Oil well cement adheres to API Specification 10 and is categorized into eight classes, labeled A to H, based on its specific properties. Among these, Class G and Class H serve as foundational well cements that can be employed alongside accelerators and retarders to accommodate a broad spectrum of well depths and temperature conditions. One notable distinction between these two classes lies in their particle size, with Class H being notably coarser than Class G.
The details of each cement class are as follows;
Class A: Designed for surface applications up to a depth of 6,000 feet (1,830 meters) where specific properties are not required. Similar to ASTM (American Society for Testing Materials) Type I cement.
Class B: Suitable for use from the surface down to 6,000 feet (1,830 meters) with moderate to high sulphate resistance. Comparable to ASTM Type II cement, with a lower C3A content compared to Class A.
Class C: Intended for surface-to-6,000-foot (1,830-meter) applications when early strength is essential. Available in all three sulphate resistance levels and is roughly equivalent to ASTM Type III cement. Achieves high early strength due to relatively high C3S content and surface area.
Class D: Designed for depths ranging from 6,000 feet (1,830 meters) to 10,000 feet (3,050 meters) under moderately high temperature and pressure conditions. Offered in both moderate sulphate resistance (MSR) and high sulphate resistance (HSR) variations.
Class E: Tailored for use between 10,000 feet (3,050 meters) and 14,000 feet (4,270 meters) in high-temperature and high-pressure conditions. Available in both MSR and HSR types.
Class F: Geared towards depths ranging from 10,000 feet (3,050 meters) to 16,000 feet (4,880 meters) under extremely high-temperature and high-pressure conditions. Offered in both MSR and HSR varieties.
Class G + Class H: Primarily used as fundamental well cement from the surface down to 8,000 feet (2,440 meters) in its original form. Alternatively, it can be used in conjunction with accelerators and retarders to accommodate a wide range of well depths and temperatures. These well cements are manufactured with no additives other than calcium sulphate or water, or both. They are available in both MSR and HSR variations.