Examining Uncertainty in Reserves Estimation for Oil and Natural Gas Wells Completed with Hydraulic Fracturing
Costello, Harrison C.
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The recent innovations in horizontal drilling technology, paired with hydraulic fracturing (HF), have opened up vast reserves of petroleum across the world, particularly the United States. This recent surge in oil and gas production has numerous implications for energy security and international relations and will weigh heavily on future US energy policy decisions. However, wells in HF-stimulated reservoirs behave differently than their conventional counterparts, estimating recoverable resources difficult and often highly uncertain. Historically, recoverable reserves have been estimated using decline curve analysis, a method utilizing empirical curve fits production data to predict long-term good production. This analysis sought to understand the degree of uncertainty in unconventional reserve estimates using standard decline curve analysis through a comparison of representative well estimated ultimate recovery (EUR) in four tight oil plays and two tight gas plays. Mean EUR data from the US Energy Information Administration (EIA) and industry were compared directly with modeled representative well EURs. The high variability seen in the resulting comparison indicated significant uncertainty in mean EUR estimates for the same plays. More comprehensive reservoir modeling techniques like rate-transient analysis (RTA), which incorporates geologic data, fracture geometry, and flow regime analysis, have been demonstrated in conventional reservoirs to yield more accurate estimates of recoverable reserves and reduce uncertainty. As HF-stimulated oil and gas production in the United States continues to play a larger role in future energy policy decisions, reducing uncertainty, including by utilizing RTA, in future estimations of recoverable reserves will be critical to developing sustainable and effective policies.