Upper Paleozoic-Mesozoic Sedimentary Facies and Evaluation of Hydrocarbon Prospect in the Junggar Basin, China

Kevin Gao, Qiang Wu, Jiajie Chen

The Upper Paleozoic (Permian and Carboniferous, about 1000~4000m thick) and Mesozoic (Jurassic and Triassic, about 500 ~ 2000m thick) are the most important source and productive horizons in the Junggar Basin (44-50°N, 85-89°E, 130,000 km² in area). Studies on the distribution of sedimentary facies during different geological intervals indicate that the basin had undergone significant shifts in the lacustrine and fluvial environment. Due to the favorable tectonic constrains of the basin, these lacustrine facies has evolved to become important source horizons. Here we further synthesize well data, seismic, outcrop and other geological data from the Junggar Basin. We then present a series of diagrams to summarize the evolution of various sedimentary fac es, such as pluvial-aluvial fan, fluvial, deltaic and lacustrine. The distribution of these facies is clearly controlled by paleogeography and plaeostructures.

The regional S-N cross section and the composite stratigraphic column display a comprehensive configuration of the basin. The transit of basin-wide cross section reveals three major play types and multi-oil-bearing horizons.

We also use geochemical data to understand the characteristics of the possible source rocks. Based on the data of TOC, Ro and other reservoir quality indices, we suggests that the north-west, south-west and south-east areas are the most significant hydrocarbon generation and trapping locations. The major source beds are the Lucaogou formation (P₂l), the Sangonghe formation (J₁s) and the Xishanyao Formation (J₂x), which are dominated by deep lacustrine facies; while the detrital rock of lacustrine, deltaic, pluvial and fluvial facies could serve as important reservoirs. Further studies should concentrate on gathering more seismic data and understanding the detailed structures of the basin, in order to locate possible exploratory wells.

AAPG Search and Discovery Article #91020©1995 AAPG Annual Convention, Houston, Texas, May 5-8, 1995