Recent Advances and Future Perspectives in Additives and Technologies for Low-Density Drilling Fluids

This review investigates the evolution of additives and technologies developed for density reduction in drilling fluids and discusses their applicability and main trade-offs. The authors present the main advantages, limitations, and economic and environmental implications of each additive class and discuss their influence on fluid stability, rheology, and operational safety. A literature search was carried out in the ScienceDirect, Web of Science, and Scopus databases, using the following keywords: "low-density drilling fluid additives," "lightweight drilling fluid additives," "density reduction drilling fluid additives," and "underbalanced drilling fluid additives," covering experimental and review papers published between 2015 and 2026. A second search was performed using the same keywords, substituting "drilling fluid" with "drilling mud" to broaden the scope of the search. Most of the studies were experimental and focused on water-based systems, identifying hollow glass spheres as the most investigated and widely adopted additive for density reduction. Emerging materials such as polymeric and biobased additives also show promising potential for sustainable and low-cost formulations. Oil-based systems remain underrepresented in the literature despite the lower density of oil as a base fluid compared to water and the rise of environmentally friendly base oils. By clarifying technological trade-offs, identifying knowledge gaps, and outlining concrete innovation pathways, this review consolidates fragmented literature into a unified review specifically focused on density-reducing additives. In addition, by evaluating the technical, economic, and environmental factors involved, it supports the advancement of next-generation lightweight drilling fluids. Overall, the findings indicate that research on density-reducing additives is still limited, revealing a clear need for further studies and field-scale validation to support the development of the next generation of ultralightweight and sustainable drilling fluids.