Accumulated salinized lake basin deposition ancient landform restoration method based on gypsum salt rock distribution

Abstract

The invention discloses a gypsum salt rock distribution-based mixed salinized lake basin deposition ancient landform restoration method, and belongs to the technical field of oil-gas exploration. According to the principle and the characteristic that evaporated and concentrated heavy brine in the lake basin environment flows back to the low part of the landform to form gypsum salt rock, the gypsum salt rock distribution data is creatively introduced to invert the difference of the sedimentary ancient landform, and the method is a new sedimentary ancient landform restoration technical means for the mixed salinized lake basin geological environment. And the applicability and the accuracy of the sedimentary ancient landform restoration technology are enhanced. The method comprises the following steps: selecting a target layer; gypsum salt rock logging identification is carried out; drawing a gypsum salt rock distribution diagram; and utilizing gypsum salt rock distribution to invert sedimentary ancient landform differences, and generating a sedimentary ancient landform map.

Description

Technical Field

[0001] The present invention relates to the field of oil and gas exploration, and in particular to a method for restoring the sedimentary paleo-geomorphology of a mixed saline lake basin based on the distribution of gypsum-salt rocks. Background Art

[0002] Oil and gas exploration practice has confirmed that saline lake basins are one of the important places for oil and gas storage and migration. At present, a large amount of oil and gas resources have been found in saline lake basin mixed sediments in key areas and strata such as the Paleogene of the Qaidam Basin, the Permian of the Junggar Basin, the Paleogene of the Jiyang Depression, and the Paleogene of the Biyang Sag. Saline lake basin mixed sediments mainly refer to mixed deposits composed of carbonate and sulfate sediments formed by chemical sedimentation and felsic clastic sediments formed by mechanical sedimentation of traction flow (or other transporting forces). As a response to the periodic evolution of the sedimentary environment, saline lake basin mixed sediments mostly show frequent interbedded characteristics of felsic clastic rock-carbonate rock-sulfate rock (gypsum salt rock) in the vertical direction. For oil and gas exploration in saline lake basins, the difference in sedimentary paleo-geomorphology has a significant impact on the distribution of different types of mixed sediments, the vertical sequence structure, and the development of reservoir pores. Therefore, the detailed description of paleo-geomorphological features is of great significance for predicting and evaluating the reservoir distribution and oil and gas enrichment patterns in saline lake basins.

[0003] At present, there are many research reports on paleo-geomorphology, which are mainly divided into two categories: karst paleo-geomorphology and sedimentary paleo-geomorphology. Among them, the methods for restoring karst paleo-geomorphology mainly include the impression method and the residual thickness method, which are mainly aimed at carbonate rock strata after uplift and weathering and erosion, and do not fall within the scope of this patent. The methods for restoring sedimentary paleo-geomorphology mainly include sedimentological analysis method, sequence stratigraphy method and geophysical method. The sedimentological analysis method is a rough paleo-geomorphological reconstruction method that outlines the relative landform undulations based on the distribution of different sedimentary phases and different hydrodynamic conditions; the key to the sequence stratigraphy method is the selection of isochronous datum, which has a better application effect on marine carbonate rocks or terrestrial sandstone and mudstone strata with a single sedimentary type, but it is difficult to apply to the mixed sedimentary system of saline lake basins due to the coexistence of two different sedimentary mechanisms: carbonate-sulfate chemical deposition and clastic rock mechanical deposition; the geophysical method is greatly constrained by the quality of seismic data, and is limited by the vertical and horizontal resolution, making it difficult to accurately identify the micro-geomorphological undulation differences of the mixed sedimentary system of saline lake basins with meter-level thin interlayer characteristics. It can be seen that there is currently a lack of reliable means of restoring sedimentary paleo-geomorphology in the special geological environment of mixed saline lake basins. Summary of the invention

[0004] In response to the problems in the prior art, the present invention provides a method for restoring the ancient landforms of mixed saline lake basin sediments based on the distribution of gypsum-salt rocks, according to the principle and characteristics that evaporation and concentration of heavy brine in the lake basin environment flows back to the low parts of the landform to form gypsum-salt rocks, so as to solve the technical problem that the prior art methods have poor applicability to the geological environment of mixed saline lake basins.

[0005] To achieve the above object, the present invention provides the following technical solution: a method for restoring the ancient landform of mixed saline lake basin sedimentation based on the distribution of gypsum-salt rock, comprising the following steps:

[0006] (1) Target layer selection

[0007] ① In the selected work area, carry out the division and comparison of the mixed sedimentary rock strata in the saline lake basin. On this basis, select the layer section with clear stratigraphic division and relatively complete logging data as the target layer. The sedimentary time corresponding to the bottom of the target layer is the time interface of sedimentary paleo-geomorphological restoration, and the top of the target layer is a flexibly selected isochronous interface, which is easy to identify in the characteristics of drilling or logging curves;

[0008] ② According to the top and bottom interfaces of the target layer, the formation thickness H of the target layer of all drillings is counted;

[0009] (2) Well logging identification of gypsum-salt rock

[0010] ① Use conventional and imaging logging data to identify gypsum-salt rock: gypsum rock has the characteristics of high resistivity, low natural gamma, high density, and no obvious expansion of the borehole diameter curve; salt rock has the characteristics of high resistivity, very low natural gamma, low density, and obvious expansion of the borehole diameter curve. In imaging logging, both gypsum rock and salt rock appear as bright yellow;

[0011] ② Establish core-calibrated logging identification criteria for gypsum-salt rock: compare and match the drilling core with the logging curve to clarify the quantitative basis for logging identification of gypsum and salt rock. Among them, the identification parameters and range of gypsum rock are: density (DEN)>2.8g / cm 3 , natural gamma (GR) <60API, deep directional resistivity (RD)>100Ω·m, (CAL)>20; the identification parameters and range of salt rock are density (DEN) <2.4g / cm 3 , natural gamma (GR) <60API, well diameter (CAL) >20cm;

[0012] ③ According to the gypsum-salt rock logging identification standard, the cumulative thickness h of gypsum-salt rock in all drilling target layers is calculated;

[0013] (3) Distribution map of gypsum-salt rock

[0014] ① Calculate the ratio of the thickness of the gypsum-salt rock in all drilling target layers h to the formation thickness H, that is, the gypsum-to-ground ratio m = h / H;

[0015] ② Draw the contour map of the paste-to-ground ratio plane;

[0016] (4) Restoration of sedimentary paleo-geomorphology

[0017] ① Inverting paleo-geomorphological differences using gypsum-salt rock distribution data: Inverting sedimentary geomorphological differences based on the gypsum-to-land ratio plane contour map drawn in step (3), and dividing the corresponding geomorphological units, wherein a high gypsum-to-land ratio indicates a relatively low landform, and a low gypsum-to-land ratio indicates a relatively high landform. Specifically, the area with a gypsum-to-land ratio greater than 0.25 is divided into a geomorphological depression, the area with a gypsum-to-land ratio between 0.10 and 0.25 is divided into a slope area, and the area with a gypsum-to-land ratio less than 0.10 is divided into a geomorphic uplift;

[0018] ② According to the above-mentioned division standards of sedimentary paleogeomorphic units, draw the scope and boundary lines of different geomorphic units, and mark the corresponding geomorphic categories. According to the relevant mapping specifications of the petroleum industry, improve the map elements (including map name, legend and scale), and finally obtain the sedimentary paleogeomorphic plan map.

[0019] Preferably, step (1) carries out the specific operation of the division and comparison of the mixed sedimentary rock stratigraphic units in the saline lake basin: first, the drilling and logging data are collected and sorted, and 3-5 wells that can cover the entire work area and are representative of a small area are selected as skeleton wells. Based on the identification marks of the lithology mutation surface, sedimentary cycle interface and special rock layer (such as mudstone interlayer and weathering crust breccia) with significant logging curve response, the stratigraphic sequence and interface characteristics of the single well are clarified.

[0020] Preferably, the skeleton well is then connected to wells in different blocks to form well sections in different directions, and each set of formations is laterally tracked and closed in sequence according to the stratigraphic interface characteristics of the skeleton well, thereby establishing a stratigraphic grid system covering the entire work area.

[0021] Preferably, the specific operation of step (2) establishing the core-calibrated gypsum-salt rock logging identification standard is as follows: first, a systematic coring well is selected for core observation to clarify the distribution of gypsum and salt rock. Considering that the resolution of the logging curve is 0.125 m, the top and bottom depths of thick layers (greater than 0.5 m) and pure gypsum and salt rock sections should be recorded during core observation.

[0022] Preferably, the logging data of this depth section is carefully analyzed and compared with the logging data of other lithologies (including sandstone, limestone and dolomite) in the area, and several curve types (such as natural gamma, density and resistivity) that respond significantly to gypsum salt and salt rock are screened out respectively, and then the value ranges of these logging data are integrated to form the logging identification standard for gypsum salt rock.

[0023] Compared with the prior art, the present invention has the following beneficial effects:

[0024] 1. Based on the principle and characteristics of gypsum-salt rock formed by evaporation and concentration of heavy brine in the lake basin environment and its reflux to the low-lying parts of the landform, the present invention creatively introduces the distribution data of gypsum-salt rock to invert the differences in sedimentary paleo-landforms, thus solving the problem of poor applicability of the existing technical methods to the geological environment of mixed saline lake basins.

[0025] 2. The present invention uses the parameter of the ratio of gypsum-salt rock to stratum thickness (i.e., gypsum-to-ground ratio) to divide sedimentary paleogeomorphological units. Compared with directly using the thickness of gypsum-salt rock or stratum thickness to indicate geomorphological differences, it can avoid the problem of duplication or missing of gypsum-salt rock or stratum due to faults and folds in structurally complex areas, and the resulting large errors in paleogeomorphological restoration results. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 A flow chart of the method for restoring the ancient landform of mixed saline lake basin sediments provided by the present invention;

[0027] Figure 2 This is a schematic diagram of the principle of the present invention that the heavy brine evaporates and concentrates in the lake basin environment and flows back to the low part of the landform to form gypsum salt rock;

[0028] Figure 3 This is a core characteristic diagram of gypsum salt rock in Example 1 of the present invention;

[0029] Figure 4 This is a gypsum-salt rock logging identification characteristic diagram of Example 1 of the present invention;

[0030] Figure 5 It is a paste-to-ground ratio contour map of Example 1 of the present invention;

[0031] Figure 6 This is a sedimentary paleo-geomorphological map of Example 1 of the present invention. DETAILED DESCRIPTION

[0032] The technical solutions in the embodiments of the present invention are described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0033] See also Figure 1-Figure 6 The research objective of this embodiment is to restore the sedimentary paleo-geomorphology of the saline lacustrine mixed sedimentary rocks of the fourth oil layer group of the Lower Ganchaigou Formation of the Paleogene in the Yingxi area of ​​the Qaidam Basin. The research is carried out according to the following steps:

[0034] S1: Target layer selection

[0035] According to the stratigraphic division and comparative data of the Qaidam Basin, the target layer was selected as the target layer. The target layer has various lithologies, including mud carbonate, silty carbonate, calcareous mudstone, calcareous siltstone, gypsum and salt rock. The bottom interface of the target layer is the interface of the Ⅳ-Ⅴ oil layer group, and the top interface is the interface of the Ⅲ-Ⅳ oil layer group. On this basis, the target layer thickness H of all wells drilled in the research area was statistically analyzed.

[0036] S2: Logging identification of gypsum-salt rock

[0037] First, the characteristics of gypsum salt rock were identified using drilling core and microscopic thin section data. Gypsum rock is mainly produced in the form of gray-white gypsum mass aggregates, which are relatively dense, with a small amount of siltstone or mudstone impurities. Single gypsum minerals can show petal-shaped, radial and strip-shaped morphological characteristics; salt rock is transparent, pure, and its main component is rock salt. Transparent crystalline coarse salt grains can be seen, which are soluble in water and contain a small amount of mudstone impurities in some parts.

[0038] The gypsum salt rock identified on the core is compared and matched with the logging curve to establish the core-calibrated gypsum salt rock logging identification standard. Among them, due to the solubility of salt rock, it shows obvious expansion characteristics on the wellbore logging, and the density is relatively small. At the same time, the radioactivity content of salt rock is low, the natural gamma is extremely low, and the salt rock also has high resistivity characteristics. Gypsum rock is similar to salt rock, with high resistivity and low natural gamma characteristics, but the density of gypsum rock is larger, and the expansion characteristics of the wellbore curve are not obvious. In the imaging logging, both gypsum rock and salt rock show bright yellow characteristics. Specifically, the density (DEN)>2.8g / cm 3 The layers with natural gamma (GR) <60API, deep directional resistivity (RD) >100Ω·m, and (CAL) >20cm are identified as gypsum; the layers with density (DEN) <2.4g / cm 3 The layers with natural gamma (GR) <60API and well diameter (CAL) >20cm are identified as salt rocks.

[0039] According to the above-mentioned gypsum-salt rock logging identification standard, the gypsum-salt rock development intervals in the uncored wells were identified, and the cumulative thickness h of the gypsum-salt rock in all the wells drilled in the study area was statistically analyzed.

[0040] S3: Mapping of gypsum-salt rock distribution

[0041] According to the above statistical data, the ratio of gypsum-salt rock to the total thickness of mixed rock formations in all drilling target intervals is calculated, that is, the ratio of gypsum-salt rock thickness h to formation thickness H, which can be abbreviated as: gypsum-to-ground ratio m = h / H. On this basis, the interpolation method is used to draw the plane contour map of the gypsum-to-ground ratio in the study area.

[0042] S4: Sedimentary paleo-geomorphological restoration

[0043] According to the plane contour map of the paste-land ratio drawn in step S3, the differences in sedimentary paleo-geomorphology are inverted, and the geomorphological units are divided. Among them, a high value of the paste-land ratio indicates that the landform is relatively low, and a low value of the paste-land ratio indicates that the landform is relatively high. Specifically, the area where the paste-land ratio is greater than 0.25 is divided into a geomorphic depression, the area where the paste-land ratio is between 0.10 and 0.25 is divided into a slope area, and the area where the paste-land ratio is less than 0.10 is divided into a geomorphic uplift. Finally, the industrial mapping elements are improved, and a plane map of sedimentary paleo-geomorphology is generated, which is applied to and guides the exploration of mixed rock reservoirs in saline lake basins.

[0044] It should be noted that, in this article, relational terms such as first and second, etc. are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, technique, article or equipment including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, technique, article or equipment.

[0045] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for restoring paleo-geomorphology of mixed saline lake basin sediments based on the distribution of gypsum-salt rocks, characterized in that: The steps include: (1) Target layer selection ① In the selected work area, carry out the division and comparison of the mixed sedimentary rock strata in the saline lake basin. On this basis, select the layer section with clear stratigraphic division and relatively complete logging data as the target layer. The sedimentary time corresponding to the bottom of the target layer is the time interface of sedimentary paleo-geomorphological restoration, and the top of the target layer is a flexibly selected isochronous interface, which is easy to identify in the characteristics of drilling or logging curves; ② According to the top and bottom interfaces of the target layer, the formation thickness H of the target layer of all drillings is counted; (2) Well logging identification of gypsum-salt rock ① Use conventional and imaging logging data to identify gypsum-salt rock: gypsum rock has the characteristics of high resistivity, low natural gamma, high density, and no obvious expansion of the borehole diameter curve; salt rock has the characteristics of high resistivity, very low natural gamma, low density, and obvious expansion of the borehole diameter curve. In imaging logging, both gypsum rock and salt rock appear as bright yellow; ② Establish core-calibrated logging identification criteria for gypsum-salt rock: compare and match the drilling core with the logging curve to clarify the quantitative basis for logging identification of gypsum and salt rock. Among them, the identification parameters and range of gypsum rock are: density (DEN)>2.8g / cm 3 , natural gamma (GR) <60API, deep directional resistivity (RD)>100Ω·m, (CAL)>20; the identification parameters and range of salt rock are density (DEN) <2.4g / cm 3 , natural gamma (GR) <60API, well diameter (CAL) >20cm; ③ According to the gypsum-salt rock logging identification standard, the cumulative thickness h of gypsum-salt rock in all drilling target layers is calculated; (3) Distribution map of gypsum-salt rock ① Calculate the ratio of the thickness of the gypsum-salt rock in all drilling target layers h to the formation thickness H, that is, the gypsum-to-ground ratio m = h / H; ② Draw the contour map of the paste-to-ground ratio plane; (4) Restoration of sedimentary paleo-geomorphology ① Invert paleo-geomorphological differences using gypsum-salt rock distribution data: Invert sedimentary geomorphological differences based on the gypsum-to-land ratio plane contour map drawn in step (3), and divide the corresponding geomorphological units, where a high gypsum-to-land ratio indicates a relatively low landform, and a low gypsum-to-land ratio indicates a relatively high landform. Specifically, the area with a gypsum-to-land ratio greater than 0.25 is divided into a geomorphological depression, the area with a gypsum-to-land ratio between 0.10 and 0.25 is divided into a slope area, and the area with a gypsum-to-land ratio less than 0.10 is divided into a geomorphological uplift; ② According to the above-mentioned division standards of sedimentary paleogeomorphic units, draw the scope and boundary lines of different geomorphic units, and mark the corresponding geomorphic categories. According to the relevant mapping specifications of the petroleum industry, improve the map elements (including map name, legend and scale), and finally obtain the sedimentary paleogeomorphic plan map.

2. The method for restoring paleo-geomorphology of mixed saline lake basin sediments based on the distribution of gypsum-salt rock according to claim 1, characterized in that: Step (1) Carry out the specific operations of the division and comparison of the mixed sedimentary rock stratigraphy in the saline lake basin: First, collect and sort out the drilling and logging data, select 3-5 wells that can cover the entire work area and are representative of a small area as skeleton wells, and clarify the stratigraphic sequence and interface characteristics of the single well based on the identification marks of the lithology mutation surface, sedimentary cycle interface and special rock layer (such as mudstone interlayer and weathering crust breccia) logging curve response.

3. The method for restoring paleo-geomorphology of mixed saline lake basin sediments based on the distribution of gypsum-salt rock according to claim 2, characterized in that: The skeleton well is connected with the wells in different blocks to form well sections in different directions. According to the stratigraphic interface characteristics of the skeleton well, each set of strata is traced laterally and closed in sequence to establish a stratigraphic framework system covering the entire work area.

4. The method for restoring paleo-geomorphology of mixed saline lake basin sediments based on the distribution of gypsum-salt rock according to claim 1, characterized in that: Step (2) Specific operations for establishing the core-calibrated gypsum-salt rock logging identification standard: First, select the systematic coring wells for core observation to clarify the distribution of gypsum and salt rocks. Considering that the resolution of the logging curve is 0.125m, the core observation should focus on recording the top and bottom depths of thick layers (greater than 0.5m) and pure gypsum and salt rock sections.

5. The method for restoring paleo-geomorphology of mixed saline lake basin sediments based on the distribution of gypsum-salt rock according to claim 4, characterized in that: Subsequently, the logging data of this depth section were analyzed in detail and compared with the logging data of other lithologies in the area (including sandstone, limestone and dolomite). Several curve types (such as natural gamma, density and resistivity) that responded significantly to gypsum-salt and salt rock were screened out, and then the value ranges of these logging data were integrated to form the logging identification standard for gypsum-salt rock.

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