Silica sand enhanced cement mortar for cementing steam injection well up to 380 °C

Abstract

In this study, an ultra-high temperature of 380 °C was used to simulate the high-temperature condition of steam injection wells. The silica sand with different particle sizes was applied to prepare the silica-enhanced cement with various Ca/Si ratios. The compressive strength, hydration products, and microstructure of silica-enhanced cement were evaluated to probe the influence of high-temperature steam curing (from 50 to 380 °C), silica particle size (from 150 to 500 mesh), and Ca/Si ratio (from 0.7 to 1.44) on the performance of cement. The corresponding mechanism was also revealed. Test results show that the particle size of silica influences the compressive strength of cement mainly by changing the mineral composition in cement matrix, rather than altering the microstructure of cement. The Ca/Si ratio affects the compressive strength of silica-enhanced cement by controlling both hydration products and micropore structure of cement. Based on the experimental results, a silica-enhanced cement system was proposed. The rheology, thickening and fluid loss properties of cement slurry were evaluated, and proved to be suitable in cementing the steam injection wells. The proposed cement system shows an excellent compressive strength of more than 50 MPa even under 7th-round of steam curing conditions.