Evaluation of the impact of CO2 geological storage on tight oil reservoir properties

Carbon capture, utilization, and storage (CCUS) is an emerging methodology to mitigate CO2 emissions. When injected into the subsurface, there are potential interactions between CO2, pore fluids, and the reservoir rock. To determine analyzed the effect of CO2 on the physical properties of geological reservoirs, the pore structure, and mineral composition of cores before and after CO2 static soaking. The samples were analyzed using nuclear magnetic resonance (NMR), X-ray diffraction (XRD), scanning electron microscope (SEM), and energy dispersive spectrometer (EDS). This study found that the pore size of tight sandstone core samples increases with time under the same formation water condition. At the same time, the pore changes of tight sandstone samples are different under different CO2-formation water immersion. The experimental results show that the degree of dissolution of minerals with CaCl2 formation water is negligible. Often, When CO2 injection, two phenomena usually occur. First, mineral dissolution enlarges pores. Second, the diagenetic crystallization of salt and illite divides the pores will increase the pore size. The results of the CO2-NaHCO3 static immersion show experiments that within seven days, due to salt diagenesis and mineral precipitation than mineral dissolution, the pores decrease. With the further strengthening of mineral dissolution, the pores increase during 7-12 days. In addition, in CO2-CaCl2 type formation water, only pore size decreases within the reaction time of 12 days, indicating that precipitation is more excellent than dissolution in this water environment. The comprehensive analysis shows that the effect of CO2 on pore enlargement is not unidirectional but first inhibits and then promotes pore size. After CO2 injection into the formation, it is dissolved in formation water with different chemical properties, influencing reservoir rocks. Compared with CO2- CaCl2 formation water, CO2-NaHCO3 formation water has a noticeable effect of increasing porosity, which has the potential of improving oilfield tight reservoir conditions to a certain extent.