Shaanxi Bin County Anatomical Area is located in Bin County, Shaanxi Province, with geographical coordinates: 108°4'55″～108°18'44″ east longitude, 34°58'24″～35°8'8″ north latitude between. It includes two exploration areas: Zhanghong and Shuibei Village. There is no railway passing through the area. Only the Xian (Yang) Copper (Sichuan) Railway passes through Yao County, about 45km southeast of Yaoqu on the eastern edge of the area. The West (An) Lanzhou (Prefecture) Highway passes through Bin County, and the Zhanghong Exploration Area reaches Bin County is also accessible by highway (Bin County to Xunyi), but the terrain of the area has large vertical and horizontal valleys with large height differences, deep valleys, steep slopes, and cliffs, making transportation inconvenient.
This area is located at the southern edge of the Loess Plateau in northern Shaanxi, with an altitude of 1000-1800m. It is low in the west and high in the east, the terrain is sharply cut, and the loess layer is thick in the west and thin in the east. The east is mountainous and the west is loess plateau (Xunyi District, Bin County). The mountainous area is a zone between the Loess Plateau of northern Shaanxi and the Guanzhong Plain. The altitude is about 1,600m. The loess coverage is not thick. It is a mountainous terrain left by denudation. The relative height difference is 100-400m. The mountains are mostly northeast-southwest, and the valleys are North-south direction. The terrain is high in the north and low in the south, and the gravel layers are mostly steep cliffs, making it inconvenient to pass. The land is barren, agricultural production is not abundant, and residential areas are sparse. The Loess Plateau District (Xunyi District, Bin County) is the southern edge of the Loess Plateau in northern Shaanxi, with an altitude of about 850 to 1,300m. The erosion is severe and deep trenches and canyons are widespread. The height difference between the plateau top and valley bottom is 200~300m. There are many flat terraces on both sides of the river, with sufficient soil and water, which is conducive to agricultural production, so there are many residents.
The Jinghe River is the largest river in this region. It originates from Gansu and flows through the southeast suburbs of Bin County to Jingyang and flows into the Weihe River. Near Bin County, the river is about 0.5km wide, with obvious terraces on both sides. In addition, there are Jinghui River and Liulin River, but the rivers are not deep. There are many water flows in various gullies in the area, but the amount of water is small or intermittent.
1. Geological background
(1) Regional structure
1. Geotectonic location
The geotectonic location of this area is in the Ordos Basin On the southern edge, its regional structural unit belongs to the Binxun depression zone on the Weibei uplift belt. In the late Yanshanian movement, it was slightly folded, and the folds were mostly broad and gentle backclines, so the structure is relatively simple.
2. Regional structural characteristics
(1) Structural characteristics.
From a regional perspective, the structure of the Binxun Sag has the following characteristics:
① Folds are relatively developed and faults are rare. The pleats are arranged in rows and have good belting properties. The anticline and syncline structures form belts alternately from north to south, and are intermittently connected from east to west, with the characteristics of flying geese. In strike direction, it deflects from nearly east-west to north-east to north-east.
②The fold shape is characterized by wide and gentle-gentle wavy anticlines and trough-gentle synclines. The amplitude and intensity of folds gradually weaken from south to north. From bottom to top, from old to old From strata to new strata, the fold shape changes from tight, wide and gentle to wavy. ( coal control) characteristics. Coal-bearing deposits are good in synclines and poor in anticlines, showing the characteristics of striped distribution. The dorsal and syncline structures in the Triassic, Jurassic, and Cretaceous are overlaid on top and bottom, and their positions are basically consistent, reflecting the dual characteristics of structural inheritance and stability.
(2) Fold structure.
The main regional fold structures include Luodian anticline (Z1), Shijiahe syncline (Z2), Tingkou anticline (Z3), Xunyi anticline (Z4), Dafosi syncline ( Z5), Binxian anticline (Z6), Zhengjia syncline (Z7), etc. The map area is about 8 to 20km long. The axial direction is from northeast (65° to 70°) to nearly east-west (about 275°). The strata that constitute the fold structure are mainly the Mesozoic Jurassic, Cretaceous, and Triassic. The fold shape is generally gentle and the two wings are asymmetrical. Generally, the northern wing of the anticline is steep (dip angle 5°~40°) and the southern wing is gentle (dip angle 2°~8°). The southern limb of the syncline has a larger inclination angle (15° to 20°), while the northern limb has a slightly smaller inclination angle (4° to 6°).
①The Luodian anticline (Z1) is located in Luodian, Jinghe River. Its axis is NE (65°~70°), and it slopes westward to the west of the Jinghe River. The anticline fluctuates slightly, and the Jurassic system in the axis is often thinned or missing. The dip angle of the northern limb is 5° to 8°, and the dip angle of the southern limb is 2° to 3°.
②The Shijiahe syncline (Z2) is located between the Luodian anticline and the Tingkou anticline, with the axis oriented NNE (60°~65°). The center of the syncline is gentle and shows a trough. The core is the upper part of the Lower Cretaceous Luohe Formation, and the two wings are the lower part of the Luohe Formation. The dip angle is 3° to 7°, and it is a gentle trough-like syncline.
③Tingkou anticline (Z3) spreads in the north-northeast (70°~78°) direction along Lujia-Tingkou Town-Xiaolingtai-Liujiacun area, with a comb-shaped anticline in the east. The core is composed of the Jurassic Formation, and the two wings are the Yijun Formation of the Lower Cretaceous System. The north wing has an inclination angle of 5° to 10°, and the south wing is slightly gentler at 2° to 4°, showing a slightly asymmetrical shape.
④The Xunyi anticline (Z4) is located on the line between Jierzui and Baizigou coal mine in Bin County in the south of Xunyi County. Its axis is NE (65°~70°) and dips to the west. In the Dafosi syncline, the exposed strata in the core are Triassic, and the two wings are Jurassic and Cretaceous. The north limb has an inclination angle of 10° to 15°, and the southern limb has an inclination angle of 3° to 5°. The overall shape is an asymmetrical comb-shaped-wide and gentle anticline with a steep north and a gentle dip to the south.
⑤The Dafosi syncline (Z5) is located between the Tingkou anticline and the Binxian anticline, extending along the Dafosi-Shuiliandong-Xianbaigou line of Baizigou, with the axis running east-west . The core is composed of Jurassic and Cretaceous strata, and the two wings are composed of Triassic strata. Its southern wing has a steeper inclination angle (15°~20°), while its northern wing has a gentler inclination angle (4°~6°), making it an asymmetric wide and gentle syncline.
⑥Binxian anticline (Z6) is located on the line between Shangwanwancun-south of Binxian and Baizigou mouth, with an axis close to east-west (275°). The core is Triassic strata, and the two wings are Jurassic and Cretaceous. The stratigraphic dip angle in the Triassic east of Bin County is relatively large, ranging from 12° to 40° on the northern flank and 2° to 8° on the southern flank, forming an asymmetric comb-shaped anticline. In the Jurassic and Cretaceous systems to the west of Binxian County, there is a comb-shaped-broad and gentle anticline, with an inclination angle of 4° to 9° in the north limb and an inclination angle of 2° to 6° in the south limb, leaning westward.
⑦The Zhengjia syncline (Z7) is located in the south area of ??Zhengjia, with an axial direction of about 70° to the northeast. The trough is Jurassic and Cretaceous, and the wings are Triassic. It is a wide and gentle syncline. .
(3)Fault structure.
The fault structure is mainly the Baizigou reverse fault, which is located at the boundary between the Triassic strata and the Jurassic strata near the Baizigou Highway Bridge in Bin County. The fault faces southward, and the hanging wall is an extension of the Upper Triassic. Formation (T3y) feldspathic quartz sandstone and shale, the footwall is Yan'an Formation (J2y) quartz sandstone and black mudstone, and the fault plane occurrence is 190°∠60°.
3. Regional stratigraphy
According to the stratigraphic division of Shaanxi Province, the stratigraphy of this area belongs to the southern part of the Shaanxi-Gansu-Ningxia Basin Division in North China. The exposed strata from old to new include the Mesozoic Triassic, Jurassic, Cretaceous, and Cenozoic. They are distributed in a band from Xingshuping in Tongchuan County to Baijiahe in Bin County. They are all continental sedimentary rocks. . The total thickness of strata in the area is 568-2259m, and sedimentary rocks are extremely developed. Among them, only about 10% are bedrock outcrops, and the rest are loose accumulation layers.
(1) Triassic (T).
The oldest formation seen in this area is the Upper Mesozoic Triassic Yanchang Formation. The traditional Yanchang Group was originally named in Yanchang County, northern Shaanxi, and is divided into five sections. Among them, the first, second and third layers are mainly developed in this area, while the fourth and fifth layers are basically missing. The surface is exposed on the north and south banks of the Jinghe River east of Binxian City, as well as at the mouth of Shuibei Gou and Baizigou Gou. It is a set of green-gray and black sand and mudstone deposits that produce Yanchang flora fossils. It is an important source of oil and gas reservoirs in the area and The main layers of oil shale distribution have no bottom boundary and a total thickness of gt; 660m.
①The first and second members of the Upper Triassic Yanchang Formation (T3y1 2). The Third Office of the Institute of Geology, Chinese Academy of Geosciences (1965) regarded it as an independent unit and named it the Tongchuan Formation. This group in the Yanchang Group area can be divided into upper and lower sections according to lithological combination. Only the upper section is visible on the surface, with a total thickness of gt; 310m. The lithology of this group is light green gray and yellow gray fine-grained feldspathic sandstone.
Mainly calcareous sandstone, interspersed with silty mudstone, siltstone, and shale. The plant fossils produced in the shale are mostly Pseudomonas daniliensis and Crab-shaped Aralia spp., while the oil shale produces fossils of squid and trace fossils.
②The third member of the Upper Triassic Yanchang Formation (T3y3). The lithology is black gray shale, intercalated with medium-thick layered fine-grained feldspathic sandstone and silty shale, often rich in black oil shale. The shale produces plant fossils such as Brachyphyllum shaanxiensis and Phyllostachys cayeensis, etc. The oil shale produces fossils of fishes and trace fossils. It is a continuous sedimentation with the underlying strata, but its grain size is finer than its sedimentation, and its thickness varies greatly (0~350m).
(2) Jurassic (J).
It is exposed in Baizigou, Shuibeigou, southeast of Hujiawan and in the valleys south of Binxian City. Outcrops are scattered in other places and the profile is incomplete. This series is a set of continental coal-bearing formations that produce Yan'an flora fossils. It is an important coal- and oil-bearing formation in the area. It is in parallel or angular unconformity contact with different layers of the underlying Triassic strata, with a total thickness of 198.4~904m.
①Lower Jurassic Fuxian Formation (J1f). There are no outcrops on the surface in the area, but they are mainly found in boreholes in the coal fields in Bin County and Xunyi. The lithology is purple-red, dark gray mudstone, sandy mudstone, sandstone intercalated with bauxite mudstone, carbonaceous mudstone, and thin layers of sandy conglomerate. The bottom is conglomerate, and the upper part is often mixed with colored mudstone. Spores produced in mudstone: Trichospora spp. Pollen: Picea, Hemlock. It is in overlapping unconformity contact with the underlying Yanchang Group, with a thickness of 0~102m.
②Middle Jurassic Yan’an Formation (J2y). The area is a set of coal-bearing rock series. The lower part of the lithology is light gray thick-bedded feldspathic sandstone. The middle and upper parts are gray-black mudstone, bauxite mudstone, argillaceous siltstone, and fine sandstone interbedded with carbonaceous mudstone and carbonaceous mudstone. Coal seam, rich in plant fossils. The surface thickness is 121.9~247m, and it is in parallel unconformity contact with the Fuxian Formation below. When the Fuxian Formation is missing, it overlies different layers of the Yanchang Formation.
③Middle Jurassic Zhiluo Formation (J2z). The lithology of this group in the area is light gray, gray-yellow thick layered gravel-bearing quartz coarse sandstone and fine conglomerate, with a small amount of purple-red or variegated mudstone and sandy mudstone. Argillaceous siltstone, plant fossils include: Cone fern, Brachyphyllum spp., and spores include Hylophylla genus, etc. The thickness of the formation varies greatly, from 48.4 to 333m. It is in parallel unconformity contact with the underlying Yan'an Formation.
④Middle Jurassic Anding Formation (J2a). The lithology in the area is purple-red, brown-red sandy mudstone, siltstone, and fine sandstone interspersed with brown-red medium-thick layered sandstone and conglomerate. Fine conglomerate and conglomerate are common at the bottom. Containing spores: Trichophylla spp., Goldendoodle spp. Pollen: Picea spruce, Picea spruce, etc. The surface thickness varies greatly, from 28.1 to 222m, and is in integrated contact with the underlying Zhiluo Formation.
(3) Cretaceous (K).
It is exposed on both sides of the Jinghe River north of the urban area of ??Bin County, as well as in areas such as Hongya River and Baizigou. It is a set of continental red bed deposits composed of shale and mudstone, which are in parallel or angular unconformity contact with the underlying Jurassic strata. The total thickness is 251~402m.
①Yijun Formation (K1y). The lithology of this group in the area is purple-gray thick layered (massive) complex conglomerate intercalated with gravelly sandstone lenses and thin layers or strips of mudstone. It is in unconformable contact with the underlying Jurassic strata. The thickness generally ranges from 30 to 60m.
②Luohe Formation (K1l). The lithology of this group in the area is purple-red and orange-red thick layered medium-coarse-grained feldspathic quartz sandstone intercalated with thin layers or strips of conglomerate and sandy mudstone. Large-scale oblique bedding is developed in the sandstone. The total number of conglomerate layers decreases and becomes thinner toward the north, while it thickens and increases toward the south, and the gravel composition is complex. The total thickness is 222~342m. Generally, this formation and the underlying Yijun Formation are deposited continuously.
(4) Recent Pleiocene (N2).
Mainly distributed in the valleys of the Jinghe River tributaries, the unconformity covers the Mesozoic planation and forms the base of the Loess Plateau. The name of the rock formation is the Baode Formation (N2b), which produces fossils of the three-toed horse fauna. The distribution in the area is stable, but the distribution in local areas is irregular or there is no sedimentation. The lithology is brown-red clay rock, calcareous nodule clay rock, intercalated with siltstone and calcareous nodules. There is often a gravel layer at the bottom, which is a fluvial and lake facies deposit. The thickness varies greatly from 14 to 73m.
(5) Recently updated system (Q).
Widely distributed in the area, fully developed, with complex sedimentary types, including fluvial and lacustrine deposits, fluvial alluvial deposits, slope deposits, aeolian deposits, etc. The lithology is mainly aeolian loess, followed by sand and gravel. The stone layers are accumulated with a total thickness of 103.5-220m, and are in unconformable contact with the pre-Quaternary strata.
(2) Igneous rocks
The magmatic activity in the area is extremely weak, and no igneous rocks have been developed.
II. Oil shale characteristics
(1) Oil shale occurrence characteristics
1. Oil shale occurrence layers
Most of the mineral-bearing areas in Bin County are covered by broad and thick loess. Only in deep gullies can the Mesozoic realm be exposed. The main exposures of the Mesozoic include the Lower Cretaceous Yijun Formation (K1y), the Middle Jurassic Anding Formation (J2a), the Middle Jurassic Yan'an Formation (J2y), and the Upper Triassic Yanchang Formation (T3y). The stratigraphy in this area is nearly horizontal with a small dip angle. K1y has a pseudo-conformity contact relationship with the underlying J2a, and J2y and T3y also have a pseudo-conformity contact relationship. The oil shale occurs in the third layer of the Upper Triassic Yanchang Formation. The characteristics of the Upper Triassic Yanchang Formation (T3y) are as follows:
(1) The first and second layers of the Upper Triassic Yanchang Formation layer (T3y1 2).
The upper part of this layer is composed of fine sandstone, sandy shale and interbedded shale, but it is mainly sandstone. The lithological changes have no obvious boundaries and are mostly gradient relationships. The sandstone is dark gray, grey-green, and bluish-gray, while weathered iron staining is yellow-brown or yellow-green in thin to thick layers, with primary small structures such as fine oblique layers and ripple marks. However, the main mineral composition is quartz, and the clay is cemented with calcium, so it is relatively hard. The sandy shale and shale are mostly dark gray or gray-black, with obvious bedding. There are muscovite fragments on the layers and contain plant fossils.
(2) The third layer of the Upper Triassic Yanchang Formation (T3y3).
The lithology is mainly dark gray and yellow-gray sandy shale and shale, interspersed with gray fine sandstone and black shale and multiple layers of gray-black and black oil shale. The oil shale is intercalated with thin layers of black gray and black sandstone. The oil shale floor is gray and yellow-green sandstone, and the roof is shale. Oil shale is distributed in layers and is generally stable in the region. It extends for more than 80 kilometers along the strike. It occurs in a monoclinic structure with an inclination angle of 5° to 10°, and the burial depth is generally less than 500m.
2. Oil shale spatial characteristics
There are three oil shale layers A1, A2 and A3 in the area. The oil shale layers from the A2 layer onwards are not suitable for industrial use. Requirements, only the A1 layer group is described in detail here. The lower part of the oil shale of the A1 layer is intercalated with one to two layers of black gray and black thin oily muddy sandstone. The mineral layer is divided into three layers: A11, A21, and A31 (Figure 7-2). The thickness varies greatly, among which A11 and A31 The thickness of the layer is relatively large, and the thickness of A21 is relatively small, so it can only be recovered locally (Table 7-1).
Figure 7-1 A-A' exploration line section of the oil shale ore-bearing area in Binxian, Shaanxi Province
Figure 7-2 Comparison of mineral strata in the oil shale ore-bearing area of ??Binxian, Shaanxi Province
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Table 7-1 Thickness of each layer of oil shale in the A1 layer of Zhanghong exploration area in Binxian oil shale mineral-bearing area, Shaanxi Province
(2) Oil shale quality characteristics
1. Ore characteristics
Oil shale is mostly black and paper-shaped, with two groups of joints developed, often forming a diamond shape. Due to long-term weathering, those exposed on hillsides and ridges are mostly gray-black flakes, with rusty limonite and light yellow natural sulfur films attached to the surface, turning into brownish yellow. Those exposed in ditches are mostly washed away by running water. In the form of thin black layers. Fresh ore is in the shape of jet black lumps, soft but not brittle, ignites immediately when lit, has the smell of asphalt and has a grease luster. There is faint bedding, which is dense and hard. The main component is hard clay material, containing a small amount of quartz and feldspar fine fragments. Occasionally, there are fleshy red hydromica clay lentils and asphalt points. It is rich in ancient cod fossils.
2. Quality characteristics
(1) Analysis of chemical properties of oil shale.
①Oil content and ash content. The oil content and ash content of oil shale generally have a significant negative correlation (Figure 7-3). The higher the oil content, the lower the ash content; the lower the oil content, the higher the ash content.
Using oil content as the dependent variable (y) and ash as the independent variable (x), perform regression analysis and get the following regression equation:
y=33.8197-0.3504x
Regression The coefficient test t=-11.588, the associated probability plt; 0.001, the regression equation is meaningful.
Figure 7-3 Correlation diagram between oil content and ash content of oil shale in the oil shale mineral-bearing area in Binxian, Shaanxi Province
②Oil content, volatile matter and moisture. The correlation between oil content, volatile matter and moisture is not obvious, and there is basically no linear relationship.
③Oil content and organic carbon. The oil content of oil shale generally has an obvious positive correlation with organic carbon (Figure 7-4). The higher the organic carbon content, the higher the oil content; the lower the organic carbon content, the lower the oil content. Using oil content as the dependent variable (y) and organic carbon as the independent variable (x), perform regression analysis and obtain the following regression equation:
y=1.237 0.369x
Regression The coefficient test t=8.680, the associated probability plt; 0.001, the regression equation is meaningful.
④Oil content and S, H, N element content. The correlation between oil content and the content of S, H, N and other elements is not obvious, and there is basically no linear relationship.
Figure 7-4 Correlation diagram between oil content and organic carbon in the oil shale mineral-bearing area in Binxian, Shaanxi Province
(2) Oil shale quality characteristics.
The oil content, ash content and other quality characteristics of each layer of the A1 layer oil shale are detailed in Table 7-2. From the table, it can be seen that the oil content of each layer of the A1 layer oil shale is not very high, but Relatively stable, all are greater than 5, with the highest around 7; the higher ash content belongs to high-ash oil shale, with the highest being 84.16, generally greater than 70; the organic carbon content is generally greater than 7.5, and the higher the oil content, the higher the organic carbon content The higher; the volatile content is also higher, up to 89.70, the moisture is not higher than 2.36, and the sulfur content is lower than 4. In general, the quality of oil shale is average. In contrast, the quality of oil shale in the A11 layer is better than that of the A21 and A31 layers. It is the most important recoverable oil shale layer in this area.
Table 7-2 Quality characteristics of each layer of oil shale in the A1 layer of the Zhanghong exploration area in the oil shale mineral-bearing area in Binxian, Shaanxi Province
3. Oil shale distribution rules
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(1) Formation environment
1. Structural environment
(1) Structural background. Due to the long-term uplift of the Shanxi Platform anticline in the east, the northern Shaanxi platform depression formed a large monocline that generally dips gently to the west. On the basis of the large monocline, some large nose-like uplifts and depressions are formed. Binxun Depression is the southernmost one. Its basement is pre-Carboniferous. The Indosinian Movement caused the Triassic in this area to uplift, fold, and suffer erosion. Later, these preformed back and syncline structures developed inheritedly during the Yanshan Movement.
(2) Structural characteristics of mineral deposits.
During the late Yanshan movement, it was slightly folded, and the folds were mostly broad and gentle anticlinal lines, so the structure of the mining area is relatively simple.
The mineral-bearing area is located on the north wing of the Binxian-Baicaopo anticline and is a gentle monoclinic layer. The anticline starts from Mozigou in Binxian County in the west and ends at Baicaopo in the east, with a length of 55km. The axial direction from Mozigou to Zhanfantou is 295°. From Zhanfantou to the east, it turns 45° to 60°. , and then east to Baicao Slope at 85°, nearly east-west direction, it is an "S" shaped anticline structure, and the core of the anticline is the first layer of the Yanchang Formation of the Upper Triassic System. Due to the axial direction of the anticline, Baicaopo extends to the southwest and turns northwest when it reaches Zaofantou Village. Therefore, the stratigraphic occurrence of the mining area also turns. To the east of Shuibei Gou (near Baizigou), the rock stratum trend is 60° to the northeast. ° is around 310°, while to the west it is around 310° NW, with inclination angles of around 10°.
The overall deflection of the fold axis in the mining area to the northeast and the north-northwest short-axis folds that appear in the eastern part of the region reflect that the area experienced a nearly east-west compressive stress in the late Yanshanian period , may be the result of further uplift and westward compression of the Shanxi platform anticline.
2. Lithofacies paleogeographic analysis
(1) Lithofacies characteristics.
①The first and second layers of the Upper Triassic Yanchang Formation (T3y1 2).
It is composed of light green gray, yellow gray feldspathic sandstone, calcareous sandstone, dark gray and gray green shale, with the first two accounting for 70% of the total rock volume. The feldspathic sandstone is mainly medium-fine grained, and its composition consists of clasts: quartz 40-50%, potassium feldspar 5-10%, plagioclase 20-30%, siliceous rock 3-5% and interstitial materials: sericite, It is composed of iron, calcite, and chlorite. The accessory minerals include zircon, magnetite, apatite, etc. Generally, cline bedding is not developed. Plant fossils mostly appear in mudstone to extend the diversity of flora. The fern Danaeopsis fecunda is represented, and freshwater fish can be seen in some areas, so it is a river facies deposit. The front edge of the river-dominated delta facies presents a large-scale, upward-coarsening sequence starting from fine-grained far-shore deposits and turning upward to near-shore deposits dominated by sandstone. Generally, the lower part of the sequence is thick-layered and irregular. Uniform interbedded mudstone and sandstone; the middle part of the sequence is repeated alternating layers of mudstone, siltstone and sandstone, with small corrugated sand laminae visible; the top is dominated by sandstone and is in the form of a lens, and the sedimentary structure reflects a unidirectional flow channel. Characteristics of sand bodies. The sedimentary characteristics of T3y1 2 belong to the river-controlled delta facies, still dominated by sandstone, but with finer grain size. From a lithological point of view, the lower part is often a set of muddy rock bottom accumulation layers, which turns into a thick and changeable layer upwards. In sandstone bodies, there are often erosion marks at the contact between sandstone and mudstone.
②The third layer of the Upper Triassic Yanchang Formation (T3y3). It is composed of black gray shale, silty shale, black oil shale, and feldspathic fine sandstone. Argillaceous rocks account for more than 90% of the total rock volume, and plant fossils are rare. Only flora represented by Cladophlebis shaanxiensis and Berhoullia zeilleripah are found. The general characteristics are fine sedimentary grain size, deep black color, rich It contains pyrite and organic matter, indicating that the water body is deep and quiet, has strong reducing effect, and has the characteristics of closed, semi-closed and semi-deep lake sedimentation. In some areas of T3y3, dark purple-red mudstone appears in some areas, showing an oxidized environment and characteristics of shallow lake sedimentation, so the overall structure is shallow lake to semi-deep lake sedimentation.
(2) Paleogeographic analysis.
① During the first and second layers of the Upper Triassic Yanchang Formation (T3y1 2), the area ended its long-term land-making movement and began to sink, receiving the deposition of sandstone and sandy mudstone, forming Fluvial-delta facies sedimentation. And as the Qinling fold belt continues to rise in this area, the depressions continue to deepen and widen, forming relatively stable shallow lake sediments. The climate also gradually changes to a humid and mild climate, allowing plankton to breed.
② During the third layer (T3y3) of the Upper Triassic Yanchang Formation, the lake basin further deepened, forming a semi-deep lake where sediments could grow. In the early stage, plankton reproduced most, and the biological remains accumulated in the lake basin decomposed over a long period of time and turned into saprolite rich in organic matter, forming the original material of oil shale. In addition, the lake basin is deep and the water flow is relatively stable, so the environment mostly changes from an oxidizing environment to a reducing environment, so oil shale is generated in the area. The oil shale deposition environment is good, forming a high-quality ore body. However, there is still oscillatory movement during the deposition process, which disturbs the tranquility of the lake water, so sandstone appears in the ore layer.
In summary, in the Late Triassic, the mid-term fluvial-delta facies transitioned to late-stage shallow lake to semi-deep lake facies sedimentation, demonstrating the stable sedimentary characteristics of Mesozoic inland basins. Although there are many flora species in Yanchang, the peat swamp phase has not been formed because the flora is not lush and the swamp is not strong. It is true that the remains of plants and freshwater organisms are buried in deep lake water bodies, and the organic matter is in a reducing environment, which is beneficial to the generation of oil and gas reservoirs and oil shale.
(2) Distribution characteristics of oil shale
1. Mineralization era and sedimentary sequence
The mineralization age of the oil shale evaluation area in Bin County is three In the third layer of the Yanchang Formation of the upper stack, the sedimentary sequence from bottom to top is the upper shale section, the middle oil shale section, and the lower sand shale section. From bottom to top, the grain size becomes finer and the sand/mud ratio decreases. Moreover, the sandstone contains quartz but no feldspar, so it is known that it is a continental freshwater lake deposit. Among them, there are three layers of oil shale in the oil shale section. The first layer of oil shale and the third layer of oil shale are well developed and distributed throughout the area. The second layer of oil shale is only recoverable in local areas. Interbedded with sandstone.
2. Oil shale distribution rules
The oil shale section in this area is 10.7m thick and contains three layers of recoverable oil shale. The A11 layer oil shale has an average thickness of 3.04m, a maximum thickness of 4.33m, a minimum thickness of 1.70m, and an average oil content of 6.96. It is the main recoverable oil shale layer in this area; the A21 layer oil shale has an average thickness of 0.88m, and an average oil content of 5.87. It is only recoverable in some areas; the A31 layer oil shale has an average thickness of 2.96m, a maximum thickness of 4.25m, a minimum thickness of 1.37m, and an average oil content of 5.66. It is also the main recoverable oil shale layer in this area. However, the main recoverable layers are the A11 layer and the A31 layer. We will only briefly discuss the distribution rules of oil shale in this area for these two layers.
(1) The depositional thickness of the A11 oil shale gradually decreases from south to north, and the oil content gradually decreases from south to north. The rich ore center and the high oil content area basically overlap, both in the oil shale exposure areas near the layer. Near the exposure of the oil shale formation, the oil content of the oil shale is lower in the east and higher in the west (Figure 7-5), and its thickness is thicker in the east and thinner in the west, but the change trend is slow. Moreover, the thickness and oil content are high, and the oil shale quality is good.
(2) The oil shale rich center of the A31 layer deviates slightly from the high oil content area, and the oil content decreases to the surrounding areas. The change is slower in the east than in the west, and the thickness is thicker in the east and thinner in the west. Compared with the A11 layer, the A31 oil shale has a lower oil content and is less stable. This is because after the formation of the A11 mineral layer, the local amplitude of up and down movements became larger, which affected the growth of plankton and the uniformity of lake basin sedimentation. Therefore, the oil shale mineral layer generated under this situation was not stable enough and of low quality. But in general, the thickness and oil content show a decreasing trend along the inclination direction of the oil shale exposed strata. The oil shale distribution is relatively stable along the strike direction, and the thickness and oil content do not change much.
Figure 7-5 Contour map of the oil shale oil content of the A11 layer in the oil shale mineral-bearing area in Binxian, Shaanxi Province
(3) Genetic types of oil shale
The oil shale in this area is a platform-type continental freshwater lake deposit, and its origin type is mostly mixed type (sapropel-humic type, humic-sapropic type).
IV. Oil shale resource evaluation
(1) Analysis of the extent of exploration work
1. Geological exploration work
(1) Before liberation, Wang Gongmu made a general survey of the oil shale in Binxian and Yongshou areas, and only analyzed the volatile content of the oil shale. Based on the volatile content, the oil content was estimated to be between 5 and 6, and no analysis was done. further work.
(2) In 1956, Comrade Liu Shaolong of the Xi'an Geological Survey Office of the former Ministry of Petroleum synthesized previous work and compiled "Oil Shale of the Ordos Platform", which gave a more systematic and clear description of the strata in this area. And the estimated reserves are 217.72 million tons.
(3) From 1958 to 1959, the Eighth Geological Team of the Shaanxi Provincial Bureau of Geology and Mineral Resources conducted a geological survey in the area and submitted reserves of 132.99 million tons in May 1959.
2. Exploration degree and accuracy
The degree of exploration in this area is general survey. The ore deposit is layered with a simple structure. The thickness and grade of the ore body are stable. It belongs to the first exploration type. According to the specification The C1 level mesh should be 2000m × 2000m, but the actual exploration mesh size is 6000m Elevation control is insufficient, and changes in thickness and grade are difficult to be accurate, and the degree of control does not meet the requirements. Moreover, there are too few boreholes (only 3 ore discovery boreholes), the accuracy is not high, and it cannot meet the census accuracy.
(2) Resource evaluation
1. Exploration area resource evaluation
The Bin County evaluation area includes two exploration areas, Zhanghong and Shuibei Village. During the evaluation, for the Zhanghong exploration area, the original data were used, according to the new evaluation standards, with the oil content rate 3.5 as the boundary, and the oil shale analysis data such as drilling and trenching were collected to determine the oil content rate and oil content of each layer of oil shale. thickness, using the volumetric method to re-estimate oil shale resource reserves. In the Shuibei Village exploration area, because its original data cannot be collected, its reserves are based on the oil shale reserves submitted by the National Reserve Committee.
The Zhanghong exploration area in Bin County has oil shale resource reserves of 482.53 million tons, technically recoverable oil shale resource reserves of 204.72 million tons, shale oil resource reserves of 30.6 million tons, and technically recoverable shale oil resource reserves of 12.98 million tons, page The recoverable rock oil resource reserves are 9.73 million tons; the oil shale resource reserves in the Shuibei Village exploration area in Bin County are 23.59 million tons, the oil shale technically recoverable resource reserves are 11.56 million tons, and the shale oil resource reserves are 1.71 million tons. Technically recoverable resource reserves are 840,000 tons, and shale oil recoverable resource reserves are 630,000 tons.
2. Resource prediction
According to the oil shale distribution characteristics and oil shale mineralization rules in the Zhanghong exploration area of ??Bin County, the volumetric method is used, and the oil content and thickness are calculated using nearby drilling methods. The oil content and thickness of the hole are averaged, and its weight adopts the weight value of the Zhanghong exploration area. The potential oil shale resources in the Zhanghong peripheral prediction area are 104.85 million tons, and the potential technically recoverable oil shale resources are 36.7 million tons. The potential oil resources are 5.58 million tons, the potentially technically recoverable shale oil resources are 1.95 million tons, and the potential recoverable shale oil resources are 1.46 million tons.
3. Resource evaluation of mineral-bearing areas
The oil shale resource reserves are 610.97 million tons, of which the identified oil shale resource reserves are 506.12 million tons and the potential oil shale resources are 104.85 million tons. t; the technically recoverable resource reserves of oil shale are 252.98 million tons, of which the identified technically recoverable resource reserves of oil shale are 216.28 million tons, and the potentially technically recoverable oil shale resources are 36.7 million tons. Shale oil resource reserves are 37.89 million tons, of which 32.31 million tons are confirmed shale oil resources and 5.58 million tons are potential shale oil resources; 15.77 million tons are technically recoverable shale oil resources, of which 32.31 million tons are confirmed and 5.58 million tons are potential shale oil resources. The technically recoverable resource reserves of shale oil are 13.82 million tons, and the potential technological recoverable resource reserves of shale oil are 1.95 million tons; the recoverable resource reserves of shale oil are 11.82 million tons, of which the recoverable resource reserves of shale oil are 10.36 million tons, page The potential recoverable resources of rock oil are 1.46 million tons.
(3) Development and utilization evaluation
1. Development technical conditions
(1) Mining technical conditions and engineering geological conditions.
The structure of the Binxian evaluation area is simple, the occurrence is gentle, and the mineral layers are layered with slight undulations. The reserves are large, but they are buried deep and are not suitable for open-pit mining, and can only be mined underground. The roof of the mine is mostly muddy rock, which is a soft rock with weak compression and shear resistance. The floor is interbedded with sandstone and sandy shale. The minerals are mainly quartz and feldspar, cemented with calcium and mud. It is dense and hard with few cracks, and its compression and shear resistance are stronger than those of the roof.
(2) Hydrogeological conditions.
This area is in a semi-arid area. There is not much precipitation in the area and the reserves of groundwater are not abundant. In the future, there will be an extremely lack of domestic and industrial water sources when large-scale mining is carried out, which limits the large-scale mining of mines. .
(3)Natural geographical environment.
The transportation in this area is not very convenient. There are no direct railways and expressways, only county-level roads pass through it. Although the economy has developed, it is not very developed.
2. Economic Review
The oil shale resource reserves in the Bin County evaluation area are large, but the oil content is not very high, and the transportation is not very convenient. Since the exploration in 1959, There has been no large-scale mineral deposit development. During the Great Leap Forward, only indigenous oil refining and some villagers used oil shale to make fertilizers on a small scale. Under the current economic and technological conditions, it is not suitable for large-scale exploitation. However, as oil resources are increasingly depleted today, oil shale resources with such large reserves can be regarded as an important alternative resource for petroleum under the conditions of future economic and technological development.