| Based on sequence stratigraphy and Sedimentary facies, the thesis applied the source rock geochemistry,combined with drilling, seismic and field survey data, and study the source rock quality and distribution forecasting analysis in the Changling fault depression layer. Through the comparison between source rocks and geochemical characteristics of natural gas, natural gas origin analysis was done from component, carbon isotope characteristics; migration and accumulation of natural gas tracer analysis was done from the characteristics of saturated hydrocarbons, aromatic hydrocarbons and light hydrocarbon in source correlation. On the basis of TSM basin simulation technique, the thesis shows the dynamic evolution process of source rock thermal hydrocarbon generation history in fault depression layer, and simulate accumulation trend of natural gas in fault depression of tectonic evolution frame in different periods of time. Combined with the reservoir characteristics and gas accumulation period, the thesis has s comprehensive analysis of natural gas reservoir forming condition, the rule of the fault depression layer, and the prospect evaluation of natural gas resource. The main conclusions and innovations are as follows:1) The source rocks in Changling faulted depression layer were developed in the Huoshiling formation, Shahezi formation and Yingcheng formation. The source rock in Shahezi Formation is the highest organic matter abundance, and then, the Huoshiling and Yingcheng formation source rocks. The higher organic matter abundance of source rock is distributed in the deep part of every sub-sag.The data of the content of organic carbon, chloroform bitumen "A", pyrolysis hydrocarbon generation potential, and total hydrocarbon show that the source rocks’ organic matter abundance in Huoshiling formation is medium- high, Shahezi formation good-medium, and Yingcheng formation medium. The source rock is obviously different in different layers of every tectonic belt, there were high organic matter abundance and the lateral variation of larger anisotropy in the Shahezi formation and Yingcheng Formation of Chaganhua sub-sag, the organic matter abundance of source rock is higher in Huoshiling formation and part of Yingcheng Formation in Dongling tectonic belt; according to the drilling speculated, the higher organic matter abundance of source rock is distributed in the deep part of Changlingmuchang sub-sag.2) The type of organic matter is Ⅱ- in general, a small amount ⅢisⅠ, the source rock’s organic matter type is slightly better in Dongling area of Huoshiling formation and Yingcheng formation.The organic matter type of source rocks shows characteristics of diversity by comprehensive analysis of the data, suchas the whole rock macerals identification, C-H-O elemental analysis, the prolysis data, the kerogen carbon isotopes test. The type of organic matter is Ⅱ1-Ⅱ2, Ⅲin general,a small amount of type isⅠ. The source rock’s organic matter type is better,which is mainly Ⅱ1-Ⅱ2 in Dongling tectonic belt of Huoshiling formation and Yingcheng formation. The source rock’s organic matter type is relatively poor, which is mainly Ⅲin Chaganhua sub-sag of Huoshiling formation and Yingcheng formation.3) The maturity of source rock is high overmature stage, which is higher in the northern area than in the southern area, and in the southern area, Dongling tectonic belt of Huoshiling formation is mature and Yingcheng formation is high mature stage. In general, the distribution of Ro in Dongling area is around 0.5~2.5% or so, which is 0.7~3.5% in Laiyingtai- Yaoyingtai- Chaganhua area.By comparing the maturity of source rock in the same layer, the Ro is highest in2.5-3.5% in the north of Chaganhua sub-sag’s Huoshiling formation, while which is highest in 1.5-1.8% in the southern; in the Yingcheng formation the Ro is highest in3% or so in the northern, while it is highest in 2% or so in the southern; in the Shahezi formation,there is no difference, which is the highest at around 2.5%.4) The origin of natural gas of Changling fault depression is the mixing of the high overmature coal type and oil-type. By analyzing the natural gas component and carbon isotope properties’ s test result, the natural gas is mainly overmature coal type gas in Yaoyingtai and Daerhan belt structure; Dongling tectonic belt the mixed high mature kerogen cracking gas with the sapropel-humus type oil associated gas, Chaganhua sub-sag the main coal type gas; part of oil type gas in the east slope of the northern.5)By comparing the Source’s biomarkers, light hydrocarbon fingerprints and other indicators,it shows that in Changling fault depression the natural gas mainly comes from the coal measure source rocks of Shahezi formation and Yingcheng formation, followed by the fault depression layer’s oil cracked gas and associated gas, which mainly comes from the source rock of good kerogen type in Huoshiling formation and Yingcheng formation. The differences of source rock development and evolution lead to differences in the origin of natural gas in the different structural belt.In Yaoyingtai structural belt the nature gas mainly comes from the source rock in the Shahezi formation--Yingcheng formation in Chaganhua sub-sag, parts of the Qianshenzi sub-sag contribution; in Dongling structural belt in addition to the nature gas which comes from its own oil associated gas of source rock in the Huoshiling formation--Yingcheng formation, the light hydrocarbon fingerprint showed that there may be derived from coal measure source rocks in Shahezi formation--Yingcheng formation in Chaganhua sub-sag.6) TSM basin simulation shows that the source rock of the fault depression layer isn’t continuous hydrocarbon generation from the end of the Yingcheng formation to the end of Qingshankou formation, and the chief source rock’s layer is different in different periods. In general, the main source of natural gas is the coal source rock in Shahezi formation, which is oil generation in the area of better type of source rock in moderate maturity conditions in Huoshiling formation and Yingcheng formation.Dynamic simulation results show that every source rock of the fault depression layer entered the oil generation threshold respectively at the sedimentary end of Shahezi formation, Yingchang formation and Quantou formation. Now the source rock is in high over mature stage in every sub-sag, after the sedimentary end of Qingshankou formation gas was mainly generated, the center of the gas generation intensity is located in the deep depression of Changlingmochang Chaganhua and Qianshenzi sub-sag. The accumulative hydrocarbon generating quantity of the source rock in the fault depression is 19.04×1012m3; the largest amount is in Shahezi formation; it is 120-140×108m3/km2 in Changlingmochang sub-sag. Due to the continuous uplifting condition in the late fault depression, the source rock in high position of Dongling structural belt entered the oil generation window at the sedimentary end of Qinshankou formation, until now it has been in the main stage of hydrocarbon generation.7) The simulation of hydrocarbon migration and accumulation showes that the multi period tectonic evolution leads to hydrocarbon migration and accumulation in different directions; the oriented region of the long-term hydrocarbon migration and accumulation is the favorable exploration belts, such as Yaoyingtai, Daerhan, Dongling, Qianqihao,etc. The oriented region of the hydrocarbon migration and accumulation in the late coincide with the exploration result, so late hydrocarbon accumulation is one of the key factors.The oriented region of the nature gas migration and accumulation in Chaganhua, Qianshenzi and Donglingmuchang sub-sag is the structural belt as Yaoyingtai, Qianshenzi, Daerhan, Beizhengzhen and Dongling. The hydrocarbon accumulation reservoir is around the ‘uplift within the sag ‘ in the deep part of the sub-sag during the fault period, while during the depression period it goes further to the high part of structural in fault depression layer. The accumulation layer of nature gas which mainly comes from the source rock of Shahezi formation is the Yingcheng formation, Denglouku formation; for example, the nature gas resource abundance is 0.7296 × 108m3/km2 in Yingcheng formation in Yaoyingtai structural belt, followed by Shahezi formation and Huoshiling formation.8) The hydrocarbon accumulation has the pattern of "multi-stage hydrocarbon generation, multiple sag for hydrocarbon, hydrocarbon accumulation near the source, late hydrocarbon accumulation "Hydrocarbon-generation evolution of source rock in fault depression layer matches with the hydrocarbon accumulation period which is revealed by reservoir inclusion. The two main periods of hydrocarbon generation in fault depression layer are the late fault depression stage and the end of the Early Cretaceous. Thick source rock supplies the gas for favorable traps respectively in multi sub-sags. The natural gas migrates and accumulates near the source, and the oriented region of the long-term hydrocarbon migration is the favorable reservoir formation area.The late Early Cretaceous(Quantou Formation sedimentary period) is the deep structure pattern formation stage, but also the deep source reservoir cap formation period. Therefore, early Late Cretaceous is the deep natural gas accumulation in the critical moment. Under the control of the faults controlling sags, tight reservoir(volcanic rock, clastic rock) and unconformity surface, the favorable belts for natural gas accumulation was formed around the high positions of structures n the three main sub-sags such as Changlingmuchang, Chaganhua, Qianshenzi. |
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