天然气水合物开采方法的应用——以Ignik Sikumi天然气水合物现场试验工程为例

The Application of Gas Hydrate Production Methods——A Case of Ignik Sikumi Gas Hydrate Field Trial in the North Slope of Alaska(USA)

天然气水合物已成为世界各国关注的焦点,对天然气水合物开采方法的研究、实践和应用是目前的重点之一。天然气水合物的开采方法主要包括注热法、降压法、注化学试剂法、气体置换法等4种以及这些方法的联用,其中注热法因能耗较大和生产层必须具有良好的孔隙度而使其成本显著提高;降压法无需消耗大量能源,因而被认为是最可行且最具经济价值的天然气水合物生产方法,这一方法可能最适合含水合物盖层以下圈闭有大量气体的矿床;注化学试剂法不是分解天然气水合物的主要方法,不适合长期或大规模使用,且成本较高;气体置换法是通过客气分子的注入来置换天然气水合物中的甲烷,使甲烷释放到孔隙流体中,在被气相包裹的水合物中,气体置换有效率可超过60%,该方法的主要制约因素是水合物储层的低渗透性。2012年5月,在美国阿拉斯加北坡完成了首个用于调查研究天然气水合物藏中CO2-CH4置换潜力的现场试验工程——Ignik Sikumi天然气水合物现场试验,成功注入约6000m3二氧化碳和氮气混合气体,累计生产气体近3×104m3,未对储层造成压裂破坏。该试验工程为水合物领域的科学研究提供了大量的数据和新的认识,美国能源部也因此宣布了新的研究举措。

Gas hydrate is attracting attention worldwide.The research,practice and application of gas hydrate recovery methods is one of the key areas in gas hydrate development.The main methods currently available for recovering gas hydrate include heat injection,pressure reduction,chemical agent injection,gas displacement and the combined use of these methods.The cost involved in the heat injection method is very high due to its high energy consumption and requirement for good porosity of the pay zone.The pressure reduction method does not consume much energy and is therefore regarded as the most feasible and economic method for recovering gas hydrate.This method may be most suitable for those deposits where large amounts of gas are trapped below gas hydrate-containing formations.The chemical agent injection method is not the main method for decomposing gas hydrate and is not suitable for long-term and massive use and is also expensive.In the gas displacement method,guest molecules are injected to displace the methane in gas hydrate and the methane is released into interstitial fluid.For gas hydrate encapsulated by gas,the gas displacement rate can exceed 60%.Low permeability of gas hydrate formations is the main constraint on this method.In May 2012,the world′s first field test program devised to examine the potential of CO2-CH4 displacement for gas hydrate deposits-the Ignik Sikumi gas hydrate field trial-on Alaska′s North Slope in May 2012.Around 6000m3 of a mixture of carbon dioxide and nitrogen was injected and nearly 3×104m3 of gas was produced.No damage was induced by fracturing to the formations.That test provided a large amount of data and new insight for scientific research on gas hydrate and prompted the US Department of Energy to announce new research initiatives.