(1) Basis for the division of coal phases

1) Taking the vitrinite content as 60%, the ratio of vitrinite to semi-vittrinite and inert groups V/(SV +I) is equal to 4, and the gelation index GI is equal to 4, which divides the two types of wet swamp and dry swamp, which further reflects the degree of water covering of the swamp.

2) Forest index WI=(T+TC)/(DC+VD), forest swamps and other swamp types are divided according to whether the WI value is greater than 0.5.

3) Coal dominated by leaf vitrinite and with more than 10% cutinite is divided into flowing swamp subphase; dominated by matrix vitrinite, containing sporophytes, detritus and suberin The coal in the body is divided into marginal swamp facies.

4) Coal with more detrital components, more sporophytes and algae, micro-triple coal, macroscopic appearance of shell fractures, massive structure, pure and light coal is divided into open water bodies Swamp phase.

5) The transitional component is the main component, showing a composite structure, and is mainly micromirror inert coal, reflecting coal with strong local short-term oxidation under water, and dividing the transitional swamp subphase.

(2) Coal facies types

Based on the above classification standards, the coal facies types in the northwest region were classified in detail, and the results are shown in Table 3-59.

Table 3-59 Coal facies division scheme in Northwest China

(3) Coal facies characteristics and distribution

1. Coal facies characteristics

(1) Dry peat swamp facies

The "dry" referred to here includes both high-level dry forest swamps and oxidative swamps (transitional swamps) near the water surface or underwater that dry for a short period of time or periodically. ). The main characteristics of this coal phase are enrichment of silk char, the sum of the microscopic components of silk body, semi-silk body, and semi-vittrinite is greater than 50%, the V/(SV+I) value is less than 2, and the gelation The index GI value is less than 4, and the hydrogen index HI is less than 100. It reflects that the swamp environment is not covered by water or is covered by shallow water. For example, this type of coal facies is widely developed in the J2x coal seam of Fukang Sangonghe Coal Mine.

It can be roughly divided into two types: the first type takes the J2x coal seam of Mulei Coal Mine in the eastern Junggar Basin and the J2x coal seam of Santanghu Coal Mine as examples. The main feature is that macroscopically, it is rich in fire silk charcoal lenses or 0.5 to 10 cm thick silk charcoal layers, which are fibrous, crumb-like or thin strip-like structures. Under the microscope, they appear as fire silk bodies and semi-silk bodies. Mainly, the sum of the two is at least greater than 20%, and many transition phenomena from vitrinite to inertinite can be seen. The vitrinite group is mainly composed of structural vitrinite and basically does not show fluorescence. In addition, it also contains coarse grains and detrital inertinites. The V/(SV+I) value and the gelation index GI are both less than 1, the plant preservation coefficient TPI is large, the microstructure is a patchy structure, and the microscopic coal and rock types are mainly micro-inert coal and micromirror inert coal. This reflects that the entire swamp is above the terrestrial phreatic surface, dry forest fires often occur, and there is periodic drying. Some may be rich in clay minerals and present an ancient soil phase. Its main identification signs are: high content of fire-burned silk plastids and rich silk charcoal layers.

The second type takes the J2x Zhong3 coal group in Well 21 of Barkol County Coal Mine in the eastern Junggar Basin and the J2x coal seam of Fukang Sangonghe Coal Mine as examples. The main feature is the extremely high content of transition groups such as semi-vittrinite, semi-filite, and coarse-grained A. This type of transition component can be seen under the microscope as interlayered with vitrinite, forming a composite structure or strip structure. Macroscopically, it appears as dark coal with rich silky carbon clast structure or light dark coal with thin strip structure. Microscopically, the coal rock types are mainly microscopic inert coal, poor spore dark coal, and slightly inert coal. The origin of microscopic coal rock is On the sign, V/(SV+I) is less than 1.2, GI is less than 4, and the flow index MI is high, which reflects that the swamp is located near the water surface and has a periodic oxidation environment. Its main identification signs are high transition components and high MI.

(2) Forest peat swamp facies

The main characteristics of this facies are that it has an obvious uniform structure on a macro scale, with eyeball-shaped fractures and striped structures of mirror coal and bright coal. Endogenous cleft development. Under the microscope, it is marked by the enrichment of structural vitrinite and homogeneous vitrinite. The forest index WI is greater than 0.5, GI is greater than 4.0, TPI is greater than 0.5, V/(SV+I) is greater than 4, and MI is less than 0.1. Microscopic coal rock The main type is micromirror coal. The environment in which it is formed is an extremely humid forest with deep water cover. At the same time, plant remains suffer weak decomposition damage and poor water flow activity. This facies is widely developed in the upper delta plain, such as the J2x coal seam of the Liuhuanggou 755 mine.

The main identification signs of this phase are that T, TC, and WI are greater than 0.5, and GI and V/(SV+I) are both greater than 4. This facies takes the J2x upper 4 coal group of Well 23 in Barkol County Coal Mine in the eastern Junggar Basin and the J1b coal seam of Fukang Sangonghe Coal Mine as examples.

(3) Living peat swamp phase

The so-called "living peat swamp" means that the peat formation environment is under flowing hydrodynamic conditions, with strong microbial activity and strong water covering swamp environment. The coal formed in this environment is mainly composed of matrix vitrinite, and can also be enriched with a large number of cutinites, sporophytes, suberin, etc., with GI and V/(SV+I) both greater than 4, and many even greater than 10 , TPI and WI are less than 0.5. Macroscopically, it is bright coal and dark coal with uniform or thin strips of layered or massive structure. Microscopically, the coal rock types are bright coal with rich spores and rich horniness, etc. Since the living peat swamps formed by different depositional environments and depositional systems are the same, this phase is divided into two subphases.

It can be roughly divided into two types: the first type is located on the edge of forest swamps. Due to deep water cover, strong flowing water or because lower organisms are very active, the water is active and the plants are strongly decomposed, forming a matrix. The peat swamp phase dominated by vitrinite (or hydrogen-rich vitrinite) is equivalent to the "reed swamp" referred to by Teichmüller. This phase can enrich a large number of sporophytes or cork bodies. Due to the strong decomposition of plant bodies by living and flowing water, they are often brought to strong reducing environments for deposition. Therefore, a large amount of berry granular pyrite can appear, the gelation index GI and mirror inert ratio V/I and V/(SV+I) are very high, while the WI and TPI are very low. Macroscopically, it is bright coal with bright line texture and shell fracture. The microscopic coal rock types are slightly bright coal, spore-rich slightly bright coal or cork-rich slightly bright coal, with uniform structure. Its main identification mark is that stromal vitrinite is the main component, and GI and V/(SV+I) are very high.

The second type is mainly bright coal and dark coal with a lamellar structure, ladder-like fractures, and layered structure from a macro perspective. Under the microscope, it is characterized by enrichment of cutin, which is generally greater than 10%. Mainly composed of matrix vitrinite, it is oxidized due to the action of running water, so the fluorescence is not as strong as the matrix vitrinite of the previous subphase. Can contain a lot of pyrite. GI and V/(SV+I) are very high, but TPI is not necessarily very low. This is due to the development of many leaf vitrinites. It has few inert components and can contain high clay content. The microscopic coal rock type is mainly horny and slightly bright coal, with thin strip structure and horizontal bedding. However, it is often seen that the horny body is systematically wrinkled, which reflects that this swamp has a certain slope and the action of swamp water caused early diagenetic formation. Peat tanning wrinkles. Generally formed in the nearshore environment of lakes. Its main identification signs are cutin enrichment, greater than 10%, and high GI and V/(SV+I).

(4) Open water facies

This facies belongs to the lake and bay coal facies. Its sediments are produced in swamp lakes or ponds and are mainly composed of floating plants (algae, submerged aquatic plants). Plants), aquatic animals and abundant bacterial substances are accumulated, and other fine clay, spores, detrital inertinites are blown by wind or water flow. This phase is composed of dull coal containing lipid-rich slightly bright coal and slightly dark coal, as well as saprolite coal and high-carbon mudstone. Under the microscope, the content of vitrinite is relatively small, and it is mainly matrix vitrinite, containing agglomerated vitrinite formed by the strong decomposition of aquatic plants. Because it is underwater sedimentation, the GI is greater than 4, but the flow index MI is high or extremely high. The open water phase is dominated by dark coal, mineralized coal, sapropel humic coal, and saprolite coal, with shell-shaped fractures and massive structures. Under the microscope, stable components such as sporophytes and algal bodies (more than 1%) are relatively enriched, with an MI greater than 1. The microstructure is a clastic structure, with microsanhe coal and microspore bright coal as the majority, and vitrinite. The group content is relatively small, but it is dominated by DC. The asphaltene content is large and transitions to DC. The GI is greater than 4 to 10, and V/(SV+I) is greater than 1 to 4. The identification marks are mostly algae and sporophytes, MI is greater than 1, and the sum of algae and asphaltene is greater than 10.

2. Coal facies distribution in the Junggar Basin

Based on the above comprehensive coal facies signs, the early and middle Jurassic Badaowan and Xishanyao period coal seams in the Junggar Basin can be divided into dry peat swamps There are four coal facies: forest peat swamp facies, living peat swamp facies and open water body facies. The coal facies characteristics of the Badaowan Formation (Figure 3-52) are: the northwest edge of the basin, the west of the south margin, and the northern part of the east edge are mainly dry peat swamp facies; the eastern part of the south margin of the basin, the south of the east margin, and the southeast of the northwest margin are forest peat swamp facies. , living peat swamp phase and open water phase develop in a ring shape towards the belly of the basin. The forest peat swamp phase and its transition zone with the dry peat swamp phase are more favorable for coalbed methane.

The coal facies characteristics of the Xishanyao Formation (Figure 3-53) are: dry peat swamp facies develops in the northern part of the basin, the western part of the southern edge and the east corner of Fukang, and the southern part of the northwest edge of the basin, the eastern part of the southern edge and the eastern edge of the basin. Forest peat swamp facies develops in a wide area, and living peat swamp facies and open water body phase develop in a ring shape towards the belly of the basin. Among them, the forest peat swamp facies is a favorable phase zone for the formation of coal bed methane. Vertically, during the depositional period from Badaowan Formation to Xishanyao Formation, the range of dry peat swamp facies shrank and the area of ??forest peat swamp facies expanded, while the range of living peat swamp facies and open water facies did not change much. It shows that the late Middle Jurassic is more conducive to coal formation and coalbed methane generation.

Figure 3-52 Distribution map of the Badaowan Formation coal formation in the Junggar Basin

3. Coal facies distribution in the Tarim Basin

The Jurassic coal seams in the Tarim Basin are mainly dry Peat swamp facies, forest peat swamp facies, living peat swamp facies and a small amount of transitional peat swamp facies. The coal facies of the Kizilnur Formation coal seam in the Yangxia coal producing area are mainly dry peat swamp facies and forest peat swamp facies. The coal seam coal facies of the Taliqike Formation coal seam in the Ohobulake mining area are mainly forest peat swamp facies and living peat swamp facies. Mainly, the coal facies of the Taliqike Formation coal seam in Aai Dongfeng Mine is mainly forest peat swamp facies, while the coal facies of Group A coal seam in Hotan Buya Mining Area is mainly transitional peat swamp facies (Table 3-60).

The Jurassic coal facies are mainly forest peat swamp facies in the Kongquehe-Lop Nur coalfield and Wuqia coalfield in the east of Tariffa and in the area from Wuitak to Yarkand and Qipan in southwestern Tariff. The Duwa-Hotian Buya area in the southwestern part of Tarzan and the southeastern part of Tarzan are dominated by dry peat swamp facies and transitional peat swamp facies.

On the plane, in most areas on the northern edge of the Tarim Basin, the Kongque River-Lop Nur area in the east of Tarim Basin, the Wuqia area and the western area of ??southwest Tarim, coal seams are formed in a shallow lake to semi-deep lake environment, and forest peat develops Swamp facies and living peat swamp facies. Alluvial fan and river environments are mainly developed in the eastern end of the northern edge of the Tarim Basin, the eastern part of southwestern Tarim and the southeastern part of Tarim Basin. Coal seams are formed in dry peat swamp phase and transitional peat swamp phase (Figure 3-54).

Figure 3-53 Coal facies distribution map of the Xishanyao Formation coal seam in the Junggar Basin

Table 3-60 Jurassic coal facies characteristics table in the Tarim Basin

Continued table

Figure 3-54 Jurassic coal facies distribution map in the Tarim Basin

4. Coal facies distribution in the Tuha Basin

(1) Badaowan Formation coal facies And distribution

The dry peat swamp facies is mainly distributed in the south near the Liodun uplift, such as the Sandaoling mining area and the Qiketai to Shisanjianfang area. During the deposition period, these areas were mainly peat swamps developed after the abandonment of braided rivers or braided river deltas or in inter-river areas. Because this type of environment is unstable, peat bogs often expose the underwater surface, and peat bogs are prone to forming an oxidative environment. Therefore, in these areas, the content of inert components in coal is quite high. For example, dark coal layers rich in silk bodies can appear nearly 2 m thick in the Sandaoling mining area; forest peat swamps are mainly distributed from Tuokxun to Hami, around Qiketai and the Sandaoling mining area. The vitrinite of coal in these areas is dominated by structural vitrinite, containing more semi-vitrinite; the living peat swamp phase is mostly distributed in the central zone of the northern depression, and this coal phase is mainly developed in the inter-delta distributary bays, prodeltas and In the swamp phase at the edge of the lake, there are often deposits of higher plant leaves carried by running water in the swamp environment, such as Qiquan Lake and Kekeya Mine; open water peat swamps are distributed from Qiquan Lake to Shanshan, Xiaocao Lake and Taoshuyuan area (Figure 3-55).

Figure 3-55 Coal facies distribution map of the Badaowan Formation in the Tuha Basin

Figure 3-56 Coal facies distribution map of the Xishanyao Formation in the Tuha Basin

( 2) Coal facies and distribution of the Xishanyao Formation

The coal facies types of the Xishanyao Formation are similar to those of the Badaowan Formation. Generally speaking, the water covering depth of swamps in the eastern zone increases, and a large area of ??open water swamp facies appears in the Sandaoling mining area; the Dananhu mining area and the Shaer Lake mining area are mainly dry forest peat swamp facies; the northern part of the northern depression is still covered with peat swamps and open areas. The water body is dominated by swamp phase (Figure 3-56).

5. Coal facies distribution in the Ili Basin

The coal facies of the Jurassic coal seams in the Ili Basin are divided according to coal facies indices such as GI, TPI, MI and WI. The results show that the Jurassic coal seams in the Yili Basin mainly develop dry peat swamp facies, transitional peat swamp facies, forest peat swamp facies and living peat swamp facies. The coal facies of the Badaowan Formation coal seam are dominated by forest peat swamp facies and living peat swamp facies, while the coal seams of the Xishanyao Formation coal seam are dominated by dry peat swamp facies and transitional peat swamp facies (Table 3-61). On the plane, the surrounding areas of the basin mainly develop alluvial fan and river environments. The coal seams are formed in dry peat swamp phase and transitional peat swamp phase. In the eastern part of the basin near the uplift, such as Nilek, a semi-deep lacustrine environment develops. The coal seams are formed in living peat char. Swamp phase. In the central part of the basin near the B-2 hole, the coal seam was formed in a shallow lake to semi-deep lake environment, and developed forest peat swamp facies and living peat swamp facies.

Table 3-61 Coal facies parameters of the Jurassic coal seam in the Yili Basin

6. Coal facies distribution in the northern Qaidam Basin-Qilian area

Qaidam Basin and The Jurassic coal seams in the Qilian area mainly develop dry peat swamp facies, transitional peat swamp facies, living peat swamp facies and a small amount of forest peat swamp facies (Table 3-62).

Table 3-62 Characteristics of Jurassic coal facies in Qaidam Basin and Qilian area

Figure 3-57 Distribution map of Jurassic coal facies in northern Qaidam Basin and Qilian area

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The coal facies of the coal seam in the Yuka mining area in the western part of Qaidam Basin are mainly living peat swamp, dry peat swamp and transitional peat swamp facies. To the east, the coal facies of Jurassic coal seam in Dameigou mining area are dry peat swamp and transitional. The coal facies of the Jurassic coal seams in the Lvcaoshan mining area and the Datouyang mining area are dominated by transitional swamp facies, while the Jurassic coal facies in the Wanggaxiu mining area at the eastern end of the northern Qaidam Basin is dominated by living peat swamp facies.

The Jurassic coal facies in the Muli mining area in the western Qilian region are transitional peat swamp facies and living peat swamp facies. The hot water mining area is dominated by forest peat swamp facies, followed by transitional peat swamp facies. The Haider mining area is a living peat swamp facies, and the Moeller mining area is a transitional peat swamp facies. The Jurassic coal facies in the eastward Datong mining area is dominated by dry peat swamp facies and transitional peat swamp facies (Table 3-62 and Figure 3-57).

On the plane, the peripheral areas of the Qaidam Basin mainly develop alluvial fan and river environments. Coal seams are formed in dry peat swamp phase and transitional peat swamp phase. The Yuka Mining Area, Dameigou Mining Area, and Baishushan Mining Area The lower layers of the Hewanggaxiu mining area develop a shallow lake to deep lake environment, and the coal seams are formed in the active peat swamp phase (Figure 3-57).

Alluvial fan and river depositional environments are mainly developed around the Qilian Mountain Basin Group, and coal seams are formed in dry peat swamp phase and transitional peat swamp phase. Some layers in the Hotwater Basin, Muli Basin and Yaojie Basin develop a humid shallow lake to deep lake facies environment, and the coal seams are formed in the forest peat swamp facies. The Haider mining area develops a lake environment, and the coal seams are formed in the living peat swamp phase (Figure 3-57).

Figure 3-58 Carboniferous-Permian coal facies distribution map in the Ordos Basin

7. Coal facies distribution in the Ordos Basin

(1) Carboniferous-Permian Coal facies distribution

The coal facies of the Carboniferous-Permian coal seams in the Ordos Basin have the characteristics of zoning distribution (Figure 3-58). The dry swamp facies is mainly distributed from the northern edge of the basin to the meander, Fugu and Zhuizhi. The northern part of the mountain and the southern edge of Tongchuan; the living water swamp facies is distributed in the central part of the basin from Liulin to Hengshanbao; the open water facies is mainly distributed in the area south of Wulusitai in Ningxia; the southern part of Zhuizhuishan to Shenmu and the line from Huanxian to Hancheng Develop forest peat swamp facies. From bottom to top on the profile, the depth of swamp water cover during the coal seam formation period has an increasing trend. For example, the lower part of the coal seam in Baode, Pangpangta and Hejin mines in Shanxi is dominated by living water swamp facies, gradually turning into dry peat swamp upwards (Table 3- 63).

Table 3-63 Characteristics of Carboniferous-Permian coal facies in the Ordos Basin

Continued table

Figure 3-59 Coal facies of the Jurassic Yan'an Formation in the Ordos Basin Distribution map

Table 3-64 Jurassic coal rock component analysis and coal phase parameter statistical table

Continued table

(2) Jurassic coal phase Distribution

The coal facies distribution pattern of the Jurassic Yan'an Formation is relatively obvious (Figure 3-59). On the plane, the western edge of the basin is dominated by dry peat swamps, but there are some forest peat swamp facies and living peat swamp facies distributed in Rujigou, Carbonshan, Huating and other mining areas; the northern edge of the basin mainly distributes dry peat swamp facies; Ningxian, The Yanchi area is a forest peat swamp facies; living peat swamps are distributed along the Shenmu, Yulin, and Hengshan lines; and the central areas of the basins such as Fuxian, Yan'an, and Zichang are open water facies.

The coal phase also has obvious patterns in the longitudinal direction. For example, the lower part of the main mining coal seam in Rujigou Mining Area in Ningxia and Dongsheng Coalfield in Inner Mongolia is mostly dry peat swamp facies, which gradually changes upward to transitional peat swamp or living peat swamp facies (Table 3-64), reflecting the increase in overlying water during the deposition of Jurassic coal seams. trend.