Configuration types of fault-sand and its control on hydrocarbon accumulation in the East Slope of Chengdao, Bohai Bay Basin

Faults and sand bodies are the main transport elements of hydrocarbon migration of the Dongying Formation in the East Slope of Chengdao. In order to explore the mechanism of hydrocarbon migration and accumulation under the control of fault-sand configuration transportation conditions, the types of fault-sand configuration of the Dongying Formation in the East Slope of Chengdao are first divided based on the precise interpretation of seismic data and RMS attribute analysis of sand body. The fault-sand configuration transport properties are quantitatively evaluated by using the relative transport index of the sandstone transport layer RT_i and fault lateral conductivity index F_LSI indices. The control effect of different types of fault-sand configuration on hydrocarbon migration and accumulation was then analyzed with the HMIE index and Trinity hydrocarbon migration numerical simulation. The results show that the fault-sand configuration in the East Slope of Chengdao can be divided into three types, forward configuration of fault-sand, reverse configuration of fault-sand and compounds of primary faults and secondary faults configuration of fault-sand according to the spatial superposition relationship between faults and sand bodies. The controlling effect of fault-sand configuration on hydrocarbon accumulation is mainly reflected in the following aspects: (1) Control the area of hydrocarbon migration and accumulation; the hydrocarbon migration and accumulation was controlled by transportation conductivity of fault-sand configuration when RT_i > 0.15, RT_i are positively associated with the degree of hydrocarbon accumulation on the slope region, hydrocarbons are easily sealed laterally to form reservoirs on the fault terrace zone when F_LSI≥0.45. (2) Control the dominant migration path of hydrocarbon; the types, the communicating effectiveness with the source rock and transport capacity of fault-sand configuration determine the dominant migration paths of hydrocarbon. The HMIE index and Trinity simulation analysis show that there are three dominant migration paths, namely, the depression area towards the fault belt of southern Shenghai 10, the depression area towards the fault belt of southern Shenghai 8, and the depression area belt towards the fault terrace area. (3) Control the distribution and accumulation of hydrocarbon; The forward configuration of fault-sand mainly plays the role of stepping hydrocarbon transport, the reverse configuration of fault-sand type can block hydrocarbon accumulation laterally, and the compounds of primary faults and secondary faults configuration of fault-sand plays the role of diverting hydrocarbon first and then enriching it. Different types of fault-sand configuration control the hydrocarbon accumulation pattern, which has the characteristics of “zonal control, vertical differentiation and multi-layer system enrichment”.