四川盆地自贡地区龙一₁ 亚段富有机质页岩储层特征和主控因素

Characteristics and main controlling factors of organic-rich shale reservoirs in the Long 1₁ Sub-member, Zigong Area, Sichuan Basin

摘要

四川盆地西南部下志留系龙马溪组为海相优质烃源岩，具备重要勘探价值。以四川盆地自贡地区龙一  ₁亚段富有机质页岩为研究对象，采用总有机碳质量分数、 X 线衍射全岩分析、扫描电镜、二氧化碳和氮气吸附等实验方法，分析储层特征、孔隙结构特征和主控因素。结果表明：研究区页岩矿物成分主要由黏土矿物和石英组成。研究区龙一  ₁ 亚段富有机质页岩孔隙类型为有机孔、无机孔与微裂缝，其中有机孔占比为 42.31%∼93.04% ，平均为 66.88% ，为主要的孔隙类型。研究区龙一₁ 亚段富有机质页岩总有机碳质量分数为 0.16%∼5.05% ，平均为 1.63% 。页岩有机质类型以I型为主，镜质体反射率平均为 2.30% 。页岩的总孔隙体积在 0.0180∼0.0310 cm³/g 之间，总比表面积在 23.15∼45.26 m²/g 之间。龙一₁ 亚段页岩储层发育以介孔为主，微孔次之，二者占总孔体积的 95% ，宏孔占比最小。有机质丰度和成熟度是影响有机质孔隙发育的主控因素，生烃作用促进纳米级孔隙的发育，热演化成熟度高，干酪根开始收缩，部分有机质孔隙闭合；黏土矿物的相互转化及压实作用对孔隙的发育具有消极作用；石英、方解石等脆性矿物在埋藏成岩过程中为孔隙空间提供支撑，粒间孔保留，孔隙数增加。该结果为四川盆地深层海相页岩气勘探的甜点预测提供依据。

Abstract

The Lower Silurian Longmaxi Formation in the Southwestern Sichuan Basin represents a highquality marine hydrocarbon source rock with significant exploration value. Focusing on organic-rich shale from the Long 1₁ Sub-member in the Zigong Area of the Sichuan Basin, this study employed techniques including total organic carbon mass fraction analysis, whole-rock X-ray diffraction, scanning electron microscopy, and CO₂ and N₂ adsorption to characterize reservoir properties, pore structure features, and their governing factors. Results indicate that the shale mineral composition in the study area is primarily clay minerals and quartz. Pore types in the organic-rich shale of the Long 1₁ Sub-member include organic pores, inorganic pores, and microfractures. Organic pores constitute the dominant pore type, accounting for 42.31%-93.04% of total porosity with an average of 66.88%. The total organic carbon (TOC) content in the organic-rich shale of the Long 1₁ Sub-member ranged from 0.16% to 5.05%, averaging 1.63%. The shale organic matter predominantly belonged to type I, with an average vitrinite reflectance of 2.30%. The shale's total porosity ranged from 0.0180 to 0.0310 cm³/g, with a total specific surface area ranging from 23.15 to 45.26 m²/g. The Long 1₁ Sub-member shale reservoirs predominantly developed mesopores, followed by micropores, which together accounted for approximately 95% of the total pore volume, while macropores constituted the smallest proportion. Organic matter abundance and maturity are the primary factors controlling organic pore development. Hydrocarbon generation promotes the formation of nanoscale pores, while high thermal maturity causes kerogen shrinkage and partial closure of organic pores. Clay mineral interconversion and compaction negatively impact pore development. Brittle minerals like quartz and calcite provide structural support for pore spaces during diagenesis, preserving intergranular pores and increasing porosity. These findings provide a basis for predicting sweet spots in deep marine shale gas exploration within the Sichuan Basin.

关键词

四川盆地 / 自贡地区 / 龙马溪组 / 有机质 / 深层海相页岩 / 储层特征 / 孔隙结构 / 定量表征 / 主控因素

Key words

Sichuan Basin / Zigong Area / Longmaxi Formation / organic matter / deep marine shale / reservoirs characteristics / pore structure / quantitative characterization / main controlling factors

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基金资助

国家自然科学基金项目(42202150)