Method for recovering collapse thickness of gypsum-containing carbonate rock karst

Abstract

The invention discloses a method for recovering the collapse thickness of gypsum-containing carbonate rock karst. The method for recovering the collapse thickness of gypsum-containing carbonate rock karst comprises the specific steps that S100, whether lithology of a research area is gypsum-containing carbonate rock or not and karst action occurs is analyzed through data such as a rock core and a slice; s200, selecting a standard well based on the logging information; s300, determining a thickness recovery ratio of each small layer by comparing logging curve forms and thickness differences of other wells in each small layer and the standard well; and S400, performing karst collapse thickness recovery according to the thickness recovery ratio. According to the method, whether the lithology of a research area is the gypsum-containing carbonate rock or not is analyzed through data such as a rock core and a slice, the karst effect occurs, and the collapse thickness of the gypsum-containing carbonate rock karst can be recovered by selecting and referring to a standard well, so that the thickness of a gypsum-containing carbonate rock karst collapse stratum is accurately recovered in ancient landform recovery.

Description

Technical Field

[0001] This invention relates to the field of oil and gas exploration technology, specifically a method for restoring the thickness of karst collapse in gypsum-bearing carbonate rocks. Background Technology

[0002] Numerous studies have shown that in actual sedimentary processes, evaporation and crystallization do not strictly follow the ideal sequence of calcite (dolomite)-gypsum-halite precipitation. Instead, intermittent sea-level fluctuations cause changes in the aquatic medium, resulting in mineral "symbiosis." This is the reason for the formation of gypsum-bearing carbonate rocks. Gypsum-bearing carbonate rock systems have been widely developed throughout geological history and are important factors controlling the sedimentary facies and reservoir development and distribution in oil and gas basins, influencing the reservoir-seal assemblages of later oil and gas reservoirs to a certain extent. Currently, the methods used in oil and gas field exploration and development to restore the thickness of karst collapses in gypsum-bearing carbonate rocks mainly rely on rock fragment data combined with the reconstruction of paleogeographic frameworks during the sedimentary period. This method has effectively guided the exploration process in the oil and gas field exploration stage, but it is difficult to apply to the thickness of karst collapses in gypsum-bearing carbonate rocks.

[0003] For example, the invention patent with patent number CN202210022378.6 discloses a method for lithological restoration of paleogeography, including: differential subsidence correction of residual landforms; fault restoration; tectonic-sedimentary unit division; erosion restoration; correction of differential subsidence and restoration of erosion in residual paleogeography to improve the restoration of the paleogeographic framework during the depositional period; characterization of uplift parent rock types and residual parent rock distribution; analysis and statistics of drilling cuttings components, statistical analysis of core and cuttings components revealed by drilling in the depositional area, and drawing a characteristic distribution map of cuttings components; qualitative restoration of the source area parent rock type and distribution during the depositional period, based on the source-sink unit division, inversion of sink area cuttings back to the corresponding source area, correction of the lithology of the source area parent rock, and correction of the distribution range of different parent rocks according to the relative relationship of cuttings content, to obtain a restored map of parent rock lithology and distribution. This method for lithological restoration of paleogeography, by establishing paleogeography and prototype basins during the depositional period, provides guidance for research on material distribution, geomorphological evolution, reservoir characteristics, and distribution of favorable reservoirs in erosion and depositional areas.

[0004] Although this method of paleogeographic lithological reconstruction can provide guidance for the study of material distribution, geomorphological evolution, reservoir characteristics, and distribution of favorable reservoirs in erosion and sedimentary areas by establishing paleogeographic features and prototype basins during sedimentary periods, and effectively guides the exploration process in the oil and gas field exploration stage, this method is not applicable to the reconstruction of the thickness of karst collapses in gypsum-bearing carbonate rocks, making it difficult to accurately reconstruct the thickness of karst collapse strata in paleogeographic reconstruction. Summary of the Invention

[0005] The purpose of this invention is to provide a method for restoring the thickness of karst collapses in gypsum-bearing carbonate rocks, aiming to improve the problem that paleogeographic restoration methods are not applicable to the restoration of the thickness of karst collapses in gypsum-bearing carbonate rocks, which makes it difficult to accurately restore the thickness of karst collapse strata in paleogeographic restoration.

[0006] This invention is implemented as follows: a method for restoring the thickness of karst collapses in gypsum-bearing carbonate rocks, the specific steps of which are as follows:

[0007] S100. Analyze the lithology of the study area through core, thin section and other data to determine whether it is gypsum-bearing carbonate rock and whether karstification has occurred.

[0008] S200, Selecting standard wells based on well logging data;

[0009] S300. By comparing the logging curve morphology and thickness differences between other wells and standard wells within each sub-layer, the thickness recovery ratio of each sub-layer is determined.

[0010] S400, restore the thickness of karst collapse according to the thickness restoration ratio.

[0011] Preferably, in S100, the lithology of the study area is analyzed to determine whether it is gypsum-bearing carbonate rock and whether karstification has occurred; that is, gypsum, gypsum mold pores, etc. can be seen in the core and thin section data, and large dissolution pores, caves, fissures, etc. can be seen, or the core is severely brecciated, all of which are gypsum-bearing carbonate rock strata that have undergone karstification.

[0012] Preferably, the method for selecting the standard well in S200 is as follows: compare the logging curves of all single wells in the work area, and select the well with the most complete logging curve characteristics and the largest thickness as the thickness recovery standard well for that layer.

[0013] Preferably, the standard well is a well that is less affected by karst processes compared to other wells.

[0014] Preferably, the method for determining the thickness recovery ratio in S300 is as follows: the thickness of the standard well is h, and the thickness of other wells is h / 2. The logging curve characteristics of other wells are compared with those of the standard well. The part missing from the logging curve characteristics of other wells relative to those of the standard well is l. Therefore, the thickness recovery ratio of other wells relative to the standard well is (hl) / h / 2.

[0015] Preferably, in the formula, h is the thickness of the standard well; h / 2 is the thickness of other wells; and l is the thickness missing from other wells relative to the standard well.

[0016] Preferably, the method for comparing and restoring the karst collapse thickness of other wells in the same stratum in S400 is as follows: the karst collapse thickness of other wells is h / 3 = (hl) / h / 2 × l, and the original thickness of other wells is H = h / 2 + h / 3.

[0017] Preferably, in the formula, h / 3 is the thickness restored proportionally by other wells; H is the original thickness of other wells.

[0018] Compared with the prior art, the beneficial effects of the present invention are:

[0019] 1. This invention analyzes whether the lithology of the research area is gypsum-bearing carbonate rock and whether karstification has occurred by using core and thin section data. By selecting and referring to standard wells, the thickness of karst collapse of gypsum-bearing carbonate rock can be restored, so that the thickness of karst collapse strata of gypsum-bearing carbonate rock can be accurately restored in paleogeographic restoration.

[0020] 2. By restoring the thickness of karst collapse in gypsum-bearing carbonate rocks, this invention can provide a basis for exploring the lithofacies paleogeographic division, sedimentary environment, sedimentary facies, oil and gas reservoirs, and finding favorable oil and gas reservoir development zones of gypsum-bearing carbonate rocks. It can also provide a good reference for oil and gas exploration and development in oil and gas basins. Attached Figure Description

[0021] Figure 1 This is a flowchart of the method for restoring the thickness of karst collapse in gypsum-bearing carbonate rocks according to the present invention;

[0022] Figure 2 This is a schematic diagram illustrating the principle of karst collapse thickness restoration in this invention. Detailed Implementation

[0023] In this invention, unless otherwise explicitly specified and limited, the terms "installation," "connection," "linking," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0024] The following description, in conjunction with the accompanying drawings and specific embodiments, provides further details:

[0025] Example 1

[0026] like Figure 1 and Figure 2 As shown, a method for restoring the thickness of karst collapses in gypsum-bearing carbonate rocks is characterized by the following specific steps:

[0027] S100. Analyze the lithology of the study area through core, thin section and other data to determine whether it is gypsum-bearing carbonate rock and whether karstification has occurred.

[0028] S100 analyzes whether the lithology of the study area is gypsum-bearing carbonate rock and whether karstification has occurred; that is, gypsum, gypsum mold pores, etc. can be seen in the core and thin section data, and large dissolution pores, caves, and fissures can be seen, or the core is severely brecciated, all of which are gypsum-bearing carbonate rock strata that have undergone karstification.

[0029] S200, Selecting standard wells based on well logging data;

[0030] The selection method for standard wells in S200 is as follows: compare the logging curves of all single wells in the work area, and select the well with the most complete logging curve characteristics and the largest thickness as the thickness recovery standard well for that formation. A standard well is one that is less affected by karst processes compared to other wells.

[0031] S300. By comparing the logging curve morphology and thickness differences between other wells and standard wells within each sub-layer, the thickness recovery ratio of each sub-layer is determined.

[0032] The method for determining the thickness recovery ratio in S300 is as follows: the thickness of the standard well is h, and the thickness of other wells is h / 2. The logging curve characteristics of other wells are compared with those of the standard well. The missing portion of the logging curve characteristics of other wells relative to the standard well is l. Therefore, the thickness recovery ratio of other wells relative to the standard well is (hl) / h / 2. In the formula, h is the thickness of the standard well; h / 2 is the thickness of other wells; and l is the missing thickness of other wells relative to the standard well.

[0033] S400, restore the thickness of karst collapse according to the thickness restoration ratio.

[0034] In S400, the method for comparing and restoring the karst collapse thickness of other wells in this stratum is as follows: the karst collapse thickness of other wells is h / 3 = (hl) / h / 2 × l, and the original thickness of other wells is H = h / 2 + h / 3. In the formula, h / 3 is the thickness restored proportionally from other wells; H is the original thickness of other wells.

[0035] Example 2

[0036] Taking gas field A as an example, the study area is known to be a karst-bearing carbonate rock formation. First, standard wells were selected by comparing the logging morphology and layer thickness of each well in each sub-layer within the karstified formation. The well with the most complete logging curve morphology and the largest thickness in each sub-layer was determined as the standard well for that sub-layer. The standard well selected for the 4th sub-layer was well D1, with a thickness of 32m. Third, by comparing the logging curve morphology and thickness differences between other wells (well D2, with a thickness of 27m) and the standard well (well D1) in each sub-layer, the thickness recovery ratio of the 4th sub-layer of well D2 was determined to be 27 / 32. Based on the thickness recovery ratio, the karst collapse thickness of this well was calculated as h3 = 6 × 27 / 32 = 5.06m. Finally, the original thickness of this well was calculated as H = h3 + h2 = 5.06 + 27 = 32.06m.

[0037] The thickness of the standard well is h, and the thickness of the other wells is h2. Comparing the logging characteristics of the other wells with those of the standard well, the missing portion of the logging characteristics of the other wells relative to the standard well is l. Therefore, the thickness recovery ratio of the other wells relative to the standard well is (hl) / h2; the karst collapse thickness of the other wells is h3 = (hl) / h2 × l; the original thickness of the other wells is H = h2 + h3.

[0038] Where h is the thickness of the standard well; h2 is the thickness of other wells; l is the missing thickness of other wells relative to the standard well; h3 is the thickness of other wells restored proportionally; and H is the original thickness of other wells.

[0039] In summary, this invention analyzes core and thin section data to determine whether the lithology of the study area is gypsum-bearing carbonate rock and whether karstification has occurred. By selecting and referencing standard wells, the thickness of karst collapse in gypsum-bearing carbonate rocks can be restored, allowing for accurate reconstruction of the thickness of karst collapse strata in paleogeographic restoration. This invention, by restoring the thickness of karst collapse in gypsum-bearing carbonate rocks, can provide a basis for exploring the lithofacies paleogeographic division, sedimentary environment, sedimentary facies, oil and gas reservoirs, and for identifying favorable oil and gas reservoir development zones. It can provide a valuable reference for oil and gas exploration and development in oil and gas basins.

[0040] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention can have various modifications and variations. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for restoring the thickness of karst collapse in gypsum-bearing carbonate rocks, characterized in that, The specific steps for restoring the thickness of karst collapses in gypsum-bearing carbonate rocks are as follows: S100. Analyze the lithology of the study area through core, thin section and other data to determine whether it is gypsum-bearing carbonate rock and whether karstification has occurred. S200, Selecting standard wells based on well logging data; S300. By comparing the logging curve morphology and thickness differences between other wells and standard wells within each sub-layer, the thickness recovery ratio of each sub-layer is determined. s400, restore the thickness of karst collapse according to the thickness restoration ratio.

2. The method for restoring the thickness of karst collapse in gypsum-bearing carbonate rocks according to claim 1, characterized in that, The S100 analysis determines whether the lithology of the study area is gypsum-bearing carbonate rock and whether karstification has occurred; that is, gypsum, gypsum mold pores, etc. can be seen in the core and thin section data, and large dissolution pores, caves, and fissures can be seen, or the core is severely brecciated, all of which are gypsum-bearing carbonate rock strata that have undergone karstification.

3. The method for restoring the thickness of karst collapse in gypsum-bearing carbonate rocks according to claim 1, characterized in that, The selection method for the standard well in S200 is as follows: compare the logging curves of all single wells in the work area, and select the well with the most complete logging curve characteristics and the largest thickness as the thickness recovery standard well for that layer.

4. The method for restoring the thickness of karst collapse in gypsum-bearing carbonate rocks according to claim 3, characterized in that, The standard well is a well that is less affected by karst processes compared to other wells.

5. The method for restoring the thickness of karst collapse in gypsum-bearing carbonate rock according to claim 1, characterized in that, The method for determining the thickness recovery ratio in S300 is as follows: the thickness of the standard well is h, and the thickness of other wells is h / 2. The logging curve characteristics of other wells are compared with those of the standard well. The part missing from the logging curve characteristics of other wells relative to those of the standard well is 1. Therefore, the thickness recovery ratio of other wells relative to the standard well is (h-1) / h / 2.

6. The method for restoring the thickness of karst collapse in gypsum-bearing carbonate rock according to claim 5, characterized in that, In the formula, h is the thickness of the standard well; h / 2 is the thickness of other wells; and 1 is the thickness missing from the standard well in other wells.

7. The method for restoring the thickness of karst collapse in gypsum-bearing carbonate rock according to claim 1, characterized in that, The method for comparing and restoring the karst collapse thickness of other wells in the S400 is as follows: the karst collapse thickness of other wells is h / 3=(h-1) / h / 2×1, and the original thickness of other wells is H=h / 2+h / 3.

8. The method for restoring the thickness of karst collapse in gypsum-bearing carbonate rock according to claim 7, characterized in that, In the formula, h / 3 represents the thickness restored proportionally by other wells; H represents the original thickness of other wells.

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