下扬子区海陆过渡相不同沉积环境页岩气成藏条件对比

以下扬子区二叠系龙潭组富有机质泥页岩为研究对象,通过岩石热解模拟、元素分析测试、物性测试和X-射线衍射等实验,结合前人研究成果,对泥页岩空间展布特征、沉积微相类型、有机地球化学特征、储层特征和含气性特征等页岩气藏评价参数开展对比分析,结果表明:下扬子区龙潭组富有机质泥页岩广泛发育在滨岸平原、障壁-泻湖、三角洲前缘和浅海陆棚等海陆过渡相沉积环境中;泥页岩中有机质丰度较高,总有机碳(TOC)含量平均值为2.43%;干酪根主要为Ⅱ型、Ⅲ型;镜质体反射Ro分布范围是0.55%~2.66%,多数有机质处于中—高热成熟阶段;生烃潜力(S1+S2)平均值为2.96 mg/g,具备较大的页岩气生成潜能;研究区泥页岩物性较差,属于特低孔特低渗储层,但石英、长石、方解石等脆性矿物含量丰富,脆性指数(Ⅰ,Ⅱ)较高,有利于页岩气储层的压裂开发;保守估算下扬子区龙潭组吸附气量为0.34~0.96 m3/t,且物性封闭和烃浓度封闭作用进一步增强了页岩气的储存能力。对比不同沉积环境下页岩气成藏条件参数,综合研究认为下扬子地区障壁-泻湖相具备更为优势的页岩气成藏环境。

Contrast of reservoir-forming conditions of marine-continental transitional shale gas in different sedimentary environments in the Lower Yangtze area of China

In terms of the organic-rich shale of Longtan Formation in different sedimentary environments，some geologic parameters，such as thickness and distribution characteristics，sedimentary facies，organic geochemistry，reservoir characteristics and gas-bearing properties，were tested by means of rock pyrolysis analysis，organic element analysis，physical property measurement and X-ay diffraction.The results prove that the organic-rich shale of Longtan Formation in the Lower Yangtze area are widely distributed in strand plain，barrier-lagoon，littoral delta and shallow sea.The average content of total organic carbon (TOC) of shale is about 2.43%.The organic matter types are dominated by Ⅱ and Ⅲ.Organic maturity (Ro) varies from 0.55% to 2.66% and the organic matters of shale are at medium-high mature stage.The average value of hydrocarbon potential (S1+S2) is 2.96 mg/g.Hydrocarbon potential of shale is at the stage of massive gas generation.The physical property of shale in the study area is poor，which belongs to the special low porosity and permeability reservoir.Content of brittle minerals，such as quartz，feldspar and calcite，is abundant and it is conducive to the development of fracturing of shale gas reservoir.A conservative estimate of adsorption gas content of Longtan Formation is from 0.34 m3/t to 0.96 m3/t and the storage capacity of shale gas is further enhanced by capillary sealing and hydrocarbon concentration sealing.In the Lower Yangtze area，the comprehensive studies show that the favorable shale gas accumulation environment is in the barrier-lagoon by comparing the reservoir-forming conditions of shale gas in different sedimentary environments.