Method and system for identifying single sand body combination relationship of meandering river reservoir

Abstract

The application discloses a method and system for identifying single sand body combination relationship of meandering river reservoirs, comprising: obtaining the correlation between the length of the well track section corresponding to each resistivity change state on the resistivity logging curve in the horizontal well drilling process and the apparent dip angle of the sand-shale interface corresponding to the corresponding well track section; based on the correlation, determining the apparent dip angle of the corresponding sand-shale interface by using the length of the well track section corresponding to each resistivity change state on the resistivity logging curve of the target single sand body combination, thereby obtaining the distribution characteristics of the sand-shale interface in the target single sand body combination; by using the numerical distribution characteristics and the curve section shape corresponding to each resistivity change state on the resistivity logging curve of the target single sand body combination, combining the distribution characteristics of the sand-shale interface, obtaining the geological structure change along the drilling direction in the target single sand body combination, thereby forming the identification result of the target single sand body combination relationship. The application realizes accurate identification of the underground single sand body combination relationship.

Description

Technical Field

[0001] This invention belongs to the field of petroleum exploration and development technology, and in particular relates to a method and system for identifying the combination relationship of single sand bodies in meandering river reservoirs. Background Technology

[0002] Analyzing sedimentary sand bodies using well logging curve morphology is known as well logging facies analysis, also called electrical facies analysis, and was first proposed by Schlumberger and well logging analyst Serra in 1979. In well logging facies analysis, the correspondence between lithology and electrical properties is established by analyzing the well logging curve responses corresponding to typical sedimentary microfacies types from cored wells. Ultimately, this allows for the identification and determination of subsurface lithofacies and sedimentary facies based on well logging curves. The purpose of well logging facies analysis is to extend the lithofacies types determined by cored wells to non-cored wells.

[0003] Currently, well logging facies correlation techniques have matured, and numerous scholars have established corresponding well logging curve response templates based on the characteristics of different lithofacies / sedimentary facies. For example, well logging facies response models have been established for alluvial fans, fluvial facies, lacustrine facies, deltaic facies, estuarine facies, coastal facies, shallow marine shelf facies, semi-deep marine facies, and deep marine facies in China, targeting microfacies and even lithofacies scales. This has laid the foundation for the in-depth development of continental basin sedimentology and quantitative well logging sedimentology.

[0004] However, most existing well logging facies identification templates are based on vertical or directional wells, while well logging facies templates based on horizontal wells have been almost entirely neglected. Since horizontal wells typically drill along the top surface of sand bodies, the angles of the sandstone-mudstone interfaces encountered are gentle and small, resulting in smooth curve changes and high ambiguity. This makes it difficult to determine subsurface lithofacies relationships using the logging response characteristics of horizontal wells. Therefore, new technologies adapted to horizontal wells are needed to identify subsurface lithofacies sand bodies. Summary of the Invention

[0005] To address the aforementioned problems, this invention provides a method for identifying the relationships between single sandstone body combinations in meandering river reservoirs. The method includes: obtaining the correlation between the length of the well trajectory segment corresponding to each resistivity change state on the resistivity logging curve during horizontal well drilling and the apparent dip angle of the sand-mudstone interface corresponding to that well trajectory segment; based on this correlation, determining the corresponding apparent dip angle of the sand-mudstone interface using the length of the well trajectory segment corresponding to each resistivity change state on the resistivity logging curve of the target single sandstone body combination, thereby obtaining the distribution characteristics of the sand-mudstone interface within the target single sandstone body combination; and using the numerical distribution characteristics and curve segment morphology corresponding to each resistivity change state on the resistivity logging curve of the target single sandstone body combination, combined with the distribution characteristics of the sand-mudstone interface, obtaining the geological structural changes along the drilling direction within the target single sandstone body combination, thereby forming the identification result of the target single sandstone body combination relationship.

[0006] Preferably, the target single sand body assemblage is located in a sedimentary region of a single-phase or multi-phase meandering river deposit in the meandering river reservoir.

[0007] Preferably, the step of obtaining the geological structural changes along the drilling direction within a target single sand body assembly in a single-stage meandering river depositional area includes: determining the geological structural change as a transition from a point bar to an abandoned channel and back to a point bar when the continuous resistivity change states sequentially correspond to high values ​​and a flat curve segment, low values ​​and a flat curve segment, and high values ​​and a flat curve segment; determining the geological structural change as a transition from overflow sand to an abandoned channel and back to a point bar when the continuous resistivity change states sequentially correspond to a median value and a fluctuating curve segment, low values ​​and a flat curve segment, and high values ​​and a flat curve segment; and determining the geological structural change as a transition from overflow sand to an abandoned channel and back to a point bar when the continuous resistivity change states sequentially correspond to low values ​​and a flat curve segment, low values ​​slowly rising to high values ​​and a sloping curve segment, and high values ​​and a flat curve segment. When the continuous resistivity change states correspond to successively high values ​​and flat curve segments, high values ​​decreasing to low values ​​and sloping curve segments, and low values ​​and flat curve segments, the geological structure change is determined to be one of the following: drilling out of the top of the reservoir, from the point dam to the bay mud, or encountering a fault. When the continuous resistivity change states correspond to successively high values ​​and flat curve segments, high values ​​decreasing to the middle values ​​and sloping curve segments, and the middle values ​​and fluctuating curve segments, the geological structure change is determined to be from the point dam to the overflow sand. When the continuous resistivity change states are all at high values ​​and flat curve segments, and there is an intermittent curve return characteristic between adjacent resistivity change states, the geological structure change is determined to be the lateral accumulation layer inside the point dam.

[0008] Preferably, when the curve segment is straight, the current drilling stage is determined to be within a homogeneous sand body; when the curve segment fluctuates and is sawtooth-shaped, the current drilling stage is determined to be within a non-homogeneous sand body.

[0009] Preferably, after determining that the geological structural change is one of drilling to the top of the reservoir, from a point bar to an inter-bay mudflat, or encountering a fault, the method further includes: determining that the geological structural change is drilling to the top of the reservoir when the numerical value slowly decreases from a high level to a low level and no polarization angle is generated at the starting point of the numerical decrease; determining that the geological structural change is from a point bar to an inter-bay mudflat when the numerical value rapidly decreases from a high level to a low level and a polarization angle is generated at the starting point of the numerical decrease; and determining that the geological structural change is encountering a fault when the numerical value rapidly decreases from a high level to a low level.

[0010] Preferably, the step of obtaining the geological structural changes along the drilling direction within the target single sand body assemblage in a multi-stage meandering river depositional area includes: when the continuous resistivity change states correspond sequentially to high values ​​and straight curve segments, low values ​​and straight curve segments, and high values ​​and straight curve segments, the geological structural changes are determined to be one of late-stage abandoned river channel erosion of early-stage river channel point bars, late-stage point bars eroding early-stage abandoned river channels, or a progression from point bars to bays and back to point bars.

[0011] Preferably, after determining that the geological structural change is one of late-stage abandoned river channel erosion of early-stage river channel point bar, late-stage point bar erosion of early-stage abandoned river channel, or a change from point bar to bay and back to point bar, the method further includes: identifying the polarization angle of the continuous resistivity change state to further determine the current geological structural change.

[0012] Preferably, the correlation is represented by the following expression:

[0013] α = Arctan[(R+r) / L]

[0014] Where α represents the apparent dip angle of the sandstone-mudstone interface, R represents the radial detection radius of the electrode system in the sandstone, r represents the radial detection radius of the electrode system in the mudstone, L represents the length of the well trajectory segment corresponding to the resistivity change state, and Arctan represents the inverse trigonometric function.

[0015] The present invention also provides a computer-readable storage medium comprising a series of instructions for performing method steps for identifying the assemblage relationship of single sand bodies in a meandering river reservoir.

[0016] On the other hand, the present invention also provides a system for identifying the relationships of single sand body combinations in meandering river reservoirs. The system includes the following modules: a correlation construction module, used to obtain the correlation between the length of the well trajectory segment corresponding to each resistivity change state on the resistivity logging curve during horizontal well drilling and the apparent dip angle of the sand-mudstone interface corresponding to the corresponding well trajectory segment; an interface distribution feature acquisition module, used to determine the corresponding apparent dip angle of the sand-mudstone interface based on the correlation and the length of the well trajectory segment corresponding to each resistivity change state on the resistivity logging curve of the target single sand body combination, thereby obtaining the sand-mudstone interface distribution features within the target single sand body combination; and a combination relationship identification module, used to obtain the geological structural changes along the drilling direction within the target single sand body combination by combining the numerical distribution features and curve segment morphology corresponding to each resistivity change state on the resistivity logging curve of the target single sand body combination with the sand-mudstone interface distribution features, thereby forming the target single sand body combination relationship identification result.

[0017] Compared with the prior art, one or more embodiments of the above solutions may have the following advantages or beneficial effects:

[0018] This invention proposes a method and system for identifying the relationships between individual sandstone bodies in meandering river reservoirs. This method identifies these relationships based on horizontal well resistivity logging curves. First, using the length of the well trajectory segment corresponding to each resistivity change state on the horizontal well resistivity logging curve, and the radial probe radius during drilling, the apparent dip angle of the sandstone-mudstone interface corresponding to the well trajectory is qualitatively and quantitatively determined based on trigonometric functions. This determines the distribution characteristics of each sandstone-mudstone interface and clarifies its occurrence. Combining the numerical distribution characteristics and curve segment morphology corresponding to each resistivity change state on the resistivity logging curve, the target individual sandstone body relationship identification result is formed. This invention achieves accurate identification of individual sandstone body relationships, establishes a realistic horizontal well logging response template, and clarifies the true characteristics of individual sandstone body combinations.

[0019] Other features and advantages of the invention will be set forth in the description which follows, and will be apparent in part from the description, or may be learned by practicing the invention. The objects and other advantages of the invention may be realized and obtained by means of the structures particularly pointed out in the description, claims and drawings. Attached Figure Description

[0020] The accompanying drawings are provided to further illustrate the invention and form part of the specification. They are used in conjunction with the embodiments of the invention to explain the invention and do not constitute a limitation thereof. In the drawings:

[0021] Figure 1 This is a step diagram illustrating the method for identifying the combination relationship of single sand bodies in a meandering river reservoir according to an embodiment of this application.

[0022] Figure 2 This is an example diagram illustrating the resistivity logging curve formation process of the method for identifying the combination relationship of single sand bodies in a meandering river reservoir according to an embodiment of this application.

[0023] Figure 3 This is an example diagram of a single-stage meandering river reservoir from point dam to abandoned channel and back to point dam, illustrating the method for identifying the combination relationship of single sand bodies in a meandering river reservoir according to an embodiment of this application.

[0024] Figure 4 This is an example diagram of a single-stage meandering river reservoir from overflow sand to abandoned channel and then to point dam, which is an embodiment of the method for identifying the combination relationship of single sand bodies in meandering river reservoirs according to this application.

[0025] Figure 5 This is an example diagram of a single-stage meandering river sedimentary drilling into the top of a reservoir, illustrating the method for identifying the assemblage relationship of individual sand bodies in a meandering river reservoir according to an embodiment of this application.

[0026] Figure 6This is an example diagram of a single-stage meandering river sedimentary drilling at the top of a reservoir, illustrating the method for identifying the assemblage relationship of individual sand bodies in a meandering river reservoir according to an embodiment of this application.

[0027] Figure 7 This is an example diagram of a single-stage meandering river sedimentary deposition from point bar to interbay mud, which is an embodiment of the method for identifying the assemblage relationship of single sand bodies in meandering river reservoirs according to this application.

[0028] Figure 8 This is an example diagram of a single-stage meandering river sedimentary drilling encountering a fault, which is part of the method for identifying the assemblage relationship of single sand bodies in a meandering river reservoir according to an embodiment of this application.

[0029] Figure 9 This is an example diagram of a single-stage meandering river deposition from point bar to overflow sand, representing a method for identifying the assemblage relationship of single sand bodies in a meandering river reservoir according to an embodiment of this application.

[0030] Figure 10 This is an example diagram of a method for identifying the assemblage relationship of single sand bodies in a meandering river reservoir according to an embodiment of this application. It illustrates the method for identifying the assemblage relationship of single sand bodies in a meandering river reservoir during late-stage abandoned channel erosion and early-stage point bar formation in a multi-stage composite meandering river deposition.

[0031] Figure 11 This is an example diagram of a method for identifying the assemblage relationship of single sand bodies in a meandering river reservoir according to an embodiment of this application, showing the late-stage point bar erosion and early-stage abandoned river channel in a multi-stage complex meandering river deposition.

[0032] Figure 12 This is an example diagram of a method for identifying the combination relationship of single sand bodies in a meandering river reservoir according to an embodiment of this application, showing a multi-stage composite meandering river sedimentary point dam to inter-bay and then to point dam.

[0033] Figure 13 This is a block diagram of a system for identifying the combination relationship of single sand bodies in a meandering river reservoir, according to an embodiment of this application. Detailed Implementation

[0034] The embodiments of the present invention will be described in detail below with reference to the accompanying drawings and examples, so that the process of how the present invention uses technical means to solve technical problems and achieve technical effects can be fully understood and implemented accordingly. It should be noted that, as long as there is no conflict, the various embodiments and features in the various embodiments of the present invention can be combined with each other, and the resulting technical solutions are all within the protection scope of the present invention.

[0035] Furthermore, the steps shown in the flowchart in the accompanying drawings can be executed in a computer system such as a set of computer-executable instructions, and although a logical order is shown in the flowchart, in some cases the steps shown or described may be executed in a different order than that shown here.

[0036] Analyzing sedimentary sand bodies using well logging curve morphology is known as well logging facies analysis, also called electrical facies analysis, and was first proposed by Schlumberger and well logging analyst Serra in 1979. In well logging facies analysis, the correspondence between lithology and electrical properties is established by analyzing the well logging curve responses corresponding to typical sedimentary microfacies types from cored wells. Ultimately, this allows for the identification and determination of subsurface lithofacies and sedimentary facies based on well logging curves. The purpose of well logging facies analysis is to extend the lithofacies types determined by cored wells to non-cored wells.

[0037] Currently, well logging facies correlation techniques have matured, and numerous scholars have established corresponding well logging curve response templates based on the characteristics of different lithofacies / sedimentary facies. For example, well logging facies response models have been established for alluvial fans, fluvial facies, lacustrine facies, deltaic facies, estuarine facies, coastal facies, shallow marine shelf facies, semi-deep marine facies, and deep marine facies in China, targeting microfacies and even lithofacies scales. This has laid the foundation for the in-depth development of continental basin sedimentology and quantitative well logging sedimentology.

[0038] However, most existing well logging facies identification templates are based on vertical or directional wells, while well logging facies templates based on horizontal wells have been almost entirely neglected. Since horizontal wells typically drill along the top surface of sand bodies, the angles of the sandstone-mudstone interfaces encountered are gentle and small, resulting in smooth curve changes and high ambiguity. This makes it difficult to determine subsurface lithofacies relationships using the logging response characteristics of horizontal wells. Therefore, new technologies adapted to horizontal wells are needed to identify subsurface lithofacies sand bodies.

[0039] Therefore, to address the aforementioned problems, this invention proposes a method and system for identifying the combination relationships of single sand bodies in meandering river reservoirs. This method identifies the combination relationships of subsurface single sand bodies based on horizontal well resistivity logging curves. First, using the length of the well trajectory segment corresponding to each resistivity change state on the horizontal well resistivity logging curve, and the radial probe radius during drilling, the apparent dip angle of the sandstone-mudstone interface corresponding to the corresponding well trajectory is qualitatively and quantitatively calculated based on trigonometric function relationships. This determines the distribution characteristics of each sandstone-mudstone interface and clarifies the occurrence at each interface. Combining the numerical distribution characteristics and curve segment morphology corresponding to each resistivity change state on the resistivity logging curve, the target single sand body combination relationship identification result is formed. This invention achieves accurate identification of subsurface single sand body combination relationships, establishes a realistic horizontal well logging response template, and clarifies the true combination characteristics of subsurface single sand bodies.

[0040] Example 1

[0041] Figure 1 This is a step diagram illustrating the method for identifying the assemblage relationship of single sand bodies in a meandering river reservoir according to an embodiment of this application. See below for reference. Figure 1 This will explain each step of the method.

[0042] like Figure 1 As shown, in step S110, the correlation between the length of the well trajectory segment corresponding to each resistivity change state on the resistivity logging curve during horizontal well drilling and the apparent dip angle of the sandstone-mudstone interface corresponding to the well trajectory segment is obtained.

[0043] Specifically, during horizontal well resistivity logging, the thruster propels the logging instrument forward, and the logging electrode system inside the logging instrument measures and records the properties of the surrounding reservoir while drilling. The radial detection radius corresponding to different reservoir electrical properties (e.g., mudstone reservoir, sandstone reservoir) can be found in the equipment manual for each logging electrode system. Figure 2 This is an example diagram illustrating the resistivity logging curve formation process of the method for identifying the single sand body combination relationship in a meandering river reservoir according to an embodiment of this application. Figure 2 As shown, the radial detection radius of the logging electrode system under the electrical properties of sandstone in region A is R, and the radial detection radius under the electrical properties of mudstone in region B is r. During drilling exploration, the actual radial detection radius is usually affected by various factors and exhibits a complex elliptical structure. First, in homogeneous sandstone, the resistivity logging curve remains stable, indicating the sandstone reservoir resistance. Then, the logging electrode system advances along the well trajectory to the vicinity of the sandstone-mudstone interface. When the upper edge of the radial detection radius reaches the sandstone-mudstone interface (point M), the curve begins to decline. Then, the logging electrode system continues to advance, and when the lower edge of the radial detection radius reaches the sandstone-mudstone interface (point M'), the curve reaches its minimum value. Finally, the curve remains horizontal and stable in homogeneous mudstone, indicating the mudstone resistance.

[0044] In one specific embodiment of this application, the well trajectory segment length L corresponding to each resistivity change state on the resistivity logging curve during horizontal well drilling, as well as the radial detection radius R and r, are used to construct the correlation between the well trajectory segment length L corresponding to each resistivity change state on the resistivity logging curve during horizontal well drilling and the apparent dip angle α of the sandstone-mudstone interface corresponding to the corresponding well trajectory segment, based on trigonometric function relationships.

[0045] In this embodiment of the application, the correlation is represented by the following expression:

[0046] α=Arctan[(R+r) / L] (1)

[0047] Where α represents the apparent dip angle of the sandstone-mudstone interface, R represents the radial detection radius of the electrode system in the sandstone, r represents the radial detection radius of the electrode system in the mudstone, L represents the length of the well trajectory segment corresponding to the resistivity change state, and Arctan represents the inverse trigonometric function.

[0048] Next, analysis of the constructed correlations reveals that, under the premise of limited variation in the detection radius, the apparent dip angle α of the sandstone-mudstone interface is primarily inversely correlated with the corresponding well trajectory segment length L. Specifically, the longer / shorter the well trajectory segment L corresponding to the resistivity variation state, the smaller / larger the corresponding apparent dip angle α of the sandstone-mudstone interface. Given that subsurface sand bodies often possess fixed arrangements and different geometric shapes, this invention utilizes the constructed correlations to achieve qualitative and quantitative calculations of the apparent dip angle of the sandstone-mudstone interface at the end of the corresponding well trajectory segment within a target sandstone body combination. This allows for the determination of the distribution characteristics of each sandstone-mudstone interface, thereby providing a basis for judging the combination relationships of subsurface sand bodies.

[0049] Furthermore, in step S120, based on the correlation, the length of the well trajectory segment corresponding to each resistivity change state on the resistivity logging curve of the target single sand body combination is used to determine the corresponding dip angle of the sand-mudstone interface, thereby obtaining the distribution characteristics of the sand-mudstone interface within the target single sand body combination.

[0050] Specifically, in this embodiment, the length of the well trajectory segment corresponding to each resistivity change state on the resistivity logging curve of the target single sand body combination is substituted into the correlation constructed in step S110 to qualitatively calculate the apparent dip angle of the corresponding sand-mudstone interface, thereby determining the number of sand-mudstone interfaces, their location, and the magnitude of their dip angles within the target single sand body combination, as well as other sand-mudstone interface distribution characteristics. If the geological conditions of the target single sand body combination are complex, further quantitative and precise calculations are performed on the apparent dip angle of the sand-mudstone interface to accurately obtain the distribution characteristics of the sand-mudstone interface.

[0051] Furthermore, in step S130, the numerical distribution characteristics and curve segment morphology corresponding to each resistivity change state on the resistivity logging curve of the target single sand body combination are used, combined with the distribution characteristics of the sandstone-mudstone interface, to obtain the geological structural changes of the target single sand body combination along the drilling direction, thereby forming the target single sand body combination relationship identification result.

[0052] Specifically, in this embodiment, the determination of the target single sand body combination relationship is based on obtaining the distribution characteristics of the sand-mudstone interface. First, using the numerical distribution characteristics and curve segment morphology corresponding to each resistivity change state on the resistivity logging curve of the target single sand body combination, the geological structural changes at the sand-mudstone interface between adjacent single sand bodies within the target single sand body combination are described. Then, the described geological structural changes are integrated with the sand-mudstone interface distribution characteristics to obtain the geological structural changes at different locations within the target single sand body combination, and these are used as the geological structural changes along the drilling direction. Based on this, the purpose of identifying the target single sand body combination relationship can be achieved.

[0053] In the embodiments of this application, the sedimentary region in which the target single sand body assemblage is located in the meandering river reservoir is a single-stage meandering river deposition or a multi-stage meandering river deposition.

[0054] In the step of obtaining the geological structural changes along the drilling direction within a target single sand body assembly in a single-stage meandering river depositional area, when the continuous resistivity change states sequentially correspond to high values ​​and flat curve segments, low values ​​and flat curve segments, and high values ​​and flat curve segments, the geological structural change is determined to be from a point bar to an abandoned channel and back to a point bar; when the continuous resistivity change states sequentially correspond to mid-range values ​​and fluctuating curve segments, low values ​​and flat curve segments, and high values ​​and flat curve segments, the geological structural change is determined to be from overflow sand to an abandoned channel and back to a point bar; when the continuous resistivity change states sequentially correspond to low values ​​and flat curve segments, low values ​​slowly rising to high values ​​and sloping curve segments, and high values ​​and flat curve segments, the geological structural change is determined to be from overflow sand to an abandoned channel and back to a point bar. The geological structural change is determined as drilling into the top of the reservoir; when the continuous resistivity change states correspond to successively high values ​​and flat curve segments, high values ​​decreasing to low values ​​and sloping curve segments, and low values ​​and flat curve segments, the geological structural change is determined to be one of the following: drilling out of the top of the reservoir, from the point dam to the bay mud, or encountering a fault; when the continuous resistivity change states correspond to successively high values ​​and flat curve segments, high values ​​decreasing to the middle values ​​and sloping curve segments, and the middle values ​​and fluctuating curve segments, the geological structural change is determined to be from the point dam to the overflow sand; when the continuous resistivity change states are all at high values ​​and flat curve segments, and there is an intermittent curve return characteristic between adjacent resistivity change states, the geological structural change is determined to be the lateral accumulation layer inside the point dam.

[0055] Figure 3 This is an example diagram illustrating the method for identifying the assemblage relationship of single sand bodies in a meandering river reservoir according to an embodiment of this application, from point bar to abandoned channel and back to point bar. (See diagram for reference.) Figure 3 As shown, in a specific embodiment of this application, the continuous resistivity change states on the resistivity logging curve of the target single sand body combination correspond sequentially to a high value and a flat curve segment, a low value and a flat curve segment, and a high value and a flat curve segment. The curve segment morphology changes as follows during drilling: First, when drilling inside point dam 2 (sandstone), the curve segment remains high and flat overall (A to M parts); then, after encountering the abandoned river channel (mudstone), the curve segment begins to drop rapidly (M to M' parts); next, when drilling inside the abandoned river channel (mudstone), the curve remains low and flat overall (M' to N' parts); then, after encountering point dam 1 (sandstone), that is, after drilling out of the abandoned river channel (mudstone), the curve segment begins to rise slowly again (N' to N parts); finally, when drilling inside point dam 1 (sandstone), the curve segment remains high and flat overall (N to B parts). Based on this, the geological structure change was determined to be from point dam 2 (sandstone) to abandoned river channel (mudstone) and then to point dam 1 (sandstone).

[0056] In one specific embodiment of this application, the slope of the curve segment during the drilling process of encountering an abandoned riverbed (mudstone) is greater than that during the drilling process of exiting an abandoned riverbed (mudstone), and the length of the well trajectory segment is shorter. Therefore, the drilling process of encountering an abandoned riverbed (mudstone) corresponds to the concave bank of the abandoned riverbed, and the drilling process of exiting an abandoned riverbed corresponds to the convex bank of the abandoned riverbed.

[0057] Figure 4 This is an example diagram illustrating a single-stage meandering river reservoir, from overflow sand to abandoned channel and then to point dam, as described in the method for identifying the composite relationship of individual sand bodies in a meandering river reservoir according to an embodiment of this application. Figure 4 As shown, in a specific embodiment of this application, the continuous resistivity change states on the resistivity logging curve of the target single sand body combination correspond sequentially to the median value and fluctuating curve segment, the low value and flat curve segment, and the high value and flat curve segment. The curve segment morphology changes during drilling as follows: First, when drilling inside the overflow sand (siltstone), the curve segment remains in the median and fluctuates (A to M parts); then, after encountering the abandoned river channel (mudstone), the curve segment begins to drop rapidly (M to M' parts); next, when drilling inside the abandoned river channel (mudstone), the curve segment remains low and flat overall (M' to N' parts); then, based on the aforementioned analysis of the concave bank and convex bank of the abandoned river channel, after drilling out of the convex bank of the abandoned river channel, the curve segment begins to rise slowly again (N' to N parts); finally, when drilling inside the point dam (sandstone), the curve segment remains high and flat overall (N to B parts). Based on this, the geological structure changes were determined to be from overflow sand (siltstone) to abandoned river channel (mudstone) and then to point dam (sandstone).

[0058] Figure 5 This is an example diagram of a single-stage meandering river sedimentary drilling into the top of a reservoir, illustrating the method for identifying the assemblage relationship of single sand bodies in a meandering river reservoir according to an embodiment of this application. Figure 5 As shown in a specific embodiment of this application, the continuous resistivity change states of the target single sand body combination correspond sequentially to a low value and a straight curve segment, a low value slowly rising to a high value and a sloping curve segment, and a high value and a straight curve segment. The curve segment morphology changes during drilling as follows: First, before landing on the reservoir, the curve segment remains low and straight (A to N'); then, influenced by the high resistivity of the sand body, the curve segment shows a slow upward trend during reservoir landing (N' to N), at which point the slope of the curve segment is extremely small; finally, during drilling inside the sand body, the curve segment remains high and straight (N to B). Based on this, the geological structure change is determined to be drilling into the top of the reservoir. In practical applications, during reservoir landing, meandering river reservoirs often have a flat-top, convex-bottom structure, with a very small occurrence of the sandstone-mudstone interface at the top, resulting in a very slow upward trend in the curve segment and an extremely long corresponding well trajectory segment, verifying the rationality of this invention in determining that the geological structure change is drilling into the top of the reservoir.

[0059] When the continuous resistivity change states correspond to successively high values ​​and flat curve segments, high values ​​decreasing to low values ​​and sloping curve segments, and low values ​​and flat curve segments, the corresponding geological structure changes are not unique. They may be drilling out of the top of the reservoir, or they may be drilling from the point dam to the bay mud or encountering a fault.

[0060] Figure 6 This is an example diagram of a single-stage meandering river sedimentary drilling at the top of a reservoir, illustrating the method for identifying the assemblage relationship of single sand bodies in a meandering river reservoir according to an embodiment of this application. Figure 6 As shown, besides encountering abandoned channels, drilling from the top of the sand body to exit the reservoir can also cause the resistivity logging curve to show a downward trend. Considering that sand bodies in meandering river reservoirs usually have a flat-top, convex-bottom structure, and that the dip angle of the reservoir top (apparent dip angle of the interface) is usually much smaller than the apparent dip angle of the sandstone-mudstone interface corresponding to the abandoned channel, the slope of the curve segment corresponding to the abandoned channel is greater than that of the segment when drilling from the top of the reservoir. Therefore, it is possible to make a simple distinction between these two geological structural changes: encountering an abandoned channel and drilling from the top of the sand body to exit the reservoir. The curve segment morphology changes during drilling as follows: First, when the drill bit is drilling inside the point bar (sandstone), the curve segment remains high and straight (A to M); during the process of drilling from the top of the reservoir, the curve segment shows a very slow downward trend (M to M'); finally, after drilling from the top of the reservoir, the curve segment remains low and straight (M' to B). In addition, the connection points between adjacent curve segments must also meet the condition that no polarization angle is generated. Therefore, when the value slowly decreases from a high level to a low level, the slope of the curve segment is extremely small, and no polarization angle is generated at the starting point of the value decrease, the geological structure change is determined to be drilling out of the top of the reservoir.

[0061] Figure 7 This is an example diagram of a single-stage meandering river sedimentary deposition from point bars to interbay mud, illustrating the method for identifying the assemblage relationship of single sand bodies in a meandering river reservoir according to an embodiment of this application. Figure 7 As shown, in a specific embodiment of this application, the continuous resistivity change state of the target single sand body assembly corresponds sequentially to a rapid decrease from a high value to a low value, with a polarization angle generated at the starting point of the decrease. The morphological changes of the curve segment during drilling are as follows: First, the drill bit drills inside the point dam (sandstone), and the curve segment remains high and straight overall (parts A to M); after encountering the inter-bay mud, the curve segment begins to decrease (parts M to M'), at which point the slope of the curve segment is relatively large; finally, drilling inside the inter-bay mud, the curve segment remains low and straight overall (parts M' to B). In addition, point dams generally have a flat top and convex bottom structure, with the bottom sandstone-mudstone interface having a larger dip than the top, resulting in a larger slope in the descending section of the curve. Furthermore, when the drill bit enters the inter-bay mud from the bottom of the point dam, the sandstone and mudstone abruptly contact each other, generating a polarization angle at point M. Based on this, the geological structural change is determined to be from the point dam (sandstone) to the inter-bay mud.

[0062] Due to the influence of faults, the point dam reservoir in the meandering river may suddenly pinch out. Figure 8 This is an example diagram of a single-stage meandering river sedimentary drilling encountering a fault, illustrating the method for identifying the assemblage relationship of single sand bodies in a meandering river reservoir according to an embodiment of this application. Figure 8 As shown, in a specific embodiment of this application, the continuous resistivity change state of the target single sand body assembly corresponds sequentially to a rapid decrease from a high value to a low value. The morphology of the curve segment changes as follows during drilling: when the drill bit is drilling inside the point dam (sandstone), the curve segment remains high and straight overall (sections A to M); after encountering a fault, the curve segment begins to drop rapidly (sections M to M'), meaning that the slope of the curve segment is almost steep at this point; finally, when drilling inside the mudstone, the curve segment remains low and straight overall (sections M' to B). Furthermore, since faults typically have a large apparent dip angle, the curve segment usually drops sharply during fault encounters, and at point M, a polarization angle is generated due to the abrupt change between sandstone and mudstone. Based on this, the geological structural change is determined to be the encounter of a fault.

[0063] Figure 9 This is an example diagram of a single-stage meandering river depositional process from point bar to overflow sand, illustrating the method for identifying the assemblage relationship of single sand bodies in a meandering river reservoir according to an embodiment of this application. Figure 9 As shown in a specific embodiment of this application, the continuous resistivity change states on the resistivity logging curve of the target single sand body combination correspond sequentially to a high value and a flat curve segment, a high value decreasing to a mid-value and a fluctuating curve segment. The curve segment morphology changes during drilling as follows: First, drilling inside the point dam (sandstone), the curve segment remains high and flat overall (A-M portion); then, after encountering overflow sand, the curve segment begins to decline (M-M' portion); finally, drilling inside the overflow sand, the curve segment remains mid-value and fluctuates overall (M'-B portion). The fluctuation amplitude is mainly affected by the heterogeneity of the internal physical properties of the overflow sand. Based on this, the geological structural change is determined to be from the point dam to the overflow sand.

[0064] In practical applications, lateral accretion layers are the most important interlayers within a point bar, consisting of fine-grained overburden deposits formed by periodic weakening of hydrodynamics, typically distributed intermittently at certain intervals in a plane. Due to the limited thickness of lateral accretion layers, usually ranging from tens of centimeters to one meter, excessively thin layers only cause a slight backsliding phenomenon in the resistivity logging curve. Therefore, in this embodiment, in a specific instance of this application, when the continuous resistivity changes on the resistivity logging curve of the target single sand body combination are all at high values ​​and the curve segments are flat, and when there are intermittent backsliding characteristics between adjacent resistivity change states, the geological structural change is determined to be a lateral accretion layer within the point bar.

[0065] When the curve segment is straight, the current drilling stage is determined to be within a homogeneous sand body; when the curve segment fluctuates and is sawtooth-shaped, the current drilling stage is determined to be within a non-homogeneous sand body.

[0066] Specifically, the straightness or undulation of the curve segment depends on the homogeneity of the lithology within the corresponding single sand body. For example, a straight curve segment corresponds to homogeneous sand bodies such as point dams, bay mud, and abandoned river channels, while a undulating curve segment, especially a sawtooth-shaped undulation, corresponds to heterogeneous sand bodies such as overflow sand and natural levees.

[0067] Example 2

[0068] In practical oilfield applications, meandering river reservoirs not only exhibit single-stage sedimentation but also multi-stage composite meandering river deposition. In these multi-stage composite meandering river deposits, sand bodies are also separated by mudstone deposits such as abandoned channels or inter-bay mud. When the continuous resistivity change corresponds sequentially to high values ​​with a flat curve segment, low values ​​with a flat curve segment, and high values ​​with a flat curve segment, the geological structural change is determined to be either late-stage abandoned channel erosion of early-stage channel point bars, or late-stage point bars eroding early-stage abandoned channels, or a progression from point bars to inter-bays and back to point bars.

[0069] Figure 10 This is an example diagram of a method for identifying the assemblage relationship of single sand bodies in a meandering river reservoir, based on embodiments of this application, illustrating the process of identifying the relationship between single sand bodies in a meandering river reservoir during late-stage abandoned channel erosion and early channel point bars in a multi-stage complex meandering river deposition. (See diagram for example.) Figure 10 As shown in a specific embodiment of this application, in the superposition of two-stage meandering river zones, the continuous resistivity change states on the resistivity logging curve of the target single sand body combination in the later stage abandoned river channel eroding the previous stage point dam (within the meandering river channel) correspond sequentially to high value and flat curve segment, low value and flat curve segment, and high value and flat curve segment. That is, the change in curve segment shape during drilling is related to... Figure 3 The curve segments shown exhibit similar morphological changes, therefore, it is necessary to combine them with the comprehensive thickness map of regional sand bodies generated by earthquakes and dense well networks for further determination. For example: if the thickness map shows that the river channel is clearly a single strip, and the abandoned river channel meanders and cuts along the perimeter of the strip, then the geological structure change is determined to be consistent with a single-phase meandering river depositional area, from point bar to abandoned river channel and back to point bar; if the thickness map shows that the river channel is clearly superimposed in multiple phases, with sand bodies developing in the middle of the abandoned river channel, and mainly meandering around the perimeter of a river channel strip, then the geological structure change is determined to be consistent with a late-phase abandoned river channel eroding an early-phase river channel point bar in a multi-phase meandering river depositional area.

[0070] After determining that the geological structural change is one of the following: late-stage abandoned channel erosion of early-stage point bars, late-stage point bars eroding early-stage abandoned channels, or a progression from point bars to bays and back to point bars, this invention further determines the current geological structural change by identifying the polarization angle of the continuous resistivity change. In meandering river deposits with multiple overlapping channel phases, given the issue of various sand body assemblages exhibiting similar continuous resistivity change states, to accurately determine whether the geological structural change is late-stage point bars eroding early-stage abandoned channels or a progression from point bars to bays and back to point bars, it is necessary to further assess the overall channel morphology and whether polarization angles appear on both sides of the mudstone.

[0071] Because point dams typically erode abandoned river channels through scouring, they create abrupt contact at the interface. The resistivity curve often exhibits polarization angles where the slope changes gently, which contradicts the formation pattern of abandoned river channels. In other words, if a polarization angle appears on the resistivity curve where the slope changes gently, the geological structure is determined to be a late-stage point dam eroding an early-stage abandoned river channel. Furthermore, since point dam sand bodies often cut through intermontane mudstone, the interface between the two is abruptly contacted. Therefore, if polarization angles appear on both sides of the mudstone due to the abrupt change between sandstone and mudstone, the geological structure is determined to be a transition from point dam to intermontane and back to point dam.

[0072] Figure 11 This is an example diagram of a method for identifying the assemblage relationship of single sand bodies in a meandering river reservoir, based on an embodiment of this application, illustrating the late-stage point bar erosion and early abandoned channel in a multi-phase complex meandering river deposition. (See diagram for example.) Figure 11 As shown, in a specific embodiment of this application, in the superposition of two-stage meandering river zones, the continuous resistivity change state on the resistivity logging curve of the target single sand body combination is similar to that of the abandoned river channel inside the meandering river channel in the later stage of point dam erosion of the earlier stage. Figure 3 The curve segments shown show similar morphological changes. At this point, based on the fact that point dams typically erode abandoned river channels through scouring, causing abrupt contact at the interface between the two and forming a polarization angle, that is, if a polarization angle appears on the resistivity curve where the slope changes gently, then, combined with a judgment method similar to the geological structural changes along the drilling direction within the target single sand body assemblage in a single-stage meandering river depositional area, the geological structural change is determined to be late-stage point dam erosion of an early-stage abandoned river channel.

[0073] Figure 12 This is an example diagram illustrating the method for identifying the assemblage relationship of single sand bodies in meandering river reservoirs according to embodiments of this application, showing a multi-stage composite meandering river sedimentary point bar to inter-bay and then to point bar formation. (See diagram below.) Figure 12 As shown, in a specific embodiment of this application, two point dams in a meandering river are arranged facing each other, with a section of intermontane mudstone in between. The drill bit enters / exits from the bottom of the two point dams. The continuous resistivity variation state on the resistivity logging curve of the target single sand body combination is also similar to... Figure 3The curve segments shown show similar morphological changes. At this point, based on the polarization angles formed by the abrupt changes in sandstone and mudstone on both sides of the mudstone, combined with the judgment method similar to the geological structural changes along the drilling direction within the target single sand body assemblage in a single-stage meandering river depositional area, the geological structural changes are determined to be from point bar to bay and then back to point bar.

[0074] Example 3

[0075] This invention also provides a computer-readable storage medium storing at least one instruction that is loaded and executed by a processor to perform the operation of identifying the assemblage relationship of single sand bodies in a meandering river reservoir, as performed in the method of the above embodiments. For example, the computer-readable storage medium may be a ROM (Read Only Memory), RAM (Random Access Memory), CD-ROM (Compact Disc-Read Only Memory), magnetic tape, floppy disk, or optical data storage device, etc.

[0076] Example 4

[0077] Based on the method for identifying the combination relationship of single sand bodies in meandering river reservoirs described in Embodiment 1 above, this embodiment of the invention also provides a system for identifying the combination relationship of single sand bodies in meandering river reservoirs (hereinafter referred to as "single sand body combination relationship identification system").

[0078] Figure 13 This is a block diagram of a system for identifying the assemblage relationships of single sand bodies in meandering river reservoirs, according to an embodiment of this application. Figure 13As shown, the single sand body combination relationship identification system in this embodiment of the invention includes: a correlation relationship construction module 131, an interface distribution feature acquisition module 132, and a combination relationship identification module 133. The correlation construction module 131 is implemented according to the method described in step S110 above, and is configured to obtain the correlation between the length of the well trajectory segment corresponding to each resistivity change state on the resistivity logging curve during horizontal well drilling and the apparent dip angle of the sandstone-mudstone interface corresponding to the corresponding well trajectory segment; the interface distribution feature acquisition module 132 is implemented according to the method described in step S120 above, and is configured to determine the corresponding apparent dip angle of the sandstone-mudstone interface based on the correlation and using the length of the well trajectory segment corresponding to each resistivity change state on the resistivity logging curve of the target single sandstone body combination, thereby obtaining the sandstone-mudstone interface distribution features within the target single sandstone body combination; the combination relationship identification module 133 is implemented according to the method described in step S130 above, and is configured to obtain the geological structural changes along the drilling direction within the target single sandstone body combination by using the numerical distribution features and curve segment morphology corresponding to each resistivity change state on the resistivity logging curve of the target single sandstone body combination, combined with the sandstone-mudstone interface distribution features, thereby forming the target single sandstone body combination relationship identification result.

[0079] This invention discloses a method and system for identifying the combination relationships of single sand bodies in meandering river reservoirs. The method identifies these relationships based on horizontal well resistivity logging curves. First, using the length of the well trajectory segment corresponding to each resistivity change state on the horizontal well resistivity logging curve, and the radial probe radius during drilling, the apparent dip angle of the sand-mudstone interface at the end of the corresponding well trajectory segment is qualitatively and quantitatively calculated based on trigonometric functions. This determines the distribution characteristics of each sand-mudstone interface and clarifies its occurrence. Combining the numerical distribution characteristics and curve segment morphology corresponding to each resistivity change state on the resistivity logging curve, the target single sand body combination relationship is identified. This invention achieves accurate identification of subsurface single sand body combination relationships, establishes a realistic horizontal well logging response template, and clarifies the true combination characteristics of subsurface single sand bodies.

[0080] The above description is merely a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

[0081] Of course, the present invention may have other various embodiments. Without departing from the spirit and essence of the present invention, those skilled in the art can make various corresponding changes and modifications according to the present invention, but these corresponding changes and modifications should all fall within the protection scope of the claims of the present invention.

[0082] Those skilled in the art will understand that the modules or steps of the present invention described above can be implemented using general-purpose computing devices. They can be centralized on a single computing device or distributed across a network of multiple computing devices. Optionally, they can be implemented using computer-executable program code, thereby storing them in a storage device for execution by a computing device, or fabricating them separately as individual integrated circuit modules, or fabricating multiple modules or steps as a single integrated circuit module. Thus, the present invention is not limited to any particular hardware and software combination.

[0083] While the embodiments disclosed in this invention are as described above, the content is merely for the purpose of facilitating understanding of the invention and is not intended to limit the invention. Any person skilled in the art to which this invention pertains may make any modifications and variations in form and detail of the implementation without departing from the spirit and scope disclosed herein; however, the scope of patent protection for this invention shall still be determined by the scope defined in the appended claims.

Claims

1. A method for identifying the assemblage relationship of single sand bodies in meandering river reservoirs, characterized in that, include: The correlation between the length of the well trajectory segment corresponding to each resistivity change state on the resistivity logging curve during horizontal well drilling and the apparent dip angle of the sandstone-mudstone interface corresponding to the well trajectory segment is obtained. Based on the aforementioned correlation, the length of the well trajectory segment corresponding to each resistivity change state on the resistivity logging curve of the target single sand body combination is used to determine the apparent dip angle of the sand-mudstone interface, thereby obtaining the distribution characteristics of the sand-mudstone interface within the target single sand body combination. By utilizing the numerical distribution characteristics and curve segment morphology corresponding to each resistivity change state on the resistivity logging curve of the target single sand body combination, combined with the distribution characteristics of the sand-mudstone interface, the geological structural changes along the drilling direction within the target single sand body combination are obtained, thereby forming the target single sand body combination relationship identification result.

2. The method according to claim 1, characterized in that, The target single sand body assemblage is located in a depositional region of either a single-phase or multi-phase meandering river deposition within a meandering river reservoir.

3. The method according to claim 2, characterized in that, The steps for obtaining the geological structural changes along the drilling direction within a target single sand body assembly in a single-stage meandering river depositional region include: When the continuous resistivity change states correspond sequentially to high values ​​and flat curve segments, low values ​​and flat curve segments, and high values ​​and flat curve segments, the geological structure change is determined to be from point dam to abandoned river channel and back to point dam. When the continuous resistivity change states correspond sequentially to the median value and fluctuating curve segment, the low value and flat curve segment, and the high value and flat curve segment, the geological structure change is determined to be from overflow sand to abandoned river channel and then to point dam. When the continuous resistivity change states correspond to successively low values ​​and flat curve segments, low values ​​slowly rising to high values ​​and sloping curve segments, and high values ​​and flat curve segments, the geological structure change is determined to be drilling into the top of the reservoir. When the continuous resistivity change states correspond to the following conditions in sequence: high value and flat curve segment, high value decrease to low value and sloping curve segment, and low value and flat curve segment, the geological structure change is determined to be one of the following: drilling to the top of the reservoir, from the point dam to the bay mud, or drilling encountering a fault. When the continuous resistivity change states correspond to the following values ​​in sequence: high value and flat curve segment, high value decrease to middle value and sloping curve segment, and middle value and fluctuating curve segment, the geological structure change is determined to be from point dam to overflow sand. When the continuous resistivity change states are all at high values ​​and the curve segments are flat, and there is an intermittent curve return characteristic between adjacent resistivity change states, the geological structure change is determined to be the lateral accumulation layer inside the point dam.

4. The method according to claim 3, characterized in that, When the curve segment is straight, it is determined that the current drilling stage is within a homogeneous sand body; When the curve segment fluctuates and exhibits sawtooth-like fluctuations, it is determined that the current drilling stage is within a non-lithological homogeneous sand body.

5. The method according to claim 3 or 4, characterized in that, After determining that the geological structural change is one of the following: drilling to the top of the reservoir, from a point bar to an inter-bay mudflat, or encountering a fault, the method further includes: When the numerical value slowly decreases from a high level to a low level, and no polarization angle is generated at the starting point of the decrease, the geological structure change is determined to be drilling out of the top of the reservoir. When the numerical value rapidly decreases from a high level to a low level, and a polarization angle is generated at the starting point of the numerical decrease, the geological structure change is determined to be from point dam to inter-bay mud. When the numerical value drops rapidly from a high level to a low level, the geological structure change is determined to be an encounter with a fault.

6. The method according to any one of claims 2 to 5, characterized in that, The steps for obtaining the geological structural variations along the drilling direction within a target single sand body assembly in a multi-stage meandering river depositional region include: When the continuous resistivity change states correspond sequentially to high values ​​and flat curve segments, low values ​​and flat curve segments, and high values ​​and flat curve segments, the geological structure change is determined to be either late-stage abandoned river channel erosion of early-stage river channel point dams, late-stage point dam erosion of early-stage abandoned river channels, or a process from point dams to bays and back to point dams.

7. The method according to claim 6, characterized in that, After determining that the geological structural changes are one of late-stage abandoned river channel erosion of early-stage river channel point bars, late-stage point bars eroding early-stage abandoned river channels, or a progression from point bars to bays and back to point bars, the method further includes: By identifying the polarization angle of continuous resistivity changes, the current geological structural changes can be further determined.

8. The method according to any one of claims 1 to 7, characterized in that, The correlation is represented by the following expression: α = Arctan[(R+r) / L] Where α represents the apparent dip angle of the sandstone-mudstone interface, R represents the radial detection radius of the electrode system in the sandstone, r represents the radial detection radius of the electrode system in the mudstone, L represents the length of the well trajectory segment corresponding to the resistivity change state, and Arctan represents the inverse trigonometric function.

9. A computer-readable storage medium, characterized in that, It includes a series of instructions for performing the method steps of identifying the assemblage relationship of single sand bodies in meandering river reservoirs as described in any one of claims 1 to 8.

10. A system for identifying the assemblage relationships of single sand bodies in meandering river reservoirs, characterized in that, The system includes the following modules: The correlation construction module is used to obtain the correlation between the length of the well trajectory segment corresponding to each resistivity change state on the resistivity logging curve during horizontal well drilling and the apparent dip angle of the sandstone-mudstone interface corresponding to the well trajectory segment. The interface distribution feature acquisition module is used to determine the apparent dip angle of the sand-mudstone interface based on the correlation relationship and the length of the well trajectory segment corresponding to each resistivity change state on the resistivity logging curve of the target single sand body combination, thereby obtaining the sand-mudstone interface distribution features in the target single sand body combination. The combination relationship identification module is used to obtain the geological structural changes along the drilling direction within the target single sand body combination by utilizing the numerical distribution characteristics and curve segment morphology corresponding to each resistivity change state on the resistivity logging curve of the target single sand body combination, combined with the distribution characteristics of the sand-mudstone interface, thereby forming the target single sand body combination relationship identification result.

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