天然气水合物有时会以结核状、层状、脉状或块状等裂隙形态发育在深水盆地的细粒泥质沉积物中, 该类型天然气水合物被称为裂隙充填型. 与孔隙充填型不同, 裂隙充填型天然气水合物储层由于裂隙的出现, 在测井速度、电阻率和地震数据上会呈现明显的各向异性特征. 本文利用细层层状介质模型和有效介质理论(EMT)新估算出印度克里希纳—戈达瓦里(K-G)盆地NGHP-01-10A和10D孔裂隙充填型水合物储层的各向异性饱和度, 纵波(Vp)和垂直极化横波(Vsv)测井速度估算的平均饱和约为20%, 明显优于水平极化横波(Vsh)估算结果, 且与压力取心估算结果更为一致. 倾角随深度变化曲线和不同角度估算的水合物饱和度结果都表明10A孔浅部以高倾角裂隙为主, 深部出现低倾角裂隙;10D孔以垂直裂隙为主, 这说明两口相距10 m的孔中裂隙在空间上延伸长度较小;而10B-08Y岩心的X射线成像定量评价结果显示水平裂隙倾角位于0°~21°, 高倾角裂隙倾角位于68°~89°, 裂隙尺度为厘米级, 最大高度、宽度和纵横比分别为27.66 cm、6.71 cm和170. 此外, 水合物饱和度估算的影响因素分析表明, 地层岩性和方程计算参数对饱和度估算的准确与否至关重要, 与简化三相方程相比, 有效介质理论计算参数的物理意义明确, 参数选择简易, 因此计算也更为准确与便捷.
In the deepwater basin, gas hydrates are sometimes developed in the form of nodular, veins, layers or massive of pure gas hydrate within the fine-grained sediments, which we called fracture-filling gas hydrate. Fracture-filling gas hydrate is distinguished from pore-filling gas hydrate because velocity, resistivity and seismic data always appear to be anisotropy in the fractured reservoir. Based on the layered medium model, the effective medium theory was used to newly estimate anisotropic saturation in the fracture-filling gas hydrate reservoir for the two holes of NGHP-01-10A and -10D, Krishna-Godavari Basin, India. The average anisotropic hydrate saturations estimated from P-wave velocity and vertical polarized S-wave velocity are consistent with those estimated from pressures cores with the value of 20%. Dip curve and anisotropic saturations show that fractures in shallow sediments has remained predominantly with high angles and fractures with small angles appear in deep sediments while only vertical fractures exist in the hole 10D, which illustrates the extent of gas hydrate filled fractures is short between the two holes with 10 m apart. X-ray image shows the dip of fractures with centimeter scale are concentrated at 0° to 21° and 68° to 89° and the maximum height, width, and aspect ratio of fractures are 27.66 cm, 6.71 cm, and 170, respectively. In addition, the analysis of influencing factors shows that both sediment lithology and calculation parameters of equation are very important to accurately estimate the gas hydrate saturation. Compared with the three-phase simplified equation, the calculation of effective medium theory is more accurate and convenient because of its explicit physical meaning and simple calculation parameters.