(537d) Extraction of Diesel From Drill Cuttings Using Compressed Carbon Dioxide

Drilling for oil and gas wells produce large amounts of drill cuttings. The oil content of these drill cuttings, using oil-based muds, is usually above 15 wt% after undergoing physical separation using shaker table. Environmental regulations require oil or hydrocarbon content to be reduced to less than 1 wt% in the cuttings prior to disposal. Current disposal methods involve re-injecting the cuttings into the formation which poses environmental issues, or transporting the cuttings to land for incineration or burial, which is expensive. Therefore, there is a need for a cost-effective, energy-efficient, environmentally acceptable and safe technique to recover hydrocarbon from drill cuttings. Recently, a process based on compressed carbon dioxide is identified as a promising alternative for the oil recovery from drill cuttings. The advantages are better handling, easier recycling, recovering pristine oil and lesser energy requirements when compared to existing techniques. The recovery process is designed to take place in an extraction unit, where liquid CO₂ stream is continuously added and mixed with drill cuttings. At certain operating conditions, liquid CO₂ stream dissolves the oil and progressively decreases the oil content in drill cuttings. This stream is flashed at low pressure in a separator. CO₂ is recovered as vapor and recycled. Oil is collected as the liquid from the separator. The essential information required to determine the operating conditions are the phase behavior data for carbon dioxide-oil mixtures. In this presentation, thermodynamic data generating the CO₂-diesel phase diagram and its application in the optimization of the extraction cycle will be discussed.

Results, observations and conclusions

Carbon dioxide-diesel mixtures exhibit a complex phase behavior at certain pressure and temperature conditions. For example, liquid-liquid immiscibility region is observed at pressures between the vapor-liquid region and the single phase liquid region. In the liquid-liquid equilibrium region, the majority of the lighter diesel components are soluble into carbon dioxide-rich liquid phase. The partitioning of diesel components into the CO₂ liquid phase has been experimentally established. In this work, the phase behavior data is collected at 17 and 25°C for various carbon dioxide-diesel mixtures. Specifically, the liquid-liquid and the vapor-liquid-liquid phase transition pressures are measured for each mixture. When the mixture is depressurized at constant temperature, the phase transitions occur from a single liquid region to the liquid-liquid region and from the liquid-liquid region to the liquid-liquid-vapor region. Based on these measurements for mixtures of several compositions, a pressure-composition phase diagram has been established for the carbon dioxide-diesel system. Consequently, the operating pressures of the extraction cycle are determined for test temperatures.