The presence of "exotic" scale such as Zinc Sulfide (ZnS), Lead Sulfide (PbS) and Iron Sulfide (FeS) in HP/HT reservoirs has been identified. "Exotic" scale materials come as a new challenge in HP/HT reservoirs. This has led to the development of more advanced tools to predict their behavior at extreme conditions. The aim of this work is to include ZnS into the group of scale materials that can be modeled with the Extended UNIQUAC model. Solubility data for ZnS are scarce in the open literature. In order to improve the available data, we study the experimental behavior of ZnS solubility at high temperatures. The determination of the solubility of ZnS is carried out at temperatures up to 250°C. Zinc sulfide (99.99%) and ultra-pure water are placed in a vial in a reduced oxygen atmosphere. The sample is placed in a controlled bath and stirred until equilibrium is attained. The suspension is filtered at the same process temperature and diluted immediately. Afterwards the aqueous solution is analyzed using Inductively Coupled Plasma Optical Emission Spectroscopy (ICP-OES) as analytical technique. The concentrations of Zn2+ and S2− ions are analyzed. The experimental data are used for parameter estimation in the Extended UNIQUAC model presented by Villafafila et al. (2005); (2006). The solid-liquid phase equilibria of the system is represented using the Extended UNIQUAC model. This model is chosen due to its versatility and fewer number of parameters (two parameters per species plus two parameters per species pair) to be estimated compared to other models (Pitzer's model). It is observed that ZnS solubility increases with increasing the temperature. This temperature dependency is very well represented by the Extended UNIQUAC model. The model is capable of predicting experimental data within the experimental error. The agreement between experimental data and the Extended UNIQUAC model shows that this thermodynamic model is a promising tool capable of determining the occurrence of ZnS scaling in HP/HT reservoirs. This methodology can be extended to other scaling materials (PbS, FeS), making the Extended UNIQUAC model a leading model in predicting scaling in HP/HT reservoirs.

Fluids produced from deep underground reservoirs may result in exponential increase in temperature. It is a consequence of adiabatic fluid decompression from the inverse Joule Thomson Effect (JTE). The phenomenon requires analysis in order to avoid any operational risks. This study evaluates the JTE upon decompression of black oil in high pressure-high temperature reservoirs. Also the effect caused by the presence of water and brine on the black oil is studied.The final temperature is calculated from the corresponding energy balance at isenthalpic and nonisenthalpic conditions. It is found that the final temperature of black oil increases upon adiabatic decompression. In the case of the isenthalpic process at initial conditions of the reservoir, e.g. 150°C and 1000 bars, it is found that the final temperature can increase to 173.7°C. At non-isenthalpic conditions the final temperature increases as well, but the increase is less. The effect of water is studied at different water fractions; it results in lower increase of the final temperature than observed for black oil. The presence of brine in black oil is also studied at different brine fractions. The addition of brine increases the final temperature but the increase is less than for pure black oil. Therefore, the presence of water and brine in black oil diminishes the heating effect observed initially for black oil.