Polymer Flooding in Artificial Hydrate Bearing Sediments for Methane Gas Recovery

Polymer flooding has been one of the most promising methods used for enhanced oil recovery from matured crude oil reservoirs across the globe due to its distinct advantages over simple water flooding. However, the use of polymer flooding has not yet been investigated for methane recovery from hydrate reservoirs. In our earlier work, we have investigated the effect of various molecular weights and concentrations of polyethylene glycol (PEG) polymer on the phase stability and kinetics of methane hydrate. This information has been explored for successful use of PEG as a chemical agent for polymer flooding from hydrate reservoirs. In this work, detailed experimental investigations on methane production from hydrate bearing sediments have been carried out using PEG polymer flooding in a three-dimensional hydrate reactor. Initially, methane hydrate formation has been investigated using two silica sand porous beds (viz., 0.16 and 0.46 mm), and pure water at an initial hydrate formation pressure of 8 MPa and 277.15 K. Subsequently, hydrate dissociation studies have been carried out using polymer flooding at a final hydrate reservoir pressure of ∼4.3 MPa and 277.15 K. The effect of molecular weights (200 and 600 kg/kmol, viz., PEG-200 and PEG-600, respectively), concentrations (0.2 and 0.4 mass fractions), and injection rates (1 and 5 mL/min) of PEG aqueous solution has been analyzed for methane gas recovery. PEG-200 is observed to be an effective flooding agent as compared to PEG-600 and other inhibitor such as ethylene glycol used in the literature. In addition, studies on the total dissolved solids (TDS) and electrical conductivity of PEG aqueous solutions have also been investigated before and after flooding to check the efficacy of polymer flooding for methane production. PEG has a much lower freezing point (208.15 K, i.e., −65 °C) compared to ethylene glycol (260.25 K, i.e., −12.9 °C); therefore, polymer flooding is expected to be more beneficial for methane gas production from hydrate bearing zones with low reservoir temperatures.