Prediction method for development range of difficult-to-recognize tiny fault and oilfield development method

Abstract

The invention belongs to the field of oil and gas exploitation, and particularly discloses a difficult-to-recognize tiny fault development range prediction method and an oil field development method based on difficult-to-recognize tiny fault prediction. The difficult-to-recognize tiny fault development range prediction method comprises the following steps: S1, recognizing a reservoir control fault and a four-level fault in a target oil reservoir fault block; s2, determining a micro fault development area based on the reservoir control fault and the four-stage fault; and S3, predicting the development range of the difficult-to-recognize tiny fault according to the relationship between the tiny fault development area determined based on the reservoir control fault and the tiny fault development area determined based on the four-level fault. In the scheme of the invention, the reservoir control fault and the four-level fault which can be identified by the existing means are utilized to predict the tiny fault which is difficult to identify by the existing means, and the existence of the tiny fault which is difficult to identify is represented in the form of the development range, so that the tiny fault which is difficult to identify is prevented from being directly identified.

Description

Technical Field

[0001] The present invention belongs to the field of oil and gas exploitation, and particularly relates to a method for predicting the development range of difficult-to-identify micro-faults and an oilfield development method based on the prediction of difficult-to-identify micro-faults. Background Art

[0002] Many petroleum geologists at home and abroad have focused more on the geometry and morphology of main controlling faults and have conducted in-depth research on aspects such as hydrocarbon migration and accumulation relationships; little attention has been paid to small-scale faults within oilfields and difficult-to-identify micro-faults around large faults; faults are not only closely related to hydrocarbon migration and accumulation, but also one of the key factors affecting oilfield development and production. Especially during the injection-production development process of oilfields, some faults are initially closed, and as the development process progresses, some faults may become activated later, resulting in the spillage of injected water, increasing the injection-production contradiction in actual production, seriously affecting the development effect of the oilfield, and even causing communication between different types of faults, leading to more catastrophic accidents.

[0003] During the development of onshore oilfields, water breakthrough, blowout, and well kick accidents caused by faults occur frequently, and it is also common for injected water to break through the surface along faults. Since the difficulty of handling accidents on land is relatively easy, insufficient attention has been paid to the causes of these accidents. In recent years, with the increasing emphasis on safe production operations and environmental protection in offshore oilfield development and overseas oilfields controlled by Chinese capital, due to the lack of systematic research on fault hazard assessment, the land development concept is still used. Natural energy development is initially adopted and then gradually transitioned to artificial water injection development; at the same time, for the treatment plans of cuttings, produced water, etc. generated during offshore and overseas oilfield development, after environmental protection and economic benefit demonstration, it is basically necessary to inject them back into the underground formation under high pressure. Due to the lack of in-depth research on different types of faults, especially difficult-to-identify micro-faults, although conventional technical means cannot distinguish and identify them, it does not mean that micro-faults do not exist. This leads to the situation that during the construction process, development engineers do not adopt corresponding countermeasures for the development areas of micro-faults, often causing the gradual activation of micro-faults, conventional faults within the oil reservoir, and reservoir-controlling faults, resulting in the communication between different types of faults and triggering oil reservoir development contradictions, and serious ones may also cause major human accidents.

[0004] In view of this, the existing technology needs to be further improved. Summary of the Invention

[0005] Aiming at at least one of the above problems, one of the purposes of the present invention is to provide a method for predicting the development range of difficult-to-identify micro-faults to simplify the identification of difficult-to-identify micro-faults; another purpose of the present invention is to provide an oilfield development method based on the prediction of difficult-to-identify micro-faults to solve the injection-production contradiction existing in oilfield development and production and prevent various accidents caused by the communication between different types of faults, thereby ensuring the safe and effective production of the oilfield.

[0006] According to a first aspect of the present invention, a method for predicting the development range of difficult-to-identify micro-faults is provided, which includes the following steps:

[0007] S1: Identify the reservoir-controlling faults and fourth-order faults within the target oil reservoir block;

[0008] S2: Based on the reservoir-controlling faults and the fourth-order faults respectively, determine the micro-fault development areas;

[0009] S3: According to the relationship between the micro-fault development area determined based on the reservoir-controlling faults and the micro-fault development area determined based on the fourth-order faults, predict the development range of difficult-to-identify micro-faults.

[0010] According to some embodiments of the present invention, in step S1, identifying the reservoir-controlling faults and fourth-order faults within the target oil reservoir block includes: identifying the quantities, positions, and fault parameters of the reservoir-controlling faults and the fourth-order faults, where the fault parameters include fault throw, fault plane, fault line, and extension length.

[0011] According to some embodiments of the present invention, in step S2, based on the reservoir-controlling faults and the fourth-order faults respectively, determining the micro-fault development areas includes: determining the micro-fault development area based on the fault parameters of the reservoir-controlling faults in combination with the development well spacing; determining the micro-fault development area based on the fault parameters of the fourth-order faults in combination with the development well spacing.

[0012] According to some embodiments of the present invention, determining the micro-fault development area based on the fault parameters of the reservoir-controlling faults or the fourth-order faults in combination with the development well spacing includes:

[0013] Respectively determine the upper boundary and the lower boundary in the direction parallel to the extension length of the reservoir-controlling fault or the fourth-order fault. The upper boundary extends a first distance in the direction of the downthrown side from the fault line, and the lower boundary extends a second distance in the direction of the upthrown side from the fault line;

[0014] Respectively determine the left boundary and the right boundary in the direction perpendicular to the extension length of the reservoir-controlling fault or the fourth-order fault. The left boundary extends a third distance away from the fault line from the left endpoint of the fault line, and the right boundary extends a fourth distance away from the fault line from the right endpoint of the fault line, where the first distance, the second distance, the third distance, and the fourth distance are determined according to the development well spacing;

[0015] Based on the upper boundary, the lower boundary, the left boundary, and the right boundary, determine the micro-fault development area. The corresponding micro-fault development area is the area enclosed by the upper boundary, the lower boundary, the left boundary, and the right boundary.

[0016] According to some embodiments of the present invention, the first distance is equal to one development well spacing, and the second distance, the third distance, and the fourth distance are respectively equal to half of the development well spacing.

[0017] According to some embodiments of the present invention, in step S3, predicting the development range of hard-to-identify minor faults based on the relationship between the minor fault development area determined based on the reservoir-controlling fault and the minor fault development area determined based on the fourth-level fault includes: determining the most developed area of hard-to-identify minor faults, the relatively developed area of hard-to-identify minor faults, and the undeveloped area of hard-to-identify minor faults based on the relationship between the minor fault development area determined based on the reservoir-controlling fault and the minor fault development area determined based on the fourth-level fault.

[0018] According to some embodiments of the present invention, determining the most developed area of hard-to-identify minor faults, the relatively developed area of hard-to-identify minor faults, and the undeveloped area of hard-to-identify minor faults based on the relationship between the minor fault development area determined based on the reservoir-controlling fault and the minor fault development area determined based on the fourth-level fault includes:

[0019] Determining the area where the minor fault development area determined based on the reservoir-controlling fault overlaps with the minor fault development area determined based on the fourth-level fault as the most developed area of hard-to-identify minor faults;

[0020] Determining the area where the minor fault development area determined based on the reservoir-controlling fault does not overlap with the minor fault development area determined based on the fourth-level fault and the area outside the minor fault development area determined based on the reservoir-controlling fault but within the minor fault development area determined based on the fourth-level fault as the relatively developed area of hard-to-identify minor faults;

[0021] Determining the area outside the minor fault development area determined based on the reservoir-controlling fault and not within the minor fault development area determined based on the fourth-level fault as the undeveloped area of hard-to-identify minor faults.

[0022] According to some embodiments of the present invention, the method includes: verifying the existence of hard-to-identify minor faults before predicting the development range of hard-to-identify minor faults.

[0023] According to some embodiments of the present invention, verifying the existence of hard-to-identify minor faults based on imaging logging data and core data.

[0024] According to some embodiments of the present invention, verifying the existence of hard-to-identify minor faults based on the relationship model between fault throw and fault number constructed.

[0025] According to some embodiments of the present invention, the relationship model between fault throw and fault number is constructed based on historical data on fault throw and fault number, and the constructed relationship model between fault throw and fault number is y = a * x -b, where y is the number of faults, x is the fault throw, and a and b are the parameters obtained by fitting.

[0026] According to a second aspect of the present invention, there is provided an oilfield development method based on the prediction of hard-to-identify micro-faults, comprising the following steps:

[0027] S11: Predict the development range of hard-to-identify micro-faults within the target reservoir block by using the hard-to-identify micro-fault development range prediction method according to the first aspect of the present invention;

[0028] S12: Classify the risk types of the target reservoir block based on the development range of hard-to-identify micro-faults;

[0029] S13: Develop corresponding oilfield development countermeasures for the classified risk types.

[0030] According to some embodiments of the present invention, in step S12, classifying the risk types of the target reservoir block based on the development range of hard-to-identify micro-faults includes:

[0031] Defining the area with the most developed hard-to-identify micro-faults as a Class I risk area;

[0032] Defining the area with relatively developed hard-to-identify micro-faults as a Class IIa risk area or a Class IIb risk area. Among them, the area within the development area of micro-faults determined based on the controlling reservoir faults that does not overlap with the development area of micro-faults determined based on the fourth-order faults is defined as a Class IIa risk area, and the area outside the development area of micro-faults determined based on the controlling reservoir faults and within the development area of micro-faults determined based on the fourth-order faults is defined as a Class IIb risk area;

[0033] Defining the area with underdeveloped hard-to-identify micro-faults as a Class III risk area.

[0034] According to some embodiments of the present invention, in step S12, classifying the risk types of the target reservoir block based on the development range of hard-to-identify micro-faults includes: Adjusting the classified risk types based on the development area of the main channels of medium-high permeability reservoirs. If the development area of the main channels of medium-high permeability reservoirs overlaps with the development range of hard-to-identify micro-faults, upgrade the Class IIb risk area to a Class IIa risk area and upgrade the Class IIa risk area to a Class I risk area.

[0035] According to some embodiments of the present invention, the method further includes: Before classifying the risk types of the target reservoir block, evaluating the sealing property of hard-to-identify micro-faults. The evaluation is mainly carried out by using static reservoir methods to evaluate the sealing properties of the controlling reservoir faults and the fourth-order faults, so as to predict the sealing properties of the associated hard-to-identify micro-faults in this area. In step S12, classifying the risk types of the target reservoir block based on the development range of hard-to-identify micro-faults includes: Adjusting the classified risk types based on the evaluation results of the sealing properties of hard-to-identify micro-faults.

[0036] According to some embodiments of the present invention, a sealing evaluation is performed on the reservoir-controlling fault and the fourth-order fault, so as to determine the sealing of the associated hard-to-identify minor faults in the area, including: when the sealing evaluation results of the reservoir-controlling fault and the fourth-order fault are consistent, it is considered that the sealing of the associated hard-to-identify minor faults is the same as that of the reservoir-controlling fault and the fourth-order fault; when the sealing evaluation results of the reservoir-controlling fault and the fourth-order fault are inconsistent, it is considered that the sealing of the associated hard-to-identify minor faults is the same as the poorer one of the sealing of the reservoir-controlling fault and the fourth-order fault.

[0037] According to some embodiments of the present invention, based on the sealing evaluation results of the hard-to-identify minor faults, the divided risk types are adjusted, including: if the sealing of the hard-to-identify minor faults is good, the risk area of grade IIa is downgraded to the risk area of grade IIb, and the risk area of grade IIb is downgraded to the risk area of grade III; if the sealing of the hard-to-identify minor faults is medium or poor, the divided risk types are not adjusted.

[0038] According to some embodiments of the present invention, based on the sealing evaluation results of the hard-to-identify minor faults, the divided risk types are adjusted, including: if the sealing of the hard-to-identify minor faults is good and the development range of the hard-to-identify minor faults does not overlap with the main channel development area of the medium-high permeability reservoir, the risk area of grade IIa is downgraded to the risk area of grade IIb, the risk area of grade IIb is downgraded to the risk area of grade III, and the risk area of grade I is not downgraded; if the sealing of the hard-to-identify minor faults is good and the development range of the hard-to-identify minor faults overlaps with the main channel development area of the medium-high permeability reservoir, the risk area of grade IIb is upgraded to the risk area of grade IIa, and the risk area of grade IIa is upgraded to the risk area of grade I.

[0039] According to some embodiments of the present invention, in step S13, corresponding oilfield development countermeasures are formulated for the divided risk types, including:

[0040] For the risk area of grade I, water injection development operations are prohibited, and high-pressure injection wells or high-injection volume reinjection wells are avoided.

[0041] For the risk areas of grade IIa and grade IIb, during the water injection development operation, monitoring and dynamic adjustment work should be done well. Once it is found that the injection well overflows or ineffective water injection occurs, the injection-production well pattern should be adjusted in time, and the injection wells should be further optimized.

[0042] For the risk area of grade III, conventional oilfield water injection development operations can be carried out, and the injection pressure of high-pressure injection wells or high-injection volume reinjection wells should be lower than the formation fracture pressure.

[0043] According to some embodiments of the present invention, when performing water injection development operations in a Class IIa risk area, when calculating the bottom hole flowing pressure of the maximum injection well, the fracture probability of the injection well is selected as 10-15%, and the reservoir depth is selected as the upper part or the top depth of the reservoir; when performing water injection development operations in a Class IIb risk area, the fracture probability of the injection well is selected as 5%, and the reservoir depth is selected as the middle depth of the reservoir.

[0044] Due to the adoption of the above technical solutions, the present invention has the following beneficial effects:

[0045] The method for predicting the development range of difficult-to-identify microfaults provided by the present invention predicts the microfaults that are difficult to identify by existing means by using the reservoir-controlling faults and fourth-order faults that can be identified by existing means, and characterizes the existence of the microfaults in the form of the development range, avoiding directly identifying the difficult-to-identify microfaults.

[0046] The oilfield development method based on the prediction of difficult-to-identify microfaults provided by the present invention can guide the oilfield injection-production development work for the potential risks of microfaults by identifying the development range of microfaults, classifying the risk types, and formulating corresponding oilfield development countermeasures, so as to prevent the gradual activation of microfaults, conventional faults inside the oil reservoir, and reservoir-controlling faults, resulting in the communication of different types of faults and triggering oil reservoir development contradictions, and can ensure the effective water injection development of the fault development area, the reinjection of the produced substances in the offshore oilfield, and the safe production operations such as gas storage caverns. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the following drawings are only some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0048] Figure 1 It is a flowchart of the method for predicting the development range of difficult-to-identify microfaults provided by the present invention;

[0049] Figure 2 It is a flowchart of the method for predicting the development range of difficult-to-identify microfaults provided by the present invention;

[0050] Figure 3 It is a flowchart of the oilfield development method based on the prediction of difficult-to-identify microfaults provided by the present invention;

[0051] Figure 4 It is a flowchart of the oilfield development method based on the prediction of difficult-to-identify microfaults provided by an embodiment of the present invention;

[0052] Figure 5 It is an analysis diagram of the correlation of conventional faults provided by an embodiment of the present invention;

[0053] Figure 6 The micro - fault map of the T12C coring well provided by an embodiment of the present invention;

[0054] Figure 7 The schematic diagram for determining the development area of micro - faults based on reservoir - controlling faults provided by the present invention;

[0055] Figure 8 The distribution map of different risk types of micro - faults provided by the present invention. Detailed implementation manners

[0056] In order to make the objectives, technical solutions and advantages of the present invention more clear and understandable, the present invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0057] According to the first aspect of the present invention, a method for predicting the development range of difficult - to - identify micro - faults is provided. As Figure 1 shown, it includes the following steps:

[0058] S1: Identify the reservoir - controlling faults and fourth - order faults within the target oil - reservoir block.

[0059] In the present invention, the "target oil - reservoir block" refers to the block in the area where oil - field injection and production development work is to be carried out.

[0060] The "difficult - to - identify micro - fault" refers to a fault that is difficult to find using the usual fault - identification criteria in conventional geological methods, and has a relatively small fault throw and extension length. Generally, the fault throw of a micro - fault is less than 5m, and it is easy to be ignored due to precision errors during stratigraphic correlation and structural interpretation. The coring well is the most direct and effective means to verify the existence of micro - faults, or special logging such as micro - resistivity scanning imaging logging in imaging logging can identify micro - faults. Since the discovery probability of micro - faults is relatively low and the discovery difficulty is relatively large, their existence is presented in the form of the development range in this patent.

[0061] The "reservoir - controlling fault" is a third - order fault that has a certain control effect on the distribution law of oil, gas and water and the connectivity of oil - sand bodies in a complex fault - block area. It can be identified with the help of seismic data and is also easy to interpret. Generally, the fault throw of this type of fault is greater than 100m, and the lateral extension length is 1 - 10km.

[0062] The "fourth - order fault" is small in scale, numerous in quantity, and has poor directionality and variable strikes. The fault throw is generally between 10m and 100m, and the extension length is 0.5 - 1km. The interpretation of this type of fault requires comprehensive discrimination relying on stratigraphic correlation, imaging logging or fine interpretation of high - resolution seismic data.

[0063] Identify the reservoir-controlling faults and fourth-order faults within the target reservoir fault block, including: identifying the quantity, location, and fault parameters of the reservoir-controlling faults and fourth-order faults within the target reservoir fault block. The fault parameters include fault throw, fault plane, fault line, extension length, etc. Fault throw refers to the relative distance between the corresponding rock layers on both sides of the faulted rock layer. The fault plane refers to the fracture surface of the fault, that is, the surface along which significant sliding displacement occurs between the rock masses on both sides of the fault. The fault line refers to the intersection line of the fault plane and the ground surface, that is, the outcrop line of the fault plane on the ground surface. The extension direction of the fault line is the fault strike, and the disappearing point of the extension is called the fault end point. The extension length is the length of the fault line on the plane.

[0064] S2: Respectively based on the reservoir-controlling faults and fourth-order faults, determine the micro-fault development areas.

[0065] In the present invention, the "micro-fault development area" refers to the possible extension range or extension area of micro-faults. Since the complex fault block area is formed by the mutual cutting of multiple and multi-level faults, therefore, only by considering the fault block as a whole can a more objective and realistic risk type division be obtained.

[0066] In some embodiments, the micro-fault development area can be determined according to the relevant fault parameters of the reservoir-controlling faults or fourth-order faults identified in step S1 in combination with the development well spacing within the target area where the target reservoir fault block is located. For example, the micro-fault development area can be determined respectively according to the fault line and extension length of the reservoir-controlling faults or fourth-order faults identified in step S1 in combination with the development well spacing.

[0067] Specifically, as Figure 2 shown, to determine the micro-fault development area, the following steps are included:

[0068] S21: Respectively determine the upper boundary and the lower boundary in the direction parallel to the extension length of the reservoir-controlling fault or fourth-order fault. The upper boundary extends a first distance in the direction of the downthrown side from the fault line, and the lower boundary extends a second distance in the direction of the upthrown side from the fault line;

[0069] S22: Respectively determine the left boundary and the right boundary in the direction perpendicular to the extension length of the reservoir-controlling fault or fourth-order fault. The left boundary extends a third distance away from the fault line from the left end point of the fault line, and the right boundary extends a fourth distance away from the fault line from the right end point of the fault line;

[0070] S23: Based on the upper boundary, the lower boundary, the left boundary, and the right boundary, determine the micro-fault development area. The corresponding micro-fault development area is the area enclosed by the upper boundary, the lower boundary, the left boundary, and the right boundary, where the first distance, the second distance, the third distance, and the fourth distance are determined according to the development well spacing.

[0071] In some embodiments, the first distance is equal to one development well spacing, and the second, third, and fourth distances are equal to half of the development well spacing. The well pattern design for oilfield development must conform to the actual production of the oilfield. For key factors such as the reservoir type, sand body scale, reservoir physical properties, and development stage in different blocks, different well patterns (well spacings) must be adopted to ensure stable production and efficiency of the oilfield. The deployment and adjustment of the injection-production well pattern are often calculated based on the well spacing as the basic unit. For example, in the initial stage of developing medium-high permeability reservoirs, one well spacing is 400 - 600 m, and in the later stage, it is adjusted and densified to 200 - 300 m.

[0072] With the help of the normal fault evolution experimental model, it can be observed that the evolution of minor faults is mainly controlled by the fault plane morphology of the reservoir-controlling (block) faults. Under the physical stretching experiment simulation, the reservoir-controlling (block) faults mainly form two deformation zones, which also provide extremely favorable development space for the existence of minor faults. The geometric characteristics, structural positions, and development sequences of the evolved faults all have certain regularities. According to statistical analysis, there is a certain linear relationship between the number of minor faults in the hanging wall and the number of minor faults in the footwall of the reservoir-controlling (block) faults, and there is also an approximate relationship between the area of the minor fault development area in the hanging wall and the area of the minor fault development area in the footwall. Among them, more minor faults can be seen attached to the reservoir-controlling (block) faults in the footwall than in the hanging wall of the reservoir-controlling (block) faults.

[0073] The development ranges of minor faults in the hanging wall and footwall of the reservoir-controlling (block) faults are mainly related to parameters such as the number of conventional faults, development well spacing, reservoir physical properties, and fault sealing. The entropy weight method is used to determine the weights of each sensitive parameter, and it is verified through the time and distance of water injection well overflow in the actual water injection fault blocks, so as to predict the laws of minor fault development areas in different structural zones, and finally establish an ideal development model for minor faults.

[0074] For the fine dissection of the on-site water injection overflow fault blocks, it is found that there are certain objective laws or empirical parameters regarding the position of the injection wells that cause the activation of the faults on both sides of the fault controlling the reservoir (block) relative to the main fault. Through repeated production practice, it is proven that generally, water breakthrough occurs quickly within one well spacing, and the probability of observing violent water flooding in oil wells and water injection overflow in injection wells is the highest. Therefore, a distance of one well spacing (R) is selected along the vertical extension of the segment of the downthrown side of the fault controlling the reservoir (block), that is, the segment where minor faults are more developed and have stronger activation ability. Based on the fitting results of the theoretical experimental model, the vertical distance from the fault controlling the reservoir (block) to the concentrated development area of minor faults on the upthrown side is approximately half of its distance to the downthrown side. Therefore, a distance of half a well spacing (1 / 2R) is extended vertically on the upthrown side of the fault controlling the reservoir (block). The extension direction of the fault line is the fault strike. The fault extends towards both end points, and the fracture surface and distance between the corresponding rock layers on the upper and lower plates gradually disappear, and the stress also weakens accordingly. Considering the complexity and multi-solution nature of fault characterization, a distance of half a well spacing (1 / 2R) is extended from the end points of the fault controlling the reservoir (block) to both sides respectively.

[0075] Figure 7 The schematic diagram showing the determination of the minor fault development area based on the fault controlling the reservoir is presented. This figure is a top view of the fault controlling the reservoir L1. The extension length of the fault controlling the reservoir L1 is L. The upper half is the downthrown side, and the lower half is the upthrown side. The development well spacing is R. When determining the minor fault development area based on the fault controlling the reservoir, first, the upper boundary a and the lower boundary b are determined in the up-down direction shown in the figure. The upper boundary a extends upward by one development well spacing R from the fault line, and the lower boundary b extends downward by half a development well spacing from the fault line. Then, the left boundary c and the right boundary d are determined in the left-right direction shown in the figure. The left boundary c extends leftward by half a development well spacing from the left end point of the fault line, and the right boundary d extends rightward by half a development well spacing from the right end point of the fault line. The area enclosed by the upper boundary a, the lower boundary b, the left boundary c, and the right boundary d is the minor fault development area determined based on the fault controlling the reservoir.

[0076] The process of determining the minor fault development area based on the fourth-order fault is similar to that based on the fault controlling the reservoir, and will not be elaborated here.

[0077] S3: Predict the development range of difficult-to-identify minor faults based on the relationship between the minor fault development area determined based on the fault controlling the reservoir and the minor fault development area determined based on the fourth-order fault.

[0078] The prediction of the development range of difficult-to-identify micro-faults includes: determining the most developed area, the relatively developed area, and the undeveloped area of difficult-to-identify micro-faults based on the relationship between the micro-fault development area determined based on the reservoir-controlling faults and the micro-fault development area determined based on the fourth-order faults. Specifically: the area overlapping between the micro-fault development area determined based on the reservoir-controlling faults and the micro-fault development area determined based on the fourth-order faults is determined as the most developed area of difficult-to-identify micro-faults; the area within the micro-fault development area determined based on the reservoir-controlling faults that does not overlap with the micro-fault development area determined based on the fourth-order faults and the area outside the micro-fault development area determined based on the reservoir-controlling faults but within the micro-fault development area determined based on the fourth-order faults are determined as the relatively developed area of difficult-to-identify micro-faults; the area outside the micro-fault development area determined based on the reservoir-controlling faults that is not within the micro-fault development area determined based on the fourth-order faults is determined as the undeveloped area of difficult-to-identify micro-faults.

[0079] Figure 8 This is a schematic diagram for predicting the development range of difficult-to-identify micro-faults provided by the present invention. In this embodiment, the reservoir-controlling fault L1 and two fourth-order faults L2 and L3 are shown. Among them, the shaded part in the figure is the area overlapping between the micro-fault development area determined based on the reservoir-controlling fault L1 and the micro-fault development areas determined based on the fourth-order faults L2 and L3, which is the most developed area of difficult-to-identify micro-faults; the area within the micro-fault development area determined based on the reservoir-controlling fault L1 that does not overlap with the micro-fault development areas determined based on the fourth-order faults L2 and L3 and the area outside the micro-fault development area determined based on the reservoir-controlling fault L1 but within the micro-fault development areas determined based on the fourth-order faults L2 and L3 are the relatively developed areas of difficult-to-identify micro-faults; the area outside the micro-fault development area determined based on the reservoir-controlling fault L1 that is not within the micro-fault development areas determined based on the fourth-order faults L2 and L3 is the undeveloped area of difficult-to-identify micro-faults.

[0080] In some embodiments, before predicting the development range of difficult-to-identify micro-faults, the existence of difficult-to-identify micro-faults is verified. The existence of difficult-to-identify micro-faults can be verified according to imaging logging data and core data. It can also be verified based on the relationship model constructed between the fault throw and the number of faults. The relationship model between the fault throw and the number of faults is constructed based on historical data on fault throw and the number of faults. In some cases, as Figure 5 shown, the relationship model constructed between the fault throw and the number of faults is:

[0081] y = 3904.1 * x -1.58 ,

[0082] where y is the number of faults and x is the fault throw.

[0083] The method for predicting the development range of hard-to-identify microfaults provided by the present invention predicts the hard-to-identify microfaults that are difficult to be identified by existing means by using the reservoir-controlling faults and fourth-order faults that can be identified by existing means, and characterizes the existence of the microfaults in the form of the development range, avoiding directly identifying the hard-to-identify microfaults.

[0084] According to the second aspect of the present invention, there is provided an oilfield development method based on the prediction of hard-to-identify microfaults, as Figure 3 shown, which comprises the following steps:

[0085] S11: Predict the development range of hard-to-identify microfaults in the target reservoir block by using the method for predicting the development range of hard-to-identify microfaults according to the first aspect of the present invention. For details, reference can be made to the foregoing text, which will not be elaborated herein.

[0086] S12: Based on the development range of hard-to-identify microfaults, classify the risk types of the target reservoir block.

[0087] Based on the development range of hard-to-identify microfaults, classifying the risk types of the target reservoir block includes: defining the area with the most developed hard-to-identify microfaults as the Class I risk area; defining the area with relatively developed hard-to-identify microfaults as the Class IIa risk area or Class IIb risk area, wherein the area that does not overlap with the development area of microfaults determined based on the fourth-order faults within the development area of microfaults determined based on the reservoir-controlling faults is defined as the Class IIa risk area, and the area outside the development area of microfaults determined based on the reservoir-controlling faults and within the development area of microfaults determined based on the fourth-order faults is defined as the Class IIb risk area; defining the area with underdeveloped hard-to-identify microfaults as the Class III risk area.

[0088] On the basis of classifying the risk types of the target reservoir block in the above manner, the classified risk types can also be adjusted based on other factors. In some embodiments, the classified risk types can be adjusted based on the main channel development area of medium-high permeability reservoirs. If the main channel development area of medium-high permeability reservoirs overlaps with the development range of hard-to-identify microfaults, the Class IIb risk area is upgraded to the Class IIa risk area, and the Class IIa risk area is upgraded to the Class I risk area.

[0089] Before classifying the risk types of the target reservoir block, the sealing properties of the reservoir-controlling faults and fourth-order faults can be evaluated by using reservoir static methods, so as to determine the sealing properties of the associated hard-to-identify microfaults in this area. Then, based on the evaluation results of the sealing properties of hard-to-identify microfaults, the classified risk types are adjusted.

[0090] Evaluating the sealing property of the associated hard-to-identify minor faults in this area by the sealing property evaluation of the controlling faults and fourth-order faults means determining the sealing property of the associated hard-to-identify minor faults in this area based on the sealing property evaluation results of the controlling faults and fourth-order faults. When the sealing property evaluation results of the controlling faults and fourth-order faults are consistent, it is considered that the sealing property of the associated hard-to-identify minor faults is the same as that of the controlling faults and fourth-order faults. Specifically, when the sealing property of both the controlling faults and fourth-order faults is good, it is considered that the sealing property of the associated hard-to-identify minor faults is good; when the sealing property of both the controlling faults and fourth-order faults is medium, it is considered that the sealing property of the associated hard-to-identify minor faults is medium; when the sealing property of both the controlling faults and fourth-order faults is poor, it is considered that the sealing property of the associated hard-to-identify minor faults is poor. When the sealing property evaluation results of the controlling faults and fourth-order faults are inconsistent, it is considered that the sealing property of the associated hard-to-identify minor faults is the same as the poorer one of the sealing properties of the controlling faults and fourth-order faults. For example, when the sealing property of the controlling faults is good and the sealing property of the fourth-order faults is medium, it is considered that the sealing property of the associated hard-to-identify minor faults is medium; when the sealing property of the controlling faults is medium and the sealing property of the fourth-order faults is poor, it is considered that the sealing property of the associated hard-to-identify minor faults is poor, and so on.

[0091] Based on the evaluation results of the sealing property of the hard-to-identify minor faults, adjust the classified risk types, including: if the sealing property of the hard-to-identify minor faults is good, downgrade the risk area of grade IIa to grade IIb, and downgrade the risk area of grade IIb to grade III; if the sealing property of the hard-to-identify minor faults is medium or poor, do not adjust the classified risk types.

[0092] When adjusting the classified risk types based on both the evaluation results of the sealing property of the hard-to-identify minor faults and the development area of the main channels in medium-high permeability reservoirs, if the sealing property of the hard-to-identify minor faults is good and the development range of the hard-to-identify minor faults does not overlap with the development area of the main channels in medium-high permeability reservoirs, the risk area of grade IIa can be downgraded to grade IIb, the risk area of grade IIb can be downgraded to grade III, and the risk area of grade I will not be downgraded; if the sealing property of the hard-to-identify minor faults is good and the development range of the hard-to-identify minor faults overlaps with the development area of the main channels in medium-high permeability reservoirs, the risk area of grade IIb can be upgraded to grade IIa, and the risk area of grade IIa can be upgraded to grade I.

[0093] The meaning of "good sealing property" in the above text is: when evaluating the sealing property of the controlling faults and fourth-order faults by the static reservoir method, the evaluation standard value is greater than 0.7. The meaning of "medium sealing property" in the above text is: when evaluating the sealing property of the controlling faults and fourth-order faults by the static reservoir method, the evaluation standard value is between 0.5 and 0.7. The meaning of "poor sealing property" in the above text is: when evaluating the sealing property of the controlling faults and fourth-order faults by the static reservoir method, the evaluation standard value is less than 0.5.

[0094] S13: Develop corresponding oilfield development countermeasures for the classified risk types.

[0095] Develop corresponding oilfield development countermeasures for the classified risk types, including: For Class I risk areas, prohibit water injection development operations and avoid deploying high-pressure injection wells or high-injection-volume reinjection wells; For Class IIa and Class IIb risk areas, during water injection development operations, do a good job in monitoring and dynamic adjustment. Once it is found that the injection well overflows or there is ineffective water injection, the injection-production well pattern should be adjusted in a timely manner and the injection wells should be further optimized; For Class III risk areas, conventional oilfield water injection development operations can be carried out, and the injection pressure of high-pressure injection wells or high-injection-volume reinjection wells should be lower than the formation fracture pressure.

[0096] If water injection development operations are carried out in Class IIa risk areas, when calculating the maximum bottom-hole flowing pressure of injection wells, the fracture probability of injection wells is selected as 10 - 15%, and the reservoir depth is selected as the upper part or the top depth of the reservoir; If water injection development operations are carried out in Class IIb risk areas, the fracture probability of injection wells is selected as 5%, and the reservoir depth is selected as the middle depth of the reservoir.

[0097] Figure 4 The flowchart of the oilfield development method based on the prediction of difficult-to-identify microfaults provided by an embodiment of the present invention is shown. As shown in the figure, the method includes the following steps: 1) Basic data sorting, mainly the collection and sorting of seismic, geological, laboratory, drilling, logging, dynamic and other data; 2) Conventional fault identification, which is carried out according to seismic interpretation, stratigraphic correlation and dynamic data, etc.; 3) Microfault identification, which is carried out according to imaging logging, core sampling, conventional faults and other data for identification and prediction; 4) Fault sealing evaluation, which evaluates the sealing of conventional faults and microfaults based on dynamic and static data; 5) Prediction of the distribution range of microfaults, and predict the development range of microfaults through experimental models and on-site dynamic implementation; 6) Risk type classification, classify different risk types according to the distribution range of microfaults; 7) Formulate reasonable development countermeasures.

[0098] The following will specifically describe each step.

[0099] 1) Basic data sorting

[0100] For seismic data, geological data, logging data, drilling data, laboratory data, and dynamic data, whether it is a new area or an old area, 5 kinds of results are required, such as structural interpretation results, oil-bearing area maps, reservoir distribution maps, microfault risk distribution maps, injection-production well pattern deployment maps, etc. Based on this, oilfield development is carried out.

[0101] 2) Conventional fault identification

[0102] Five research objects were selected from the Dagang complex fault block oilfield in eastern my country. The conventional discovered faults were divided into four types: the first-level fault controls the depression, the second-level fault controls the second-level structural belt, and the third and fourth levels are internal faults of the oil and gas reservoir. The above three types are also relatively clear in reflection on the seismic profile and easy to identify; while the small fault has a small fault throw and a short extension, and its identification is somewhat difficult. It is mainly based on high-resolution seismic fine interpretation, isochronous stratigraphic fine comparison, oil-water relationship and production dynamics for comprehensive judgment. Through research, it is found that within a tectonic unit, the large fault is often surrounded by secondary faults. There is a certain relationship between the number of secondary faults and the number of faults of the previous level. The smaller the fault throw of the fault, the more faults there are. This law indicates that there may be a large number of small faults and micro faults in a certain tectonic unit area. Secondary, tertiary, quaternary and small faults can be identified based on seismic interpretation, stratigraphic comparison and dynamic data, while micro faults are difficult to identify and can be predicted by different conventional fault relationship models (see Table 1).

[0103] Table 1 Distribution of fault data in different regions

[0104]

[0105] According to the relevant data of 20 sample points in 5 oil fields of the above four types, it is found that the fault throw (X) of different types of faults has a good correlation with their number of faults (Y), and a relationship model of different conventional faults in the same tectonic unit is established, y = 3904.1*x -1.58 , which can predict the number of faults under different fault throw conditions (see Figure 5 ).

[0106] 3) Identification of micro-faults

[0107] Micro-fault identification can be discovered based on imaging logging, coring and other data. Due to the low probability of discovery, many geological engineers ignore the existence of micro-faults and their hazards. The current technology is difficult to identify, but it does not mean that micro-faults do not exist. Many micro-faults were found in the coring well of Tanggu T12C well. Figure 6 a. Figure 6 b shows the two sides of a core. The small fault section is still full of oil traces. The core length is 18cm and the logging depth is 3138m. Figure 6 c. Figure 6 d respectively Figure 6 a. Figure 6 b Schematic diagram of micro-fault interpretation. The black color in the core strata is carbonaceous interlayer rich in organic matter. The thickness of a single layer is about 0.3 cm. The micro-fault distance varies from 0.4 cm to 4 cm. There is a fault fracture zone between F1 and F2, and between F3 and F4 faults.

[0108] The coring well is the most direct and effective means to verify the existence of minor faults, breaking various speculations of people and confirming the existence of minor faults. At the same time, the conventional fault relationship model in step 2) can be used to predict the number of minor faults, and the fault relationship model is y = 3904.1 * x -1.58 , it is estimated that when the fault throw is 8 meters, there are 146 minor faults predicted; when the calculated fault throw is 1 meter, it is expected that there will be 3904 minor faults. This law indicates that there may be a large number of faults with a smaller fault throw level than minor faults in a certain structural unit area.

[0109] 4) Fault sealing evaluation

[0110] With the progress of oilfield development, when the injected medium breaks through the faults in the target oil reservoir block, it is easy to induce the activation of faults at all levels, resulting in problems such as water breakthrough, blowout and well kick, seriously affecting the safe production of oil reservoir development. Therefore, the fault sealing evaluation should be an important assessment index for its risk type classification.

[0111] For conventional waterflooding development oil reservoirs, generally, the larger the fault throw in the original state, the better the relative sealing property. Some third- and fourth-order oil reservoir controlling faults belong to medium sealing, and there are also cases with poor sealing. Due to objective factors such as the difficult identification of the scale of minor faults, when evaluating the sealing property of such faults, a series of qualitative and quantitative research and analysis on the oil reservoir controlling faults and fourth-order faults in the block are needed to deduce the risk types of minor faults with different strain modes, different levels and different scales in the stress field, and make timely adjustment and classification.

[0112] For the fault sealing evaluation, in the initial stage of oilfield development, mainly the static oil reservoir method is adopted. After the development and production, the static oil reservoir method and on-site dynamic method are combined for comprehensive evaluation, so that high-pressure injection wells and high-injection-volume reinjection wells are far away from the fault risk area, and the injection-production adjustment plan is prepared to serve the oil and gas exploration and development work. Among them, the static oil reservoir method is to comprehensively analyze the lithologic configuration relationship, oil-water interface, fault dip angle, fault activity time, fault type, lateral sealing coefficient, and mudstone smear coefficient, then select the faults to be evaluated, establish the membership value standard, and finally obtain the discrimination result: when the discrimination standard value is greater than 0.7, the sealing property is good; when it is between 0.5 and 0.7, the sealing property is medium; when it is less than 0.5, the sealing property is poor.

[0113] For example, when evaluating the sealing property of the oil reservoir controlling faults in the Z34 block of the WGT oilfield, it was initially measured by the static oil reservoir method that its sealing property was 0.58, and it was judged to have medium sealing; later, based on the principle of material balance, on the basis of analyzing data such as oil reservoir characteristics, oil reservoir energy, and actual injection volume of the oil reservoir, it was found that the injection volume of the block was far greater than the production volume, indicating that the oil reservoir controlling faults were not sealed. At the same time,Figure 6 Core sampling has confirmed that the fracture surfaces of micro-faults are open in rock formations with high temperatures and high formation pressures at 3000 meters, verifying that their sealing properties are poor. Therefore, sufficient attention should be paid to this fault block during the development process, and the risk types and corresponding development strategies should be adjusted in a timely manner.

[0114] For conventionally water-injected developed oil reservoirs, faults with larger throw have relatively better sealing properties in their original state, while micro-faults generally have poor sealing properties. Therefore, the risk area division of micro-faults does not require special adjustment. If the micro-faults around the reservoir-controlling (block) faults have good sealing properties, the Class IIa risk area can be downgraded to the Class IIb risk area, and the Class IIb risk area can be downgraded to the Class III risk area.

[0115] 5) Prediction of the distribution range of micro-faults

[0116] To predict the distribution range of micro-faults, the development range of micro-faults is predicted by referring to the normal fault evolution experimental model and the on-site dynamic implementation situation. The main controlling faults in the fault-depressed basins in the eastern part of China have syn-sedimentary characteristics. In the syn-sedimentary strata, in the extensional fault-bend folds, active deformation zones are likely to form. The evolution of micro-faults in the active deformation zones is mainly controlled by the fault surface morphology of the main controlling faults. By means of the normal fault evolution experimental model, it can be observed that micro-faults exist attached to the main controlling faults. After experimental stretching, mainly two deformation zones are formed. Small normal faults with the same dip direction develop in the hanging wall of the main fault, and different types of reverse small normal faults develop in the footwall area of the main fault. There is a certain linear relationship between the statistical analysis of the number of micro-faults in the footwall and that in the hanging wall, and there is also an approximate relationship between the areas of the micro-fault development areas in the footwall and those in the hanging wall. Through the dissection of the water-injected overflow fault blocks on site, it is found that there is a certain rule or empirical parameter between the distance of the water injection wells that cause fault activation in the hanging wall from the main fault and the distance of the water injection wells in the footwall that cause the main fault to be activated.

[0117] The main distribution areas of micro-faults in the upper and lower plates are related to parameters such as the number of conventional faults, development well spacing, and reservoir physical properties. The weights of each parameter are determined by the entropy weight method to obtain the main distribution areas of micro-faults, which can also be verified by the time and distance of water injection well overflow in the actual water-injected fault blocks. The main development ranges of micro-faults in conventionally water-injected developed oil reservoirs are divided according to the hanging wall, footwall, starting end, and ending end of the fault extension length, so as to predict the laws of micro-fault development areas in different structural zones.

[0118] Figure 7 It is only a display method of an ideal distribution pattern of micro-faults.

[0119] S = 3R / 2(L + R)

[0120] S_hanging wall = R / 2(L + R), S_footwall = R(L + R)

[0121] Where S is the main development range of micro - faults, S_up is the development range of the hanging wall of micro - faults, S_down is the development range of the footwall of micro - faults, R is the distance between development wells, and L is the length of the fault.

[0122] For high - pressure injection wells or high - injection - volume reinjection wells, special attention should be paid to preventing the development areas of micro - faults of secondary faults and different types of surrounding faults.

[0123] Based on the prediction model of the distribution range of micro - faults, when the length of the conventional fault is 2,800 meters and the distance between development wells is 200 meters, S = 3R / 2(L + R). The total distribution range of the micro - fault development area is 0.9 square kilometers, of which the hanging wall is 0.3 square kilometers and the footwall development range is 0.6 square kilometers. The injection wells and reinjection wells deployed in this area should be optimized and adjusted, and preventive measures should be taken in advance.

[0124] 6) Risk classification

[0125] For risk classification, different risk types are classified according to the distribution range of micro - faults. Secondary faults have large throw and long extension, posing the greatest risk to the safe production of the oilfield. For high - pressure injection wells or high - injection - volume reinjection wells, the key is to avoid the activation of secondary faults. According to the extension law and influence range of micro - faults and reservoir - controlling (block) faults, four risk levels of "Ⅰ, Ⅱa, Ⅱb, Ⅲ" are mainly classified. Figure 8 For Figure 7 On the basis of the distribution range of micro - faults around the L1 reservoir - controlling fault in, two fourth - order faults L2 and L3 are added. First, the development range of micro - faults is determined based on the L1 reservoir - controlling fault with large throw. Secondly, the two fourth - order faults L2 and L3 are respectively superimposed on the hanging wall and footwall of the L1 reservoir - controlling fault. The superimposed shaded part is the most developed area of micro - faults, defined as the Ⅰ - level risk area; secondly, within the main development range of micro - faults determined by the L1 reservoir - controlling fault, which does not overlap with the development range of micro - faults of the two fourth - order faults L2 and L3, it is defined as the Ⅱa - level risk area; thirdly, outside the main development range of micro - faults determined by the L1 fault, it is defined as the Ⅲ - level risk area; the development range of micro - faults of the two faults L2 and L3 in this area is defined as the Ⅱb - level risk area; if the main channel development area of medium - high - permeability reservoirs overlaps with the micro - fault development area, the Ⅱb - level risk area can be upgraded to the Ⅱa - level risk area, and the Ⅱa - level risk area can be upgraded to the Ⅰ - level risk area.

[0126] 7) Formulation of development countermeasures

[0127] Corresponding preventive measures should be taken for different - level risk areas. Among them, water injection development operations should be prohibited in the Ⅰ - level risk area where micro - faults are concentrated; high attention should be paid to the Ⅱa and Ⅱb - level risk areas where micro - faults are relatively developed, and monitoring and dynamic adjustment work should be done well; for the Ⅲ - level risk area where micro - faults are generally developed or not developed, normal and reasonable injection - production well pattern adjustment can be carried out. Specifically:

[0128] First, during oil field development, it is necessary to avoid deploying high-pressure injection wells or high-injection-volume reinjection wells in Level I risk areas to prevent tiny faults from being compressed and extending through larger faults, causing different types of faults to be activated, resulting in ineffective water injection or casing change and damage.

[0129] Second, for conventional oilfield water injection development, the injection pressure of high-pressure injection wells or high-injection-volume reinjection wells should be lower than the formation fracture pressure. If operations are carried out in the IIa-level risk area, the maximum water injection well bottom flow pressure is usually calculated, and the probability of water injection well fracture (X) is selected as 10-15%, and the oil layer depth (Hz) is selected from the upper part of the oil layer or the top of the oil layer to avoid activation and channeling of different types of faults caused by excessive injection pressure; if operations are carried out in the IIb-level risk area, the probability of water injection well fracture (X) is selected as 5%, and the oil layer depth (Hz) is selected from the middle depth of the oil layer.

[0130] Third, dynamic monitoring of injection wells in risk areas of level Ⅱa and Ⅱb should be strengthened. Once overflow or ineffective water injection is found in injection wells, the injection-production well network should be adjusted in time to further optimize the injection wells. For injection wells with water overflow exceeding 80%, or well groups or fault blocks with a pressure drop of about 20%, measures such as stopping injection or switching injection wells to production should be adopted; for favorable phases where micro-faults and high-permeability reservoirs are developed, it is easier to form large pore development areas, and injection wells must also be reasonably regulated to tap the remaining oil near different types of faults.

[0131] Fourth, for special areas such as offshore and desert, high-pressure reinjection wells should try to avoid shallow sandstone formations or oilfield development target layers. The best choice is to drill in the sandstone formation beneath the development target layer to avoid the safe drilling of adjustment wells in the later stage of oilfield development.

[0132] In summary, according to the second aspect of the present invention, the oilfield development method based on the prediction of difficult-to-identify micro-faults can guide the oilfield injection and production development work based on the potential risks of difficult-to-identify micro-faults by identifying the development range of micro-faults, classifying risk types, and formulating corresponding development countermeasures, so as to prevent the gradual activation of micro-faults, conventional faults inside the reservoir, and reservoir-controlling faults, which may lead to conflicts in reservoir development caused by the connection of different types of faults, and ensure effective water injection development in fault development areas, reinjection of offshore oilfield outputs, and safe production operations such as gas storage.

[0133] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention, including the combination of various technical features in any other appropriate manner, these simple variations and combinations should also be regarded as the contents disclosed by the present invention and should be included in the protection scope of the present invention.

Claims

1. A method for predicting the development range of difficult-to-identify small faults, characterized in that, It includes the following steps: S1: Identify the reservoir-controlling faults and fourth-order faults within the target reservoir fault block; S2: Respectively determine the micro-fault development areas based on the reservoir-controlling faults and the fourth-order faults; S3: Predict the development range of hard-to-identify micro-faults according to the relationship between the micro-fault development area determined based on the reservoir-controlling faults and the micro-fault development area determined based on the fourth-order faults.

2. The prediction method for the development range of difficult-to-identify microfaults according to claim 1, characterized in that In step S1, identifying the reservoir-controlling faults and fourth-order faults within the target reservoir fault block includes: Identifying the quantity, positions, and fault parameters of the reservoir-controlling faults and the fourth-order faults, where the fault parameters include fault throw, fault plane, fault line, and extension length.

3. The prediction method for the development range of difficult-to-identify micro-faults according to claim 2, characterized in that In step S2, respectively determining the micro-fault development areas based on the reservoir-controlling faults and the fourth-order faults includes: Determine the micro-fault development area based on the fault parameters of the reservoir-controlling faults in combination with the development well spacing; Determine the micro-fault development area based on the fault parameters of the fourth-order faults in combination with the development well spacing.

4. The method for predicting the development range of difficult-to-identify micro-faults according to claim 3, wherein Determining the micro-fault development area based on the fault parameters of the reservoir-controlling faults or the fourth-order faults in combination with the development well spacing includes: Respectively determine the upper boundary and the lower boundary in the direction parallel to the extension length of the reservoir-controlling fault or the fourth-order fault. The upper boundary extends a first distance in the direction of the downthrown side from the fault line, and the lower boundary extends a second distance in the direction of the upthrown side from the fault line; Respectively determine the left boundary and the right boundary in the direction perpendicular to the extension length of the reservoir-controlling fault or the fourth-order fault. The left boundary extends a third distance away from the fault line from the left endpoint of the fault line, and the right boundary extends a fourth distance away from the fault line from the right endpoint of the fault line, where the first distance, the second distance, the third distance, and the fourth distance are determined according to the development well spacing; Based on the upper boundary, the lower boundary, the left boundary, and the right boundary, determine the micro-fault development area. The corresponding micro-fault development area is the area enclosed by the upper boundary, the lower boundary, the left boundary, and the right boundary.

5. The method for predicting the development range of difficult-to-identify microfaults according to claim 4, wherein The first distance is equal to the development well spacing, and the second distance, the third distance, and the fourth distance are respectively equal to half of the development well spacing.

6. The method for predicting the development range of difficult-to-identify micro-faults according to claim 1, characterized in that In step S3, predicting the development range of hard-to-identify micro-faults according to the relationship between the micro-fault development area determined based on the reservoir-controlling faults and the micro-fault development area determined based on the fourth-order faults includes: Determine the most developed area of hard-to-identify micro-faults, the relatively developed area of hard-to-identify micro-faults, and the non-developed area of hard-to-identify micro-faults according to the relationship between the micro-fault development area determined based on the reservoir-controlling faults and the micro-fault development area determined based on the fourth-order faults.

7. The prediction method for the development range of difficult-to-identify microfaults according to claim 6, characterized in that, Determining the most developed area of hard-to-identify micro-faults, the relatively developed area of hard-to-identify micro-faults, and the non-developed area of hard-to-identify micro-faults according to the relationship between the micro-fault development area determined based on the reservoir-controlling faults and the micro-fault development area determined based on the fourth-order faults includes: Determine the most developed area of hard-to-identify micro-faults as the area overlapping between the micro-fault development area determined based on the reservoir-controlling faults and the micro-fault development area determined based on the fourth-order faults; Determine the area that does not overlap with the micro - fault development area determined based on the fourth - level fault within the micro - fault development area determined based on the reservoir - controlling fault, and the area outside the micro - fault development area determined based on the reservoir - controlling fault but within the micro - fault development area determined based on the fourth - level fault as the area with relatively developed hard - to - identify micro - faults; Determine the area outside the micro - fault development area determined based on the reservoir - controlling fault and not within the micro - fault development area determined based on the fourth - level fault as the area with under - developed hard - to - identify micro - faults.

8. The method for predicting the development range of difficult-to-identify micro-faults according to claim 1, wherein Including: Before predicting the development range of hard - to - identify micro - faults, verify the existence of hard - to - identify micro - faults.

9. The prediction method for the development range of difficult-to-identify microfaults according to claim 8, characterized in that Verify the existence of hard - to - identify micro - faults according to imaging logging data and core - taking data.

10. The method for predicting the development range of difficult-to-identify micro-faults according to claim 8, wherein, Verify the existence of hard - to - identify micro - faults based on the relationship model constructed between fault throw and the number of faults.

11. The prediction method for the development range of difficult-to-identify microfaults according to claim 10, wherein, The relationship model between fault throw and the number of faults is constructed based on historical data on fault throw and the number of faults. The constructed relationship model between fault throw and the number of faults is y = a * x -b , where y is the number of faults, x is the fault throw, and a and b are parameters obtained by fitting.

12. An oilfield development method based on the prediction of hard-to-identify microfaults, characterized in that, Including the following steps: S11: Predict the development range of hard - to - identify micro - faults within the target reservoir block by using the hard - to - identify micro - fault development range prediction method described in any one of claims 1 - 11 above; S12: Classify the risk types of the target reservoir block based on the development range of hard - to - identify micro - faults; S13: Develop corresponding oilfield development countermeasures for the classified risk types.

13. The oilfield development method based on the prediction of difficult-to-identify microfaults according to claim 12, characterized in that, In step S12, classifying the risk types of the target reservoir block based on the development range of hard - to - identify micro - faults includes: Define the area with the most developed hard - to - identify micro - faults as the Class - I risk area; Define the area with relatively developed hard - to - identify micro - faults as the Class - IIa risk area or Class - IIb risk area. Among them, define the area that does not overlap with the micro - fault development area determined based on the fourth - level fault within the micro - fault development area determined based on the reservoir - controlling fault as the Class - IIa risk area, and define the area outside the micro - fault development area determined based on the reservoir - controlling fault but within the micro - fault development area determined based on the fourth - level fault as the Class - IIb risk area; Define the area with under - developed hard - to - identify micro - faults as the Class - III risk area.

14. The oilfield development method based on the prediction of difficult-to-identify microfaults according to claim 13, wherein In step S12, classifying the risk types of the target reservoir block based on the development range of hard - to - identify micro - faults includes: Based on the main channel development area of medium - high - permeability reservoirs, adjust the classified risk types. If the main channel development area of medium - high - permeability reservoirs overlaps with the development range of hard - to - identify micro - faults, upgrade the Class - IIb risk area to the Class - IIa risk area, and upgrade the Class - IIa risk area to the Class - I risk area.

15. The oilfield development method based on the prediction of difficult-to-identify microfaults according to claim 14, characterized in that, Also including: Before classifying the risk types of the target reservoir block, use the static reservoir method to evaluate the sealing of the reservoir - controlling fault and the fourth - level fault, so as to judge the sealing of the associated hard - to - identify micro - faults in this area; In step S12, classifying the risk types of the target reservoir block based on the development range of hard - to - identify micro - faults includes: Based on the evaluation result of the sealing of hard - to - identify micro - faults, adjust the classified risk types.

16. The oilfield development method based on the prediction of difficult-to-identify microfaults according to claim 15, wherein Evaluate the sealing properties of the controlling reservoir faults and fourth-order faults, so as to determine the sealing properties of the associated hard-to-identify minor faults in this area, including: when the sealing property evaluation results of the controlling reservoir faults and fourth-order faults are consistent, it is considered that the sealing property of the associated hard-to-identify minor faults is the same as that of the controlling reservoir faults and fourth-order faults; when the sealing property evaluation results of the controlling reservoir faults and fourth-order faults are inconsistent, it is considered that the sealing property of the associated hard-to-identify minor faults is the same as the poorer one of the sealing properties of the controlling reservoir faults and fourth-order faults.

17. The oilfield development method based on the prediction of hard-to-identify micro-faults according to claim 15, characterized in that, Based on the sealing property evaluation results of the hard-to-identify minor faults, adjust the classified risk types, including: if the sealing property of the hard-to-identify minor faults is good, downgrade the risk area of class IIa to class IIb, and downgrade the risk area of class IIb to class III; if the sealing property of the hard-to-identify minor faults is medium or poor, do not adjust the classified risk types.

18. The oilfield development method based on the prediction of difficult-to-identify microfaults according to claim 15, characterized in that, Based on the sealing property evaluation results of the hard-to-identify minor faults, adjust the classified risk types, including: If the sealing property of the hard-to-identify minor faults is good and the development range of the hard-to-identify minor faults does not overlap with the main channel development area of the medium-high permeability reservoir, the risk area of class IIa can be downgraded to class IIb, the risk area of class IIb can be downgraded to class III, and the risk area of class I will not be downgraded; If the sealing property of the hard-to-identify minor faults is good and the development range of the hard-to-identify minor faults overlaps with the main channel development area of the medium-high permeability reservoir, upgrade the risk area of class IIb to class IIa, and upgrade the risk area of class IIa to class I.

19. The oilfield development method based on the prediction of difficult-to-identify microfaults according to claim 13, characterized in that, In step S13, for the classified risk types, formulate corresponding oilfield development countermeasures, including: For the risk area of class I, prohibit water injection development operations and avoid deploying high-pressure injection wells or high-injection-volume reinjection wells; For the risk areas of class IIa and class IIb, during the water injection development operation, do a good job in monitoring and dynamic adjustment. Once it is found that the injection well overflows or there is ineffective water injection, the injection-production well pattern should be adjusted in time to further optimize the injection well; For the risk area of class III, conventional oilfield water injection development operations can be carried out, and the injection pressure of high-pressure injection wells or high-injection-volume reinjection wells should be lower than the formation fracture pressure.

20. The oilfield development method based on the prediction of hard-to-identify microfaults according to claim 19, wherein, If water injection development operations are carried out in the risk area of class IIa, when calculating the maximum bottom-hole flowing pressure of the injection well, the fracture probability of the injection well is selected as 10-15%, and the oil layer depth is selected as the upper part or the top depth of the oil layer; If water injection development operations are carried out in the risk area of class IIb, the fracture probability of the injection well is selected as 5%, and the oil layer depth is selected as the middle depth of the oil layer.

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