Abstract:

Junggar basin is an oscillated flooding basin in Jurassic, forming several unconformities, and its sequence stratigraphic units whose sequence boundaries are defined by unconformity, have a close relationship with the distribution and accumulation of reservoir. LST (Lowstand System Tract) and HST (Highstand System Tract) lying around the unconformity develop glutenites that possess better reservoir quality, from alluvial fan, river, and delta. TST (Transgressive System Tract) is mainly characterized by lake facies mudstone whose thickness distribution is stable and extensive. In Junggar basin of Jurassic, considering the multiple phases of unconformity, the stability of distribution and the constraint of sequence stratigraphy to source rock, reservoir, and caprock, the authors establish the unconformity complex which is constructed by a unconformity and LST or HST existing above and below the unconformity. Several sets of source reservoir caprock assemblages are formed by mutual superimposition of multiple unconformity complexes and mudstone of TST. Unconformity complex plays a vital role in oil and gas migration, accumulation, and forms multiple styles of stratigraphic traps in its interior. Unconformity complexes with different levels control the distribution and enrichment of source reservoir caprock assemblage. Meanwhile, the interior units of unconformity complex define stratigraphic traps style and distribution. Specifically, the large scale alluvial fan and delta developed in the unconformity's LST and HST constrain the lithologic traps  distribution, and the thinning out lines control the stratigraphic traps.

Key words: Junggar basin, Jurassic, unconformity complex, lithologicstratigraphic trap, sequence stratigraphy