| The Sinian Dengying Formation in the frontal area of Micang Mountain is an important position for oil-gas exploration. Focusing on Tianxing No.1 Well and the profile of Yangba in Nanjiang region and combining previous research data, this thesis analyzes the development characteristics of source rock, reservoir stratum, bitumen and oil-gas preservation in the Sinian Dengying Formation in the frontal area of Micang Mountain, and discusses the prospect of petroleum exploration in the Sinian Dengying Formation in Micang Mountain front area.The Lower Cambrian Qiongzhusi Formation in the frontal area of Micang Mountain is the main source rocks of the Sinian Dengying Formation, including black carbonaceous shale, silty mudstone and argillaceous siltstone in the environment of shelf sedimentary, the organic matter type of which is type I in the over-mature stage. The reflectance of vitrinite is high in East and low in Eest, with the highest ratio(Ro>3.0%) in the Guiming Town and Nanmushu region in the Southeast and the lowest ratio(Ro<1.5%) in the Qiangzhuyuan and Yangba area in the Southwest. The organic matter abundance is comparatively low(the average value of Tianxing No.1 Well is 1.21%, the average value of Yangba profile is 2.34%) and is higher in North than that in South, declining from the mountain to the basin, and from the East side and the West side to the central region along the surrounding areas of Micang Mountain uplift. Effective source rock is thick(Tianxing No.1 Well is 269 m, Yangpa profile is 173m), the thickness of which decreasing from the Northwest to the Southeast. Generally, the source rocks in Tianxing No.1 Well of Micang Mountain uplift develops best, followed by Qiaoting and Guimin Town in Nanjiang.The reservoir stratum of the Sinian Dengying Formation in the frontal area of Micang Mountain mainly develops at the second section and fourth section of Dengying Formation. The lithology of the second section mainly includes prehnite dolomite, dolomite containing gravel and sand, laminated dolomite, maerl dolomite, stromatolitic dolomite and siliceous dolomite. The type of pore space includes intergranular(micro) pore, dissolved pore, fracture and cavern developed along formation, forming a reservoir space combination of intergranular(micro) hole, dissolved pore, fracture and dissolution pore-cavern. The lithology of the fourth section mainly includes psammitic dolomite, stromatolitic dolomite, laminated dolomite, thrombolite dolomite and dolomicrite.The type of pore space includes intracrystalline(micro) pore, intergranular pore, dissolution pore, framework pore and structural seam, forming a reservoir space combination of intracrystalline(micro) pore, intergranular pore, dissolution pore, and fracture, which mainly contains tectonic fractures. The reservoir has low reservoir physical property and small correlation coefficient of porosity-permeability, belongs to fractured or pore-fractured type of reservoir. Vertically, the fourth reservoir stratum of the Dengying Formation is a better favorable reservoir. Horizontally, Tianxing No.1 Well in the southwest of Micang Mountain uplift is a better reservoir development area in the investigated area.The reservoir bitumen of the Sinian Dengying Formation in the frontal area of Micang Mountain commonly developed. Vertically, bitumen mainly developed in the fourth section of Dengying Formation, while there is very little bitumen on the top of the second section, which is significantly less that in in the fourth section, with characteristics of obvious continuous concentration and high filling rate in upper section, as well as dispersal development from top to bottom and low filling rate in lower section. The development of bitumen of the fourth section of Dengying Formation mainly occurs in the top area covering from 0-80 m, followed by the middle area covering from 90-220 m, bitumen in the bottom area develops worst. Horizontally, the distribution of bitumen content declines from the uplift of Micang Mountainto the surrounding areas.The cap rocks in Micang Mountain front area develop completely, including the mudstone of Lower Cambrian Qiongzhusi Formation, mudstone of Lower Silurian Longmaxi Formation, Lower-Middle Trias Series Leikoupo Formation, gypsum salt rock of Jialingjiang Formation and mudstone of Upper Triassic-Jurassic. They are thick and stable, with good continuity and tight physical characteristics, which provides good static-preservation condition for the preservation of reservoir stratum of Dengying Formation.Although the reservoir stratum of Sinian Dengying Formation in the detachment fold belt in the south edge of Micang Mountain has good reservoir conditions and was once formed large-scale paleo-reservoir, it cannot preserve oil and gas anymore beacuse its cover suffered serious denudation from tectonic uplift and cutting from fault. Therefore, the region does not have good prospects for oil and gas exploration. However, the Sinian Dengying Formation in the anticline of Tongnanba, located at the southeast of the depression-basin-superimposed fold belt of North Sichuan depression Basin, even with poor petroleum geological conditions when compared with the detachment fold belt in the south edge of Micang Mountain, is preserved profoundly and has good prospects for oil and gas exploration. |
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