Elementary Analysis Of The Relation Between Tectonic Evolution, Lithology And Crack Formation In Upper Paleozoic Of Ordos Basin

During the evolution of sedimentation and burial, loose sediments experience plastic compaction, elastic-plastic compression and ruptured finally in petroliferous basin. Not only does crack help to form storage space and migration pathway, but also plays an essential role in the formation and distribution of oil and gas reservoir. Based on the analysis of tectonic evolution characteristics, stratigraphic lithology and sedimentary characteristics of Upper Paleozoic in Ordos Basin, this paper partitions the sedimentary and buried phase of sediment by means of the acoustic time curve of sand and mudstone. Besides, it analyses the lithologic character of cracks through core image, thin section and the whole rock mineral content by X-ray diffraction. Achieved the following understanding:(1) The characteristics of tectonic division and evolutionStructural map of the bottom surface of Taiyuan Formation is divided into four concave and uplift areas, including Etuoke Banner—Erdos area, Etuokeqian Banner—Wushen Banner Shenmu area, Huanxian County—Wuqi—Suide area and Qingyang—Fuxian County— Jixian County area. Area, east of Ejinholo Banner—Sulige—Jingbian—Zizhou area, which is belonging to the overlying strata of Taiyuan Formation, appears similar to ancient structure in the process of different geological evolution. In addition, the rest area seems different.(2) The characteristics of stratigraphic lithology and sedimentationLagoon, shallow lake, tidal flat, underwater distributary channel and branches’ sedimentary develop the lower position of concave and uplift area, whose lithology is clay rocks, quartz complexes, clay complexes and coals while the rest is composed of deltaic plains and delta front sediments with the lithology of quartz sandstones, arkoses and a few complexes.(3) The partition of sediment in sedimentary and buried phase and the lithologic characteristics of crack developmentThe evolution process of sedimentation and burial of sand and mudstone in Ordos Basin can be divided into three phases, plastic compaction segment, elastic-plastic compression segment and rupture segment. In addition, depth of plastic compaction segment is 1509 meters; elastic-plastic compression segment,1509～2218 meters; rupture segment, below 2218 meters. Cracks in Shanxi Formation and Xiashihezi Formation develop universally, among which quartz sandstones, clay rocks and coal rocks develop better while complexes develop less or even not. As for characteristics of these rocks, brittle minerals content of quartz and clay remain higher in terms of rock composition while concerning to structure, it contains compact particles and homogeneous structure. Apart from this, rocks with lower or similar mineral content and compact mixed structure are less develop or even not.(4) The development rule of crack in Upper Paleozoic of Ordos BasinCracks develop universally in Upper Paleozoic of Ordos Basin, the development of which begin primarily in the lower part of concave and uplift area or deeper part of buried area. Besides, structure in the lower part of concave and uplift area develops better than higher part.