Volcanic Rock Assemblage, Stratigraphic Attribution and Geological Significance of Volcanic Reservoir in Kebai Fault-trough in Karamay: Constraints from Well Gu 66

The Kebai fault-trough originates from the Kebei fault at the southwest end and extends northeastward, intersected by the Dazhuluogou fault, which begins in the northern region of Karamay City. It is bounded by the basin-edge fault on its northwest edge and the Kebai fault on its southeast edge. The primary reservoirs within this fault-trough are composed of volcanic rock. However, the stratigraphic allocation, age, and sequence of these volcanic rocks remain uncertain. This study employs a comprehensive approach involving detailed core logging, lithodensity identification using well logging curves, and zircon U-Pb dating of key volcanic rock layers within the interval of 242.14～800.18 m in the well Gu 66, located within the Kebai fault-trough. The results of our investigation reveal the following insights: The interval from 242.14～800.18 m in the well Gu 66 encompasses three distinct sets of volcanic rock formations, interspersed by two layers of terrestrial clastic rocks functioning as marker beds. Through zircon LA-ICP-MS U-Pb dating, we determined ages of 304±3 Ma and 303±2 Ma for the andesite in the well Gu 66. The rock composition, ages, stratigraphy, and thickness of these formations show notable similarity to the C₂h¹～C₂h³ sections of the Hala’alate Formation profile situated in the northern edge of the Hashan region. The Kebai fault-trough, hosting the well Gu 66, represents a distinctive fault-trough characterized by volcanic rock reservoirs, enclosed by surrounding fault structures. This novel type of hydrocarbon reservoir expands the repertoire of oil and gas reservoir types found in the western Junggar. Furthermore, the fault-trough exhibits structural attributes, reservoir characteristics, and trap styles that extend southwestward, rendering it a promising new target area for forthcoming oil and gas exploration.