Influence of polyvinyl alcohol coated porous Al2O3 ceramic waste particles on cement properties in geothermal applications

Abstract

To improve the low strength of the existing geothermal temporary sealing cement (GTSC) and figure out the influence of PACW on cement performances in geothermal applications, the hard porous Al2O3 ceramic waste (PACW) was introduced into oil well cement. The water-soluble PVA was coated on PACW particles to wrap the porous ceramic at relatively low temperature for geothermal drilling, and dissolve in water at ≥ 90 ℃ for hot water flow. The compressive strength, hydrates, pore structures and interface transition zone of cement with raw or modified PACW were tested. The results showed that 10% raw and modified PACW enhanced the compressive strength of oil well cement by 57.69% and 60.31% respectively, during the 90 ℃ water immersing. For the cement containing 10% raw and modified PACW, thermal weight loss related to degradation of hydrates and CH increased, meso pores fraction rose to 52.73% and 51.93 % respectively, and the deeper etch pits on surfaces of the mineral suggested the promoting effect of PACW on cement hydration. The promoted cement hydration and formed hydrates with their filling effect contributed to the cement strength enhancement. As the thermal weight loss attributed to AFm increased after immersion, the thermodynamic parameters of the possible transformation reaction of AFt to AFm were calculated. The standard molar Gibbs free energy change of the reactions are negative, and microstructure images showed that the PACW surface was covered by lots of flaky AFm crisscrossed with large hexagonal AFt crystals, proving that the alumina in PACW participated in and promoted the transformation of AFt to AFm. In addition to reservoir protection, simplifying construction procedures and reducing the time cost of geothermal development, the high-strength GTSC will further strengthen the hole wall and reduce the risk of borehole collapse.