Pore Characterization of Pyrite in the Longmaxi Formation Shale in the Upper Yangtze Area of China

Abstract

Pyrite is widely distributed in the Longmaxi marine shale in the Upper Yangtze area of China. Pyrite, one of the important components of shale, has an important influence on the enrichment of shale gas. However, there are currently only a few studies on this topic. Based on shale samples from drilling cores using field emission scanning electron microscopy, the pore characteristics of pyrite from the Longmaxi Formation in the Upper Yangtze area of China are studied. The results showed that the intergranular pores of pyrite and abundant organic pores in the organic matter pyrite assemblages are developed in the Longmaxi Formation shale in the study area. Most pyrite framboid pores have triangular or irregular quadrilateral shapes, with pore diameters ranging from 0 to 240 nm. Pores with diameters of 80–240 nm are the major reservoir spaces for shale gas within the pyrite framboids. The average contribution rate of pyrite framboids to shale pores reaches 3.21%, and the highest contribution is 5.66%, indicating that the pyrite pores may have a favorable contribution to the shale reservoir pore system, but the contribution degree is low.

Impact of Pyrite Oxidation on the Pore-Structure Characteristics of Shale Reservoir Rocks under the Interaction of Fracturing Fluid

“…18 Chen demonstrated that the pores within the pyrite framboids, which were as high as 5.66%, had a favorable contribution to the pore system of shale reservoir, and these pores could reserve free gas and promote gas enrichment. 19 In addition, the presence of pyrite in shale reservoirs can accelerate the oxidation of shale. A previous study indicated that most fracturing fluids contained dissolved oxygen (9 mg/L) and some oxidants, which were used as glue-breaking agents.…”

“…It has been illustrated that pyrite has positive correlations with liquid hydrocarbon and total organic carbon (TOC), and it can promote the pyrolysis of organic matter and catalyze hydrocarbon generation . Chen demonstrated that the pores within the pyrite framboids, which were as high as 5.66%, had a favorable contribution to the pore system of shale reservoir, and these pores could reserve free gas and promote gas enrichment . In addition, the presence of pyrite in shale reservoirs can accelerate the oxidation of shale.…”