Geologists Shanley, Robinson and Cluff have developed some conclusions
and future directions for exploration of and production from low-permeability
Exploration efforts in low-permeability settings must be deliberate
and focus on fundamental elements of hydrocarbon traps.
"Improvements in completion and drilling technology will allow
well identified geologic traps to be fully exploited, and improvements
in product price will allow smaller accumulations or lower-rate
wells to exceed economic thresholds, but this is true in virtually
every petroleum province," they say.
Petrophysics is a critical technology required for understanding
Low-permeability reservoir systems like those found in the Green
River Basin are not examples of "basin-center" or "continuous-type"
accumulations, nor are they a unique type of petroleum system.
"We suggest that the only truly continuous-type
gas accumulations are found in hydrocarbon systems in which gas
entrapment is dominated by adsorption, such as coalbed methane,
or where the reservoirs are in close juxtaposition with their source
rocks," they wrote.
Resource assessments of these regions have assumed a continuous,
recoverable gas accumulation exists across a large area locally
interrupted by the development of "sweet spots."
"Our work suggests, however, that this viewpoint is at odds
with the reservoir characteristics of low-permeability reservoirs,
and we find little support for this model," they wrote.
Significant production is dependent on the presence and identification
of conventional traps, they believe; existing resource estimates,
therefore, are likely overestimated.
Resource assessments in these low-permeability "basin-centered"
regions must recognize the reservoir properties inherent to these
rocks and should integrate the necessary concept of source, trap,
seal, migration and charge, and be conducted in a manner consistent
with the assessment of conventional oil and gas systems.