SEISMIC ANISOTROPIC MODELING OF FRACTURE-FILLING GAS HYDRATE
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摘要: 裂隙充填型天然气水合物广泛发育在深水盆地的泥质沉积物中,呈结核状或脉状充填于近似垂直的高角度裂隙中,导致含水合物层出现明显的高电阻率各向异性异常,但是地震波传播的各向异性特征目前还不清楚。本文以印度克里希纳-戈达瓦里(K-G)盆地NGHP01-10井的速度、密度和地层倾角等测井数据为基础,建立含水合物层地质-地球物理模型,运用弹性波方程的交错网格有限差分数值分析方法,模拟了各向同性和各向异性条件下均匀和层状水合物层的地震波响应特征与传播规律。地震波正演数值模拟结果表明,对裂隙充填型水合物层,基于各向异性的地震波速度和振幅与各向同性有明显不同,不但各向异性的水合物层内部反射明显多于各向同性的情况,而且各向异性情况下,其平均速度也要高于各向同性情况下的平均速度。Abstract: Gas hydrate, existed as solid nodules or near-vertical veins filled in high angle fractures, is widely developed in the argillaceous deposits in deep basins. Such a fracture-filling gas hydrate may produce an anisotropic anomaly of high apparent resistivity. However, seismic wave propagation in the anisotropic hydrate layer is unclear. In this paper, a geophysical model of hydrate layer as such is established on the basis of logging data including velocity, density and dip of NGHP01-10 in the Krishna-Godavari (KG) basin of India. Then seismic response and propagation of gas hydrate-filled in fractures are modeled both in isotropic and anisotropic elastic wave conditions using the staggered-grid finite-difference method. Seismic modeling results show that isotropic velocity and amplitude are significantly different from anisotropic velocity and amplitude for gas hydrate-filled in fractures. Not only there are more reflections in anisotropic hydrate than those in isotropic hydrate, but also the average velocities of anisotropy are faster than those of isotropy.
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Key words:
- gas hydrate /
- fracture /
- anisotropy /
- modeling
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