Secondary recovery techniques are methods used in oil extraction to increase the amount of crude oil that can be recovered from a reservoir after primary recovery has taken place. Primary recovery typically uses natural pressure or mechanical pumps, but as the pressure decreases, secondary techniques become necessary. These methods often involve injecting water or gas into the reservoir to maintain pressure and push more oil towards the production wells. One common secondary recovery technique is water flooding, where water is injected into the reservoir to displace oil and drive it towards production wells. Another method is gas injection, which involves injecting gases like carbon dioxide to enhance oil flow. Both techniques help maximize oil recovery and improve the efficiency of extraction operations.