Nanoengineered solution for repairing cement leakage in deep wells

Abstract

In addition to the sharp growth of unconventional natural gas wells in the past decade, there are few hundred thousands of abandoned and orphaned wells across the world, potentially contributing to gas emissions. Failure in the barrier and sealing capabilities of the cement and casing are of factors playing role in these leakages. Squeeze job as a remedial treatment is performed to place cement slurry from the surface to the target points to seal narrow spaces behind the casing and/or perforations placed in the casing. In this study, a novel additive for the squeeze-cement is proposed by introducing surface-modified graphite nanoplatelets (GNPs) to carefully adjust rheology and mechanical properties of the prepared cement slurry to remediate some flaws in pre-existing cement sheaths. We seek for better penetration into narrow spaces behind the casing with appropriate thickening time, low fluid-loss, and high final strengths. The process of surface modification is very important to generate a homogeneous cement composite with superior mechanical properties. We develop a chemical method for the surface treatment of GNPs to alter their intrinsically hydrophobic properties to hydrophilic, making them compatible with the aqueous medium of cement. Details of surface modification approach and the concentration of surface-modified nanoparticles are tailored to achieve a desirable slurry for squeeze treatments following API RP 10B-2 (2013) procedures. We believe that these nanoparticles due to their 2D nanostructure not only improve cement movability, but also provide appropriate sealing in the target zones. To assess the performance of the prepared cement slurry to effectively seal narrow targets, narrow-slot tests with 120 microns thickness are conducted to show the supremacy of the proposed solution in sealing narrow spots. We also investigate the effect of adding a commercial superplasticizer on the properties of nanoengineered cement slurry to better resemble field practices. Results show that the presence of surface-modified GNPs provide cement slurry with low rheological properties, zero free fluid, low fluid-loss, and deep penetration which are promising for future field trials.