Experimental study of two-phase fluid flow in two different porosity types of sandstone by P-wave velocity and electrical Impedance measurement

Abstract:

Carbon dioxide (CO₂) capture and storage (CCS) is recently expected as the promising method to reduce greenhouse gas emissions. It is important to investigate CO₂ behavior in the reservoir, to evaluate the safety and to account the stored CO₂ volume. In this study, experimental investigation is conducted to discuss the relationships between injected fluid speed (Flow rate: FR) or capillary number (Ca) and non-wetting fluid flow by compressional wave velocity (V_p) and electrical impedance (Z). In the experiment, N₂ and supercritical CO₂ were injected into the two sandstones with different porosity (φ), Berea sandstone (φ: 18 %), and Ainoura sandstone (φ: 11.9 %). The dimension of the rock specimens is cored cylinder with a 35 mm diameter and 70 mm height. Experimental conditions are nearly same as the reservoir of deep underground (Confining pressure:15MPa, 40℃). Initial conditions of the specimen are brine (0.1wt%-KCl) saturated. Four piezo-electrical transducers (PZTs) are set on the each surface of the top, middle, lower of the specimen to monitor the CO₂ bahavior by Vp. To measuring Z, we use for electrodes method with Ag-AgCl electrodes. Four electrodes are wounded around specimen on the both sides of PZTs. We measured the changes of these parameters with injecting N₂, injected fluid speed (FR), the differential pore pressure (DP), N₂ saturation (S_N2), P-wave velocity (V_p) and electrical impedance (Z), respectively. We also estimated the Ca from measured FR. From these experimental results, there are no obvious V_p changes with increasing Ca, while Z measurement indicates clear and continuous increment. In regards to V_p, V_p reduced at the small FR (0.1 to 0.2 ml/min). As the Ca increases, V_p doesn’t indicate large reduction. On the other hand, Z is more sensitive to change the fluid saturation than V_p. It is well-known that both of V_p and Z are the function of fluid saturation. Though, these experimental results are not consistent with previous studies. In this study, we will discuss this mismatch by using fluid mechanical theory and numerical simulation of two-phase fluid flow in porous geological medium based on experimental results of two different types of sandstone.