| The Yingxi area is located in the Yingxiong ridge tectonic belt of western Qaidam basin.Recently,which has achieved significant progress in the under-salt oil and gas exploration of Paleogene.Continuous drilling has been made in daily output of thousands tons.Based on previous research,shi 41-2 well and shi 49-1 well are choosed as the study objects,focusing on the weakeness of study on characteristics of sedimentary and reservoir,diagenesis and the mechanism of reservoir formation,accumulation regularity,conducting comprehensive core observation and the sedimentary facies analysis,thin section identification and diagenetic facies analysis,field emission scanning electron microscopy and electron probe microanalysis,whole rock geochemical analysis and the of sedimentary environment analysis.The study obtained the following main results:The typical phase markers such as botryococcus braunii,pellets and rhythmic layer,as well as typical lithofacies such as saline shale,algal limestones,mud limestones and dolomicrite are identified in study area of upper Xiaganchaigou formation.It is suggested the enrichment of algal,halophilic organisms and high biological productivity of lake basin in the paleogene in western Yinxi area;Faecal-granulite and fresh-water disturbed limestone are favorable for forming dessert reservoirs,which have the characteristics of source-reservoir interaction,source-in-source accumulation and oil-bearing accumulation in a large area.The typical facies markers such as storm debris,storm stirred structure and storm mixed structure,as well as typical lithofacies types of storm clastic rock and storm mixed rock are identified.The research indicates that the Paleozoic climate of qaidam basin is hot and dry,and the occurrence of storm events is high.Storm deposition promotes the salinity of lake water,sediments mixing and dolomitization of carbonate rocks.The typical flood disturb phase markers such as sandy clastic,asphaltic clastic,turbidite laminae,grain sequence stratification and deformation stratification,as well as the typical lithofacies assemblages such as Metalitite,turbidite,sandy limestone,argillaceous limestone areidentified.It indicates that there is a short rainy season in the hot and dry climate background.The hypopycnal flow and turbidity current induced by the rainy season inject a large amount of fresh water and terrestrial sediments into the saline lake basin,promote the mixing of desalination and sediments in the lake basin,and improve the biological productivity,which is conducive to the formation of high-quality iron dolomite reservoir with high order.It is characterized by near source accumulation of turbidite in saline lake basin.The achievements mentioned above have a great scientific significance to reveal the mechanism of which the The north drift of Indian plate and Tibetan plateau uplift effect on the Paleoclimatic change and sedimentary response in Qaidam basin,as well as storm deposition,flood deposition effect on sedimentation,diagenesis,reservoir formation,hydrocarbon formation and association formation,which have an important practical significance for the scientific evaluation of the oil and gas exploration potential in deep water area of paleogene saline lacustrine basin. |
PDF Full Text Request