Estimating potential hydrocarbon recoveries from greenfield (but resource-rich) unconventional gas plays remains a challenge. While analogs are routinely employed for this purpose, there is no shortage of examples of how new tight sand, coalbed methane and organic shale plays have defied historical experience.
An analytic approach is presented to account for whatever limited geologic and reservoir information might be available for a new resource play, and based upon sound engineering principles, make predictions of potential gas recoveries, their variability, and identify areas of uncertainty. In summary, the methodology involves selecting the potential ranges (and distributions where appropriate) of reservoir parameters across a particular acreage position, such as depth and pressure, formation thickness, porosity, fluid saturations, permeability, relative permeability, etc. Ranges in geostatistical variogram parameters are also often established.
Where no data exists, analogs and experience must still be employed. Single-well probabilistic reservoir simulation forecasting is then performed using Monte Carlo and/or experimental design methods to establish a distribution of potential well recoveries, which are in turn used for field development economic analysis. Factors having the greatest impact on well recoveries and economics can be identified via statistical analysis of the results, thus focusing field data collection efforts on topics with the greatest potential for uncertainty reduction. Each step in the methodology, and its value, will be presented as examples from a series of case studies.