海拉尔盆地呼和湖凹陷深层煤岩气赋存条件及勘探方向

Occurrence conditions and exploration targets of deep coal-rock gas in the Huhehu Sag， Hailar Basin

白雪峰 高庚 王彪 李敬生 李军辉 徐慧 马文娟 刘璐

Xuefeng BAI Geng GAO Biao WANG Jingsheng LI Junhui LI Hui XU Wenjuan MA Lu LIU

海拉尔盆地呼和湖凹陷白垩系南屯组二段（南二段）已发现油气藏，但对其中的深层煤岩气赋存条件及勘探方向研究较少。分析了烃源岩、沉积和构造等油气成藏基础条件，研究了深层煤储层发育特征及含气规律，探讨了呼和湖凹陷深层煤岩气赋存条件，提出了下一步勘探方向。研究结果表明：①南屯组发育泥岩及煤岩2套成熟源岩，深层煤岩气具有良好的气源物质基础。②断陷湖盆沼泽发育，成煤环境优越，初始期煤岩厚度大，煤-泥共生；稳定期和萎缩期煤岩厚度小，砂-煤共生。③缓坡断阶带煤岩厚度小，含气量低；洼槽带及陡坡带煤岩厚度大，割理裂隙发育，微裂隙沟通有机孔，连通性好，孔-缝体系发育，富游离气。④早期断裂体系为深层煤岩气垂向与侧向运移提供通道。⑤呼和湖凹陷预测深层煤岩气资源量1.79×10 m，勘探潜力大，将成为断陷盆地重要风险勘探新领域，洼槽带和陡坡带是深层煤岩气最有利的勘探方向。

Hydrocarbon reservoirs have been identified in the 2 member of the Cretaceous Nantun Formation （also referred to as the Nan 2 Member） in the Huhehu Sag， Hailar Basin. However， limited studies have been conducted on the occurrence conditions and exploration targets of deep coal-rock gas therein. In this study， we analyze the fundamental conditions for hydrocarbon accumulation， including source rocks， deposits， and structures， in the Huhehu Sag and examine the developmental characteristics and gas-bearing features of deep coal reservoirs. Accordingly， we explore the occurrence conditions of deep coal-rock gas in the sag and propose potential exploration targets. The findings reveal that in Nantun Formation there are two suites of mature source rocks in the mudstones and coals， which provide a favorable material basis for the deep coal-rock gas generation and accumulation. During the deposition of the Nan 2 Member， Hailar Basin， a faulted lacustrine basin， exhibits swamps， which create a favorable coal-forming setting. The initial extension stage of the basin witnessed the formation of thick coals and coal-mudstone coexistence， while its stable extension and contraction stages featured thin coals and sandstone-coal coexistence. The ramp-faulted terrace zone exhibits thin coals and low gas content. In contrast， the trough and steep slope zones are characterized by thick coal rocks and well-developed cleats， with organic pores interconnected by microfractures， contributing to high connectivity and a well-developed pore-fracture system. So it is rich in free gas. The fault system formed in the early extension stage provides pathways for the vertical and lateral migration of deep coal-rock gas. The Huhehu Sag exhibits deep coal-rock gas resources predicted at 1.79×10 m， suggesting considerable exploration potential and establishing this sag as an important new risk exploration target in the faulted lacustrine basin. Additionally， the trough and steep-slope zones are identified as the most favorable exploration targets for deep coal-rock gas.

10.11743/ogg20240618