Using seismic methods to detect connectivity of fracture networks controlled by strike-slip faults in ultra-deep carbonate reservoirs: A case study in northern tarim basin, China

Abstract

Ordovician tight carbonate rocks in the Tarim Basin are typically ultra-deep, with targets deeper than 7000 m. The fracture networks associated with strike-slip faults are the primary reservoir space. Fracture intensity near faults is higher than in wall rock areas and decreases with distance from faults. Based on the relationships of fracture network with the structure of strike-slip faults imaged by seismic data, adjacent to faults (in the ‘fault wall’) there are small-scale wall damage zones (SML SC WALL DMG ZONE) having fault widths is less than 250m, length less than 5 km; large-scale damage zones (LRG SC WALL DMG ZONE) having fault widths are greater than 250m, lengths greater than 5 km; intersection damage zones (INT DMG ZONEs), linking damage zones (LINK DMG ZONEs), overlapping zones between the linking damage zones and intersection damage zones (OL ZONE LINK INT DMG ZONEs).Increasing fracture intensity can be incorporated into fracture network models using well data and seismic data. We used the bounding box and scan line methods to evaluate fracture network connectivity and predict flow. The reliability of the results was verified by interference well tests. The fracture network connectivity based on the bounding box and scan line method is consistent with interference well test data, demonstrating that the bounding box and scan line method can effectively evaluate fracture network connectivity. The fracture network connectivity ranges from high to low in this order: overlapping zones between linking and intersecting zones, linking, intersecting, and large- and small parallel zones. Based on outcrop pattern and 3D discrete element simulation results we infer that connectivity is caused by stress concentration and perturbation in the evolution of strike-slip fault. The LINK DMG ZONE raises the displacement gradient and causes local rotation of the stress field, resulting in increased intensity, complex fracture directions, and high connectivity of fractures. The slip gradient of the INT DMG ZONE grows significantly due to stress perturbations, culminating in more fractures and increased connectivity. The OL ZONE LINK INT DMG ZONE generates more complex fracture networks with better connectivity.