渝东南地区海相页岩有机质孔隙发育特征

有机质孔隙是高—过成熟海相页岩主要的气体储集空间。基于四川盆地东南部(渝东南地区)五峰组—龙马溪组页岩研究,将有机质划分为干酪根和沥青两种基本类型,其中,干酪根可进一步划分为无结构型干酪根和结构型干酪根两种类型,沥青可划分为固体沥青和复合有机质; 根据有机质孔隙的分布和发育特征,将其划分为干酪根内孔隙、海绵状孔隙和气泡状孔隙3种类型。通过扫描电镜实验和ImageJ软件提取有机质孔隙,结合圆度、凸性、伸长率、分形维数等孔隙形态参数分析不同类型有机质孔隙发育特征。结果表明:①随总有机碳的增加,有机质面孔率逐渐增加; ②当总有机碳低于2%时,随总有机碳的增加,平均孔径、分形维数逐渐减小,有机质孔隙趋于均一; 当总有机碳高于2%,随总有机碳的增加,平均孔径、分形维数逐渐增大,有机质孔隙趋于复杂; ③无结构型干酪根有机质孔隙以微孔(孔径小于25 nm)和小孔(孔径为25～100 nm)为主,发育少量中孔(孔径为100～1 000 nm); 结构型干酪根有机质孔隙以微孔为主,小孔其次,中孔发育较少; 沥青有机质孔隙以小孔为主,发育部分中孔和大孔(孔径大于1 000 nm); ④与沥青有机质孔隙相比,干酪根有机质孔隙圆度、凸性较大,伸长率较低; 但由于干酪根有机质孔隙的平均孔径较小,小孔含量高,分形维数相较于沥青偏高。

Development Characteristics of Organic Matter Pores of Marine Shale in the Southeastern Chongqing,China

Organic matter pores are the main contributors to the gas storage space in high-over mature marine shales. Based on the research of the shale from Wufeng-Longmaxi Formations in the southeastern Sichuan Basin(the southeastern Chongqing), the organic matter is divided into two types of kerogen and bitumen. Kerogen is further sub-divided into two types of unstructured kerogen and structural kerogen, bitumen is sub-divided into solid bitumen and composite organic matter. Organic matter pores are divided into three types according to the distribution and development characteristics, including kerogen-inner pore, sponge-shaped pore and bubble-shaped pore. The organic matter pores were extracted using scanning electron microscopy(SEM)and image processing software ImageJ, and the development characteristics of different types of organic matter pores were analyzed by pore morphology parameters, such as roundness, convexity, elongation and fractal dimension. The results show that ①the surface porosity of organic matter is positively related to total organic carbon(TOC); ②when the TOC is lower than 2%, the average pore size and fractal dimension decrease with the increase of TOC, indicating that organic matter pores tend to be uniform with the increase of TOC; when the TOC is higher than 2%, on the contrary, the organic matter pores tend to be complicated with the increase of TOC; ③unstructured kerogen mainly develops micropores(<25 nm)and small pores(25-1 000 nm), and few mesopores(100-1 000 nm); structural kerogen mainly develops micropores, followed by small pores, and less mesopores; bitumen mainly develops small pores and a few of mesopores and large pores(>1 000 nm); ④compared with organic matter pores in bitumen, the pores in kerogen have larger roundness and convexity, and lower elongation; however, due to the small average pore size and high contents of small pore in kerogen, the fractal dimension is higher in kerogen than that in bitumen.