Analysis of Inversion Structure and Trap Diversity in a Block of Western Qaidam Basin

Abstract

Western Qaidam basin which was confined by two boundary zones of Eastern Kunlun and Altin zones endured two phases of tectonic movement during the Cenozoic. Complex in depositional fillings and structure deformations hinders the judgment for early Himalayan effective traps, which lead to troubles in choosing for exploration targets. To solve these problems, regional sequence stratigraphy correlations on seismic and logs data were performed. Then, based on core, logs, and cuttings of wells, lithology and sedimentary facies were identified. In the region of non-well, two dimensions (2D) seismic facies interpretation and well-to-seismic integration method were used to depict the sedimentary systems and their distributions on the plane. Two tectonostratigraphies of Early Himalayan cycle with pan-lake facies and late Himalayan cycle with alluvial-braided river facies were, respectively, recognized by the faces variance sharply and basins superimposition characters. And then by backstrip technique in assistance of 2D fault combination, thickness variance, and seismic facies, two kinds of reversion structures can be identified. One is the reversion in fault dip direction of large boundary faults when geotectonic setting varied. Another is the reversion of basement by warping and plastic flow of deep geological structure during later Himalayan movement, and the deposition centers shifted from west to the east parallel to strike-slip faults of East Kunlun belts. Finally, by seismic interpretation, paleo-structure maps, and facies distribution, faulted anticlines, faulted noses, paleo-high, paleo-clinoforms of early Himalayan stage, and compressive anticlines of late Himalayan period were delineated and they constituted traps diversity of this area. Discerning two types of inversion structures and paleo-traps could contribute to recover the direction and paths of oil migration and enhance the evaluation of favorable targets.