Performance Evaluation of Bentonite Muds Formulated using Cassava Starch Treated with Preservatives
Abstract
Extensive works have been done on the subject matter of local sourcing of drilling fluid additives to reduce our importation burdens especially in this era of dwindling oil fortunes. This local sourcing will bolster industrialization and reduce unemployment in a vast economy like Nigeria. The results of the previous studies have shown promising potentials which are in tandem with our local content mandate of the government. Cassava starch has been identified as one of these additives and our ranking as the world largest producer of cassava remains instructive. Currently, all the starch used in the oil and gas industry is imported. The major constraint to the use of cassava starch is their extreme susceptibility to postharvest degradation. This work, therefore, is an attempt to address this problem of stability by the application of appropriate preservatives without prejudice to the rheological properties of the mud. In carrying out this study at temperatures of 80, 120, 150 and 1900F, three cassava starch cultivars TMS 92/0057, TMS 98/0581 and TMS 96/1632 and four common preservatives in the food industry; the salts of benzoate, propionate, sorbate and metabisulphite were used in the bentonite mud formulations. The result showed that out of the sixty-one mud formulations, only five of them adequately met the API rheological properties threshold. These five muds exhibited properties that compare favourably to the imported starch sample. This stabilized product holds much promise as a substitute to the imported starch for use in water-based drilling mud formulations for the Nigerian oil industry.
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Introduction
The use of preservatives predates history. The prehistoric men were known to have preserved their perishables with substances such as salt and vinegar [1]. The ante of the preservation industry has since then moved up to the present day whereby it is almost possible to preserve anything so desired. More often than not, this is done through a myriad of processes and operations that sometimes see a combination of such, to achieve some complex and even conflicting requirements [2].
A preservative is a substance that is added to a product to maintain an existing condition or prevent decomposition by microbial attacks or degradation through other undesirable changes. However concerning food preservation which starch belongs to, preserving what is, may not be just adequate as additional requirements of improving flavour, texture and visual appearance may also be imposed [3].
Preservatives are classified into two groups according to the form of attack as antimicrobial or antioxidants. The antimicrobial preservatives prevent the attacks from micro-organisms such as moulds, yeasts and bacteria and some common ones are the salts of benzoate, sorbate, propionate and metabisulphite [4]. The antioxidants prevent the oxidation of foods and especially those containing unsaturated fats and oils. It is this oxidation which produces the rancid taste in such foods and typical examples are the butylated hydroxyl toluene (BHT), butylated hydroxyl anisole (BHA) and the ascorbates [5].
Conclusion
In this work, a total of sixty-one mud samples were prepared and analyzed. The deliberate and elaborate sampling and analyses were to ensure that the results will make a good contribution towards the closure of the work that has been done towards the industrial application of local cassava starches in drilling fluid formulations. Accordingly, we conclude as follows:
The application of benzoate preservatives at low concentration of 0.05% to each of the two cassava starch cultivars holds much promise as a substitute to the imported starch, for use in water-based drilling mud formulations for the Nigerian oil and gas industry
Both mud formulations showed similar rheological characterization with the imported starch sample (control sample) and all the parameters conformed to the API standard.
The last step in these positive closure efforts is ongoing and that will be the deployment of moisture sorption studies to validate the acceptable shelf life for these stabilized cassava starch products.