113 / 2022-02-21 10:36:48

有机质分异规律、成孔效率及其对储层质量的制约——以中国川南地区海相龙马溪组页岩储层为例

Weiyuan area,Silurian,organic matter type,organic matter pores,scanning electron microscope

Abstract: The composition and content of macerals control the types of organic matter. Previous evaluations of organic matter types have shown that the hydrocarbon generation and pore formation capacity of the various types of organic matter are significantly different. However, previous identification and evaluation of organic matter types have mainly used organic geochemical procedures for destructive testing, making it impossible to quantitatively evaluate the type and content distribution of the organic matter on a microscopic scale. This study takes as an example the shale reservoirs of the Silurian Longmaxi Formation in the Weiyuan gas field in the Sichuan Basin, focusing on organic matter enrichment in the Long-1 sub-segment using two-dimensional large-area multi-scale combined SEM to qualitatively and quantitatively identify different organic macerals and their pore development capacity. The modular automated processing system (MAPS) technique was used for maceral analysis to quantitatively identify types of organic matter and analyze their vertical distribution. The results showed that (1) pore-forming efficiency is one controlling factor over pore development of organic matter. Sapropelinite shows the highest pore-forming efficiency (avg. 38.5%) and while the vitrinite, inertinite, and exinite have the lower pore-forming efficiency. (2) The content of sapropelinite is the highest (avg. 82.4%), and the content of sapropelinite is higher in the Long1₁¹ and Long1₁³ layers. The content of sapropelinite has a strong positive correlation with the total organic surface porosity. (3) The organic matter in the Long-1 sub-segment consists mainly of types I and II₁ kerogen, with a predominance of type II₁. The change in organic matter type with depth was determined as a sedimentary facies belt. Sublayers Long1₁¹ and Long1₁³ were formed in a stranded anoxic graptolite shale microfacies sedimentary environment. Weak hydrodynamic conditions make T index high. However, the Long1₁² and Long1₁⁴ sublayers were developed in a low oxygen environment and contain graptolite shale microfacies. Strong hydrodynamic conditions make T index low. (4) Organic surface porosity, organic porosity, and total porosity present basically consistent variations along the vertical direction of single well. Organic surface porosity restricts the organic porosity which is the dominant type in total porosity. Hence, pore-forming efficiency of organic macerals restricts performances of the reservoir.