Abstract:

The ascertain of Aogula fault and its nearby structures has important significance in exploration and development of Qijiagulong sag in the northern Songliao basin. During the seismic interpretation of the footwall of Aogula fault, from 4 aspects like regional structure, logging curve comparison, structural interpretation of dense well pattern and seismic forward modeling, it is proved that a previously interpreted near-upright fault is a pseudo-fault due to the inaccurate structural imaging and the existence of fault shadow. It is concluded that all or partial low-velocity intervals are broken in local areas and the interval velocities of the strata located on both sides of the fault abruptly change laterally, resulting in an inaccurate fault shadow in the footwall of the fault, both of which can be attributed to a large fault-throw normal fault passing through the low-velocity interval of the Lower Cretaceous Nenjiang formation in the northern Songliao basin. The paper proposes that the pre-stack depth migration technology based on high-precision velocity modeling can improve the phenomenon of the fault shadow. Regarding the seismic data in conventional time domain, structural interpretation can be carried out by using seismic forwarding modeling results and logging-seismic integration. The identification of the pseudo-fault in the fault shadow provides technical support for well allocation in Aogula oilfield.

Key words: Songliao basin, Aogula fault, fault shadow, low-velocity interval, well logging-seismic integration, seismic forward modeling