Abstract

The Blossom Sand is a formation within the Austin Group (Fig. 1) that crops out in northeastern Texas and found in the subsurface of Arkansas, Louisiana, and the East Texas Basin. The Blossom Sand ranges in thickness from 50 to 90 ft and consists of primarily glauconitic sandstone (Fig. 2). In the Carthage Field of Panola County, Texas, the Blossom Sand is a historic gas reservoir located at depths of approximately 2000 ft (Rodgers, 1968). Since the discovery of the Carthage Field in 1918, the Blossom Sand has produced approximately 26 billion cubic ft of gas along with minor amounts of oil (Enverus, 2020; Rodgers, 1968). Despite its notoriety in the Carthage Field, there is very little research that has been conducted on this unit and the origin of its sediments and clay minerals have gone unknown.

This study determined the depositional environment and diagenetic history of the Blossom Sand using well logs and a combination of X-ray diffraction (XRD), X-ray fluorescence (XRF), and scanning electron microscopy (SEM) on six core samples from Panola County, Texas. These data determined mineralogy, porosity, permeability, and clay characteristics in the pore throats.

Well log correlations were performed with the use of Petra software to demonstrate variation of thickness and structure within the Blossom Sand. Formation tops were chosen in Petra based on its gamma ray, spontaneous potential, and resistivity responses (Fig. 3). Due to the Blossom Sand being bound by the Bonham Clay below and the Brownstown Marl above, the Blossom Sand displays a significantly lower gamma ray response as opposed to its neighboring formation above and below (Fig. 3). Its spontaneous potential response deflects approximately 18 mV further to the left than those belonging to its bounding formations. Finally, the Blossom Sand’s bounding formations exhibit higher resistivity responses. To confirm lithologies, XRD was used to determine the mineral assemblages within the core samples. Geochemical analysis was conducted with the use of XRF to identify the varying amounts of clay minerals throughout the core samples. Locations from which porosity and permeability data were to be derived were then chosen based on the geochemical data. The resulting porosity and permeability measurements were compared to the clay content to display the relationship between the two. The porosity and permeability measurements were then correlated to the corresponding well logs and extrapolated across the county to illustrate the extent of the various lithologies and display the variation of porosity and permeability within the Blossom Sand. Finally, the orientation of the sand grains, glauconite, and structure of the pore spaces, as well as other clay minerals present were displayed with the use of SEM.

The results of each of the analyses led to determining the order of events that would have occurred from deposition through diagenesis of the Blossom Sand. Results show that the sands were sourced from fluvial systems that stemmed from the Ouachita Mountains. The sands are the result of reworking within the nearshore tidal environment that existed in Panola County in the Late Cretaceous. The glauconite is secondary and reduces the overall porosity and permeability within the formation. These glauconitic lenses can be traced across the county, showing the heterogeneity of the Blossom Sand. Noting areas of high permeability as well as low permeability within this gas reservoir will aid in future enhanced recovery efforts of the Blossom Sand.