HYDROCARBON SOURCE ROCKS AND GENERATION HISTORY IN THE LUNNAN OILFIELD AREA, NORTHERN TARIM BASIN (NW CHINA)

摘要

In this paper we report on source rocks and maturation history at the Lunnan oilfield, northern Tarim Basin (NW China), using a combination of organic petrographic and geochemical techniques. Three separate source rock intervals are present here: Cambrian mudstones and argillaceous limestones; Middle and Upper Ordovician argillaceous limestones; andTriassic mudstones. Reservoir rocks comprise Lower Ordovician carbonates, Carboniferous sandstones, andTriassic and Jurassic sandstones. Structural traps were formed principally during the Silurian and Jurassic. The Lunnan field is located on a small-scale palaeo uplift which developed during the Early Palaeozoic. Hydrocarbons migrated updip from source areas in surrounding palaeo-lows along faults and unconformities. Major phases of hydrocarbon generation and migration occurred in the Early Silurian - Late Devonian, Cretaceous - Early Tertiary and Late Tertiary. Uplift and intense erosion at the end of the Devon/on destroyed Early Palaeozoic oil and gas accumulations sourced from the Cambrian source rocks, but hydrocarbons generated by Middle and Upper Ordovician source rocks during the Mesozoic and Tertiary have been preserved. At the present day, accumulations are characterized by a range of crude oil compositions because source rocks from different source areas with different maturation histories are involved.