FRACTURES SYETEMS IN THE DISTRICT 4 OF TAHE OIL-FIELD IN XINJIANG, CHINA

Tarimu basin is a largest one in China, over an area of 560000 km², bounded by Kunlun Mountain in the south edge, Tianshan Mountain in the north edge and Altyn Mountain in the east edge and has a great deal oil and gas resources. The oil and gas pool develop mainly in the limestone of Yingshan and Yijianfang formation of lower Ordovian system. Tahe oil-field in Tarim basin is a famous one that is typically of fracture-cave system and so the fracture is a mostly important factor that influence and control the oil and gas pool. Baced on 20 well cores observation, micro-section identification, FMI analysis and other data including field study, we investigate particularly the fractures of District 4 of Tahe oil-field. The fractures are subdivided into four epochs: I. Pre-Calidonian; II. Calidonian; III. Early Hercynian IV. Early Hercynian-Yanshanian. The geometric features of the fracture have exclusively been reconstructed. According to their occurrence in cores, the fractures are of three types: I. high angle dipping(＞75°)-vertical; II.medium angle dipping(approximately 30° to 75°) and III. lower angle dipping(＜30°) and the first is statistically more likely to be common. This result is particularly well compatible with that of direct crops observation. Some of the fractures generally are filled with calcite or detritus material and may become more attenuated and decrease in accumulation pasibility . The study reveals that the fractures would be most effective in oil and gas migration. Commonly, the fracture is directly linked to faults.