The exothermic hydration of oil well cement leads to hydrate decomposition, making deepwater cementing difficult. Therefore, we designed a new heat storage agent (HSA), which can absorb the heat released during cement hydration. HSA uses multi-component alkanes as the heat storage component and uses high-strength ceramics as the wall material. The tests found that HSA has a wide application temperature range and high resistance, and its application in cement meets the industry standard with no significant effect on cement density, settlement stability, consistency, or rheological properties, and can effectively avoid the decomposition of hydrates during cementing construction.
Although marine oil and gas resources are plentiful, the low temperature and high pressure in deep water areas can cause hydrate layers to form on the shallow layers of the seafloor (Armstrong, 2002; Ravi, 1999; Xu, 2005). Deepwater shallow hydrate layers are normally stable, but oil well cement slurry will release a large amount of heat during the hydration process, causing high temperatures around the cement ring. Once the hydration temperature exceeds the phase equilibrium temperature of the hydrate layer where the deepwater cementing operation is located, it will cause the hydrate to absorb heat and decompose, releasing natural gases such as methane, which may lead to the following serious consequences (Wang, 2019; Bu, 2020a): (1) When the amount of hydrate decomposition is small, it will lead to borehole enlargement, water and gas runoff, and well wall destabilization. (2) When a large amount of hydrate decomposes in the formation, the static pressure in the pore space of the formation will increase, leading to well surge and even well blowout. (3) The local uncontrollable gas release in the formation will cause a reduction in the strength of the hydrate formation, which may cause a variety of catastrophic damages such as landslides, wellhead sinking, and rig overturning. Submarine landslides caused by hydrate decomposition at the Norwegian continental shelf have removed 2500-3200 km3 of sediment, making it the largest submarine landslide ever discovered (Wu, 2008).