Petrographic Analysis of Subsurface Part of Glen Rose Formation (Lower Cretaceous), South Texas: ABSTRACT

Abstract

ABSTRACT The main cause of poor hydrocarbon production from the Glen Rose is poor porosity throughout most of the section along with the lack of suitable structural features. Though the Glen Rose may be a source rock for other units, the presence of impermeable micrites in its lower portion may act as a barrier to oil migration into the Glen Rose from below. Analysis of 72 electric logs and 475 thin sections from 6 selected wells were used to determine the depositional history of the Glen Rose across the San Marcos Platform and Maverick Basin. Five limestone facies (Micrite, biomicrite, poorly washed biomicrite, washed intrabiopelsparite, and well washed intrapelsparite), dolostone (fine to medium grained), and some anhydrite were found. The Glen Rose is fairly constant in thickness across the San Marcos Platform (1400 ± 200 ft.), and thickens into the Maverick Basin (2200 + ft.). The Stuart City Reef trend became a barrier between these areas and the open ocean during middle Glen Rose time and affected environments during later Glen Rose time.