Accumulation Of The Central Basin...
Accumulation of the Central Basin Platform, West Texas, U.S.A
The Central Basin Platform found in West Texas is the Simpson-Ellenburger petroleum system. It is composed of more than fifty mine fields and it covers an area of close to 9600km2. The system formerly contained close to 3 billion bbl of oil. However, approximately180 to 540 billion bbl was produced from the place thus implying that the system’s oil trapping capability is between 4.3% and 14.3%.
Fluvial and eolian processes are charged with the transportation of sandstone bits eroded from the highs to the north and east and depositing them in the cratonic margins. This deposition to form middle Ordovician Simpson Group rocks took place under a greenhouse setting. This was at a time when there was a general rise in sea-level and formation of a jagged karst landscape on Lower Ordovician Ellenburger carbonates that underlie it.
The sandstone bits that got deposited and form part of Simpson rocks include McKee, Waddell and Connell. There is however less production of Simpson rocks in the Texas and New Mexico sections of the Permian Basin as compared to places like Oklahoma. In Texas, Reeves and Pecos Counties are the wealthiest in Simpson deposits whereas the north and east have the least amounts. Underlying the Simpson Group is a huge hiatus located in the Lower Ordovician with a rare Middle Ordovician Depositional atmosphere. There are organic carbon-rich Simpson shales that are known to produce the Ordovician oil present in most Central Basin Platform area reservoirs.
Early diagenesis and evolution in porosity took place in this region at a time when tropical humid conditions were experienced. This period was marked by high-frequency cycles in sea level and increased amplitude. Distribution of porosity was linked to the sedimentological design regulated by the sea level. Early climatic-controlled diagenetic processes determined the nature of adjustment and preservation of porosity.
Icehouse conditions caused the sea level amplitude to change and also raised the frequencies thus depositing carbonates in the Andrews area. Porosity distribution in Wolf camp interval was made up of a mixture of sandstones, evaporites and carbonates. It is due to this that the lithostratigraphic framework dramatically changed between the area’s two blocks. A sequence by the name Cenomanian made up of a number of ramps deposited when there was a general subsidence-elicited second order transgression, each of which was caused by low-amplitude greenhouse third order cycles in sea level that were superimposed on the total transgression. There were other subsequent drift-related differentials that produced sandstone and carbonate characteristic.
Every carbonate underwent pervasive early water mixing, what is referred to as dolomitization. Nondolomitized particles were later dissolved through water flushing and resulted in secondary porosity. The most outstanding reservoirs are formed in the coarse and oolitic sandstones. Aquicludes develop from the silty dolomites of the extreme flood. These have a tendency of compartmentalizing the reservoir
Theoretically, the Ordovician was a period in time when there was only one super continent by the name Gondwana. There were three major terrains and these later on parted due to mountain building, for example between the northern coast of present day U.S. and Canada that caused narrowing of the Iapetus Sea found on the east of Laurentia. During this time greenhouse climate conditions was the order of the day and glaciation was relatively minor. Changes in sea levels were relatively of low amplitude and frequent. Carbonates were therefore deposited in some areas prior to clastics, for example in Oklahoma, north Texas and West Texas that are found in the subsiding basins of the south-central part of the U.S.References
Jones, R. (1997). The Middle-Upper Ordovician Simpson Group of the Permian Basin: Deposition, Diagenesis, and Reservoir Development. Retrieved on 13, Nov 2010 from http://www.beg.utexas.edu/resprog/permianbasin/PBGSP_members/writ_synth/Simpson.pdf
Katz, J. et al (1994) Simpson—Ellenburger: Petroleum System of the Central Basin Platform, West Texas, U.S.A: Chapter 28: Part V. Case Studies--Western Hemisphere. Retrieved on 13, Nov 2010 from http://search.datapages.com/data/open/offer.do?target=%2Fspecpubs%2Fmethodo2%2Fdata%2Fa077%2Fa077%2F0001%2F0450%2F0453.htm
Scholle, P. (2005) Regional aspects of the Wristen petroleum system, Southeastern New Mexico. Retrieved on 13, Nov 2010 from http://geoinfo.nmt.edu/publications/openfile/downloads/ofr400-499/476-499/485/485_CDROM/Wristen%20petroleum%20system.pdf
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