Liu, Keyu (CSIRO Earth Science and Resource Engineering) | Clennell, Michael Benedict (CSIRO Earth Science and Resource Engineering) | Honari, Abdolvahab (University of Western Australia) | Sayem, Taschfeen (University of Western Australia) | Rashid, Abdul (CSIRO Earth Science and Resource Engineering) | Wei, Xiaofang (Research Institute of Petroleum Exploration and Development, PetroChina) | Saeedi, Ali (Curtin University)
A series of laboratory investigation on factors affecting Enhanced Oil and Gas Recovery and CO2 geo-sequestration were conducted. The coreflooding experiments were done using a relatively heavy crude oil (18° API), a number of brines of 0.18%-2.5% NaCl and varieties of cores with a range porosity and permeability from 15% and 17 mD to 19% and 330 mD under some typical reservoir pressure-temperature condition of 1164-3300 psi and 50-83 °C. Factors affecting CO2 enhanced oil and gas recovery including the effects of the petrophysical properties of the reservoir rocks, formation water salinity, reservoir pressure, the Minimum Miscibility Pressure (MMP), total volume (PV) injected and injection rate and gravity segregation.
Excellent recovery factors in the range of 27%-34% Original Oil In Place (OOIP) and almost 100% gas recovery were achieved through immiscible and miscible CO2 flooding. Some of the coreflooding experiments were monitored with a medical CT in real time. The coreflooding experiments have shown that (1) reservoir petrophysical properties with permeability difference of up to an order of magnitude do not affect the CO2 EOR factor; (2) variable EOR can be achieved both at reservoir pressures below or above the CO2-oil MMP; (3) Incremental oil recovery is proportional to the pore volume (PV) of CO2 injected up to 3PV; (4) No significant additional recovery was observed beyond the MMP; (5) CO2-Water alternating gas (WAG) flooding can be quite effective in EOR in terms of the less amount of CO2 injected as compared to that for the single CO2-water flooding to achieve the same EOR; (6) there is no benefit to use low-salinity CO2 WAG flooding; (7) the optimum injection rate in the laboratory is around 1 cc/minute. These finding may provide some useful insight and guide for the field application of CO2 enhanced oil and gas recovery; (8) During enhanced gas recovery using supercritical CO2, gravity segregation may occur in some porous-permeable reservoir with denser supercritical CO2 preferentially enter through the bottom of the reservoir.
In order to screen various chemical and microbial EOR methods for core-flooding experiments and potential field trials, a laboratory investigation of evaluating the effect of micro-emulsion on the reduction of interfacial tension (IFT) was recently carried out at CSIRO by using commercially available chemical and bio-surfactants. Environment friendly non-ionic, anionic surfactants and a biosurfactant (Bacillus subtilis) were used to create micro-emulsion in an oil-brine system. Stable micro-emulsion (ME) was achieved by proportionally mixing various alcohols with surfactants.
Twenty-four micro-emulsion samples with five different chemical combinations were prepared for screening. All samples were stirred to create a stable ME phase. The volume changes of the ME phase were monitored over two weeks and their density, viscosity, and IFT were measured. The size distribution of ME phases was also characterised using optical microscopy equipped with an UV light source.
The micro-emulsion created by co-surfactants were found to be quite effective in reducing the oil-brine IFT and oil viscosity, and achieved ultra low IFT under reservoir pressure and temperature. There appears to be a linear relationship between the size of micro-emulsion and IFT reduction. ME with small sizes results in more IFT reduction and achieve stable ME at high temperature and pressure. Compared with the IFT reduction from the surfactant or microbial metabolism, the reduction of IFT through stable ME can be several orders of magnitude larger and may thus achieve better enhanced oil recovery in suitable reservoir systems.