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Description:
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The Rodessa Formation is one of the major oil and gas reservoirs in the East Texas Basin . In Van Field , the upper Rodessa Formation consists of interbedded biotic and abiotic mudstones to grainstones . The lower Rodessa is composed of interbedded sandstones , shales , and limestones called the Carlisle Member . Based on core and well log interpretation , the Rodessa Formation was deposited on a broad , restricted , shallow marine platform interpreted to be lagoonal , subtidal , and intertidal .
Both Rodessa limestone and sandstone have been altered significantly by diagenetic processes that include micritization , cementation , dissolution , neomorphism and compaction . Dissolution is the main factor that resulted in enhanced porosity and permeability while cementation adversely affected porosity . Diagenesis is interpreted to have begun in the marine phreatic environment and continued through the freshwater phreatic and shallow burial environments .
Two reservoir units have been identified from core and well log interpretations . The potential reservoir within the Rodessa Formation occurs in the Carlisle Member which is composed mainly of medium to coarse grained sandstone with porosities and permeabilities in ranges of 8 to 11 percent and 46 to 896 millidarcies , respectively . The water saturation analysis has also shown the reservoir to be hydrocarbon bearing , having water saturation below 46 percent . |