| dc.description.abstract | Due to the complex nature and importance of porosity in carbonate systems, it has been extensively studied and characterized. Many porosity types and textures have been strongly
associated with certain chemical and physical conditions that they became cliché indicators of
those conditions. Such associations exist for moldic and oomoldic porosity in carbonate rocks.
The selective dissolution of metastable (Aragonitic or HMC) allochems has been all but accepted
to indicate diagenesis by fresh waters. In this study, oomoldic porosity in the Permian Happy
Spraberry Field reservoir is closely examined, in an effort to decipher the conditions that led to
its creation. It is suggested that oomolds were created in a marine phreatic to shallow burial
environment, with no influence whatsoever of meteoric/fresh waters.
In order to accurately characterize the conditions that led to the creation of oomolds,
cement types were characterized and ranked using optical microscopy and SEM, bulk rock
minerology by XRD, δ^18O and δ1^3C isotope analysis, and trace element analysis by laser ablation
on select samples that represent the oomoldic-rich reservoir unit of the Happy Spraberry Field
Reservoir. Cements identified were mostly equant blocky LMC cements filling in primary pore
spaces between ooid and bioclast molds, and some bladed isopachous LMC cements. These
cements have been interpreted to be precipitated as early initial-stage cementation, and
synchronous to the dissolution of the aragonitic ooids. The prominent equant LMC cement
texture mimics textures associated with meteoric water diagenesis, however, further analysis
proves otherwise. The LMC cements have δ^18O (VPDB) ratios that range between -2‰ and -
3.5‰, and δ^13C (VPDB) ratios that range between 4‰ and 5‰. These values conform with
typical low latitude Permian marine carbonate values, and further signify diagenesis within a
marine water realm. Trace element analysis of those early cements show slightly elevated Sr
content, and low Fe and Mn, which is typical of marine water chemistry. Although oomolds and
equant blocky cement textures are typically associated with meteoric water diagenesis, it is
believed that marine waters can mimic and produce similar, if not identical textures. To explain
this process, we suggest that the dissolution of aragonite ooids and precipitation of early cements
to have occurred below the aragonite lysocline. | en |
