Characteristics And Mineralization Controlling Factors Of Oil Shale In Maoming Basin

Maoming basin is one of most famous oil shale producing area in China. Maoming basin is located in east of Guangdong province, covers the area of E110°38′～111°00′, N21°40′～21°54′,with total area of 400 km2。It's a Mesozoic- Cenozoic basin and stretches in N-W direction, lean to N-E. The Sediment of stratum was under the control of the Gaopengling fracture in Northeast.The predecessors mainly studied biomarkers, Hydrocarbon generation potential and its exploitation of oil shale in Maoming basin. There is lack of studying on the forming environment and ore-controlling factors of oil shale. The study of this thesis not only help to develop the theories of oil shale's cause of formation, but also has a huge realistic meaning.Oil shale in the Maoming Basin deposited in Youganwo formation of the Eocene-Oligocene and in Shangcun formation of Miocene. There are three mineral area deposited in Maoming basin from northern to southern, including Gaozhou oil shale,Maoming oil shale and Dianbai oil shale. The Youganwo formation distributed almost of the Maoming basin,but it only exposure in the southwest of Maoming Basin because of denudation. The Shangcun formation only develops in some area and distributes discontinuously in Maoming basin.Generally, the oil shale has the characters of light color in the top and of weight color like black or brown in the deep. The weight changes little along stretches orientation but increase greatly along incline orientation.The oil length augment gradually from west to east. The average oil length is 5.71% in Gaozhou ,6.23% in Maoming and 8.39% in Dianbai. There are some apparent negative correlation between oil grade and ash content, the ash content is 77.58% in west,74.20% in middle and 72.06% in east. And there are some positive correlation between oil grade and their calorigic value, the calorigic value is 5.24 MJ/kg in west, 6.89 MJ/kg in middle and 7.37 MJ/kg in east. By studying the types of pollen resolution record, kerogen in hydrocarbon source rocks by transmitted light fluorescence, chemical composition, pyrolysis parameters, The main type of kerogen is the sapropelic type and secondly is humic-sapropelic type.By analyzing H:C atomic ratio and O:C atomic ratio,the thesis conclude that the H:C atomic ratio between 1.3 and 1.46 and the O:C atomic ratio between 0.08 and 0.19,which belong to high H:C and low O:C.Through analysis of X-diffraction, the clay minerals in oil shale in Maming Basin mainly contain kaolinite,and illite,few montmorillonite and quartz . The maximun content of which can exceed 80%.The Character of Compositions of clay minerals indicate indirectly immature-low mature character of Organic matter evolution.The vitrinite reflectance of oil shale in Maming Basin is commonly 0.51-0.58,which is the beginning of oil -farming stage.The deciduous and broadleafed pollen is predominant in Youganwo formation , the average proportion of which occupies 73.1% in total Angiospermous Pollen, the average proportion of Subtropics and temperperate familiesor genera occupies50.8% in total seed plants xerophyte pollen such as Ephedra and Sedge ,which has the extensive distribution in Continental Asia in Middle Paleogene ,are uncommon in sample .based on analysis on pollen character in youganwo formation, the envirment then was warm and moist Subtropics and temperperate zone .on the basis of core, outcrop and testing analysis indoor data etc. We comprehensively analyzed distributed feature of stratum asynchronous in the basin. Studied result indicate that the thin gray oil shale and lignite interlayer, charcoal- shale was deposited in the fleet-lake environment. The thick puce oil shale was deposited in the semi-deep and deep lacustrine environment.The basin formed under the control of Gaopengling fault in northeast. Oil shale mineral belt was controlled by Jintang fault and Xinyu in the west. The seam strike was consistent with the fault strike and the mineral belt distributed NW-SE.The Youganwo and Shangcun group were controlled obviously by Jintang fault, while Dianbai mineral area was under the partly control of fault.The Yangjiao fault stretched from east to west is the south boundary of Dianbai mineral area and did not influence the oil shale. In Gaozhou mineral area, Shaocun oil shale only partly reserved half-baked ledge because of the uplifting in south of Jintang fault.The ledge thickness and deepness increased because of the ledge angle change steep in the north of Jintang fault.There are three depression from northwest to southeast on account of gurgitation in the basin's floor and under the control of Jintang fault and Yangjiao fault.the oil shale in the depression is thick and high oil percentage.But the thickness is thin in the middle of the basin and two blankness was find in the north of the basin.The fossil of tortoise, turtle, alligator and hydrophyte pollen are very abundant,which indicate that the organic matter source is exuberance including terraneous plant and hydrophily biology. These opinions accord with results of micro-constituents.The type of organic matter is sapropelic and humic-sapropelic.in the same time, some productions of experts have proved these results.In Gaozhou mineral area, the lake level changed frequently, disadvantage to organic matter sediment, lead to the thin thickness and oil percentage was laminated and lower than Maoming and Dianbai. In Shangcun stratum.On the condition of Subtropics and temperperate,there are a lot of plant and hydrophily biology,a great deal of crumb of terrestrial altitude plant flow into lake,which result in primary production augmented, and hydrophily biology and algae increased,this is the precondition of oil shale deposition.Conservation of OM need steady anoixc,this is the key factor of oil shale deposition. Delamination of lake by temperature and transgression formed steady configuration of liquid.Under oxic water,high sedimentation rates also can be helpful for OM conservation.