3D synchrotron computed tomography study on the influence of fines on gas driven fractures in Sandy Sediments

Abstract

Production of methane from hydrate-bearing sediments requires hydrate dissociation for releasing mobile methane gas in sediments prior to gas production operations. Fines may migrate through or clog the pore space of sandy sediments depending on the geometry and topology of the pore space. Multiphase flow experiments were conducted on brine saturated uniform silica sand mixed with different percentages of kaolinite. Fines concentrations were correlated to computed tomography (CT) numbers in their host brine phase. Representative element volume (REV) procedure was used to study local porosity and local fines concentration. A cubical REV with a side length of 850 µm was selected. For low fines content (less than 6%), gas percolated through the specimens with no major particle translation or porosity change. For 6% kaolinite specimen, fractures were initiated, and propagated by densifying surrounding sediments. Local fines concentration study showed that fines migrated through the pores for specimens with fines content less than 6%. For the 6% kaolinite specimen, fines concentrated near fractures due to clogging. Clogging induced an increase in the capillary pressure at the pore throats and caused the capillary pressure to overcome the effective stress between sand particle, and fractures to be initiated. Sand particles experienced up to 200 µm translation and 15◦ rotation due to gas driven fracture in the 6% kaolinite specimen