Hao, Jianrong¹, Yiqun Liu¹, Wan Yang², Qiao Feng², Qin Cao¹
(1) Northwestern University, Xian, China
(2) Wichita State University, Wichita, KS

ABSTRACT: Source Rock Maturity in Santanghu Basin, Northwestern China

The frontier Santanghu Basin is an intermontane petroliferous basin and covers 23,000 km² in northwestern China. It contains two source rock successions ? Guadalupian (P₂) Lucaogou Fm and Huangshanjie-Haojiagou Fms (T₃). Their degree and timing of maturation were studied through analyses of vitrinite reflectance (34 samples of coal and carbonaceous shale, corrected for vitrinite reflectance suppression), biomarkers (31 samples), and homogenization temperature of secondary inclusions (71 samples in 6 wells). Coupled inverse thermal modeling, modified from existing models (EASY%Ro, Loptin-Waples, Middleton-Falrey, and Lerche models), indicates decreasing thermal gradient through basin history. The Early-Middle Permian gradient reached 4.4-5.2^oC/100 m, induced by local magmatic activities, and caused maturation of Middle-Permian source rocks at end of Permian; Triassic-Jurassic gradient is normal (3.12-3.93^oC/100 m). Most Middle Permian and Upper Triassic source rocks matured and accumulated during Late Jurassic-Early Cretaceous. Jurassic coals have not entered the oil window. Late Hercynian folding of pre-Permian basement caused erosion, uplifting, and cooling, resulting in a pause of hydrocarbon generation. High heat flow during late Yanshanian Orogeny, as indicated by homogenization temperature of 230-250^oC in some Jurassic inclusions, significantly promoted source rock maturation and generated abundant fractures, which facilitated hydrocarbon migration. The results will direct future exploration activities in this basin.

AAPG Search and Discovery Article #90026©2004 AAPG Annual Meeting, Dallas, Texas, April 18-21, 2004.