# Influence of Stress Anisotropy on Petrophysical Parameters of Deep and Ultradeep Tight Sandstone
## 2 Geological Setting  
The Kuqa Depression, located at the junction of the Tarim Basin and Southern Tianshan Mountains, is a typical deep-ultradeep gas-rich area [35; 36; 37]. The Kelasu tectonic belt is the second row of the thrust belt in the northern Kuqa Depression, which was formed during the evolution of the Kuqa Depression. The burial depth is between 6000-8000 m, and it is an ultradeep reservoir. The Kelasu tectonic belt is divided into the Kela zone and Keshen zone, and the Keshen zone is divided into four sections from east to west, namely, Keshen, Dabei, Bozi and Awat (Figure 1). Ground stress and fracture development scale are important factors controlling production [38; 39]. The Kuqa Depression experienced an evolution stage from a passive continental margin to a peripheral foreland basin in the late Permian to Triassic. Late Cretaceous regional uplift and denudation, regional peneplain stage; Paleogene weakly extensional tectonic setting; and Neogene to Quaternary compressive stress made the Kuqa Depression enter the evolutionary stage of the Paleozoic basin. The compression was most intense in the middle and late Neogene, and the current tectonic deformation of the Kelasu tectonic belt mainly occurred during this period [40]. The tectonic stress environment can be roughly divided into four periods. The Triassic compressional tectonic environment was mainly a contracting tectonic deformation. Based on stratigraphic and lithofacies data, the Kelasu tectonic belt through the Jurassic and Cretaceous periods was a variation zone with rapid thickening from south to north and had a regional tectonic setting with high-angle normal faults [41; 42; 43]. In the Paleogene, the relatively weak extensional tectonic stress environment or stable tectonic environment mainly formed depression basins and developed a large number of salt rocks. The Neogene to Quaternary compression in the near north-south region formed intercontinental or foreland-like basins before the new Tianshan intraplate orogenic belt [44]. The strata of the Kelasu tectonic belt are divided into suprasalt strata, salt strata and subsalt strata. The subsalt strata include the Triassic, Jurassic and Lower Cretaceous strata. The salt rock is from the Paleogene Kumugeliemu Group. The upper and lower salt strata include the Suweiyi Group of Paleogene, Jidike Group of Neogene, Kangcun Group of Neogene, and Kuqa Group of the Neogene and Quaternary system [45; 46; 47; 48]. In the late Cenozoic period, the Kuqa foreland thrust belt was strongly compressed. The anticlinal three-layer structure with different vertical stresses was formed by the tectonic compression of the southern Tianshan Mountains, the induction and equalization of the overlying salt layer, and the arch extension of the very thick mudstone of the Cretaceous Shushanhe  
Figure 1: Fault Outline Map of Kelasu Structural Belt. Group. Under the influence of stress, the Cretaceous Bashijiqike Group reservoir can be divided into a vertical three-layer structure, which consists of the stress sections of tensile, transitional, and compression torsion from top to bottom. In the longitudinal direction, the productivity of different stress sections varies greatly [49]. [PERSON] et al. (2004) used the fault slip data inversion method to recover Neogene paleotectonic stress in the Kuqa Depression based on field observations of faults developed in the Neogene, Paleogene and Cretaceous periods that were simultaneously involved in deformation [50]. The results show that the tectonic stress direction of the Kuqa Depression had little spatial variation in the Neogene and experienced a NNW-SSE compression deformation stage in the Miocene Jidike Group-Kangcun Group and a WNW-ESE compression deformation stage in the Pliocene Kuqa Group. Reservoir heterogeneity is strong in the Kuqa Depression, which affects well productivity.