Upper Triassic

Yanchang Formation in Ordos Basin and its surrounding areas, Yaoshan Formation in Liupanshan Basin, Nanying Group 2 in Dingxi Basin and the east of Hexi Corridor, Yanchang Formation in Qinshui Basin of Shanxi Province, Youfangzhuang Formation, Chunshuyao Formation and Tanzhuang Formation in Jiyuan Basin and Yichuan Area of Henan Province are syngenetic deposits, all of which belong to Upper Triassic (Table1-kloc-0/).

Table 1- 1 Brief Table of Mesozoic Stratigraphic Division and Correlation in Ordos Basin and Its Adjacent Areas

1. Yanchang Formation in Ordos Basin

Yanchang Formation of Upper Triassic in Ordos Basin is the stratotype section with the best outcrop, the earliest research and the complete development among the continental Triassic strata in China (Hacken Lee,1982; Song Guochu,1993; Li (1999) is the first source reservoir series after the formation of inland lake basin in Ordos basin, and it is also the main exploration and development target series in the study area.

For the study of Yanchang Formation in Ordos Basin, many geologists have done a lot of work and put forward various stratigraphic division schemes (table 1-2) since Clark and others began more than half a century in the early 20th century. The Yanchang Formation has been renamed many times, and Clark et al. (19 16) defined it as the extension zone of the lower part of Shaanxi Formation for the first time. Wang Zhuquan and Pan Zhongxiang (1934) studied the "extensional layer" established after the extensional zone and defined it as the Late Triassic. 1974 Changqing Oilfield adopts the name of Yanchang Formation, and thinks that Yanchang Formation belongs to Late Triassic, including Tongchuan Formation, Hujiacun Formation, Yongping Formation and Wayaobao Formation, and is a complete continental river-delta-lake sedimentary system, which is divided into five sections according to lithological characteristics, from bottom to top, it is feldspathic sandstone belt (T3y 1) and oil shale belt (800. At the same time, in order to meet the needs of oil and gas exploration, production and scientific research, according to the characteristics of lithologic combination, sedimentary structure, biological combination and logging curve, as well as the characteristics of source-reservoir-cap combination, the five lithologic sections are further divided into 10 oil-bearing group; 1980, the Institute of Geology, Chinese Academy of Geological Sciences renamed the Yanchang Formation divided by Gan (1959) and still subdivided it into five sections. Because of the different plant assemblages, the middle and lower plant assemblages corresponding to the first and second sections are named Tongchuan Formation, which belongs to the late Middle Triassic, and the plant assemblages of the third to fifth sections are named Yanchang Formation, which belongs to the late Triassic. 1983 Shaanxi Stratigraphic Table and 1976 "Northwest Mesozoic and Cenozoic Stratigraphic Conference" restored Yanchang Formation and further divided it into 4 groups from bottom to top; During the period of 1997, the comparative study of several strata in China shows that Tongchuan Formation is a stratigraphic unit with biological and chronological boundaries, and the Yanchang Formation should be discontinued, and its age should be from late Middle Triassic to late Triassic. The normal section is the "Yanhe section" from Hujiacun to Zhangjiatannanzhuang in Yanchang County. At present, most geologists believe that Yanchang Formation belongs to Late Triassic.

Table 1-2 stratigraphic division and evolution table of Triassic Yanchang formation in Ordos basin

Due to the development of uneven uplift and subsidence of the basement, the southern part of the basin was in a state of continuous depression for a long time, and by the late Triassic, it had developed into a gentle large inland lake basin. During the evolution of lake basin, Yanchang Formation developed a set of sedimentary series from lake advance to lake retreat. The northern part of the basin is a set of alluvial plain deposits with coarse grain size and small thickness (100 ~ 600 m), and the southern part of the basin is mainly developed with a set of river and lake delta deposits with relatively fine grain size and large thickness (100~600m ~ 1400 m). According to the characteristics of sedimentary cycle and lithologic combination, it is divided into five oil-bearing formations 10 from top to bottom (table 1-3).

Table 1-3 Stratigraphic Characteristics Division of Triassic Yanchang Formation in Ordos Basin

Member 1 (T3y 1): feldspathic sandstone belt, equivalent to Chang 10 oil group. Mainly a set of grayish green and fleshy red feldspathic sandstone mixed with purple sandy mudstone, argillaceous siltstone and siltstone. The content of feldspar in sandstone is high (generally above 40%), and it is rich in turbidite and calcite cement, and spots often appear because of uneven distribution of cement. Most of the sand bodies are lenticular channel sandstone with large cross bedding of grooves and plates, and the scouring surface of the basement fluctuates obviously. The argillaceous rocks contain plant fossils. From north to south, the stratum granularity in this section gradually becomes finer, and the stratum thickness becomes thicker from thin. The electrical characteristics are very clear, the apparent resistivity curve is generally finger-shaped with high resistance, and the natural potential is negative, which is bell-shaped with high amplitude and box-shaped. This section is characterized by obvious lithology and ore electricity, stable formation thickness, generally about 250 ~ 350 m, and oil-bearing is common in Longdong area, but it is one of the main oil-producing layers in Majiatan area.

The second section (T 3y2): oil shale belt, including Chang 9 and Chang 8 oil layers. Dark gray, gray-black mudstone mixed with silty fine sandstone or thin interbedded. Generally, the lower part is thin, the upper part is thick, and the argillaceous content is high, mainly mudstone, which is divided into Chang 9, and the upper part is mainly sandstone, which is divided into Chang 8. Chang 9 is the product of large-scale lake invasion. Black shale and oil shale, commonly known as "Lijiapan shale", are widely developed in the upper part of Chang 9 except the basin edge, and the thickness is about 20 ~ 40m. This set of shale is distributed stably in the basin, often showing high natural gamma and high resistivity, which is an important symbol of underground stratigraphic correlation. Chang 8 is mainly a delta deposit under the background of lake regression, with coarse grain size, grayish white, gray and grayish black medium-fine sandstone, which has good oil-bearing property and is an important oil-producing layer in Longdong and Lingyan areas.

The third member (T3y3): oil-bearing layers, including Chang 7, Chang 6 and Chang (4+5) oil layers. The lithology is dark gray and gray-black shale mixed with gray and gray-green siltstone and fine sandstone. Chang 7 in Longdong area is mainly composed of mud shale, and the deep lake oil shale of Chang 7 contains sandy turbidite and oil. This stratum is an important source rock formed in the heyday of Yanchang Formation lake basin, commonly known as "Zhang Jiatan shale", which is widely distributed in the lake basin. The downhole logging curve shows the characteristics of "three highs and one low" (high resistivity, high natural gamma, high acoustic time difference and low natural potential). Chang 6 is mainly a set of gray-green medium-fine grained sandstone deposits, and delta deposits are developed in the north and northeast of the basin, which is the main reservoir section of Yanchang Formation. The spontaneous potential curve shows the characteristics of inverted triangle and negative value from bottom to top. Chang (4+5) is generally composed of mudstone and siltstone, commonly known as "thin neck section", with a total thickness of about 300m, which is another main source rock.

The fourth member (T3y4): massive sandstone belt, which consists of Chang 3 and Chang 2 oil layers. Chang 3 oil formation is mainly gray white and gray feldspar with gray and gray black mudstone, with obvious electrical characteristics, negative natural potential, box-shaped or finger-shaped, and sawtooth apparent resistivity curve. The lithology of Chang 2 oil formation is relatively simple, mainly composed of light gray and gray green fine sandstone mixed with gray black and gray silty mudstone.

The fifth section (T3y5): Wayaobao coal measure, which consists of Chang 1 oil group. The lower part is interbedded with dark gray, yellow-green mudstone, silty mudstone and silty sandstone, and the upper part is dark gray, gray-green mudstone and gray-black carbonaceous mudstone mixed with shale and coal seam, containing a large number of plant fossils. The natural potential is generally flat, the middle amplitude is negative anomaly, and the resistivity is sawtooth. It is a regional caprock of Chang 2 oil group. Due to the later erosion, the remaining thickness of this section changed greatly in the north, west and south of the basin, especially in the south of the basin, and completely eroded in the west of Mafang-Jiyuan-Qingyang-Zhengning-Malan line. Qingyang-Huachi area is only distributed on the "remnant hills". In angular unconformity contact with the overlying Jurassic.

2. Yaoshan Formation in Liupanshan Basin,

Yaoshan Formation is a lithostratigraphic unit of Upper Triassic in Liupanshan Basin, which was established by the former Changqing Petroleum Exploration Bureau. It is in unconformity contact with the underlying Precambrian or Paleozoic strata, and it is a set of sandstone-mudstone coal measures strata in rivers, lakes and limnetic facies.

Yaoshan Formation is widely exposed in Zhongyaoshan, Mahuangou and Shangliushui in Liupanshan Basin, Pantan 3 well in Haiyuan County, tan shan Coal Mine and Minjiagou in Guyuan. The Yaoshan Formation in Yaoshan Coal Mine is 320m thick, which is a set of coal-bearing deposits dominated by river-controlled delta facies composed of light gray, grayish yellow and grayish green sandy mudstone, and contains unstable coal seams or thin coal seams of about 10 layer. The Yaoshan Formation in Mahuanggou, Tongxin County is 525.6 meters thick, which is a medium-thick yellowish brown and grayish yellow sandstone with black mudstone and coal lines, and has the sedimentary characteristics of delta plain facies and lake facies. On the Shangshui section of Tongxin County, the Yaoshan Formation is 232 meters thick and can be divided into two parts: the lower part is about 77 meters thick, which is lacustrine fine clastic rock, argillaceous rock mixed with thin coal and inferior coal line; The upper part is 156m thick, which can be divided into three small positive cycles, consisting of fluvial facies, coastal facies and limnetic facies. Minjiagou section in Tanshan, Guyuan is 78m thick and consists of two coarse sandstone cycles, which are composed of river channel, beach and flood plain facies, and contain thin coal seams, coal lines and plant fossils. The underground Yaoshan Formation of Tanshan Coal Mine in Guyuan is 600m thick, which is a set of clastic rock deposits, with lake facies in the lower part, delta plain and river facies in the middle and upper part, and coal seam and thin coal are about 18 layers. There are abundant sporopollen fossils in each horizon. In the fifth layer of Yaoshan Formation in Yaoshan Coal Mine, fern spores account for 78% and gymnosperms pollen accounts for 22%. The layer 12 contains 39.4% fern spores and 60.6% gymnosperms pollen. It is equivalent to the second segment (T3y2) and the third segment (T3y3) of the expansion group. Well Pantan 3, Haiyuan County, Yaoshan Formation is 870.3 meters thick (not drilled), and its lithology is light gray and grayish yellow calcareous silty sandstone, with silty mudstone mixed with dark gray and grayish black mudstone and coal seam and oil shale. Shallow lakes and delta facies deposits.

3. Nanyinger Group in Dingxi Basin and Hexi Corridor

Nanyinger Group is a lithostratigraphic unit of Upper Triassic in Dingxi Basin and Hexi Corridor. It is a set of gray-green clastic sedimentary rocks dominated by rivers, with a small amount of limnetic facies and coal lines. Mainly distributed in Haiyuan County Oil Well Mountain, Jingyuan Ciyao, the northern slope of Wuqu Mountain, Jingtai Fulu Village, Baiyin Dingjiayao, Zhongwei Xiaohongshan, Inner Mongolia Heishan Coal Mine and southern Wuwei, Gansu Province. Among them, the visible thickness of oil well hill is 4 15m, the thickness of Jingyuan magnetic kiln is 976m, and the thickness of Montenegro area is 1034m. According to lithology, it can be divided into upper and lower rock groups: the lower rock group usually has conglomerate and gravelly sandstone at the bottom, while the upper rock group is mainly red medium-coarse grained sandstone, with grayish green, purplish red sandstone, siltstone, siliceous lens and carbonaceous mudstone; The upper strata are a set of gray-green sandstone, siltstone, shale and a small amount of carbonaceous mudstone, which produce a large number of plant fossils.

4. Yanchang Group in Qinshui Basin

Yanchang Group in Qinshui Basin, Shanxi Province is composed of five lithologic members T3y 1-T3Y5 from bottom to top. The Institute of Geology and Mineral Resources of China Academy of Sciences (1965) divided the lower two groups (T3y 1 and T3Y 1) of Yanchang Formation into Tongchuan Formation, and named the upper three members as (T3Y3-0).

The representative section of Tongchuan Formation in Shanxi Province is the Yu Di section in Xixu Township, shilou county. Tongchuan Formation mainly produces grayish green, grayish yellow and fleshy red thick-layer medium-fine grained feldspathic sandstone, which is composed of grayish green, grayish purple and grayish black sandy mudstone and shale mixed with tuff, and the grain size from coarse to fine constitutes a complete sedimentary cycle. Tongchuan Formation has stable lithology, thick in the south and thin in the north (465,438+03.8 ~ 483.7 m thick in the south of Lishi-Taiyuan line; 275 meters north of Lishi-Taiyuan line), which is in integral contact with the underlying Ermaying Formation.

Yanchang Formation (narrow sense) is distributed in the north-central Qinshui District and the southwest Luxi District, especially in Daning and Jixian County. The rock stratum is mainly composed of slender sandstone in yellow-green, gray-green, gray-yellow and fleshy red medium-thick layers, with gray-green, yellow-green, gray-black, gray sandy mudstone and shale. It is integrated with the underlying Tongchuan Formation, and is an inland river and lake facies deposit in a warm and humid climate.

5. Upper Triassic in Jiyuan, Henan Province

Residual strata of Upper Triassic in Henan Province are mainly distributed in Jiyuan, Luoyang, Yichuan Basin and Liu Shan Basin, and there are also many in Waxuezi Basin. Yima, Zhongmou, Tangyin Graben and Yiyang strata are incomplete or strongly eroded, and the rest areas are basically missing, with a residual area of about 6360km 2 (Zheng Qiugen,1998; Liu Shaolong, 1986). The Upper Triassic in Jiyuan area is generally a fluvial-lacustrine delta deposit in humid climate, and the strata include Youfangzhuang Formation, Chunshuyao Formation and Tanzhuang Formation from bottom to top.

Youfangzhuang Formation consists of upper and lower layers: the lower layer is interbedded with yellow-green feldspathic sandstone, purple-gray fine sandstone and claystone with unequal thickness, which is lakeside facies deposit; The upper member is medium-coarse grained feldspathic sandstone mixed with apricot thick layer, and medium-fine grained feldspathic sandstone mixed with purple clay rock, which belongs to fluvial facies deposition. The stratum thickness gradually becomes thinner from west to south, and it is only 350m thick near Changyao in yima city, 488m thick at Gaomen in Yiyang County and 694m thick at Yangying in Dengfeng County.

The lithology of Chunshuyao Formation is relatively stable, mainly composed of grayish yellow, grayish brown and yellowish green thick-medium thick fine-grained feldspathic sandstone, siltstone mixed with yellowish green, grayish yellow claystone and sandy claystone, mixed with medium fine-grained feldspathic sandstone, feldspathic sandstone, marl and several layers of coal lines. There is little change in lithology in Yima area, which is mainly composed of meat-red thick layer and extremely thick layer of fine-grained feldspar timely sandstone, siltstone and yellow-green claystone with a small amount of coal lines, with a thickness of 967.5 meters. ..

The lithology of Tanzhuang Formation is mainly grayish yellow, beige and yellowish green calcareous claystone, and claystone is interbedded with grayish yellow and brownish gray calcareous siltstone. The lower member is sandwiched with medium-fine feldspar timely sandstone, calcareous fine sandstone, gray-black mudstone and coal line; The upper section is sandwiched by multiple layers of coal lines and oil shale, and the top is a layer of gray clay rock. It is a freshwater lake-swamp facies deposit. From the west to Yima area, the thickness becomes thinner (563.2m) and the lithology becomes thicker. The lower member is grayish yellow fine sandstone, siltstone mixed with grayish yellow and grayish green claystone, pink and grayish white medium-grained feldspar timely sandstone, and two layers of acidic volcanic rocks are mixed locally; The upper member is gray, dark gray and grayish yellow silty fine sandstone, with multiple coal lines or thin coal seams, with occasional siderite nodules and thin siderite layers.