The Upper Jurassic Formations of the Arabian Basin and the Guadalupe Formations of the Permian Basin of West Texas and southeast New Mexico represent excellent examples of ancient shelf margin carbonate basins. These basins were filled at different geological times and had different eustatic histories, but had similar climates and geography. Both basins contain super hydrocarbon reservoirs and are economically important.
Through understanding the depositional history of these two basins, it should be possible to establish the primary controls that contributed to the generation and preservation of these large hydrocarbon accumulations.
The planned program of study for this research was to provide answers to the following fundamental questions:
Why are specific carbonate geometries found in these basins?
What are the deposition settings of the source-reservoir-seal for each basin?
What role did the tectonic history of these two basins play in the development of these reservoirs?
What are the most important facies from an economic perspective?
Why have hydrocarbons accumulated here and where are they preserved?
An overview of the depositional setting, the tectonic history, the role of eustasy, and the primary depositional facies found in these reservoirs and the sequence stratigraphy of both basins is explored. Where well log data were available they were utilized to establish more complete depositional models.The thesis that follows contains a brief overview of the structural development of each basin so as to discern the primary causes of the development of these basins and the eventual entrapment of the vast hydrocarbon reserves. Additionally, a brief examination of the history of oil exploration and production for the basins is provided.
A detailed study was made for the thesis involving the Hanifa formation of the Arabian and 14 wells provided by Saudi Aramco. A literature review of the Permian Basin regional sequence stratigraphy was made to determine the controls of low and high frequency sequence stratigraphy on the sedimentary section since no regional data was available at the time of this research. The shoaling-upward Hanifa sequence provided both the source for the overlying prolific hydrocarbon reservoirs and also contains important reservoirs. Both the source and reservoirs appear to have been deposited within the same time interval. Thus the TST, HST organic-rich lime mudstones of the southwest of the basin constitute the source, while here the HST high-energy shallow shelf facies constitute the reservoir. This source rock deposition coincides with the TST limbs of the first, second, and third order sea level cycles which caused a maximum rate of sea level rise and provided ideal conditions for source facies deposition and preservation.
Seals are either dense lime mudstones deposited in the lower sequences, and these changed to evaporitic seals in the overlying the Jubaila and the Arab Members.The ability to determine lithofacies distribution enables predictability of best reservoirs, sources, seals, and migration paths for the preserved hydrocarbons. This study was successful in constructing a general depositional profile for the section and determined the localities of best source and reservoir rocks. Using Fischer diagrams the study was also successful in reconstructing the 3-order sea level trends of the peritidal shelfal regions. These diagrams revealed three fourth-order sequences within the section that were not identified earlier. They also confirmed the general trend of the original Haq eustatic sea level curve for the time period. The Permian basin is characterized by a progressive shallowing upward trend with increased steepness of the shelf margin as the basin became more regressive. The basin is characterized by TST and HST keep-up carbonates on the shelf, constituting the primary hydrocarbon reservoirs, while the basin deposits consisted of LST basinal sandstones constituting further important reservoirs. The source for the Guadalupian reservoirs has not been definitely determined, but most workers agree that it probably is the Ordovician or Permian organic-rich calcareous shale. Finally, a comparison was made of the two basins and this is expressed as a table. As part of this thesis research, some of the results of the study of these two basins has been posted on the World Wide Web (WWW) in order to help train geologists in the fundadamentals of sequence stratigraphy. Geology traditionally been taught through formal class lectures augmented laboratory exercises and some field trips but a different approach has been used in this study. The resulting USC web site on sequence stratigraphy has been used to teach in much the same way but with on-line with material covering all aspects of this topic.The San Andres formations of Permian basin-West Texas and the Arab Formations of the Eastern Arabia Basin are used with this site to illustrate the basic concepts of sequence stratigraphy accompanied by exercises that provide a framework on which students can build their ideas.
The materials of this thesis are available on site through the items on the side bar menu.