Structural diagenesis in carbonate fault damage zone: A case study of the No. 1 fault zone in the Tarim basin

Due to the extremely complicated deformation and diagenetic process in fault damage zone of the multicycle superimposed basin, structural diagenesis of cross-disciplinary approach provides a powerful tool for the study of the mechanism and evolution, and fluid-rock interaction in fault damage zone. Based on the integrated analysis of cores, thin-section and geochemistry data, this paper presents the carbonate structural diagenesis along No. 1 fault zone in the Tarim basin. It is showed that there is multi-types and multi stages structural diagenesis in the Ordovician carbonate fault damage zone, which is obvious different from the country rocks. The fault damage zone, having characteristic of fracture zones of multi-types and high degree of opening with frequently lateral variation, is up to 2 similar to 4km wide. There is weaker compaction with varied degrees, but compaction deformation bands were identified in fault damage zone, which also occurred localized high permeability by the late fracturing and dissolution process. The stronger pressure solution resulted in low-angle and high-angle stylolites, part of them had seepage performance. There are 4 5 stages of multi-types cementation, and more of meteoric cements in early diagenesis, and with weaker cement filling in damage zones compared with country rocks. The meteoric dissolution lens in penecontemporaneous diagenesis and localized karstification, and stronger buried dissolution occurred mainly in fault damage zones, which resulted in the development of large scale fracture-cavity reservoirs and dissolution porosity-vug reservoirs in the Upper Ordovician carbonate. It is also indicated by structural diagenesis that there are 5 stages evolution in fault damage zone: fault initiation stage-forming stage-finalizing stage-resurrection stage-local opening stage, and different evolution period has distinct structural diagenesis. Therefore, the discrepancy of multi-phase structural diagenesis process plays a crucial role in the complexity of the ancient carbonate damage zone.