A Study of the Relations of Depth, Porosity and Clay Mineral Orientation in Pennsylvanian Shales

Abstract

ABSTRACT Factors related to depth of burial, porosity, and clay mineral orientation in Pennsylvanian shales of western Kentucky were investigated. An attempt was made to determine some of the major factors affecting porosity and clay mineral orientation. The factors investigated were (1) depth of burial, (2) porosity, (3) preferred clay mineral orientation, (4) clay mineralogy, and (5) grain size. Simple and partial correlation analyses were used to determine statistical correlations among the various shale characters and to determine the relative influence of one or more characters on a particular correlation. Porosity was found to decrease slightly with increasing depth of burial. This negative correlation was found to be strongly influenced by illite content and clay mineral orientation. No correlation was detected between depth of burial and preferred clay mineral orientation. Porosity was found to decrease with an increase in preferred clay mineral orientation and an increase in illite content. Preferred clay mineral orientation was found to increase with increasing clay content, whereas, increasing silt content was accompanied by a decrease in preferred clay mineral orientation. A positive correlation was detected between illite content and depth of burial; chlorite was found to be positively correlated with depth. These relations, alongwith a decrease in chlorite content with increasing illite, suggest the possible alteration of chlorate to illite with increasing depth of burial and age.