祁连山冻土区三露天天然气水合物矿藏勘查模型

An exploration model of gas hydrate in Sanlutian permafrost region,Qilian Mountain

祁连山三露天天然气水合物矿藏不同于海域,需要研究冻土区天然气水合物地质模型和勘查模型。根据天然气水合物地质、物化探和钻探成果,应用含油气系统理论建立了三露天天然气水合物矿藏的"五位一体"地质模型。在总结了近几年祁连山木里物化探勘查成果的基础上,建立了冻土区天然气水合物勘查模型。不同地球化学指标分别发育顶部异常、环状异常和负异常;冻土层音频大地电磁测深出现连续分布的高阻,探地雷达的特征是电磁波速度快、衰减慢,在冻土底界处有明显的反射信号;控矿断裂的地震标志主要是反射波同向轴发生错断、终止、扭曲、突变或分叉合并等,AMT的主要特点是电性不连续;天然气水合物矿层形成的反射波组呈现低速、高频、弱振幅的特征,测井响应特征为高电阻率、低声波时差、低自然伽马、低密度。

Gas hydrate in Sanlutian area of Qilian Mountain is different from that of marine gas hydrate, and hence it is very urgent to study geosieience and exploration model. According to the theory of petroleum system and the achievements of geology, geography, geo- chemistry and drilling, the authors created a four-in-one geological model for gas hydrate deposit. Based on the summary of geophysical and geochemical exploration in recent years, the authors further established a model of gas hydrate exploration in permafrost region. Va- rious geochemical indicators show top anomaly, annular anomaly and negative anomaly. Continuous distribution of high resistance was detected by audio magnetotelluric survey （AMT）, the feature of ground penetrating radar is high-speed electromagnetic wave, slow at- tenuation and obvious reflected signal along bottom boundary of permafrost. The seismic indicators of ore-controlling fault find expres- sion in such phenomena as faulting, termination, distortion, mutation or bifurcation in accordant axis of reflection wave, and the feature of AMT is electrical discontinuity. The reflected signal in gas hydrate bed is low velocity, high frequency and weak amplitude. The log- ging response is high resistivity, low acoustic time, low natural gamma and low density.