Adsorption of four dyes, namely methyl violet (MV), rhodamine 6G (R6G), acid chrome blue K (AK) and xylenol orange (XO) onto sodium alginate graft poly(acrylic acid-co-2-acrylamide-2-methyl-1-propanesulfonicacid)/kaolin (SA-g-P(AA-co-AMPS)/KL) hydrogel composite is studied. The factors influencing the adsorption capacities, including the initial concentrations of dye solutions, contact time, initial pH values and dosage of the adsorbent as well as ionic strength of the solution are discussed. It is more effective for the composite to adsorb cationic dyes such as MV and R6G rather than anionic dyes AK and XO. The maximum adsorption capacities of MV, R6G, AK and XO are 1361.1, 1627.8, 563.5 and 312.4 mg/g, respectively. The adsorption thermodynamics for the four dyes are in accordance with both the Freudlich and Redlich-Peterson equations. It is shown that adsorption of the cationic dyes R6G and MV is spontaneous, while that of anionic dyes AK and XO is not. The kinetics studies show that the adsorption of the four dyes fitted a pseudo-second-order equation.

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Carbonated water injection (CWI) is a modified CO2 flooding technique for enhanced oil recovery, which takes advantage of both CO2 flooding and water injection and has attracted much attention recently. However, the dedicated research so far has focused heavily on conventional reservoirs. The objective of this research is to investigate the performance of CWI in a tight oil reservoir. First, a set of well-designed multiple contact tests were conducted to simulate the dynamic mass transfer process of fresh carbonated water (CW) to live crude oil. In each test, CW was brought into contact with live crude oil in a high-temperature and high-pressure PVT cell. Pressure changes during the test were observed and recorded. After equilibrium, all the transferred CW was taken out of the cell and the swelled oil proceeded to the next contact. The volumes of water and liberated gas were measured. Then, the oil swelling factor could be calculated, which would verify the existence of the moving interface between CW and live crude oil. It was observed that the system pressure built up immediately after CW was mixed with live crude oil in the PVT cell. For the first contact, the equilibrium pressure increased by 6.46 MPa, and the equilibrium pressure increased by 2.16 MPa at the last contact. This result indicates a strong interaction between CW and live crude oil, which is beneficial to maintain reservoir pressure. Because a large amount of CO2 from CW was transferred to the live crude oil, the swelling factor of 1.26 was obtained at the end of the tests. The diffusion of CO2 into the live crude oil also leads to subsequent oil viscosity reduction. In addition, a series of coreflood experiments under real reservoir conditions were carried out to evaluate the performance of CWI for improving oil recovery in core samples from a tight sandstone reservoir. Coreflood results showed that both secondary and tertiary CWI recovered additional oil compared to water flooding. Finally, a significant amount of CO2 was stored in the cores. Our experimental results clearly indicate the potential of CWI for improving oil recovery and CO2 storage capacity in tight oil reservoirs.