit layer connection line tool.

[0040] Furthermore, for the acquisition of reservoir characteristics, reservoir characteristic parameters include, but are not limited to, reservoir porosity, permeability, pore structure, reservoir space type, clay mineral content, etc.

[0041] Reservoir characteristics are obtained through analysis and testing processes such as core data analysis and mercury injection experiments.

[0042] The weighted average value is selected as a representative for each sandstone reservoir section.

[0043] The classification of sandstone reservoir sections includes the following steps:

[0044] S31: If only considering the maximum influencing factor permeability that affects the quality of the reservoir as the classification standard for sandstone reservoir sections, reference can be made to the division of clastic rock reservoir permeability types in the oil and gas reservoir evaluation method standard (SY-T 6285-2011): Class I low-permeability reservoir - 10×10 -3 μm 2 ≤K<50×10 -3 μm 2 ; Class II extra-low-permeability reservoir - 1×10 -3 μm 2 ≤K<10×10 -3 μm 2 ; Class III ultra-low-permeability reservoir - K<1×10 -3 μm 2 .

[0045] S32: If comprehensive evaluation of sandstone reservoir sections is required for research, multiple factors such as reservoir type (lithofacies, sedimentary facies), reservoir permeability (porosity, permeability), reservoir thickness (sand body thickness, effective thickness), microscopic structure characteristics (pore structure), and reservoir heterogeneity (permeability variation coefficient, breakthrough coefficient) can be comprehensively considered. Multiple reservoir evaluation methods such as neural network method, cluster analysis method, and weight analysis method are adopted to calculate comprehensive evaluation indicators, and the category division of the drainage layer section is carried out according to the results.

[0046] If there are adjustments in step S5, steps S1 to S5 should be re-run until the sand body division and comparison results are more objective and have a higher matching degree with sedimentary understanding and production capacity testing.

[0047] A physical property comparison mapping method for low-permeability sandstone reservoir sections provided by the present invention is further illustrated by taking Block X of BZ Oilfield in the Bohai Sea in the eastern part of China as an example.

[0048] The lower member of the Shahejie Formation in Block X of BZ Oilfield is a sedimentary formation of fan delta facies, and the oil group level is equivalent to the medium-term cycle scale. For the low-permeability sandstone reservoir in this area, the present invention adopts the following technical solutions for physical property comparison mapping of the drainage layer section, as Figure 1 shown:

[0049] Under the stratigraphic framework of isochronous correlation, sand body connection and sand body correlation are carried out according to sedimentary cycles;

[0050] Sand body correlation is carried out based on sedimentary rhythm and sedimentary facies evolution law;

[0051] Reservoir type division and correlation are carried out based on reservoir sedimentary characteristics, physical property characteristics and heterogeneity characteristics within the sand body, etc.;

[0052] The target reservoir is filled with different colors according to the physical property classification results; and

[0053] Reservoir physical property correlation is carried out, and the sand body correlation relationship with abrupt changes in reservoir physical properties is corrected according to the heterogeneity of the sand body.

[0054] In some embodiments, the following steps are included:

[0055] S11: Selection of sensitive logging curves: In the background of clastic sedimentation, curves with large differences in responses between sandstone and mudstone usually have the most obvious influence on the sedimentary environment. In this case, three curves, namely natural gamma (GR), spontaneous potential (SP), and shale volume (VSH), are selected as sensitive logging curves.

[0056] S12: Select wells in the backbone profile perpendicular or parallel to the sediment source direction for INPEFA curve reconstruction. The key features of the INPEFA curve are the curve trend itself and the application of its inflection points in the middle. A positive trend (the curve shape rises from left to right) means a transgressive process with gradually humid climate; a negative trend (the curve shape decreases from right to left) means a regressive process with gradually arid climate; the turning point indicates a sequence boundary or a characteristic boundary within the sequence. Different levels of sequence boundaries are identified according to the inflection points of the INPEFA curve.

[0057] S13: Carry out cycle division and stratigraphic correlation for the target interval: The deep lake facies oil shale and mudstone are developed stably in the mudstone section at the top of the third member of the Shahejie Formation. The logging characteristics show that the resistivity curve presents a "bow-shaped" feature. According to the identification results of the inflection points of the spectral variation curve (INPEFA) and combined with the principle of "cycle correlation, hierarchical control", the oil-bearing intervals in Block X of BZ Oilfield are divided into oil groups ( Figure 2 ).

[0058] S23: Establishment of sand body correlation profile: The strata divided in step S12 are flattened, and comprehensive research is carried out in combination with logging data. The development stages of sand bodies are divided, mainly based on (1) the well section position where the sand body is located and the distance from the top of the sub-layer; (2) the similarity of logging curve characteristics; (3) the change in sand body thickness; (4) If within the resolvable range of seismic reflection isochrones, the sand body boundary can be discriminated by the change points of observability (the seismic resolution in this study area does not support this).

[0059] Establish the sand body correlation profile based on the identified sedimentary stages and possible sand body boundaries. At the same time, use the Shiwen software to perform well-to-well interpolation on the GR curve within the sub-layers to generate the GR curve interpolation correlation profile for verifying well-to-well correlation and checking for cross-strata ([ Figure 3 ).

[0060] S3: Only consider the permeability as the classification standard for sandstone reservoirs and classify the reservoir section.

[0061] S4: Color the sandstone reservoir correlation profiles of different categories.

[0062] S5: Analyze the physical property correlation profile of the sandstone reservoir after coloring. Taking the profile along the sediment source direction as an example, Y1 - Y2 - Y3 is the well profile along the sediment source direction. The well spacing between Y1 and Y2 is 130m, and the well spacing between Y2 and Y3 is 400m. The permeability of wells Y1 and Y3 is significantly one order of magnitude higher than that of Y2 ([ Figure 4A ). According to geological understanding, the three wells are still in the same river channel, but the permeability interpretation of well Y2 shows that it is low throughout the well section, and such a low permeability is difficult to explain the high productivity of well Y2. Therefore, in cooperation with the logging specialty, a suitable logging interpretation scheme was selected to adjust the permeability of well Y2 ([ Figure 4B ). The adjusted sandstone reservoir correlation profile is more consistent with the sedimentary understanding and productivity results.

[0063] Taking the profile perpendicular to the sediment source direction as an example, X1 - X2 - X3 - X4 - X5 is the well profile perpendicular to the sediment source direction. It can be clearly seen from Figure 5 the two main sediment source supply paths, and the physical properties of the main body of the sand body are better than those of the edge of the sand body.

[0064] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements for some of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for making a comprehensive comparison chart of a porous low-permeability sandstone reservoir, characterized in that, Including: Select several profiles parallel to the cross-cut sediment source according to the sedimentary background to obtain the backbone profiles for sand body correlation. Use spectral analysis technology to extract spectral features from the original logging curves, realize the identification of sequence boundaries to avoid the influence of human factors, conduct stratigraphic division and correlation, and then build a sequence stratigraphic framework; Under the above sequence stratigraphic framework, conduct sand body correlation according to sedimentary cycles and sand body development stages; According to the physical properties, microscopic reservoir characteristics and productivity of the target sandstone reservoir section, conduct the division and correlation of sandstone reservoir types for the target sandstone reservoir section; According to the division and correlation of the sandstone reservoir types, fill the target sandstone reservoir section with different colors or patterns, and display the reservoir quality from good to poor according to the rule of changing from warm colors to cold colors or from simple patterns to complex patterns; And Conduct a comparative inspection on the types of the sandstone reservoir sections, select the comparative relationships or explanatory conclusions of the parts with abrupt or sharp changes for correction, and complete the comparative mapping; The identification of the sequence boundary includes: Selection of sensitive logging curves, select the curves and parameters mainly affected by the sedimentary environment to achieve the effect that the logging curves show consistent cyclic characteristics with the cyclic changes of the sedimentary environment; Reconstruction of the spectral change curve, apply the inflection point technology of the spectral change curve to identify sequence boundaries of different orders; Select parameters to perform trapezoidal band-pass filtering on the INPEFA curve and conduct cyclic division on the target well section; and Flatten the sequence boundary, divide the sand body development stages according to core information, logging facies and sedimentary sequence combination, and use the Stoneware software to perform well-to-well interpolation on the GR curve within the small layer. Horizontally connect the sand bodies of the same stage, verify the well-to-well correlation and conduct cross-layer inspection, and then complete the sand body correlation.

2. The method for making a comprehensive comparison map of a porous low-permeability sandstone reservoir according to claim 1, wherein Select natural gamma, spontaneous potential and shale content as sensitive logging curves, and determine the sensitive curves according to the characteristics of each research area.

3. The method for making a comprehensive comparison map of a porous low-permeability sandstone reservoir according to claim 1, characterized in that, Select wells in the backbone profiles perpendicular or parallel to the sediment source direction to reconstruct the INPEFA curve. The curve shape of the INPEFA curve showing a positive trend rising from left to right indicates a transgressive process with gradually humid climate, and the curve shape of the INPEFA curve showing a negative trend decreasing from right to left indicates a regressive process with gradually arid climate. The turning points of the INPEFA curve indicate sequence boundaries or characteristic interfaces within the sequence.

4. The method for making a comprehensive comparison diagram of a porous low-permeability sandstone reservoir according to claim 3, characterized in that, The cyclic division of the target well section includes: According to the INPEFA curve, combined with cyclic correlation and hierarchical control, conduct oil group division on the block oil-bearing layer section.

5. The method for making a comprehensive comparison map of a porous low-permeability sandstone reservoir according to claim 1, characterized in that The physical properties of the target sandstone reservoir section include: reservoir porosity, permeability, pore structure, reservoir space type and clay mineral content. The physical properties of the target sandstone reservoir section are obtained through the analysis of core data and the analysis and testing process of mercury injection experiments.

6. The method for making a comprehensive comparison diagram of a pore-type low-permeability sandstone reservoir according to claim 5, characterized in that, The establishment of the sand body correlation profile includes: Flatten the divided strata, combine logging data, and divide the sand body development stages according to the well section position where the sand body is located, the distance from the top of the small layer, the similarity of logging curve characteristics, the change of sand body thickness, and the sand body boundary within the resolvable range of seismic reflection event.

7. The method for making a comprehensive comparison map of a porous low-permeability sandstone reservoir according to claim 6, characterized in that, The classification of the sandstone reservoir section includes: If only considering the maximum influencing factor permeability that affects the reservoir quality as the classification criterion for sandstone reservoir sections, referring to the classification of clastic reservoir permeability types in the oil and gas reservoir evaluation method standard: Class I low-permeability reservoir - 10×10 -3 μm 2 ≤K<50×10 -3 μm 2 ; Class II extra-low-permeability reservoir - 1×10 -3 μm 2 ≤K<10×10 -3 μm 2 ; Class III ultra-low-permeability reservoir - K<1×10 -3 μm 2 ; If it is necessary to conduct a comprehensive evaluation of the sandstone reservoir section, comprehensively consider the reservoir type, storage and seepage capacity, reservoir thickness, microscopic structure characteristics and reservoir heterogeneity, adopt the neural network method, cluster analysis method and weight analysis method to calculate the comprehensive evaluation index, and classify the diversion layer section according to the results.

8. The method for making a comprehensive comparison map of a porous low-permeability sandstone reservoir according to claim 1, characterized in that It also includes classifying the reservoir section according to the sandstone reservoir classification standard for different research needs, and coloring the contrast profiles of different types of sandstone reservoirs.

9. The method for making a comprehensive comparison diagram of a porous low-permeability sandstone reservoir according to claim 8, characterized in that, Analyze the physical property contrast profile of the colored sandstone reservoir. According to the contrast results, quickly clarify the change trend of the reservoir quality in the sand body and analyze and process the abnormal points of the physical property changes, and simply and intuitively lock the distribution area of the sweet spot reservoir.

Images