中亚阿姆河盆地天然气成藏控制因素

Controlling factors of natural gas accumulation in the Amu Darya Basin,Central Asia

中亚阿姆河盆地构造变形复杂,发育多种类型圈闭和气藏,不同类型气藏主控因素既有共性,又有一定的差异性。为了明确盆地气藏分布规律,寻找下一步勘探接替领域,利用油藏及单井产能资料、地球物理资料,结合区域石油地质特征,沉积背景、储层特征对研究区气藏特征进行了全面剖析。研究认为,阿姆河盆地气藏形成的共性控制因素包括两个方面:平面上,气藏分布受古隆起和礁滩体的发育控制,古隆起的地貌背景为礁滩体的发育提供构造背景,且容易发生暴露溶蚀,形成有效的储集空间,同时构造高部位,为油气运移的优势指向区,有利于油气聚集成藏;纵向上,气藏的分布受断裂、不整合和渗透性砂体等输导体系及圈闭封闭条件控制。两方面三个关键因素共同控制了气藏的空间分布。通过主控因素的分析,认为下部成藏组合的勘探应在古隆起背景下礁滩体发育区与断裂/不整合输导体系和膏岩盖层叠合发育区寻找有利靶区,而上组合则应在古隆起背景下礁滩体发育区与下部膏岩尖灭区以外的白垩系泥岩盖层发育叠合区开展勘探。

Amu Darya Basin in Central Asia features in complex structural deformations and multiple types of traps for natural gas accumulation.The major factors controlling gas accumulation in various reservoirs have both similarities and differences.In order to reveal reservoir distribution and select new targets for next phase of exploration in the Basin,reser-voir and single well production data and geophysical data are integrated with regional geological characteristics,deposi-tional settings and reservoir property to analyze the reservoir characteristics in the targeted area.It is suggested that two common controlling factors have played main roles in the formation of the natural gas reservoirs in the region.Laterally, gas reservoir distribution were controlled by the development of paleo-highs and reef complex,and the paleo-highs provid-ed favorable structure settings for hydrocarbon accumulation and formation of effective reservoir spaces from exposure and dissolution.Meanwhile,the structural highs are the preferential target areas for hydrocarbon migration and accumulation. Vertically,gas reservoir distribution was controlled dominantly by trap conditions and carrier systems like faults,uncon-formities and permeable sandstones.These factors jointly controlled the spatial distribution of natural gas reservoirs.Based on the analysis,it is recommended that exploration of the lower play should be focused on the target areas with well-develo-ped reef complex within paleo-highs,fault/unconformity carrier systems and evaporite cap rocks.In contrast,exploration of the upper plays should be focused on areas where well-developed reef complex within paleo-highs are overlain by the Cretaceous mudstone seals outside the pinch-out areas of the lower evaporates.