Abandoned drilling fluids at well sites have become a major source of pollution in the petroleum industry. According to statistics, each well team in China currently discharges about 50m3 of wastewater per day, and each fracturing well produces 100-200m3 of wastewater; drilling a well with a depth of 3000-5000m according to the conventional drilling process produces about 600-1000m3 of waste drilling fluid. With the development of drilling technology, the composition of drilling fluid is becoming more and more complex, and more than 200 kinds of chemical reagents are added. Most of these added chemicals are discharged into waste drilling mud storage pits along with waste drilling fluid sewage. Nearly half of these waste drilling fluid sewage is directly discharged into the surrounding environment, causing serious pollution to the surrounding ground environment, farmland soil, surface water, and groundwater. Due to the increasingly strict requirements of China's environmental protection authorities on environmental pollution control, people's awareness of environmental protection, and the harmless treatment of drilling fluids have become an important issue facing the petroleum industry and environmental protection.
Through the above analysis, it can be seen that the composition of drilling fluid wastewater is very complicated. From the environmental indicators, the main pollutants are: (1) solid particles, mainly mud and bentonite particles; (2) petroleum substances, mainly from Oils carried from underground and cleaning fluids of drilling equipment during drilling. During the operation and treatment of sewage, the low-boiling organic substances contained in it will volatilize into the atmosphere and cause pollution; (3) heavy metals mainly come from the weighting materials of drilling fluid and the carried cuttings; (4) polymer organic substances and their decomposition According to environmental indicators, the main products are COD, BOD and high chroma; (5) Acids and alkalis, mainly some strong acids and weak bases or strong alkalis and weak acid salts, will affect the pH value of sewage and have certain effects on the soil. (6) Chloride, a salt compound mainly composed of chloride ions and other cations. A large amount of chloride enters the surrounding environment, which will destroy the physical and chemical properties of the soil, inhibit the absorption of nitrogen and phosphorus by crops, and cause large areas of saline-alkali land. , Which will result in reduced crop yields. Therefore, if there is no appropriate method for the harmless treatment of drilling fluid sewage, it will cause great harm to the environment, animals and plants, and people, which are mainly manifested in:
(1) There are many pollution pathways, which are determined by various reasons such as the fluidity, dispersion and the diversity of sewage generated at the drilling site.
(2) Macromolecular organics and heavy metal ions (such as Cr6 +, Hg2 +, Cd2 +, Pb2 +), once they flow into or infiltrate the water body, or are absorbed by passive plants, enter the food chain, accumulating in the human body, endangering human health and even endangering life and safety Existing hidden dangers are getting more and more attention.
(3) Harmful substances such as petroleum, COD, chloride, etc., which are seriously over-standard, will cause serious pollution to the water body if it is improperly handled, flowing into or infiltrating into the water body, entering the river or ocean, and causing aquatic organisms to fail to grow normally. Pollution of groundwater sources, and even endangering personal safety.