Undiscovered Oil and Gas of the Baltic Depression, 2014: A USGS Assessment

The Baltic Depression Province (dashed black line) and its assessment units. USGS.

The estimate

As part of its National and Global Petroleum Assessment Project, the U.S. Geological Survey estimated the undiscovered, technically recoverable oil and gas of the Baltic Depression Province (mean values):

The province

The Baltic Depression covers about 232,410 square kilometers, partly offshore, with onshore areas in Poland, Russia (Kaliningrad), Lithuania, Latvia, Estonia and Sweden.

Conventional oil and gas

The USGS defined a Lower Paleozoic Composite Total Petroleum System, with lower Paleozoic source rocks and conventional reservoirs, and one assessment unit — the Lower Paleozoic Reservoirs — bounded partly by the Silurian outcrop and the line where Cambrian rocks are 500 meters thick.

The oil and gas already found there prove the system works: the source rocks exist, generated hydrocarbons, and those hydrocarbons migrated into lower Paleozoic reservoirs. The province held 45 conventional oil and 6 conventional gas accumulations above the assessment's minimum size of 1 million barrels of oil or 6 billion cubic feet of gas.

Continuous (unconventional) resources

To count as a source of continuous oil or gas, a rock had to:

1. contain more than 2% total organic carbon by weight;
2. hold Type I or Type II organic matter;
3. be within the thermal window that generates oil and gas;
4. include organic-rich shale more than 15 meters thick.

Two systems met the test, each with an oil unit and a shale gas unit:

• the Cambrian–Ordovician Total Petroleum System
• the Silurian Total Petroleum System

Key input assumptions

Well drainage areas, success ratios and recovery per well come from U.S. shale-gas and shale-oil analogs. For every unit, well drainage averaged 167 acres (range 120–220) and the success ratio averaged 50% (10–90%).

The big uncertainty

Oil and gas began forming from Cambrian, Ordovician and Silurian rocks in the Late Silurian, before the Hercynian mountain-building of the Devonian to Carboniferous. Uplift and erosion then stripped at least 1,000 meters of lower Paleozoic rock — which may have let hydrocarbons escape. That is a major source of geologic uncertainty in the estimate.

Results by unit

Mean estimates, with the range from a 95% chance (F95) to a 5% chance (F5) of at least that amount. Values are fully risked.

The two Cambrian–Ordovician units were assessed with a probability of 0.9 that they hold at least one accumulation of the minimum size; the Silurian and conventional units with a probability of 1.0.

More results: the USGS World Oil and Gas Assessments.

Sources

Based on the Baltic Depression Assessment Team (Michael E. Brownfield, Christopher J. Schenk, Ronald R. Charpentier, Timothy R. Klett, Janet K. Pitman, Marilyn E. Tennyson, Stephanie B. Gaswirth, Tracey J. Mercier, Phuong A. Le and Heidi M. Leathers), "Assessment of undiscovered conventional and continuous oil and gas resources of the Baltic Depression Province, 2014," U.S. Geological Survey Fact Sheet 2015–3015 (2015); a work of the United States government in the public domain. The map and tables are taken from the fact sheet's PDF.