Browsing by Subject "Clay minerals"
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Item A simplified method for identifying the predominant clay mineral in soil(Texas Tech University, 1979-12) Mojekwu, Eugene ChukwunonsoIncreased construction activity in sites that contain very active clay minerals has greatly expanded the necessity for engineering knowledge related to the type and amount of clay minerals in a given soil. Presently, there are varying methods of predominant clay mineral identification. These methods are, however, frequently time consuming and laborious and require expensive equipment that is not commonly found in the ordinary commercial soils testing laboratories. Pearring in 1968 and, later, Holt in 1970 developed a correlation chart to aid in the identification of the predominant clay mineral in a given soil. The two parameters involved are Cation Exchange Activity and Activity Ratio. These two parameters require the plasticity index, the cation exchange capacity, and the percent of clay in the soil fraction passing the No. 200 sieve. Presently, cation exchange capacity determination is not devoid of expense and time problems. These problems prompted this research which is intended to relate the cation exchange capacity of a clay soil to the easily obtainable Atterberg limits (plastic limit and liquid limit) and plasticity index. A detailed study was made of selected soils of varying geographic locations and geologic origins to establish data related to the chemical (cation exchange capacities) and engineering index properties of such materials. A study of the test results discloses that it is possible to predict the cation exchange capacity of a soil and, hence, the predominant clay mineral in the soil, using the plastic limit. The result of the correlation study shows a strong relation to exist between the cation exchange capacity and the plastic limit of all soils tested. This relation may be approximated by the expression CEC = PL^1.17.Item Authigenic clays and stylolites in the carbonate reservoirs of the Permian Basin(Texas Tech University, 1997-05) Kumar, AnishAuthigenic clay minerals are found in back-reef carbonate rocks ofthe Upper Permian Artesia Group ofthe northwestern shelf of the Delaware Basin. The authigenic clays are located in the vugs and pore spaces of the carbonates. Stylolites from these rocks do not show clays of authigenic origin, however detrital clays and other minerals such as illite, quartz, feldspar, and pyrite are accumulated in the stylolite seams in these carbonates. Authigenic clays in pores and vugs of carbonate samples were studied using x-ray diffraction, and electron imaging such as SEM, TEM, and STEM. Dickite is the predominant authigenic clay mineral. It occurs mostly in euhedral hexagonal platelets. Authigenic illite is rarely observed, and it occurs as laths and fibers.Item Nature of the changes in clay minerals of the high temperature drilling fluids(Texas Tech University, 1984-05) Lee, Li-JeinThe mineral reactions in the sepiolite- and palygorskite-based drilling fluids were systematically examined with X-ray diffraction and analytical electron microscopy before and after hydrothermal treatments. Both sepiolite and palygorskite were converted into smectites and other mineral phases in fluids containing either chlorides or hydroxide. The conversion rate usually increased with increasing temperature. Below 600''F, the smectite occurred as thin films with irregular outlines with a high layer charge, whereas discs or platelets with hexagonal outlines were formed above 600°F. The conversion of sepiolite (or palygorskite) to smectite at low temperatures (<600ºF) was accomplished through epitaxial growth of smectite films around sepiolite (or palygorskite) fibers. At higher temperatures (>600ºF), smectites and other new mineral phases were formed through a dissolution-precipitation mechanism. Smectite formed from sepiolite was chemically and structurally a trioctahedral variety; however, smectite formed in the palygorskite fluids consisted of trioctahedral and di-trioctahedral phases. The di-trioctahedral phase with approximately equal amounts of Al and Mg in the octahedral sheets was an unusual reaction product. Other commonly observed reaction products, besides smectite, were feldspars, illites, cement minerals,zeolites, amphiboles, talc, and silica spherules. The formation of non-clay minerals resulted from reactions between additives and the chemicals released from the decomposition of original materials. The chemical properties of the additives apparently had profound effects on the formation of new mineral phases as well as on the stability of parent materials. The high alkalinity generated by hydroxides adversely affected the stability of sepiolite (or palygorskite) and favored the formation of framework silicates at lower temperatures. The promoting effect of the added cations on the conversion rate of sepiolite and palygorskite to smectite seemed to be Ca>Mg>Na>K for both sepiolite/chloride and palygorskite/chloride systems, and Mg>Na>Ca>K for sepiolite/hydroxide, Mg>Ca>Na>K palygorskite/hydroxide systems. The rheological properties of the fluids, such as viscosity and fluid loss, were related to the mineralogical changes at elevated temperatures. The formation of smectite platelets, discs, and other new mineral phases obviously exerted a detrimental effect on the rheology of the fluids.