| Based on abundant application of sedimentology, mineralogy, petrology, structural geology, geochemistry and other multi-disciplinary theory, this paper studied the types of mineral resources in coal measures,distribution, geological factors of enriched and association characteritics of the western margin of Ordos Basin. Through the core sampling test of 4 drills, cbm, shale gas and coal coal measure dense gas and geochemical characteristics of hydrocarbon source rock, reservoir characteristics and gas bearing characteristics were detailly analysised. By trace elements in coal and coal ash composition analysis, combined with previous data, this paper analyzes aluminum, gallium, lithium and other metal minerals of the research area, as well as enrichment characteristics of uranium and oil shale. Comprehensive analysis of the results, the distribution layer segment and a combination of features of the coal bed methane, shale gas and coal dense coal gas were studied, a symbiotic combination of coal mineral resource model was established, 3 kinds of symbiotic combination type were divided.There are two categories of the mineral resources types in the western margin of Ordos Basin, which are relatively independent and have different degree of genetic relationships and coupling relationship: coal, coal bed gas, shale gas, tight sandstone gas, oil shale and uranium deposit are primary energy mineral resources; Coal metal mineral includes bauxite, gallium, lithium, etc.. The western margin of the basin is rich in coal resources, coal reserves accumulated exploration eligible 65,748,310,000 tons, forecast resources 214,413,980,000 tons, both total 280,162,290,000 tons. The metamorphic grade of coal is decreasing from north to south, in the north of Zhuozishan, Helanshan coalfield to fat coal, coking coal, anthracite,mainly to Ningdong southward coalfield southward with gas coal, non-caking, to Ningnan and Longdong coalfield with long flame coal.According to the collected information and the tested data that including coal distribution rules, porosity and permeability characteristics, isothermal adsorption experiments, gas content and gas content, we can see the western margin of the basin CP coal measure shale gas is developed in the Zhuozishan, Shizuishan, Weizhou etc, the gas content are respectively 5.6 m3 / t, 3.5 ~ 8.4 m3 / t and 2.87 ~ 10.68 m3 / t.J Coal measure cbm is developed in Rujigou region, the Ro is in the range of 2.54 ~ 3.46%, the porosity degree is in the range of 1.2 ~ 7.8%; the gas content is about 0.25 ~ 15.47 m3 / t above 250 m, 7.49 ~ 21.06 m3 / t under 250 m. Oxidation zone affected by wind, red baidunzi, horizontal relative Emission Gas City area for 1.38 ~ 4.37 m3 / t, Huating region of gas relative Emission 1.82 m3 / t, with the mining depth increasing, it can be speculated that these areas have great potential of the deep CBM resources.According to the geochemical characteristics test of distribution rules, TOC, rock pyrolysis, Ro and the reservoir test analysis of XRD, porosity and permeability characteristics of dark mudstone, we can see the western margin of the basin CP coal measure shale gas is developed in the Zhuozishan, the average TOC content of Z hole dark mudstone in Taiyuan group lower section, upper section and Shanxi group lower section are respectively 3.00%, 10.39% and 2.74%, the type of organic matter is Ⅲ type, the Ro is in the range of 0.86 ~ 0.94%; The content of brittle mineral in mudstone is 45.5%, the porosity degree is in the range of 1.07 ~ 1.22%, the permeability is in the range of 0.001 ~ 0.01 m D, with good reservoir-condition. J coal measure shale gas is developed in the Jijiajing and Anjia Village, the TOC content of J hole dark mudstone in five segments of Yan’an group are respectively 3.97%, 3.57%, 7.69%, 8.74% and 1.67%, has higher organic matter content and organic matter types Ⅰ~Ⅲ, the Ro is in the range of 0.64 ~ 0.92%, in the high maturity large gas generation stage;The content of brittle mineral in mudstone is in the range of 31.8 ~ 39.1%, the porosity degree is in the range of 2.51 ~ 4.77%, the permeability is in the range of 0.003 ~ 0.004 m D, with good raw shale gas reservoir conditions. The average TOC content of Anjia Village A hole dark mudstone in the first segment of Yan’an group is between 0.11 to 0.85%, only individual samples are up to 59.43%, the average content of the second and third segment of Yan’an group are respectively 4.35% and 19.62%, has organic matter types Ⅰ ~ Ⅲ, the Ro is in the range of 0.67 ~ 1.02%, in the high maturity large gas generation stage; the content of brittle mineral in the mudstone is in the range of 29.6 ~ 34.1%, with good raw shale gas reservoir conditions.According to the reservoir test analysis of the distribution law, porosity, and permeability of tight sandstone, we can see the CP coal measure dense gas of the western margin of the basin coal is developed in the Zhuozishan, the thickness of the Zhuozishan coal seam and the dark mudstone is 51.6~73.8m, the Ro are respectively in the range of 0.62~1.04% and 0.86~0.94%, the ZX08 hole permeability of tight sandstone is 0.059 m D, the porosity degree is 0.79%, with good reservoir-condition. Although the dark mudstone of the Helan Mountain Coalfield is too mature, but the Ro of Shanxi group coal seam in the area of Shitanjing and Shizuishan is in the range of 0.83~1.19%, in the high maturity large gas generation stage, the average thickness of tight sandstone layers is about 61.62 m, the thickness is up to 107.96 m in Qingshuigou of Shitanjing mine area, also is the possible favorable area of dense gas.The J Coal measure dense gas is developed in the Jijiajing area, the thickness of the Ningdong Yan’an group coal seam and dark mudstone is 44.65 m, the Ro are respectively in the range of 0.46~0.83% and 0.64~0.92%, the JM107 hole permeability of tight sandstone is 0.019 m D, the porosity degree is 6.65%, with good reservoir-condition.According to the coal ash composition analysis, the content of aluminium oxide in Carboniferous--Permian coal is much higher than that in Jurassic coal measures in the western margin of Ordos Basin. The content of aluminium oxide in Yanan Formation’s coal ash is generally not more than 20%.Helan mountain coalfield, the average is about 40.78%, The highest content of aluminium oxide is in no. 3 coal of Shizui mountain mine, up to 49.14%.Average content of aluminium oxide in Shanghaimiao mining area is about 38.53%,including Al2O3 content as high as 44.06% in No.9 coal of the Great Wall three mine.In Hongdunzi mine and Hengcheng mine, the content of Al2O3 is in the range of 29.66~ 40.21%, average about 36.54%.The Al2O3 content is as high as 40.56% in No.2 coal of hengcheng mine.According to the trace elements in coal testing, Compared to the average of the trace elements in Chinese C-P coal,in C-P coal of the western margin of Ordos Basin Li is enriched, Ga is slightly enriched. The Li content was the highest in Shitanjing mine, up to 294ug/g, the highest content of Ga is in Sabatai mine, up to 40ug/g.Uranium mineralization in the western margin of the Ordos Basin mainly develops in Yanan Formation and its overlying Zhiluo Formation in Yuanyang Lake, Ciyaopu, Wang Wa area.At the top of the Yanan Formation develops roll type of uranium mineralization, roll uranium orebody is about 6km long, continuous distribution, in the depth of 250~420m.The 1-4 member of Yanan Formation developed lamellar uranium mineralization,the distribution direction is north-south along Yuanyang Lake-Fengjigou anticline.Roll type of uranium mineralization develops in the upper part of Yanan Formation and lower part of Zhiluo Formation in Wangwa of Ningnan coalfield.The grade of uranium mineralization is in commonly 0.012% ~ 0.06%, the thickness is about 0.1~3.80 m, the highest industrial grade in 404 drilling of yuanyang lake mine, up to 990 PPM.Jurassic coal measures in Yanan Formation in the western margin of the basin contains multiple oil shale layer, mainly distributed in Tanshan mine of Ningxia, Huating mine of Gansu, Ankou and other regions.Oil shale layer is often located in the upper coal seam, or interbedded with coal and mudstone layer. Tanshan region mainly has 8 layer of oil shale,which is distributed in the 1,2,3 member of Yanan Formation coal-bearing section. The total thickness is about 15 m, oil content is 2.0% ~ 2.0%.Oil shale in Ankou is located in the black mudstone,which is in the upper of the third coal-bearing member of Yanan Formation,with the thickness of about 4.8m.Oil shale in Huating mine is located at the bottom of No.4 coal in No.3 member of Yanan Formation, With the thickness of about 3.66 m. On the top of No.2 coal in No 4 member of Yanan Formation contains a small amount of oil shale,with the thickness of about 0.4m.The thickness of oil shale in Longdong area is commonly 4 to 36 m, oil content is about 1.5 ~ 13.7%.According to TOC, Ro, rock pyrolysis, pore permeability, XRD and other data tested from the actual core samples of the four drilling, we can analysis the possible distribution layer in each column of coalbed methane, coal shale gas, tight gas and the combination characteristics of the three kinds of gas. In the depth of 356~362m of Taiyuan Formation in ZX08 drilling, dark mudstone with higher TOC content, 1.86~27.96%, Ro is 0.86%, Tmax is 455~461 ℃;The reservoir’s brittle mineral content is as high as 45.2%,the porosity is 1.17%,the permeability is 0.01 m D. This section has the ability of hydrocarbon generation and good reservoir conditions, so it is the favorable section of shale gas. At the bottom of about 340 m of the No 9, 10 coal in shanxi Formation, coal seam’s roof and floor are black mudstone, the thickness of black mudstone which is in the upper of No 9 coal is about 20 m, The black mudstone samples derived from the floor of No 10 coal in Z64 drilling, TOC content is 7.38%, Ro is 0.94%. So it is a favorable section for shale gas and coal-bed methane.In the depth of 286 ~ 300 m,coal-bearing formation are mainly composed of alternation of mudstone and siltstone, the TOC content of mudstone samples at that point is 0.19 ~ 2.25%,Tmax is 472 ℃. The porosity of siltstone of sample Z44 is 0.79%, the permeability is 0.059 m D.So it is a favorable alternation section for tight gas and shale gas.In the depth of 740 m of the lower Shanxi Formation in G702 drilling,the primary mineable coal seam is No 4 and No 5 coal.The Ro value of coal seam is 0.9~1.1%,and coal seams are in the stage of high mature gas generation.The overlying strata and the underlying strata are black siltstone and fine sandstone,and the thickness of sandstone is about 15 m.This section may be a potential coal-seam methane and tight gas interbedding strata.The TOC content tested from sample J72 about 954 m of JM107 drilling is 9.4%,the value of Ro is 0.7%,Tmax is 432 ℃,S1 + S2 is up to 25.15 mg/g, organic matter belongs to Ⅰ style kerogen, the ability of hydrocarbon generation is good, the brittle mineral content of mudstone is 39.1%, and the reservoir conditions is favorable.Underlying formation is coal seam and black siltstone with the thickness of 11.9 m,overlying strata is No 8 coal and black siltstone with the thickness of 12 m.So it is a favorable section for tight gas.No 4 coal is in the depth of 876 ~ 897 m,its roof and floor are black siltstone.The TOC content of Samples J48 reaches 23.58%, Ro is 0.64%, Tmax is 427 ℃, S1 + S2 is up to 44.69 mg/g, organic matter belongs toⅠstyle kerogen, the ability of hydrocarbon generation is good, the brittle mineral content of mudstone is 35.5%, and the porosity is 4.77%, the permeability is 0.004 m D, the reservoir conditions is good,so it is a favorable section for Coal-bed methane.The thickness of No 5-1 coal of the member of Yanan Formation in A drilling is about 1.9 m, Its floor is the dark grey argillaceous siltstone with a thickness of 2.65 m.The thickness of No 5-2 coal is about 0.82 m, its floor is black mudstone with the thickness of 0.5 m. The TOC contentit of black mudstone samples is 4.89 ~ 34.34%, the value of Ro is 0.86%, Tmax is 427 ℃, S1 + S2 is 17.65 mg/g, organic matter belongs to Ⅱ1 style kerogen,the ability of hydrocarbon generation is good, the brittle mineral content of mudstone is 34.1%, the interval for the good of the coal reservoir.So it is a favorable section for coal-bed methane.Contrast the characteristic parameters of coal, coal gas, uranium, oil shale and aluminum, gallium, lithium and other coal mineral resources between C- P coal and J coal in the western margin of Ordos Basin,coal mineral resources’ paragenetic association model is established:C- P coal mainly develops coal, coal measures gas, aluminum, gallium, lithium and other metal mineral.Coal species mainly are gas coal, coking coal, fat coal. Coal-bed methane, shale gas and tight gas develop mainly in the upper of Taiyuan Formation and in the lower of Shanxi Formation.The enrichment of aluminum, gallium, lithium is related to the source and marine deposits;J coal mainly develops coal, coal measures gas, uranium, and oil shale.Coal species mainly are long-flame coal and non-caking coal, coal species in Rujigou is anthracite.Coal measures gas mainly develop in the upper No 1,No 2 and No 3 member of Yanan Formation.Uranium mainly develops at the top section of Yanan Formation and the bottom of Zhiluo Formation, Oil shale mainly develops in the No1,2,3 member of Yanan Formation. Coal measures mineral in the western margin of Ordos Basin could be divided into three paragenetic association types:In the northern area coal measures mineral combination type is coal-coal measures gas-coal measures metal mineral, In the middle area Ningdong coalfield the combination type is coal-coal measures gas-uranium.In the southern area Huating and Tanshan coalfield the combination type is coal-coal measures gas-oil shale.The symbiotic coupling mechanism of coal measures mineral resources in the western margin of Ordos Basin are analysed.We can conclude that the sedimentary environment controls the material basis and enrichment center of coal mineral resources. Structure and thermal evolution controls the coupling metallogenic and the quality characteristics of coal mineral resources.The late tectonic movement controls the final positioning of the coal mineral resources and mining conditions. |
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