珠江口盆地白云凹陷天然气水合物成藏条件及资源量前景

Accumulation Conditions and Prospect for Natural Gas Hydrate Resources in Baiyun Sag, Pearl River Mouth Basin

天然气水合物是一种新型、清洁、高效的替代能源,资源量巨大。珠江口盆地白云凹陷有良好的天然气水合物成藏的水深、温压条件和基本地质条件,发育两套主要的烃源岩(文昌组和恩平组),TOC和Ro都较高,以生气为主,生烃潜力极大,为水合物成藏提供了充足的气源。白云凹陷水合物成藏的运移条件优越,有两类运移通道:一是沟通气源的断层,二是底辟;运移模式有3种:一是单一断层运移,二是单一底辟运移,三是先底辟运移再断层运移。首次初步预测了白云凹陷存在两类水合物:一是有BSR(似海底反射)标志甚至双BSR标志的水合物沉积、二是与底辟或泥火山有关且无BSR标志的水合物沉积。白云凹陷水合物厚度预测为30～100m。乐观预测白云凹陷及周边深水区水合物资源量为6.04×1013m3;保守预测白云凹陷及周边水合物资源量为8.70×1012m3。白云凹陷天然气水合物勘探潜力极大。

Natural gas hydrate is a new alternative energy which is clean and high efficient. Baiyun Sag has favorable water depth, thermobaric and basicgeological conditions for the accumulation of natural gas hydrate. Two sets of main sources rocks developed in the sag, i.e., Wenchang Formation and Enping Formation, of which TOC and Ro contents are high. The source rocks are gas-prone and have great potential of hydrocarbon generation, providing sufficient gas for hydrate accumulation. What's more, the sag has excellent migration conditions for hydrate accumulation. There are two types of migration pathways: the first one is faults connecting gas resources; the second one is diapirs. There are three kinds of migration patterns, i.e., single-fault migration, single-diapir migration, and diapir-before-fault migration. Gas hydrates are predicted in the sag for the first time and they are divided into two groups: hydrate deposits with BSR and hydrate deposits without BSR. Both single BSR hydrate deposits and double BSR hydrate deposits are discovered in the sag. Hydrate thickness of the sag is predicted to be ranging from 30m to 100m. Optimistically speaking, the hydrate resources is predicted to reach 60.4 trillion cubic meters, while it is conservatively predicted to be about 8.7 trillion cubic meters in the sag. It is shown that Baiyun Sag has broad prospect for exploration for natural gas hydrate.