Zahra Rashedi MSc Chemistry Thesis Defence
A STUDY IN LIGNIN CAPABILITY TO IMPROVE STRENGTH AND WATER ABSORBENCY OF STARCH POLYMERS: A POTENTIAL HEAT-RESISTANT FLUID- LOSS-CONTROLLER IN WATER BASED DRILLING FLUIDS
Time: Oct 4, 2021 09:00 AM Eastern Time (US and Canada)
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https://lakeheadu.zoom.us/j/92408194640
Meeting ID: 924 0819 4640
Abstract:
In the oil and gas industries, drilling deep wells has rapidly become more significant to meet the global demand. The design of drilling fluids and choosing the proper additives are very important for the drilling operation's success. Rheological behaviour and filtration-loss properties are the main factors to control for effective drilling operations. So, the study of an effective fluid loss controller and a rheology modifier is necessary to designing drilling fluids formulations and determining their proper performance during operations. Starch, as a natural polymer, is broadly utilized in the drilling industry, thanks to its specific structure and solubility in water. The main duties of starch in drilling fluids formulations are reducing fluid loss and improving the viscosity of fluid during drilling operations. One of the main problems of using starch in water-based fluids (WBFs) is being inefficient in high pressure and high temperature (HPHT) condition and shear force. Numerous studies have been conducted to elevate the thermal stability of starch to strengthen it for harsh conditions. In some studies, starch was replaced by new polymers like Carboxymethyl Cellulose (CMC) and other synthetic polymers, to overcome these problems. These polymers are not effective enough and are relatively expensive, so one needs to consider using alternative materials or natural ingredients to make drilling more economical and more efficient, especially in deeper wells with higher temperatures.
The main goal of this work was to develop a novel starch-based polymer for the synthesis of a new fluid loss controller (FLC) and rheology modifier using lignin as a support to raise its mechanical and thermal stability. Starch and lignin were crosslinked in the presence of a crosslinking agent, a type of substitution reaction, leading to the formation of a new compound of starch-lignin polymers. The mechanical and thermal properties of synthesized starch-lignin crosslinked polymers were investigated to demonstrate their potential for use in drilling operations. Addressing all drawbacks of native starch, using lignin as a biopolymer with the potential of improving starch mechanically and thermally was studied in this research. It is shown that Kraft lignin can be crosslinked with starch via ether covalent bonds to successfully increase the viscoelasticity and water absorption. Rheology analysis showed that in the temperature range of 25 to 90 °C, lignin-starch polymers are more viscoelastic and stable than unmodified starch. The results showed that the rheological behaviour of lignin-starch crosslinked polymers was different from the natural starch at the same concentration and temperature. The change in viscoelastic properties caused by crosslinking reaction and etherification significantly depended on the amount of lignin and crosslinking agent incorporated. Modified starches with higher lignin content displayed higher values of storage and loss module than those with lower lignin content. This finding was due to the fact that ether groups in modified starches were more polar than natural starch, thus forming stronger hydrogen bonds with water restricting the movement of the chain of starches and leading to an increase of the elastic modulus. In addition, the presence of lignin in starch polymers influences its thermo-reversibility characteristics significantly and increases the storage and loss modulus of starch. Moreover, water absorption of starch was found to increase when it was crosslinked to lignin via proposed reaction conditions.
Our new polymer has the advantage of being produced using a renewable source, which is biodegradable and abundantly available in nature for a very low cost. In this work, based on results from XPS and TGA, we see the impact of the new covalent ether linkages between starch and lignin(-C-O-C-) improving the thermal stability, especially at the main weight loss steps. These structural changes, as highlighted by X-ray measurements, associated with morphological ones, shown by SEM images, could affect the mechanical properties of the modified fibers, compared to unmodified ones, that we will attempt to verify by means of suitable mechanical measurements.