Dissociation characteristics of water-saturated methane hydrate induced by huff and puff method

The world has huge reserves of gas hydrates which are considered to be a potential energy resource. Therefore, developing methods for commercial gas production from hydrate reservoirs are attracting extensive attention. In order to mimic the geological condition of the practical oceanic hydrate reservoir, water-saturated hydrate sample with low gas saturation (8.27%) was obtained by the formation process of multi-step water injection. The huff and puff (H&P) method (above or below the equilibrium pressure for hydrate dissociation) was applied for hydrate dissociation. Results show that the system pressure rises with the increase of the H&P cycle for the H&P method above the equilibrium pressure. Furthermore, the dissociated hydrate in the injection period can be reformed in the soaking and production periods, and hydrate saturation increases mildly after each cycle of H&P. Hence, the H&P method above the equilibrium pressure is unpractical for hydrate dissociation with low gas saturation. However, the hydrate in the reservoir can be completely dissociated by the H&P method below the equilibrium pressure. Therefore, in the water-saturated hydrate reservoir, the regular H&P method is not suitable. The regular H&P should combine with depressurization method for gas recovery from the water-saturated hydrate reservoir.