Scale Prediction for Oil and Gas Production

Scale prevention is important to ensure continuous production from existing reserves that produce brine. Wells could be abandoned prematurely due to poor management of scale and corrosion. The objective of this paper is to present an overview of scale prediction and control and the current research at Rice University to solve these problems. In this paper, the challenges of scale prediction at high temperature, pressure, and TDS are reviewed. An accurate model to predict pH, scale indices, density, and inhibitor needs at these conditions are discussed. First, the various scale types found in oil and gas production and the condition under which they form are discussed. Secondly, the relationship of pH, alkalinity, organic acids, carbonates and CO₂ distribution is discussed. Thirdly, the temperature, pressure, TDS dependence of the thermodynamic equilibrium constants and activity coefficients is discussed. Lastly, the accuracy of a scale prediction program and its application is discussed. Based on a simple propagation of error estimation, the overall estimated error for calcite SI is ± 0.1. The program has been validated with literature solubility data for 6 minerals, pH data at 25 and 60 °C, and density of high TDS solutions and up to 12.7 lb/gal weighting fluid.