Understanding multiple factors which impact unconventional production: Guidelines to evaluate liquid rich unconventional resource plays

As the petroleum industry builds long-term production histories in major liquid-rich unconventional resource (UCR) plays, development geologists and engineers have come to realize the production GOR, petroleum type, and ultimate recoveries do not always match the predictive petroleum system models. Early studies suggested the UCR petroleum systems neither require traditional petroleum traps nor major migration systems, but simply an organic-rich source within the optimal maturity window. Possible explanations for these production discrepancies that were not fully characterized in the initial models include uncertainties in source rock characteristics, primary migration fractionation, fractionation related to storage, and production fractionation. Long term empirical observations suggest off-structure migration contribution, trapping mechanisms, and reservoir phase (single versus two) play an important role in the liquid rich UCR production. If the liquid-rich UCR petroleum system is a well-behaved predominantly local charge system, then the generation product can be estimated with an understanding of the local organic matter type and in-situ level of maturity, but if the UCR play is hybrid with significant migrated down-dip charge contribution, then a more complicated work program will be required to estimate well rates and volumes. The liquid rich unconventional resource play evaluation should reflect these additional factors which can greatly impact surface production rate and liquid recovery.