Resource Evaluation of Oil Shale Mining Area (Anatomical Area) in Binxian County, Shaanxi Province

The anatomical region of Binxian County, Shaanxi Province is located in Binxian County, Shaanxi Province, with geographical coordinates of1084' 55 "~10818' 44" and 34 58' 24 "~ 35 8' 8" north latitude. Includes two exploration areas, Zhang Hong and Shuibei Village. Except for the Xian (Yang)-Tong (Chuan) Railway passing through Yaoxian County, about 45km southeast of Yaoqu on the eastern edge of the area, there is no railway passing through the area, and Binxian County can be reached from the exploration area through Xi 'an-Lanzhou Highway (Binxian to Xunyi). However, there are great differences in the vertical and horizontal topography of the valleys in the area, and the deep slopes of the valleys are steep, so the traffic is inconvenient.

This area is located in the southern edge of the Loess Plateau in northern Shaanxi, with an altitude of 1000 ~ 1800 m ... low in the west and high in the east, with severe terrain cutting and thick loess layer in the west and thin in the east. The mountains in the east and the Loess Plateau in the west (Xunyi District and Binxian County). The mountainous area is located between the Loess Plateau in northern Shaanxi and the Guanzhong Plain, with an altitude of about1.600 m. The loess cover is not thick, and it is a denuded and residual mountainous terrain with a relative elevation difference of1.000 ~ 400 m. Most of the mountains are northeast-southwest and the valleys are north-south. The terrain is high in the north and low in the south, and the gravel layer is steep and steep, which is inconvenient to pass. The land is barren, agricultural products are not rich, and residential areas are sparse. The Loess Plateau (Xunyi District, Bin County) is the southern edge of the Loess Plateau in northern Shaanxi, with an altitude of about 850 ~ 1300m. Erosion and cutting are serious, and deep valleys and canyons are widely distributed. The height difference between the plateau and the plateau is 200 ~ 300 m, and there are many flat terraces on both sides of the river, which is rich in soil and water, which is beneficial to agricultural production, so there are more residents.

Jinghe River is the largest river in this area, which originates in Gansu and flows into Weihe River through the southeast suburb of Bin County to Jingyang. The river near Binxian County is about 0.5km wide, and there are obvious terraces on both sides. In addition, there are Jinghui River and Liulin River, but the rivers are not deep. In the gullies in this area, there is a large amount of water, but the amount of water is very small or intermittent.

I. Geological background

domain structure

1. Structural position

The geotectonic position in this area is located in the southern margin of Ordos basin, and its regional tectonic unit belongs to Binxun depression belt on Weibei uplift belt. In the late Yanshanian movement, there were some folds, most of which were broad and gentle anticlines with relatively simple structures.

2. Regional structural characteristics

(1) structural features.

Regionally, the structure of Binxun Depression has the following characteristics:

① Folds are well developed and fractures are rare. Folding in rows is good. The anticline and syncline structures alternate north and south, and are intermittently connected east and west, with the characteristics of flying geese. It deflects from near east-west and northeast to northeast.

② The fold pattern is characterized by wide gentle anticline and trough gentle syncline. The amplitude and intensity of the fold gradually weaken from south to north, and from bottom to top, the shape of the fold changes from tight, wide and gentle to wavy from the old stratum to the new stratum.

(3) The Jurassic stratigraphic syncline is thick and thin, the axis of anticline is thin and thick, and the Fuxian Formation of the Lower Jurassic is often missing, showing the characteristics of structural ore control (coal control). Coal-bearing deposits are characterized by good syncline and poor anticline, and are distributed in strips. During Triassic, Jurassic and Cretaceous, anticline and syncline structures overlapped each other and their positions were basically the same, which reflected the dual characteristics of structural inheritance and stability.

(2) Fold structure.

Regional fold structures mainly include Luodian syncline (Z 1), Shijiahe syncline (Z2), Tingkou syncline (Z3), Xunyi syncline (Z4), Dafo Temple syncline (Z5), Binxian syncline (Z6) and Jiazheng syncline (Z7). The map area is about 8 ~ 20km long. The axial direction is northeast (65 ~ 70) to nearly east-west (about 275), and the strata that constitute the fold structure are mainly Mesozoic Jurassic, Cretaceous and Triassic. Generally, folds are flat in shape and asymmetrical in wings. Generally, the northern wing of anticline is steep (dip angle 5 ~ 40) and the southern wing is gentle (dip angle 2 ~ 8). The dip angle of the south wing of the syncline is relatively large (15 ~ 20), and the dip angle of the north wing is slightly small (4 ~ 6).

① Luodian anticline (Z 1) is located in the territory of Luodian, Jinghe River, with the axial northeast (65 ~ 70) and inclined westward to the west of Jinghe River. The anticline fluctuates slightly, and the axial Jurassic tends to be thinner or absent, with the dip angle of the north wing of 5 ~ 8 and the dip angle of the south wing of 2 ~ 3.

② Shijiahe syncline (Z2) is located between Luodian anticline and Tingkou anticline, with the northeast axis (60 ~ 65), and the center of syncline is flat and trough-shaped. The core is the upper part of the Lower Cretaceous Luohe Formation, and the two wings are the lower part of the Luohe Formation, with a dip angle of 3 ~ 7, which is a slow trough syncline.

③ Tingkou anticline (Z3) is distributed in the northeast direction (70 ~ 78) along Yan Jia-Tingkou Town-Xiaolingtai-Liucun, with comb anticline in the east, Jurassic in the core and lower Cretaceous Yijun Formation on both wings. The dip angle of the north wing is 5 ~ 10, and the south wing is slightly reduced to 2 ~ 4, which is slightly asymmetrical.

④ Xunyi anticline (Z4) is located in the first line of Jirzui-Baizigou Coal Mine in the south of Xunyi County, with the axial northeast (65 ~ 70), and the Great Buddha Temple is inclined to the west. The core exposed stratum is Triassic, and the two wings are Jurassic and Cretaceous. The inclination of the north wing is 10 ~ 15, and the inclination of the south wing is 3 ~ 5. The overall shape is an asymmetric comb-shaped wide gentle anticline, steep in the north and gentle in the south.

⑤ The syncline (Z5) of the Great Buddha Temple is located between Tingkou Anticline and Binxian Anticline, and it is distributed along the Xianbaigou line from the Great Buddha Temple to water curtain cave and Bai Zi Gully, and its axis is close to the east and west. The core is Jurassic and Cretaceous strata and the wings are Triassic strata. The dip angle of the south wing is steep (15 ~ 20), and the dip angle of the north wing is gentle (4 ~ 6), which is an asymmetric wide gentle syncline.

⑥ Binxian anticline (Z6) is located on the line of Wanrencun, south of Binxian-Baizigoukou, and its axial direction is nearly east-west (275). The core is Triassic strata, and the wings are Jurassic and Cretaceous. The Triassic in the east of Binxian County has a large dip angle, with12 ~ 40 in the north wing and 2 ~ 8 in the south wing, which is an asymmetric comb anticline. To the west of Binxian, Jurassic and Cretaceous are comb anticlines with a dip angle of 4 ~ 9 in the north wing and 2 ~ 6 in the south wing, which are inclined to the west.

⑦ Jiazheng syncline (Z7) is located in the south of Jiazheng, with an axial direction of about 70 northeast. The trough is Jurassic and Cretaceous, and the wing is Triassic, which is a broad and gentle syncline.

(3) Fault structure.

The fault structure is dominated by Baizigou reverse fault, which is located at the junction of Triassic strata and Jurassic strata near Baizigou highway bridge in Bin County. The fault faces south. The upper wall is feldspar sandstone and shale of Yanchang Formation (T3y) of Upper Triassic, and the lower wall is feldspar sandstone and black mudstone of Yan 'an Formation (J2y). The fault plane occurrence is 190 ∠ 60.

3. Regional strata

According to stratigraphic regionalization, Shaanxi Province, the strata in this area belong to the south of the Shaanxi-Gansu-Ningxia Basin in North China. The exposed strata include Triassic, Jurassic, Cretaceous and Cenozoic in Mesozoic from old to new, and are distributed in strips between Xingshuping in Tongchuan County and Baijiahe in Binxian County, all of which are continental sedimentary rocks. The total thickness of strata in the area is 568 ~ 2259 meters, and sedimentary rocks are extremely developed. Among them, the outcrop of bedrock only accounts for about 10%, and the rest is loose accumulation layer.

Triassic (t).

The oldest stratum in this area is Yanchang Formation of Upper Triassic in Mesozoic. The traditional Yanchang Formation was originally named Yanchang County in northern Shaanxi and divided into five sections. Among them, the first, second and third floors are mainly developed in this area, and the fourth and fifth floors are basically missing. The surface is exposed in the north and south banks of Jinghe River, Shuibeigou and Bai Zi Gou to the east of Binxian County. It is a set of greenish-gray, black sandstone and mudstone deposits, resulting in extended flora fossils. It is the main horizon of oil and gas reservoirs and oil shale distribution in this area, bottomless, with a total thickness of >: 660m.

① Upper Triassic Yanchang Formation (T3y 1+2). Room 3, Institute of Geology, Chinese Academy of Geological Sciences (1965) took it as an independent unit and named it Tongchuan Formation. Yanchang Formation can be divided into upper member and lower member according to lithological combination. Only the upper member is seen on the surface, with a total thickness of >: 3 10m. The lithology of this formation is light green-gray and yellow-gray fine-grained feldspathic sandstone. Calcareous sandstone is dominant, mixed with silty mudstone, siltstone and shale. Middle-yielding plant fossils in shale are mostly Dryopteris lepidoptera and crab-shaped new trees, while scales and trace fossils are mostly found in oil shale.

② The third member of Upper Triassic Yanchang Formation (T3y3). The lithology is black-gray shale, sandwiched with medium-thick layered fine-grained feldspathic sandstone and silty shale, and is often rich in black oil shale. Fossils of middle-producing plants in shale include Dryopteris Shaanxi and Dryopteris multicolored, and there are Dryopteris fossils and trace fossils in oil shale. It is continuously deposited with the underlying stratum, but the particle size is finer than that of the underlying stratum, and the thickness changes greatly (0 ~ 350 m).

(2) Jurassic (J).

It is exposed in Bai Zi Gully, Shuibeigou, southeast of hu jia wan and south of Binxian County, with sporadic outcrops and incomplete sections in other places. This system is a set of continental coal-bearing formations, which produces Yan 'an flora fossils and is an important coal-bearing and oil-bearing stratum in this area. It is in parallel unconformity or angular unconformity contact with different horizons of the underlying Triassic strata, with a total thickness of198.4 ~ 904m.

① Lower Jurassic Fuxian Formation (J 1f). There is no surface exposure in this area, which is mainly found in the boreholes in the coalfields near Binxian and Xunyi. Lithology is purplish red, dark gray mudstone, sandy mudstone, sandstone mixed with aluminum mudstone, carbonaceous mudstone and thin-layer glutenite, with conglomerate at the bottom and colored mudstone at the upper part. Spores in mudstone: Echinacea, Tricycladus. Pollen: spruce, cycad. Overlapping unconformity contact with the underlying extension group, with a thickness of 0 ~102 m.

② Middle Jurassic Yan 'an Formation (J2y). This area is a set of coal-bearing measures, the lower part is light gray thick layered feldspathic sandstone, and the middle and upper part is interbedded with gray black mudstone, aluminum mudstone, argillaceous siltstone and fine sandstone, sandwiched with carbonaceous mudstone and coal seam, which is rich in plant fossils. The surface thickness is 12 1.9 ~ 247 m, and the lower part is in parallel unconformity contact with Fuxian Formation. When Fuxian Formation is missing, it overlaps with different horizons of Yanchang Formation.

③ Middle Jurassic Zhiluo Formation (J2z). The lithology of this formation in the area is light gray and grayish yellow thick layered gravelly quartz sandstone and fine conglomerate, with a small amount of purplish red or variegated mudstone and sandy mudstone. Muddy siltstone, plant fossils are: Dryopteris truncatum, Dryopteris clavata, spores are Lygodium japonicum and so on. The stratum thickness varies greatly, from 48.4 to 333 meters to 333 meters, and it is in parallel unconformity contact with the underlying Yan 'an Formation.

④ Middle Jurassic Anding Formation (J2a). The lithology in the area is purplish red and brownish red sandy mudstone, siltstone and fine sandstone mixed with brownish red medium-thick sandstone and glutenite, and fine conglomerate and conglomerate are common at the bottom. Spores: Dryopteris Dryopteris, Golden Hairs. Pollen: Picea, Picea, etc. The thickness of the surface layer varies greatly, from 28. 1 to 222 m, which is in integral contact with the underlying Zhiluo Formation.

(3) Cretaceous (K).

Exposed in the north of Bin County, on both sides of Jinghe River, Hongya River and Baizigou. It is a set of continental red bed deposits composed of shale and argillaceous rocks, which are in parallel unconformity or angular unconformity contact with the underlying Jurassic strata. The total thickness is 251~ 402 m.

① Yijun Group (K 1y). The lithology of this group in this area is purple-gray thick layered (massive) composite conglomerate, gravel sandstone lens and mudstone thin layer or strip. It is in unconformity contact with the underlying Jurassic strata. Generally speaking, the thickness varies from 30 meters to 60 meters.

② Luohe Formation (K 1l). The lithology of this group in this area is purplish red and orange thick layered medium-coarse grained feldspar, and the sandstone is mixed with conglomerate and sandy mudstone thin layer or strip, and large oblique bedding is developed in the sandstone. The total number of gravel layers decreases, becoming thinner to the north and thicker to the south, with more layers and complex gravel composition. The total thickness is 222 ~ 342 m. Generally speaking, this formation and the underlying Yijun Formation are continuously deposited.

(4) Neogene Pliocene (N2).

It is mainly distributed in the valley of Jinghe tributary, and unconformity covers the Mesozoic planation plane, which constitutes the basement of the Loess Plateau. The name of this rock formation is Baode Formation (N2b), which contains fossils of Tridactyl fauna. The distribution in the area is stable, but some areas are irregular or have no deposits. The lithology is brownish red claystone, calcareous nodule claystone, mixed with siltstone and calcareous nodule, and there is often a gravel layer at the bottom, which belongs to river and lake deposits, and the thickness varies greatly, ranging from 14 to 73m.

(5) Neogene Pleistocene (Q).

This area is widely distributed, well developed and complicated in sedimentary types, including river and lake sediments, river alluvial sediments, slope sediments and aeolian sediments. The lithology is mainly aeolian loess, followed by gravel accumulation, with a total thickness of 103.5 ~ 220 m, which is in unconformity contact with pre-Quaternary strata.

(2) Igneous rocks

The magmatic activity in the area is extremely weak, and there is no igneous rock development.

Second, the characteristics of oil shale

(A) the occurrence characteristics of oil shale

1. Oil shale occurrence horizon

Most of the mining areas in Binxian County are covered with broad and thick loess. Only in deep ditches can there be Mesozoic outcrops. Mesozoic strata are mainly exposed in Lower Cretaceous Yijun Formation (K 1y), Middle Jurassic Anding Formation (J2a), Middle Jurassic Yan 'an Formation (JY2Y) and Upper Triassic Yanchang Formation (T3y). The occurrence of strata in this area is nearly horizontal and the dip angle is small. K 1y is in pseudo-integrated contact with underlying J2a, and J2y and T3y are also in pseudo-integrated contact. The occurrence horizon of oil shale is the third layer of Upper Triassic Yanchang Formation, and the characteristics of Upper Triassic Yanchang Formation (T3y) are as follows:

(1) The first and second layers of Upper Triassic Yanchang Formation (T3y 1+2).

The upper part of this layer is interbedded with fine sandstone, sandy shale and shale, but it is dominated by sandstone, and the lithologic change has no obvious boundary, mostly gradual change. Sandstone is dark gray, gray-green, and blue-gray, while weathered iron is yellowish brown, yellowish green and thin to thick layered, with tiny primary structures such as oblique layers and ripple marks. However, the mineral composition is mainly timely, and the argillaceous calcium is cemented and hard. Sandy shale and shale are mostly dark gray or gray-black, with obvious bedding and muscovite fragments and plant fossils on the surface.

(2) The third layer of Upper Triassic Yanchang Formation (T3y3).

Lithology is mainly dark gray and yellow gray sandy shale and shale, mixed with gray fine sandstone and black shale and multi-layer gray black and black oil shale. Oil shale is mixed with black gray and black thin sandstone. The bottom plate of oil shale is gray and yellow-green sandstone, and the top plate is shale. Oil shale is distributed in layers, which is generally stable in the region, extending more than 80 km along the strike, with monoclinic structure, dip angle of 5 ~ 10, and buried depth generally less than 500m m.

2. Spatial characteristics of oil shale

There are three oil shale horizons in the area (A 1, A2 and A3), and the oil shale horizon above A2 does not meet the industrial requirements. Only A 1 is described in detail here. A 1 oil shale lower clip 1-2 layer is dark gray, black and thin oily muddy fine sandstone. The coal seams are divided into A 1 1, A2 1, A3 1 (Figure 7-2), and the thickness varies greatly, among which A.

Fig. 7- 1 A-A-A' Profile of Exploration Line in Oil Shale Mining Area of Binxian County, Shaanxi Province

Figure 7-2 Comparison of Oil Shale-bearing Mining Areas in Binxian County, Shaanxi Province

Table 7- 1 A 1 oil shale layer thickness table of Zhang Hong exploration area in Binxian oil shale mining area, Shaanxi Province

(2) Quality characteristics of oil shale

1. Ore characteristics

Oil shale is mostly black and paper-shaped, with two groups of joints developed and mostly rhombic. Due to long-term weathering, the surface exposed on hillsides and ridges is mostly gray-black flake, with rusty limonite and yellowish natural sulfur film attached to the surface, which is brownish yellow, while those exposed in ditches are mostly black thin layers eroded by running water. Fresh ore is black, soft but not brittle, and will burn when ignited, with asphalt taste and oily luster. It is slightly layered, dense and hard, mainly composed of hard clay, with a small amount of timely and feldspar fine debris, occasionally red hydromica clay lentils and asphalt particles, rich in ancient cod fossils.

2. Quality characteristics

Analysis of chemical properties of (1) oil shale.

① Oil content and ash content. The oil content of oil shale is generally negatively correlated with ash (Figure 7-3). The higher the oil content, the lower the ash content. The lower the oil content, the higher the ash content. Taking oil content as the dependent variable (y) and gray value as the independent variable (x), the following regression equation can be obtained through regression analysis:

y=33.8 197-0.3504x

Regression coefficient test t =- 1 1.588, correlation probability p.

Figure 7-3 Correlation between oil content and ash content of oil shale in Binxian oil shale mining area, Shaanxi Province

② Oil content, volatiles and moisture. The correlation between oil content and volatile matter and moisture is not obvious, and there is basically no linear relationship.

③ Oil content and organic carbon. The oil content of oil shale is generally positively correlated 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. Taking oil content as the dependent variable (y) and organic carbon as the independent variable (x), the following regression equation can be obtained through regression analysis:

y= 1.237+0.369x

Regression coefficient test t=8.680, correlation probability p.

④ Oil content and content of sulfur, hydrogen and nitrogen. There is no obvious correlation between oil content and the contents of S, H, N and other elements, and there is basically no linear relationship.

Figure 7-4 Correlation between Oil Content and Organic Carbon in Binxian Oil Shale Mining Area, Shaanxi Province

(2) Quality characteristics of oil shale.

See Table 7-2 for oil content and ash content of oil shale in A 1 layer. As can be seen from the table, the oil content of A 1 layer oil shale is not very high, but it is relatively stable, all above 5%, and the highest is around 7%. The high ash content belongs to high ash oil shale, the highest is 84. 16%, generally above 70%; The organic carbon content is generally greater than 7.5%, and the higher the oil content, the higher the organic carbon content; The volatile matter is also high, up to 89.70%, the moisture content is not higher than 2.36%, and the sulfur content is lower than 4%. Generally speaking, the quality of oil shale is average. In contrast, the quality of A 1 1 oil shale is better than A2 1 and A3 1 oil shale, and it is the most important recoverable oil shale layer in this area.

Table 7-2 Quality Characteristics of A 1 Oil Shale Layer in Zhang Hong Exploration Area of Binxian Oil Shale Mining Area, Shaanxi Province

Three. Distribution law of oil shale

(A) the formation of the environment

1. Tectonic environment

(1) tectonic background. Due to the long-term uplift of the platform anticline in eastern Shanxi, the platform depression in northern Shaanxi has formed a large monocline gently dipping westward. On the basis of large monoclinics, some large nose-shaped bulges and depressions have been formed. Binxun sag is the southernmost one. Its basement is pre-Carboniferous. The Indosinian movement caused the Triassic uplift and fold in this area and suffered erosion. Later, these pre-existing anticline and syncline structures developed during the Yanshan movement.

(2) Structural characteristics of the deposit.

There are some folds in the late Yanshanian movement, most of which are wide and gentle anticlines, and the structure of the mining area is relatively simple.

The ore-bearing area is located in the northern wing of Binxian-Baicaopo anticline, which is a gentle monocline. The anticline starts from Mozigou in Bin County in the west and reaches Baicaopo in the east, with a total length of 55 kilometers. The axial direction from Mozigou to breakfast head is 295, from breakfast head to Jierzui east, turn 45 ~ 60, and then turn 85 east to Baicaopo. It is an S-shaped anticline structure, and the core of the anticline is the first stratum of the Upper Triassic Yanchang Formation. Due to the axial direction of the anticline, Baicaopo extends to the southwest, turns to the northwest at Zaotou Village, and the occurrence of strata in the mining area also turns. The strike of the strata in the east of Shuibeigou (near Bai Zi Gully) is about 60 NE, and that in the west is about 365,438+00 NW, with dip angles of about 65,438+00.

The axial deflection of the folds in the mining area as a whole and the short-axis folds in the east of the area show that the area experienced nearly east-west compressive stress in the late Yanshan period, which may be the result of the further uplift and westward compression of the Shanxi platform anticline.

2. Lithofacies palaeogeographic analysis

Lithofacies characteristics of (1).

① The first and second layers of Upper Triassic Yanchang Formation (T3y 1+2). It is composed of light green gray, yellow gray feldspathic sandstone, calcareous sandstone, dark gray and gray green shale, and the former two account for 70% of the total rock. Feldspar sandstone is mainly medium-fine grained, and its composition is composed of detritus: 40% ~ 50% timely, 5% ~ 10% potash feldspar, 20% ~ 30% plagioclase, 3% ~ 5% siliceous rock, interstitial materials: sericite, iron, calcite and chlorite, and auxiliary minerals are zircon, magnetite and apatite. The front of river-controlled delta facies presents a large-scale upward thickening sequence, which starts from fine-grained offshore sediments and turns upward into coastal sediments dominated by sandstone. Generally, the lower part of the sequence is thick and uneven interbedded mudstone and sandstone; In the middle of the sequence, mudstone, siltstone and sandstone are repeated alternating layers, and small wavy sand layers can be seen. The top is dominated by sandstone, which is lenticular, and the sedimentary structure reflects the characteristics of one-way channel sand body. The sedimentary characteristics of T3y 1+2 belong to river-controlled delta facies, and sandstone is still dominant, but the grain size is fine. From the lithologic point of view, the lower part is often a set of muddy bedrock, and the upper part becomes a very thick and changeable sandstone body, and there are often scouring marks at the contact between sandstone and mudstone.

② The third layer of Upper Triassic Yanchang Formation (T3y3). It consists of black-gray shale, silty shale, black oil shale and feldspar fine sandstone. Muddy rocks account for more than 90% of the total number of rocks, and there are few plant fossils. Only the flora represented by Dryopteris Shaanxi and Dryopteris Shaanxi were found. The overall characteristics are fine grain size, dark color, rich in pyrite and organic matter, indicating that the water body is deep and quiet, with strong reduction, and has the characteristics of closed, semi-closed and semi-deep lake facies deposition. T3y3 has dark purple mudstone locally, which is in an oxidizing environment and is characterized by shallow lake deposition, so it is generally shallow lake-semi-deep lake deposition.

(2) Paleogeographic analysis.

① During the first and second layers of Upper Triassic Yanchang Formation (T3y 1+2), this area ended its long-term land-making movement and began to sink, accepting the deposition of sandstone and sandy mudstone, forming river-delta facies deposition. With the uplift of the Qinling fold belt, the depression in this area deepened and widened, forming a relatively stable shallow lake facies deposit, and the climate gradually changed to humid and mild, and plankton could reproduce.

② The lake basin in the third layer (T3y3) of Yanchang Formation of Upper Triassic deepened further, forming a semi-deep lake deposit. In the early stage, plankton was the most productive, and the biological debris accumulated in the lake basin turned into sapropel rich in organic matter after long-term decay, resulting in the original material of oil shale. In addition, the lake basin is deep, the water flow is relatively stable, and the environment is mostly changed from oxidation environment to reduction environment, so oil shale is generated in the region. The sedimentary environment of oil shale is good, forming high-quality ore bodies. However, there are still oscillating movements in the process of its deposition, which stirs up the tranquility of the lake, so sandstone appears in the seam.

To sum up, the late Triassic changed from the middle river delta facies to the late shallow lake-semi-deep lake facies, showing the stable sedimentary characteristics of Mesozoic inland basins. Although there are many species and genera of slender flora, peat bog facies cannot be formed because of the lush flora and swamp. It is true that the remains of plants and freshwater organisms are buried in deep lakes, and the organic matter is in a reducing environment, which is conducive to the formation of oil and gas reservoirs and oil shale.

(2) Distribution characteristics of oil shale

1. Metallogenic age and sedimentary sequence

The metallogenic age of Binxian oil shale evaluation area is the third layer of Yanchang Formation of Upper Triassic. The sedimentary sequence from bottom to top is upper shale section, middle oil shale section and lower sand shale section. From bottom to top, the grain size becomes finer, the sand/mud ratio decreases, and the sandstone is chronological, but there is no feldspar, which shows that it is a continental freshwater lake deposit. Among them, there are three layers of oil shale in the oil shale section. The first and third layers of oil shale are well developed and distributed in the whole region. The second layer of oil shale is only recoverable in some areas, and there are sandstone in the oil shale.

2. Distribution law of oil shale

The thickness of the oil shale section in this area is10.7m, including three layers of recoverable oil shale. A 1 1 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%, which is the main recoverable oil shale layer in this area. A2 1 oil shale has an average thickness of 0.88m and an average oil content of 5.87%, which is only recoverable in some areas. The average thickness of oil shale in layer A3/kloc-0 is 2.96m, the maximum thickness is 4.25m, the minimum thickness is1.37m, and the average oil content is 5.66%. It is also the main recoverable oil shale layer in this area. But the main minable layers are A 1 1 and A3 1. Based on these two layers, the distribution law of oil shale in this area is briefly discussed.

The sedimentary thickness of oil shale in (1)A 1 1 layer decreases gradually from south to north, and the oil content decreases gradually from south to north. The ore-rich center and high oil-bearing area basically overlap, both near the outcrop formation of oil shale. Near the outcrop of oil shale formation, the oil content of oil shale is low in the east and high in the west (Figure 7-5), and the thickness is thick in the east and thin in the west, but the change trend is slow. High thickness and oil content, good oil shale quality.

(2) The enrichment center of 3 1 oil shale in Layer A slightly deviates from the high oil-bearing area, and the oil around it decreases. The change in the east is slower than that in the west, and the thickness is thicker in the east and thinner in the west. Compared with A 1 1 layer, the oil content of oil shale in A3 1 layer is low and unstable. This is because after the formation of A 1 1 coal seam, the local fluctuation amplitude becomes larger, which affects the growth of plankton and the uniformity of lake basin deposition, so the oil shale coal seam generated in this case is not stable enough and the quality is not high. But in general, the thickness and oil content decrease along the dip direction of oil shale outcropping strata, and the distribution of oil shale along the strike direction is relatively stable, with little change in thickness and oil content.

Fig. 7-5 Isogram of Oil Content of A 1 1 Layer Oil Shale in Binxian Oil Shale Mining Area, Shaanxi Province

(3) Genetic types of oil shale

Oil shale in this area belongs to platform-type continental freshwater lake deposits, and the genetic types are mostly mixed (sapropelic saprophytic type and sapropelic sapropelic type)

Four. Evaluation of oil shale resources

(1) Analysis of the degree of exploration work

1. Geological exploration work

Before liberation (1), Wang Gongmu made a general survey of oil shale in Binxian and Yongshou areas, and only analyzed the volatile content of oil shale. According to the volatile matter content, the oil content is estimated to be between 5% and 6%, and there is no further work.

(2) 1956, comrade Liu Shaolong of Xi Geological Survey of the former Ministry of Petroleum compiled Ordos Platform Oil Shale, which made a systematic and clear description of the strata in this area and estimated the reserves of 217.72 million t.

(3) 1958 ~ 1959, the eighth geological team of Shaanxi Bureau of Geology and Minerals conducted geological survey in this area, and submitted the reserves of132.99 million t in May/959.

2. Degree and accuracy of exploration

The exploration degree in this area is general survey. The deposit is layered, simple in structure and stable in thickness and grade. It belongs to the first exploration type. According to the specification C 1, the grid should be 2,000 m× 2,000 m, but the actual exploration grid is 6,000 m× 2,000 m (to determine the C-level reserves), and the line spacing is diluted by 3 times, and the grid is too thin, which is unfavorable to the occurrence of ore bodies and floor elevation. Moreover, there are too few boreholes (see only three boreholes in the mine), and the accuracy is not high, which can not reach the accuracy of the census.

(2) Resource evaluation

1. Resource evaluation of exploration area

Binxian evaluation area includes two exploration areas, Zhang Hong and Shuibei Village. In this resource evaluation, aiming at Zhang Hong exploration area, according to the new evaluation standard, the oil shale analysis data such as drilling holes and exploratory trenches are counted to determine the oil content and thickness of oil shale in each layer, and the oil shale resource reserves are re-estimated by volume method. Because the original data of Shuibeicun exploration area cannot be collected, its reserves refer to the oil shale reserves reported by the State Reserve Committee. The reserves of oil shale resources in Zhang Hong exploration area of Binxian County are 482.53 million tons, 204.72 million tons, 30.6 million tons,12.98 million tons and 9.73 million tons respectively. The oil shale resource reserves in Shuibeicun exploration area of Binxian County are 23.59 million tons, the oil shale technical recoverable resource reserves are 1 1.56 million tons, the shale oil technical recoverable resource reserves are 17 1.00 tons and the shale oil recoverable resource reserves are 630,000 tons.

2. Resource forecast

According to the distribution characteristics and metallogenic regularity of oil shale in Zhang Hong exploration area of Binxian County, the oil content and thickness are obtained by averaging the oil content and thickness of adjacent boreholes, and the potential resources of oil shale in the peripheral prediction area of Zhang Hong 10485 million t, the potential technical recoverable resources of oil shale are 36.7 million t, the potential resources of shale oil are 5.58 million t and the potential technical recoverable resources of shale oil are 6.5438+.

3. Evaluation of mineral resources

The oil shale reserves are 6 10.97 million t, of which the proven oil shale reserves are 506120,000 t and the potential oil shale resources are 10.485 million t; The recoverable resources of oil shale technology are 252.98 million tons, of which the proven recoverable resources of oil shale technology are 216.28 million tons and the potential recoverable resources of oil shale technology are 36.7 million tons. The shale oil reserves are 37.89 million tons, of which the proven shale oil reserves are 323 1 10,000 tons and the potential shale oil resources are 5.58 million tons. The recoverable resources of shale oil technology15.77 million tons, of which the proven recoverable resources of shale oil technology13.82 million tons and the potential recoverable resources of shale oil technology1950,000 tons. The recoverable resources of shale oil are165438+820,000 tons, of which the recoverable resources of shale oil are136,000 tons and the potential recoverable resources of shale oil are 654.38+460,000 tons. ..

(3) Development and utilization evaluation

1. Technical conditions for development

(1) mining technical conditions and engineering geological conditions.

Binxian evaluation area has simple structure, gentle occurrence, layered coal seam and slight fluctuation. The reserves are large, but the buried depth is large, so it is not suitable for open-pit mining and can only be mined underground. The roof of coal seam is mostly argillaceous rock, which belongs to soft rock and has weak compressive and shear resistance. The bottom plate is interbedded with sandstone and sandy shale, and the minerals are mainly timely and feldspar, with calcareous and argillaceous cementation, dense and hard, with less developed cracks, and stronger compressive and shear resistance than the top plate.

(2) Hydrogeological conditions.

The area is located in semi-arid area, with little precipitation and not rich groundwater reserves. In the future, domestic water and industrial water are extremely scarce when mines are exploited in large quantities, which limits the large-scale mining of mines.

(3) Natural geographical environment.

The traffic in this area is not very convenient. There are no direct railways and highways, only county-level highways pass by. Although the economy has developed, it is not very developed.

2. Economic Review

The oil shale resources in Binxian evaluation area are large, but the oil content is not very high and the traffic is not very convenient. Since 1959, there has been no large-scale mineral deposit development. Only during the Great Leap Forward, indigenous oil refining and some villagers used oil shale to make fertilizer on a small scale. Under the existing economic and technological conditions, it is not suitable for large-scale exploitation, but today, with the increasing depletion of oil resources, such a large oil shale resource can be regarded as an important alternative resource for oil in the future economic and technological development.