Using a geology-based assessment methodology, the US Geological Survey (USGS) has estimated some 19 million barrels of undiscovered, technically recoverable oil and 244 billion cubic feet of undiscovered natural gas in the Puerto Rico-US Virgin Islands Exclusive Economic Zone (EEZ).
The assessment was based on the postulated presence and viability of petroleum-system elements including petroleum source rocks (quality, source-rock maturation, generation, and migration), reservoir rocks (depositional environments, sequence stratigraphy, and petrophysical properties), traps (type and formation), and timing considerations.
Using this geologic framework, the USGS defined three hypothetical petroleum systems and five assessment units (AUs) (table 1). This study assessed the potential for technically recoverable resources in new field discoveries; economic resources were not evaluated.
Five hypothetical AUs were geologically defined to encompass those areas of the EEZ that were further evaluated for potential oil and gas resources (see map): North Coast Basin AU, San Juan Basin AU, South Coast Basin AU, North Mona Basin AU, and the Muertos Deformed Belt AU. The five AUs combine to form about 13 percent of the total area of evaluation. Most of the evaluation area, including Atlantic oceanic crust, Caribbean oceanic crust, Puerto Rico Trench area, and shelf areas have no petroleum potential and were not considered further. In addition, there is no potential for oil and gas resources within the onshore area of Puerto Rico or the US Virgin Islands.
The areas represented by the AUs of the Puerto Rico-US Virgin Islands EEZ, with the exception of the Muertos Deformed Belt AU, have been considered in previous oil and gas investigations.
In this study the postulated petroleum-system elements of the North Coast Basin AU, San Juan Basin AU, South Coast Basin AU, and the North Mona Basin AU are highly uncertain, resulting in low geologic probabilities (that is, the geologic probability of at least one oil or gas accumulation of 5 million barrels of oil equivalent or greater based on postulated petroleum-system elements) (table 1) and were not quantitatively assessed.
The petroleum-system elements of the Muertos Deformed Belt AU, although largely uncertain and risked, resulted in geologic AU probability above the threshold of 10 percent, and the AU was assessed quantitatively (table 1). Within the portion of the Muertos Deformed Belt AU that is part of the Puerto Rico-US Virgin Islands EEZ, the USGS estimated fully risked means of 19 million barrels of oil, 244 billion cubic feet of gas, and 6 million barrels of natural gas liquids.
The assessment of undiscovered petroleum resources at the 95th and 50th fractiles (table 1) is zero and reflects the low geologic AU probability of 20 percent and high geologic uncertainty on petroleum-system elements.
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