【作者】 宁伏龙；

【导师】 汤凤林； 蒋国盛；

【作者基本信息】 中国地质大学 ， 地质工程， 2005， 博士

【摘要】 天然气水合物是由水分子和天然气分子在一定温度和压力下形成的似冰雪状结晶化合物，又称笼形水合物或“可燃冰”。由于形成天然气水合物的气体主要为甲烷，因而也常被称为甲烷水合物。自然界中的天然气水合物主要分布在海洋的大陆边缘和陆上永冻地区，前者占了已发现数量的绝大多数。天然气水合物研究已成为当代地球科学研究和能源工业发展的一大热点，该研究涉及到新一代能源的探查开发、温室效应、全球碳循环和气候变化、古海洋、海洋地质灾害、天然气运输、油气管道堵塞、船艇能源更新和军事防御等，并有可能对地质学、环境科学和能源工业的发展产生深刻的影响。因而世界上许多国家都从各自的关注点对天然气水合物展开了广泛的调查研究。特别是近来能源短缺日益加剧，油气价格又居高不下，使得各国更加关注具有能量密度高、储量大和分布广等特点的天然气水合物，纷纷加大对其勘探和开发研究的力度。对于我国来说，本身油气资源就不足，加之经济的快速发展，导致能源缺口越来越大。专家预测到2010年我国需进口原油接近2亿吨才能满足经济发展需求，仅此一项就要花费好几百亿美元的外汇储备。加之能源结构不合理以及《京都议定书》的正式生效，都迫使我们去寻求可替代的清洁环保新能源。因此，从我国能源战略安全和经济可持续发展角度来说，也应加大对天然气水合物勘探开发的力度。 而要对赋藏在地下一定深处的天然气水合物进行勘探和开发，钻井是必不可少的。天然气水合物的热压力特性决定了此类地层钻井与一般油气地层钻井有很大不同，也导致这类地层钻井面临更加复杂的井内问题。首先在钻井(进)时，储层井壁和井底附近地层应力会释放，地层压力会降低；同时，钻头切削岩石、井底钻具与井壁及岩心的摩擦都会产生大量的热能，此外循环泥浆温度控制不当，这些都可能使孔内温度升高。因此在钻井过程中井壁地层压力和温度的变化将不可避免地导致天然气水合物发生分解。当固态水合物起胶结或骨架支撑作用时，分解本身就会使井壁坍塌。而分解产生的水增加了井壁地层的含水量，使颗粒间的联系减弱，导致井壁不稳；逸出的气体又影响了钻井液的比重和流变性，对井壁稳定愈发不利，甚至还可能引发井涌和井喷等钻井事故。其次钻井过程是一个非绝热过程，钻井液和地层之间的热交换以及水合物的分解吸热都会使井内流体温度和井壁温度发生变化，这种温度变化会影响钻井液的粘度、密度、化学稳定性、井眼周围的应力和孔隙水压力，进而影响井壁稳定和井内安全。最后分解进入井内的气体同钻井液一起上返到地面，在这过程中如果井内温压条件合适，它们又会重新在钻井管线和阀门特别是防喷器内形成水合物，导致意想不到的钻井事故发生。因此井壁稳定和井内安全控制是天然气水合物地层钻井所面临的主要难题。加之水合物地层骨架一般为未固结和半固结的砂岩或泥质砂岩，使得在此类地层钻井时井壁稳定问题尤为突出。而井壁不稳定会导致井壁坍塌，钻具卡钻，井壁破裂，泥浆漏失，以致井的报废，损失大量人力物力。据有关资料更多还原

【Abstract】 Gas hydrate is a ice-like crystalline compound, formed by water molecules and natural gas molecules under certain temperature and pressure conditions, also called clathrate hydrate or "fire ice". For the gas forming gas hydrate is mainly methane, it is also called methane hydrate. Natural gas hydrate distributes mainly in the marine continental margin sediments and permafrost environments, and most of found gas hydrate existed in the former. The research of gas hydrate has become the hotspot of the development of the geosciences research and the energy industry of the present age. The research is involved with many fields, such as the exploration of a new type of energy, greenhouse effect, global carbon cycle, climatic change, ancient ocean, the ocean geological calamity, oil gas transportation, the blockage in the pipeline, the renewal of ship energy and military defense, and may also have the profound influence on the development of geology, environmental sciences and the energy industry. So many countries in the world research gas hydrate broadly from their respective different attention aspects. Especially for the severity shortage of energy resources and the high oil gas price in the recent years, many countries pay more attention to gas hydrate, with the traits of high energy density, large reserves and wide-ranging distribution, and the exploration and the research of gas hydrate .For our country, the shortage of oil gas resources and the fast economy development make the gap of energy resources bigger and bigger. Experts predict petroleum crude will be imported 2 hundreds million tons in 2010, which costs hundreds million foreign exchange reserves. Moreover, the inconsequence of the energy configuration and the becoming effective of the Kyoto Protocol force us to find a new type of substituted clear energy .From the aspects of the security of our country energy strategy and the economy’s persistent development, the extent of the exploration and the research of gas hydrate will be enlarged.In order to explore and exploit gas hydrate in the certain underground depth, drilling wells are absolutely necessary. The temperature and pressure characteristics of gas hydrate make the wells in these sediments different from the wells in the general oil gas sediments, and also make the wells confronted with the more difficult problems. Firstly, while drilling, the stratum stress near the borehole and the bottom of hole is released and depresses. At the same time, the heat energy generated by the friction of the bit cutting rocks and the friction of the drilling tools, the更多还原