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

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^(12)m^(3),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^(nd)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^(12)m^(3),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.