The nanometer-scaled pore systems of gas shale reservoirs have a prominent contribution for gas storage. To obtain information about the characteristics of the nanopore structure within lacustrine organic-rich shales during their thermal evolution, artificial shale samples with different thermal maturities were obtained from a hydrous pyrolysis experiment. Nitrogen adsorption, field emission scanning electron microscopy, and porosity tests were used to investigate the characteristic pore structures of lacustrine shales with different thermal maturities from the Minhe Basin. The results show that the total organic carbon content decreased from 41.89% (unheated) to 27.7% (370 C) and that organic pores, intragranular pores of pyrite, and intergranular pores of clay minerals began to form with an increase in the simulated temperature and pressure. The porosity increased from 3.57% (unheated) to 26.09% (350 C) and then decreased to 20% (370 C) on the whole. The pore sizes were distributed from 1.7 to 500 nm, and the average pore diameter first showed a decreasing trend and then an increasing trend. The cumulative pore volume and cumulative specific surface area both presented a slowly increasing trend from an unheated status to 325 C, exhibited a rapid increase at 350 C, and then showed a slow increase at 370 C. This study could provide a reference for the exploration of shale gas in lacustrine shales with different thermal maturities.
Based on porosity and permeability measurements, mercury porosimetry measurements, thin section analyses, SEM observations, X-ray diffraction (XRD) analysis and granulometric analyses, diagenetic features of reservoir sandstones taken from the Zhuhai formation in the Panyu low-uplift of the Pear River Mouth Basin were examined. This study shows that chlorite cements are one of the most important diagenetic features of reservoir sandstones. The precipitation of chlorite was controlled by multiple factors and its development occurred early in eo-diagenesis and continued till Stage A of middle diagenesis. The precipitation of chlorite at the early stage was mainly affected by the sedimentary environment and provenance. Abundant Fe-and Mg-rich materials were supplied during the deposition of distributary channel sediments in the deltaic front setting and mainly in alkaline conditions. With the burial depth increasing, smectite and kaolinite tended to be transformed into chlorite. Smectite cements were completely transformed into chlorite in sandstones of the studied area. Volcanic lithics rich in Fe and Mg materials were dissolved and released Fe 2+ and Mg 2+ into the pore water. These cations precipitated as chlorite cements in middle diagenesis in an alkaline diagenetic environment. Chlorite coatings acted as porosity and permeability, thus helping preserve cements in the chlorite cemented sandstones. The reservoir quality of chlorite cemented sandstones is much better than sandstones without chlorite cements. Chlorite cements play an important role in the reservoir evolution that was mainly characterized by preserving intergranular porosity and forming better pore-throat structures of sandstones.
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