Parameter optimization for low-temperature catalytic pyrolysis in oil-based drilling cuttings treatment

Waste oil-based drill cuttings are one of the most severe environmental pollutants generated during oil and gas field exploitation. They are hazardous wastes characterized by high production volume, elevated oil content, complex composition, and extreme difficulty in proper disposal. Among various methods such as centrifugal separation, solvent extraction, surfactant hot washing, pyrolysis, etc., the thermal treatment method that removes volatile and semi-volatile pollutants (such as hydrocarbons) by pyrolysis is widely favored due to its short processing time and high removal efficiency. However, conventional pyrolysis methods operate at high temperatures, consume significant energy, and exhibit high material selectivity, which makes them prone to coking and ultimately results in low treatment efficiency. Based on conventional pyrolysis techniques, the required pyrolysis temperature can be significantly lowered by adding catalysts and anti-coking agents to pretreat oil-based drill cuttings. The removal efficiency of oil in oil-based drill cuttings was studied using three different catalysts, CA, CB, and CC (representing catalysts A, B, and C), at temperatures of 200, 250, and 300 ℃. The CA and CC catalysts with superior performance were then compounded, and it was found that a compounding ratio of 2∶1 (CA∶CC) significantly improves the treatment effect. Screening of anti-coking agents JA, JB, and JC (representing coking agents A, B, and C) revealed that JB effectively reduces the adhesion of solid residues on the inner wall of the reactor. Utilizing central composite design (CCD) and response surface methodology (RSM) ensures the accuracy of the results while reducing the number of required experiments. The response surface methodology (RSM) model results indicate that the optimal treatment parameters are as follows: for 300 g of oil-based drill cuttings, a composite catalyst addition ratio of 4.417% (with a CA∶CC atio of 2∶1), a reaction temperature of 285.43 ℃, and a reaction time of 97.17 min, under which the oil content of the drill cuttings is reduced from 14.76% to 0.20%. Analysis of the products after treating the oil-based drill cuttings under the optimal conditions, in reference to the Sichuan Provincial Local Standard of the People’s Republic of China “Standard for the Utilization and Disposal of Residual Solid Phases after Comprehensive Utilization of Oily Sludge in Natural Gas Exploitation: DB51/T 2850-2021”, revealed that the heavy metals and other key indicators in the solid phase residues are effectively removed. The resulting solid residue, once treated, can be repurposed to pave the well site, thereby achieving both effective removal of oil-based drill cuttings and waste utilization.