贵州省科技计划项目(黔科合基础1407); 高层次人才科研启动基金项目(院科合字G2017006号); 贵州省青年科技人才成长项目(黔教合KY字283); 创新创业项目(S202210668115)
黔西北大方地区龙潭组以泥页岩、煤层与砂岩交替互层发育为特点,具有典型的海陆过渡相特征。文章在剖面实测和样品采集的基础上,结合全岩和黏土矿物XRD分析、总有机碳(TOC)含量测定、岩石热解、干酪根显微组分及镜质体反射率(RO)等分析,对研究区龙潭组烃源岩发育特征进行了研究和评价。结果表明: ① 龙潭组矿物以黏土矿物为主,具有较强的吸附能力,但黏土矿物含量与石英含量呈明显的负相关关系(R>0.8),尤其是泥页岩中70%以上的黏土含量以及较低的脆性指数增加了压裂开发的难度。 ② 龙潭组有机质丰度受岩性变化控制明显。煤层具有最高的TOC含量(平均值42.9%)和生烃潜量(平均值为2.68 mg/g),显示强大的煤层气生烃潜力;泥页岩生烃潜量均小于2 mg/g,但约有80%样品的TOC含量超过2%,页岩气资源潜力不及煤层气;粉砂岩生烃潜力最差,生烃潜量平均值为0.13 mg/g,TOC含量为1.4%~5.6%,显示一定的致密气潜力。 ③ 龙潭组有机显微组以壳质组和镜质组占主导,干酪根以Ⅲ型为主,Ⅱ2型为辅,热演化程度高,处于高-过成熟的生干气阶段。 ④ 煤层更为发育的龙潭组中段是大方地区煤层气、页岩气和致密砂岩气联合勘探的有利层段。
The Longtan Formation in the Dafang area of Northwest Guizhou is characterized by alternated shale, coal seams, and sandstones, with typical characteristics of marine-terrestrial transitional facies. On the basis of profile measurement and sample collection, combined with XRD analysis of whole rock and clay minerals, determination of total organic carbon (TOC) measurement, rock pyrolysis, kerogen macerals, and vitrinite reflectance (RO) analysis, the development characteristics of hydrocarbon source rocks of the Longtan Formation in the study area are studied and evaluated. The results indicate that: ① The minerals in the rocks of the Longtan Formation are mainly clay minerals with strong adsorption capacity, but there is a significant negative correlation between clay mineral content and quartz content (R>0.8), especially the clay content of over 70% in shale and the lower brittleness index, which is very unfavorable for fracturing development; ② The abundance of organic matter in the Longtan Formation is significantly controlled by lithology. The coal seam has the highest TOC content (average 42.9%) and hydrocarbon generation potential (average 2.68 mg/g), indicating strong hydrocarbon generation potential of coalbed methane; The hydrocarbon generation potential of shale is less than 2 mg/g, but about 80% of the samples have TOC content exceeding 2%, and the shale gas resource potential is less than that of coalbed methane; Silty sandstone has the worst hydrocarbon generation potential, with an average hydrocarbon generation potential of 0.13 mg/g and a TOC content of 1.4%~5.6%, indicating a certain degree of tight gas potential; ③ The macerals of the Longtan Formation kerogen are mainly composed of liptinite and vitrinite, with type Ⅲ kerogen being the main type and type Ⅱ2 being the auxiliary type. They have a high degree of thermal evolution and are in the stage of high-over mature dry-gas generation; ④ The middle section of the Longtan Formation, where coal seams are more developed, is a favorable zone for joint exploration of coalbed methane, shale gas, and tight sandstone gas in the Dafang area.