Embodiments disclosed herein relate to reservoir characterization techniques and methods for accurately predicting scale tendencies of formation fluids, developed with the newly discovered phenomena that extreme downhole conditions affect the properties of reservoir fluids, including both the brine and dense hydrocarbon gas phases. In one aspect, there is disclosed a method for producing fluids from a geological formation. The method comprises inputting at least one property of a geological formation into an equation of state (EOS) model. The EOS model accounts for bound water, a high temperature effect on the brine and a high temperature effect on the dense gas phase. The EOS model is solved to determine a character of fluids contained in the geological formation, and inputting a production condition or a plurality of production conditions into the EOS model. A character of the fluids is determined based on the determined character of the fluids in the geological formation and the input production conditions. The solution can be output to a display device. Planning of the production of fluids from the geological formation can be performed. Production conditions can be controlled or adjusted.