南八仙复杂断裂系统形成机理及油气富集模式

The Formation Mechanism of the Complex Fault System and the Mode of Oil and Gas Enrichment in South Baxian

深入研究南八仙地区主控断裂、各级微断裂的形成机理、组合关系以及对油气的控制作用,可以有效预测含油气砂体分布。综合应用地震、钻井、测井等资料,结合几何学、动力学对南八仙地区的断裂及微构造进行了梳理,在此基础上,通过分析油气成藏演化史及储层岩性、物性特征确定了复杂断裂系统的油气富集模式。研究认为,仙北断裂是受马仙断裂影响下的反S型右旋三级走滑断裂,控制南八仙中浅层构造带的形成,伴生各级张性微断裂由西向东发散,发育斜列带、羽状带、马尾带3种微断裂构造样式。南八仙油气田属于同源油气,两期成藏,其中,中浅层油气藏是构造-岩性次生断块油气藏类型。建立了断层控油、微构造控油、沉积相控油3种油气富集模式,确定了仙北断裂羽状带中单层厚度小的滩坝砂体内微构造是油气富集区域,据此在油气富集区部署5口开发井,试气效果良好。

An in-depth study was performed on the formation mechanism of dominant faults and all levels of micro-faults in the South Baxian area,and on the relationship between their combination and the mechanism of its control over oil and gas,on the basis of which,the distribution of oil sands can be effectively predicted.By using seismic,drilling,and logging data,combined with knowledge of geometry and dynamics,we have obtained a more systematic understanding of the faults and their microstructures in the South Baxian area.On this basis,we have confirmed the mode of oil and gas enrichment in complex fault systems by analyzing the evolution history of oil and gas accumulation,reservoir lithology,and physical properties.This study shows that the Xianbei fault is a reversed-S-shaped right-lateral three-step strike-slip fault under the influence of the Maxian fault.The Xianbei fault controls the formation of the South Baxian middle and shallow tectonic belt.The associated microfaults of the extensional zone expand from west to east,developing into three types of micro-faults,namely oblique bands,pinnate bands,and horsetail bands.The South Baxian oil and gas field is a homologous oil-gas reservoir.It was formed in two stages,its middle and shallow reservoirs being the tectonic-lithologic secondary fault block reservoir type.Three modes of oil and gas enrichment,namely fault oil control,micro-structure oil control,and sedimentary-phase control,are established.It is determined that the micro-structure of small beach-bar sand bodies with single-layer thickness in the pinnate band of the Xianbei fault is the area of oil and gas enrichment.Accordingly,five development wells are deployed in this area and the result of gas-testing is good.