Development Characteristics and Exploration Implications of Low-Order Fault Systems in Tarim Basin: An Example from Shunbei Oil and Gas Field

The deep-margin carbonate rocks in the Tarim basin exhibit dense physical properties and are prone to brittle deformation under stress concentration, resulting in the development of multi-order strike-slip fault systems. However, due to the characteristics of low-order faults being 'small in scale, weak in activity, and diverse in direction', their distribution and genesis have been argumentative in current structural research. Based on the high-quality 3D seismic data of the Shunbei area, it built the geophysical identification methods and distribution prediction of low-order faults. Through the systematic analysis of seismic, drilling, logging and field survey data, the distribution patterns, genesis models, and characteristics of reservoir formation of low-order faults in the Shunbei area were revealed. Preliminary suggestions for exploration evaluation and deployment strategies were proposed.(1) A technical sequence for identifying low-order faults was developed, which involves 'enhanced geophysical preprocessing first, followed by optimal attribute selection of sub-regions'. This results in improving the identification accuracy of low-order faults to 1 km in length. (2) Five sets of NE, NEE, NW, near NS, and near EW trending low-order faults in the northeastern central Shunbei area were recognised, and classified into three genetic types: nearly parallel system, acute angle system, and near vertical system. (3) Low-order faults typically do not develop a complete fault core-damage zone architecture, but consist of multiple sets of fracture zones, lacking large angular gravel breccia zones and angular gravel cavities. It is smaller in scale and weaker with connectivity compared to main strike-slip faults, making them preferred for forming overpressured oil and gas reservoir systems. Identifying target reservoirs with a certain scale is crucial for the decision of the low-order faults exploration, requiring consideration of geology-engineering integration, preferentially selecting beads-shaped reflections in high-density areas of low-order faults and designing Multi-Target Well.