Experimental Study On The Influence Factors Of Exploiting Methane Hydrate By Replacement With CO₂

Natural gas hydrate is deemed to be a new energy with large commercial exploitation value in the 21th century because of its advantages of abundance resource, high combustion value and low pollution. At present, the traditional methods of natural gas hydrate exploration include depressurization, thermal stimulation, and adding inhibitors. However, all of the three methods are easily to cause hydrate zone geological instability, underwater landslides and other natural disasters. Exploiting methane hydrate by replacement with CO2, as a kind of new technology, can not only exploit the natural gas storage in hydrate, but also can bury the greenhouse gas CO2 on the sea bottom in the form of hydrate at the same time, and the method also can reduce the risk of geological disasters. Therefore, researching the method of exploiting methane hydrate by replacement with CO2 has important scientific and practical significance.In this paper, we completed methane hydrate synthesis and CO2 replacement experiment in porous sediments, studied the change of the temperature, pressure and the components of gas content of gas phase, and mainly analyzed the influencing factors of the replacement experiment. The results showed that:In the early replacement reaction, the changing speed of CH4 and CO2 content in gas phase was very fast, and then it decreased.The replacement efficiency of methane hydrate with CO2 replacement increased with increasing of the temperature. The higher the temperature was, the greater it influenced the replacement efficiency. Replacement efficiency decreased with the increasing of the pressure. The higher the pressure was, the greater it influenced the replacement efficiency. The higher the initial saturation of hydrates was, the greater the amount of replacement of CH4 was; the lower replacement efficiency was, the less CO2 was comsumed; the smaller the hydrate saturation was, the greater the effect on replacement efficiency was. Adding N2 to CO2 could increase replacement efficiency. From the change of CH4 content in the replacement process of gas-phase, as we can see, N2 mainly affected the late replacement reaction, which has little effects on the early replacement reaction. Comparing salt water, pure water and SDS system, replacement efficiency in brine system was significantly higher than the other two systems, and the replacement efficiency in the SDS system was slightly higher than that of pure water system. Smaller sediment particle size could make greater replacement efficiency. Increasing the contact area could obviously increase replacement efficiency, but from the perspective of the change of CH4 content in the gas, the influence of the contact area mainly played a role in the early replacement reaction.