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Title: Resource Assessment of the In-Place and Potentially Recoverable Deep Natural Gas Resource of the Onshore Interior Salt Basins, North Central and Northeastern Gulf of Mexico

The objectives of the study were: (1) to perform resource assessment of the thermogenic gas resources in deeply buried (>15,000 ft) natural gas reservoirs of the onshore interior salt basins of the north central and northeastern Gulf of Mexico areas through petroleum system identification, characterization and modeling; and (2) to use the petroleum system based resource assessment to estimate the volume of the deep thermogenic gas resource that is available for potential recovery and to identify those areas in the interior salt basins with high potential for this thermogenic gas resource. Petroleum source rock analysis and petroleum system characterization and modeling, including thermal maturation and hydrocarbon expulsion modeling, have shown that the Upper Jurassic Smackover Formation served as the regional petroleum source rock in the North Louisiana Salt Basin, Mississippi Interior Salt Basin, Manila Subbasin and Conecuh Subbasin. Thus, the estimates of the total hydrocarbons, oil, and gas generated and expelled are based on the assumption that the Smackover Formation is the main petroleum source rock in these basins and subbasins. The estimate of the total hydrocarbons generated for the North Louisiana Salt Basin in this study using a petroleum system approach compares favorably with the total volume of hydrocarbonsmore » generated published by Zimmermann (1999). In this study, the estimate is 2,870 billion barrels of total hydrocarbons generated using the method of Schmoker (1994), and the estimate is 2,640 billion barrels of total hydrocarbons generated using the Platte River software application. The estimate of Zimmermann (1999) is 2,000 to 2,500 billion barrels of total hydrocarbons generated. The estimate of gas generated for this basin is 6,400 TCF using the Platte River software application, and 12,800 TCF using the method of Schmoker (1994). Barnaby (2006) estimated that the total gas volume generated for this basin ranges from 4,000 to 8,000 TCF. Seventy-five percent of the gas is estimated to be from late cracking of oil in the source rock. Lewan (2002) concluded that much of the thermogenic gas produced in this basin is the result of cracking of oil to gas in deeply buried reservoirs. The efficiency of expulsion, migration and trapping has been estimated to range from 0.5 to 10 percent for certain basins (Schmoker, 1994: Zimmerman, 1999). The estimate of the total hydrocarbons generated for the Mississippi Interior Salt Basin is 910 billion barrels using the method of Schmoker (1994), and the estimate of the total hydrocarbons generated is 1,540 billion barrels using the Platte River software application. The estimate of gas generated for this basin is 3,130 TCF using the Platte River software application, and 4,050 TCF using the method of Schmoker (1994). Seventy-five percent of the gas is estimated to be from late cracking of oil in the source rock. Claypool and Mancini (1989) report that the conversion of oil to gas in reservoirs is a significant source of thermogenic gas in this basin. The Manila and Conecuh Subbasins are oil-prone. Although these subbasins are thermally mature for oil generation and expulsion, they are not thermally mature for secondary, non-associated gas generation and expulsion. The gas produced from the highly productive gas condensate fields (Big Escambia Creek and Flomaton fields) in these subbasins has been interpreted to be, in part, a product of the cracking of oil to gas and thermochemical reduction of evaporite sulfate in the reservoirs (Claypool and Mancini, 1989). The areas in the North Louisiana and Mississippi Interior Salt Basins with high potential for deeply buried gas reservoirs (>15,000 ft) have been identified. In the North Louisiana Salt Basin, these potential reservoirs include Upper Jurassic and Lower Cretaceous facies, especially the Smackover, Cotton Valley, Hosston, and Sligo units. The estimate of the secondary, non-associated gas generated from cracking of oil in the source rock from depths below 12,000 feet in this basin is 4,800 TCF. Assuming an expulsion, migration and trapping efficiency of 1 to 5%, 48 to 240 TCF of gas is potentially available. The final recoverable gas is some percent of this estimated thermogenic gas resource based on the recovery factor for the specific reservoir. To date, some 29 TCF of gas have been produced from this basin. Also, the thermogenic gas, whether generated from late secondary cracking of oil to gas in the source rock or from oil to gas conversion in deeply buried reservoirs, migrated updip into shallower reservoirs, including the Monroe gas rock at depths of some 2,000 feet.« less
Authors:
Publication Date:
OSTI Identifier:
902843
DOE Contract Number:
FC26-03NT41875
Resource Type:
Technical Report
Research Org:
University Of Alabama
Sponsoring Org:
USDOE
Country of Publication:
United States
Language:
English
Subject:
03 NATURAL GAS; 02 PETROLEUM; NATURAL GAS DEPOSITS; GAS CONDENSATE FIELDS; GULF OF MEXICO; RESOURCE ASSESSMENT; ONSHORE SITES; SALT DEPOSITS; FORECASTING