延长油田东北部延长组宏观天然裂缝古地磁定向分析

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

延长油田东北部三叠系延长组长6油层组为典型的特低渗碎屑岩储层,普遍发育天然裂缝,裂缝发育程度及方向是油田注水开发井网部署的关键考虑因素。引进岩心样品古地磁测定技术确定裂缝方位,为注采井网部署提供依据。研究认为,裂缝形成时期主要为燕山期和喜山期,燕山期裂缝主要为EW、SN向区域裂缝,喜山期裂缝则主要为NE向裂缝;长6油层裂缝以构造裂缝为主,主要发育高角度张性垂直缝,裂缝有开启、半开启、闭合多种形态;裂缝主要以北东方向为主,约占58%;北西方向次之,约占33%;东西与南北方向裂缝各一条,占8%。

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 o- rientation 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%.