Reinforcement of oil well cement composites with alumina nanofibers under high temperature/pressure curing condition: Mechanical and microstructural properties

In this paper, alumina nanofibers (ANFs) are studied as an additive in the reinforcement of the mechanical properties for oil well cement composite. To simulate the subsurface conditions during cementing operations of steam injection wells, the cement composite pastes were firstly cured at 50 degrees C (standard curing condition), and thereafter were cured at 300 degrees C/13 MPa (ordinary condition during steam injection operation). Four proportion of ANFs (from 0.1 to 0.4 % by wt. of cement) were added into the oil well cement composite. Their effects on the rheological property, the compressive and tensile strength were studied. Moreover, stress-strain behavior is analyzed. The mineralogical and microstructural characterization of the ANFs-affected pastes after the curing regime were tracked by X-ray diffractometer, thermogravimetric analysis, mercury intrusion porosimetry, scanning electron microscopy with energy dispersive X-ray spectroscopy. The results show that there is an optimal addition for ANFs and that more is not necessarily better when considering the reinforcement of the cement composite. Adding 0.3 % ANFs can improve the compressive and tensile strength by maximum increase of 9.18 % and 28.85 %, respectively. On the other hand, the incorporation of ANFs into the cement matrix resulted in the pore-size refinement, more formation of hydration gels but less formation of xonotlite. Two pa-rameters, R100 and C-S-H gel/xonotlite ratio were defined by MIP and DTA results respectively. A great rela-tionship was correlated between the R100, C-S-H gel/xonotlite ratio and mechanical strength, which can describe the relationship between hydration products, pore structure and mechanical strength quantitatively.