Engineer Norhan Thamer Assi Crude oil preparation is one of the most important stages preceding refining operations in petroleum refineries. Its primary purpose is to remove substances associated with crude oil that may adversely affect operational efficiency and the quality of final products. Crude oil extracted from reservoirs is not pure; it is commonly accompanied by gases, water, salts, and solid impurities such as sand and clay, making treatment necessary before it enters distillation and refining units. The preparation process begins with the removal of associated gases. When crude oil emerges from a well, it is mixed with varying amounts of natural gas that must be separated from the liquid phase. This separation is achieved by reducing the flow velocity of the oil-gas mixture inside separation equipment, allowing the gas to separate from the liquid due to differences in density. In high-pressure wells, multistage separation units are employed to maximize gas recovery and enable its utilization for various industrial purposes. The second stage involves the removal of water, salts, and solid impurities from crude oil. Water, salts, sand, and clay are commonly produced along with crude oil from petroleum reservoirs. In some cases, water separates easily from the oil; however, in other cases, stable oil-water emulsions are formed, requiring specialized treatment methods for effective separation. The removal of these impurities is essential because they can cause numerous operational problems within the refinery. For example, solid deposits may accumulate on heat exchanger surfaces, reducing heat transfer efficiency and increasing energy consumption. Furthermore, impurities contribute to equipment wear and corrosion, shortening operational life and negatively affecting the quality of heavy petroleum products by increasing their ash content. The water associated with crude oil contains significant amounts of dissolved salts, primarily sodium chloride (NaCl), calcium chloride (CaCl₂), and magnesium chloride (MgCl₂). These salts are among the most harmful contaminants found in crude oil because they decompose when exposed to the high temperatures used during distillation processes. This decomposition results in the formation of hydrochloric acid (HCl), a highly corrosive substance that attacks refinery pipelines and metal equipment, causing severe damage and increasing maintenance costs. Therefore, the removal of associated gases, water, salts, and other impurities represents a critical step in crude oil preparation for refining. These processes help protect industrial equipment, improve operational efficiency, enhance the quality of refined petroleum products, and reduce maintenance and operating costs within petroleum refineries.