The Energy Information Administration has issued (and updated) an initial assessment of global shale oil and natural gas resources. Among its conclusions: "[It] is evident that shale resources that were until recently not included in technically recoverable resources constitute a substantial share of overall global technically recoverable oil and natural gas resources. The shale oil resources assessed in this report, combined with EIA's prior estimate of U.S. tight oil resources that are predominantly in shales, add approximately 11 percent to the 3,012 billion barrels of proved and unproved technically recoverable nonshale oil resources identified in recent assessments. The shale gas resources assessed in this report, combined with EIA's prior estimate of U.S. shale gas resources, add approximately 47 percent to the 15,583 trillion cubic feet of proved and unproven nonshale technically recoverable natural gas resources. Globally, 32 percent of the total estimated natural gas resources are in shale formations, while 10 percent of estimated oil resources are in shale or tight formations."
There's a lot of interesting information. For example: "[T]he production of shale oil requires that at least 15 percent to 25 percent of the pore fluids be in the form of natural gas so that there is sufficient gas-expansion to drive the oil to the well-bore. In the absence of natural gas to provide reservoir drive, shale oil production is problematic and potentially uneconomic at a low production rate. Consequently, producer drilling activity that currently targets oil production in the Eagle Ford shale is primarily focused on the condensate-rich portion of the formation rather than those portions that have a much greater proportion of oil and commensurately less natural gas."
As we say - read the whole thing.