尼日尔三角洲前缘挤压带的古今BSRs分布特征

doi:10.11743/ogg20190613

摘要/Abstract

摘要： 本文通过对尼日尔三角洲前缘挤压带的三维地震资料进行解释和属性提取，结合BSR数值模拟，分析了与天然气水合物相关的古今BSRs的分布特征及其发生垂向运移的主控因素。古今BSRs分别代表了天然气水合物稳定底界过去和现今的位置，在研究区古今BSRs均分散分布且主要位于褶皱带断层、气烟囱或者底辟构造等流体运移通道发育的地区，反映了流体运移条件对BSR的形成具有控制作用。古BSRs的反射特征较现今BSR弱，分布范围也更局限，其振幅特征可能是由先前存在的天然气水合物所导致的成岩作用引起的。现今BSR深度与海底深度呈正相关，但水合物稳定区厚度随海底深度的增加变化不大，约为425 m。BSR在地质历史时期的垂向迁移是诸多因素综合作用的结果。尼日尔三角洲挤压带的构造活动强烈且目的层沉积速率较高，深部热流也可沿断层、底辟等通道运移至浅部；下伏地壳是洋壳和过渡壳，大地热流值较高，且海相泥页岩热封盖能力强，这些条件均有利于BSR的向上迁移。另外，研究区的高饱和度水合物层表现为BSR上部的正极性、强振幅异常，主要位于气烟囱和背斜顶部，指示了流体运移通道对水合物成藏的控制作用。研究区BSR下伏游离气FGZs发育较为局限，仅在褶皱带流体运移通道发育的位置发育较薄的FGZs。

关键词: BSR, 地震解释, 流体运移, 天然气水合物, 尼日尔三角洲

Abstract: Interpretation of 3D seismic data from the compression domain of Niger Delta,related seismic attribute extraction and BSR numerical modelling are carried out in this paper to study the seismic characteristics of the present and paleo-bottom simulating reflections (BSRs),and the controlling factors of BSR vertical migration.In the study area,the present and paleo-BSRs,representing present previous and locations of the base of gas hydrate stability zones (GHSZ),are scattered and mainly located in areas with well-developed fluid pathways including folding faults,gas chimneys,and diapire structures.This indicates that fluid migration conditions control the occurrence of BSR.Compared with the present BSR,the paleo-BSRs are of weaker amplitude,and distributed in much more limited areas.The amplitude of the paleo-BSRs is interpreted to represent petrophysical interfaces caused by diagenesis driven by previous gas hydrate.The depth of the present BSR deepens as the seabed water depth increases,but the thickness of GHSZ is relatively stable,about 425 m.The upward resetting of the BSR is a result jointly contributed by various factors in the geological history.The toe-thrust belt of the Niger delta is characterized by intense tectonic activities,high sedimentary rate,and well developed fluid migration pathways,including fault and diapire,for heat flows from deep to shallow.Besides,the underlying oceanic and transitional crusts allow higher heat flows,and marine mudstones have higher heat sealing capacity.All these are driving the upward resetting of the BSR.In addition,higher gas hydrate saturation formations in the study area feature higher amplitude anomalies on the present,upper BSR with positive polarity,mainly on top of anticlines and gas chimneys,indicating the effective control of fluid migration pathways on gas hydrate accumulation.The occurrence of free gas zones (FGZs) underlying the present BSR is limited,and only thin FGZs occurred in fold belts with well-developed fluid migration pathways.

Key words: bottom simulating reflection (BSR), seismic interpretation, fluid migration, gas hydrate, Niger Delta

中图分类号:

TE132.2

杨金秀,宋朋霖,何巍巍,等. 尼日尔三角洲前缘挤压带的古今BSRs分布特征[J]. 石油与天然气地质, 2019, 40(6): 1295-1307. doi: 10.11743/ogg20190613 Yang Jinxiu,Song Penglin,He Weiwei,et al. Distribution pattern of paleo and present BSRs in the toe-thrust belt of Niger Delta front[J]. Oil & Gas Geology, 2019, 40(6): 1295-1307. doi: 10.11743/ogg20190613

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