| dc.description.abstract | Cementing high-pressure/high-temperature (HP/HT) gas wells is a challenging and expensive job in the oil and gas industry. Gas migration through the cement column has major safety, environmental, and economic concerns. Problems such as weighting material segregation, excessive fluid loss, and shortages of water available for cement hydration can produce high-porosity cement structures that are prone to progressive gas migration. This work aims to increase hydration efficiency, develop sufficient gel strength, reduce fluid loss, and enhance mechanical properties to produce gas-migration-resistant HP/HT cement slurries. This work developed an HP/HT cement slurry with high resistance to gas migration by optimizing a new additive, Maxcrete, which replaces multiple common gas-migration-control additives. The experimental slurry was prepared and evaluated following the API RP 10B-2 procedures. Fluid loss was optimized through various iterations of additive combinations at different concentrations. The cement hydration process was monitored over 24 hours using computed tomography (CT) scans and compressive-strength analysis. The optimized cement slurry with the new additive showed superior enhancement in the main properties that control the gas migration process. A class G cement slurry with 2.5 lb/100 lb by weight of cement (BWOC) of the new additive showed an enhancement in the cement hydration capacity, fluid loss control, and compressive strength compared to a slurry without the additive. These improvements resulted from coating the cement particles with a layer that is capable of attracting more water molecules, which prevented quick free-water separation and provided for better and faster hydration. The suggested mechanism was supported by gas migration evaluation and rheology assessment. The results of these tests showed rapid development of an initially low gel strength that mitigated the initial induction of gas channels in the cement body during the setting time. The CT-scans showed that the cement blocks were more hydrated and, with time, demonstrated a reduction in the cube porosity. This work introduces and evaluates a new additive with the capability to replace multiple additives in cement slurries for better gas-migration control. The suggested chemistry has the potential to work synergistically with fewer additives and deliver superior cement properties for HP/HT wells. | en |
