Method for quantitatively describing fault inversion process based on balanced section

Abstract

The application discloses a kind of quantitative description fault inversion process method based on balanced section, comprising the following steps: S1: selecting geological profile;S2: division different inversion stage sequence stratigraphy;S3: determine the geologic time of different activity stages of inversion fault;S4: use balanced section technology to restore the evolution history of inversion fault;S5-S7: calculate the slip distance of different stages inversion fault, and calculate the slip rate, inversion intensity coefficient of different inversion stages;S8: establish equivalent point distance, total slip distance, slip rate and inversion intensity coefficient trend chart with geologic time variation, the application is suitable for basin structural analysis technical field, introduce balanced section technology, can more accurately restore fault inversion process;Moreover, can clearly, accurately, quantitative characterization fault inversion process from fault slip distance, the activity intensity of different stages and inversion intensity etc., facilitate different inversion structure contrast, basin structural analysis etc. work is carried out.

Description

Technical Field

[0001] This invention belongs to the field of basin tectonic analysis technology, specifically a method for quantitatively describing fault reversal processes based on equilibrium profiles. Background Technology

[0002] Inversion structures are superimposed composite structures, resulting from the vertical superposition of extensional or compressional structures caused by stress changes in the same geological body at different geological historical periods (Hou Xubo, 2010). As an important structural type, inversion structures are widely developed in basins. Inversion faults are a typical manifestation of inversion structures. Based on the superposition sequence of extensional and compressional structures, inversion faults can be divided into positive inversion faults and negative inversion faults. Quantitative description of the fault inversion process has significant theoretical and practical value for basin evolution, stress field analysis, and oil and gas exploration.

[0003] Previous research on inversion faults has largely focused on analyzing the inversion intensity, using methods such as inversion rate, tectonic elevation, and inversion intensity coefficient (Williams, 1989; Song T, 1997; Hou Xubo, 2010). These methods primarily describe the inversion intensity at the end of the fault inversion and cannot reflect the intermediate inversion process. Furthermore, the values ​​of inversion intensity-related parameters are subject to considerable uncertainty. Therefore, how to accurately and quantitatively describe the fault inversion process is a problem that geological researchers urgently need to solve. Summary of the Invention

[0004] The purpose of this invention is to overcome the shortcomings of the prior art and provide a method for quantitatively describing the fault reversal process based on equilibrium profiles.

[0005] To achieve the above objectives, the present invention adopts the following technical solution:

[0006] A method for quantitatively describing fault reversal processes based on equilibrium profiles includes the following steps:

[0007] S1: Select a geological profile;

[0008] S2: Sequence stratigraphy is divided into different inversion stages;

[0009] S3: Determine the geological history of different active stages of the inversion fault;

[0010] S4: Using balanced profiling techniques to reconstruct the evolutionary history of inverted faults;

[0011] S5: Based on the fault evolution history restored in step S4, determine the equivalent point distances at different stages, and calculate the slip distances of the inverted faults at different stages based on the equivalent point distances.

[0012] S6: Based on the slip distance determined in S5, calculate the slip rate in different reversal stages;

[0013] S7: Based on the slip distance determined in S5, calculate the reversal intensity coefficient for different reversal stages;

[0014] S8: Establish the trend diagram of equivalent point distance, total slip distance, slip rate and reversal intensity coefficient with geological age.

[0015] Preferably, in step S1, the profile is required to be a geological profile perpendicular to the strike of the inversion fault, and the sequence characteristics are obvious, which can clearly reflect the structure and sequence characteristics of the inversion fault.

[0016] Preferably, in step S2, the sequence of the inverted fault includes the pre-inverted sequence, the inverted-period sequence, and the post-inverted sequence.

[0017] Preferably, step S2 includes the following forward and reverse fault sequence features:

[0018] ① Pre-inverted sequence: The sequence characteristics and thickness of the two sides of the fault are consistent, and the sedimentary filling characteristics are unrelated to fault activity;

[0019] ② Reversal sequence: The lower strata of the hanging wall have typical sedimentary filling characteristics of a rift basin, overlapping along the direction away from the fault and forming an angular unconformity with the underlying strata; the seismic profile at the top of the hanging wall shows obvious erosion along the same axis, and the erosion thickness increases along the direction pointing towards the fault.

[0020] Post-inversion sequence: The sequence characteristics of the strata on the hanging wall and footwall of the fault are almost identical, and they are in angular unconformity contact with the sequence during the inversion period.

[0021] Preferably, step S2 includes the following negative inversion fault sequence features:

[0022] Pre-inversion sequence: Affected by fault compression and erosion, the pre-inversion sequence on the hanging wall of the fault is a wedge-shaped fault with a negative inversion thickness, and the thicker erosion points in the direction of the fault.

[0023] Reversal sequence: Externally, it is a wedge-shaped structure that thins away from the fault, and the overlap direction points from the near fault end to the far fault end, reflecting the control of extensional faults on the sedimentary filling process of the reversal sequence.

[0024] Post-inversion sequence: The thickness of the post-inversion sequence is relatively stable, and it has an angular unconformity contact relationship with the inversion sequence.

[0025] Preferably, in step S3, the reversal stage should correspond to the stratigraphic sequence of the inverted fault, that is, the pre-reversal stratigraphic sequence, the inverted-period stratigraphic sequence, and the post-reversal stratigraphic sequence correspond to the three stages of pre-reversal, inverted-period, and post-reversal, respectively.

[0026] Preferably, in step S3, the period before reversal includes the stage before the fault begins to move, the reversal period includes the stage of compression → tension or tension → compression, and the period after reversal includes the stage after the fault stops moving.

[0027] Preferably, in step S3, the reversal period needs to be further divided into a tension-extension stage and a compression-reverse stage based on the unconformity surface and sequence characteristics.

[0028] Preferably, in step S4, the equilibrium profile technique in structural geology is used to reconstruct the fault inversion evolution history.

[0029] Preferably, in step S4, during the equilibrium profile restoration process, in the extensional stage, newly deposited strata are restored using a vertical shear model, and profiles with oblique shear mechanisms are restored using an oblique shear model; in the compressional thrust stage, a triangular shear model is used.

[0030] Preferably, step S4 further includes: marking the changes in the positions of equivalent points on the hanging wall and footwall of the fault during the equilibrium profile restoration process.

[0031] Preferably, in step S5, the formula for calculating the total slip distance of the forward and reverse faults during the tension-extension stage and the compression-rebound stage is as follows:

[0032] Tension-extension stage: De = D0;

[0033] Extrusion and reverse thrust stage: Dc = D0 - De max ;

[0034] Where D0 is the distance between the equivalent points of the upper and lower plates parallel to the fault plane; D0 is positive when Ep is below Ep and negative when Ep is above Ep. De is the total slip distance during the extension phase. max Dc represents the maximum slip distance at the end of the extension phase, and Dc represents the slip distance during the compression phase. max This represents the maximum slip distance at the end of the compression stage.

[0035] Preferably, in step S5, the formula for calculating the total slip distance of the negative inversion fault during the tension-extension stage and the compression-rebound stage is as follows:

[0036] Extrusion and reverse thrust stage: Dc = D0;

[0037] Tension-extension phase: De = D0 - Dc max ;

[0038] Where D0 is the distance between the equivalent points of the upper and lower plates parallel to the fault plane; D0 is positive when Ep is below Ep and negative when Ep is above Ep. De is the total slip distance during the extension phase. maxis the maximum slip distance at the end of the stretching stage, Dc is the slip distance in the squeezing stage, Dc max is the maximum slip distance at the end of the squeezing stage.

[0039] Preferably, in step S6, the slip rate is the ratio of the slip distance between the hanging wall and the footwall of the fault within a certain geological stage to the time, that is, V = D / t;

[0040] where D is the slip distance of the reverse fault in different activity stages; t is the geological time interval of this activity stage. When the fault is in the tensile stretching stage, V is positive; when the fault is in the compressive thrust stage, V is negative.

[0041] Preferably, in step S7, the reverse intensity coefficient Ci of the positive and reverse fault = |Dc / De max |, and the reverse intensity coefficient of the negative reverse fault is C i = |De / Dc max |;

[0042] where the reverse intensity coefficient is a dimensionless value, and its geological significance is to reflect the degree of reverse of the fault. The larger Ci is, the higher the degree of reverse. When 0 < Ci < 1, the fault is not completely reversed; when Ci = 1, the fault is exactly completely reversed; when Ci > 1, the fault has been completely reversed, the positive and reverse fault shows a reverse fault, and the negative reverse fault shows a normal fault.

[0043] Preferably, in step S8, using a rectangular coordinate system, establish a trend diagram of the equivalent point distance, total slip distance, slip rate and reverse intensity coefficient changing with geological time.

[0044] To sum up, due to the adoption of the above technical solution, the beneficial effects of the present invention are:

[0045] In the present invention, by introducing the balanced cross-section technology, the reverse process of the fault can be restored more accurately; at the same time, the selection of the equivalent point is relatively easy, and the relevant parameters are easier to obtain and more accurate; moreover, it can clearly, accurately and quantitatively characterize the reverse process of the fault from aspects such as the fault slip distance, the activity intensity and reverse intensity in different stages, which is convenient for the comparison of different reverse structures and the analysis of basin structures. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] Figure 1 is the technical flow chart of the present invention;

[0047] Figure 2 is the seismic profile of the positive and reverse fault in the embodiment of the present invention;

[0048] Figure 3 is the restoration of the balanced cross-section of the positive and reverse fault in the embodiment of the present invention;

[0049] Figure 4 This is a comprehensive illustration of the fault forward and reverse rotation process in an embodiment of the present invention;

[0050] Figure 5 This is a seismic profile of a negative inversion fault in an embodiment of the present invention;

[0051] Figure 6 This is the restoration of the negative inversion fault equilibrium profile in the embodiments of the present invention;

[0052] Figure 7 This is a comprehensive illustration of the fault negative reversal process in an embodiment of the present invention. Detailed Implementation

[0053] The following is in conjunction with the appendix Figure 1-7 This invention further illustrates specific embodiments of a method for quantitatively describing fault reversal processes based on equilibrium profiles. The method for quantitatively describing fault reversal processes based on equilibrium profiles is not limited to the descriptions in the following embodiments.

[0054] Example 1:

[0055] A method for quantitatively describing fault reversal processes based on equilibrium profiles, such as Figure 1 As shown, it includes the following steps:

[0056] S1: Select a geological profile;

[0057] S2: Sequence stratigraphy is divided into different inversion stages;

[0058] S3: Determine the geological history of different active stages of the inversion fault;

[0059] S4: Using balanced profiling techniques to reconstruct the evolutionary history of inverted faults;

[0060] S5: Based on the fault evolution history restored in step S4, determine the equivalent point distances at different stages, and calculate the slip distances of the inverted faults at different stages based on the equivalent point distances.

[0061] S6: Based on the slip distance determined in S5, calculate the slip rate in different reversal stages;

[0062] S7: Based on the slip distance determined in S5, calculate the reversal intensity coefficient for different reversal stages;

[0063] S8: Establish the trend diagram of equivalent point distance, total slip distance, slip rate and reversal intensity coefficient with geological age.

[0064] Example 2:

[0065] A method for quantitatively describing fault reversal processes based on equilibrium profiles, such as Figure 1As shown, the other steps are similar to those in Example 1. Furthermore, in step S1, the profile is required to be a geological profile perpendicular to the strike of the inversion fault, and the sequence characteristics are obvious, so as to clearly reflect the structure and sequence characteristics of the inversion fault.

[0066] Example 3:

[0067] A method for quantitatively describing fault reversal processes based on equilibrium profiles, such as Figure 1 As shown, the other steps are similar to those in Example 1. Further, in step S2, the sequence of the inverted fault includes the pre-inversion sequence, the inversion period sequence, and the post-inversion sequence.

[0068] Example 4:

[0069] A method for quantitatively describing fault reversal processes based on equilibrium profiles, such as Figure 1 As shown, the other steps are similar to those in Example 1. Further, step S2 includes the following forward and reverse fault sequence features:

[0070] ① Pre-inverted sequence: The sequence characteristics and thickness of the two sides of the fault are consistent, and the sedimentary filling characteristics are unrelated to fault activity;

[0071] ② Reversal sequence: The lower strata of the hanging wall have typical sedimentary filling characteristics of a rift basin, overlapping along the direction away from the fault and forming an angular unconformity with the underlying strata; the seismic profile at the top of the hanging wall shows obvious erosion along the same axis, and the erosion thickness increases along the direction pointing towards the fault.

[0072] Post-inversion sequence: The sequence characteristics of the strata on the hanging wall and footwall of the fault are almost identical, and they are in angular unconformity contact with the sequence during the inversion period.

[0073] Furthermore, step S2 includes the following negative inversion fault sequence features:

[0074] Pre-inversion sequence: Affected by fault compression and erosion, the pre-inversion sequence on the hanging wall of the fault is a wedge-shaped fault with a negative inversion thickness, and the thicker erosion points in the direction of the fault.

[0075] Reversal sequence: Externally, it is a wedge-shaped structure that thins away from the fault, and the overlap direction points from the near fault end to the far fault end, reflecting the control of extensional faults on the sedimentary filling process of the reversal sequence.

[0076] Post-inversion sequence: The thickness of the post-inversion sequence is relatively stable, and it has an angular unconformity contact relationship with the inversion sequence.

[0077] Example 5:

[0078] A method for quantitatively describing fault reversal processes based on equilibrium profiles, such as Figure 1As shown, the other steps are similar to those in Example 1. Furthermore, in step S3, the reversal stage must correspond to the stratigraphic sequence of the inverted fault, that is, the pre-reversal sequence, the inverted-period sequence, and the post-reversal sequence correspond to the three stages of pre-reversal, inverted-period, and post-reversal, respectively.

[0079] Furthermore, in step S3, the period before reversal includes the stage before the fault begins to move, the period of reversal includes the stage of compression → extension or extension → compression, and the period after reversal includes the stage after the fault stops moving.

[0080] Furthermore, in step S3, the reversal period needs to be further divided into a tension-extension stage and a compression-rebound stage based on the unconformity surface and sequence characteristics.

[0081] Example 6:

[0082] A method for quantitatively describing fault reversal processes based on equilibrium profiles, such as Figure 1 As shown, the other steps are similar to those in Example 1. Furthermore, in step S4, in order to accurately describe the fault reversal process, the equilibrium profile technique in structural geology is used to reconstruct the fault reversal evolution history.

[0083] Furthermore, in step S4, the basic principle of area conservation is generally followed during the equilibrium profile restoration process. During the extensional stage, newly deposited strata are restored using a vertical shear model, while profiles exhibiting oblique shear mechanisms are restored using an oblique shear model; during the compressional thrust stage, a triangular shear model is employed.

[0084] Furthermore, step S4 also includes: to facilitate a precise and quantitative description of the fault reversal process, an equivalent point Ep (Ep) is introduced. An equivalent point is a point where the hanging wall and footwall of the fault were in the same location before fault activity. The equivalent point is generally selected from a sequence boundary before fault activity, and this boundary is relatively well preserved during subsequent extension or compression. During the equilibrium profile restoration process, the changes in the positions of the equivalent points on the hanging wall and footwall are marked.

[0085] Example 7:

[0086] A method for quantitatively describing fault reversal processes based on equilibrium profiles, such as Figure 1 As shown, the other steps are similar to those in Example 1. Further, in step S5, the formula for calculating the total slip distance of the forward and reverse faults during the tension-extension and compression-rebound stages is as follows:

[0087] Tension-extension stage: De = D0;

[0088] Extrusion and reverse thrust stage: Dc = D0 - De max ;

[0089] Where D0 is the distance between the equivalent points of the upper and lower plates parallel to the fault plane; D0 is positive when Ep is below Ep and negative when Ep is above Ep. De is the total slip distance during the extension phase. max Dc represents the maximum slip distance at the end of the extension phase, and Dc represents the slip distance during the compression phase. max This represents the maximum slip distance at the end of the compression stage.

[0090] Furthermore, in step S5, the formula for calculating the total slip distance of the negative reversal fault during the extensional and compressional thrust stages is as follows:

[0091] Extrusion and reverse thrust stage: Dc = D0;

[0092] Tension-extension phase: De = D0 - Dc max ;

[0093] Where D0 is the distance between the equivalent points of the upper and lower plates parallel to the fault plane; D0 is positive when Ep is below Ep and negative when Ep is above Ep. De is the total slip distance during the extension phase. max Dc represents the maximum slip distance at the end of the extension phase, and Dc represents the slip distance during the compression phase. max This represents the maximum slip distance at the end of the compression stage.

[0094] Example 8:

[0095] A method for quantitatively describing fault reversal processes based on equilibrium profiles, such as Figure 1 As shown, the other steps are similar to those in Example 1. Further, in step S6, the slip rate is the ratio of the slip distance between the hanging wall and footwall of the fault to the time within a certain geological stage, i.e., V = D / t.

[0096] Where D is the slip distance of the reverse fault in different active stages; t is the geological time interval of the active stage. When the fault is in the extensional stage, V is a positive value; when the fault is in the compressional thrust stage, V is a negative value.

[0097] Example 9:

[0098] A method for quantitatively describing fault reversal processes based on equilibrium profiles, such as Figure 1 As shown, the other steps are similar to those in Example 1. Further, in step S7, the reversal intensity coefficient Ci of the positive and negative faults is |Dc / De|. max | The inversion strength coefficient of a negative inversion fault is C i =|De / Dc max |;

[0099] Among them, the reverse intensity coefficient is a dimensionless value, and its geological significance is to reflect the degree of fault inversion. The larger the Ci, the higher the degree of inversion. When 0 < Ci < 1, the fault is not completely inverted; when Ci = 1, the fault is exactly completely inverted; when Ci > 1, the fault has been completely inverted, and the positive and reverse fault appears as a reverse fault, while the negative reverse fault appears as a normal fault.

[0100] Example 10:

[0101] A method for quantitatively describing the fault inversion process based on a balanced section, as Figure 1 shown. Other steps are similar to those in Example 1. Further, in step S8, a rectangular coordinate system is used to establish a trend diagram of the equivalent point distance, total slip distance, slip rate, and reverse intensity coefficient with respect to geological age.

[0102] Example 11:

[0103] A method for quantitatively describing the fault inversion process based on a balanced section. Taking the positive and reverse fault F1 in a certain area as an example, as Figure 2-4 shown, it includes the following steps:

[0104] Step 1: Select a seismic section perpendicular to the strike of fault F1 with obvious inversion characteristics.

[0105] Step 2: According to the sequence characteristics of the positive and reverse fault horizons, divide the sequence strata of different inversion stages. The in-phase axes in the middle and Paleozoic strata in the hanging wall of the fault are continuous and parallel, and the overall thickness tends to be consistent. It shows an angular unconformity contact relationship with the overlying EK + Es4 strata, which is the pre-inversion sequence. Ek - Ed1 is the sequence during inversion, with typical sedimentary filling characteristics of a fault depression basin. The bottom of Ek overlaps along the direction away from the fault plane, and its sedimentary filling characteristics are significantly controlled by fault F1. The truncation characteristics of the upper Es3 - Ed are obvious, and the erosion thickness increases along the direction pointing to the fault plane, which is significantly affected by the later thrust activity of fault F1. N + Q is the post-inversion sequence, showing an angular unconformity contact relationship with the underlying strata, with parallel and continuous in-phase axes inside, and stable distribution on both the hanging wall and footwall of the fault, which is the regional depression sedimentation.

[0106] Step 3: According to the sequence division and the development characteristics of unconformity surfaces, divide it into pre-inversion (before Ek deposition), inversion period (Ek - Ed deposition period), and post-inversion (after N). Combining with the regional geological structure background and stress field analysis, the inversion period can be further divided into a tensile extension stage (Ek - Ed1) and a compressive thrust stage (Ed2).

[0107] Step 4: Convert the selected seismic profile into a geological profile. Use the equilibrium profile technique to reconstruct the evolution of fault F1 from the Mz-N geological history. Fault F1 is a boundary fault; in the early Ek-Ed stage, it was in a extensional phase, and a vertical shear model was used for reconstruction; in the late Ed stage, it was in a compressional thrust phase, and a triangular shear model was used for reconstruction. To more accurately and quantitatively describe the fault's activity characteristics, based on sequence stratigraphy, the inversion-period fault evolution is further subdivided into four stages: EK+Es4, Es3+Es2, Es1+Ed1, and Ed2. The equivalent point Ep is selected at the bottom of the Paleozoic strata in the pre-inversion sequence, a point that was not eroded during the later evolution. During the equilibrium profile reconstruction process, the equivalent points (Ep) on the hanging wall and footwall must be clearly marked. 上 With Ep 下 The location is convenient for later calculation of slip distance, slip rate and reversal strength.

[0108] In steps 5-7, based on the forward and reverse process of fault F1 restored using the equilibrium profile, the distance between equivalent points at different stages, the total slip distance, the slip distance at each stage, the slip rate, and the reversal intensity coefficient are shown in Table 1.

[0109] Table 1. Calculation table of relevant parameters for fault forward and reverse processes.

[0110]

[0111] In step 8, curves are established showing the variation of fault equivalent point distance, total slip distance, slip rate, and inversion intensity coefficient with geological age, as shown below. Figure 4 As shown, fault F1 began activity during the Ek period, transitioning from extensional to compressional thrust at the end of Ed1, and ceasing activity at the end of Ed2. The total slip distance of fault F1 during the extensional phase was 81.1 km, and the total slip distance during the compressional thrust phase was -14.4 km. Fault F1 exhibited the highest slip rate at Es3+Es2, reaching a maximum of 4.16 km / Ma. At the end of Ed2, the inversion strength coefficient of fault F1 was 0.18, indicating that the fault was not completely inverted.

[0112] Example 12:

[0113] A method for quantitatively describing fault reversal processes based on equilibrium profiles, taking the negative reversal fault F2 in a certain region as an example, such as... Figure 5-7 As shown, it includes the following steps:

[0114] Step 1: Select a seismic profile that is perpendicular to the strike of fault F2 and has obvious reversal characteristics.

[0115] Step 2: Based on the sequence stratigraphic characteristics of the negative inversion fault, sequence strata are divided into different inversion stages. CP is a wedge-shaped stratigraphy that thins towards fault F2, with obvious truncation at the top and increasing erosion thickness along the fault-facing direction, indicating a pre-inversion sequence. K1-Ed is a wedge-shaped stratigraphy that thickens along the fault-facing direction, with the bottom overlapping the fault away from it. The stratigraphic deposition is clearly controlled by the extensional activity of fault F2, therefore K1-Ed belongs to the inversion stage sequence. Notably, although the external morphology of J is the same as the pre-inversion sequence, there are no erosion traces at the top of J, and the bottom overlaps the fault, indicating that J was formed in the early stage of the extensional activity of fault F2, belonging to the extensional sequence. The N+Q region has a stable thickness and parallel continuous internal phase axes, showing an angular unconformity contact with the lower inversion sequence, indicating a regional depression deposition. Its sedimentary filling characteristics are unrelated to fault F2, indicating a post-inversion sequence.

[0116] Step 3: Based on sequence stratigraphy and the development characteristics of unconformities, the region is divided into pre-inversion (T1+2 and earlier), inversion period (T3-Ed depositional period), and post-inversion (N+Q). Combining regional geological tectonic background and stress field analysis, the inversion period can be further divided into the compressional thrust stage (T3) and the extensional stage (J, K1, Es4-Ed).

[0117] Step 4: Convert the selected seismic profile into a geological profile. Use the balanced profile technique to reconstruct the evolution of fault F2 from the geological history of T1+2 to N+Q. Since fault F2 exhibits different fault characteristics at different stages, different models are selected during the reconstruction process. In the pre-inversion sequence, the Cambrian-Ordovician basal surfaces of both the hanging wall and footwall of fault F2 were not eroded; therefore, the intersection of the Cambrian-Ordovician basal surface and the fault profile is selected as the equivalent point. The positions of the equivalent points on the hanging wall and footwall at different stages are shown below. Figure 6 As shown.

[0118] In steps 5-7, based on the forward and reverse process of fault F2 restored using the equilibrium profile, the distance between equivalent points at different stages (D0), total slip distance (De, Dc), slip distance at each stage (D), slip rate (V), and reverse intensity coefficient (Ci) are shown in Table 2.

[0119] Table 2. Calculation table of relevant parameters for fault negative reversal process.

[0120]

[0121] In step 8, curves are established showing the variation of fault equivalent point distance, total slip distance, slip rate, and inversion strength coefficient with geological age, as shown below. Figure 7As shown. Fault F2 became active from the T3 period. At the end of T3, the fault began to change from compressional thrust to extensional extension, and by the end of Ed, the fault had ceased activity. The total slip distance during the compressional thrust phase was -10.1 km, and the total slip distance during the extensional phase was 77.3 km. The fault slip rate was at its maximum between Es4 and Ed, reaching a maximum of 0.83 km / Ma. At the end of the Jurassic, the inversion strength coefficient was 1, indicating that fault F2 had completely reversed. Later, the fault continued to extend and stretch, reaching an inversion strength coefficient of 7.7 by the end of Ed, indicating that fault F2 had completely reversed from a reverse fault to a normal fault.

[0122] Comparing the inverted faults of Example 11 and Example 12, the inversion period of F1 in Example 11 was short, the fault activity intensity was high, and the degree of inversion was weak; while the inversion period of F2 in Example 12 was long, the activity intensity at each stage was low, but the degree of inversion was high.

[0123] Compared with existing methods:

[0124] ① In the quantitative analysis of inversion faults, the inversion rate Rfi (Song T, 1997) and the inversion intensity coefficient Ci (Hou Xubo, 2010) are commonly used quantitative characterization methods. Both of these calculation methods involve extensional and compressional displacements. For inversion faults with syn-sedimentary characteristics, the values ​​of compressional and extensional displacements are relatively clear. However, for inversion faults similar to the boundary normal fault in Example 11, both the hanging wall and footwall strata are eroded, making it difficult to directly obtain the values ​​of compressional and extensional displacements from the current profile, resulting in significant uncertainty. In contrast, according to the technical method provided by this invention, the evolution process of the inversion fault is first reconstructed using balanced profile technology; based on this, the displacement or slip distance at different stages can be read more accurately according to the set equivalent points on the hanging wall and footwall, improving the accuracy of the inversion rate Rfi or the inversion intensity coefficient Ci.

[0125] ② In the comparative analysis of inversion faults, most analyses utilize the inversion rate or inversion intensity coefficient for lateral comparison. However, a single method is insufficient to comprehensively and accurately describe the characteristics of inversion faults. Taking normal and inversion faults with the same inversion intensity as an example, the inversion intensity coefficient Ci of inversion fault a... a = (-100m) / (-200m) = 0.5, the reversal strength coefficient Ci of the reversal fault b b= (-10km) / (-20km) = 0.5. Although fault a and fault b have the same inversion intensity, their activity intensity and impact on the basin during the inversion process are drastically different. Assuming the duration of the compressional thrust stage is 10 Ma, according to the technical method provided by this invention, the slip distance of fault a is -0.1km, and the slip rate Va = (-0.1km) / 10Ma = -0.01km / Ma; the slip distance of fault b is -10km, and the slip rate is Vb = (-10km) / 10Ma = -1km / Ma. |Vb| is much greater than |Va|. That is, fault a is small in scale and has low activity intensity during the inversion process, only affecting local minor structures; fault b is large in scale and has high activity intensity during the inversion process, playing an important role in the tectonic pattern of the zone and even the entire basin.

[0126] Compared with existing methods, the present invention has the following advantages:

[0127] 1. The introduction of balanced profile technology enables more accurate reconstruction of the fault reversal process;

[0128] 2. The selection of equivalent points is relatively easy, and the relevant parameters are easier to obtain and more accurate;

[0129] 3. It can clearly, accurately, and quantitatively characterize the fault reversal process from aspects such as fault slip distance, activity intensity at different stages, and reversal intensity, which facilitates the comparison of different reversal structures and the analysis of basin structures.

[0130] The above description, in conjunction with specific preferred embodiments, provides a further detailed explanation of the present invention. It should not be construed that the specific implementation of the present invention is limited to these descriptions. For those skilled in the art, various simple deductions or substitutions can be made without departing from the concept of the present invention, and all such modifications and substitutions should be considered within the scope of protection of the present invention.

Claims

1. A method for quantitatively describing a fault inversion process based on balanced section, characterized in that, The method comprises the following steps: S1: selecting a geological profile; S2: dividing different inversion stage sequence stratigraphy; S3: determining the geological history period of different activity stages of the inversion fault; S4: restoring the evolution history of the inversion fault by using the balanced profile technology; S5: determining the equivalent point distance of different stages according to the fault evolution history restored in step S4, and calculating the slip distance of the inversion fault in different stages according to the equivalent point distance, wherein the equivalent point refers to the point where the upper and lower walls of the fault are in the same position before the fault activity; S6: calculating the slip rate of different inversion stages on the basis of the slip distance determined in S5; S7: calculating the inversion intensity coefficient of different inversion stages on the basis of the slip distance determined in S5; S8: establishing the trend graph of the equivalent point distance, total slip distance, slip rate and inversion intensity coefficient with geological time.

2. The method for quantitatively describing the fault inversion process based on balanced section according to claim 1, wherein, In the step S1, the profile requires selecting a geological profile perpendicular to the strike of the inversion fault, and the sequence characteristics are obvious, which can clearly reflect the inversion fault structure and sequence characteristics.

3. The method for quantitatively describing the fault inversion process based on balanced section according to claim 1, wherein, In the step S2, the sequence of the inversion fault includes pre-inversion sequence, inversion sequence and post-inversion sequence.

4. The method for quantitatively describing the fault inversion process based on balanced section according to claim 3, characterized in that, In the step S2, the following sequence characteristics of the positive inversion fault are included: ① Pre-inversion sequence: the sequence characteristics and thickness of the two walls of the fault are consistent, and the sediment filling characteristics are irrelevant to the fault activity; ② Inversion sequence: the lower stratum of the upper wall has typical sediment filling characteristics of the rift basin, and overlaps along the direction away from the fault surface, forming an angular unconformity with the underlying stratum; the top seismic profile of the upper wall has obvious erosion phenomenon of the phase axis, and the erosion thickness increases along the direction pointing to the fault surface; Post-inversion sequence: the sequence characteristics of the strata on the upper and lower walls of the fault are nearly consistent, and the post-inversion sequence is in angular unconformity contact with the inversion sequence.

5. The method for quantitatively describing the fault inversion process based on balanced section according to claim 3, characterized in that, In the step S2, the following sequence characteristics of the negative inversion fault are included: Pre-inversion sequence: affected by the extrusion denudation of the fault, the pre-inversion sequence on the upper wall of the fault is a wedge shape thinning towards the negative inversion fault, and the denudation thickness is larger in the direction pointing to the fault; Inversion sequence: the external shape is a wedge shape thinning away from the fault, and the overlapping direction points from the near-fault end to the far-fault end, which reflects the control effect of the tensile extension fault on the sediment filling process of the inversion sequence; Post-inversion sequence: the thickness of the post-inversion sequence is relatively stable, and the post-inversion sequence is in angular unconformity contact with the inversion sequence.

6. The method for quantitatively describing the fault inversion process based on balanced cross section according to claim 1, wherein, In the step S3, the inversion stage should correspond to the sequence of the inversion fault, that is, the pre-inversion sequence, the inversion sequence and the post-inversion sequence correspond to the pre-inversion stage, the inversion stage and the post-inversion stage respectively.

7. A method for quantitatively describing a fault inversion process based on balanced cross-section according to claim 6, characterized in that, In the step S3, the pre-inversion stage includes the stage when the fault does not start to act, the inversion stage includes the stages of extrusion and tensile stretching or tensile stretching and extrusion, and the post-inversion stage includes the stage after the fault stops to act.

8. The method for quantitatively describing a fault inversion process based on balanced cross-section according to claim 6, wherein, In the step S3, the inversion stage needs to be further divided into the tensile stretching stage and the extrusion thrust stage according to the unconformity surface and sequence characteristics.

9. The method for quantitatively describing the fault inversion process based on balanced section according to claim 1, wherein, In the step S4, the balanced profile technology in structural geology is used to restore the inversion evolution history of the fault.

10. The method for quantitatively describing a fault inversion process based on balanced cross-section according to claim 9, wherein, In the step S4, in the process of restoring the balanced profile, in the tensile stretching stage, the newly deposited stratum is restored by using the vertical shear model, and the profile with oblique shear mechanism is restored by using the oblique shear model; in the extrusion thrust stage, the triangular shear model is used.

11. A method for quantitatively describing a fault inversion process based on balanced cross-section according to claim 1, characterized in that, The step S4 further comprises: in the balanced profile recovery process, marking the equivalent point position change of the upper and lower wall of the fault.

12. The method for quantitatively describing a fault inversion process based on balanced cross-section according to claim 1, wherein, In the step S5, the calculation formula of the total slip distance of the normal and reverse fault in the tensile extension stage and the compression thrust stage is as follows: Tensile extension stage: De=D0; Pushing stage: Dc = D0 - De max ; wherein D0 is the distance between the equivalent points of the upper and lower plates parallel to the fault plane, D0 is positive when Epup is below Epdown, and D0 is negative when Epup is above Epdown, De is the total slip distance during the extensional phase, De max is the maximum slip distance at the end of the extensional phase, Dc is the slip distance during the compressional phase, Dc max is the maximum slip distance at the end of the compressional phase.

13. The method of claim 1, wherein the method is based on balanced cross-sections for quantitatively describing fault inversion processes. In the step S5, the calculation formula of the total slip distance of the negative reverse fault in the tensile extension stage and the compression thrust stage is as follows: Compression thrust stage: Dc=D0; Tensile extension phase: De = Do - Dc max ; wherein D0 is the distance between the equivalent points of the upper and lower plates parallel to the fault plane, D0 is positive when Epup is below Epdown, and D0 is negative when Epup is above Epdown, De is the total slip distance during the extensional phase, De max is the maximum slip distance at the end of the extensional phase, Dc is the slip distance during the compressional phase, Dc max is the maximum slip distance at the end of the compressional phase.

14. The method of claim 1, wherein the method is quantitative and based on balanced cross-sections to describe the fault inversion process. In the step S6, the slip rate is the ratio of the slip distance of the upper and lower wall of the fault to the time in a certain geological stage, that is, V=D / t. Wherein, D is the slip distance of the reverse fault in different activity stages; t is the geological time interval of the activity stage, when the fault is in the tensile extension stage, V is positive; when the fault is in the compression thrust stage, V is negative.

15. A method for quantitatively describing fault inversion process based on balanced cross-section according to claim 1, characterized in that: In the step S7, the inversion strength coefficient Ci = |Dc / De of the normal and reverse faults max |, and the inversion strength coefficient C i = |De / Dc max | of the negative reverse faults is calculated. where De is the total slip distance in the extension stage, De max is the maximum slip distance at the end of the extension stage, Dc is the slip distance in the compression stage, Dc max is the maximum slip distance at the end of the compression stage, and Ci is the inversion intensity coefficient, which is a dimensionless value and reflects the inversion degree of the fault. The greater Ci is, the higher the inversion degree is. When 0 < Ci < 1, the fault is not completely inverted. When Ci = 1, the fault is completely inverted. When Ci > 1, the fault has been completely inverted. A positive inversion fault behaves as a reverse fault, and a negative inversion fault behaves as a normal fault.

16. A method for quantitatively describing fault inversion process based on balanced cross-section according to claim 1, characterized in that: In the step S8, the trend graph of the equivalent point distance, the total slip distance, the slip rate and the reverse intensity coefficient with the change of the geological time is established by using the rectangular coordinate system.

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