Productivity decline in a Salamander geothermal well: experiment, modelling and case study

Abstract

Substantial formation damage and productivity decline have been observed in numerous geothermal fields. Comprehensive analysis of formation damage and prediction of productivity specifically for geothermal reservoirs, however, are not available in the literature. On the basis of laboratory study and mathematical modelling, the present work is focused on the analysis of formation damage mechanism to diagnose and predict the productivity decline. A case study of a typical Australian geothermal reservoir (Salamander field) is performed. In this case, fines migration is recognised as the most likely candidate of all formation damage mechanisms. The attaching electrostatic forces are weak at high temperatures if compared with drag and lifting forces, which detach the particles from rock surfaces. Mobilisation of lifted fines results in particle straining in thin pore throats preferentially near the well, causing severe permeability and well productivity decline. A new model based on laboratory study is developed and field production data are successfully treated by the model. The potential for fines migration and induced formation damage in geothermal wells is significantly higher than that for conventional oil and gas wells due to the weakening of attaching electrostatic forces under high temperatures. The evaluated well index from field data is in good agreement with mathematical modelling prediction. The proposed model allows for long-term productivity prediction from a short production period, which allows recommending methods of skin prevention, mitigation and removal. The model is also applicable to shale, CBM, and tight oil and gas reservoirs.