A Failed Hydrocarbon System—Rawson Basins, Argentina
The business environment of the petroleum industry over the past 10 years has exerted increasing pressure on companies to improve exploration success with a corresponding reduction in costs and cycle time. Companies have responded by establishing processes for geologic risk assessment, volumetric estimation, and economic analysis. The ‘hydrocarbon system’ concept is integral to all of these processes because it focuses evaluation drilling programs to address fundamental uncertainties of the petroleum geology. In this manner, companies can significantly cut the cycle time to key decisions, move quickly into appraisal or to other opportunities, and thereby reduce costs and allow evaluation of additional prospective areas.
The hydrocarbon system concept was used in a frontier exploration program in the Rawson Basins, offshore Argentina. The focus of the postulated play was a test designed to prove or disprove the presence of a hydrocarbon system in any of the basins, rather than the more classic approach of testing the most economically viable (i.e., largest) prospect. The exploration program commenced with acquisition and interpretation of seismic and potential field data. A geologic model was developed assuming a hydrocarbon system composed of a lacustrine source rock associated with early rifting of the Atlantic Ocean, interbedded shales and fluvial–deltaic sandstones for seal and reservoir rocks, and structural closures for trap. An evaluation drilling program was developed to test the presence of an active hydrocarbon, and a single obligation well was positioned to test for a lacustrine source rock in the basin center, migration pathways, and reservoir and seal. Drilling encountered a sequence of red beds that lacked discrete reservoir sandstones or organic shales. The well penetrated the ‘basement’ Paleozoic strata and was abandoned without any drill-stem testing.
The absence of a hydrocarbon system was clear, and the decision to abandon the area was validated. The appraisal of the Rawson Basins was done quickly, had clear objectives for evaluation (to prove or disprove the hydrocarbon system), and resulted in a sound and timely decision, based on clear, definitive data, to pursue other opportunities elsewhere.
Figures & Tables
Petroleum Systems of South Atlantic Margins
“Giant oil and gas fields have been discovered through recent exploration in the deep and ultra-deep water regions of Angola, Brazil, and Nigeria. This volume includes 1. Descriptions of the petroleum geology of more than 12 basins along the two margins 2. Discussion of various components of the petroleum systems within these basins 3. Discussion on the use of the petroleum systems concept in the South Atlantic marginal basins to classify and characterize the diversity of the systems 4. Methodologies used in the assessment of petroleum system components 5. Overviews of the different components of the region's petroleum systems. Petroleum explorationists and researchers working in the South Atlantic will welcome this addition to their libraries.
The printed version of Memoir 73 was the Winner of the 2000 Dott Award for best AAPG Special Publication.”