祁连山冻土区天然气水合物储层结构模式研究

Gas hydrate was successfully sampled by drilling and experimentation on gas hydrate production test was of preliminary success in the Qilian Mountain permafrost. However, it is not clear up to date for detailed gas hydrate distribution characteristics and its favorable reservoir space in the reservoir, which is involved into reservoir superposition style, extension range, reservoir space type, pore structure etc., namely the reservoir architecture. Therefore, to study gas hydrate reservoir architecture pattern in the Qilian Mountain permafrost, is not only helpful to probe into gas hydrate spatial accumulation regularity, but also to understand gas hydrate occurrence feature and its constraint factors, and thus it is of scientific and realistic significance. In this proposal, gas hydrate reservoir is to be chosen as a subject in the Qilian Mountain permafrost. By some special oil & gas methods and technologies, lithological features, sedimentary micro-facies, reservoir spatial distribution characteristics, reservoir space type, pore structure, and favorable reservoir space are to be respectively viewed within the gas hydrate reservoir. An emphasis is to put on analyzing reservoir composition, pore type, pore & throat structure and their relation to reservoir property and gas hydrate occurrence characteristics within gas hydrate accumulation intervals, which aims at finding out favorable gas hydrate reservoir space and further establishing a gas hydrate reservoir architecture pattern in the study area.

祁连山冻土区成功钻获天然气水合物实物样品，并取得试开采试验的初步成功。但天然气水合物在储层中的具体分布特征及有利储集空间目前还不明确。这涉及到天然气水合物储层的叠加样式、延伸范围、储集空间类型、孔隙结构等即储层结构问题。因此开展祁连山冻土区天然气水合物储层结构研究不仅有助于探讨该区天然气水合物的空间赋存规律，而且有助于了解该区天然气水合物的产出状态及其控制因素，具有重要的科学和现实意义。项目以祁连山冻土区天然气水合物储层为研究对象，借鉴油气储层研究的方法和技术，分别从天然气水合物储层的岩石学特征、沉积微相、储层空间分布特征、储集空间类型、孔隙结构及有利储集空间等方面入手，重点分析天然气水合物产出层段的储层矿物组分、孔隙类型、孔隙结构及其与储层物性、天然气水合物产出状态的关系，探讨天然气水合物有利的储集空间，并在此基础上建立该区天然气水合物储层结构模式。

综合利用岩心、薄片和测井资料，对祁连山冻土区天然气水合物储层的岩石学特征、沉积相、储集空间类型、孔隙结构及有利储集空间等开展研究。研究表明：祁连山冻土区天然气水合物储集层段产出在冻土层下130~400m之间，其层位属于中侏罗统江仓组和木里组，沉积相类型包括辫状河、辫状河三角洲、湖泊和沼泽相。根据储集岩石类型，天然气水合物储层可以分为泥岩储层和砂岩储层。泥岩储层岩性为深灰色、灰黑色、黑褐色泥岩和油页岩，局部夹薄层粉砂岩，主要产出于半深湖相，页理及裂隙发育，基本不发育孔隙，其储集空间主要为裂缝，天然气水合物呈白色薄冰状固体赋存其中。砂岩储层岩性主要为灰色、深灰色粉砂岩、细砂岩和中砂岩，主要发育在三角洲分流河道和浅湖砂滩中，砂岩储层储集空间除了构造控制的宏观裂缝外，还包括粒间孔、溶蚀孔和微裂缝，但是由于强烈的压实作用以及泥质杂基的充填，孔隙和微裂缝对储层储集空间的贡献相对较低，因此，砂岩储层天然气水合物储集空间主要为裂缝，其次为孔隙。因此祁连山冻土区天然气水合物储集层储集空间主要为受区域断裂控制的裂缝系统。在空间上，钻探区天然气水合物储层在垂向上可以划分为三层，第1层：深度133-150m，为泥岩型兼有砂岩型储层，主要分布在钻探区西北部；第2层：深度在260m左右，为泥岩型储层，在钻探区广泛分布；第3层：深度约为345-360m，为砂岩型储层，主要分布在钻探区中部和东南部。根据天然气水合物成藏的主要控制因素气源、运移通道、储集空间、冻土等，建立了研究区“源岩-断裂-冻土”控制的“生成-运移-成藏-平衡”的天然气水合物动态成藏模式。