Abstract
Abstract Organic matter pores are of important significance in the shale formation system rich of organic matters. Although a lot of studies have discussed controlling factors of organic matter pores in the past, it still lacks a quantitative analysis on contributions of organic macerals to organic matter pores. In this study, a case study based on the overmature marine facies shale reservoir in the first submember of the Longmaxi Formation of Silurian in the Weiyuan area was carried out. Besides, qualitative and quantitative identifications of organic macerals and their pore development capacity were provided using the scanning electron microscopy (SEM). 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. (3) The content of sapropelinite has a strong positive correlation with the organic surface porosity. (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.
Highlights
The success of “shale gas revolution” in America has changed the public understanding on pulverytes, especially shale
As a self-generation and self-storage unconventional gas reservoir in continuous distributions, shale reservoir is characteristic of low porosity and low permeability, and it is mainly composed of micron-nanometer pore throat systems [3,4,5]
Pores which are developed in organic matters, hereinafter referred as organic matter pores, are viewed as one of the most extensive pore types in shale reservoirs [9,10,11,12]
Summary
The success of “shale gas revolution” in America has changed the public understanding on pulverytes, especially shale. The pore-forming efficiency of different organic macerals (PFEDOM) refers to the ability to develop pores in the four organic macerals of sapropelinite, exinite, vitrinite, and inertinite, respectively It is measured by the surface porosity of different macerals in a certain period and under certain geological conditions. The sum of the contents of organic macerals multiplied by the pore-forming efficiency can be used to obtain the surface porosity of organic matter, which is a certain amount to describe the development degree of organic matter, and is of general significance. With respect to pore-forming efficiencies of different organic macerals, different scholars reported greatly different results for organic-rich shale in different regions, different eras, and different maturity of organic matters. Pore-forming efficiency is a key parameter to evaluate quality of shale reservoir which is rich of organic matters
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