Prieto, A.M. 2014 Rock typing, applications of petroleum geology to geothermal reservoirs of New Zealand. Lower Hutt, N.Z.: GNS Science. GNS Science report 2014/03 48 p.
Abstract: Petrophysical properties play an important role in reservoir performance and the recovery of any fluid therein. However, petrophysical data of geothermal reservoirs is sparse and its impact on reservoir behaviour is mainly inferred from the estimates given by sensitivity analyses and inverse models in simulators. In order to build better calibrated and bigger numerical models of geothermal reservoirs, complexity should be added to their characterisation by means of integrating more petrophysical data into the description of the reservoir quality. However, this process depends on the availability of appropriate data. This study explores an option to overcome the lack of data. In order to use petrophysical properties to characterise petroleum reservoirs, especially at early stages of exploration when data is sparse, rock classes and analogues from outcrops and wellbores are used. These rocks are classified based on their geological, geophysical and engineering properties, and have been compiled in catalogues that provide the petroleum industry with more accurate estimates of formation parameters to be used in non-cored reservoir intervals. In order to develop a similar reference collection that allows the use of analogues to estimate unknown parameters of available samples of geothermal reservoirs, a calibrated procedure applicable to effusive and volcaniclastic rocks is needed using key descriptors. This study explores the applicability of a rock typing method based on descriptors and comparators to characterise geothermal reservoirs and shows its potential to provide a means to predict petrophysical properties as indicators of permeability. (auth)
