四川盆地下古生界五峰组-龙马溪组海相页岩气储层孔隙分类及特征

Classification and characteristics of pores in marine shale gas reservoirs in the Lower Paleozoic Wufeng-Longmaxi formations， Sichuan Basin

胡宗全 王倩茹 申宝剑 冯动军 杜伟 孙川翔

Zongquan HU Qianru WANG Baojian SHEN Dongjun FENG Wei DU Chuanxiang SUN

页岩气储层含有复杂的无机矿物成分和丰富的有机质，又经历了成岩、成油和成气等多期演化，导致孔隙类型多样、成因和形成过程复杂。国际上对页岩气储层的分类研究总体较为系统，国内研究多限于借鉴常规储层进行成因分类，在无机矿物与有机质的相互作用、无机孔与有机质孔的演化和相互转化方面的研究尚不深入，以四川盆地下古生界五峰组-龙马溪组典型海相页岩气储层为研究实例，以孔隙支撑载体作为孔隙特征描述切入点，分析了无机矿物、有机质以及二者共同支撑的孔隙特征，建立了“支撑载体类型 + 孔隙部位 + 孔隙成因”的孔隙分类方案，将孔隙类型划分为无机矿物孔、有机质孔及有机质-无机矿物复合孔，并进一步细分亚类。深化了孔隙演化与转化研究，在无机矿物成岩作用与有机质成油和成气作用耦合的基础上，将海相页岩气储层孔隙演化划分为3个阶段：① 沉积期—早成岩期主要发育大量无机矿物孔，以含水为主；② 成油期主要发育无机孔和少量原地有机质孔，以含油为主；③ 成气期主要发育大量迁移有机质孔和少量无机孔，以含气为主。分析了无机矿物孔、原地有机质孔和迁移有机质孔的演化及转化关系，指出优质储层经历的演化序列依次为沉积期的放射虫硅质页岩、成岩期的生物硅与有机质耦合、成油期硅质矿物粒间孔和晶间孔充填液态烃以及成气期硅质矿物晶间孔内充填沥青并发育有机质孔。

Shale gas reservoirs contain complex inorganic minerals and abundant organic matter， and have experienced a multistage evolutionary process including diagenesis and hydrocarbon generation. All these lead to the formation of diverse pore types with complex origins and formation processes. Internationally， systematic， in-depth studies on the classification of shale gas reservoirs have been conducted generally. However， in China， the genetic classification of these reservoirs largely relies on the criteria used for conventional reservoirs. Accordingly， there remains a lack of detailed studies on the interactions between inorganic minerals and organic matter， as well as on the evolution of inorganic and organic pores and their potential mutual transformation. In this study， we investigate typical marine shale gas reservoirs in the Wufeng-Longmaxi formations within the Sichuan Basin. By characterizing pores based on their props， we analyze the characteristics of pores propped by inorganic minerals， organic matter， and a combination of them， and accordingly propose a pore classification scheme in terms of prop types， pore development locations， and pore origins. Using this scheme， pores in marine shale gas reservoirs are categorized into inorganic， organic， and composite pores， each of which are further subdivided. To deepen the pore evolution and transformation， we integrate the diagenetic processes of inorganic minerals with the hydrocarbon generation of organic matter， and thereby the pore evolution in marine shale gas reservoirs can be divided into three distinct stages， namely， the sedimentary to early diagenetic stage， the oil generation stage， and the gas generation stage. The first stage is characterized by the development of abundant inorganic pores， most of which are saturated with water. The oil generation stage features the development of inorganic pores and a small quantity of pores within in situ organic matter （also referred to as in situ organic pores）， which are dominated by oil. The gas generation stage is marked by the formation of numerous pores in migrated organic matter and a small number of inorganic pores. Most of the pores formed in this stage contain gas. By analyzing the evolution of inorganic pores， in situ organic pores， and pores in migrated organic matter， along with the transformation among these pore types， we propose that the evolutionary sequence of high-quality reservoirs consists of the formation of radiolarian-rich siliceous shales during the sedimentary stage， the coupling of biogenic silicon and organic matter during the diagenetic stage， the infilling of liquid hydrocarbons into the intergranular and intercrystalline pores of siliceous minerals during the oil generation stage， and finally， the infilling of asphalt into the intercrystalline pores of siliceous minerals and the development of organic pores within the asphalt during the gas generation stage.

10.11743/ogg20250302