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The Research On Distribution Regularities Of Shale Gas In Upper Paleozoic In The Guangxi Area

Posted on:2014-10-31Degree:MasterType:Thesis
Country:ChinaCandidate:Y GongFull Text:PDF
GTID:2250330401480691Subject:Mineral prospecting and exploration
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With the sustained and rapid development of economic society and the adjustment of energy structure in our country, the demand for clean energy such as natural gas is increasing rapidly, hence the contradiction between energy supply and demand would be more and more obvious.The emergence and development of shale gas brings hope to solve the problem of energy crisis, because of its great resource potential and economic benefits.Shale gas is a natural gas which is found in organic-rich shale formation in adsorption state and free form. In Guangxi region of China, mud shale is widely distributed in the upper Paleozoic. Residual organic matter is very rich, the thermal evaluation of organics is moderate and the hydrocarbon generation potential is very large. It’s petroleum geologic characteristics, is very similar with the gas shale of United States of America and the study of the reservoir formation conditions and regularities of distribution will most likely achieve the breakthrough of shale gas exploration in Guangxi area. This will open up a new field of natural gas exploration in Guangxi area.According to the petroleum geological survey conducted in Qiannan depression, Guizhong depression, and Nanpanjiang depression in Guangxi area, we judged that the permain to Triassic of Upper Paleozoic has well-developed marine black shales deposition, which is mainly distributed inYujiang formation of Lower Devonian and Donggangling formation of Middle Devonian, Yanguan formation and Datang formation of Lower Carboniferous and Longtan formation of Upper Permian. Combined with drilling data and results of previous studies, by measuring the field geological profile and practical exploration, it suggests that, the Middle Devonian and Upper Triassic shale form two sets of regional shale while the Lower Devonian and Lower Carboniferous shale also form two sets of local shale. During the early Devonian period, the study area mainly developed basin facies dark mudstone shale deposition which was found in Yujiang formation in the upper part of Lower Devonian. This deposition is mainly distributed in Guizhong and Nanpanjiang depression with the thickness of200~300m. In the Middle Devonian, due to the high sea level rise, the study area has mainly developed bathyal water to deep water basin facies of dark mudstone shale deposition. It is distributed in Qiannan depression, Guizhong depression and Nanpanjiang depression with the thickness of300~600m. With the descending of sea level in Early Carboniferous, black shales were mainly distributed in Yanguan formation in the Guizhong depression sedimentary basin facies, but little were distributed in Qiannan depression and Nanpanjiang depression. The thickness of dark mud shale in Guizhong depression is400-500m. In upper Permian period, the study area mainly developed back-arc rift basin and bathyal dark mud shale deposition, which are distributed in Qiannan depression, Guizhong depression and Nanpanjiang depression, with the thickness of150-250m.The geochemical index analysis of the rock samples collected from the wild shows that TOC high value areas of Lower Devonian shale are mainly distributed in Nandan-leye-Wangmo area which forms the junction of Nanpanjiang depression and Qiannan depression, and the northern area of luzai in Guizhong depression. TOC value is more than1%and the type of organic matter is generally dominated by carbon type Ⅱ1. Ro is distributed in2.0%-3.0%in Qiannan depression and Guizhong depression and more than3%in Nanpanjiang depression. In the Middle Devonian, TOC value in Guizhong depression is above1%. High TOC value distribution is Ceheng-Tian’e-Nandan area, which is in between Qiannan and Nanpanjiang depression and most of the organic matter types are of carbon type Ⅰ-Ⅱ1. The Ro value in the Middle Devonian shale in Qiannan depression and Guizhong depression is between2.0%-3.0%, while the Ro value is above3%in most regions of Nanpanjiang depression. The area where Lower Carboniferous dark-colored shale TOC is more than1%is distributed in Guizhong depression and the southern of Qiannan depression, most of the organic matter is type II. In most of the Qiannan region and the northeast and southeast of Guizhong depression, Ro is between1.0%-2.0%, in the southwest of Qiannan depression, Western and southern of Guizhong depression and southern of Nanpanjiang depression, Ro ranges from2.0%-3.0%, and Ro is above3%in most regions of Nanpanjiang depression. In most regions, Upper Triassic shale TOC is lower than0.6%and the organic matter types are of carbon type Ⅱ-Ⅲ. Ro is less than2%in most regions of Qiannan depression and Guizhong depression, while in most regions of the Nanpanjiang depression Ro is more than3%. In summary, the Lower Carboniferous shale is widely distributed, with high organic abundance, and organic matter type is carbon type Ⅱ, so shale gas generating conditions is good. The Middle-lower Devonian shale is more wildly distributed, with maximum thickness and maximum abundance of organic matter, and for this reason, the shale gas generation conditions are the best. The Upper Triassic shale has a wide distribution, because of its limited thickness. Shale organic matter abundance is therefore low, and shale gas generating conditions has not developed.By doing the whole rock analysis and X diffraction analysis on the collected samples, compared with the shale reservoir physical data in Sichuan area, we find that the preservation condition and the sealing ability of cap rock are good in Guangxi area. Reservoir physical property of Lower Carboniferous shale in Guizhong depression is better than that of Cambrian and Silurian gas in the Sichuan Basin. Shale reservoir physical property of Middle-Lower Devonian is close to that of Sichuan Basin. In view of the industrial gas flow which have been obtained from Well201in the Sichuan Basin in the Cambrian, Silurian shale, it can be concluded that the Lower Devonian-lower Carboniferous shale gas in the Guizhong depression has well enrichment conditions.Considering the actual situation of shale gas exploration in Guangxi area, the enrichment characteristics of shale gas in the Guangxi area are ultimately identified in that, the thickness of shale is above100m, burial depth is above500m, and TOC of shale is above1%, Ro ranged from1%to3%. Considering the shale gas exploration prospect of Upper Paleozoic in Guangxi area, the most favorable exploration area of Upper Paleozoic shale gas in Guangxi is distributed in the areas around Nandan, Du’an and the Eastern area of Liuzhou. The second favorable zone distribution is located in Tian’e-Hechi and Dahua-Xincheng-Heshan-Laibin-Luzhai areas. The third favorable zone is located in Huanjiang-Luocheng-Liuzhou and Wuxuan-Binyang areas.Through comparing the accumulation conditions in the neighboring area of Sichuan Basin, with reservoir-forming condition of Devonian-Permian shale in Guangxi area, such as the sedimentary thickness of shale, maturity of organic matter, organic matter content and type, fracture development degree,is very similar to that in Sichuan basin. They can be compared, according to calculations by using analogy method. Geological resources of Upper Devonian shale gas is3400.10~6136.98×108m3, geological resources of Middle Devonian shale gas is15958.38~33667.70×108m3and the geological resources of Lower Carboniferous shale gas is20584.4349370.74×108m3. Prospective resources of shale gas of the three layers add up to3.99-8.92×1012m3.
Keywords/Search Tags:hydrocarbon potential, reservoir physical property, favorableexploration area of shale gas, the upper Paleozoic, Guangxi area
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