Oil well cement is a special type of cement used for securing oil, gas, or water wells. When mixed with water in the right ratio, it forms a slurry that hardens underground, creating a strong, low-permeability cement structure. Its production is much stricter than that of regular cement, requiring careful control of raw materials, burning process, and preparation conditions, along with thorough quality checks. Although oil well cement has some similarities with construction cement in production, it differs greatly in chemical composition and physical properties, such as fineness. Because of its unique formula and performance needs, special chemical additives for oil well cement (like accelerators and retarders) cannot be replaced by those used in construction.
API oil well cement is a special type of cement made according to the standards of the American Petroleum Institute (API). It is classified into six grades-A, B, C, D, G, and H-based on different downhole conditions and performance needs. Among them, Class G cement is the most widely used.
Additionally, API oil well cement is further divided into three types based on its resistance to sulfate attack: Ordinary (O), Moderate Sulfate Resistance (MSR), and High Sulfate Resistance (HSR). This classification helps meet the cementing needs of different geological conditions.
Oil well cement slurry is a fluid mixture used for well cementing in oil and gas wells. It is made by mixing oil well cement (usually Class G cement), mixing water (freshwater, seawater, or brine), additives (less than 5% of the dry cement weight), and supplementary materials (more than 5% of the dry cement weight) in a specific ratio.
The properties of cement slurry include fluid loss, rheology, thickening time, and density etc. Additives are used to adjust these properties: dispersants improve rheology, cementing retarders control thickening time, fluid loss additives reduce water loss, and weighting agents increase density. These cementing chemical additives help optimize slurry performance for specific well conditions during cementing.
