Investigating the Performance of Cassava-Based Starches as Viscosifiers on Class-G Cement Slurry for Oil-Well Cementing Operations

Cementing technology has evolved significantly over time as one of the most critical completion tasks in the petroleum industry. Viscosity is pivotal in slurry formulation, impacting pumpability, thickening time, and overall slurry behaviour. Therefore, viscosifiers are always incorporated to modify slurry viscosity to achieve ultimate performance under varying downhole conditions. However, environmental concerns and the high costs of synthetic viscosifiers have driven interest in natural, organic alternatives. This study evaluates cassava starch, a locally sourced and renewable biopolymer, as a viscosifier in Class-G cement slurries. Cassava starch was extracted, processed into powder, and incorporated into cement formulations at concentrations of 0.1–0.4% BWOC. Rheological properties, gel strength, thickening time, compressive strength, free fluid, and pH stability were assessed following API standards and benchmarked against a synthetic viscosifier. Results showed that cassava starch enhanced plastic viscosity and yield point, with shear stress values of 105–127 lbf/100 ft² at 300 rpm, providing more stable flow behaviour after conditioning compared to synthetic starches. Thickening time was extended to 107 minutes, offering longer pumpability windows essential for deep and complex wells. Compressive strength exceeded 2600 psi at 24 hours, confirming that cassava starch did not hinder hydration. Free fluid values (0.36–1.2 ml) remained within API limits, though slightly higher than synthetic controls. The pH decreased from 6.3 to 5.8 over three days, confirming biodegradability. The findings demonstrate that cassava starch is an effective and environmentally friendly alternative to synthetic viscosifiers, offering enhanced thickening time, comparable compressive strength, and rheological stability.