Research And Application Of Harmless Treatment Technology For Waste Water - Based Drilling Fluids

Most water based drilling fluid will be discarded after drilling operation, which pollutes the environment worst. It contains mainly inorganic salt, alkali, heavy metal, oil and hard degradable organics with different degrees of toxicity. If the drilling fluid is abandoned at the well site, it will penetrate into the farmlands, rivers or seas, which bring harmful influence to the drinking water, soil, plants and animals. What’s worse, it will threaten the health and safety of people directly or indirectly through food chain. Currently, more attention is paid on post-processing in China Many methods, such as solidification, solid-liquid separation, direct disposal and land filling, are used at the site to treat the waste drilling fluid. However, all the technologies have their own disadvantages, such as high cost, halfway treatment and environmental risk, which limit their usage. Meanwhile, the current methods have the similar disadvantages of no systematicness, missing the ink of precaution and control and ignoring the reutilization of available constituent, which cause the methods hard to meet the requirements of cleaner production.In this paper, the evaluation index and methods for drilling fluid additives and waste drilling fluid was established according to the emission standard of solid waste and the requirement of harmless treatment of Petrochina Southwest Oil&gasfield Company. Meanwhile, twenty-one kinds of drilling fluid additives and five kinds of waste drilling fluid samples were evaluated. The result show that heavy metal content of all tested substances are lower than the limit of toxicity evaluation criteria. Only one addtive is slightly toxic and the rest substances are nontoxic. The mumber of hard biodegradation, biodegradable and easily biodegradable additives is nine, seven, five, respectively. One waste drilling fluid is easily degradable and the rest are degradable.The laboratory research indicate that the waste drilling fluid can be efficiently handled by the treatment process of gel breaking, solid-liquid separation, oxidation of waste water and harmlessly disposal of waste residue. The main indexes of treated wastewater and lixivium of waste solid, such as pH, suspended solids, chromaticity, COD and petroleum, met the primary standard of Integrated Wastewater Discharge Standard(GB8978-1996). The processing cost was lower than330yuan/m3. The spot equipments can disposal32m3waste drilling fluids every day and the main indexes of effluent can also met the primary standard of Integrated Wastewater Discharge Standard (GB8978-1996). The final water content of on-site waste solid was lower than52.4%. So, the treatment process can realize the harmless treatment of drilling fluids.