中建南盆地泥火山和麻坑群的形成机理及差异性地貌的成因

Numerous mud volcanoes and pockmarks occur in the Zhongjiannan Basin. The former and the latter are shown as positive and negative seabed morphologies, respectively. However, their formation mechanisms and the factors which cause their reversed seabed morphologies are still not uncovered. The methods of geophysical interpretation, well/core analysis together with numerical simulation are used in this study. Firstly, the detailed internal structures of fluid pathways will be depicted and geological model will be built, basing on reflection seismic interpretation; Secondly, the temperature-pressure fields and geochemical characteristics of cores are analyzed, which provides the constraint conditions for the numerical simulation; Lastly, the formation processes of mud volcanoes and pockmarks will be simulated, basing on the Neville - Stokes Equation and Distinct Element Method. Through these studies, three innovative points will be achieved: (1) to uncover the detailed internal fluid pathways of mud volcanoes and pockmarks; (2) to conform the controlling factors which cause the different seabed morphologies of mud volcanoes and pockmarks and (3) to clarify the formation mechanism of overpressure which cause the occurrence of mud volcanoes and pockmarks. This study is advantage for both the theoretical improvement of mud volcanoes and pockmarks and the practical applications for deep-water hydrocarbon exploration, geological risk estimation and extreme environment study.

目前，在中建南盆地发现了大量的泥火山和麻坑构造。前者在海底表现为正地貌，而后者表现为负地貌。两者的形成机理以及在相同的构造和沉积背景下差异性地貌的成因是尚未解决的科学问题。本申请拟根据大量地球物理资料解释、岩石样品分析和数值模拟相结合的研究方法。首先通过地震解释获得精细地质结构，建立合理的地质模型；其次通过样品分析了解温、压场特征和岩石地化参数，为模拟提供约束条件；最后以改进的纳威-斯托克斯方程为依托利用离散元法对泥火山和麻坑构造的形成过程进行数值模拟。本申请期望在以下三个方面取得创新性成果：（1）探明研究区泥火山和麻坑构造的精细流体通道特征；（2）确定在研究区相同构造和沉积背景下形成海底地貌差异性的主控因素；（3）阐明形成研究区泥火山和麻坑构造的超压形成机制。本研究成果不仅在理论上能够促进泥火山和麻坑构造的研究，而且也有利于该盆地深水资源勘探、地质灾害评估和深水极端环境生态系统等的研究。

根据对大量2D/3D地震资料和多波束资料的解释，在南海中建南盆地及其周缘地区发现麻坑、泥火山、火山和海底滑坡等地质体广泛分布。研究和揭示这些地质现象对深水资源、环境和地质灾害等方面都有重要的实践和理论意义。一方面超压流体喷出地表，形成麻坑或者泥火山，从而改变原来的海底地貌形态；另一方面浅部超压流体可以导致地层失稳形成海底滑坡；最后，超压流体可以促进浅部天然气水合物和浅层气成藏以及海底冷泉生物的繁盛、冷泉碳酸盐岩的形成等。本研究通过地球物理资料解释，解析了麻坑、泥火山、火山和海底滑坡的精细结构和三维形态，并建立可靠的地质模型；根据表沉积物测试化验分析，获取数值模拟所需的岩石物性参数；利用有限体积法对超压流体的向上侵入过程（麻坑和泥火山形成必经阶段）进行模拟，初步揭示了麻坑和泥火山等地质体的形成机制及其主要影响因素。本研究认识到从超压源区到超压流体水力压裂上覆地层以及最后喷出海底形成泥火山/麻坑的系统演化过程；阐明了深部流体超压形成、演化到最后消减的过程和机理，并确定了各参数的敏感性。该项目的研究成果可以应用到别的沉积盆地，并能够直接指导南海资源勘探和地质灾害评估。