摘要:
BSR被认为是海域天然气水合物最有效、最直接的识别标志,但BSR与水合物并非一一对应。为有效甄别假BSR,分析其成因,结合研究区高分辨率3D地震资料、测井资料及钻井结果,通过属性分析和精细测井解释,对研究区内的类似BSR特征进行深入分析。结果表明,研究区内的真假BSR在地震剖面上均具有强相对声波阻抗、穿层、低相似性等特点,很难判定其是否与水合物相关,假BSR在测井曲线上虽然也表现出高速、高电阻率等与真BSR类似的特征,但BSR之上的异常段具有更高的泥质含量,较低的电阻率增量,较低的含水饱和度,且体应变增量具有随深度逐渐增大的特点,表明该异常段与泥岩压实作用密切相关。考虑到地震剖面上该BSR与MTD底界吻合,且在异常段附近未发现游离气、矿物相界面以及构造差异的显著影响,认为WELL2井的BSR很可能为MTD引起的假BSR。
关键词:
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BSR
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水合物
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MTD
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神狐
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南海
Abstract:
The bottom simulating reflector (BSR) is considered as the most important indicator of gas hydrates, but it is not a indespensable indicator since there is no strict correspondent relationship between gas hydrate and the BSR. The bottom of the mass transport deposits may have similar features to gas hydrate-related BSR in seismic profiles. The MTD is often mis-interpretated as gas hydrate, and may become a trap in seismic data interpretation. In order to effectively differentiate the MTD-related BSR from the gas hydrate-related BSR, seismic attribute analysis and fine logging interpretation technology are both used for interpretation of the 3D seismic data and logging curves acquired from the Shenhu Area of the South China Sea. The results show that MTD are characterized by strong relative acoustic impedance, cut-crossing, low-similarity, and chaotic reflection on seismic profiles and high velocity and high resistance on logging curves, which are hard to be differentiated from hydrate caused BSR. However, MTD usually have higher clay content, lower resistivity increment, and lower water saturation, indicating that the abnormal log responses to the beds overlying the BSR are related to the process of compaction of sediments. The data from the Well 2 is carefully studied in this paper. Considering the facts that BSR is consistent with the bottom of the MTD, and there is no evidence to prove the occurrence of free gas in the underlying layer, phase-boundary or geotectonic difference, we conclude that the BSR there may indicate the bottom of a MTD.
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