Abstract
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 A 0.06) were superior compared to standard (2.58 A 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.
Highlights
Oil is still an important source of energy, mainly in developing countries, with demands ranging up to about 65 million oil barrels per day in a near future
In the presence of low amounts of Ca2+ ions, the Ca/Si molar ratios in the interlayer space of C-S-H are typically less than unity, and the silicate chains are typically long and linear with compensation charges made by alkaline ions (Na+ and/or K+)
For Ca/Si molar ratios of about 1.5, tetrahedral silicate sheets contain mainly dimers, and for Ca/Si ratios higher than 1.5, and CH may be in the interlayer space, with Al redistribution in the tetrahedral C-S-H sites and absence of Si4+ substitutions, leading to mainly formation of silicate chains constituted of dimers [21]
Summary
Oil is still an important source of energy, mainly in developing countries, with demands ranging up to about 65 million oil barrels per day in a near future. Driven by such needs, oil and natural gas were recently found to lie below a 2,000-3,000 meter deep saline geological formation of the coast of South America and Africa (the pre-salt region), formed in remote ages due to evaporation of seawater [1]. Most of oil below pre-salt layers has not leaked properly, because drilling through rocks to extract the pre-salt oil is very expensive and dangerous. Significant research efforts are being spent on new cementing procedures to provide safe and cost-effective oil exploration below pre-salt layers.
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
