鄂尔多斯盆地北部中元古界潜山圈闭特征与成藏模式

Characteristics and reservoir forming model of Mesoproterozoic buried hill traps in the northern Ordos basin

鄂尔多斯盆地深层发育长城纪裂陷槽,但相关的圈闭类型和成藏条件不清。近期,在盆地北部杭锦旗地区发现了长城系砂岩潜山气藏,揭示该领域具有较好的勘探前景。通过最新的三维地震和钻井资料综合分析,结合区域构造演化阶段和典型气藏解剖,本次研究针对中元古界潜山圈闭的分布、类型及天然气成藏模式展开。结果表明:(1)研究区长城纪发育三个NW向裂陷槽,其中的独贵、蒋家梁裂陷槽受基底断裂反转活动影响,隆升剥蚀,形成低幅度的潜山隆起带;(2)残丘、隐丘及断丘型圈闭沿潜山隆起带呈带状分布,其中断丘型圈闭的闭合幅度最高;(3)潜山圈闭的成藏模式可分“上生下储”、“源储侧接”及“源外运移”等三种类型;(4)天然气藏分布受四个因素控制,其中烃源岩分布制约潜山气藏的分布范围;圈闭类型控制气藏规模与富集程度;断-缝发育程度控制储层物性及含气性;而侧向输导控制源外圈闭的成藏效率。因此,邻近煤系烃源岩的断丘型、残丘型圈闭将是研究区中元古界潜山勘探的首要目标。

There are a series of NE trending Changcheng rift troughs in the deep Ordos basin,which has attracted much attention recently,but the trap types and reservoir forming conditions are still unclear.In a recent exploration,Changcheng buried hill gas reservoir has been found in Hangjinqi area,in the northern part of the basin,which indicates that this area has good exploration prospects.Based on the comprehensive analysis of the latest 3D seismic and drilling data,combined with regional structural study and typical gas reservoir anatomy,the distribution characteristics,types and gas accumulation model of Mesoproterozoic buried hill traps in this area are identified.The results show that:(1)three NW trending fault depression troughs developed in Hangjinqi area during the Changcheng Period,which are different from the main trend of the rift trough group in the basin.Among them,the Dugui and the Jiangjialiang fault depression troughs formed a low amplitude buried hill uplift belt controlled by the basement fault due to the late inversion;(2)the residual hill,hidden hill and fault mound type traps are distributed along the basement fault developed in the Dugui and Jiangjialiang buried hill uplift belts.Among them,fault mound type traps have the highest closure amplitude;(3)buried hill traps can be divided into three types,i.e.“upper generation and lower reservoir”,“source reservoir side connection”and“external source migration”;(4)the distribution of natural gas is controlled by four factors,in which the distribution of hydrocarbon source rock affects the distribution range of Buried Hill gas reservoir;the trap type controls the scale and enrichment degree of gas reservoir;the development of fault fracture controls the physical property and gas bearing property of reservoir;the reservoir forming efficiency is controlled by lateral transport.Therefore,the fault hill type and residual hill type traps adjacent to coal measure source rocks on the buried hill uplift belt will be the main targets for the Middle Proterozoic exploration in the study area in the near future.