Chemical compaction of deep buried mudstone and its influence on pressure prediction

The chemical compaction of mudstones which is dominated by the transformation of clay minerals leads to significant changes in the mineral composition and microstructure of mudstone during process of deep burial. In particular, the transformation of smectite to illite in mudstones results in noticeable impact on the pore pressure formation and the overpressure logging responses. At present, the study about the pressurization mechanism of chemical compaction and the impact on overpressure logging responses is really weak, which made it hard to pore pressure identification and pressure prediction for deep buried formations. Taking the Paleogene Shahejie Formation in the Dongying depression of the Bohai Bay Basin in eastern China as typical case, this paper analyses the characteristics of clay mineral transformation of the Shahejie Formation in the Dongying depression, the logging responses of overpressures, and the influence of chemical compaction on the prediction of pore pressure. The results showed that the chemical compaction of mudstones changes the relationship between the petrophysical properties of mudstone and vertical effective stress and the logging responses of overpressure. The typical characteristic of chemical compaction manifested as density increase continuous with the depth. The normal compaction trends of the different compaction stages are the basis for overpressure mechanisms identification and pore pressure prediction. The depth of the rapid transformation of clay minerals has a good consistency with the top of overpressure zone (2000–2800 m) in Dongying depression, which indicates that the overpressure and its logging responses may be related to the chemical compaction of mudstones. The measured pressure in intervals deeper than 3000 m is closer to the predicted pressure based on the normal compaction trend of chemical compaction.

Microbial Interaction with Clay Minerals and Its Environmental and Biotechnological Implications

Clay minerals are very common in nature and highly reactive minerals which are typical products of the weathering of the most abundant silicate minerals on the planet. Over recent decades there has been growing appreciation that the prime involvement of clay minerals in the geochemical cycling of elements and pedosphere genesis should take into account the biogeochemical activity of microorganisms. Microbial intimate interaction with clay minerals, that has taken place on Earth’s surface in a geological time-scale, represents a complex co-evolving system which is challenging to comprehend because of fragmented information and requires coordinated efforts from both clay scientists and microbiologists. This review covers some important aspects of the interactions of clay minerals with microorganisms at the different levels of complexity, starting from organic molecules, individual and aggregated microbial cells, fungal and bacterial symbioses with photosynthetic organisms, pedosphere, up to environmental and biotechnological implications. The review attempts to systematize our current general understanding of the processes of biogeochemical transformation of clay minerals by microorganisms. This paper also highlights some microbiological and biotechnological perspectives of the practical application of clay minerals–microbes interactions not only in microbial bioremediation and biodegradation of pollutants but also in areas related to agronomy and human and animal health.

TRANSFORMATION OF CLAY MINERALS IN SOILS OF SANDY DESERTS UNDER DIFFERENT SAXAUL SPECIES

As a result of experimental studies carried out for the first time with the aim at determining the impact of black (Haloxylon aphyllum) and white Saxaul (Haloxylon persicum) on the mineralogical composition of fine-dispersed fractions in sandy desert soils, it seemed reasonable to conclude that the transformation of minerals is quite different in soils used under different Saxaul species. This is explained by differences in biogeochemical turnover of elements in soils under black Saxaul and as a consequence by a higher Na content in the litter and the soda for-mation in the soil profile. The latter serves as a cause of alkalinization of soil solutions and transformation of minerals affected by alkaline hydrolysis.

Process evaluation of profile-differentiated gleyed soils of Precarpathians

Process analysis of profile-differentiated soils of the Precarpathians dismembered them to ESP set: basic processes (lessivage, oxidative segregation, spotty gley formation, the surface flow of organic matter, its nutrient transformation, gley (Fe, Mn) migration of substances); allocated linked processes (mineralization of organic matter and humus, humification), background processes (coagulation and biogenic structure formation, the disintegration of mineral matter, the transformation of clay minerals, calcium and salt migration). Sometimes occurs processes of subsurface input of organic matter, migration and immobilization of humic substances, the destruction of silicates, abiogenic (cryogenic) and biogenic pedoturbations. Creation of possible process soil types support the hypothesis of their geterogenetics. Key words: elementary soil processes, profile-differentiated soils, Precarpathians.