Method for restoring original sedimentary facies of piedmont overthrust fault zone

Abstract

This invention provides a method for reconstructing the original sedimentary facies of a piedmont thrust fault zone. The method includes: Step 1, establishing a tectonic model of the piedmont zone based on seismic interpretation profiles; Step 2, calculating the erosion amount of each step stratum; Step 3, establishing a sedimentary facies discrimination chart; Step 4, establishing a numerical model for reconstructing the sedimentary facies of the footwall strata of the thrust fault; Step 5, inputting the calculated values ​​into a sedimentary facies template to predict the sedimentary facies of the footwall strata of different stacks. This method organically combines numerical statistics, erosion recovery, and sedimentary facies identification to establish a computational model for predicting the sedimentary facies of deeper strata buried in the footwall of the thrust fault. It provides important basis for determining the potential and scale of oil and gas resources in piedmont oil and gas exploration, and can effectively guide oil and gas drilling work in the middle and deep strata of the piedmont zone.

Description

Technical Field

[0001] This invention relates to the field of oil and gas geological exploration technology, and in particular to a method for restoring the original sedimentary facies of a foreland thrust fault zone. Background Technology

[0002] The basin-mountain junction, or piedmont zone, holds immense oil and gas exploration potential, with 20% of the world's discovered oil and gas reserves located there. However, piedmont zones are often subject to multiple tectonic cycles, particularly multiple phases of thrust and burial, resulting in repeated strata and a "multi-story" structural pattern. The strata in the footwall of thrust fault zones are deeply buried, making drilling difficult. Known wells are often located in the hanging wall, and the oil and gas generation potential and scale of the footwall strata remain unclear.

[0003] Chinese patent application CN201510915723.9 discloses a method and apparatus for reconstructing lithofacies paleogeography. The method includes: acquiring stratigraphic exploration data; restoring stratigraphic erosion and missing data based on the exploration data to restore the thickness of exposed and eroded strata; wherein the exploration data includes at least outcrop data, drilling data, and seismic data; spatially relocating the distribution and thickness of each stratum according to the principle of volume balance to determine the true distribution characteristics of strata during their respective depositional periods; spatially relocating the lithology and sedimentary facies in wells and outcrops based on the true distribution characteristics of strata during their respective depositional periods; reconstructing a lithofacies paleogeographic map based on the spatially relocated lithology and sedimentary facies according to the regional tectonic background; and generating the distribution patterns of lithofacies after multiple tectonic changes based on the restored lithofacies paleogeographic map by applying forward modeling of the sedimentary process according to the tectonic evolution process. This method requires a large amount of known drilling data and is mainly aimed at areas with a high degree of exploration and relatively stable stratigraphic distribution. It can restore and reconstruct lithofacies paleogeographic patterns, but it cannot restore the original sedimentary facies of complex thrust tectonic zones in front of mountains.

[0004] Chinese patent application CN201710292348.6 discloses a method for identifying sedimentary facies using lithological assemblages, comprising the following steps: S1, collecting and processing lithological assemblages of the study section; S2, using mudstone color index to determine the sedimentary environment; S3, using mudstone thickness index to determine the sedimentary facies zone; S4, using sandstone thickness differentiation to determine provenance stability; S5, using the aforementioned lithological indices to determine the lithology of the study section; S6, using sandstone grain size index to determine hydrodynamic intensity; S7, using sandstone grain size differentiation index to determine grain size differentiation; S8, using sandstone thickness index to determine provenance intensity; S9, for steps S2 to S8, narrowing down the sedimentary facies range step by step based on the obtained lithological assemblages of the study section to determine the sedimentary facies; steps S2 to S8 have no specific order. This method is applicable to areas with simple geological structures and abundant drilling and logging data, but it only identifies sedimentary facies and does not address methods for predicting and reconstructing sedimentary facies in complex piedmont thrust fault footwall areas with few or no wells.

[0005] Chinese patent application CN202010901432.5 discloses a method for analyzing the sedimentary facies of thin interbedded sandstone and mudstone based on lithofacies assemblages and seismic spectral characteristics. This method involves selecting typical wells within the study area, creating synthetic seismic records, tracing seismic reflection layers, and establishing a seismic sequence framework for key target sections in key areas. Based on core data from cored wells and logging data, sedimentary facies types are classified, and single sedimentary microfacies models are established. Using an overlay method, sedimentary microfacies assemblages are constructed. By combining well and seismic data, the seismic reflection characteristics and spectral curve types corresponding to each sedimentary microfacies assemblages are obtained. A planar map of the sedimentary microfacies assemblages in the study area is drawn and regions are divided. Combining the amplitude seismic attribute planar distribution map and well data for each region, the extension direction of the sedimentary system is determined. Virtual well data is added, and a planar distribution map of the sedimentary facies is drawn. This method uses changes in seismic spectral characteristics to qualitatively predict reservoirs, providing guidance for the exploration and development of thin interbedded sandstone and mudstone formations. Chinese patent application CN201811620333.9 discloses a method for quantitatively identifying sedimentary facies using apparent resistivity logging curves, aiming to quantitatively interpret sedimentary facies using apparent resistivity logging curves. Its features include the following steps: Step 1, regional geological data collection and comprehensive study; Step 2, establishing a regional typical borehole sedimentary system map; Step 3, establishing a regional sedimentary facies quantitative discrimination function; Step 4, regional single-well sedimentary facies quantitative discrimination; Step 5, regional sedimentary facies quantitative discrimination. Both of these applications utilize known logging and seismic data for sedimentary facies analysis and identification, and are similarly unsuitable for sedimentary facies prediction and recovery in the footwall of complex thrust-thrust zones with few or no wells.

[0006] Existing patents only involve the restoration of lithofacies paleogeography in areas with simple structures and underdeveloped fractures and abundant drilling data, which are quite different from the present invention and have failed to solve the technical problem we want to solve. Therefore, we have invented a new method for restoring the original sedimentary facies of piedmont thrust fault zones. Summary of the Invention

[0007] The purpose of this invention is to provide a method for restoring the original sedimentary facies of the foreland thrust fault zone, which is of great significance for understanding the oil and gas exploration potential of the foreland zone and evaluating the scale of oil and gas in the foreland zone.

[0008] The objective of this invention can be achieved through the following technical measures: a method for restoring the original sedimentary facies of a piedmont thrust fault zone, comprising:

[0009] Step 1: Establish a piedmont structural model based on the seismic interpretation profile;

[0010] Step 2: Calculate the erosion amount of each step stratum;

[0011] Step 3: Establish a sedimentary facies discrimination chart;

[0012] Step 4: Establish a numerical model for the restoration of sedimentary facies in the footwall of the thrust fault, including:

[0013] Since the distance L from the source at different points is a function of the mudstone ratio K and the thickness Z of a single mudstone layer, specifically including:

[0014] (1) Let L be the distance between the known well and the source. The distances between the quasi-in-situ wells a, b, and c and the source are respectively: L a L b L c The erosion rates of quasi-in-situ drilling a, b, and c are respectively H a H b H c ;

[0015] Distance of borehole b from the source material in the footwall of fracture F1:

[0016] L b d =L a -(D 1+ H b ) / tanθ1; Formula (2);

[0017] In the formula, D1 is the fault displacement of F1 fracture, and θ1 is the fault dip angle;

[0018] Distance of well c from source material in the footwall of F2 fracture:

[0019] L c d =LC - (D 2+ H c ) / tan(θ2+θ1); Formula (3);

[0020] In the formula, D2 is the fault displacement of F2 fracture, and θ2 is the fault dip angle;

[0021] Distance of the source material from the footwall of F1 fracture in well c of stacked section 2:

[0022] L c d2 = L c d - (D 2+ H c ) / tan(θ 2- θ1); Formula (4);

[0023] (2) Establish relevant charts for different well-to-source distances L, well-to-soil ratio K, and single-layer mudstone thickness Z: L=f(K) Formula (5);

[0024] L=f(Z) Formula (6);

[0025] (3) Drilling of laminate 1 and laminate 2 in the L-shaped section of the fractured footwall b d L c d L c d2 Substitute these values ​​into formulas (5) and (6) to obtain the corresponding K and Z values;

[0026] Step 5: Input the calculated values ​​into the sedimentary facies template to predict the sedimentary facies of the footwall strata of different stacks.

[0027] The objective of this invention can also be achieved through the following technical measures:

[0028] In step 1, a development model of thrust faults in the foreland of the orogenic belt is established to clarify the number of thrust stacks in the foreland belt, the angle of different thrust faults, and the distance at which the thrust faults slip.

[0029] In step 2, wells that encounter the same strata in different structural stacks are selected, and the mudstone ratio and average thickness of single mudstone layers in the drilled wells of different geological units are statistically analyzed to establish a sedimentary facies identification chart for known wells.

[0030] In step 2, using the sonic transit time curve of the drilling, the sonic transit time curve corresponding to the mudstone section with a thickness of not less than 1.5m is selected for curve fitting; the erosion amount of each well is calculated respectively.

[0031] In step 2, when performing curve fitting, the horizontal axis represents the logarithmic coordinate of the acoustic transit time, and the vertical axis represents the depth. The compaction curve is extended outwards, intersecting the logarithmic horizontal axis at the acoustic transit time value at the paleosurface. The horizontal extension line at this point represents the paleosurface H0, and the distance from the paleosurface to the top surface of the present-day residual target layer represents the erosion amount H.

[0032] ; Formula (1)

[0033] In the formula, H0 is the paleosurface, m; H1 is the thickness from the paleosurface to the top of the current residual target layer, m; and H is the amount of erosion, m.

[0034] In step 3, the amount of erosion of the wells in different stacks is calculated using the sonic transit time method to obtain the true thickness of the formation before the occurrence of the thrust structure.

[0035] In step 3, the mudstone-to-stratum ratio (cumulative mudstone thickness / stratum thickness) of the formations in the same target section of each stack is statistically analyzed: K; the mudstone single-layer thickness (cumulative mudstone thickness / number of mudstone layers) is analyzed: Z; a scatter plot of formation mudstone-to-stratum ratio and single-layer thickness is established, with the mudstone-to-stratum ratio K on the horizontal axis and the mudstone single-layer thickness Z on the vertical axis; and a sedimentary facies division chart is established based on the known sedimentary facies from the statistical points.

[0036] In step 4, based on the established reverse thrust-overlap geological model, numerical models of different tectonic stratigraphic layers with thrust distance and fault scale are established, and the mudstone ratio and mudstone single-layer thickness of the footwall strata of different stratigraphic layers are calculated.

[0037] In step 5, the calculated drilling mudstone ratio K and the single-layer mudstone thickness Z of different stacks are input into the sedimentary facies discrimination chart to obtain the sedimentary facies of the footwall of different stacks.

[0038] The method for restoring the original sedimentary facies of thrust fault zones in the foreland region, as described in this invention, can infer the lithological assemblage and sedimentary facies characteristics of the footwall of thrust faults in un-drilled areas based on well-drilled areas, thereby determining the source rock potential and reservoir development characteristics of the footwall. This invention proposes a method for obtaining the sedimentary facies of un-drilled strata in the footwall of thrust fault zones in foreland regions using structural and numerical models. This method organically combines numerical statistics, erosion recovery, and sedimentary facies identification to establish a computational model for predicting the sedimentary facies of deeper strata buried in the footwall of thrust faults. This provides important evidence for determining the potential and scale of oil and gas resources in foreland oil and gas exploration. Simultaneously, it can effectively guide oil and gas drilling work in the mid-to-deep strata of foreland regions. Attached Figure Description

[0039] Figure 1 This is a schematic diagram of a geological interpretation model of a thrust-tectonic structure in a specific embodiment of the present invention;

[0040] Figure 2 This is a schematic diagram of the structural model of the middle section of the Hala Alat Mountains in a specific embodiment of the present invention;

[0041] Figure 3 This is a calculation diagram of the erosion amount of well Fenggu 3 in a specific embodiment of the present invention;

[0042] Figure 4 This is a calculation diagram of the erosion amount of well Haqian 23 in a specific embodiment of the present invention;

[0043] Figure 5 This is a sedimentary profile of the middle section of the Hala Alat Mountains in a specific embodiment of the present invention.

[0044] Figure 6 This is a sedimentary facies diagram of the Fengcheng Formation of the Permian System in the Hala Alat Mountains, according to a specific embodiment of the present invention.

[0045] Figure 7 This is a schematic diagram of the sedimentary facies division of the Permian Fengcheng Formation in the Hala Alat Mountain thrust plate according to a specific embodiment of the present invention;

[0046] Figure 8 This is a relative sedimentary profile (reconstruction) of the middle section of the Hala Alat Mountains in a specific embodiment of the present invention.

[0047] Figure 9 This is a flowchart of a specific embodiment of the method for restoring the original sedimentary facies of the piedmont thrust fault zone of the present invention. Detailed Implementation

[0048] It should be noted that the following detailed descriptions are exemplary and intended to provide further illustration of the invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0049] It should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the exemplary embodiments of the present invention. As used herein, the singular form is intended to include the plural form as well, unless the context clearly indicates otherwise. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, and / or combinations thereof.

[0050] The following are several specific embodiments of the application of the present invention.

[0051] Example 1

[0052] In a specific embodiment 1 of the present invention, such as Figure 9 As shown, Figure 9The flowchart illustrates a specific embodiment of the method for restoring the original sedimentary facies of a piedmont thrust fault zone according to the present invention. This method mainly includes the following steps:

[0053] 101. Establish a development model of thrust faults in the foreland of orogenic belts, and clarify the number of thrust stacks in the foreland belt, the angle of different thrust faults, the distance at which thrust faults slip, and other parameters.

[0054] 102. Select exploration wells that encounter the same strata in different structural stacks, and statistically analyze the mudstone ratio and average thickness of single mudstone layers in the drilled wells of different geological stacks to establish a sedimentary facies identification chart for known wells.

[0055] 103. Calculate the erosion amount of wells in different stacks using the sonic transit time method to obtain the true thickness of the formation before the occurrence of the thrust structure.

[0056] 104. Based on the established geological model of thrust-nappe stratigraphy, establish numerical models of stratigraphic strata with different tectonic structures, thrust distances, and fault scales, and calculate the mudstone-to-soil ratio and mudstone layer thickness of the footwall strata of different stratigraphic structures.

[0057] 105. Input the calculated values ​​into the sedimentary facies template to predict the sedimentary facies of the footwall strata of different stacks.

[0058] Example 2

[0059] In a specific embodiment 2 of the present invention, the method for restoring the original sedimentary facies of the piedmont thrust fault zone includes the following steps:

[0060] 1. Establish a piedmont structural model based on the seismic interpretation profile, such as... Figure 1 As shown: the fault displacements D1, D2, ..., Dn of the thrust faults F1, F2...Fn in front of the mountain are clearly defined, as well as the fault dip angles θ1, θ2...θn.

[0061] 2. Calculate the amount of erosion in each step: During the thrusting process in the piedmont zone, uplift is often accompanied, which leads to erosion of the strata. The amount of erosion can be well recovered by using sonic transit time.

[0062] (1) Using the sonic transit time curve of the well, select the sonic transit time curve corresponding to the mudstone section with a thickness of not less than 1.5m for curve fitting. The horizontal axis is the logarithmic coordinate of sonic transit time, and the vertical axis is the depth. Extend the compaction curve and intersect it with the logarithmic horizontal axis at 600μs / m (sonic transit time value of the paleosurface). The horizontal extension line at this point is the paleosurface H0, and the erosion amount H from the paleosurface to the top surface of the current residual target layer is the erosion amount of the stratum:

[0063] ; Formula (1)

[0064] In the formula, H0 is the paleosurface, m; H is the thickness from the paleosurface to the top of the current residual target layer, m; and H is the amount of erosion, m.

[0065] (2) Calculate the erosion amount Ha, Hb, Hc...Hn of wells a, b, c... respectively.

[0066] 3. Establish sedimentary facies discrimination charts

[0067] (1) Statistical analysis of mudstone-to-formation ratio (cumulative mudstone thickness / formation thickness value) of wells drilling in the same target section for stacked sections 1, 2, ..., n: K1, K2, ..., Kn; mudstone single-layer thickness value (ratio of cumulative mudstone thickness to number of mudstone layers): Z1, Z2, ..., Zn. n .

[0068] (2) Establish a scatter plot of mudstone-soil ratio and single-layer thickness, with the horizontal axis representing mudstone-soil ratio K and the vertical axis representing mudstone single-layer thickness Z. Based on the known sedimentary facies from the statistical points, establish a sedimentary facies classification chart.

[0069] 4. Establish a numerical model for reconstructing the sedimentary facies of the footwall of the thrust fault.

[0070] The distance L from the source of the material at different points is a function of the mudstone ratio K and the thickness m of a single mudstone layer.

[0071] (1) The distance between the known well and the source is assumed to be L (unit: m).

[0072] The distances from the source to the quasi-in-situ drilling wells a, b, and c are La, L, L, and L, respectively. b L c

[0073] (Unit: m);

[0074] Distance of borehole b from the source material in the footwall of fracture F1:

[0075] L b d =L a -(D 1+ H b ) / tanθ1 (unit: m); Formula (2);

[0076] Distance of well c from source material in the footwall of F2 fracture:

[0077] L c d =L C - (D 2+ H c ) / tan(θ2+θ1)(unit:m); Formula (3);

[0078] Distance of the source material from the footwall of F1 fracture in well c of stacked section 2:

[0079] L c d2 = L c d - (D 2+ H c ) / tan(θ 2- θ1) (unit: m); Formula (4);

[0080] (2) Establish relevant charts for different well-to-source distances L, well-to-mud ratio K, and single-layer mudstone thickness Z. L=f(K) Formula (5);

[0081] L=f(Z) Formula (6);

[0082] (3) Drilling of laminate 1 and laminate 2 in the L-shaped section of the fractured footwall b d L c d L c d2 Substitute these values ​​into formulas (5) and (6) to obtain the corresponding K and Z values.

[0083] 5. By inputting the calculated K and Z values ​​of different stacks into the sedimentary facies discrimination chart, the sedimentary facies of the footwall of different stacks can be obtained.

[0084] Example 3

[0085] In a specific embodiment 3 of this invention, the Hala Alat piedmont zone in the northern part of the Mahu Depression in the Junggar Basin is used as an example. Since the Permian, the Hala Alat piedmont zone has undergone the Hercynian, Indosinian, and Yanshanian orogenies, with the development of thrust faults, forming the current "multi-story" tectonic structure. The Lower Permian Fengcheng Formation is an important source rock system in the Mahu Depression and adjacent areas, and also an oil and gas enrichment system. The characteristics of the rock assemblage of the Lower Fengcheng Formation in the Hala Alat Mountains and whether the Fengcheng Formation source rocks are developed directly affect the potential and scale of oil and gas exploration in the entire northern margin piedmont zone of Mahu. This study takes the middle section of the Hala Alat Mountains as an example. Multiple exploration wells in the hanging wall of this area have revealed the Fengcheng Formation, but the hanging wall has not yet been encountered. Therefore, the lithological assemblage and sedimentary facies of the hanging wall are still unknown. This study, which restores the original sedimentary facies of the hanging wall, is of great significance for clarifying the scale and exploration direction of oil and gas in the Hala Alat piedmont zone.

[0086] 1. Based on the seismic interpretation profile of the middle segment of the Hala Alate Mountains on the northern margin of Mahu Lake, a piedmont tectonic model was established. Figure 2It is determined that the fault displacements of the thrust faults F1 and F2 in front of the mountain are D1=780m and D2=560m, and the fault dip angles are θ1=30° and θ2=45°.

[0087] 2. Calculate the erosion amount of each step stratum.

[0088] (1) Select the acoustic transit time curve of the Fengcheng Formation mudstone and shale of Well Fenggu 3 in the selected stacked section, and remove the abnormal jump segments on the curve ( Figure 3 The acoustic time difference curve and burial depth were fitted together. The horizontal axis is the logarithmic coordinate of the acoustic time difference data ln(AC), and the vertical axis is the burial depth. According to the fitted curve: H=(-920)xln(AC)+5600;

[0089] The calculated depth of the ancient surface is 816m.

[0090] Therefore, the erosion amount H of the Fengcheng Formation in Well Fenggu 3 fg3 =1324-816=508(m).

[0091] (2) Select the acoustic transit time curve of the Fengcheng Formation mudstone and shale of well Haqian 23 in the second section of the selected area, and remove the abnormal jump segments on the curve ( Figure 4 The acoustic time difference curve and burial depth were fitted together. The horizontal axis is the logarithmic coordinate of the acoustic time difference data ln(AC), and the vertical axis is the burial depth. According to the fitted curve: H=(-1390)xln(AC)+6530;

[0092] The calculated depth of the ancient surface is -698m.

[0093] Therefore, the erosion amount H of the Fengcheng Formation in Well Haqian 23 hq23 =698+417=1115(m).

[0094] 3. Establish sedimentary facies discrimination charts

[0095] The Permian Fengcheng Formation in the Hala Alat Mountains region mainly consists of sedimentary facies zones including semi-deep lacustrine, deep lacustrine, littoral-shallow lacustrine, delta front, and fan delta. From the cross-section... Figure 5 As can be seen from the data, for the drilled exploration wells, sedimentary facies zones can be divided based on rock assemblage, mud-to-bottom ratio, and mudstone single-layer thickness. However, for the footwall of the fault zone, due to its deep burial, it is impossible to obtain the characteristics of its sedimentary facies zones.

[0096] (1) The mud-to-ground ratio K and the thickness Z of the mudstone of the Fengcheng Formation mudstone in the in-situ system of Fengnan 4, Fengnan 1, Fengnan 7 in the middle section of Hala Alat Mountain, as well as Xia 69 and Fenggu 3 in the first layer and Haqian 23 in the second layer are respectively counted.

[0097] Table 1. Statistics of Permian Fengcheng Formation Drilling Mudstone in the Piedmont Zone of Hala Alat Mountain

[0098] Fengnan 7 Well P1f3 0.69 7.18 Deep Lake Ma Ye 1 Well P1f3 0.67 4.5 Deep Lake Fenggu 3 Well P1f3 0.72 12 Deep Lake Haqian 6 well P1f3 0.97 8.94 Deep Lake Fengnan 4 Well P1f2 0.7451 5.92 Deep Lake Fengnan 1 Well P1f2 0.95 5.6 Deep Lake Fengnan 7 Well P1f2 0.79 4.98 Deep Lake Haqian 6 well P1f2 0.94 7.5 Deep Lake Fengnan 7 Well P1f1 0.81 5.93 Deep Lake Hashan 1 Well P1f1 0.85 4.21 Deep Lake Fengnan 4 Well P1f3 0.3422 6.7 Semi-deep lake Fengnan 1 Well P1f3 0.6877 9.08 Semi-deep lake Harbin Deep Slope 1 Well P1f2 0.41 2.98 Semi-deep lake Ma Ye 1 Well P1f2 0.95 7.5 Semi-deep lake Fenggu 3 Well P1f2 0.37 4 Semi-deep lake Hashan 1 Well P1f2 0.90 4.26 Semi-deep lake Fenggu 3 Well P1f1 0.61 7.57 Semi-deep lake Xia 12 well P1f3 0.17 2.6 Shallow Lake Fengnan 4 Well P1f1 0.2388 5.4 Shallow Lake Fengcheng 1 Well P1f1 0.1519 3 Shallow Lake Harbin Deep Slope 1 Well P1f1 0.14 5 Shallow Lake Harbin Deep Slope 1 Well P1f3 0.36 3.1 Delta front Haqian 23 well P1f3 0.55 3 Delta front Xia 69 Well P1f2 0.24 0.5 Delta front Haqian 23 well P1f2 0.25 1.9 Delta front Fengnan 1 Well P1f1 0.3818 4.6 Delta front Ma Ye 1 Well P1f1 0.32 3.6 Delta front Haqian 23 well P1f1 0.241 2.13 Delta front Fengcheng 1 Well P1f3 0.2842 6.38 near crater Fengcheng 1 Well P1f2 0.23 9 near crater

[0099] (2) Establish a scatter plot of mudstone-soil ratio and single-layer thickness, with the horizontal axis representing the mudstone-soil ratio K and the vertical axis representing the mudstone single-layer thickness Z. Based on the known sedimentary facies from the statistical points, establish a sedimentary facies classification chart. Figure 6 ).

[0100] 4. Establish a numerical model for the restoration of sedimentary facies in the footwall of the middle section of the Hashanla Alate Mountain thrust block.

[0101] (1) Structural reconstruction and sedimentary facies studies suggest that the provenance of the Hala Alat Mountain area is located near the northern Darbut Fault. The distance from well Haqian 23 in the stacked section 2 to the provenance is L. c =2800m, distance L from the source of the wind-blown 3 well in stacked plate 1 b =4800m, distance L from source material of Fengnan 4 well in the in-situ system a =5900m,

[0102] The distance L from the source of the material at different points is a function of the mudstone ratio K and the thickness m of a single mudstone layer.

[0103] (2) Distance of the source material from the footwall of the F1 fault in well Fenggu 3 of the Diebian 1 drilling project:

[0104] L fg3 d = L a -(D 1+ H fg3 ) / tanθ1=5900-(780 + 508) / tan30°=3640m;

[0105] The distance from the source material in the footwall of the F2 fault of well Haqian 23 in the stacked section 2:

[0106] L hq23 d =Lc- (D2+Hc) / tan(θ2+θ1)=2800- (560 + 1115) / tan(45+30) =2351m;

[0107] The distance from the source material in the footwall of the F1 fault of well Haqian 23 in the stacked section 2:

[0108] L hq23 d2 = L hq23 d -(D 2+ H hq23 ) / tan(θ1)

[0109] =2300- (560+ 1115) / 0.57 = 239m;

[0110] (3) Establish relevant charts for different well-to-source distances L, well-to-soil ratio K, and single-layer mudstone thickness Z. L=f(K)=10103*K-1286.6;

[0111] L=f(Z)=1415.3*Z-2401.3;

[0112] The distance between Fenggu 3 well and the source is 4800m, with calculated K=0.602 and Z=5.08m; the distance between Haqian 23 well and the source is 2800m, with calculated K=0.404 and Z=3.67m.

[0113] (4) The calculated K and Z values ​​of Fenggu 3 and Haqian 23 wells were substituted into the sedimentary facies identification chart. From the chart, it can be seen that the quasi-in-situ lower plate of Fenggu 3 well is located in the semi-deep lacustrine to deep lacustrine facies zone, and the quasi-in-situ system of Haqian 23 well is located in the fan delta front facies zone. Figure 7 Therefore, it is believed that the footwall of the thrust fault in the middle section of the Hala Alat Mountains is located in a semi-deep to shallow lacustrine sedimentary facies zone, possessing the conditions for the development of lacustrine source rocks. Figure 8 This has enhanced the oil and gas exploration potential of the foreland belt.

[0114] The above analysis can determine the lithostratigraphic assemblage and sedimentary facies characteristics of the footwall of the piedmont zone, thus providing a basis for judging whether the piedmont zone has exploration potential and resource scale, which is very important for carrying out oil and gas exploration work in the piedmont zone.

[0115] Finally, it should be noted that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

[0116] Except for the technical features described in the specification, all other technologies are known to those skilled in the art.

Claims

1. A method for restoring the original sedimentary facies of a piedmont thrust fault zone, characterized in that, The methods for restoring the original sedimentary facies of the thrust fault zone in the foreland area include: Step 1: Establish a piedmont structural model based on the seismic interpretation profile; Step 2: Calculate the erosion amount of each step stratum; Step 3: Establish a sedimentary facies discrimination chart; Step 4: Establish a numerical model for the restoration of sedimentary facies in the footwall of the thrust fault, including: Since the distance L from the source at different points is a function of the mudstone-to-soil ratio K and the thickness Z of a single mudstone layer, specifically including: (1) Assuming the distance from the known well to the source is L, the distances from the quasi-in-situ wells a, b, and c to the source are respectively: L a L b L c The erosion rates of quasi-in-situ drilling a, b, and c are respectively H a H b H c ; Distance of borehole b from the source material in the footwall of fracture F1: L b d =L a -(D 1+ H b ) / tanθ1; Formula (2); In the formula, D1 is the fault displacement of F1 fracture, and θ1 is the fault dip angle; Distance of well c from source material in the footwall of F2 fracture: L c d = L C - (D 2+ H c ) / tan(θ2 + θ1); Equation (3); In the formula, D2 is the fault displacement of F2 fracture, and θ2 is the fault dip angle; Distance of the source material from the footwall of F1 fracture in well c of stacked section 2: L c d2 = L c d - (D 2+ H c ) / tan(θ 2- θ1); Equation (4); (2) Establish relevant charts for different well-to-source distances L, well-to-soil ratio K, and single-layer mudstone thickness Z: L=f(K) Formula (5); L=f(Z) Formula (6); (3) Drilling of laminate 1 and laminate 2 in the L-shaped section of the fractured footwall b d L c d L c d2 Substitute these values ​​into formulas (5) and (6) to obtain the corresponding K and Z values; Step 5: Input the calculated values ​​into the sedimentary facies discrimination chart to predict the sedimentary facies of the footwall strata of different stacks.

2. The method for restoring the original sedimentary facies of the piedmont thrust fault zone according to claim 1, characterized in that, In step 1, a development model of thrust faults in the foreland of the orogenic belt is established to clarify the number of thrust stacks in the foreland belt, the angle of different thrust faults, and the distance at which the thrust faults slip.

3. The method for restoring the original sedimentary facies of the piedmont thrust fault zone according to claim 1, characterized in that, In step 2, wells that encounter the same strata in different structural stacks are selected, and the mudstone ratio and average thickness of single mudstone layers in the drilled wells of different geological units are statistically analyzed to establish a sedimentary facies identification chart for known wells.

4. The method for restoring the original sedimentary facies of the piedmont thrust fault zone according to claim 3, characterized in that, In step 2, using the sonic transit time curve of the drilling, the sonic transit time curve corresponding to the mudstone section with a thickness of not less than 1.5m is selected for curve fitting; the erosion amount of each well is calculated respectively.

5. The method for restoring the original sedimentary facies of the piedmont thrust fault zone according to claim 4, characterized in that, In step 2, when performing curve fitting, the horizontal axis represents the logarithmic coordinate of the acoustic transit time, and the vertical axis represents the depth. The compaction curve is extended outwards, intersecting the logarithmic horizontal axis at the acoustic transit time value at the paleosurface. The horizontal extension line at this point represents the paleosurface H0, and the distance from the paleosurface to the top surface of the present-day residual target layer represents the erosion amount H. Official (1) In the formula, H0 is the paleosurface, m; H1 is the thickness from the paleosurface to the top of the current residual target layer, m; and H is the amount of erosion, m.

6. The method for restoring the original sedimentary facies of a piedmont thrust fault zone according to claim 1, characterized in that, In step 3, the amount of erosion of the wells in different stacks is calculated using the sonic transit time method to obtain the true thickness of the formation before the occurrence of the thrust structure.

7. The method for restoring the original sedimentary facies of a piedmont thrust fault zone according to claim 6, characterized in that, In step 3, the mudstone-to-stratum ratio (cumulative mudstone thickness / stratum thickness) of the formations in the same target section of each stack is statistically analyzed: K; the mudstone single-layer thickness (cumulative mudstone thickness / number of mudstone layers) is analyzed: Z; a scatter plot of formation mudstone-to-stratum ratio and single-layer thickness is established, with the mudstone-to-stratum ratio K on the horizontal axis and the mudstone single-layer thickness Z on the vertical axis; and a sedimentary facies division chart is established based on the known sedimentary facies from the statistical points.

8. The method for restoring the original sedimentary facies of the piedmont thrust fault zone according to claim 1, characterized in that, In step 4, based on the established reverse thrust-overlap geological model, numerical models of different tectonic stratigraphic layers with thrust distance and fault scale are established, and the mudstone ratio and mudstone single-layer thickness of the footwall strata of different stratigraphic layers are calculated.

9. The method for restoring the original sedimentary facies of a piedmont thrust fault zone according to claim 1, characterized in that, In step 5, the calculated drilling mudstone ratio K and the single-layer mudstone thickness Z of different stacks are input into the sedimentary facies discrimination chart to obtain the sedimentary facies of the footwall of different stacks.

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