Integrated treatment and disposal of waste drilling fluid onshore China: Laboratory investigation and process design

The traditional methods of treating and disposing waste drilling fluid are encountering severe challenges with the tightening of environmental regulations in China. Commonly used chemical destabilization technology needs to be improved, and treating processes are required to be optimized and updated. This paper details a laboratory investigation on two waste water-based drilling fluids (a high-density drilling fluid and a reservoir drilling fluid) from the rig sites, as well as the corresponding treatment and disposal process design. The laboratory work focused on a solid-liquid separation technique on the basis of chemical flocculation and centrifugation. According to the properties of each waste drilling fluid, different flocculants were added to initiate chemical flocculation. The effects of type and concentration of flocculants as well as treating conditions (including sulfuric acid, dilution ratio, centrifugal speed and agent adding sequence) on the degree of separation were comprehensively investigated. To apply the separation technology in various fields, two integrated processes for collective and in-site treatments were designed and discussed respectively. The results showed that the correct combination of inorganic and polymeric flocculants can lead to a great degree of separation. In particular, a novel flocculant based on modified starch exhibited excellent performance. The molecular weight of polymeric flocculant substantially influences treatment efficiency, which can be explained by the combination of adsorption-bridging and sweep-flocculation mechanisms. Adding sulfuric acid to the waste drilling fluid in treatment is beneficial to solid-liquid separation due to the reduction of electrostatic repulsion between solid particles. Molecular weight of flocculant is also a crucial factor influencing the separation effectiveness and rate. For the two waste fluids studied, the optimal treating conditions were proposed. The weight fraction of separated liquid phase reached higher than 80% and the liquid content of the solid phase was lower than 30%. Detailed analysis and discussion of the advantages of this process were presented. Preliminary field practice of this technique exhibited its satisfactory performance. This highly-integrated technique based on novel chemical agents, rational design and high-efficiency equipment is helpful to deal with the increasing technical and environmental challenges. The information provided in this work offers a reference to relevant researchers, designers and engineers.