How do fault systems and seafloor bathymetry influence the structure and distribution characteristics of gas chimneys?
How do fault systems and seafloor bathymetry influence the structure and distribution characteristics of gas chimneys?
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DOI：
10.1111/bre.12770
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发表时间：
2023-04
期刊：
影响因子：
3.2
通讯作者：
Boda Zhang;M. Su;Hui Chen;Fang Liu;Wenyi Zheng;Pibo Su;Jinqiang Liang;Z. Kuang;C. Yang
中科院分区：
文献类型：
--
作者：
Boda Zhang;M. Su;Hui Chen;Fang Liu;Wenyi Zheng;Pibo Su;Jinqiang Liang;Z. Kuang;C. Yang
气烟囱是地球流体垂向运移的重要通道，研究其形成演化规律对油气勘探和地质灾害风险评价具有重要意义。然而，环境条件（如水深，构造，沉积物供应通量）对气烟囱发展的影响尚未得到彻底的研究。利用高分辨率三维地震资料，在南海北方边缘的神湖斜坡（一个天然气水合物试采区）识别出59个气烟囱，其中35个与断层相交。在断层界面之上，内部地震结构由混乱的不连续反射控制。界面以下的内部结构显示出更连续的反射，这在气烟囱中也很明显，而不是交叉断层。更高程度的混乱或不连续的地震反射可能表明更破碎的网络。这可能是由于沿沿着断层的流体流量增加和伴随的流体超压而发生的。现今起伏的海底包括峡谷间（IT）区域、峡谷内（IN）区域和峡谷下游的平坦斜坡（FD）区域。IT和IN区域下方的气烟囱在平面上呈细长椭圆形，长轴方位角（亚）平行于峡谷的主走向。IT区域下方的烟囱高度大于IN和FD区域下方的烟囱高度。IT区较厚的沉积物对应于较高的上覆压力，这可能会在地下储层区引起更强的超压。这种超压可能会促进烟囱聚集在IT区域。由于上覆沉积物应力场之间的最大梯度边界，岩石的主要方向可能限制水力压裂。这项研究提供了深入了解气烟囱分布，形态和结构演变的水深和断层条件。它有助于更好地了解地质流体如何在边缘洋盆迁移。
Gas chimneys are key pathways for geofluid vertical migration; therefore, deciphering their formation and evolution is crucial for hydrocarbon exploration and geohazard risk assessment. However, the influences of ambient conditions (e.g. bathymetry, tectonics, sediment supply flux) on gas chimney development have not been thoroughly investigated. Using high‐resolution 3D seismic data, we have identified 59 gas chimneys beneath the Shenhu Slope (a gas hydrate test production area on the northern South China Sea margin), 35 of which intersect faults. Above fault interfaces, internal seismic structures are dominated by chaotic discontinuous reflections. Internal structures below interfaces display more continuous reflections, which are also apparent in gas chimneys, not intersecting faults. A higher degree of chaotic or discontinuous seismic reflections may indicate more fragmented networks. This may occur due to increased fluid flow along faults and concomitant fluid overpressure. The present‐day undulating seafloor comprises the inter‐canyon (IT) region, intra‐canyon (IN) region and flat slope (FD) region downstream of canyons. Gas chimneys beneath IT and IN regions exhibit elongated elliptical shapes in the plane, with the long axis azimuth (sub‐) parallel to the main strike of canyons. Chimneys beneath the IT region have larger heights than those beneath the IN and FD regions. Thicker sediment in the IT region corresponds to a higher overburden pressure, which may induce stronger overpressure in the subsurface reservoir region. This overpressure may promote chimneys gathering in the IT region. Canyons' main directions are likely to limit hydraulic fracturing due to maximum gradient boundaries between overlying sediment stress fields. This study provides insights into gas chimney distribution, morphology and structure evolution in relation to bathymetry and fault conditions. It contributes to an improved understanding of how geofluids migrate in marginal ocean basins.