Tectonic Evolution Of Southwestern Margin In Ordos Basin And Sedimentary Response Of Interval 8 To 6 Of Yanchang Formation

Jiyuan area is located in the southwest of Ordos Basin. Interval 6 & 8 of Yanchang Formation are principally producing formations of the study area. The thickness of single sand body varies greatly with bad physical property and obvious anisotropies, and complex relationship between oil and water is the typical characteristics of the two layers. In view of the needs of exploration and development in the study area, provenance, sedimentary facies and evolution ofstructure-sedimentation history are studied. The laws of hydrocarbon accumulation were concluded, and the distribution of reservoir in the sequence stratigraphic frame was analyzed. By the study of the relationship between tectonic movement, sedimentary evolution and hydrocarbon accumulation and the affection to reservoir, favorable belts for the development of reservoirs were forecasted. The research have acquire following results:1. Based on the core observation, analysis of logging and debris and minerals data, and combined with the fruit of predecessors this paper points out for the first time that the Interval 8 of Yanchang Formation in Jiyuan area in Ordos Basin developed shallow water delta. Interval 7 of Yanchang Formation developed subaqueous fans -semi-deep lake facies sedimentation and Interval 6 of Yanchang Formation developed meandering-delta and meare deposition system that has deep water depth.2. Guided by the high-resolution sequence stratigraphy theories and methods, the authors studied the high-resolution sequence of the Interval 8 & 6 of Yanchang Formation. Distribution, structure and stacking pattern correlation of sequence of Interval 6 and 8 of Yanchang Formation in Jiyuan area have been described and compared.3. Provenance analysis and sequence-paleogeographic mapping based on the careful sedimentation and sequence analysis of the Interval 8 & 6 of Yanchang Formation indicated that the sedimentation was controlled by the northeast, northwest and southwest sources of the study area. The sedimentary system was controlled by tectonic movement of the southern margin and the southwestern margin of the Ordos Basin in different stage.4. This paper analyzed the relationship between tectonic evolution and sedimentary response from Chang-8 to Chang-6 sedimentary stage in the southwest of the Ordos Basin first time, and draw a conclusion that Qinling where is far from study area had uplifted in Chang-8 stage, while no obvious tectonic movement in the west of the Ordos Basin where is close to the study area, and developed shallow water delta that controlled by southern margin tectonic activity of the basin. The southwestern margin of the Ordos Basin began move intensely with strong volcanic activity in Chang-7 stage. Liupanshan began uplift and compress the base which led intensely depress of the lake basin, and the study area characterized by semi-deep lake that develops subaqueous fans in Chang-7 depositional stage. The volcanic action of Chang-6 depositional stage became weak, but the tectonic action of faulted zone in the west of Ordos Basin is also intense. The basin depressing continuously and develop meandering-delta with deep lake water in Chang-6 stage, which controlled by the tectonic movements of the western margin of the Ordos Basin.5. The paper concludes the reservoir types and hydrocarbon generation conditions of different layer on the base of sedimentary response of tectonic movement, sequence-paleogeographic mapping and organic geochemical characteristics of Interval 6 & 8 of Yanchang Formation. And favorable belts for hydrocarbon accumulation in the study area have been pointed out as basis of next exploration and development.