A structural interpretation method for fault-block oil and gas fields

Abstract

The present invention relates to a structural interpretation method for fault-block oil and gas fields, comprising the following steps: collecting seismic data and logging data of the study area, and performing preliminary fault interpretation and preliminary structural interpretation; on the basis of the preliminary fault interpretation, interpreting the backbone profiles to form an initial framework; the backbone profiles include the profiles corresponding to the main logging lines passing through wells and the connecting well lines; on the basis of the initial framework, selecting a profile every N main logging line distances and selecting a profile every M connecting line distances, interpreting these profiles to obtain an initial fault interpretation model; on the basis of the initial fault interpretation model, gradually interpolating more profiles for interpretation to obtain a final fault interpretation model; establishing a structural model according to the preliminary structural interpretation and the final fault interpretation model; and verifying according to the seismic data and logging data. The interpretation method of the present invention can improve the interpretation accuracy by gradually interpolating profiles.

Description

Technical Field

[0001] The present invention relates to the technical field of geophysical exploration, and particularly to a structural interpretation method for complex fault blocks in fault-block oil and gas fields. Background Art

[0002] A fault refers to a structure formed by the displacement of a rock stratum or rock mass under the action of stress during crustal movement. Multiple faults form a fracture zone. Faults are widely developed in the earth's crust and are one of the most important structures in the crust. In the oil and gas-bearing basins in China, most are fault-depressed basins, and faults control the formation process of fault-depressed basins. Faults cut strata to form fault blocks. After the fault blocks contain oil and gas, fault-block oil and gas reservoirs (i.e., fault-block oil and gas fields) can be formed. Fault-block oil and gas reservoirs often exist attached to faults. The nature, size, and position of faults control the position, boundary, and scale of the formed fault-block oil and gas reservoirs. The more complex the intersection relationship between different faults, the more complex the spatial relationship of the controlled fault-block oil and gas reservoirs, and the more complex the oil-water relationship between fault blocks, which directly leads to a decrease in the understanding of the oil reservoir, severely restricts the development and utilization of the oil reservoir, and affects the economic and social benefits of the oil field.

[0003] During the exploration and development of fault-block oil and gas fields, structural interpretation, that is, the interpretation of fault blocks, the key is the accuracy and reliability of fracture (spatial relationship of fault blocks) interpretation. The structural interpretation method plays a crucial role.

[0004] Currently, there are many structural interpretation methods. With the continuous progress and development of computer technology and onshore oil and gas exploration theories and methods, the identification and interpretation technologies of faults are also constantly advancing. Conventional structural interpretation methods such as micro-fracture identification, etc., mainly use main survey lines for interpretation and use connecting survey lines to close horizons, etc. In areas with simple structures and relatively good data quality, high accuracy can be achieved, and their applicability is relatively strong. Their defect is that they mainly use main survey lines, and less use connecting survey lines (i.e., connecting lines, which are survey lines perpendicular to the main survey lines) and slice data for interpretation, which will cause certain differences in the strike and combination of faults; in complex structural areas, the action of multiple stresses causes the intersection relationship of multiple-stage faults to be complex, the multi-solution property of fault combination in structural interpretation is strong, it is difficult to accurately determine the spatial relationship between fault blocks, and the uncertainty of the relationship between fault blocks causes difficulties for the design of new well positions and the understanding of oil reservoirs, etc., affecting the exploration and development effects. The so-called three-dimensional interpretation developed in the past two years based on conventional interpretation methods only increases the visualization application of slices and interpretation, still mainly uses main survey lines and supplemented by connecting lines, mainly uses horizons and supplemented by faults, and there is no essential difference compared with conventional interpretation.

[0005] For example, a conventional interpretation method is as follows:

[0006] First, interpret faults and horizons on a certain main seismic line profile, then interpret faults and horizons on the next main seismic line at a certain interval, and continue in this order until the faults and horizons on the main seismic lines in the entire seismic work area are completely interpreted. Connect the breakpoints of the main seismic lines on the plane to form the planar strike of the faults. This structural interpretation method is actually a two-dimensional interpretation of three-dimensional seismic data, which can achieve relatively high accuracy in areas with simple structures and relatively good data quality, and has strong applicability. However, in areas with complex structures, for example, there is only one fault on Profile A, and when reaching the next interval Profile B, multiple faults are interpreted on the profile. It is not clear which fault on Profile B corresponds to the one fault on Profile A, resulting in multiple solutions for the planar combination of faults. Summary of the Invention

[0007] The purpose of this application is to provide a structural interpretation method for fault-block oil and gas fields to solve the problem of low interpretation accuracy of existing methods.

[0008] To achieve the above purpose, the present invention proposes a structural interpretation method for fault-block oil and gas fields, including the following steps:

[0009] Collect seismic data and logging data in the study area, and conduct preliminary fault interpretation and preliminary structural interpretation;

[0010] On the basis of the preliminary fault interpretation, interpret the backbone profiles to form an initial framework; the backbone profiles include the main seismic lines passing through wells and the profiles corresponding to the connecting well lines;

[0011] On the basis of the initial framework, select a profile every N main seismic line distances and a profile every M connecting line distances, interpret these profiles, and obtain an initial fault interpretation model; N and M are powers of 2 and less than or equal to 128;

[0012] On the basis of the initial fault interpretation model, gradually and evenly interpolate more profiles for interpretation to obtain a final fault interpretation model;

[0013] According to the preliminary structural interpretation and the final fault interpretation model, establish a structural model;

[0014] Verify according to the seismic data and logging data.

[0015] Furthermore, when interpreting the backbone profiles, fault interactive interpretation is also carried out using the main seismic lines, connecting lines, and horizontal slices.

[0016] Furthermore, the preliminary fault interpretation includes: establishing a seismic database based on the seismic data, further generating time slices and coherence volume slices, so as to determine the identification of large faults of Grade I and II and the strike of the fault system in this area.

[0017] Further, the preliminary structure interpretation includes: making seismic synthetic records using logging data and seismic data, calibrating fault breaks and horizons based on the seismic synthetic records, and establishing the correspondence between drilling stratification and seismic data.

[0018] Further, the verification based on seismic data and logging data includes: verifying the fault combination relationship according to time slices and coherence body slices; verifying the structure interpretation results according to the reservoir relationships of each sand group in the drilled wells, and adjusting the inconsistent fault interpretations.

[0019] The beneficial effects of the present invention are as follows: The existing methods are interpreted in a fixed order, and the interpretation is mainly affected by the previous section. The planar combined faults are prone to the problem of multiple solutions, resulting in low accuracy. Different from the prior art, the present invention first selects some sections to form a larger grid, and then continuously interpolates more sections to gradually form a smaller grid. The interpretation method of the present invention is to gradually interpolate sections, and each section can be interpreted by referring to multiple sections on both sides, avoiding the problem that the errors generated during sequential interpretation will continue, thereby avoiding multiple solutions and improving the interpretation accuracy. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 is a schematic flowchart of an embodiment of the present invention;

[0021] Figure 2 is a seismic profile of the study area;

[0022] Figure 3 is a time slice map of the study area;

[0023] Figure 4 is a coherence body slice map of the study area;

[0024] Figure 5 is a well-seismic calibration profile of a certain well in the study area;

[0025] Figure 6 is a diagram showing the correspondence between the fault strike and the fault dip of the profile in a certain fault block area of the study area;

[0026] Figure 7 a is a schematic diagram of a conventional interpretation method 1;

[0027] Figure 7 b is a schematic diagram of a conventional interpretation method 2;

[0028] Figure 7 c is a schematic diagram of the interpretation method of the present invention;

[0029] Figure 8 is a structure map of a certain fault block area in the study area. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0030] As Figure 1As shown in the figure, the present invention includes the following steps:

[0031] 1) Select a certain fault depression basin as the research area, and load the post-stack 3D seismic data and logging data in a computer workstation to construct a seismic database. The logging data includes: well coordinates, logging curves, geological stratification, well deviation data, hydrocarbon shows, and production data (including oil testing, oil production results, etc.). The present invention utilizes interpretation software such as Geoframe and Landmark.

[0032] 2) Generate a seismic data volume from the seismic data, conduct preliminary analysis and processing on the seismic data volume, generate time slices and coherence slices, and understand the maximum and minimum amplitudes of seismic waves, as well as the frequency band width and dominant frequency characteristics of the seismic data. As Figure 2 is the seismic profile of the research area.

[0033] 3) According to the regional tectonic background of the research area, the depth variation of the target layer, and the complexity of faults, select 10 - 12 horizontal time slices and coherence slices of shallow, medium, and deep layers (for example, if according to the regional tectonic background, the main fault-developed positions are in the middle layer, then select more slices in the middle layer). As Figure 3 , Figure 4 shown, first observe and judge the large faults of grade I and II and the strike of the fault system in this area. The positions where the waveforms are offset and disturbed on the time slices are the locations of faults, and the line connected by multiple waveform disturbance points is the fault strike; in the coherence slices, the light color indicates less coherence, the dark color indicates greater coherence, and the dark-colored connection line is the fault strike.

[0034] 4) Use the logging data and seismic data to make seismic synthetic records. As Figure 5 shown, according to the seismic synthetic records, calibrate the fault points and horizons, establish the correspondence between drilling stratification and seismic data, and prepare for subsequent interpretation.

[0035] The above steps 1) - 4) all belong to the preliminary preparation work, the purpose of which is to conduct a preliminary analysis of the geological structure of the research area and lay a foundation for the subsequent seismic interpretation work. Steps 1) - 3) are used for preliminary fault interpretation, and step 4) is used for preliminary structural interpretation.

[0036] 5) Interpret the faults of the backbone profiles such as the main logging line and the well-connected line, and conduct interactive fault interpretation through the main logging line, connection line, and horizontal slices, so as to interpret the faults of the backbone profiles and form an initial framework, that is, the initial fault interpretation model.

[0037] As Figure 6As shown, the AA` section is the main survey line section. On this section, the F1 and F2 faults dip eastward. At the same horizon, the connecting line BB` passing through the F1 fault shows that the F1 fault dips southward. Combining the horizontal slice and the AA` and BB` sections, it can be known that the planar strike of the F1 fault is as shown by F1 on the plan. Similarly, the planar strike of the F2 fault can be judged based on the horizontal slice and the AA` and CC` sections. According to the comparison of the projection points of the main survey line, connecting survey line, and horizontal slice, judge whether the fault position and fault occurrence are reasonable, modify and close the unreasonable faults, and establish the initial framework for the fault interpretation of the backbone section.

[0038] 6) According to the principle of "first interpreting the faults with large throw, then interpreting the faults with small throw, first interpreting the faults that are easily recognized from seismic data, then interpreting the difficult-to-recognize faults, first interpreting the areas with many drilled wells, and then interpreting the areas without drilled wells", select equally spaced main survey lines and connecting survey lines according to the complexity of the faults (generally, the survey line interval is preferably a power of 2 for easy uniform interpolation), and establish an initial fault interpretation model.

[0039] For example, select a section at intervals of 128 main survey lines and interpret this section; select a section at intervals of 128 connecting survey lines and interpret this section, and finally form an initial fault interpretation model of 128×128.

[0040] As another implementation method, 128×64 can also be selected, that is, select a section for every 128 main survey lines and select a section at intervals of 64 connecting survey lines.

[0041] 7) Based on the initial fault interpretation model, gradually and uniformly interpolate the sections, densify the grid, and conduct interpretation. For example, first form a 32×32 interpretation grid on the basis of 128×128, then form 16×16, 8×8, and 4×4 interpretation grids to form the final fault interpretation model. The interpretation density of the final fault interpretation model depends on the interpretation task, trace interval, and CDP interval.

[0042] Steps 6)-Step 7) are the main innovations of the present invention. Conventional interpretation methods (such as Figure 7 As shown in a and 7b, in the order of the main survey lines L1, L2, L3 and the connecting lines C1, C2, C3 for interpretation, there is one break point on the main survey line L1 and two break points on the main survey lines L2 and L3. The planar combination of the faults has Figure 7 a and Figure 7 b shown two fault combination methods, resulting in multiple solutions. According to the interpretation method of the present invention, Figure 7 As shown in c, when forming the initial fault interpretation model during interpretation, an initial grid is formed through the interpretation of the main survey lines L1, L2 and the connecting lines C1, C2. There is a fault point in the part of the connecting line C1 on the left side of the main survey line L1, and the planar position of this break point is the same as Figure 7The fault combination shown in b does not conform; Step 7) Interpolate and interpret based on the initial interpretation model as Figure 7 shown in c. Interpolate and interpret the main survey line L3 and the connecting line C3. It can be predicted that there are two faults in the profile of the main survey line L3. Similarly, it is predicted that there is one fault in the connecting line C3. If there are errors between the actual interpretation and the prediction, the fault plane combination should be adjusted according to the actual interpretation. On the contrary, if the actual interpretation and the prediction are consistent, it proves that the fault plane combination is correct. Correct the fault plane position according to the breakpoint positions of the main survey line L3 and the connecting line C3, so that the fault plane position and the intersection relationship are the only solution, and finally form the final interpretation model of the fault. The key to the above steps does not refer to the denser selected profiles, but changes the conventional method of interpreting along a certain order to the method of "interpolating" profiles. Since the "interpolated" profiles can be interpreted by referring to the profiles on both sides, the problem of multiple solutions is avoided and the interpretation accuracy is improved.

[0043] 8) Establish a structural model: Combine the calibrated synthetic seismogram in Step 4), and interpret the horizons (sand group and oil group horizons) by densifying them in units of fault blocks formed by the cutting of faults and faults, ensuring the correct relationship between fault blocks.

[0044] 9) Apply the time slices and coherence slices generated in Step 3) to verify the fault combination relationship. Verify the structural interpretation results according to the reservoir relationships of each sand group in the drilled wells, and adjust the inconsistent fault interpretations. Use the velocity field to perform variable velocity mapping to obtain a hierarchical evaluation map that is consistent with the existing reservoir understanding to guide the next well location design. As Figure 8 shown, finally obtain a hierarchical evaluation map that is consistent with the existing reservoir to guide the next well placement.

Claims

1. A structural interpretation method for fault-block oil and gas fields, characterized in that: The following steps are involved: Collect seismic data and well logging data in the study area and conduct preliminary fault interpretation and preliminary structural interpretation; Based on the preliminary fault interpretation, the backbone sections are interpreted to form an initial framework; the backbone sections include sections corresponding to the main survey line through the well and the connecting well line; On the basis of the initial grid, a section is selected every N main survey lines and every M tie lines, and these sections are interpreted to obtain the initial interpretation model of the fault; N and M are multiple powers of 2 and less than or equal to 128; On the basis of the initial interpretation model of the fault, more sections are gradually and evenly interpolated to interpret the fault and obtain the final interpretation model; Establishing a structural model based on the preliminary structural interpretation and the final interpretation model of the fault; Verification is carried out based on seismic data and well logging data.

2. A structural interpretation method for fault-block oil and gas fields according to claim 1, characterized in that: When interpreting the backbone profile, the main survey lines, connecting lines and horizontal slices are also used for interactive interpretation of faults.

3. The structural interpretation method for fault-block oil and gas fields according to claim 1, characterized in that: Preliminary fault interpretation includes: establishing a seismic database based on seismic data, further generating time slices and coherence volume slices, so as to determine the direction of major faults of level I and II and the fault system in this area.

4. The structural interpretation method for fault-block oil and gas fields according to claim 1, characterized in that: The preliminary structural interpretation includes: using well logging data and seismic data to produce seismic composite records, calibrating breakpoints and layers based on the seismic composite records, and establishing the corresponding relationship between drilling layers and seismic data.

5. The structural interpretation method for fault-block oil and gas fields according to claim 3, characterized in that: Verification based on seismic and logging data includes: verifying the fault combination relationship based on time slices and coherence volume slices; verifying the structural interpretation results based on the oil reservoir relationship of each sand group that has been drilled, and adjusting the inconsistent fault interpretations.

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