A method for determining a hydrocarbon charging point related to a strike-slip fault of a sedimentary basin

Abstract

This invention relates to the field of geological exploration technology and proposes a method for determining hydrocarbon injection points related to strike-slip faults in sedimentary basins. The steps include: collecting geological information of the target area; using qualitative analysis to obtain the segmented characteristics, fault properties, and fracture grid of strike-slip faults in the overlying tight layers (such as gypsum-salt layers) of the source rocks in the target area to determine the approximate range of injection points; calculating the key layer thickness of the source rock and tight layers, and the transport coefficient at the top of the tight layer, and performing normalization; correcting the injection points based on the calculated quantitative data and the segmented characteristics of the strike-slip faults; and verifying the corrected injection points based on the fluctuation points of segmented changes in hydrocarbon migration indicators and crude oil physical property parameters. The method proposed in this invention can significantly improve the accuracy and reliability of determining hydrocarbon injection points related to strike-slip faults, providing guidance for oil and gas exploration and greatly improving exploration efficiency.

Description

Technical Field

[0001] This invention relates to the field of geological exploration technology, and more specifically, to a method for determining oil and gas injection points associated with strike-slip faults in sedimentary basins. Background Technology

[0002] Strike-slip faults are an important structural type in sedimentary basins, influencing not only the basin's structural framework and sedimentary system distribution but also playing a crucial role in controlling the generation, migration, accumulation, and preservation of hydrocarbons. Unlike simple extensional or compressional structures, strike-slip faults possess unique structural features, including flower-like structures along vertical fault zones, pull-apart basins, and compressional uplift zones. In recent years, strike-slip fault-related hydrocarbon reservoirs have been discovered in the Tarim and Sichuan cratonic basins. In the Tarim Basin, strike-slip faults can serve as pathways for hydrocarbon migration and can also form fractured reservoirs that store hydrocarbons.

[0003] Oil and gas charging points refer to the key locations where oil and gas are vertically or laterally injected from deep source rocks or conduits into shallow traps. Accurate identification of these charging points is crucial for predicting oil and gas enrichment areas, reducing exploration risks, and improving drilling success rates. In strike-slip fracture systems, oil and gas charging points are usually closely related to specific structural locations. At the inflection points or bends of the main fracture, such as stress release zones, the rock is fractured and highly porosity, facilitating fluid passage. The intersections of secondary and main fractures form "crossroads" for fluid migration, connecting multiple conduits. Extensional sections of strike-slip fracture zones, used as structurally weak zones, are advantageous channels for vertical fluid migration. The roots or tops of flower-like structures are transition zones for stress concentration and release, with highly developed fracture systems.

[0004] However, despite the industry consensus on its importance, existing technologies still face significant challenges in accurately identifying hydrocarbon charging points in strike-slip fault zones. Traditional seismic interpretation struggles to effectively distinguish between currently active transport channels and closed paleochannels. Strike-slip faults are characterized by multi-phase activity, and their transport capacity exhibits spatial and temporal heterogeneity and dynamic evolution. Existing static tectonic interpretations are insufficient to effectively characterize the opening and closing of faults at different geological periods, making it impossible to accurately determine effective transport channels during the main hydrocarbon charging period.

[0005] Therefore, there is an urgent need in this field for an innovative technical method that can overcome the above-mentioned technical bottlenecks and achieve efficient, accurate, and quantitative identification of oil and gas injection points in strike-slip fault zones of sedimentary basins, so as to guide the selection of target areas for oil and gas exploration and significantly improve exploration efficiency. Summary of the Invention

[0006] In view of this, the present invention proposes a method for determining oil and gas charging points related to strike-slip faults in sedimentary basins. Addressing the technical problem that oil and gas need to be transported upwards through strike-slip faults when source rocks are covered by tight layers (such as gypsum-salt layers), leading to inaccurate identification of oil and gas charging points in strike-slip fault zones and the inability to accurately determine effective transport channels during the main charging period, the method first uses the segmented characteristics, fracture properties, and fracture grid of the top surface of the tight layer overlying the source rock to initially determine the charging points. Then, it uses the thickness of key stratigraphic layers and the conductivity coefficient to quantitatively evaluate the conductivity of the fault at the top of the tight layer. Finally, combining oil and gas migration indicators and crude oil physical properties, the method determines the final charging point.

[0007] To achieve the above objectives, this invention proposes a method for determining hydrocarbon injection points related to strike-slip faults in sedimentary basins, characterized by the following steps:

[0008] Geological information of the target area was collected, and qualitative analysis was used to obtain the segment characteristics of strike-slip faults, fault properties and strike-slip fault fracture grids of the dense layer overlying the source rock in the target area, and to determine the approximate range of the injection point.

[0009] The thickness of the key layers of the source rock strata and the tight layer, and the transport coefficient of the top of the tight layer are calculated and normalized. Based on the calculated quantitative data, the filling point is corrected in combination with the segmentation characteristics of the strike-slip fault.

[0010] The corrected injection point is verified based on the fluctuation points of the segmented changes in oil and gas migration indicators and crude oil physical property parameters.

[0011] Furthermore, the segmentation characteristics of the strike-slip fracture are determined by combining coherence or other fracture properties with manual interpretation;

[0012] The nature of the fault is determined by the interpretation of seismic profiles and is divided into extensional-torsional, compressional-torsional, and translational faults. Extensional-torsional faults refer to the subsidence deformation caused by the fault, compressional-torsional faults refer to the convex deformation caused by the fault, and translational faults refer to the basic horizontality of the strata with no vertical deformation.

[0013] The analysis process of the strike-slip fracture crack mesh includes: using topological methods or other fracture density prediction methods to obtain the crack density at different locations of the fracture zone.

[0014] Furthermore, the key layer thickness of the source rock layer is specifically the thickness of the top and bottom surfaces of the source rock layer, which is calculated based on the seismic profile;

[0015] The critical layer thickness of the dense layer is specifically the thickness of the top and bottom surfaces of the dense layer, which is calculated based on the seismic profile.

[0016] The conductivity coefficient at the top of the compact layer is specifically the strike-slip fracture conductivity coefficient at the top interface of the compact layer. The calculation method is as follows: multiply the vertical height difference at the top interface of the compact layer by the width of the fault fracture zone, and then normalize the product.

[0017] Furthermore, the vertical height difference at the top interface of the dense layer is calculated by the absolute value of the difference between the uplift or subsidence height of the strike-slip fault and the horizontal plane of the layer, and the product normalization method is Min-Max normalization.

[0018] Furthermore, the conductivity coefficient at the top of the dense layer is calculated using the following formula:

[0019] The conductivity coefficient of the top surface of the compact layer = height difference of the fracture zone * width of the fracture zone * thickness of the source rock / maximum thickness of the source rock * maximum thickness of the compact layer / thickness of the compact layer.

[0020] Furthermore, the process of correcting the injection point based on the calculated quantitative data and the segmented characteristics of the strike-slip fracture includes:

[0021] Based on the key layer thickness of the source rock layer and the tight layer, and the conductivity coefficient at the top of the tight layer, the vertical transport capacity of the strike-slip fault penetrating the tight layer is calculated. The vertical charging capacity of the strike-slip fault is then calculated and used as a quantitative basis for selecting the charging point of the strike-slip fault.

[0022] Furthermore, the calculation method for the vertical charging capacity of the strike-slip fault is as follows: Vertical charging capacity of strike-slip fault = conductivity coefficient of the tight layer × source rock thickness / thickness of the tight layer.

[0023] Furthermore, using the vertical injection capacity of strike-slip fractures as a quantitative basis for selecting injection points for strike-slip fractures includes:

[0024] Based on the rough range of the filling point, the filling point is corrected by overlapping it with the position with the greatest filling capacity.

[0025] Furthermore, the oil and gas migration index and crude oil physical property parameters are obtained by collecting parameters along strike-slip fractures and plotting them. The oil and gas migration index is specifically 4-1-MDBT, and the crude oil physical property parameters include oil column height, oil-gas ratio, crude oil density, wax content, and natural gas drying coefficient.

[0026] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0027] The method for determining hydrocarbon injection points related to strike-slip faults in sedimentary basins provided by this invention utilizes the segmented characteristics, fracture properties, and fracture fracture grid of the fault at the top of the tight layer to initially determine the injection point. Then, it uses a weighted quantitative evaluation of the fault's conductivity at the top of the tight layer using key stratigraphic thickness (positive effect of source rock thickness and negative effect of tight layer thickness) and conductivity coefficient (quantitative fault conductivity). Finally, it combines hydrocarbon migration indicators and crude oil physical properties to definitively determine the injection point. This method significantly improves the accuracy and reliability of determining hydrocarbon injection points related to strike-slip faults, providing guidance for oil and gas exploration and greatly enhancing exploration efficiency. Attached Figure Description

[0028] Various other advantages and benefits will become apparent to those skilled in the art upon reading the following detailed description of preferred embodiments. The accompanying drawings are for illustrative purposes only and are not intended to limit the invention. In the drawings:

[0029] Figure 1 This is a schematic diagram of the overall process of the method proposed in this invention;

[0030] Figure 2 This is a schematic diagram illustrating the segmentation of strike-slip fracture characteristics in an embodiment of the present invention;

[0031] Figure 3 This is a schematic diagram of crack density statistics in an embodiment of the present invention;

[0032] Figure 4 This is a schematic diagram illustrating the division of the key layer thickness coefficients of the source rock layer and the compact layer in an embodiment of the present invention;

[0033] Figure 5 This is a schematic diagram illustrating the vertical filling capacity division of strike-slip fracture in an embodiment of the present invention. Detailed Implementation

[0034] Exemplary embodiments of the present disclosure will now be described in more detail with reference to the accompanying drawings. While exemplary embodiments of the present disclosure are shown in the drawings, it should be understood that the present disclosure may be implemented in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided to enable a more thorough understanding of the present disclosure and to fully convey the scope of the disclosure to those skilled in the art. It should be noted that, unless otherwise specified, the embodiments and features described herein can be combined with each other. The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0035] Example 1

[0036] This embodiment provides a specific implementation of a method for determining hydrocarbon injection points related to strike-slip faults in sedimentary basins, such as... Figure 1 As shown, it includes the following steps:

[0037] Step S1: Collect geological information of the target area, clarify the segmentation characteristics of strike-slip faults in the dense layer overlying the source rock of the target area, the fault properties and the strike-slip fault fracture grid, and preliminarily identify the injection points;

[0038] The target area is the Halahatang Depression in the northern Tarim Basin. The source rock is the Cambrian Yuertus Formation, overlain by a tight layer, which seals the source rock. The reservoir is Ordovician limestone. Strike-slip faults cut through the Cambrian source rock and its overlying tight layer, migrating into the overlying reservoir. The segmentation characteristics of the strike-slip faults are determined through coherence or other fault attributes combined with artificial interpretation, such as... Figure 2 As shown; the nature of strike-slip faults is determined through seismic profile interpretation, and is classified into extensional-torsional, compressional-torsional, and translational faults. Extensional-torsional faults cause subsidence deformation of the strata, compressional-torsional faults cause convex deformation of the strata, and translational faults refer to strata that are basically horizontal with no vertical deformation. The fault grid of the dense overlying layer of the source rock is clearly defined, i.e., the fracture density at different locations of the fault zone is obtained using topological methods. Other fault density prediction methods can also be used to determine the fracture density of the fault zone, specifically as follows: Figure 3 As shown;

[0039] Step S2: Calculate quantitative parameters such as the key layer thickness of the source rock layer and the tight layer, and the transport coefficient at the top of the tight layer, and perform normalization processing, such as... Figure 4 As shown, based on its quantitative data and combined with the structural characteristics of the preceding fracture, the original filling points are corrected, reduced, or eliminated.

[0040] The thickness of the source rock refers to the thickness of the top and bottom surfaces of the source rock layer, which can be calculated from the seismic profile.

[0041] The thickness of the compact layer refers to the thickness of the top and bottom surfaces of the compact layer, which can be calculated from the seismic profile.

[0042] The strike-slip fracture conductivity at the top interface of a tight layer refers to the strike-slip fracture conductivity at that interface. It is calculated by multiplying the vertical height difference at the top interface of the tight layer by the width of the fault fracture zone and then normalizing the product.

[0043] The vertical height difference at the top interface of the compact layer is the absolute value of the difference between the uplift or subsidence height of the strike-slip fault and the horizontal plane of that layer. The product normalization method is Min-Max normalization.

[0044] The vertical transport capacity of strike-slip fractures through the tight layer is calculated based on the conductivity coefficient of strike-slip fractures in the tight layer and the thickness of the key layer. The vertical charging capacity of strike-slip fractures is then calculated and used as a quantitative basis for selecting the charging points of strike-slip fractures.

[0045] The calculation method for the vertical charging capacity of strike-slip faults is as follows: Vertical charging capacity of strike-slip faults = Conduction coefficient of tight layer × Source rock thickness / Thick layer thickness, such as... Figure 5 As shown.

[0046] Based on the filling point determined in the previous steps, the filling point is corrected by superimposing it with the position with the greatest filling capacity, so as to achieve both qualitative and quantitative evaluation.

[0047] Step S3: Verify the modification of the oil and gas injection point by combining the fluctuation points of the segmented changes of oil and gas migration indicators and crude oil physical property parameters.

[0048] Oil and gas migration indicators, along with other parameters such as crude oil properties, are collected and plotted by collecting parameters along strike-slip faults, as shown in the following examples. Figure 5 As shown.

[0049] Through the calculation of the source conductivity of strike-slip fractures, such as Figure 4 As shown, the vertical charging of the strike-slip fractures illustrated in the examples can be divided into four levels, with Class I representing the optimal oil and gas charging location and Class IV representing the worst oil and gas charging point location. The accuracy of the charging point can be verified by superimposing fluctuation points of oil and gas migration indicators and crude oil physical properties with the optimal oil and gas charging location. The coincidence rate between high-yield wells and Class I charging points is over 70%.

[0050] Example 2

[0051] This embodiment proposes a method for determining hydrocarbon injection points associated with strike-slip faults in sedimentary basins, including the following steps:

[0052] Step S1: Collect geological information of the target area and determine the approximate range of the injection point through qualitative analysis;

[0053] Step S2: Correct, reduce, or eliminate existing filling points using other parameters (quantitative analysis);

[0054] Step S3: Verify the oil and gas injection point by analyzing the fluctuation points of segmented changes in oil and gas migration indicators and crude oil physical properties.

[0055] As a preferred embodiment, the qualitative analysis in step S1 refers to clarifying the fracture segmentation characteristics, fracture properties, and fracture crack grid of the top surface of the dense layer at the top of the source rock, wherein the preferred location is the fault tension and torsion part and the part with the highest degree of fracture development as the initial filling location.

[0056] Among them, the segmentation characteristics and fracture properties of the top surface of the dense layer at the top of the source rock are interpreted by the seismic profile and plan view of the target area. The fracture grid is constructed by topological analysis of the strike-slip fracture at the top surface of the dense layer at the top of the source rock, combined with the fracture density and the degree of connection.

[0057] As a preferred embodiment, the step S2, which involves correcting, reducing, or eliminating the original injection points through other parameters (quantitative analysis), refers to the quantitative evaluation of the conductivity of the fault at the top surface of the tight layer of the source rock by using the thickness of the key stratigraphic layer and the conductivity coefficient.

[0058] The critical layer thickness refers to the thickness of the source rock and the thickness of the compact layer. The source rock thickness refers to the depth of the top surface, with priority given to injection points that are thicker and deeper at the top surface, while the compact layer preferentially selects injection points that are thinner.

[0059] The conductivity coefficient refers to the product of the height difference of the fracture zone and the width of the fracture zone, and the filling point with a large conductivity coefficient is preferred.

[0060] The calculation method for quantitatively evaluating the conductivity of the top surface of the compact layer is shown in the following formula:

[0061] The conductivity of the top surface of the compact layer = the height difference of the fracture zone * the width of the fracture zone * the thickness of the source rock / the maximum thickness of the source rock * the maximum thickness of the compact layer / the thickness of the compact layer.

[0062] In a preferred embodiment, step S3 maps the oil and gas injection point by the fluctuation points of segmented changes in parameters such as oil and gas migration indicators and crude oil physical properties. Specifically, it includes:

[0063] By combining oil and gas migration indicators and crude oil physical property parameters, the fluctuation points of segmented changes are used to verify the injection point determined by a combination of qualitative and quantitative methods.

[0064] The oil and gas migration index refers to 4-1-MDBT. The crude oil physical properties include oil column height, oil-gas ratio, crude oil density, wax content, and natural gas drying coefficient. The calculation method for the normalization process is shown in the following formula:

[0065] β = crude oil physical property parameter / maximum crude oil physical property parameter.

[0066] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the specific implementation of the present invention. Any modifications or equivalent substitutions that do not depart from the spirit and scope of the present invention should be covered within the scope of protection of the claims of the present invention.

Claims

1. A method for determining hydrocarbon injection points associated with strike-slip faults in sedimentary basins, characterized in that, Includes the following steps: Geological information of the target area was collected, and qualitative analysis was used to obtain the segment characteristics of strike-slip faults, fault properties and strike-slip fault fracture grids of the dense layer overlying the source rock in the target area, and to determine the approximate range of the injection point. The thickness of the key layers of the source rock strata and the tight layer, and the transport coefficient of the top of the tight layer are calculated and normalized. Based on the calculated quantitative data, the filling point is corrected in combination with the segmentation characteristics of the strike-slip fault. The corrected injection point is verified based on the fluctuation points of the segmented changes in oil and gas migration indicators and crude oil physical property parameters. The process of correcting the injection point based on the calculated quantitative data and the segmented characteristics of the strike-slip fracture includes: Based on the key layer thickness of the source rock layer and the tight layer, and the conductivity coefficient at the top of the tight layer, the vertical conductivity capacity of the strike-slip fault through the tight layer is calculated. The vertical charging capacity of the strike-slip fault is then calculated and used as a quantitative basis for selecting the charging point of the strike-slip fault. The key layer thickness of the source rock layer is specifically the thickness of the top and bottom surfaces of the source rock layer, which is calculated based on the seismic profile. The critical layer thickness of the dense layer is specifically the thickness of the top and bottom surfaces of the dense layer, which is calculated based on the seismic profile. The conductivity coefficient at the top of the dense layer is specifically the strike-slip fracture conductivity coefficient at the top interface of the dense layer. The calculation method is as follows: multiply the vertical height difference at the top interface of the dense layer by the width of the fracture zone, and then normalize the product. The vertical height difference at the top interface of the dense layer is calculated by the absolute value of the difference between the uplift or settlement height of the strike-slip fracture and the horizontal plane of the layer, and the product normalization method is Min-Max normalization.

2. The method of claim 1, wherein, The segmentation characteristics of the strike-slip fracture are determined by combining coherence or other fracture properties with manual interpretation. The nature of the fault is determined by the interpretation of seismic profiles and is divided into extensional-torsional, compressional-torsional, and translational faults. Extensional-torsional faults refer to the subsidence deformation caused by the fault, compressional-torsional faults refer to the convex deformation caused by the fault, and translational faults refer to the basic horizontality of the strata with no vertical deformation. The analysis process of the strike-slip fracture crack mesh includes: using topological methods or other fracture density prediction methods to obtain the crack density at different locations of the fracture zone.

3. The method of claim 1, wherein, Using the vertical injection capacity of strike-slip fractures as a quantitative basis for selecting injection points includes: Based on the rough range of the filling point, the filling point is corrected by overlapping it with the position with the greatest filling capacity.

4. The method of claim 1, wherein, The oil and gas migration index and crude oil physical property parameters are obtained by collecting parameters along strike-slip fractures and plotting them. The oil and gas migration index is specifically 4-1-MDBT, and the crude oil physical property parameters include oil column height, oil-gas ratio, crude oil density, wax content, and natural gas drying coefficient.

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