| Summary: | The 2010 updated assessment of NPRA evaluated each of the 24 plays based on the availability of new geologic data available from exploration activities and scientific research. Quantitative assessments were revised for 11 plays, and no revisions were made for 9 plays. Estimates of the volume of technically recoverable, undiscovered oil and nonassociated gas resources in these 20 plays are reported elsewhere (Houseknecht and others, 2010). The NPRA assessment study area includes Federal and Native onshore land and adjacent State offshore areas. A map showing the areal extent of each play was prepared by USGS geologists as a preliminary step in the assessment process. Boundaries were drawn on the basis of a variety of information, including seismic reflection data, results of exploration drilling, and regional patterns of rock properties. Play boundary polygons were captured by digitizing the play maps prepared by USGS geologists.
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