It seems the concepts of risk, whether high or low, are connected to economic viability and backing by investors/banks.
As I understand the terms 'risked' or 'un-risked', they indicate whether active exploratory drilling has commenced or not, ie if the company has started to try to extract the raw material from the ground, they call what they believe to be in the ground a 'risked' reserve (- trying to get at the oil/gas obviously involves spending/risking invested money); if the assumed reserves are left in the ground, they are at that point in time still 'un-risked'.

As you yourself have probably discovered, anything containing the term 'Risiko' in the German equivalents just doesn't seem to be used. (I only found mention of 'risikoarme Resteverwertung' in the context of the oil industry, but that's something else.)
'mit Risiken behaftete xyz..' produces hits in purely financial/economic contexts - but standing right next to 'Vorraete' or the like, they're refusing to come up for me.


Insgesamt lagen die " sicheren" Ölvorräte zum 30. Juli bei 1,44 Mio. Barrel, die vorhandenen Gasvorkommen werden mit 2,34 Mio. mcf angegeben. Diese Größen sind deshalb sicher, weil sie auch von Banken als Sicherheiten anerkannt werden, um beispielsweise Kredite zu bekommen.

Lewis: Historically, oil and natural gas prices have been volatile and are likely to continue to be volatile. While this volatility presents an inherent risk, it also represents new opportunities. Risks present challenges that must be addressed and difficult times often create the best opportunities for future success.

More recently, the company has expanded into the Powder River Basin in Wyoming. Prima typically devotes a substantial portion of its budget to lower-risk development drilling or recompletion activities, but targets 10% to 20% of its capital budget to participation in higher-risk, high-potential exploration plays.

Presently, the company holds nearly 135,000 net acres in this emerging play. We believe that the unrisked reserve potential of its acreage could total as much as 100 Bcf to 300 Bcf of gas. The Powder River Basin is expected to be the center of much of Prima's growth over the next several years.