Enhanced Thermal Desorption Process Can Extend Life of Base Oil and Reduce Energy Costs

Abstract

In many cases, the primary waste management challenge facing operators is drilled cuttings generated using oil- or synthetic-based fluids (OBF, SBF). Low temperature thermal desorption units (TDUs) are commonly used treatment systems for removing oil from cuttings. The oil recovered from the thermal desorption process is often reused to make oil-based fluids. However, base oils change during the thermal desorption process, and these changes can have a detrimental impact on the performance of the base oil. In some cases the base oil can break down. Typically the base oil used to formulate an OBF or SBF is selected for economical, drilling and logistical reasons and rarely, if ever, the thermal properties of the base oil. The thermal treatment company is left to determine how best to recover the oil so that the thermal degradation is minimal and the oil is suitable for reuse. To lower energy consumption and preserve the performance of the base oil, it is important to identify a base oil that has either a lower temperature for desorption or higher resistance to thermal degradation during the thermal desorption process. Ideally, a base oil would be chosen that incorporated both properties. The results of this study show that by correctly evaluating and selecting the base oil, the operator can benefit from using a fluid that may be much more suitable for reuse and will require much less energy to thermally treat. This paper describes how to achieve both of these goals using Thermal Gravimetric Analysis, Gas Chromatography / Mass Spec and a low-temperature retort. Determining the optimal desorption temperature is also an important factor. The oils recovered using these methods contain no oxygenated products and exhibit little thermal degradation. Residual oil from on cuttings is less than 1% (w/w). A practical methodology for base oil selection also is included in this discussion. Introduction Thermal desorption technology is designed to produce oil-free (or ultra-low TPH) solids for disposal by distilling off oils from the cuttings and recovering oil to be re-used for drilling fluid. However, base oils can change during the thermal desorption process, and these changes can have a detrimental impact on the performance of the base oil. Highly refined, ultra low aromatic, highly saturated, mineral- or synthetic- based oils may "crack" when exposed to the level of thermal energy required to render cuttings suitable for disposal. The process may also create aromatics and other undesirable unsaturated hydrocarbons that can affect the toxicity of the drilling fluid.1 The use of a base oil with higher resistance to thermal degradation during the thermal desorption process can allow the operator to recover and continue to reuse recovered base oils with minimal impacts on fluid and environmental performance. Modern TDUs have variable temperature control. If the oil on cuttings can be removed at a lower temperature, significant savings can be realized by the operator because less energy will be required by the TDU to reach the required less than 1% residual oil on cuttings. Therefore, it is important to identify a base oil that has a lower temperature for desorption so that it may be effectively removed from cuttings at a lower temperature. A further benefit of the lower temperature will be less inherent thermal degradation of the base oil. The ideal base oil choice would be one with both high resistance to thermal degradation as well as low desorption temperature. This study was conducted to help establish a reliable methodology for selecting the best base oils for use in drilling fluid systems where the thermal desorption process will be used to process cuttings and recover base oil for re-use. Base Oil Screening, Selection and Testing Nineteen base oils were screened using Thermal Gravimetric Analysis (TGA). The screening identified those base oils with a narrow evaporation range and relatively lower boiling points. Base oils were examined in air and under nitrogen; no significant differences were seen between the TGA results for oils in air and those under nitrogen (Table 1).

Remediation of oil-based drill cuttings using low-temperature thermal desorption

“…It has been demonstrated that LTTD is sufficient to treat OBDCs, wastes with light oils (Kapila and Thomas, 2003;Seaton et al, 2006). Besides, less inherent thermal degradation of the base oil in OBDCs under LTTD treatment, and thus recovered oil can be reused in the mud system (Fang et al, 2007). Falciglia et al (2011) environmental functions was enhanced after LTTD, indicating that LTTD could be a better alternate method compared to other harsh remediation processes.…”