A method for seismic interpretation of low-order faults

Abstract

The present application relates to a kind of low-order fault seismic interpretation method.Seismic interpretation method includes: obtaining the time-depth conversion relationship of target area;According to the time-depth conversion relationship, the seismic profile of target area is converted;According to more than three small breakpoint information or two more fault trace lines on the seismic profile not on a straight line, low-order fault is constrained seismic interpretation;The mode of small breakpoint information or fault trace line of target area is B mode or A+B mode, A mode is: if there is well drilling small breakpoint in target area, well drilling small breakpoint is corresponded with seismic phase one by one;B mode is: in seismic interpretation software, change the polarity of sandstone to corresponding negative polarity, and reduce the intensity of seismic polarity, obtain small breakpoint information or fault trace line.The present application only needs to find out small breakpoint or fault trace line by changing software setting in interpretation process, and low-order fault can be accurately interpreted, which is simple and reliable.

Description

TECHNICAL FIELD

[0001] The present application relates to a low-order fault seismic interpretation method, belonging to the technical field of oil and gas exploration and development. BACKGROUND

[0002] The exploration and development of domestic oilfields have mostly entered the middle and late stages, and more accurate and more detailed structural research results are needed to accurately interpret faults. In the current exploration and development activities, there are mainly three methods for interpreting faults using seismic information:

[0003] 1. Seismic profile manual interpretation method: identify faults according to the faulting, number increase and decrease, shape mutation, splitting, merging, twisting, strong phase conversion of seismic reflection wave reflection axis, and the appearance of diffraction wave and section wave;

[0004] 2. Seismic attribute assisted identification method: perform seismic coherence analysis, seismic data frequency division, seismic attribute extraction, etc., and use three-dimensional closure to assist in identifying low-order faults;

[0005] 3. Use certain algorithm to identify faults: such as ant tracking, etc., extract fault information, then manually combine and correct to complete fault interpretation.

[0006] In the above several fault interpretation methods, the limit of the fault throw that can be identified and interpreted is greater than 20 meters. For fault planes with a fault throw less than 20 meters, the manual interpretation of the seismic profile method has great difficulty in identifying, has many interference factors, and cannot be completed manually. The seismic attribute assisted identification method is greatly affected by the opened time window, technical ability, noise wave, etc., and the fault signal with a fault throw less than 20 meters is easily covered or missed. The ant tracking method cannot distinguish and identify the phenomena of seismic phase bending and folding that often occur in faults with a fault throw less than 20 meters. Therefore, faults with a fault throw less than 20 meters cannot be interpreted and described by relying on the current conventional seismic interpretation technology due to the fuzzy, intermittent and multi-solution factor interference of the fault characteristics on the seismic profile.

[0007] Faults with a fault throw of about 10 meters are low-order faults. Low-order faults can play a good lateral sealing role for thin reservoirs and control the enrichment of remaining oil. Therefore, the seismic interpretation technology of low-order faults is a very important scientific research achievement in oilfield structural research, which is of great significance.

[0008] For this purpose, some people have proposed technical solutions for interpreting low-order faults, for example: the Chinese patent application for invention with the application publication number CN109490959A discloses a method for identifying low-order faults in complex structure areas, which obtains high-quality and high-signal-to-noise ratio seismic information to provide intuitive and reliable basis and relevant geological information for the next step of data interpretation; LandMark seismic comprehensive interpretation software is applied to load data, make synthetic seismograms and complete three-dimensional seismic data interpretation to display seismic sections; low-order fault identification and description are performed according to the seismic identification marks of low-order faults.

[0009] Although the above application file identifies low-order faults according to the seismic identification marks of low-order faults, the seismic identification marks of low-order faults are the results obtained through a large number of application researches: the performance rules of the same low-order fault under different seismic main frequencies need to be repeatedly compared and studied to correctly identify the low-order fault, so the overall process of the above seismic identification method of low-order faults is relatively complex. SUMMARY

[0010] The purpose of the present application is to provide a seismic interpretation method for low-order faults to solve the problem of complex interpretation process of existing low-order faults.

[0011] To achieve the above purpose, the present application proposes a technical scheme of a seismic interpretation method for low-order faults, which includes the following steps:

[0012] 1) Obtain the time-depth conversion relationship of the target area;

[0013] 2) Perform time-depth conversion on the seismic section of the target area according to the time-depth conversion relationship;

[0014] 3) According to more than three small breakpoint information or more than two fault trace lines on the seismic section that are not on a straight line, simulate a fault surface using seismic interpretation software, and perform constrained seismic interpretation on the low-order fault in the order of near and far, inside and outside;

[0015] Among them, the way to obtain small breakpoint information or fault trace line of the target area is B way or A+B way,

[0016] The A way is: if a well encounters a small breakpoint in the target area, the well encounters the small breakpoint and the seismic phase are one-to-one corresponding;

[0017] The B way is: in the seismic interpretation software, change the seismic polarity to the negative polarity corresponding to the sandstone and reduce the seismic polarity strength to highlight the fault trace line of the low-order fault corresponding to the small breakpoint to obtain the small breakpoint information or the fault trace line.

[0018] The beneficial effects of the technical scheme of the low-order fault seismic interpretation method of the application are as follows: the time-depth conversion of the target area is performed on the seismic profile (or seismic body) of the target area by the time-depth conversion relationship of the target area, the one-to-one correspondence between the small breakpoints and the seismic phases is accurately established under the condition that the small breakpoint information has been obtained, and the position of the small breakpoint in the seismic profile is determined; then, according to the principle that the low-order fault is more easily identified under the condition of low seismic polarity intensity in the negative polarity phase, and the small breakpoint at the low-order fault changes when the positive polarity phase is converted into the negative polarity phase, the seismic polarity is changed into the negative polarity and the seismic polarity intensity is reduced, the fault trace line of the low-order fault corresponding to the small breakpoint is highlighted, and more small breakpoints are displayed in the negative polarity phase; finally, the seismic interpretation of the low-order fault is performed according to the more small breakpoints or the highlighted fault trace line, in the condition that there is no small breakpoint information, the seismic polarity is directly changed into the negative polarity and the seismic polarity intensity is reduced, the fault trace line of the low-order fault corresponding to the small breakpoint is highlighted, and the small breakpoint is displayed in the negative polarity phase; finally, the seismic interpretation of the low-order fault is performed according to the small breakpoint or the highlighted fault trace line. The seismic phase is changed by the characteristics of the sandstone in the target area, richer information is used for seismic interpretation, the interpretation accuracy of the low-order fault is improved, and only the small breakpoint or the fault trace line needs to be found by changing the software setting in the interpretation process, so that the overall interpretation process is simple and reliable.

[0019] Further, in order to more accurately obtain the time-depth conversion relationship of the target area and improve the accuracy of time-depth conversion, a well in the target area is selected, a synthetic record of the well is made according to the electric logging acoustic wave data of the well, the time-depth conversion relationship of the well is obtained, and the time-depth conversion relationship of the well is used as the time-depth conversion relationship of the target area to perform time-depth conversion on the seismic profile of the target area.

[0020] Further, in order to more accurately interpret the low-order fault, after a fault surface is simulated in the step 3), the low-order fault is interpreted by using the fault surface indication guidance, combining the seismic phase change and the seismic polarity change.

[0021] Further, in order to more accurately interpret the low-order fault, after a fault surface is simulated in the step 3), the low-order fault is interpreted by using the fault surface indication guidance, combining the seismic phase change and the seismic polarity change.

[0022] Further, affected by low-order faults, the polarity of the sandstone is changed to negative polarity, if the negative polarity phase disappears, twists, polarity strength, width changes, combined with the obtained fault plane indicating position, a new low-order fault is determined, and then small breakpoint information is obtained.

[0023] Further, in order to improve the accuracy of low-order fault interpretation, the display information of the positive polarity of the seismic polarity is used as a reference for the seismic interpretation of the low-order fault.

[0024] Further, in order to facilitate the interpretation of the low-order fault, the seismic interpretation software is Geoframe seismic comprehensive interpretation software. BRIEF DESCRIPTION OF DRAWINGS

[0025] Figure 1 is a flowchart of the first embodiment of the seismic interpretation method of the low-order fault of the present application;

[0026] Figure 2 is a composite record diagram of a certain representative well in a certain area of the target area of the present application;

[0027] Figure 3 is a time-depth conversion relationship formula diagram of a certain area of the target area of the present application;

[0028] Figure 4 is a depth domain seismic profile diagram of the normal polarity setting (before optimization) of the present application;

[0029] Figure 5 is a depth domain seismic profile diagram of the seismic polarity being negative polarity and the seismic polarity strength being reduced (after optimization) of the present application. DETAILED DESCRIPTION

[0030] The first embodiment of the seismic interpretation method of the low-order fault is as follows:

[0031] The main idea of the seismic interpretation method of the low-order fault proposed in this embodiment is that drilling is carried out in the target area, the small breakpoint drilled by the well is accurately corresponded to the seismic phase (i.e. the position of the small breakpoint drilled by the well in the seismic body) through the well drilling small breakpoint and the well logging data of the electric logging acoustic wave data to make the well logging composite record, the seismic polarity is set to negative polarity and the seismic polarity strength is reduced in the seismic interpretation software to clearly display the fault trace line position of the low-order fault in the local area, to determine the small breakpoint position of the same low-order fault which is not in a straight line or the position of two or more fault trace lines, to simulate the approximate simulation fault plane of the fault by using the seismic interpretation software, to use the indicating position constraint of the simulation fault plane projection, to correct the position of the simulation fault plane in the order of near and far, inside and outside, combined with the seismic phase change of the indicating position, to complete the seismic interpretation of the low-order fault.

[0032] The main principle of the present application is that seismic phase has two existing forms of positive polarity and negative polarity, the two polarities represent the relative density of corresponding lithology respectively, the relative density high corresponds to positive polarity, the relative density low corresponds to negative polarity, the large difference in relative density corresponds to the large intensity of polarity, the existing interpretation process is carried out under positive polarity, the seismic positive polarity corresponds to the stable distribution of mudstone or shale formation, and therefore more information of low-order faults cannot be identified, therefore, under the setting of negative polarity of seismic phase polarity, at the same time, the intensity of seismic polarity is moderately reduced, combined with the uneven development characteristics of low-order faults: some low-order faults have large fault throw in the middle section and gradually decrease towards both ends, some low-order faults have large fault throw at one end and gradually decrease towards the other end, some low-order faults also affect local strata deposition, thereby making the polarity intensity and amplitude of the upper and lower plates of low-order faults different, and highlighting the fault track of low-order faults.

[0033] The seismic interpretation method of low-order faults of the present application will be described in detail below taking a certain area as an example.

[0034] The seismic interpretation method of low-order faults, as shown in Figure 1 , includes the following steps:

[0035] 1) Drilling in a certain area to find out the small points drilled by the well; and selecting the electric logging acoustic data of a certain well to make a synthetic record to obtain the time-depth conversion relationship between the strata drilled by the well and the seismic profile beside the well.

[0036] Specifically, after drilling in a certain area, the small points drilled by the well are found out through well correlation layering (i.e. fine correlation between wells and wells);

[0037] At the same time, a representative well is selected from the drilled wells in the certain area, and the electric logging acoustic data of the well is input into the seismic interpretation software (the seismic interpretation software is Geoframe seismic comprehensive interpretation software, which has the functions of data loading, making synthetic seismic record, three-dimensional data interpretation, time-depth conversion and graph construction) to obtain the single-well synthetic record of the well as shown in Figure 2 ;

[0038] The single-well synthetic record is moved and compressed to establish a one-to-one correspondence between the single-well synthetic record and the seismic phase beside the well (the seismic phase beside the well is the seismic phase information in the seismic profile beside the well, and the seismic profile beside the well here is a time profile) to obtain the time-depth conversion relationship as shown in Figure 3 ;

[0039] The time-depth conversion relationship is y=0.0002393470x 2+0.8734429115x+39.7639944886; x represents time, unit: ms, y represents depth, unit: m. The essence of the time-depth conversion relationship is the average velocity of the formation, that is, the ratio of the total thickness of the seismic wave vertically through each layer above the interface to the total propagation time.

[0040] 2) Take the time-depth conversion relationship of a representative well obtained in step 1) as the time-depth conversion relationship of all wells in the region, and perform time-depth conversion on all wells in the region.

[0041] Time-depth conversion is the process of converting seismic data from depth domain to time domain, that is, converting the depth domain seismic profile of a certain region to the time domain seismic profile.

[0042] 3) After time-depth conversion of all wells in step 2), combine the small faults drilled by the wells in step 1), and accurately correspond the small faults drilled by the wells to the seismic phase in the time domain seismic profile through fine well-seismic relationship calibration, to obtain the position of the small faults drilled by the wells in the seismic body (i.e. A method), and establish a seismic interpretation database of a certain region.

[0043] 4) After the establishment of the seismic interpretation database, perform structural seismic interpretation on a certain region.

[0044] a. Through the guidance of the indication of the position of the small faults drilled by the wells in the seismic body in the seismic interpretation database, observe the changes of the seismic phase near the small fault position, and optimize the seismic polarity and seismic intensity in the seismic interpretation software: set the seismic polarity to the negative polarity phase corresponding to the sandstone (under the negative polarity phase, the sandstone on both sides of the low-order fault has changes in physical properties and thickness, thereby causing changes in the strength and width of the seismic phase, which is conducive to the identification of low-order faults), and reduce the seismic polarity intensity (which can be more conducive to the appearance of seismic high-frequency components, facilitating the identification and interpretation of low-order faults, and being conducive to determining the accurate position of low-order faults on the seismic profile); when changing the seismic polarity to negative polarity, use the display information of positive polarity as a reference to assist in seismic interpretation;

[0045] After that, the small faults present a phenomenon of merging of the double-phase groups upward, clearly showing the fault trace of the low-order fault, and due to the early low-order fault controlling sedimentation and sand, the negative polarity phase above and below the small fault has changes in polarity strength, width, and polarity, and more small faults in the low-order fault are found (i.e. B method).

[0046] Compare the seismic profile after optimization of the seismic polarity and seismic intensity as shown in Figure 5 with the seismic profile before optimization of the seismic polarity and seismic intensity as shown in Figure 4 , it is found that the low-order fault position on the seismic profile is highlighted and enlarged after optimization, and the fault trace of the low-order fault on the seismic profile can be clearly determined.

[0047] b. Interpretation of low-order faults by finding more small breakpoints or fault trace lines.

[0048] The process of interpreting low-order faults according to small breakpoints is as follows: according to the principle of simulating a plane by three points not on a straight line, position combination is performed to fit the spatial distribution pattern of the simulated fault plane.

[0049] The specific means are as follows: through the calculation fitting function in the seismic interpretation software, a simulated fault plane is formed in advance by three points not on a straight line, the extension projection line of the simulated fault plane is taken as a guide to obtain the approximate three-dimensional spatial distribution of the low-order fault, the development position of the low-order fault is indicated by the simulated fault plane constraint, the position of the simulated fault plane is gradually expanded from the near to the far and from the inside to the outside, the changes of the seismic events near the projection position of the simulated fault plane on each profile, such as bifurcation, distortion, misplacement and strength change, are combined to constantly correct the position of the simulated fault plane, the three-dimensional spatial distribution pattern of the low-order fault in a certain area is interpreted, the structural map of the certain area is obtained, the three-dimensional spatial closure tracking interpretation is performed in combination with the previous data and dynamic and static data, and finally the planar structural distribution map of the target layer system in the certain area is drawn.

[0050] The process of interpreting low-order faults according to fault trace lines is as follows: a simulated fault plane is calculated by two clear fault trace lines of low-order faults, position combination is performed according to the principle of determining a plane by two straight lines to fit the spatial distribution pattern of the simulated fault plane.

[0051] The specific means are as follows: through the calculation fitting function in the seismic interpretation software, a simulated fault plane is formed in advance by two clear fault trace lines of low-order faults, the extension projection line of the simulated fault plane is taken as a guide to obtain the approximate three-dimensional spatial distribution of the low-order fault, the development position of the low-order fault is indicated by the simulated fault plane constraint, the position of the simulated fault plane is gradually expanded from the near to the far and from the inside to the outside, the changes of the seismic events near the projection position of the simulated fault plane on each profile, such as bifurcation, distortion, misplacement and strength change, are combined to constantly correct the position of the simulated fault plane, the three-dimensional spatial distribution pattern of the low-order fault in a certain area is interpreted, the structural map of the certain area is obtained, the three-dimensional spatial closure tracking interpretation is performed in combination with the previous data and dynamic and static data, and finally the planar structural distribution map of the target layer system in the certain area is drawn.

[0052] The process of interpreting faults by breakpoints and fault trace lines is prior art, and the present application does not make too many introductions.

[0053] The present application finds more abundant small breakpoints and fault track lines by combining A mode and B mode, such as three small breakpoints not in a straight line, one of which is obtained by well drilling, and then the small breakpoint is corresponded with the seismic phase, and the other two small breakpoints are obtained by changing the seismic polarity to the negative polarity corresponding to the sandstone and reducing the seismic polarity intensity, so that the low-order fault can be accurately interpreted.

[0054] The present application improves the corresponding accuracy between well and seismic by establishing the time-depth relationship of the target area, accurately positions the well drilling low-order breakpoint (i.e. small breakpoint) to the corresponding position of the seismic body, realizes the accurate correspondence of logging data, seismic data and production dynamic data in three-dimensional space, solves the problem of well-seismic correspondence difference caused by the change of seismic velocity field (i.e. time-depth relationship), and on this basis, uses the high accuracy of well drilling breakpoint position, the corresponding seismic phase can be continuously tracked and analyzed, and the newly discovered low-order fault which controls the sandstone and has a great influence on oil field exploration has the characteristics that the corresponding sandstone seismic phase changes on the hanging wall and foot wall of the fault, uses more than three breakpoint positions to calculate and simulate the fault surface, relies on the indication and guidance of the simulated fault surface, combines the specific changes of the seismic phase near the guided position, restricts the interpretation of low-order small faults, improves the interpretation and identification accuracy of low-order faults, reduces the rolling exploration and evaluation risk of low-order fault structure oil and gas traps, and realizes efficient and low-cost rolling development.

[0055] Embodiment two of the seismic interpretation method of low-order fault

[0056] The difference between the seismic interpretation method of low-order fault proposed in the present embodiment and the seismic interpretation method of low-order fault proposed in embodiment one is that in embodiment one, there is part of small breakpoint information obtained by well drilling, and the present embodiment is aimed at the seismic work area without well drilling small breakpoint, so after the time-depth conversion of the target area, the seismic interpretation method of low-order fault in the present embodiment directly uses B mode to find small breakpoint information or fault track line: sets the seismic polarity to negative polarity and reduces the seismic polarity intensity in the seismic interpretation software to clearly display the fault track line position of low-order fault in the local area, and clearly shows the small breakpoint position of the same low-order fault not in a straight line or the position of more than two fault track lines, so as to perform seismic interpretation of low-order fault.

[0057] Specifically, the seismic interpretation method of low-order fault comprises the following steps:

[0058] 1) Obtain the time-depth conversion relationship of the target area;

[0059] 2) Perform time-depth conversion on the target area;

[0060] 3) Optimizing the seismic polarity and the seismic intensity in the seismic interpretation software: setting the seismic polarity as the negative polarity phase corresponding to the sandstone and reducing the seismic polarity intensity;

[0061] 4) Finding out the fault trace of the small fault or the low-order fault;

[0062] 5) Carrying out the seismic interpretation of the low-order fault according to more than three small faults or more than two fault traces which are not in a straight line.

[0063] The low-order fault development has the unbalanced characteristics: some low-order faults have large fault throw in the middle section and gradually become small towards the two ends, some low-order faults have large fault throw in one end and gradually become small towards the other end, and some low-order faults also affect the local stratum deposition, thereby making the seismic phase polarity intensity and amplitude width of the hanging wall and the footwall of the low-order fault different, highlighting the position of the fault trace indicating the low-order fault.

[0064] The specific implementation process of each step of the seismic interpretation method of the low-order fault has been introduced in the seismic interpretation method of the low-order fault in the above embodiment one, and will not be repeated here.

[0065] Embodiment three of the seismic interpretation method of the low-order fault:

[0066] The difference between the seismic interpretation method of the low-order fault in the embodiment and the seismic interpretation method of the low-order fault in the embodiment one is the acquisition method of the time-depth conversion relationship. In the embodiment, the time-depth conversion relationship of a certain region is obtained by using the VSP data of the representative well. The present application does not limit the acquisition method of the time-depth conversion relationship of the target region, but in order to ensure the accuracy of the time-depth conversion relationship, the time-depth conversion relationship obtained by experience is generally not used.

[0067] The other implementation processes and effects of the seismic interpretation method of the low-order fault are the same as those of the seismic interpretation method of the low-order fault in the embodiment one, and will not be repeated here.

[0068] Embodiment four of the seismic interpretation method of the low-order fault:

[0069] The difference between the seismic interpretation method of the low-order fault in the embodiment and the seismic interpretation method of the low-order fault in the embodiment one is the seismic interpretation software. In the embodiment, the TomoxPro interwell seismic processing software is used to carry out the seismic interpretation of the low-order fault. The software can also realize the functions of data loading, making a synthetic seismogram, 3D data interpretation, time-depth conversion and structure mapping. The present application does not limit the seismic processing software, and any software capable of realizing the corresponding functions can be used.

[0070] Other implementation processes and effects of the seismic interpretation method of low-order faults are the same as those of the seismic interpretation method of low-order faults proposed in the first embodiment, and thus are not described herein.

Claims

1. A method of seismic interpretation of low-order faults, characterized in that, The method comprises the following steps: 1) obtaining a time-depth conversion relationship of a target area; 2) time-depth converting a seismic profile of the target area according to the time-depth conversion relationship; 3) simulating a fault plane according to more than three small fault point information or more than two fault trace lines on the seismic profile which are not on a straight line, projecting the fault plane to obtain an approximate three-dimensional space distribution of low-order faults, and using the fault plane to constrain the development position of the low-order faults, and continuously correcting the position of the simulated fault plane in the order from near to far and from inside to outside to complete the constrained seismic interpretation of the low-order faults. The small fault point information or fault trace line is obtained in the following manner: if a well drilled small fault point is present in the target area, the A method is used first, and then the B method is used; if no well drilled small fault point is present in the target area, the B method is used directly; the A method is to one-to-one correspond the well drilled small fault point with the seismic phase; the B method is to change the seismic polarity to the negative polarity corresponding to the sandstone and reduce the seismic polarity intensity in the seismic interpretation software to highlight the fault trace line of the low-order fault corresponding to the small fault point, and obtain the small fault point information or fault trace line.

2. The method of seismic interpretation of low-order faults according to claim 1, characterized in that, A well in the target area is selected, a synthetic record of the well is made according to the electric logging acoustic wave data of the well, a time-depth conversion relationship of the well is obtained, and the time-depth conversion relationship of the well is used as the time-depth conversion relationship of the target area to time-depth convert all wells on the seismic profile of the target area.

3. The method of seismic interpretation of low-order faults according to claim 1, characterized in that, After the fault plane is simulated in the step 3), the low-order faults are interpreted by combining the seismic phase change and the seismic polarity change while using the fault plane to indicate and guide.

4. The seismic interpretation method of low-order faults according to claim 1 or 3, characterized in that, The seismic polarity is changed to the negative polarity corresponding to the sandstone, if the seismic negative polarity phase disappears, twists, the polarity intensity is strong or weak, or the width changes, the obtained indicating position of the fault plane is combined to determine the position of the new low-order fault, and then the small fault point information is obtained.

5. The seismic interpretation method of low-order faults according to claim 1 or 2, characterized in that, The display information of the seismic polarity as the positive polarity is used as a reference to interpret the low-order faults.

6. The method of seismic interpretation of low-order faults of claim 1, wherein, The seismic interpretation software is Geoframe seismic comprehensive interpretation software.

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