关键词: 砂砾岩, L-CO2, 压裂, ?CT扫描, 核磁共振

Abstract: Glutenite formations usually characterized by their dense and heterogeneity, thus the fracturing effect of conventional fracturing methods is not ideal. Liquid CO2 (L-CO2) fracturing is a fracturing stimulation method proposed in recent years, and the fracturing effect has obvious advantages. Water and L-CO2 fracturing tests are conducted on downhole cores, ?CT scanning and NMR tests are used to compare the difference of breakdown pressure, fracture characteristic and crack distribution and the L-CO2 fracturing mechanism in glutenite is deeply analyzed. It is found that under the same confining pressure, L-CO2 can greatly reduce the breakdown pressure, and the difference between the breakdown pressure of L-CO2 fracturing and water fracturing increases with increasing confining pressure. ?CT scanning shows that the fractures induced by L-CO2 fracturing are irregular fractures, which are more likely to deflect between gravel particles in glutenite, causing a branch fractures and complex fractures networks. The fracture volume of L-CO2 fracturing is much larger than that of hydraulic fracturing. Nuclear magnetic resonance (NMR) results show that L-CO2 fracturing mainly breaks through the micro-cracks at the interface of gravel particles, and the shear activation mechanism has a significant effect, while hydraulic fracturing mainly takes the form of a single tensile fracture rupture. The better fracture network obtained by L-CO2 fracturing is mainly related to the strong heterogeneity caused by gravel particles in glutenite, which affects the complexity of induced fractures. Relevant research results can provide guidance for glutenite reservoir fracturing and process optimization for increasing production and efficiency.

Key words: glutenite, L-CO2, fracturing, ?CT scaning, nuclear magnetic resonance