Variability of estimated ultimate recovery in shale oil and shale gas accumulations in the U.S.

Variability of mean EURs within and between unconventional reservoirs is becoming more apparent as thousands of wells are drilled and oil and gas is produced from unconventional low-permeability reservoirs. Production from many of these reservoirs shows that there is spatial heterogeneity of EURs, which is mainly related to geologic characteristics. The more refined view of spatial heterogeneity resulting from many producing wells directly impacts the assessment of unconventional oil and gas resources through the application of more appropriate EUR distributions. The variability presented here suggests that the EURs from any one shale-oil or shale-gas accumulation should not be used as a production analog for potential shale-oil or shale-gas accumulations in frontier areas. Rather, a range of EURs utilizing several analogs is more appropriate. Shale-oil and shale-gas reservoirs were the focus of this paper, but tight-gas reservoirs and coalbed-gas reservoirs exhibit similar variation in EURs.