The Analysis Of Sedimentary Basin And Petroleum System Characteristics In Uneg Sag,Mongolia

This paper is worked out on the practical exploration in Uneg sag,Mongolia.It makes full use of sedimentary basin analysis concepts and analyzes structure characteristics and sedimentary filling based on the original force of basin formation and evolution in the study area.And then it deduces the stress mechanism of the sag,reconstructs sedimentary environment,and investigates the temporal and spatial variation of reservoir geological factors dynamically.Finally,it analyzes the major controlling factors of hydrocarbon accumulations and distinguishes the hydrocarbon enriched areas.It is shown from tectonic setting analysis of Uneg sag that Xingmeng fold belt is divided into three zones(namely north,middle and south zone)by The middle Mongolia deep major fault and Hegenshan deep major fault.There is valley-lake basin,Neierjin basin and Qiaobashan basin in north zone,south gobi basin,east gobi basin,Hailaer-Tamuchage basin in middle zone,and Yin' gen-Erjinaqi basin and Erlian basin in south zone.The flexible basement was formed due to the collision between Eurasian Plate and Pacific Plate during late Paleozoic.The basins in Mesozoic were similar in tectonic inheritance or pattern,but different in structural evolution.It is indicated from fine structural interpretation that Uneg sag is dominated by NE structures.The tectonic movement is deduced by using depositional thickness method and growth index method.And from the analysis results,the center of subsidence moved from the west to the east during the sedimentation of Tsagaantsav Formation to lower Zuunbayan Formation,and the faults were the most active during middle-late early Zuunbayan.Its structural evolution is analyzed on the basis of equilibrium profile.It is inferred that the sag experienced five stages' structural development and three types of basins occurred.On the basis of the geologic and seismic data,it is depositional system of short streams and proximal deposit in Uneg sag.Fan deltas and inshore submarine fan glutenite bodies are developed at steep slope zone,and braided deltas or fan deltas are developed at gentle slope zone.And under the effect of structural evolution,it has experienced four kinds of ancient landform and relief,presenting four sedimentary formations.The petroleum systems in Uneg sag are preliminarily evaluated on the basis of tectonic and sedimentary setting,including the characteristics of source rocks,reservoirs,source-reservoir-caprock assemblages,hydrocarbon migration and traps,the preservation conditions,as well as the time-space relationship of geologic events.And this paper analyzes the process of hydrocarbon accumulation,determines the factors controlling hydrocarbon enrichment in Uneg sag,and predicts favorable zones for hydrocarbon accumulation in Uneg petroleum system.