Experimental Study of Bentonite-Free Water Based Mud Reinforced with Carboxymethylated Tapioca Starch: Rheological Modeling and Optimization Using Response Surface Methodology (RSM).

Imtiaz Ali,Tarek Ganat,Maqsood Ahmad

doi:10.3390/polym13193320

Abstract

Drilling mud’s rheological characteristics, such as plastic viscosity and yield point, are adversely affected with an inappropriate mud formulation. Native starch is one of the most important components in water-based mud because it improves the rheological and filtration characteristics of the mud. The native starch stability under various temperature and exposure time regimes is an important concern for utilizing starch in oil and gas drilling operations. In this work, tapioca starch was modified using carboxymethylation for the first time in order to improve its performance in non-damaging water-based muds. The modified starch was characterized by Fourier-transform infrared spectroscopy and X-ray diffraction. The thermal stability was tested using thermal gravimetric analysis. Various mud blends were formulated based on the experimental design using response surface methodology (RSM) to investigate their performance at various temperature conditions. Thirty experimental runs were carried out based on the selected factors and responses considering the optimal (custom) design, and the results were analyzed through ANOVA. The Fourier-transform infrared spectroscopy and X-ray diffraction results confirmed the carboxymethylation of starch. The TGA analysis revealed strong thermal stability after modification. Additionally, the Power law model (PLM) described the obtained rheological data for the selected formulations, resulting in determination coefficients of more than 0.95. Furthermore, the examined samples showed a reduction in the flow behavior index from 0.30 to 0.21 and an increase in the consistency index from 5.6 to 15.1. Optimization and confirmation results revealed the adequacy of the generated empirical models for both plastic viscosity and yield point. The obtained consistency index values provided a direct relationship with the modified starch concentration, indicating an improvement in the cutting carrying capacity of mud. Based on the current literature survey, the studied formulation has not been reported in the literature.

Highlights

Water based muds have been used in the oil and gas drilling industry for decades
The current research demonstrated the applications of carboxymethylated tapioca starch for the non-damaging formulations of drilling mud at various temperature conditions
As a result of experiments conducted on the mud sample containing modified starch, it was concluded that the thermal stability of the native tapioca starch was enhanced with carboxymethylation

Summary

Introduction

A multi-functional drilling mud is required to perform numerous important functions including transporting cuttings, suspending cuttings, controlling formation pressure, cooling, and lubricating the bit, minimizing corrosion, providing necessary hydraulic power to down-hole equipment, and reducing formation damage. These functions can be achieved with mud exhibiting significant rheological and filtration properties. Numerous mud additives including viscosifiers, inhibitors, pH and fluid loss control agents are the primary additives used in water-based muds. Oil field applications of starch and its derivatives include fluid loss control, mud rheology improvement, shale stabilization, drag reduction, water shut-off, and oil recovery improvement [7]

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