A karst water flow direction analysis system based on weathering fracture properties

Abstract

The application provides a karst water flow direction analysis system based on weathered fracture properties, comprising a single well weathered fracture identification module, a fracture property analysis module, and a dynamic and static data verification module for paleo-water flow direction; the single well weathered fracture identification module is to identify the developed fractures by identifying the core and core slice of the coring well, and mainly aims at the weathered fractures in the non-tectonic fractures; the fracture property analysis module is to classify and count the length, occurrence and filling condition of the weathered fractures after identifying the weathered fractures; and the dynamic and static data verification module for paleo-water flow direction comprises static data verification and result verification through single well productivity data. The application can effectively support the restoration of the Ma 5 member karst paleo-geomorphology in the research area by only collecting three types of weathered fracture parameters which are easy to identify.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of geological analysis, and particularly relates to a karst water flow direction analysis system based on weathering fracture properties. BACKGROUND

[0002] Domestic carbonate rock weathering crust karst reservoirs can be traced back to the 1970s of the last century, and then the development of karst reservoirs is also reported in the Ordovician Majiagou Group Ma 5 Member in the Ordos Basin, in addition, karst reservoirs are developed in the Sichuan Basin and the Tarim Basin. The recovery of karst paleogeomorphology can effectively support the delineation of carbonate rock karst reservoir development zones and the analysis of hydrocarbon accumulation conditions. The commonly used karst paleogeomorphology recovery methods include residual thickness method, impression method, sedimentology method and the like. The impression method is simple and easy to implement, can finely recover the paleogeomorphology, and does not need to consider the denudation problem caused by tectonic movement, but the determination of the datum surface is interfered by many factors, the stratum correction is difficult to be performed due to compaction, and is affected by the erosion degree of the datum surface. The residual thickness method can semi-quantitatively recover the karst paleogeomorphology, but the terrain difference before stratum deposition and the difference in later weathering denudation will greatly affect the recovery accuracy. With the technical progress, methods such as sequence stratigraphy method and double interface method are derived, and are currently in the initial stage. However, these methods cannot directly verify the flow path of karst water. SUMMARY

[0003] In order to solve the problems in the background system, the application provides a karst water flow direction analysis system based on weathering fracture properties.

[0004] A karst water flow direction analysis system based on weathering fracture properties comprises the following modules:

[0005] 1. Single well weathering fracture identification module

[0006] The core and core slice of a coring well are identified, and the fractures developed therein are identified, mainly aiming at the weathering fractures in non-tectonic fractures.

[0007] The surface weathering leaching fracture is developed in the near-surface, and is formed under the influence of physical and mechanical weathering, mainly showing vertical dendritic fractures, and the end can be bifurcated;

[0008] The network weathering fracture often exists in the middle-late weathering broken zone, is developed relatively late, and has a high filling degree.

[0009] The karst collapse fracture has three types:

[0010] (1) The collapse fracture formed by the collapse of a large karst cave in the weathering period;

[0011] (2) The collapse formed by the steep cliff under the action of gravity;

[0012] (3) The soluble part (containing salt) developed in the stratum is dissolved to form a solution hole and collapse.

[0013] The original database of weathering fractures in different regions can be obtained by identifying the fractures observed in the cores and thin sections of different single wells in the study area. The identified weathering fractures are then manually finely divided, and the occurrence, length, and filling degree are statistically analyzed to serve as the basis for water flow direction analysis.

[0014] 2. Fracture property analysis module

[0015] The weathering fracture extension length is measured using a tape measure after the core is spliced, and the core direction is taken as the vertical direction. The fracture dip angle is measured using a protractor to obtain the weathering fracture length and dip angle parameters of the cored well in different regions. The filling degree of the fracture is evaluated and verified by macroscopic core observation and microscopic thin section identification to obtain the filling degree and the conclusion of the karst water flow direction (the catchment characteristics of the ancient landform low potential area).

[0016] 3. Dynamic and static data verification module of ancient water flow direction

[0017] (1) Static data verification: the rationality of the ancient water flow tracing results is verified by the change of the reservoir development thickness;

[0018] Reservoir development thickness verification: different landforms will lead to changes in hydrological conditions, resulting in differences in karstification intensity, and ultimately differences in the spatial distribution of karst reservoirs. Karst highlands are higher than the phreatic surface and are easily affected by atmospheric fresh water leaching, with strong dissolution and vertical seepage as the main karstification, which often results in large-scale loss of reservoirs and the inability to form high-quality reservoirs.

[0019] (2) Production dynamic data verification: the results are verified by single well productivity data, and the places with high productivity correspond to low potential areas.

[0020] Productivity verification: karst slopes and karst monadnocks are higher than the phreatic surface, with strong groundwater activity, general karstification, strong dissolution, and weak cementation, which can form favorable reservoirs with dissolution pores. Karst structures have the lowest terrain, and the overall terrain is flat, which is the water collection area. The water dynamic condition is weak, and the chemical cementation and filling are strong, so the pore space is mostly filled with cement, which is not conducive to the formation of large-area favorable reservoirs.

[0021] In the static data verification unit or production dynamic data verification unit verification process, the traditional mold method is used to divide the ancient landform unit by using the overlying Carboniferous Benxi Formation sedimentary thickness.

[0022] Advantages

[0023] 1. The paleo-water flow direction tracing and paleo-geomorphology restoration results provided by the application are not contradictory, and only collecting three types of easily identifiable weathering cracks can effectively support the restoration of the Ma 5 Member karst paleo-geomorphology in the study area.

[0024] 2. The basic data of the weathering crack identification method can be directly obtained from the cores necessary in the development process, which is simple and convenient without the need for additional experimental and research programs, and can save research costs. The results have been applied in Daniudi gas field in Ordos Basin.

[0025] 3. In the verification process, the traditional impression method is used to divide the paleo-geomorphology unit by the overlying Carboniferous Benxi Formation sediment thickness, which is convenient for comparing the weathering crack tracing results of the paleo-water flow direction. BRIEF DESCRIPTION OF DRAWINGS

[0026] Figure 1 A is a macroscopic feature diagram of core weathering cracks in the study area;

[0027] Figure 2 B is a macroscopic feature diagram of core weathering cracks in the study area;

[0028] Figure 3 C is a macroscopic feature diagram of core weathering cracks in the study area;

[0029] Figure 4 D is a macroscopic feature diagram of core weathering cracks in the study area;

[0030] Figure 5 E is a macroscopic feature diagram of core weathering cracks in the study area;

[0031] Figure 6 F is a macroscopic feature diagram of core weathering cracks in the study area;

[0032] Figure 7 A is a microscopic feature diagram of weathering cracks shown by the slice in the study area;

[0033] Figure 8 B is a microscopic feature diagram of weathering cracks shown by the slice in the study area;

[0034] Figure 9 C is a microscopic feature diagram of weathering cracks shown by the slice in the study area;

[0035] Figure 10 D is a microscopic feature diagram of weathering cracks shown by the slice in the study area;

[0036] Figure 11 E is a microscopic feature diagram of weathering cracks shown by the slice in the study area;

[0037] Figure 12 F is a microscopic feature diagram of weathering cracks shown by the slice in the study area;

[0038] Figure 13 For the well location map of the study area;

[0039] Figure 14 For the core weathering fracture length characteristic map of part of the Ma 5 submember in Daniudi;

[0040] Figure 15 For the core weathering fracture occurrence characteristic map of part of the Ma 5 submember in Daniudi;

[0041] Figure 16 For the core weathering fracture filling condition characteristic of the study area Figure I ;

[0042] Figure 17 For the core weathering fracture filling condition characteristic of the study area Figure II ;

[0043] Figure 18 For the core weathering fracture filling condition characteristic of the study area Figure III ;

[0044] Figure 19 For the core weathering fracture filling condition characteristic of the study area Figure IV ;

[0045] Figure 20 For the reservoir thickness scatter plot of different locations in the Daniudi gas field;

[0046] Figure 21 For the Benxi Formation thickness and cumulative gas production relationship diagram of the Daniudi gas field;

[0047] Figure 22 For the flow chart of the present application. Specific embodiments

[0048] In order to make the purpose, system scheme and advantages of the present application more clear, the system scheme in the present application is described clearly and completely below in combination with the drawings.

[0049] After the strata below the weathering crust unconformity surface are uplifted to the surface, they are subjected to extensive weathering and erosion, resulting in strata thinning and rock breakage due to physical and chemical effects, forming dense weathering cracks. The density, occurrence, length and other properties of weathering cracks depend on the karst paleogeomorphology where the strata outcrop. Weathering cracks often form dense vertical crack zones in high geomorphology areas, and guide atmospheric water to infiltrate downward. Towards the low, the vertical extension of the cracks tends to weaken, and tends to develop into a dispersed network. Compared with the low part of the paleogeomorphology, the weathering cracks in the high part have large infiltration space and fast speed, which is not conducive to fluid collection, and the crack filling degree is low, while the flow through the low part meets the collection conditions, and the mineral precipitation causes the crack filling degree to be high. Thus, the occurrence and filling degree of weathering cracks at different geomorphology heights are different. Based on the length, occurrence and filling condition of weathering cracks, the ancient karst water flow path can be restored, which is also an effective means for the final karst paleogeomorphology restoration.

[0050] According to Figure 22 As shown in the figure, a karst water flow direction analysis system based on weathering crack properties includes the following modules:

[0051] 1. Single well weathering crack identification module

[0052] The core and core slice of the coring well are identified, and the cracks developed therein are identified, mainly for weathering cracks in non-tectonic cracks.

[0053] Surface weathering leaching cracks develop near the surface, and their formation is affected by physical and mechanical weathering, mainly in the form of vertical dendritic cracks, and the ends can be bifurcated;

[0054] Network weathering cracks often exist in the middle and late weathering and broken zones, and develop later with high filling degree;

[0055] Karst collapse cracks have three types:

[0056] (1) Collapse cracks formed by the collapse of large caves formed during the weathering period;

[0057] (2) Collapse formed by steep scarps under the action of gravity;

[0058] (3) Dissolution pores collapse caused by dissolution of soluble parts (containing gypsum and salt) developed in the strata.

[0059] After the cracks observed in the core and slice data of different single wells in the study area are identified, the original database of weathering cracks in different regions can be obtained, and these identified weathering cracks are artificially finely divided, and the occurrence, length and filling degree are counted as the basis for water flow direction analysis.

[0060] 4. Crack property analysis module

[0061] After identifying weathering fractures, they were classified and statistically analyzed based on three properties: length, orientation, and filling condition. The length of the weathering fractures was measured using a measuring tape after core samples were spliced ​​together, and the dip angle was measured using a protractor with the core sampling direction perpendicular to the fracture direction, to obtain the parameters of weathering fracture length and dip angle from core samples taken from different locations. The degree of fracture filling was verified through both macroscopic core observation and microscopic thin section analysis to determine its extent.

[0062] 5. Verification module for paleowater flow direction using dynamic and static data.

[0063] (1) Static data verification: The rationality of the paleocurrent tracing results is verified by the changes in reservoir development thickness;

[0064] Verification based on reservoir development thickness shows that variations in topography lead to changes in hydrological conditions, resulting in differences in the intensity of karstification and ultimately, differences in the spatial distribution of karst reservoirs. Karst highlands, being above the water table, are susceptible to leaching by atmospheric freshwater, exhibiting intense dissolution. Karstification is primarily characterized by vertical infiltration, often resulting in large-area reservoir absence and preventing the formation of high-quality reservoirs.

[0065] (2) Verification of production dynamic data: The results are verified by single-well production capacity data. Areas with high production capacity correspond to areas with lower potential.

[0066] Through production capacity verification: Karst slopes and karst remnants are higher than the water table, with stronger groundwater activity, widespread karstification, strong dissolution and weak cementation, which can form favorable reservoirs with dissolution cavities. Karst structures have the lowest elevation and generally gentle terrain, which are water flow convergence areas. The hydrodynamic conditions are weak and the chemical cementation is strong. The pore spaces are mostly filled with cement, which is not conducive to the formation of large-area favorable reservoirs.

[0067] During the verification process, the traditional impression method was used to divide the paleogeographic units by utilizing the sedimentary thickness of the overlying Carboniferous Benxi Formation, which facilitates the comparison of the tracing results of weathering cracks on the paleowater flow direction.

[0068] Example 1

[0069] 1. Single-well weathering crack identification module

[0070] according to Figures 1-12 As shown, core samples and thin sections from multiple core wells in the Majiagou Formation (Ma 5 Member) of the Daniudi area in the Ordos Basin were analyzed to identify the developed fractures, primarily focusing on weathering fractures within non-tectonic fractures. Obvious karst collapse fractures were visible in the core samples, and calcite-filled network microfractures were also identified in the thin sections.

[0071] Figures 1-6 The macroscopic characteristics of weathering fractures in the core samples from the study area are as follows:

[0072] Figure 1 : DEI well, grayish marl, karst collapse fracture;

[0073] Figure 2 : DFD well, karst collapse fracture;

[0074] Figure 3 : DDA well, grayish blackish marl, weathering oblique fracture, karst cave along the fracture;

[0075] Figure 4 : DFD well, blackish limestone, karst collapse fracture;

[0076] Figure 5 : DEI well, high angle weathering fracture;

[0077] Figure 6 : DGF well, calcite filled near-vertical fracture

[0078] Figures 7-12 The microcosmic characteristics of weathering fractures shown by the thin sections in the study area are:

[0079] Figure 7 : DGH well, micritic limestone, weathering network fracture;

[0080] Figure 8 : DB-FDA well, micritic limestone, weathering network fracture, karst breccia visible;

[0081] Figure 9 : DEI well, bioclastic limestone, network fracture;

[0082] Figure 10 : DDA well, dolomite, network fracture;

[0083] Figure 11 : DJC well, micritic dolomite, network fracture;

[0084] Figure 12 : DJC well, micro-powder crystal dolomite, network fracture.

[0085] The surface weathering leaching fracture develops in the near-surface, and its formation is affected by physical and mechanical weathering, mainly showing vertical dendritic fracture, and the end can be bifurcated. The network weathering fracture often exists in the middle-late weathering broken zone, which is relatively developed in the study area and has high filling degree. The karst collapse fracture in the study area has three types, i.e. the fracture formed by the collapse of large karst cave in the weathering period, the collapse formed by the cliff under the action of gravity, and the dissolution pore collapse (such as gypsum dissolution) of the soluble part (containing gypsum salt) developed in the stratum. Figure 12 Gypsum dissolution phenomenon.

[0086] The original database of weathering fractures in different regions can be obtained by identifying the fractures observed in the cores and thin sections of different single wells in the study area, and the identified weathering fractures are manually finely divided, and the occurrence, length, and filling degree are counted as the basis for water flow direction analysis.

[0087] 2. Fracture property analysis module

[0088] According to Figures 1-19 After identifying the weathering fractures, the length, occurrence, and filling condition of the weathering fractures are classified and counted. The length of the weathering fractures is measured by using a tape measure after splicing the cores, and the dip angle of the weathering fractures is measured by using a protractor with the core direction as the vertical direction, so as to obtain the length and dip angle parameters of the weathering fractures of the coring wells in different regions.

[0089] After obtaining the basic data, the coring wells in different regions are grouped, and the weathering fractures of each well are grouped and compared from the aspects of length, dip angle, and filling degree. DB-FDA, PGCH, DFA, and DBAB wells are the first group, DDA, DEI, and DGH wells are the second group, DDH and DBCC wells are the third group, and DII well is the fourth group.

[0090] The fractures of the first group are mainly high-angle fractures, long fractures with a length of more than 10 cm are developed, and most of the fractures are fully filled with calcite or mud, and a small amount of fractures are semi-filled, indicating that the karst water mainly flows vertically and has a large vertical influence depth, indicating the water discharge characteristics of the high potential area of the karst paleogeomorphology; the fractures of the second group are still mainly high-angle fractures, but the network fractures and horizontal fractures increase obviously, the length of the fractures except the network fractures is less than 10 cm, and a small amount of fractures are not filled, indicating that the karst water begins to move horizontally, and the vertical influence depth of the single-stage active weathering fractures decreases, indicating that the paleogeomorphology is lowered; in the third group, the number of high-angle fractures has obviously decreased, network fractures, low-angle fractures, and horizontal fractures are developed, and the length of the fractures is mostly less than 10 cm, indicating that the karst water continues to flow horizontally, and the vertical influence further decreases, indicating that the paleogeomorphology continues to decrease; in the fourth group, network weathering fractures are very developed, and are all fully filled with calcite, indicating that the karst water flows horizontally, which is the water collection characteristics of the low potential area of the paleogeomorphology.

[0091] 3. Dynamic and static data verification module of paleo-water flow direction

[0092] According to Figures 20-21 Static data verification: the rationality of the paleo-water flow tracing result is verified by the change of the reservoir development thickness;

[0093] Production dynamic data verification: the results are verified by single well productivity data, and the high productivity area corresponds to the lower potential area. In the verification process, the traditional mold method is used to divide the paleogeomorphology unit by using the overlying Carboniferous Benxi Formation sedimentary thickness, which is convenient for comparing the tracing results of weathering fractures to paleocurrent direction.

[0094] Verification by reservoir development thickness: the difference in geomorphology height and low will lead to changes in hydrological conditions, making the intensity of karstification different, and finally making the spatial distribution of karst reservoirs different. Karst highlands are higher than the phreatic surface, and are easy to be affected by atmospheric fresh water leaching, with strong dissolution, and the karstification is mainly vertical percolation, which often makes the reservoirs large area missing, and cannot form high-quality reservoirs. According to the verification of the effective reservoir thickness of Ma5 submember in Daniudi gas field, it is found that the effective reservoir thickness of karst monad in the study area is larger, followed by karst slope, and the karst terrace and karst gully are the smallest. The development rule is consistent with the analysis conclusion of the four groups of single well weathering fractures in different areas.

[0095] Verification by productivity: karst slope and karst monad are higher than the phreatic surface, and the groundwater activity is strong, the karstification is universal, the dissolution is strong and the cementation is weak, which can form favorable reservoirs with dissolution pores. Karst structure terrain is the lowest, and the overall terrain is flat, which is the water flow collection area, the hydrodynamic condition is weak and the chemical cementation filling is strong, and the pore space is mostly filled with cementation, which is not conducive to the formation of large area favorable reservoirs. According to the superimposed comparison of natural gas production, it is found that the cumulative gas production of karst monad in the study area is large, followed by karst slope, and the karst terrace and karst gully are the smallest, which is consistent with the analysis conclusion of the four groups of single well weathering fractures in different areas.

[0096] Finally, it should be pointed out that: the above examples are only used to illustrate the system scheme of the present application, but not to limit it; although the present application has been described in detail with reference to the foregoing examples, those skilled in the art should understand that they can still modify the system scheme recorded in the foregoing examples, or equivalently replace part of the system features; and these modifications or replacements do not make the essence of the corresponding system scheme deviate from the spirit and scope of the system scheme of the embodiments of the present application.

Claims

1. A karst water flow direction analysis system based on weathering fracture properties, characterized by, The module comprises a single well weathering fracture identification module, a fracture property analysis module, and a dynamic and static data verification module for ancient water flow direction, wherein the single well weathering fracture identification module is to identify the fractures developed in the core and core slice of a coring well, and mainly aims at weathering fractures in non-tectonic fractures; the fracture property analysis module is to classify and count the length, occurrence and filling condition of weathering fractures after identifying the weathering fractures; and the dynamic and static data verification module for ancient water flow direction comprises a static data verification unit and a production dynamic data verification unit, wherein the static data verification unit is to verify the rationality of the tracing result of the ancient water flow through the change of reservoir development thickness; and the production dynamic data verification unit is to verify the result through single well productivity data, and the place with high productivity corresponds to a lower potential area. The single well weathering fracture identification module specifically comprises: surface weathering leaching fractures are developed near the surface, and are mainly vertical dendritic fractures with bifurcated ends, which are formed under the influence of physical and mechanical weathering; network weathering fractures are often present in the middle and late weathering broken zones, are developed relatively late, and have high filling degree; and karst collapse fractures have three types: (1) fractures formed by collapse of large solution cavities formed in the weathering period; (2) collapse formed by cliffs under the action of gravity; and (3) dissolution pore collapse of soluble parts developed in the stratum. After identifying the fractures observed in the core and slice data of different single wells in the study area, the original database of weathering fractures in different regions is obtained, and the identified weathering fractures are artificially finely divided for statistics from the aspects of occurrence, length and filling degree to serve as the basis for water flow direction analysis. The dynamic and static data verification module for ancient water flow direction further comprises: The static data verification unit is to verify the reservoir development thickness, and the difference in topography will lead to the change of hydrological conditions, the difference in karstification intensity, and finally the difference in spatial distribution of karst reservoirs; the karst highland is higher than the phreatic surface, is easy to be affected by atmospheric water leaching, has strong dissolution, and mainly has vertical percolation, which often causes large-area loss of reservoirs and makes it difficult to form high-quality reservoirs; The production dynamic data verification unit is to verify the single well productivity, and the karst slope and karst monadnock are higher than the phreatic surface, have strong groundwater activity, have general karstification, have strong dissolution and weak cementation, form favorable reservoirs with dissolution pores, the karst structure has the lowest terrain, and the overall terrain is gentle, which is a water collection area, has weak hydrodynamic conditions and strong chemical cementation, and the pore space is mostly filled with cement, which is not conducive to the formation of large-area favorable reservoirs; In the verification process of the static data verification unit or the production dynamic data verification unit, the traditional impression method is used to divide the paleogeomorphological unit according to the overlying Carboniferous Benxi Formation sedimentary thickness.

2. The karst water flow direction analysis system based on weathering fracture properties according to claim 1, characterized in that, The fracture property analysis module specifically comprises: the weathering fracture extension length is measured by using a tape measure after splicing the core, the fracture dip angle is measured by using a protractor with the core direction as the vertical direction, and the filling degree of the fracture is evaluated and verified by macroscopic core observation and microscopic slice identification to obtain the filling degree.

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