Abstract
Previous research on application of geopolymers in oil/gas wells was mainly unsuccessful due to failure to achieve a reasonable thickening time. The study here presents geopolymer slurries that have high compressive and shear bond strength, enhanced thickening time and high durability. Slurries developed in this work show durability when prone to sulphate/chloride or any other acid attack that might be encountered during cementing operations. Class F fly ash geopolymers were used for developing samples with different mix designs in this work. Class H Portland cement was used a controller on all the tests conducted in this work. Tests conducted in this research include Unconfined Compressive Strength (UCS), shear bond strength, thickening time and durability tests. Results indicate temperature as crucial factor affecting thickening time of Geopolymer mix slurry. More than four hours thickening time was achieved by optimizing mix design and application of developed mix of superplactisizer and retarder. UCS testing indicates a high compressive strength after one and fourteen days of curing for Geopolymer mixtures. This indicates gaining strength with time for Geopolymer mixture where time retrogression effects are observed for Portland cements. Results also indicate higher shear bond strength for Geopolymer mix which can better tolerate de-bonding issues. Additionally, more ductile material behavior and higher fracture toughness were observed for optimum geopolymer mixes. Final observations confirm applicability of these materials for oil and gas well cementing with circulating temperatures up to 250° F. These mixtures also show very good durability when compared with Portland cement mixtures. Higher durability will facilitate application of these materials for HPHT and corrosive wells where Portland cement shows poor performance.
Based on results from this study, Geopolymer mixtures show potentials for replacing Portland cement if they can be successfully tested in field applications. These materials can be produced cheaper with less environmental impact. The tangible benefits of the new products would be cost saving on well construction materials for operators with achieving long-time wellbore integrity goals and meeting regulators criteria for zonal isolation.
