天然气水合物人工矿体高温分解模拟实验

天然气水合物(以下简称水合物)藏对地质条件的变化较为敏感,微弱波动即可造成水合物藏被破坏。为研究水合物藏在温度突变下的分解过程,在水合物三维成藏物模实验系统(装置主体为32 MPa高压反应釜,反应釜内部由5个温度传感器和30个电阻率探测电极构成空间点阵)中合成了100 L的人工水合物矿体,测定了水合物矿体在外界温度升高到295 K后其内部温度、电阻率的变化情况,并以此为基础分析了水合物薇在温度发生突变以后的演化行为。实验结果表明:①人工水合物矿体在环境温度升高后会迅速分解(经过600 h才生成并达到稳定的矿体仅需38 h即可完全分解),通过监测实验过程中介质温度和电阻率变化,可以对分解过程中的分解量、分解速度进行考察;②分解过程中,电阻率变化受水合物饱和度、孔隙水盐度以及地层位置的影响,其中,水合物饱和度较高的区域发生少量分解时,由于孔隙水被稀释会导致电阻率上升;③对于海底水合物藏,当发生持续、显著的温度变化后,其气体组分、赋存方式等均会发生明显改变。

Simulation experiments on pyrogenic decomposition of a mature artificial hydrate ore body

Unlike the conventional hydrocarbon reservoirs, natural gas hydrate reservoirs are more sensitive to any changes of geological conditions and even a tiny variation will lead to reservoir decomposition. This study aims to study the decomposition process of a gas hydrate reservoir under the sudden change of temperatures. First, a 100 L hydrate ore body was synthesized in a large-scale three-dimensional device (space lattice were formed by 5 temperature sensors and 30 resistivity detecting electrodes in the main device of a 32 MPa high-pressure reactor), and then the changes of inside temperature and resistivity of this ore body were observed and analyzed after the ambient temperature was raised to 295 K. The following findings were obtained. (1) When the ambient temperature rises, this ore body synthesized after 600 hours will soon be decomposed completely within only 38 h; and the decomposing behavior will be obtained by monitoring the variety of medium temperature and resistivity. (2) During the decomposition process, the temperatures and resistivity of sediment will be influenced by hydrate saturation, pore water salinity, and the relative sediment location. In the areas with high hydrate saturability, the resistivity will increase because of dilution pore water when a small amount of hydrate decomposes. (3) Continuous and significant disturbance of temperatures will lead to an obvious change of gas components and occurrence ways of marine hydrate reservoirs under the sea floor.