Strata migration and fracture development under continuous extraction and continuous backfill with CO2 mineralized backfill materials

Abstract

CO₂ carbonation is currently restricted in laboratory instead of industrial application at ambient conditions. Meanwhile, few evaluations for safe storage have been made after CO₂ carbonation backfill. Herein, the continuous extraction and continuous backfill (CECB) with CO₂ mineralization backfill materials (CMBM) to storage CO₂ was proposed. The CMBM samples were prepared and the uniaxial compressive strength (UCS) and CO₂ uptake rates at various curing times and fly ash (FA)/gangue ratios were tested. The early and later strength at all ratios is more than 1 and 3.6 MPa, respectively, satisfying the requirements in underground backfill. A higher FA proportion means a higher UCS and a more significant effect of curing time on UCS as the hydration products of cement and FA contribute primarily to the early and later strength, respectively. As FA content rises, the CO₂ uptake rate increases from 3.55 to 4.25 mg-CO₂/g-CMBM since the alkaline oxides such as CaO in FA are higher than those in gangue. An analogue model was then constructed to simulate the overburden deformation. The ratio of the similar materials of CMBM at 7 d and F6G4 was determined to Water: Sand: CaCO₃: CaSO₄ of 3.56: 13.56: 0.94: 0.51. The maximum horizontal deformation of aquifuge is lower than the threshold value of 0.2–0.3 mm/m for preserving aquifer. The strain-softening parameters including cohesion, friction, dilation, and tensile strength were determined to be 0.54, 30°, 0, and 0 for UDEC simulation. The envelopes of water-conductive fractured zone (WCFZ) are saddle shaped, and the height of WCFZ is 4, 9.5, 17, and 26 m, respectively. After backfilling, there are still entire strata with thickness of 5 m between WCFZ and aquifer II. The research offers a novel way to dispose CO₂ gas, solid wastes and mitigate overburden deformation, which is conducive to geological disposal of energy wastes.

Article Highlights

The UCS and CO₂ uptake rates of CMBM were analyzed.

The key ratio of physical similar materials of CMBM w as determined

The key ratio of physical similar materials of CMBM w as determinedThe key ratio of physical similar materials of CMBM w as determined

Strata migration and fracture development was illustrated under CECB with CMBM.