Microbial Synergistic Active Magnesium Oxide Solidification of Water-Based Drilling Cuttings and Analysis of Its Durability Strength Loss Mechanism

The solidification, recycling, and reuse of water-based drilling cuttings (WDC), a waste generated during oil and gas extraction, has been the subject of intense research interest. Developing an efficient and environmentally friendly solidification method is the key objective of this research. This study employs microbial synergistic active magnesium oxide (MgO) technology to solidify WDC. The solidifying mechanism is that carbonate ions produced by microbial metabolism and hydrolysis of urea were able to react with magnesium hydroxide generated by hydration to produce different types of hydrated magnesium carbonates (HMCs), which filled the pores between the drilling cutting particles while bonding the particles to form water-based drilling cutting solidified body (WDCS). The durability and strength of the WDCS were evaluated by subjecting the WDCS to 10 freeze–thaw (FT) cycles and 6 dry-wet (DW) cycles. The main phases in the WDCS are SiO2, CaCO3, MgO, Mg(OH)2, hydromagnesite, and barringtonite. Notably, the mass and density of WDCS decreased significantly after DW cycles. The strength of WDCS improved during room-temperature curing conditioning (at 25 °C, the curing time corresponds to the durability test). However, it decreased by 23 and 75% following the FT and DW cycles, respectively. Further analysis indicates that the strength loss is related to the crystallinity and content of the main phases in WDCS, as well as changes in the pore structure. The crystallinity and content of the WDCS main phases are lower after the DW cycle than after the FT cycle. This is also consistent with changes in strength. The internal pore structure of WDCS changed differently under different cycling conditions. In comparison to the FT cycle, the number of WDCS internal pores increased following the DW cycle, and the pore size distribution exhibited uniformity and continuity.