Differential Hydrocarbon Charge and Accumulation in the Thrust and Slope Belts in the Kuqa Foreland Basin, Western China

Abstract

Hydrocarbons in the Thrust and Slope belts in the Kuqa Foreland Basin, northern Tarim Basin show contrasting phases and distributions. On the basis of oil physiochemical properties, reservoir diagenetic sequence and fluid evolution, the hydrocarbon accumulation processes in the two belts were investigated using geochemistry, microscopy, SEM, XRD and X-ray micro-CT imaging. Both paleo and present hydrocarbons were investigated using fluorescence microscopy and FT-IR spectroscopy in conjunction with bulk geochemical analysis and Principal Component Analysis. The study area initially experienced shallow burial over a prolonged period, was then buried rapidly around 5 Ma and uplifted since the Quaternary. The reservoir is characteristic of diagenesis Stage A (moderate diagenesis phase) with the diagenetic sequence characterized by an early calcite cementation→ feldspar dissolution → quartz overgrowth → kaolinite → late calcite cementation → dolomite precipitation → anhydrite precipitation → microcrystalline quartz formation. Three types of hydrocarbon inclusions are present including yellow and blue fluorescing oil inclusions and gas inclusions, representing three episodes of hydrocarbon charges in the Thrust Belt and two episodes of charges in the Slope Belt. The oil charge in the Thrust Belt occurred at 18 Ma and 5 Ma, and the gas charge occurred after 2 Ma. Reservoir oils have higher maturity than the blue fluorescing inclusion oil, indicating that later high-maturity hydrocarbon charge dominated the oil accumulation. The reservoirs in the Thrust Belt were initially charged with oil at 18 Ma with a subsequent high-maturity oil around 8-5 Ma. The oil reservoirs were subsequently destroyed by intense tectonic compression, followed by high to over-mature coal-derived gas charge in the Quaternary. The Slope Belt received a high-mature oil charge around 8-5 Ma and a gas charge since 3 Ma, characterized by a huge amount of gas charge into relatively small oil reservoirs.

AAPG Datapages/Search and Discovery Article #90259 ©2016 AAPG Annual Convention and Exhibition, Calgary, Alberta, Canada, June 19-22, 2016