Fly Ash is a light weight residue from coal fired power plants. Blends of Portland cement and Fly Ash are widely used in construction and oilfield industry. The addition of Fly Ash in cement slurries improves compressive strength, sulphate resistance, reduces cement permeability (Golapudi U et al, 1993) and allows lower density slurries while maintaining good mechanical properties (Purvis et al, 2003).
Fly ash is a cheaper, readily available by product. It brings down overall cost by reducing cement consumption. This also helps the environment as every ton of cement produce generates an average of 0.9 ton of CO2. Historically, increasing the Fly Ash ratio above 50% has resulted in significant reduction in its benefits (Purvis et al, 2003) in terms of cement mechanical properties degradation, and especially the compressive strength development at short duration.
A new Highly Reactive-Fly Ash Material (HR-FAM) was developed for higher ratios of Fly Ash in a cement blend. This paper will study and discuss the use of HR-FAM in oil well cementing applications. To prepare lightweight cement systems, various ratios of HR-FAM are blended with neat API Class H cement. All laboratory tests were carried out according to API RP 10B-2 practices for oil well cement. Results were compared against conventional Fly Ash based cement systems. The laboratory test results show that HR-FAM based blends provide better mechanical properties than regular Fly Ash in terms of compressive strength development.
The use of HR-FAM in Portland cement allows slurry designs at lower densities with mechanical properties meeting regulatory requirements. Additionally, it also reduces the consumption of Portland cement up to 33% compared to regular Fly Ash based systems currently used in the oilfield.