Pressure Sensitive Experiment of Advanced Water Flooding in Low Permeability Reservior

摘要

The exploitation low-permeability oilfield is usually difficult, due to the insufficient natural energy in the reservoirs. The major challenge lies in the fast reduction in formation pressure during the exploitation process. To keep the formation pressure stable, advanced water injection that the method is to inject water into the oil field before the oilfield is exploited can be used. To study the variation of the permeability and microscopic pore structure in the reservoir under advanced water injection and conventional water injection, we divided the permeability into four levels through changing the pore fluid pressure, monitoring the permeability, porosity, radius of pore and coordination number, among which CT scanning method and Mercury method are used to research on pore structure changes. The results showed that the porosity is not sensitive to pressure changes. Permeability, pore throat radius and coordination number all exhibit similar they have slight increase as more pressure is imposed upon, whereas big drops in these parameters can be observed as pressure deceases. After the pressure is restored, none of the three parameters can be restored to the original level. In particular, permeability decreases as much as 19.38%, and could only be restored by 3.67% when the pressure is back at the same level. The experiment demonstrates that conventional water injection in low-permeability oilfields is not only harmful to reservoirs, but also by increasing the pore fluid pressure to restore the purpose of reservoir properties can not be achieved. Advanced water injection can maintain a higher formation pressure in the reservoir, and reduce formation damage due to the decrease of formation pressure, which is a favorable approach to improve the overall recovery during the exploitation in low-permeability reservoirs.