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Probabilistic Estimation of Shale-Oil Resources in 93 Global Formations in 36 Countries

By Deepthi Sen


An in-depth probabilistic study of global shale-oil resources is presently absent in literature. In 2013, the Energy Information Agency (EIA) reported the total volumes of shale oil available in 36 countries to be 388 billion barrels of oil (BBO) following a volumetric assessment of several potentially shale-oil-rich global formations. However, their study did not take into consideration the inherent heterogeneity of shale formations and the resulting uncertainties in reservoir parameters used in the assessment. I employed a probabilistic approach to the volumetric estimation of the original-in-place shale oil (OOIPsh_oil) in 93 formations from these 36 countries (and the US) belonging to seven geographical regions. This was followed by reservoir-simulation studies of five US formations whereby generalized-recovery-factor (RF) distributions were established for three values of hydraulic-fracture stage spacing. These generalized- RF distributions were used to compute the technically-recoverable resources of shale oil (TRRsh_oil) from the 93 formations considered. The results were aggregated to regional and global levels assuming 100% dependence (arithmetic aggregation) as well as 100% independence (statistical aggregation) between summand formation-wise resource distributions. The arithmetically-aggregated volumes (P10-P50-P90) of OOIPsh_oil in the assessed global formations are 900-8,700-67,700 BBO (P90/P10 = 75), whereas the arithmetically-aggregated volumes of TRRsh_oil, using 50-ft stage spacing, are computed to be 25-374-3,906 BBO (P90/P10 = 159). Using statistical aggregation, the total volumes (P10-P50-P90) of OOIPsh_oil in the assessed global formations are 15,000-23,600-43,900 BBO (P90/P10 = 3), whereas the aggregated volumes of TRRsh_oil, using 50-ft stage spacing, are computed to be 250-1,300-3,100 BBO (P90/P10 = 12). The high values of P90/P10 highlight the large uncertainty in both arithmetically- and statistically aggregated estimates. Since true dependency between the resource distributions of aggregated formations is unknown, the actual resource estimates are expected to fall between the statistically- and arithmetically-aggregated estimates. Because this study does not consider the uncertainties in, and possible correlations between, all variables, the wider resources distributions from arithmetic aggregation may be deemed more appropriate than from statistical aggregation. This study accounts for only 41% of all global petroleum basins. Thus, actual world resources are likely to be considerably larger

Topics: Shale oil, Resource assessment, Probabilistic, Volumetric, Original oil in place, Technically recoverable resources
Year: 2018
OAI identifier:
Provided by: Texas A&M University

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