A New Experimental Procedure for Formation Damage Assessment in Geothermal Wells

Abstract

Difficulties in the reliable assessment of formation damage in numerous geothermal reservoirs, including the Salamander-1 well (Pretty Hill Sandstone Formation, Otway Basin), arise from the unavailability of cores. However, rock fragments are readily available. Thus this work presents a new method to assess the properties of permeability damage in a reservoir and other contributing reasons through laboratory tests on rock fragments. Analysis of field data from other wells of the same formation suggests that fines migration is a possible cause for permeability damage in Salamander-1. A novel approach for the assessment of formation damage using rock fragments includes the following experimental steps: development of a composite porous medium which consists of borosilicate glass beads and rock fragments; mobilisation of fines from fragments by alternation of velocity and salinity of water flowing through the composite porous medium; identification of minerals in collected fines by Scanning Electron Microscopy coupled with Energy Dispersed Analysis of X-rays; as well as calculation of the Derjaguin-Landau-Verwey-Overbeek (DLVO) total potential of interaction between fines and rock matrix, to determine experimental conditions favourable for particle immobilisation. Validation of this method was carried out via comparison of fines migration results for rock cores and fragments from Ladbroke Grove-1of the same formation. The method was successfully applied to fines migration results on fragments from Salamander-1. This method determines the fines capacity removal from rock fragments and its effect on formation damage. An analytical model taking into account the amount of particles retained in the porous media and causing formation damage was successfully applied to the experimental fines migration data, and resulted in the prediction of well clogging and a poor performance of Salamander-1.