游离甲烷气在井筒内形成水合物的动态模拟

深海油气钻井及海洋水合物钻采过程中均存在水合物形成进而阻塞井筒的风险。在恒温4.0℃,压力由3.5 MPa逐渐升至6.5 MPa的实验条件下,动态观测了甲烷气体以定速"鼓泡"形式在模拟井筒内的运移特征和井筒内不同位置水合物的形成、聚集形态,并依此对水合物的生长机制进行分析。实验结果表明:井筒内有障碍物或气体运移通道出现变径等情况时,不会改变水合物形成的相平衡条件,但会影响水合物的堆积形态和聚集过程;其次,气体在井筒内运移受阻的强弱直接决定水合物能否彻底阻塞循环通道;同时,气泡表面水合物薄膜的生长机制会受釜内压力变化及水合物膜破裂剥离等影响,并且由于气泡表面水合物膜的生长无法将气泡内气体完全消耗,使得游离气在井筒内形成的水合物体系为非均质的多孔介质体系。

Dynamic simulation of hydrate formed from free methane gas in borehole

Hydrate formation exists in deepwater hydrocarbon drilling and marine hydrate drilling, causing a risk of borehole clogging. In this study, under the constant temperature of 4.0℃ with pressure gradually increasing from 3.5 MPa to 6.5 MPa, the migration characteristics of methane gas in "bubble" form under constant speed in simulated borehole were dynamically observed, as well as the formation and aggregation patterns of hydrate at different borehole locations. On this basis, the growth mechanism of hydrate was analyzed accordingly. The experimental results show that the presence of obstacles in borehole or diameter changes in gas migration path has no influences on the phase equilibrium condition of hydrate formation, but impacts the accumulation morphology and aggregation process of hydrate. Then, the impeding degree of gas migration in borehole directly decides whether hydrate will completely clog the circulation channel. Moreover, the growth mechanism of hydrate film formed on bubble surface is controlled by the factors such as the variation of pressure in the borehole and the fracture and exfoliation of hydrate films. The growth of hydrate films on bubble surface is unable to consume the gas in bubbles completely, so that the hydrate system formed from free gas in borehole is an anisotropic porous media system.