摘要
鄂尔多斯盆地埋深大于2000 m的深部煤岩气资源十分丰富,与中浅部煤层气相比,深部煤岩气中地层水具有高矿化、高度滞留的水文地质特征,对煤岩气富集成藏和开采具有重要影响。为了阐明鄂尔多斯盆地(下文简称盆地)深部石炭系本溪组8号煤岩地层水的基本特征以及对煤岩气的影响,深入剖析了煤岩水文地质、水化学、同位素等特征,探讨了现今盆地煤岩地层水赋存状态及水化学成因机制,并研究了地层水的空间分布特征及其控制因素。研究结果表明:①盆地深部煤岩气田地层水矿化度较高,属于CaCl_(2)水,钠氯系数为0.30~0.51,水动力弱,煤岩气封闭性极佳;②煤岩储层孔缝系统导致煤岩储层内水体分布不均,煤岩储层内大尺度裂缝中水体充盈,而邻近割理、微孔裂隙区域仅含极少量水,气泡变孔成因的气孔不含地层水;③煤岩作为上古生界气藏主要气源岩层,其地质历史中的生烃强度主导了气、水的宏观分布格局,其中强生烃叠加深埋升温下的地层水汽化携液关键地质作用使煤岩干化延续至今,深部煤岩具有超低含水饱和度特征,同时煤岩中少量的地层水基本保持了地质历史上古地层水矿化度分布特征。结论认为,盆地深部8号煤岩地层水与煤系地层水的演化具有继承性,煤岩热演化对地层水滞留赋存状态和矿化度升高等具有重要影响作用,该认识对深化盆地深部煤岩气成藏与演化具有重要的指导价值。
The deep coal-rock gas(CRG)resources with a burial depth exceeding 2000 m in the Ordos Basin are extremely abundant.Compared with the mid-shallow coalbed methane(CBM)reservoirs,the deep CRG reservoirs are hydrogeologically characterized by highly mineralized and highly retained formation water,which significantly impacts the accumulation and exploitation of CRG.To clarify the basic characteristics of formation water in the No.8 coal seam of the deep Benxi Formation and its influence on CRG in the Ordos Basin,the hydrogeological,hydrochemical,and isotopic characteristics of coal seams were dissected,the current occurrence state and hydrochemically genetic mechanism of formation water in coal seams in the basin were discussed,and the spatial distribution of formation water and its controlling factors were investigated.The following results are obtained.First,the formation water in deep CRG reservoirs of the basin is highly mineralized,belonging to CaCl_(2)-type water,with a Na/Cl ratio of 0.30–0.51,weak hydrodynamics,and excellent sealing for CRG.Second,the pore and fracture system of coal reservoirs leads to uneven water distribution within the reservoirs,where large-scale fractures are filled with water,while adjacent cleats and micro-pore zones contain only a small amount of water,and gas pores formed by bubbles contain no formation water.Third,as the main source rock of the Upper Paleozoic gas reservoir,the coal rock records its hydrocarbon generation intensity in the geological history dominating the macro-distribution pattern of gas and water.Specifically,the key geological process of strong hydrocarbon generation coupled with fluid carrying by formation water vaporization under the burial-induced elevated temperature drilled the coal rock until the present.As a result,deep coal seams exhibit an ultra-low water saturation.Meanwhile,the small amount of formation water in coal seams basically maintains the salinity distribution characteristics of paleo-formation water in the geological history.It is concluded that the formation water in the No.8 coal seam of the basin has inheritance with the evolution of coal-measure formation water,and the thermal evolution of coal rock plays a crucial role in the retention/occurrence state and enhanced mineralization of formation water.The research findings provide important guidance for further understanding the deep CRG accumulation and evolution in the Ordos Basin.
作者
刘洪林
王怀厂
邓泽
黄道军
LIU Honglin;WANG Huaichang;DENG Ze;HUANG Daojun(PetroChina Research Institute of Petroleum Exploration&Development,Beijing 100083,China;CNPC Key Laboratory of Coal-Rock Gas,Langfang,Hebei 065007,China;National Energy Shale Gas R&D<Experiment>Center,Langfang,Hebei 065007,China;Research Institute of Exploration and Development,PetroChina Changqing Oilfield Company,Xi'an,Shaanxi 710021,China)
出处
《天然气工业》
北大核心
2025年第8期17-29,共13页
Natural Gas Industry
基金
中国石油天然气股份有限公司科技项目“深地煤岩气成藏理论与效益开发技术研究”(编号:2023ZZ18YJ02)
中国石油勘探开发研究院“金点子”项目“气泡变孔理论在深部煤储层增储成藏中的地质意义研究”(编号:FHG024S04801001001)。
关键词
鄂尔多斯盆地
石炭系本溪组
8号煤岩
深部煤岩气
富集特征
地层水
矿化度
Ordos Basin
Carboniferous Benxi Formation
No.8 coal
Deep coal rock gas
Enrichment characteristics
Formation water
Salinity
