Reservoir Characteristics Of Longmaxi Shale In The Southeast Of Chongqing

In order to search after reservoir characteristics of black shale in the LowSilurian Longmaxi Formation in Southeastern part of Chongqing, the paper discussestypes of main and minor minerals, pore classification, reservoir characteristics andinfluence factors based on the knowledge of previous studies and relative tests likephysical property of rock, scanning electronic microscopy analyses, mercuryporosimetry analyses and specific surface-pore size analyses. To understand in detail,we mainly take Lujiao outcrop section and Well Yuye-1for example.Both the main minerals and minor minerals in Lujiao outcrop section and WellYuye-1are quartz and clay minerals tested by X-ray diffraction analysis of bulksamples. Also, field emission scanning electron microscopy reveals similar mineralsand even more details. Quartz shows obviously preferred orientation because ofcorrosion and albite can be corroded which may result in secondary pores and thesepores may also be filled with illite later. Orthoclase also changes during compactionand cementation. The combination of clay minerals in Lujiao section is I+C+I/S. It’salso notable that there are varieties of minor minerals including pyrite, magnetite,anatase, zircon, apatite, monazite and so on. Among all of these, pyrite framboids aremost common and residual organic residue is commonly found around pyriteframboids which suggests reduction environment.We suggest to present four basic types of pores in black shales which areinterparticle pores, intraparticle pores, organic-matter intraparticle pores andmicrofractures. Interparticle pores are commonly found between clay mineralparticles or between ductile particles and rigid particles like quartz or pyrite. Many ofthe pores are appeared to be concentrated around rigid grain. Usually, pores range insize from nanometer-scaled to micrometer-scaled. Intraparticle pores are found withinparticles; some of the pores are primary in origin, although most are probablydiagentic. Organic-matter intraparticle pores have some relations with TOC, Ro andtypes of kerogen which are important to storage and migration of gas. Fractures ofLongmaxi shale occur at a variety of scales and are significant in reservoirs of shaleproperties.Moreover, there is a strong positive correlation between porosity andpermeability in Lujiao outcrop section. And with the increase of depth, porosityincreases and permeability changes little. Pore volume has correlation with quartz,clay minerals, TOC and so on. In detail, clay minerals have a positive correlation withmicropore and mesopore when TOC is between1.0and1.8. It can also conclude thatquartz contributes to macropores a lot because of the opposite content with clayminerals in black shales.