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Abstract: With the depletion of shallow and mid-depth oil and gas resources, exploration and development have increasingly shifted toward deep and ultra-deep reservoirs. However, high bottom-hole temperatures and pressures, along with complex geological conditions, pose significant challenges. Additionally, growing environmental regulations restrict the use of conventional petroleum-derived chemicals such as polyacrylamide, sulfonic acid resins, and sulfonic acid asphalt. In recent years, lignin has demonstrated significant potential in petroleum exploration and development due to their sustainability, biodegradability, and excellent thermal, chemical, mechanical, and rheological properties. This article reviews the structure, classification, preparation, and modification methods of lignin, followed by a systematic discussion of its applications in oilfield operations. In drilling fluids, lignin and its derivatives serve as rheological regulators, fluid loss control agents, and shale inhibitors, contributing to enhanced cuttings transport and wellbore stability. In fracturing fluids, they function as thickeners and breaker agents, improving fracturing efficiency while protecting the reservoir. In enhanced oil recovery, lignin-based polymers act as surfactants and profile control agents, reducing interfacial tension between water and rock surfaces and increasing the effective permeability of sandstone reservoirs. Furthermore, in oilfield wastewater treatment, lignin-based materials effectively remove oil-water mixtures, heavy metal cations, and solid particles through filtration, adsorption, and flocculation.