Abstract
The Eagle Ford shale is the shale with the greatest expectations in Mexico, given its abundant hydrocarbon liquids production and success in the US. Resource estimates were first published by the EIA and PEMEX in 2011, and new production and geologic information has been obtained in the area since then. The objective of this paper is to provide an important updated assessment of oil and gas reserves, as well as contingent and prospective resources, in the Mexican Eagle Ford shale and to quantify the related uncertainties.
Given the considerable uncertainties in shale reservoirs, a probabilistic decline-curve approach was chosen, as it allows performing a play-wide assessment with available production data, and it quantifies the uncertainty in the resource size. Analog areas in the US Eagle Ford shale were defined based on available geologic information in both the US and Mexico. The Duong model coupled with a Markov Chain Monte Carlo (MCMC) methodology was used to analyze and forecast production of wells located in the defined analog sectors in the US Eagle Ford shale. By combining the results of individual-well analyses, a type curve and estimated ultimate recovery (EUR) distribution was obtained for each of the defined analog sectors. These distributions were combined with well-spacing assumptions and sector areas to generate the prospective-resources estimates. Similar methodology was used to estimate the reserves and contingent resources associated with the few existing wells.
As of March 2013, the total prospective resources (P90-P50-P10) for the Eagle Ford shale in Mexico are estimated to be 527-1,139-7,268 MMSTB of oil and 17-37-217 TSCF of gas. Estimated reserves associated with existing wells and corresponding offset well locations are 18-35-60 BSCF for gas and zero for oil. Estimated contingent resources are 14-64-228 MSTB of oil and 8.5-13-26 BSCF of gas. For comparison, total resources (including reserves) for the US side are estimated to be 2,950-8,250-23,530 MMSTB and 34-91-266 TSCF, as reported by Gong et al. (2013). The results of the work presented here should provide a more reliable assessment of the resource size and uncertainty in the Mexican Eagle Ford shale for use in resource exploitation planning.
