"2 pore volume of water or oil injection" refers to the volume of fluid that has been injected into a reservoir relative to the total pore volume of the reservoir. Pore volume is the total volume of the pores or void spaces in the reservoir rock that can contain fluids.
When injecting fluids into a reservoir, the goal is often to displace or push out the existing fluids (usually oil) in the reservoir and replace them with the injected fluids (water or oil). The amount of injected fluid required to achieve this goal can vary depending on the specific application and the characteristics of the reservoir.
When it is mentioned 2 pore volume of water or oil injection, it means that the amount of injected fluid is two times the total pore volume of the reservoir.