Structural characteristics and physical simulation of X-shaped normal faults

The X-shaped normal fault is a common extensional tectonic fracture. However, its geometric characteristics, formation process, and genetic mechanism are lack of systematic research. Based on fine interpretation of seismic data and physical modelling, the geometric characteristics are clarified, the formation process is reconstructed, the formation mechanism is confirmed, and the reservoir control effect is discussed. The research result indicates that the X-shaped normal fault can be divided into two types: incipient X-shaped normal faults and the inherited X-shaped normal faults. The inherited X-shaped normal faults are formed by the reactivation of basement faults, including two modes of differential extension and bidirectional uniform extension. The incipient X-shaped normal faults are formed under the stress background whose tensile stress vs shear stress ratio is 1:2 ～ 2:1. In addition, the inherited X-shaped normal faults have advantages of good oil and gas migration and reservoir reconstruction. Meanwhile, they form various traps and feature “multi-storey”-styled oil-gas accumulation. This research provided a reference for hydrocarbon exploration in Bohai Bay basin, enriched the theoretical understanding of the structural patterns with a geological cue for fine structural interpretation of similar cases.