Rock Typing in Geothermal Reservoirs - A Textural Approach

Abstract

Reservoir rocks are found in a broad spectrum of effusive and volcaniclastic rocks in the geothermal fields around the world. The varying textures of these rocks are the result of the combination of formational and diagenetical processes that may strongly modify the primary rock properties. The observed textures are often related to the petrophysical properties. The petrophysical properties impact reservoir performance affecting fluid storage and flow capacity. Yet analytical petrophysical data is not fully integrated into geological and numerical models due to the complexity of the rocks, the sparsity of measurements, and the lack of understanding of the available data. This paper describes key textural parameters recognizable in hand specimens, including particle size, consolidation and porosity type, as a base for a rock-typing system applicable to geothermal reservoirs. Some or all of these textural parameters are proxies for porosity and permeability trends. A catalog, currently being developed, representing different petrophysical rock types will allow the comparison of cuttings of rocks with unknown petrophysical properties to samples with known properties. The purpose of the catalog is to provide reliable estimates of petrophysical properties where no analytical data, cores or logs are available.