CHARACTERIZATION OF DYNAMIC PORE-THROAT STRUCTURE AND PETROPHYSICAL PROPERTIES IN AN UNCONSOLIDATED SANDSTONE RESERVOIR

In this study, a comprehensive and practical technique was developed to study the dynamic changes of pore-throat structure and petrophysical properties of unconsolidated sandstone reservoirs during long-term water injection. Experimentally, core samples were gathered from unconsolidated sandstone reservoirs for thin-section preparation and analyzed using laser particle size and X-ray diffraction techniques. In addition to identifying and classifying pore types and clay minerals, the size, fraction, and distribution of particles were also determined and categorized. Furthermore, a high-pressure mercury injection test was conducted on the core after waterflooding so as to quantify alterations in the microscopic pore-throat structure. The dispersion of clay minerals breaks the formation bond, leading to the fall and migration of clay and fine silt, and the content of clay and fine silt decreases, resulting in the change of pore-throat structure. Compared with the change of pores, the change of throat has a greater influence on the seepage behaviour, but such a change mainly occurs in the early stage of waterflooding. The fractal dimension of the pore-throat structures increases from 2.51 to 2.58, enhancing the heterogeneity and making the seepage channels more concentrated. The pore-throat structure was changed by 90% when water was injected to 200 PVs, gradually changed until 300 PVs of injected water, and then remained basically unchanged afterwards.