Zhou, Dingwu1, Wan Yang2, Yiqun Liu1, Qiao
Feng1, Jianrong Hao1
(1) Northwestern University, Xian, China
(2) Wichita State University, Wichita, KS
ABSTRACT: Structural Control on Hydrocarbon Accumulation in the Intermontane Santanghu Basin, Northwestern China
The frontier Santanghu Basin covers 23,000 km2 in NW China. Structural control on hydrocarbon accumulation is studied within a seismic sequence stratigraphic framework, using 10,000-km seismic and 34 well data. The basin has a folded pre-Permian basement and two NW-trending uplifts separated by the Central Depression formed during late Yanshanian-Himalayan orogenies. The Central Depression is a complex syncline formed by NE-SW overthrusting from both sides and contain NW-trending secondary fault blocks modified by NE-trending structural highs and lows. Five stages of basin development include Early-Middle Permian rifting and thermal subsidence; Late Permian-Early Triassic compression; Middle-Late Triassic-Early Cretaceous thermal subsidence; Late Cretaceous compression; and Tertiary-Quaternary overthrusting and strike-slip faulting. Three generations of fractures include Permian calcite-filled fractures formed by gentle folding and thrusting during Late Hercynian (P3-T1) compression; Triassic-Lower Cretaceous fractures formed by gentle folding and thrusting and anticlinal faulting during late Yanshanian (K2), of which 25-30% contain oil. Hydrocarbon generation occurred during 135-160 Ma and 80-100 Ma, based on burial and thermal history modeling using homogenization temperatures (120-150 and 190-210oC) obtained from inclusions along fractures (> 500 inclusions in 46 samples). Fractures in all post-Early Permian rocks formed by transpressional faulting during Himalayan (Tr-Q) compression and dextral strike-slip faulting; some contain hydrocarbons. Fractures are oriented primarily NW-SE and secondarily NE-SW, based on core description, paleomagnetic analysis (85 samples), and computer modeling. Hydrocarbon accumulations occur in southern overthrust frontal zone and northern monoclinal zone, where fractures best developed.
AAPG Search and Discovery Article #90026©2004 AAPG Annual Meeting, Dallas, Texas, April 18-21, 2004.