Granular activated carbon (GAC) has been used to remove organics and metals simultaneously from wastewaters (4). For a regeneration procedure to be effective on GAC containing both metals and organics, it must remove both the metals and organic compounds. In this study, GAC saturated with Pb and phenol was regenerated using an NaOH rinse in batch mode. Four variables were investigated: 1) regenerant concentration (0, 0.1, and 1.0 N), 2) regenerant to carbon mass ratio (5:1 and 10:1), 3) regenerant temperature (22 and 80°C), and 4) regeneration time (0.33, 1, 3, 7, and 21 days). Maximum regenerations of 47% for Pb and 48% for phenol were observed. The 1.0 N NaOH regenerated a higher percentage of both Pb and phenol when compared to the other regenerants. The 10:1 regenerant to carbon ratio resulted in increased regeneration over the 5:1 regenerations. Pb regeneration was slightly higher at 80°C than at 22°C whereas phenol regeneration was slightly lower at 80°C than at 22°C. Maximum regenerations for both Pb and phenol were observed within the first day of regeneration, in most cases within the first 8 hours.

Strong overpressure conditions are widely distributed in the deep Longmaxi Formation (Fm) shale reservoirs in the Southern Sichuan Basin, with pressure coefficients ranging from 1.75 to 2.45. Overpressure plays a positive role in the high yield of shale gas, but a detailed study of its generation mechanism, evolution history, and potential impact on pore development is still lacking. This study’s evidence from theoretical analysis and the logging response method indicates that hydrocarbon generation expansion is the main generation mechanism for strong overpressure. Through the combined analysis of basin modeling, inclusions analysis, and numerical simulation, pressure evolution at different stages is quantitatively characterized. The results show that, during the shale’s long-term subsidence process, the shale reservoir’s pressure coefficient increased to 1.40 because of oil generated by kerogen pyrolysis. Then it increased to 1.92 due to gas generated by residual oil cracking. During the late strong uplift process of the shale, temperature decrease, gas escape, and stratum denudation caused the pressure coefficient to first decrease to 1.84 and then increased to 2.04. Comparing pore characteristics under different pressure coefficients indicates that higher pressure coefficients within shale reservoirs contribute to the maintenance of total porosity and the development of organic macropores, but the influence on the morphology of organic pores is negligible. These results will provide the scientific basis for optimizing sweet spots and guiding shale gas exploration in the study area.

The organic-rich shale of the Permian Taiyuan Formation (TYF) and Shanxi Formation (SXF) in the Southern North China Basin (SNCB) is considered a potential shale gas source. The shale was formed in a marine-continental transitional sedimentary environment, which has rarely been studied, with the enrichment mechanisms of organic matter (OM) remaining unclear. This study investigated the controlling factors and enrichment mechanisms of OM by analyzing the total organic carbon (TOC) content, paleoclimate, paleoproductivity, sedimentation rate, redox, and paleosalinity. The TOC of the TYF ranged from 0.92 to 7.43 wt.%, with an average of 2.48 wt.%, which was higher than that of the SXF (TOC = 0.36–5.1 wt.%, average of 1.68 wt.%). These geochemical indices suggest that both the TYF and SXF were deposited in warm and humid paleoclimates, with relatively high biological productivity and sedimentation rates. During the deposition process, the TYF experienced frequent transgression and regression events, leading to an enhancement of water reducibility, a relatively high sedimentation rate, reduced OM oxidation, and rapid deposition of OM, which were conducive to the preservation of OM. Moreover, a high biological productivity increased respiratory oxygen consumption in the water column, which could lead to OM accumulation. However, the regression event experienced by the SXF reduced the paleoproductivity and sedimentation rate and increased water oxidation, leading to a decrease in OM. The main controlling factors for the enrichment of OM in the TYF and SXF were the sedimentation rate, paleoproductivity, and redox conditions, thus establishing the enrichment models for OM in the TYF and SXF. This study is conducive to understanding shale enrichment mechanisms and guiding shale gas exploration.

The pore structure characterization and its controlling factors in overmature shales are keys to understand the shale gas accumulation mechanism. Organic matter in source rocks is a mixture of various macerals that have their own specific evolutionary pathways during thermal maturation. Pores within macerals also evolve following their own path. This study focused on petrographic characterization and maceral controls on porosity in overmature marine shales in China and the United States. Shale from Ordos Basin in China was also selected as an example of overmature transitional shale for maceral comparison. Organic petrology techniques were used to identify maceral types and describe morphological features in detail; scanning electron microscopy techniques were then used to document the abundance and development of pores within macerals. Helium measurement, mercury intrusion capillary pressure, and CO₂ adsorption were especially applied to quantify the pore structure of Wufeng-Longmaxi shale from Sichuan Basin in China. The vitrinite reflectance equivalent of the studied overmature samples is ~2.4%. The macerals within the studied marine shales are composed mainly of pyrobitumen and zooclasts. At this maturity, pyrobitumen develops abundant gas-related pores, and their volume positively correlates to gas content. Three types of pyrobitumen and its related pore structure are characterized in Wufeng-Longmaxi shales. Zooclasts contribute to total organic carbon (TOC) content but little to porosity. When the TOC content is above 1.51% in Wufeng-Longmaxi samples, the TOC content positively correlates to quartz content. Organic matter strongly controls micropore development. Pores of provide a significant amount of micropore volume. Clay mineral and quartz contents control micro- and macropore increments in organic-lean shales. MICP results indicate that pores within 3-12 nm and 900-2500 nm account for a major contribution to pore volume obtained. Determining the proportions of pyrobitumen to zooclasts within the total organic matter in pre-Devonian organic-rich marine shales is important in predicting porosity and gas storage capacity in high-maturity shales.

Various studies have shown that geo-catalytically mediated methanogenesis could happen in immature to early-mature source rocks at temperatures ranging from 60 to 140°C based on a series of long-term laboratory heating experimental evidences. The results of those studies show that methane yields at the given temperature are 5–11 orders of magnitude higher than the theoretically predicted yields from early thermogenic methane generation kinetic models. However, different types of source rocks in these laboratory simulation experiments generated varied CH₄ and CO₂ yields, which suggest that controls on CH₄ generation during catalytic methanogenesis are complex. This study summarizes and compares gas yield results from laboratory low-temperature heating simulation experiments. Pre-existing trapped methane in rock chips could mimic newly generated gas during heating. The yields of catalytically generated CH₄ from individual source rocks were re-quantified by subtracting the amounts of pre-existing CH₄ in the closed pores of the original source rocks from the total methane amounts released from heating experiments and pre-existing CH₄ in the closed pores in heated source rocks. The results show that heating temperature and time exert a positive influence on methane catalytic methanogenesis. Mowry and Second White Specks Formation Shale generated approximately ten times more CH₄ than New Albany Shale and Mahogany Shale per gram of total organic carbon (TOC). Samples of Springfield Coal #1 and #2 exhibited ten times yield difference from one another at the same heating temperature. Those yield differences are not strongly associated with TOC content, heating time, temperature, metal content, or kerogen type but appear to be more influenced by maceral composition and also maceral–mineral contact area within the source rocks. We conclude that macerals in the liptinite group have a propensity for methanogenesis. Specifically, amorphous organic matter undergoes transformation into hydrocarbons earlier than alginite at low-temperature heating conditions. Sporinite also contributes to higher yields of methane released from the coal source rock. Vitrinite and inertinite show a positive influence on carbon dioxide but no significant effect on increasing methane yields compared to other macerals. The strongest catalytic methanogenesis in the studied sample produced methane yields at 60°C, which amounted to ∼2.5 μmol per gram of organic carbon during one year of heating. We suggest that geocatalytic methanogenesis could generate economically sizeable gas plays from immature to early-mature source rocks over geologic time.