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Shale Gas Exploration Potential And Direction Of Upper Triassic-Lower Jurassic In Jiannan Area

Posted on:2013-07-04Degree:MasterType:Thesis
Country:ChinaCandidate:J LiFull Text:PDF
GTID:2230330374476768Subject:Mineralogy, petrology of ore deposits
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Shale gas is a kind of natural gas accumulation which is mainly assembled in the shale strata with multiple phase state. There is not only free phase gas existed in the fractures, but also absorbed gas on the surface of rock particles in the shale gas reservoirs. Its typical "self generate and self storage" feature distinguish the shale gas from other types of natural gas.With the growing demand of energy, shale gas is attracting much more concern for its emerging as an unconventional natural gas that can be got in practice. At present, large-scale commercial exploitations of shale gas have been achieved in North America. Recently shale gas has been taking a big proportion in natural gas production in the USA and still increasing. To carry out the domestic shale gas exploration and exploitation is of great practical significance.On the basis of the current situations of shale gas exploitations worldwide and the formation conditions of shale gas reservoirs,this paper surveys the depositing conditions of shale gas in Jian-nan region,and meanwhile judges whether this region exists shale gas depositing condition.Compared with the geological background of shale gas accumulation basins in U.S.A.,potential regions distributed with shale gas reservoirs are introduced macroscopically.In general,it is said that Sichuan basin,Ordos basin and the west Hubei and east Chongqing areas are the potential regions full with shale gas development.Palaeozoic formations are distributed in large areas in China with high formation thickness and generally high organic content,being able to be the key series of strata for shale gas exploration.By researching the gas reservoir characteristics in American shale basins and concluding the reservation conditions of shale gas reservoirs,we consider that the heavy shale in the anoxic environment in controlled depth can provide gas sources for shale gas and can be the reservoir strata.General organic content and thermal maturity are the geochemical indices affecting the shale gas generation; shale porosity,permeability and fractures are the main factors influencing shale gas storage; good sealing conditions can promote the shale gas accumulation,while fractures influence the shale gas reservation in a large scale.The tough shale itself can be the cap rock for its ultra low porosity and permeability sealing shale gas in the strata,being the typical continuous natural gas accumulation.Combining with the available data of upper Triassic-lower Jurassic systems,a system analysis of various aspects relating to the gas reservation is conducted.Jian-nan formation is located in Shuzhu synclinorium in the west Hubei and east Chongqing regions.The tectonic evolution of Shizhu palaeohigh region could be divided into fivephases:Caledonian,Hercynide-early Indosinian,later Indosinian-early Yanshan,later Yanshan-early Himalayan,as well as later Himalayan.The Hercynide-early Indosinian phase and later Indosinian-early Himalayan phase are key phases for the palaeohigh region’s formation and paulopast development,producing stratigraphic sequences such as Carboniferous system in Huanglong series,Permian system,Triassic system,Jurassic system and so on.The thickness is above5000m and series of reservoir combinations of generation,reservation as well as seal are formed.Further more,the lithology analysis of Triassic system-lower Jurassic system is conducted to select the ideal wells with comparably completed logging curves.Meanwhile,the typical logging curves of the massive argillutite,sandy argillutite and argillaceous sandstone in the upper Triassic system-lower Jurassic system are analyzed to get the criteria of log response.The thickness of upper Triassic-Jurassic period in deposit entering into the orgenic stage and being filled with fluvial facies and lacustrine facies is over4000m.There is good gas generation potential because the sedimentary environment is mainly wet-semi-dry fluvial facies,shallow lake facies and semi-deep lacustrine facies.Through recovering the ideal wells’denudation thickness and burial history,the geologic evolution in upper Triassic-lower Jurassic system in Jian-nan region is demonstrated,every period and the corresponding depth and thermal maturity is accumulated.Then the evolutionary process of target strata’s thermal maturity is estimated to evaluate this region’s thermal evolution degree. As to the TOC of shale, after the data analysis,we get the scope of TOC content.The shale strata in upper Triassic-lower Jurassic systems of Jian-nan region has generally low porosity,low permeability and immature fractures,so in the later exploitation stage,hydraulic fracturing method needs to be taken to promote the porosity and permeability. The upper Triassic-Jurassic systems in Jian-nan region are covered by the mid-upper Jurassic systems,of which the heavy argillite with little near surface fault is good sealing gland layer.With high mineralization and high chloride ion content as the hydrochemical characteristics,the shallow accumulation unit has favorable preserving conditions.This page mainly discussed the comprehensive application of well logging and seismic data for the prediction of shale thickness, organic matter abundance and the distribution of its maturity in upper Triassic-Lower Jurassic series of Jiannan area,then we delineated the enrichment zone of shale gas, and evaluated the amount of shale gas resources. The key shale horizon of this study area is the black shale that in the Dongyuemiao Member in ziliujing Formation of lower Jurassic.The prediction of effective shale thickness is using the amplitude-time method to caculate the interlayer time value,then multiplied by the corresponding speed value get ting from the model-based inversion.The prediction of organic matter maturity is on the basis of the velocity volume we have,calculated the porosity by using the Willie equation,then according to the the Schmoker transformation formula,the total organic carbon content can be predicted.In this process,we use Δlog R method to get a single well total organic carbon content at first, then set the single well TOC curve as the target curve,use the seismic attribute inversion technique for the horizontal prediction of the TOC,Finally,we superimposed the Ro and TOC distribution map of each shale layer to delineate enriched area of the shale gas.In addition, as the consideration of geological conditions and tectonic evolution, we use the analogy method to evaluate shale gas resources in the study area, and make a comprehensive analysis of shale gas distribution and of this area in the end.By prediction,we know that the thickness of the shale in the upper part of Dongyuemiao Member in ziliujing Formation of lower Jurassic is35.8m, and the maturity of its organic matter ranges from0.82to1.38%, and the total organic carbon content is about0.55to1.75%.While in the lower part of Dongyuemiao Member, the thickness of the shale is75.9m,and the maturity is0.65to1.90%,and total organic carbon content is0.75to1.39%. The shale organic matter abundance is (1.34to3.1)*108m3/km2effective shale area is about1570to1882.1km2, the estimated amount of resources is (2343.1-5375.1)*108m3.Thus, we believe that there is a thick shale formation in Dongyuemiao Member in ziliujing Formation of lower Jurassic, and it has a huge amount of resources.Take a consideration of the whole shallow shale formations in Jiannan, the Dongyuemiao Member in ziliujing Formation of lower Jurassic is a well-developed shale gas reservoir.
Keywords/Search Tags:shale gas, effective shale thickness, total organic carbon content, organicmatter maturity, enriched zone of shale gas, evaluation of resources
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