天然气水合物储层宽频介电测井响应数值/物理模拟研究

Natural gas hydrate is potentially a new energy source. The gas hydrate reservoir can be recognized qualitatively through geophysical well logging techniques, however, it is rather difficult to quantitatively evaluate the gas hydrate saturation due to the lack of appropriate well logging methods and interpretation models. The traditional well logging evaluation theory for oil and gas reservoir cannot be used for natural gas hydrate any more...Based on the new broadband dielectric logging method proposed in the previous work, this project focuses on investigating the characteristics and mechanism of the well logging responses to gas hydrate reservoir and establishing the corresponding evaluation method for gas hydrate. Firstly, the physical model of EM pulses radiated by the broadband dielectric logging tool is established through simulation and theoretical analysis, then the factors affecting the detection performance and the underlying mechanism are studied. Secondly, the factors affecting the frequency dispersion of the dielectric characteristics of the hydrate-bearing porous media are identified and the mechanism of the relation between these factors and hydrate saturation are investigated. Thirdly, the mechanism of the relation among the instrument response, frequency dispersion of the dielectric characteristics and hydrate saturation is disclosed and the hydrate saturation estimation method based on the broadband dielectric logging is proposed...The outcome of this project aims to enhance the existing theory and data foundation for the development of broadband dielectric logging, and to provide an innovative logging method and theoretical supports for quantitatively evaluating the gas hydrate saturation.

天然气水合物是一种极具潜力的新型能源。地球物理测井可较好地对天然气水合物储层进行定性识别，但天然气水合物饱和度的准确定量评价无论在测井方法或解释模型方面都存在许多困难，常规的油气储层测井评价理论不再完全适用。. 本项目以前期所提出的宽频介电测井方法为基础，拟进一步研究该方法对天然气水合物储层的响应特性和响应机理，并建立相应的水合物饱和度评价方法。首先，结合仿真与理论研究，建立宽频介电测井辐射电磁脉冲的传播理论模型，揭示影响探测性能的因素及影响机制；然后，研究影响含水合物多孔介质电学频散特性的因素，明确各因素与水合物饱和度之间的关联机理；最后，明确仪器响应、地层介电频散、水合物饱和度之间的内在关联机理，研究利用宽频介电测井定量计算水合物饱和度的方法。. 研究成果将为宽频介电测井仪器的开发提供理论和数据基础，为天然气水合物勘探开发中的水合物饱和度定量评价提供更有效的测井技术手段和理论支持。

本课题着眼重大未来能源需求——天然气水合物的勘探开发，提出利用新型宽频介电测井方法对水合物储层进行饱和度评价，结合电磁场数值仿真、实验室模拟地层实验、模拟储层介电特性分析等多种研究手段，明确了宽频介电测井仪器在水合物储层中的工作特性；提出了一种针对宽频介电测井的导波定量计算方法；制造理论样机，应用模拟井眼储层，验证了方法的可行性；改进实验室介电分析手段，对水合物模拟储层介电特性进行了准确测量分析，并提出用于水合物饱和度反演的物理模型，任务书所提要求均已圆满达成。.首先，基于GPU工作站集群，开展宽频介电测井仪器设计，UWB井眼天线、短节、井眼、地层结构等的整合优化，实现在不同含流体饱和度地层中200MHz-2GHz的工作带宽覆盖，总结电磁波辐射规律，发掘宽频介电测井探测分析的关键问题——导波的定量计算，结合解析、数值算法提出专用分析方法，实现介电测井中导波的定量计算，为介电测井研究、仪器设计、明确聚焦范围、探测深度提供分析手段。.然后，结合数值计算结果，制作宽频介电测井理论样机，利用微波测试平台对样机方向性、传输反射特性、增益等性能进行验证，符合设计要求。搭建模拟地层井眼，改变流体饱和度、孔隙度，获取仪器对地质参数的响应规律，实验结果表明，理论样机短节对地层因流体饱和度改变产生的介电变化响应灵敏。.最后，为明确水合物储层宽频复介电谱对地质参数的表征机理，建立了基于开口同轴探头法的宽频多点复介电检测系统，在实验室内利用多孔介质模拟水合物储层，开展了不同饱和度、粒径、温度条件的水合物生成分解实验，对温度、复介电等参数进行全程监测，明确了饱和度、孔隙度、粒径等与复介电频散间的关联机理。利用CT扫描对样品组分实时标定，结合表面电导理论提出基于Maxwell-Wagner公式的嵌套模型，弥补了现有介电测井体积分数模型在水合物储层解释中失真的不足，为应用宽频介电测井到水合物储层勘探奠定理论基础、提供解释模型和数据支撑。