Locations of 171 geologic provinces (red areas) of the world assessed in this study. Inset map shows assessed provinces of the Arctic in a polar projection; Arctic is defined as provinces above the Arctic Circle (yellow line). Arctic provinces are included in Regions 0, 1, 4 and 5.
Once again, the U.S. Geological Survey is proving itself to be a mighty busy place – and not just for the geology of the United States.
This time, its cadre of geoscientists and others who provide a seemingly endless supply of reports of high interest to the oil and gas industry, heads of state, various organizations and geoscientists around the world has tackled a big international target.
“An Estimate of Undiscovered Conventional Oil and Gas Resources of the World, 2012,” is a new report that is part of the USGS World Petroleum Resources Project.
It represents their first assessment of the world since the last report released in 2000.
By definition, the study covered a lot of territory, also yielding some big numbers.
The agency estimated mean volumes of 565 billion barrels of undiscovered conventional oil, 5,606 trillion cubic feet of undiscovered conventional natural gas and 166,668 million barrels of natural gas liquids in 171 priority geologic provinces of the world – exclusive of the United States.
A geology-based assessment methodology was used for the assessment.
Before you get a tad peeved wondering why there’s no focus on the attention-grabbing stars of the moment – such as unconventionals – be patient.
The agency reported that unconventional resource assessments – heavy oil, tar sands, shale gas, shale oil, tight gas, coalbed gas – for priority areas of the world are being wrapped up in an ongoing, separate USGS study.
The fact sheet released for the 2012 undiscovered conventional resources study noted that approximately 75 percent of the undiscovered conventional oil in the world occurs in four regions:
- South American and the Caribbean.
- Sub-Saharan Africa.
- Middle East and North Africa.
- Arctic provinces of North America.
Besides the top four, significant undiscovered conventional gas resources remain in all of the world regions.
New and Improved
It clearly was time for the new study, according to assessment team member and AAPG member Don Gautier, a USGS research geologist in Menlo Park, Calif.
“There are two or three dimensions of difference between this and the earlier study that are worthy of note,” he emphasized.
“A number of basins are included that were not in the 2000 study, and the entire Arctic is included in a systematic way that was not the case in the 2000 study,” Gautier noted. “There’s just a lot more detail in terms of what is covered.
“In many of the basins assessed previously, there were changes in estimated numbers and sizes of undiscovered accumulations,” he said. “The biggest changes are in the estimated numbers of undiscovered accumulations, and that is in part a methodological difference.”
Gautier noted that since the 2000 study was completed the USGS developed a set of global analogs.
“We classified all of the world’s known petroleum basins geologically and looked particularly at the density of fields, how many fields per unit area,” he said. “In recent assessments, we looked at these areas in terms of whether the earlier estimates of numbers of accumulations are reasonable in light of what the global exploration experience has been.
“In some cases, the numbers of anticipated fields seemed too high compared to their area, so we modified those field densities somewhat,” he said. “That explains why there’s a smaller number of oil fields estimated in some areas.”
The 2000 study used data from 1996. Needless to say, there has been significant exploration in the intervening years.
For example, Gautier noted there has been quite a lot of exploratory drilling in the sub-Arctic part of the West Siberian basin, yet not much oil was found there. This has the effect of modifying the assessment.
He noted other things that play into the changes:
- Drilling history in the intervening years.
- Addition of a number of new basins not included previously.
- Methodology refinement.
A Separate Piece
Given the importance of reserves growth in existing fields, a separate study was undertaken by the USGS to back up this new conventional resources world study. It’s the Assessment of Potential Additions to Conventional Oil and Gas Resources of the World (Outside the United States) from Reserve Growth, 2012.
“The future of conventional petroleum is two basic pots,” Gautier noted. “It’s the yet-to-find conventional fields and it’s also the addition to reserves in those fields already found – both of these are very significant volumes of resources.
“You don’t want to talk just undiscovered conventional and not think about the fact that there’s a lot of oil remaining in these existing fields,” he emphasized. “There’s quite a lot of conventional oil out there, and that’s not even mentioning the various unconventional resources.”
Gautier noted the reserves growth estimate was done from a statistical point of view. The methodology did include detailed analysis of geology and engineering practices observed in developed fields.
Owing to the lack of data for many fields outside the United States, data acquired from U.S. fields experiencing reserve growth were used as analogs in the study.
“We looked at how the big fields have grown in North America and then applied those kinds of growth functions to worldwide oil fields that haven’t grown so much,” he said, “and estimated how much might be added.
“The basic idea he added, “is, ok, if the world’s fields are developed in a way similar to those in North America, then what might we reasonably expect in terms of reserves additions to those existing fields?”
Reserve growth was estimated for fields outside the United States reporting original-in-place oil or gas volumes of 500 million boe or greater.
The mean estimated were 665 billion barrels of crude, 1,429 Tcf of natural gas and 16 billion barrels of natural gas liquids.