天然气水合物储层改造研究进展

Research progress in natural gas hydrate reservoir stimulation

天然气水合物(以下简称水合物)是一种潜力巨大的未来能源,目前阻碍水合物商业化开发的表观原因是产气量不达标,因此有必要从水合物开采方法角度思考如何增产,其中储层改造技术显得尤为重要。为此,在系统梳理了水合物储层改造理论和技术基础上,将其储层改造领域分为水力压裂、近井改造和化学改造3个方向,总结了3个方向取得的主要研究成果、存在的问题与挑战,并进行了讨论与展望。研究结果表明:①水力压裂方面进展较快,其成果验证了水合物沉积物的可压性,揭示了水合物沉积物与岩石拉伸破坏相似的压裂机理,发现裂缝在围压作用下闭合后仍具有增渗效果并有利于二次张开,分析了地应力、压裂液对水合物沉积物压裂特性的影响,构建了压裂过程数值模型,阐释了人工裂缝改善水合物储层降压和注热效果的机制,明确了人工裂缝高渗通道对产气速率等关键生产指标的提升作用;②近井改造方面,揭示了高压水射流冲蚀水合物沉积物的机制和规律,通过数值模拟验证了水射流割缝、井周注浆柱、分层劈裂注浆均可有效提升生产性能,但研究尚处于构建产气模型评估改造效果阶段,还需验证其可行性和有效性;③化学改造方面,探索了二氧化碳水合物改造盖层和甲醇吞吐对水合物储层生产性能的提升潜力,分析了二氧化碳改造盖层并实现埋存的可行性。结论认为,针对当前面临的问题和挑战,应加强构建以水力压裂为主、近井储层改造为辅、化学改造为补充的储层改造理论与技术体系,以加快推动水合物资源产业化进程。

Natural gas hydrate(hereinafter referred to as hydrate)is a kind of future energy with great potential.At present,the apparent factor hindering commercial hydrate development is the unqualified gas production rate,so it is necessary to research stimulation means from the perspective of hydrate exploitation method,and reservoir stimulation technology is particularly important.After systematically reviewing hydrate reservoir stimulation theories and technologies,this paper divides the field of reservoir stimulation into three directions,i.e.,hydraulic fracturing,near-well stimulation and chemical stimulation,summarizes the main research results,problems and challenges in these three directions,and carries out discussion and prospect.And the following research results are obtained.First,rapid progress has been made in the research of hydraulic fracturing and it results have verified the fracability of hydrate deposits.It is revealed that the fracturing mechanism of hydrate deposits is similar to the tensile failure of rocks.It is indicated that fractures can still make contribution to permeability improvement after they closed under confining pressure,which is beneficial to secondary opening.In addition,the effects of in-situ stress and fracturing fluid on fracturing behaviors of hydrate deposits are analyzed,the numerical model of fracturing process is established,the mechanisms of hydraulic fractures to improve the depressurization and heat injection effects of hydrate reservoirs are analyzed,and the improvement effects of hydraulic fractures,as high-permeability channels on gas production rate and other key production indexes are clarified.Second,the research of near-well stimulation reveals the washout mechanisms and laws of high-pressure water jet on hydrate deposits.It is verified by numerical simulation that water jet slotting,circumferential grouting column and stratified split grouting can effectively improve the production performance,but the research is in the stage of establishing gas production model to evaluate the stimulation effect and the feasibility and effectiveness needs verifying.Third,as for chemical stimulation,the potential of CO2 caprock reconstruction and methanol huff and puff to improve the production performance of hydrate reservoirs is explored,and the feasibility of CO2 caprock reconstruction and storage is analyzed.In conclusion,to deal with current problems and challenges,it is necessary to strengthen the construction of the reservoir stimulation theory and technology system with hydraulic fracturing as the leading role,near-well reservoir stimulation as the auxiliary and chemical stimulation as the supplement,so as to accelerate the industrialization process of hydrate resources.