A new cement slurry modified with chitosan/alginate interpenetrating networks and hydroxyapatite -- structural characteristics after long-term contact with hyper-saline produced water from oil well operations

Resumo

Oil is an important source of energy, mainly in developing countries. Important research has been conducted
to find cementing procedures that guarantee safe and cost-effective oil exploration below pre-salt layers. This
work aimed to make a new cement paste with cement, seawater, silica, biopolymers (chitosan and sodium
alginate) and hydroxyapatite (HA), found in nature. For comparison purposes, slurry without additives was
prepared and characterized. The HA used was extracted from fish scales (Cynoscion acoupa) in optimized
condition NaOH concentration, temperature and reaction time. Both slurry were prepared with ratios
water/cement (w/c) and silica/cement (s/c) equal to 0.50 and 0.35, respectively. The new cement slurry was
obtained with proportions of 5% of each biopolymer and HA with respect to the total weight of the cement.
In the immersion tests, specimens were immersed in samples of hyper production of saline water by 35°C for
15 days. Thereafter, they were washed, dried and its surface layers were scraped. Before, the resulting
materials were characterized. The values of the ratios Ca/Si of new cement slurry (3.38 À 0.06) were superior
compared to standard (2.58 À 0.05). The new slurry had high thermal stability and low amounts of small
crystallite-type portlandite (35.70 nm). Conversely, a slurry standard formed larger crystals of about 50.3 nm.
Significantly, after continuous long-term contact of both slurries with hyper-saline produced water from oil
well fields operations, in comparison with standard slurry structural characteristics, the new slurry has
practically maintained its pristine chemical structure, as well as has shown crystallite-type particles of NaCl
and Friedel's/Kuzel's salts with lower proportion. The presence of the biopolymers and HA has driven the
improved the self-healing properties observed in the new cement slurry. In this first study, the new slurry has
shown adequate characteristics to contribute to cost effective and environmental-friendly oil well operations.