According to the 2015 Energy Information Administration (EIA) global assessment (EIA 2015), Argentina ranks third among countries in shale-gas resources and fourth in shale-oil resources. The Vaca Muerta formation in the Neuquén basin holds most of these resources. After the first EIA assessment of these resources in 2011, there has been a huge increase in investment, given the interest of the Argentine government to recover the energy autonomy it lost in the 1990s. The objectives of this study were to update estimates of oil and gas reserves and resources with the four years of production data available, and to quantify the uncertainty in these estimates.

The Vaca Muerta formation was subdivided into sub-areas based on the fluid type. The most appropriate production decline model was determined for each sub-area and coupled with Markov-Chain-Monte-Carlo (MCMC) methodology to analyze and forecast production of existing wells to calculate reserves. The analyses of individual wells in each sub-area were used to create probabilistic type-decline curves. These curves were combined with the estimated acreage-per-well distributions and the remaining drillable areas per sub-area to estimate contingent and prospective resources. The difference between contingent and prospective resources was based on the distance from existing wells.

As of January 2018, the total reserves (P90–P50–P10) for the Vaca Muerta shale in Argentina associated with existing wells are estimated to be 8.5–17.5–38.4 MMm3 of oil and 9.5–27.2–74.6 Bm3 of gas. Estimated contingent resources are 8.8–50.6–181.1 MMm3 of oil and 2.6–16.4–51.5 Bm3 of gas. Estimated prospective resources are 424–2,464–8,771 MMm3 of oil and 211–1,279–3,483 Bm3 of gas. Resources and reserves estimates were combined to estimate technically recoverable resources (TRR). The estimated TRR are 443–2533–8992 MMm3 of oil and 223–1223–3609 Bm3 of gas.

The results of this work should provide a more reliable assessment of the reserves and resources in the Argentine Vaca Muerta shale than previous estimates based on volumetric methodologies and analogies.

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