双井周期注CO_(2)联合降压法开采天然气水合物分析

Dual-well cyclic CO_(2) injection assisted gas hydrate depressurization production

相较于单纯地封存CO_(2),CO_(2)置换法开采天然气水合物(以下简称水合物)能够满足水合物资源开采和碳封存的双重需求。为确保安全高效开发水合物的同时提高CO_(2)封存率,按照双井周期注入CO_(2)联合降压法开采水合物的思路,以中国南海典型水合物藏为研究对象,建立了矿藏尺度水合物注采热—流—固—化四场耦合数值模型,并开展了连续、间歇、循环3类注入开采方案和单井降压开采方案的对比分析,然后模拟分析注CO_(2)辅助水合物降压开采的增产效果,最后对比了不同注入方案的CO_(2)回收和封存情况,探索了水合物法碳封存的可行性。研究结果表明:(1)邻井CO_(2)的注入有助于降低产水量并缓解降压开采引起的地质沉降;(2)间歇注入较循环注入可促进储层中CO_(2)水合物生成,扩大注入井附近的高温区域,有利于生产井附近水合物的分解;(3)连续注入方式有利于分解气体的产出,但双井注采模式降低了甲烷水合物分解程度;(4)双井注采的CO_(2)注入分为快速注入阶段、反转阶段和缓慢注入阶段,其中双井间歇注入方案的CO_(2)注入效率最高。结论认为,双井间歇注入CO_(2)复合降压法能够在安全、高效开采水合物的同时具有相对可观的碳封存效果,是一种实现水合物商业化开采和助力双碳目标实现的潜在方法,研究成果对于天然气水合物开发及CO_(2)地质封存具有理论指导意义。

Different from the simple CO_(2) storage,the CO_(2) replacement method can meet the dual demands of natural gas hydrate(hereinafter referred to as hydrate) production and carbon storage when it is used to produce hydrate.To ensure the safe and efficient hydrate production while improving the CO_(2) storage ratio,this paper takes the typical hydrate in the South China Sea as the research object to establish a reservoir-scale thermal-hydraulic-mechanical-chemical field coupled numerical model of hydrate injection and production according to the idea of dual-well cyclic CO_(2) injection assisted hydrate depressurization production method.Then,the continuous,intermittent,and cyclic injection production schemes are compared with the single-well depressurization production scheme,and the stimulation effect of CO_2-assisted hydrate depressurization production is simulated and analyzed.Finally,different injection schemes are compared from aspects of CO_(2) recovery and storage,and the feasibility of hydrate method in CO_(2) storage is explored.And the following research results are obtained.First,CO_(2) injection in the neighboring well can reduce water production rate and alleviate geological subsidence caused by depressurized production.Second,compared with cyclic injection,intermittent injection can promote the formation of CO_(2) hydrates in the reservoir and enlarge the high-temperature zone near the injection well,which facilitates hydrate dissociation near the production well.Third,the continuous injection enhances the production of dissociated gas,while the dualwell injection and production diminishes the dissociation extent of methane hydrate.Fourth,CO_(2) injection in the dual-well injection and production is divided into rapid injection,inversion,and slow injection stages,and the dual-well intermittent injection scheme demonstrates the highest CO_(2) injection efficiency.In conclusion,the dual-well intermittent CO_(2) injection assisted depressurization method can achieve safe and efficient hydrate production while providing a significant carbon storage effect.It is a potential approach to achieve commercial hydrate production and contribute to the realization of dual-carbon goals.The research results are of theoretical significance to guide hydrate production and CO_(2) geological storage.