歧口凹陷埕北断阶区断砂组合样式及其对油气富集的控制作用

在陆相断陷盆地中，断裂与砂体是构成油气运移输导网络的主要要素。为了探究断砂组合输导条件控制下的油气运聚规律，本文对歧口凹陷埕北断阶区的断砂组合样式进行了划分，并通过断裂、砂体输导性的定量评价分析了不同样式断砂组合对油气运移成藏的控制作用。结果表明：依据断裂在油气成藏过程中的主要作用不同，划分了油源断裂与多套砂体上下叠置组合、输导断裂与砂体顺向或反向阶梯式组合、调节断裂与砂体"Y"字型组合，共3类4种断砂组合样式，在空间上形成了"接力式"的成藏模式。断砂组合对油气富集的控制作用主要体现在3个方面：①控制了油气藏的类型；油源断裂与多套砂体上下叠置组合主要控制形成岩性-构造、断块类油气藏，输导断裂与砂体顺向或反向阶梯式组合控制形成断块、断鼻和复合类油气藏，调节断裂与砂体"Y"字型组合控制形成断块类油气藏。②控制了油气的运移过程；油源断裂根部与大面积砂体组合沟通深层烃源，在油源断裂活动时，油气先沿断裂运移至浅层，并远距离运移至断阶区高部位富集，输导断裂与砂体顺向或反向阶梯式组合为油气提供阶梯式垂向-侧向运移通道，调节断裂与砂体组合则对油气富集起再调节分配作用。③控制了油气的聚集部位；当断裂输导概率f >50%，砂地比>0.50时，断砂组合起完全输导作用。在中浅层，油气沿输导断裂运移，输导断裂封堵性控制成藏；在中深层，油气富集程度则与砂地比值成正相关。

Configuration Types of Fault-Sand in Chengbei Fault Terrace Zone of Qikou Sag and Its Control on Hydrocarbon Accumulation

In terrestrial rift basins, faults and sand bodies are the main elements of hydrocarbon migration network. In order to explore the mechanism of hydrocarbon migration and accumulation in the Chengbei fault terrace zone of Qikou sag under the control of fault-sand configuration transportation conditions, the types of fault-sand configuration and their controlling effect on hydrocarbon migration and accumulation were analyzed through quantitative evaluation of fault and sand body conductivity. The results show that the fault-sand configuration can be divided into four types according to the main functions of faults in the process of hydrocarbon accumulation, including configuration of oil source faults and multiple sets of sand bodies superposed vertically, configurations of transport faults and sand bodies terraceped forward and backward, and configuration of adjusting faults and sand bodies in "Y" shape with a "relay-style" accumulation model formed in the space. The controlling effect of fault-sand configuration on hydrocarbon enrichment is mainly reflected in three aspects:1) Control the types of oil and gas reservoirs:The configuration of oil source faults and multiple sets of sand bodies mainly controls the formation of structural-lithologic and fault block oil-gas reservoirs, the configurations of transport faults and sand bodies in the forward or reverse direction control the formation of fault block, fault nose, and composite oil-gas reservoirs, and the configuration of regulating faults and sand bodies in "Y" shape controls the formation of fault block oil-gas reservoirs; 2) Control the hydrocarbon migration process:The configuration of oil source faults and large zone sand bodies at the fault root connects the deep hydrocarbon source, during the activity period of oil source faults, oil and gas migrate along the fault to the shallow layers, and then accumulate in the high part of fault terrace zone after a long distance migration. The terrace-by-terrace vertical or reverse configuration of transport fault and sand body provides the terrace-by-terrace vertical and lateral migration channel for hydrocarbon, and the configuration of adjusting faults and sand bodies plays a role of readjustment and distribution in the process of hydrocarbon accumulation; 3) Control the position of hydrocarbon migration and accumulation:When the probability of fault migration f is more than 50% and the ratio of sandstone thickness to total formation thickness is more than 0.50, the fault-sand configuration is considerred to be completely fluidly connected. In the middle-shallow layers, oil and gas migrate along the transport fault, and the sealing property of the transport fault controls the hydrocarbon accumulation, while in the middle-deep layers, the degree of oil and gas accumulation is positively related to the ratio of sandstone thickness to total formation thickness.