Study on the Injection Modes and Displacement Characteristics of Chemical Compound Flooding in Heavy Oil Reservoirs After Multiple Cycles of Huff and Puff

The chemical agents, the injection modes and displacement characteristics of chemical compound flooding, consisting of plugging agent, oil displacement agent, and viscosity reducer, were investigated by laboratory experiments for the target heavy oil reservoirs after multiple cycles of huff and puff. The performance of oil displacement agent, viscosity reducer and plugging agent were evaluated and the formulation and concentration were optimized. The oil displacement effects and displacement characteristics of different injection modes were studied by two-pipe models. The experiment results showed that the alternating injection of oil displacement agent and viscosity reducer yielded better results than their mixed injection, and small segments alternating injection achieved the highest recovery, which playing a role in gradual adjustment of the profile and its seepage resistance was greater. The dosage of the plugging agent should be no less than 0.5 pore volume (0.5 PV). There was a balance between the viscosity increase of polymer and the reduction of interfacial tension of viscosity reducer. The larger the dosage of the oil displacement agent, the higher the capacity to expand the swept volume and to adjust the profile enhanced, the larger the maximum liquid production ratio between high and low permeability layer, but the shorter of the liquid production reverse duration. The larger the dosage of the viscosity reducer, the greater the water cut decrease, but the smaller of maximum liquid production ratio. For chemical compound flooding in the Zhong'er block in Gudao oilfield, the recommended injection mode was 0.1 PV plugging agent + 2000mg/L oil displacement agent + 0.5wt% viscosity reducer, with small segments of oil displacement agent followed by viscosity reducer at an injection slug ratio of 6:4, which providing an efficient and economical chemical compound flooding technology solution for field application.