塔里木盆地轮西地区奥陶系潜山油藏:一个海西期充注并降解的稠油油藏成藏实例分析

塔北隆起的轮西地区具有以裂缝、溶蚀裂缝和溶洞为主的下奥陶统潜山储集体,且继承型古隆起一直成为油气运移和聚集的指向区,因此具有较为优选的成藏地质条件。海西晚期是轮西地区稠油藏的主要成藏期,海西末期石炭-二叠系地层遭受强烈剥蚀使海西晚期聚集的奥陶系潜山原油降解,成为重质稠油油藏,并不受印支晚期至喜马拉雅期运动的影响。印支晚期之后Ⅰ级断裂活动停滞,使轮西地区奥陶系潜山以稠油为主的油藏基本上未受晚期油气充注的影响。对轮西奥陶系潜山油藏研究得到的重要启示是:应加强塔里木盆地克拉通地区早期成藏勘探潜力的认识。

Ordovician buried hill oilfieid in western Lunnan area:An example of heavy oilfield formation for hydrocarbon charging and degrading in Hercynian period

Tectonically,Lunnan area was located in the North Tarim Rise of the Tarim Basin. There were good geological conditions for hydrocarbon accumulating in the western Lunnan area,a part of inherited palaeohigh,with fractures,dissolved fractures and cavernous being main reservoirs in the Ordovician buried hill. The oilfield in western Lunnan area was filled mainly during the late Hercynian period and was degraded into heavy oil during the latest Hercynian period due to the high denudation of the Carboniferous and Permian strata. Because of ceasing of regional first order faults,the hydrocarbon charging did not occur in the heavy oilfield in western Lunnan area during the late Indosinian to Himalayan periods. Based on what mentioned above,an accumulation model for Ordovician buried hill in western Lunnan area was summarized,which emphasized the Late Hercynian period being a key accumulation epoch and function of the faults with different orders. The study on accumulation process of the Ordovician buried hill reservoir represented an important implications for the exploration potential of early oil and gas accumulation in the cratonic area of the Tarim Basin.