Validation of Scale Prediction Algorithms at Oilfield Conditions

Abstract

Abstract Scale and corrosion continue to be serious and costly problems in oil and gas production facilities. Production engineers rely upon computer programs to predict the severity and location of scale deposition and corrosion. The core of these computer programs are algorithms to correlate a set of theoretically derived equations, e.g. the conditional solubility products in Oddo-Tomson saturation index and activity effect corrections in Pitzer theory of specific ion interactions, to a limited set of thermodynamic solubility data. Typically, the solubility data at various temperature and pressure are only available in low salinity matrix. The solubility in high salinity matrix is often done at STP with only simple background electrolytes, e.g. KCl. Limited mixed salt data are available and mostly consisted of seawater matrix at STP. Solubility data are more rigorously tested for halite and calcite, while they are scarce for other oil-field minerals, e.g. barite, gypsum, celestite, and metal-sulfides. Hence, the validity of these equations to extreme oil field conditions is not known. In this paper, a new corrosion-proof, high-temperature, high-pressure flow-through apparatus was developed to measure mineral salt solubilities under relevant oil and gas production conditions, i.e., high temperature, pressure, TDS (total dissolve solids), mixed ion matrices of sulfate, acetate, calcium, magnesium, and the presence of methanol and ethylene glycol. New solubility data illustrates the validity and limitation of the Pitzer activity correction of mineral salt solubilities. Pitzer equations have been shown to accurately predict scaling indices to within 0.1 SI, with ScaleSoftPitzer™, at extreme oil and gas production condition.