| dc.description.abstract | The increased demand of hydrocarbons in combination with the climate change represent a current challenge for a petroleum industry that aims to increase the production and reduce its emissions. Reaching the Paris agreements and the goal of net-zero emissions within 2050 is a huge task. Thus, low carbon solutions during hydrocarbon extraction are needed, among them Smart Water is an alternative to lower the carbon footprint of oil recovery operations.
Smart water injection is an enhanced oil recovery (EOR) method that alters the wettability of the reservoir rock and as a cause of that, water breakthrough is delayed, and more oil can be displaced. Carbonated water injection (CWI) has been proposed as a promising EOR technique in carbonates as well as it simultaneously reduces the emission of greenhouse gas as a cause of CO2 being saturated in the injection water. The hypothesis of CWI’s main mechanisms such as mass transfer between oil and water phase, wettability alteration and evolution of solution gas, are investigated in this study.
The material used in this study is Stevns Klint (SK) outcrop chalk from Denmark, which is a well-known analogue for North Sea chalk reservoirs. CWI was utilized at high temperature to optimize the production. Several analyses such as pH measuring of effluent, SEM and EDX analyses, solubility of CO2 in different carbonated liquids with simulation in PHREEQC and 3-Phase solubility test was performed to investigate, the oil/brine/rock/CO2 interactions and to evaluate the mechanisms. Normal and carbonated de-ionized water (DI), sea water (SW) and formation water (FW) was used in four injection strategies in SK chalk to investigate the effect of dissolved CO2 in Sea water.
It was observed that the solubility of CO2 in brines was low and that it was varying with pressure and salinity. The pH of the carbonated brines was reduced; however, it was observed that the acidity did not increase by increased pressures. A 3-Phase solubility test indicated that mass transfer between the CW and oil occurred but there was residual CO2 dissolved in the water phase, one third of CO2 remained in the aqueous solution.
Carbonated sea water injection (CSWI) was the best performing injection fluid. It increased the oil recovery in both secondary mode and tertiary mode, however, CSWI in secondary mode was clearly the best oil recovery strategy. The oil recovery was also increased by carbonated formation water injection (CFWI) in tertiary mode.
The assumed mechanisms of CWI are mass transfer that leads to swelling and viscosity reduction, however, in this experimental setting, this mechanism is most likely not the cause of the EOR effect observed. The effect of wettability alteration and liberated CO2 gas from CW were assumed to be the main factors for increased oil production. | |