Study and Application of Green Throwing Drilling Fluid

Abstract

This article investigates the disadvantages of polymer sulfonate and oil-based drilling fluids after use, such as pollutants seriously exceeding current standards and poor degradation. After the later stage treatments, like landfill and solidification, waste drilling fluids also have secondary pollution. Based on laboratory experiments, we established the green performance evaluation standards and specifications of drilling additives and drilling fluid systems, including chemical toxicity, biological toxicity, and biodegradability. We developed a green drilling fluid additive and drilling fluid system that are nontoxic, biodegradable, and reservoir protective. The green drilling fluid additive and drilling fluid system can effectively control the production of environmental pollutants from the source. The green drilling fluid system was successfully applied in Tarim oilfield and Karamay oilfield for the first time, fulfilling the pollution-free disposal of throwing waste drilling fluid onto the soil. This technique could be used in improving and enriching soil. The laboratory experiments and field applications indicated that the drilling fluid system had low chemical toxicity. The contents of heavy metals Cd, Hg, Pb, Cr, and As are respectively below 0.3, 0.02, 3.7, 4.9, and 3.1 mg/kg; the acute biotoxicity EC50 was greater than 30,000 mg/l; and the biodegradation index BC (Biological oxygen demand [BOD5]/Chemical oxygen demand [COD]) was greater than 0.35. Soil organic matter and the major fertility indexes, such as nitrogen, phosphorus, potassium, were increased by 40% after throwing waste drilling fluid onto the soil. The core permeability recovery value was greater than 80%. This drilling fluid system realizes the organic unity of low toxicity, biodegradability, improving soil conditions after throwing, and reservoir protection. This is an important advancement for the coordinated development of Chinese oil industry and environmental protection.