鄂尔多斯盆地三叠系长9段多源成藏模式

Formation patterns of Chang 9 oil reservoir in Triassic Yanchang Formation,Ordos Basin,NW China

基于鄂尔多斯盆地三叠系延长组长9段成藏主控因素分析,对长9段油源、运移动力、运聚方式、成藏期次、成藏模式及富集规律进行研究。姬塬、陇东地区长9段原油主要来自长7段烃源岩,志丹地区长9段原油主要来自长9段烃源岩。姬塬地区西北部古峰庄—麻黄山地区发育岩性-构造油藏,姬塬东部地区发育构造-岩性油藏,华池—庆阳地区和志丹地区发育岩性油藏。长7段过剩压力是石油运移的动力,埋藏史表明,长9段经历了晚侏罗世和早白垩世2期成藏,晚侏罗世烃类充注范围和规模较小,早白垩世为烃源岩大规模生排烃期和长9段原油运聚主成藏期。伴随构造运动,盆地长7段底面构造经历了由沉积后西高东低到成藏期东高西低,再到现今平缓的西倾单斜的构造演化过程。早白垩世,环县—华池—吴起—定边以西地区长7段底面构造最低,原油进入储集层后,向周边高部位发生侧向运移。主成藏期长7段底面在姬塬西部麻黄山—红井子一带存在古背斜构造,控制姬塬西部油藏分布。

Based on analysis of main controlling factors of Chang 9,the source rock,driving force of migration,migration and accumulation modes,reservoir forming stages and model and enrichment law of Chang 9 reservoir were examined.The study showed that the oil of Chang 9 reservoir in the Jiyuan and Longdong areas came primarily from the source rock of Chang 7 Member,but the oil of Chang 9 reservoir in the Zhidan area came primarily from the source rock of Chang 9 Member.There developed lithologic-structural oil reservoirs in Gufengzhuang-Mahuangshan area in northwest Jiyuan,structural-lithologic oil reservoirs in east Jiyuan,and lithologic reservoirs in Huachi-Qingyang area and Zhidan area.The overpressure of Chang 7 Member was the driving force of oil migration.The burial history showed that Chang 9 Member experienced two stages of reservoir forming,the reservoir formed in the Late Jurassic was smaller in charging scope and scale,and the Early Cretaceous was the period when the source rock generated oil and gas massively and the Chang 9 reservoir came into being.Along with the tectonic movements,Chang 7 bottom structure turned from high in the west and lower in the East in the sedimentary stage to high in the east and lower in the west in the hydrocarbon accumulation stage and at last to gentle western-leaning monoclinal structure at present.In Early Cretaceous,the Chang 7 bottom structure was the lowest in the west of Huanxian-Huachi-Wuqi-Dingbian areas,so the oil migrated laterally towards the higher positions around after entering the reservoir.In the main reservoir forming period,Chang 7 bottom had an ancient anticline in Mahuangshan-Hongjingzi area of west Jiyuan,controlling the oil reservoir distribution in west Jiyuan.