Print this pagePermian-Triassic Basin Evolution and Petroleum System of the Turpan-Hami Basin, Xinjiang Province, Northwest China
GREENE, T.J., A. R. CARROLL, M. S. HENDRIX, and J. LI
Field and subsurface investigations have identified potential Permian lacustrine source rocks throughout the petroliferous Turpan-Hami basin, northwest China. New data support a suspected connection between the Junggar and Turpan basins during deposition of prolific Permian organic-rich lacustrine mudstones, and hence suggest greater exploration potential than has previously been recognized. Specifically, potential Permian source rocks outcrop in three localities along the northern basin rim, as well as in subsurface cores from the basin's southern depression. Ongoing geochemical studies will characterize the source potential and thermal maturity of these facies, and attempt to correlate their extracted bitumens with produced oils from several fields.
Lower Triassic clast lithologies, combined with previous paleocurrent studies, suggest a central Tian Shan provenance. Ubiquitous alkalic granite clasts in Lower Triassic fluvial sandstones and conglomerates from the northern Turpan basin were probably derived from Late Paleozoic alkalic, anorogenic granites in the central Tian Shan to the south; significant granites are absent in the Bogda Shan to the north. In contrast, Junggar reservoir rocks and modern Turpan sandstones are dominated by reworked volcaniclastic grains derived, in part, from the Bogda Shan. This, combined with basinwide field mapping and seismic interpretation of Mesozoic stratigraphic architectures, further constrain the timing of the initial partitioning of the Turpan-Hami basin from the Junggar basin to the Middle to Late Triassic.
This result has two important implications. First, it implies Turpan's Permian lacustrine deposits were depositionally linked with southern Junggar's oil-prone Upper Permian lacustrine oil shales. Second, a significant enrichment of K-feldspar and quartz grains in Triassic sandstones of the Turpan basin likely has resulted in superior reservoir quality relative to their volcanoclastic counterparts in the Junggar basin.