Experimental Study On Gas Production From Hydrate Reservoir Using Self-heating System Injection Method

Natural gas hydrates are considered to be strategic alternative energy resources in the future,with the energy characteristics as widely distributed,large reserves,high energy density,clean and pollution-free.The hydrate production methods mainly include depressurization method,inhibitor injection method,thermal stimulation method,CO₂ replacement method,and combination of these methods.Some problems make the current hydrate exploitation face many puzzles and challenges such as ice generation and hydrate reformation in depressurization method,the heat loss control by long-distance transportation of heat flow in heat injection method,the low thermal conductivity of the reservoir in in-situ heating method,low replacement rate of CO₂replacement method.Therefore,it is especially necessary to further study more effective mining methods of hydrate.Based on the design of test equipment,this paper attempts to introduce a new kind of hydrate exploitation method—"self-heating system injection method"to overcome these shortcomings.Firstly,This paper investigated the influence of the concentration of self-heating solution and the mass fraction of hydrochloric acid on the heat-generating capacity of the self-heating system.And the injecting parameters when hydrate exploitation is processing were preliminarily selected by the self-heating experiment of pure quartz sand dispersion system.According to the primary selection parameters,the hydrate mining experiments of the self-heating system thermal stimulation method in the form of mixed injection and the self-heating system puff and huff method were carried out,and the deficiencies of mixed injection form and the self-heating system thermal stimulation method were analyzed.And then explored the feasibility of hydrate exploitation via self-heating system injection by the self-heating system puff and huff method in separate injection form.Comparing three cases of hydrate exploitation by the self-heating system puff and huff method in the form of separate injection,the effects of hydrate saturation and hydrate reservoir scale on various parameters during production process were analyzed,and the applicability and advantages of self-heating system were preliminarily evaluated.The research results mainly include:?1?The self-heating system has a certain degree of heat generation hysteresis in the pure quartz sand dispersion system.The nature of the hysteresis is due to the time process during the chemical reaction and transportation and dispersion of the heat flow.The large difference in temperature peaks between the pure self-heating system and the pure quartz sand dispersion system is attributed to?i?the lower mixing efficiency of the self-heating system in the Cylindrical Pressure Vessel when utilizing separate injection form the dispensing and?ii?the heat dispersion resulting by the concentrated self-heating system dispersed by quartz sand.?2?The injection rate in mixed injection form has a great influence on the temperature into the vessel.The smaller injection rate means longer injection time,and the chemical reaction time of self-heating solution will also become longer.Therefore,the self-heating system can reach a higher temperature before being injected into the vessel,and peaks occur due to the high temperature inertia of the heat flow after heat injection,but a longer injection time causes a large heat loss during the injection process.On the contrary,the larger injection rate makes the injection time shorter,as well as the reaction time of the self-heating system.Therefore,the temperature peak does not occur after heat injection,and the heat loss is lower during the injection process.?3?From the perspective of energy efficiency and thermal efficiency,the huff and puff method in the form of separate injection is superior to the self-heating system thermal stimulation method or the huff and puff method in mixed injection form.During the production process of the self-heating system thermal stimulation method/the huff and puff method in mixed injection form,the self-heating system huff and puff method in mixed injection form,the cumulative gas production increases with production time,which indicating that the self-heating system injection method is feasible and practicable for hydrate exploitation.The system pressure increases with time during soaking stage of the huff and puff method,which has also confirmed that the self-heating system injection has a positive effect on the hydrates decomposition;When employing the self-heating system huff and puff method in mixed injection form in separate injection form,hydrate reservoir with higher hydrate saturation have a longer-lasting gas production capacity,and one certain gas production can be still obtained after many production cycles.Hydrate reservoir of full-filled quartz sand also have long-lasting gas production capacity due to the large hydrate mass.?4?Compared with the traditional huff and puff method,hot brine injection method,the self-heating system huff and puff method in the form of separate injection has great advantages in the first few production cycles,and it is preliminarily concluded that the method will has a higher thermal efficiency when being at high reservoir scale and high hydrate saturation,and the production advantages of the first few cycles are greater.Therefore,the optimization of the first few cycles when employing this method can obtain better mining effect.