塔里木盆地下古生界碳酸盐岩油气盖层及其控藏作用——以塔西台地为例

Cap rock in Lower Proterozoic carbonate rocks and its controls over hydrocarbon accumulation, Tarim Basin: Case study from the western Tarim carbonate platfrom

塔里木盆地下古生界发育巨厚的碳酸盐岩沉积,垂向上具有良好的生储盖配置条件,在长期的地质历史演化过程中,经历了多期成藏和多期改造,油气成藏条件十分复杂,下古生界碳酸盐岩盖层研究对于优选勘探层系和钻探目标至关重要。采用典型油气藏盖层分析、地震资料解释及实验分析等手段,总结归纳出两类区域盖层与两类局部盖层:两类区域盖层分别为上奥陶统暗色泥岩(“黑被子”)与中寒武统蒸发岩(“白被子”);两类局部盖层分别为碳酸盐岩潜山上覆泥岩(“新被子”)与内幕致密碳酸盐岩,并通过地震解释与井控的方法厘定了“黑被子”“白被子”“新被子”的分布。通过对已发现油气田(藏)盖层与成藏的关系、盖层之下油气藏类型的统计分析,认为区域盖层与下伏致密碳酸盐岩构成复式盖层控制主力成藏层位;局部盖层之下的油气藏类型主要受储层渗流能力控制,即局部盖层与均质储层组合表现为构造控藏特点,局部盖层与非均质储层组合表现为大面积准层状分布特点。建议将下古生界碳酸盐岩新区勘探重点方向调整为满西低凸起奥陶系与寒武系盐下白云岩;致密高阻碳酸盐岩的封盖能力存在风险,建议在开发阶段进行精细评价。

The Lower Paleozoic strata of Tarim Basin develops extremely thick carbonate deposits, which contains excellent source-reservoir-caprock association in the vertical direction. This succession has experienced multi-stage reformation and multi-period petroleum accumulation in the long-term evolution process, and its oil and gas conditions are complicated.Research on carbonate caprock of the Lower Paleozoic strata is crucial for optimizing exploration targets in the study area. In this research,two types of regional caprocks and two types of local caprocks are summarized by means of caprock analysis of typical oil and gas reservoirs,seismic interpretation and experimental analysis in the western Tarim carbonate platfrom.These two types of regional caprocks include the Upper Ordovician dark mudstone and the Middle Cambrian evaporite,named as “black quilt” and “white quilt”,respectively. The two types of local caprocks comprise the carbonate buried hill overlying mudstone which is called “new quilt” and the inside tight carbonate rock.Through the method of seismic interpretation and well control,the distribution of the black quilt,white quilt and new quilt has been determined.According to statistical analysis of the relationship between the caprock and reservoir formation in the discovered oil and gas reservoirs and the category of oil and gas reservoirs under the caprock, it is concluded that, the regional caprock and the underlying tight carbonate rocks together constitute a compound caprock, which controls the main reservoirforming horizon. Besides, the category of oil and gas reservoirs under the local cap rocks are mainly controlled by the seepage capacity of reservoirs. Local caprock-homogeneous reservoir is characterized by structural control, whereas local caprock-heterogeneous reservoir is characterized by large-area quasi stratified distribution.This research clarifies that the critical exploration direction of carbonate new area is Ordovician and Cambrian subsalt dolomite in Manxi low uplift. In addition, the sealing ability of high-resistivity layers of locally tight carbonate is uncertain, it is suggested to conduct detailed research and exploration in the development stage.