Sequence Stratigraphy And Reservoir Sand-bodies Of Middle Jurassic Yan'an Formation In Western Area Of Mahuang Mountain, Ordos Basin

Ordos basin is the secondary petroliferous basin which located at the middle zone of sedimentary basin in China, which was affected by the east pacific tectonic process and the southwest Tethys-Himalayas tectomic process, Ordos basin is rich in oil, natural gas, coal, uranium and many other energy resources minerals, and it is an important basin with strong potential for natural gas exploration, and one of the backbone resource base for "West to East Gas Pipeline Project". Many distinct subjects and points of view are needed in order to deeply study the characteristics of the occurrence and dis tribution of there energy resources in basin. The studies of sedimentology and sequence stratigraphy are important indispensable aspects. Based on sedimentology, this thesis studied the field outcrop, well core, well logging data and sample testing result of the Yan'an formation in west area of Mahuang mountain of Ordos Basin, and discussed the controlling factor of the natural gas and oil reservoir-forming.Firstly, this thesis through the multidisciplinary analyses of sedimentary structures, vertical secessions of log information, characteristics of rocks and minerals and fossils information, we can distinguish and measure off sedimentary facies and sedimentary systems of Yan'an formation in Jurassic. The thesis expatiated the sedimentary system and the sedimentary microfacies of target formation, From bottom to top of Yan'an formation, the sedimentary system from fluvial depositional system changed into delta depositional system. Channel bar, point bar, alluvial flat and backbank swamp etc are mainly microfacies of fluvial depositional system; distributary channel, flood plain and swamp etc are mainly microfacies of delta depositional system. And analyzed the characteristics of depositional systems and pattern of deposition.Based on several outcrops and dozens of exploitation wells, this thesis reseached the high-resolution sequence stratigraphy of the Yan'an formation in the Mahuang mountain area of Ordos Basin, summarized the proper markers of stratigraphic division and correlation, and built the high resolution sequence stratigraphic framework of Yan'an formation. Consequently, one Super Long-term Sequence Cycle (SLSC) was indentified, and then, subdivided into three Long-term Sequence Cycle (LSC) and 11 Middle-term Sequence Cycle (MSC) respectively. Furthermore, it went to study the characteristics and genesis of sequence boundary, systems tracts and sequences. According to mentioned above, sequence-lithofacies paleographic map and high-resolution sequence stratigraphy correlating map were accomplished.The study of reservoir lithology indicated that there were there main types of rocks in study region: arenite-quartz sandstone; felspar-arenite sandstone; felspar-quartz sandstone, coarse medium and fine grained sandstone is the primary reservoir, the sandbodies have good component maturity, the data are between 1.2-5.3. The grain of sandstones have good separation and middling psephicity, hypo-arris or subrounded, the relation between grains is point-contact or line contact. In Yan'an formation, the filling among sandstones are mainly kaolinite, chlorite and ledikite are singularly found.The theses also simply analyzed the diagenesis of reservoir sandbody and think the diagegesis included mechanical compaction, dissolution, agglutination and dissolution, whiches strongly effected the reservoir performance and evolution of porosity. The pore are made up of intergranular pore(include intergranular pore which formed by solution and diagenesis), induced pore(include feldspar soluted pore, detritus soluted pore, carbonate soluted pore, intercrystal pore and matrix soluted pore), micropore and microcrack. Intergranular pore are primary, which account for 46%. Soluted intergranular pore of sandstone is the inportant type in Ningdong region, which account for 70%-85%. Moreover, the thesis detailed studied the porosity type, porosity structure and property of reservoir sandbodies, from the bottom to up, the petrophysical properties become better and better, the porosity and the permeability have positive correlation.Finally, based on there studies mentioned above and combine sandbody distribution regularity of target formation of study region, the thesis forecasted the advantageous exploration region for oil and gas of the Middle Jurassic Yan'an Formation which is located in west area of Mahuang mountain of Ordos Basin, all this provided theories for exploration and disposition in our country.