# Study on the Mechanism of Stress Sensitivity Changes in Ultra-Deep Carbonate Reservoirs
## 4 Example Application  
We have chosen the ultra-deep carbonate reservoirs of the T74 formation in the Shunbei area of the Tarim Basin for studying the stress sensitivity of ultra-deep carbonate reservoirs. The Tarim Basin is currently situated in the southern part of China's Xinjiang Uygur Autonomous Region. This area features broken seam cavern's ultra-deep carbonate reservoirs spanning from the eastern foothills of the Pamir Plateau in the west to the Rob Lake depression in the east, and extending from the southern foot of the Tianshan Mountains in the north to the northern foot of the Kunlun Mountains in the south [31; 32; 33]. As China's largest inland basin, the tectonic region is located between the Tianshan Mountain range and Kunlun mountain range with abundant Permian slope-deposition-environment hydrocarbon source rocks in the northern and eastern parts of the basin, where the upper stratum is home to together complete life-storage-cover geological amounts [34]. Movement by multiple fault planes serves as favorable conditions for oil and gas migration and accumulation, leading to highly optimal capture conditions. Due to the influence of the fault zone, and the matrix in the reservoir serving as the primary storage unit, the fractures  
Figure 5: Stress sensitivity curve of fractured carbonate rock under variable Young’s moduli. acting as the main fluid flow channel demonstrate strong reservoir heterogeneity and the fractures heavily impact the stress sensitivity of the reservoir. Phase 1: Middle Cambrian. This stage was the main period of formation for strike-slip fault systems within the craton. Due to the collision between the West Kunlun and Tarim blocks, the study area underwent a regional uplift leading to the formation of several compressional uplifts and small-scale regional fault systems. Phase 2: Late-middle to early-late Cambrian. This stage saw the main period of activity for the strike-slip fault system under strong compression. In the Silurian and Devonian periods, a shallow en echelon-style strike-slip fault developed due to the deep-seated fault zone. Phase 3: Late Devonian to Indosinian. During this stage, the study area was mainly affected by the compressive force of the South Tian Shan Mountains, and the strike-slip fault zone continued to be active. The deep-seated faults formed in the early stages of this period were also reactivated. Additionally, small-scale faults developed in the Carboniferous and Permian in the Shunbei area. Phase 4: Yanshan to Himalayan. This stage was the period of evolution for the Tarim Basin depression where the study area had undergone fracturing activities due to tensional stress. In the early stage, NE-trending strike-slip faults were active, while their activity diminished in the late stage, leading to the final formation of strike-slip faults in the Shunbei area. In the early stages, the northeast-trending strike-slip faults were very active. In the later stages, their activity gradually decreased, eventually leading to the formation of strike-slip faults and pattern II fractures in the Shunbei area (Table 4). The development of natural fractures in the study area was investigated through resistivity logging. Resistivity logging is relatively sensitive to fracture identification and can be affected by factors, such as fracture orientation, extension length, and mud invasion depth. In lateral logging, because the measuring circuit is in parallel with the low-resistance fracture, the resistivity is greatly affected in the vertical fracture segment and can be identified by the lateral logging for vertical fractures. In the induction logging, the measuring circuit is in parallel with the horizontal fracture, and the resistivity is greatly affected in the horizontal fracture segment such that it can identify vertical fractures. According to previous research, when high-angle fractures develop, lateral resistivity displays a positive anomaly while middle and low-angle fractures display a negative anomaly or a low-resistivity peak (Figure 6).