Paleomagnetic Orientation Analysis of Macroscopic Natural Fractures at Yanchang Formation in Northeast Yanchang Oilfield

Chang 6 oil layer group of Triassic Yanchang Formation in northeast Yanchang oilfield is a typical kind of ultra-low permeability reservoir, in which the natural fractures are widespreadly developed.The development extent and direction of these fractures are the key factors in oilfield water injection development and well pattern arrangement.In this paper, we introduce the technique of paleomagnetic determination of core samples has been introduced to determine the orientation of fractures, which can provide a basis for flooding pattern arrangement.The study suggests that the fractures are mostly formed during Yanshanian period and Himalayan period, in which the fractures formed in Yanshanian period are basically E-W and S-N trending regional fractures, while the fractures formed in Himalayan period are basically N-E trending fractures.Chang 6 reservoir fractures are mainly structural fractures, with high-angle, tensional and vertical characteristics, including various shapes, such as unsealed fractures, half-sealed fractures and sealed fractures.Around 58% of the Chang 6 reservoir fractures are N-E trending, 33% of the fractures are N-W trending, and the others are one E-W trending fracture and one S-N trending fracture, accounting for 8%.