Project Rio Blanco - Part II: Production test data and preliminary analysis of top chimney/cavity

The re-entry drilling established communication with the top Rio Blanco detonation region at a depth of 1704 m, or about 76 m above the top detonation centre. A total of 2.8 x 106m3(97 x 106ft3) of dry gas at standard conditions has now been produced during two separate test periods. Radioactive and chemical analysis of this gas and the modelling of the stimulated reservoir shows the following main result: (1) No permeable connection exists between the top and the middle detonation regions, since none of the tracer incorporated in the centre explosive canister was detected in the gas produced. As a consequence, results for the top detonation region only are available at this time; (2) The initial cavity radius is deduced to be 20 m(66 ft), or well within expectations; (3) Integration of the 85Kr produced indicates a yield of 34+-3kt for the top explosive; (4) Of the approximately 1000 Ci of tritium produced in the top explosion region, about 5% is incorporated in the gas phase, (5) Pressure draw-down and build-up data are best reproduced by a two-layer reservoir model showing stimulated permeabilities about 10 and 30 times original formation permeabilities, and extending to a distance of about three cavity radii from the well bore; (6) The capacity of the reservoir intercepted by the top explosive is deduced to be about 0.2 mdarcy.m(0.73 mdarcy.ft), as contrasted with pre-shot estimates ranging from 1.3 to 2.3 mdarcy.m(4.1 - 7.6 mdarcy.ft). The reason for this discrepancy is not resolved at this time. Additional subsurface investigations of the other detonation regions as well as a re-evaluation of the initial reservoir properties are in progress. (author)