关键词:

漏失机理, 岩石力学参数, 扫描电镜, 成像测井, 四压力剖面, 钻井液

Abstract:

Rich in natural gas resources，Misui Block is a key strategic area for accelerating the production of Changqing Oilfield. However，the frequent occurrence of lost circulation in recent years has seriously restricted improvement of cost-efficiency. Therefore，to curb the occurrence of well lost circulation，the lost circulation mechanism in this area has been studied through multi-scale quantitative experiment on rock physical property，microelectrode imaging logging observation and geo-mechanical profile analysis of wells. The results show that the thief zones in Misui Block are mainly in Liujiagou and Shiqianfeng Formations，which have large numbers of micro- and nano-scale fractures. The average calculated dynamic Yang's modulus of the cores from these formations are 17.94 GPa and 8.47 GPa，respectively，and the average dynamic Poisson's ratios are 0.394 and 0.064，respectively. The clay mineral content of Liujiagou Formation is more than 50%，and the brittle mineral content of Shiqianfeng Formation is as high as 72%. The imaging logging map shows that the area contains tensile fractures. The single well geo-mechanical profile reveals a low-pressure area in the thief zone，where the density of drilling fluid is 1.18 g/cm³. Finally，analysis shows that the high contents of clay and brittle minerals in the formation caused both hydration fractures and structural fractures，with low formation pressure causing drilling fluid to flow into natural fractures，eventually resulting in lost circulation. The research results not only reveal the lost circulation mechanism at Misui Block，but also provide technical guidance for selecting plugging methods and reducing well lost circulations at Misui Block.

Key words:

lost circulation mechanism, rock mechanics parameter, scanning electron microscope, imaging logging, geo-mechanical analysis, drilling fluid