The Study About Sedimentary System And Reservoir Characteristics Of Chang8and Chang6in The In Xunyi And Its Adjacent Area

The structural geology, logging geology, sedimentology and reservoir sedimentology are investigated in this paper based on regional geological background and situation of exploration and development of chang8and chang6in the Xunyi and its adjacent area. On the basis of predecessors’research, the stratigraphic characteristics, source direction, sedimentary characteristics, reservoir characteristics and factors impacting reservoir are in-depth analysis of chang8and chang6periods. And in the chang8and chang6, each small layer reservoirs are classified as well as the locations and scopes of each type of reservoirs are distributed, obtaining the following results:The first-order tectonic units of Wei River in the south of Ordos basin of Xunyi and around area extend the chang8period and chang6period structure which is different with the west pour monoclinic in the Shanbei slope.the Himalayan tectonic movement has significantly influence on this region. The formation erosion appears in the chang8and chang6, and the chang6denudation area is larger than chang8in the southern part of study area.The source direction of chang8and chang6in the studying area is from north to south, and provenance is in the southern Qinling area. Chang8and chang6periods are mainly composed with lacustrine facies and braided river delta sedimentary system, and further divided into two sub-phase or five micro-phases. Sand body is mainly controlled by the front underwater distributary channel in the braided river delta, mouth bar and shallow lake beach bar sand. And the sand body reservoir physical property in underwater distributary channel is the best, and in the sequence with mouth bar and lake beach bar, the reservoir physical property of shallow lake mud and bay between distributary sand body is the worst.The reservoir rock is dense, and all the particles are connected with each other by point or line contact. It has less intergranular pore. Dissolution pore development and iron carbonate content in the filler content is higher, and quartz level Ⅰ-Ⅱ increase generally, level III increases partially. Pore throat is plate shaped, curved sheet shaped or isolated disconnected die pore throat, diagenesis stage is A-substage of middle diagenesisThe reservoir of chang8and chang6can be divided into five different types according to the structure, sedimentary and reservoir characteristics, and the reservoir property of Ⅰ is the best, the sequence with the Ⅱ to Ⅴ types and so on.The local development reservoir in Ⅰ-type exists in the chang8and chang6of the study area in malan town near the normal fault in northeast. Ⅱ-type reservoirs mainly is distributed in the front underwater distributary channel sand body of braided river delta of chang8and chang6, which are distributed in the southern area of study area, and the range of variable size is not conformed. The distribution of Ⅲ-type reservoirs is similar with Ⅱ-type, and the changing of the distribution is controlled by the changing of the Ⅱ-type. Ⅳ-type reservoirs is mainly distributed in the micro-phases about the sub-phase in the shallow lake phase beach bar and braided river delta of chang8and chang6in the central and northern part of the research region, and the area is larger. Ⅴ-type reservoir is mainly distributed in the siltstone and argillaceous siltstone of the micro-phase about the bay as long as the argillaceous siltstone in the shallow lake sub-phase, which can be seen in both chang8and chang6periods with the larger area.