钻井液侵入含天然气水合物地层的机理与特征分析

Mechanism and Characteristics of Invasion of Drilling Fluid in Gas Hydrates-Bearing Formation

海洋含天然气水合物地层是具有渗透性的多孔介质体,钻进过程中钻井液不可避免地会与它发生能量和物质交换,从而影响测井响应、井壁稳定和储层评价。在过压钻井条件下,水基钻井液驱替侵入含天然水合物地层和温差下热传导导致的天然气水合物分解是耦合在一起的,其侵入可描述为一个包含相变的非等温非稳态渗流扩散过程。分析了天然气水合物在多孔介质中的分解特性,指出了多孔介质中天然气水合物分解的影响因素,通过钻井液侵入含天然气水合物地层与侵入常规油气地层的比较,提出了借鉴天然气水合物开采渗流模型建立钻井液侵入数值模型的思路。

As formations containing gas hydrate are usually permeable porous media,energy and mass exchanges between the drilling fluid and the formations will occur inevitably during drilling,which will affect log response,borehole stability and reservoir evaluation.In condition of over-balanced drilling,the drilling fluids will invade into hydrate-bearing formation and at the same time hydrate will decompose by heat transfer.So the invasion process can be described as a non-isothermal and unstable displacing and diffusing which couples phase change.The paper analyzed the properties of gas hydrate in porous media,and demonstrated the factors that affect its dissociation.By comparing the differences of drilling fluid invasion in conventional oil and gas formation and gas hydrate sediments,an approach was put forward to build a numerical model in reference with the gas hydrate exploitation models that are already exist.