Application status and prospects of solid waste disposal and resource utilization technology in natural gas extraction drilling

The natural gas drilling process generates massive drilling solid waste that contains petroleum hydrocarbon, inorganic salt and refractory organic compounds, etc., which are either poisonous or harmful species. The pH of the water-based drilling solid waste is generally 9-10, which exceeds the technical requirement of Category Ⅰ field storage and backfill of general industrial solid waste stipulated by Standard for Pollution Control on the Storage and Disposal for General Industrial Solid Wastes (GB 18599-2001). The petroleum hydrocarbon content is 4 690-15 500 mg/kg, exceeding the requirements of soil pollution risk screening value of Class Ⅱ land of Soil Environmental Quality Risk Control Standard for Soil Contamination of Development Land(Trial) (GB 36600-2018). The use of oil-based drilling fluid in some gas fields in Sichuan, Chongqing, Xinjiang, etc., due to the complexity of terrain, may lead to over standard concentrations of heavy metals, polycyclic aromatic hydrocarbons (PAHs) and petroleum hydrocarbons. The drilling solid waste is mainly composed of SiO₂, CaO, Al₂O₃, with the total content of three components can reach 72%, which contains the necessary chemical compositions for the preparation of building materials. Based on the pollution characteristics and chemical components of drilling solid waste, the solid waste disposal technologies (including curing stabilization, biodegradation, chemical leaching, downhole reinjection, source reduction technology, etc.) were systematically summarized and analyzed both at home and aboard. Further discussion was made on the characteristics and treatment effect of the technologies, as well as the research progress of resource utilization such as brick-making, wellsite roadway paving, modifier, etc. It was proposed that various treatment and disposal technologies can effectively reduce the pollutants in the drilling solid waste, and diversified resource utilization approaches can improve the utilization rate of solid waste, which tends to be prospective. It was suggested that separate treatment should performed for the drilling solid waste at the source, and multiple treatment technologies should be carried out in the process. At the end of pipe, the technologies of subgrade soil resource utilization should be explored to consume the drilling solid waste to the maximum extent, combined with the demand of gas field development area.