Expanding Cement for Improved Wellbore Sealing: Prestress Development, Physical Properties, and Logging Response

Abstract

Expansion of oilwell cement after placement in the annulus is a promising route to improve wellbore sealing. Expansion can potentially provide benefits such as: closing a microannulus, reducing the tendency for cracking/debonding, and improving cement logging evaluation. To properly evaluate the performance of expanding cement formulations in a laboratory setting, the cement should be hydrated under confined conditions similar to a wellbore. We conducted measurements using a new confinement cell developed in our laboratory. The cell provides radial confinement and elevated temperature as in a wellbore. The availability of water to the cement can also be controlled to simulate tight or porous formations. In the axial direction the cement sample contacts a piston that either confines the sample while measuring the axial stress development, or permits linear expansion that is measured. Using blends of oilwell cement with magnesium oxide (MgO), a standard expanding additive, we measured the axial stress development and linear expansion under different curing conditions. To better understand and optimize cement expansion we also characterized the hydration kinetics of the MgO additive alone and in the presence of the cement, using isothermal calorimetry. Finally, we measured the acoustic response of cement formulations with and without a commercial expanding agent with a standard ultrasonic pulseecho technique. This testing confirmed the benefits of expansion for the logging response.

Experimental Study of Hydraulic Sealability and Shear Bond Strength of Cementitious Barrier Materials

“…Expansive agents are one of the additives that can compensate the shrinkage to some extent, where the expanding agent can make crystals or generate gas bubbles during the solidification process [24]. The effectiveness of expansive cement for oil and gas applications increases if the expansion reaction occurs at the right timewhen the shrinkage starts.…”

Statistical modelling of expanding cement slurry

“…Development of an expanding cement slurry for existing mining and geological conditions provides selection of an optimal expansion mechanism, type of an expanding additive base, required expansion and matching of expansion dynamics with dynamics of a cement stone strengthening [13,14].…”

Bonding Mechanism of Zonal Isolation Materials to Clean and Rusted Casing

“…One approach to mitigate cement shrinkage is to use expansive agents that expand during hydration. The expansion occurs either by microgas bubble generation or through crystal growth in the matrix of cement (Thomas et al 2014). One of the most important aspects of using an expanding agent is that expansion should start when shrinkage initiates.…”