第一类水合物藏降压开采实验模拟

Experimental simulation of depressurization mining of the class 1 hydrate reservoir

我国南海含下伏游离气的水合物储层具有实现下伏游离气和水合物分解气“两气合采”的地质条件,开采该类型水合物藏能够增加产气量,提高经济性。但目前该类型储层的开采模拟室内实验研究较少,开采规律认识不足。本文采用实验室自行搭建的三维水合物模拟装置,建立了一套含有游离气层的第一类水合物储层制备新方法,研究了水合物藏降压开采过程的产气产水特性。结果表明,采用甲烷水合物四相点以下的生产压力能有力地加快水合物分解进程,提高开采效率,当开采压力从2.95MPa降低到2.14MPa,快速产气阶段气体采收率增加10%,总开采时间缩短约38%,总采收率从73%提高到81%。当开采井井孔位于水合物层时,可能会在井孔附近出现水合物二次生成现象,从而导致开采产气速率显著降低,相比于开采井井孔位于气层,相同累积产气量的情况下生产时间延长30%左右。对比第一、三类水合物藏发现,第一类水合物藏的快速产气阶段持续20min以上,比第三类水合物藏延长一倍多,但总的气体采收率稍低。本文塑造的是气饱和的第一类水合物藏,对实际海洋水合物藏的模拟具有一定局限性,今后研究还需从实验装置尺度、分区控温方法、实验介质筛选、储层重塑稳定性等方面着手,解决储层重塑关键技术问题,为我国含下伏游离气的泥质粉砂型天然气水合物藏开采提供基础数据参考。

Hydrate reservoirs containing underlying free gas in the South Sea have the geological conditions to realize the“two-gas production”of underlying free gas and hydrate decomposition gas,which can increase the gas production of hydrate mining and improve economic efficiency.However,there are few indoor experimental simulation studies on this type of reservoir,and there is insufficient understanding of the mining law.In this paper,a three-dimensional hydrate simulation device was developed to establish a new method for the preparation of the first type of hydrate reservoir containing free gas layers,and to study the gas and water production characteristics of the hydrate reservoir during the depressurization production process.The results showed that the production pressure below the four-phase point of methane hydrate could effectively accelerate the hydrate decomposition process and improve the mining efficiency.When the production pressure was reduced from 2.95MPa to 2.14MPa,the gas recovery rate in the rapid gas production stage was increased by 10%,the total mining time was shortened by about 38%,and the total recovery rate was increased from 73%to 81%.When the production well hole was located in a hydrate layer,secondary hydrate formation may occur near the well hole,resulting in a significant reduction in the rate of gas production.Compared with the production well in a gas layer,with the same cumulative gas production rate,the production time was extended by about 30%.Comparing the first and third types of hydrate reservoirs,the rapid gas production phase of the first type hydrate reservoir lasted for more than 20min,which was more than twice as long as that of the third type hydrate reservoir,but the total gas recovery rate was slightly lower.The first type of gas-saturated hydrate reservoir was modeled here,and to simulate actual marine hydrate reservoir,it had certain limitations.Future research will need to focus on the scale of experimental equipment,regional temperature control methods,experimental media selection,and reservoir remodeling stability.So that we can solve the key technical problems of reservoir remodeling to provide basic data reference for the mining of argillaceous silt-type natural gas hydrate reservoirs with underlying free gas in our country.