Development and Evaluation of Sealant for Controlling Annular Pressure

Solid particles in conventional cement materials are unable to be squeezed into and seal the micro fractures developed in cement sheaths in annular spaces with sustained pressures. To solve this problem, a solids-free sealant that is curable at room temperature was developed, with a composite resin as the main component. In developing the sealant, the solidification time of the cement slurry was controlled by optimizing the amount of a curing initiator, and the mobility and permeability of the cement slurry were enhanced using an optimized thinner. The sealant was tested in laboratory for its performance in sealing the cement sheath-casing system. It was found that at different environment temperatures and different concentrations of the curing initiator, the curing time of the sealant can be adjusted between 1.25 hours and 20 hours. The sealant has good flow property; its viscosity is as low as 60 mPa∙s. The density of the sealant can be raised from 1.02 g/cm³ to 1.25 g/cm³. The sealant has good mechanical properties, its compressive strength in 24 hours is greater than 18 MPa, with maximum compressive strength of 53 MPa. Laboratory experimental results have shown that the sealant can be used to effectively solve the problem of sustained annular pressure. In dry environment, the sustained annular pressure less than or equal to 6 MPa can be eliminated after WOC for 24 hours. In wet environment, the sustained annular pressure less than or equal to 3 MPa can be eliminated after WOC for 24 hours. This sealant can be used to solve the sustained annular pressure problem in different conditions by improving the tightness of the cement sheath in annular spaces.