Corrosion resistance and mechanisms of class C fly ash-based geopolymer in simulated oil well environments: Mud contamination and salt solutions at high temperature

Abstract

Geopolymer presents great potential in oil well environment. For class G oil well cement (OWC) and class C fly ash-based geopolymer, the comparative experiments under simulated oil well environment were performed. The early age properties of geopolymer were measured. Considering the higher downhole temperature, the high temperature resistance of geopolymer at 60 ℃ and 180 ℃ was investigated. Also, the mud contamination resistance of geopolymer at 60 ℃ was explored. A self-designed percolation pipe was used to simulate the process of fresh geopolymer slurry exposed to three salt solutions (5% Na2SO4, 5% NaHCO3 and 2.5% Na2SO4 + 2.5% NaHCO3). The corrosion resistance to salt solution of geopolymer at 60 ℃ was studied. The results showed that geopolymer had higher early strength and high temperature stability than OWC. Meanwhile, compared with OWC, geopolymer possessed better mud contamination resistance due to the smaller pore diameter and the denser matrix. Additionally, all of three salt solutions decreased the compressive strength of OWC, especially the simultaneous existence of Na2SO4 and NaHCO3 accelerated the deterioration of OWC. By contrast, the porosity and pore diameter of geopolymer declined and the compressive strength increased in Na2SO4 solution. Although the compressive strength of geopolymer decreased in NaHCO3 solution, the deterioration degree was lower than OWC. Overall, geopolymer presented better adaptability and durability than OWC in oil well cementing.