Hydrocarbon Generation Conditions Of Washixia Sag, Southeast Depression Of Tarim Basin

Washixia Sag located in the northeast of Southeast Depression of Tarim Basin, developed thick coal-bearing strata during the rift lacustrine period in Jurassic. The boundary of Washixia sag is mainly dicided by the distribution of Jurassic. Gas show had already been discoved in well Ruocan 1 in Kangsu group and Yangye group in Jurassic, which proved the exploration potential of Washixia sag.This thesis is based on outcrop and underground Jurassic hydrocarbon source rocks in the indoor test analysis and statistical results, combine with seismic interpretation, conduct a comprehensive evaluation on the hydrocarbon generation conditions of Jurassic hydrocarbon source rocks, including distribution, geochemistry characteristics (abundance, type and maturation), evolution and hydrocarbon generation. Different source rock have different criterion for evaluation. TOC values are the mian criterion for evaluation of abundance of organic matter, IH and the relation between IH and Tmax are used to evaluate the type of organic matter, vitrinite reflectance (Ro) and Rock-Eval highest peak temperature (Tmax) are used to judge the maturity of organic matter. Basin modeling software is used in studing the evolution of source rock, combine with actual geological data, the burial history, thermal history and mature history of Ruocan 1 Well, TD05-397-1 well and TD05-397-2 well are simulated. Backstripping method is used to restore the burial history, combine with paleotemperature data to calculate the thermal history by steady-state heat flow method, mature history is restored by Easy Ro method. Hydrocarbon generation evaluation is study by thermal simulation experiment. By analysising the hydrocarbon generation process and hydrocarbon composition, experimental evidence and basic information can be provided for evaluation of hydrocarbon generation potential and mechanism.Analysis showed that, sediments in the east part of Washixia Sag is thicker, and buried deeper. The temperature of Jurassic hydrocarbon source rocks rise quickly in Jurassic, enter hydrocarbon generation threshold, and begin to generate hydrocarbon for a long time. Jurassic source rocks have high mudstone conten, the thermal simulation show that the product is mianly hydrocarbon gas. Sediments in the west part of Washixia Sag is thinner, buried lower in Jurassic and Cretaceous, buried quickly and the temperature rise quickly in Neogene and Quaternary. In the late Neogene- Quaternary, the source rock entered hydrocarbon generation threshold, and is in low maturity period, the time of hydrocarbon generation is short. Jurassic source rocks in the west part of Washixia Sag is mianly coal-bearing carbonaceous shale and coal measures mudstone, liquid hydrocarbon genetic potential is relatively higher. Additionaly, there is a part of Jurassic is buried deeply under orogenic belt in the mountain front, the maturation is probably higher, and may become good oil-generating source rock.