International Journal of Engineering Research and Technology. ISSN 0974-3154, Volume 13, Number 5 (2020), pp. 1019-1029 © International Research Publication House. https://dx.doi.org/10.37624/IJERT/13.5.2020.1019-1029 1019 Effect of Sodium Carbonate and Bicarbonate Contamination on the Rheological Properties of Water Based Mud Hisham Ben Mahmud 1,a,* , Walid Mohamed Mahmud 2 , Rugen Ayanarappan 1 , and Saber Elmabrouk 3 1 Petroleum Engineering Department, Curtin University Malaysia, CDT 250, 98009, Sarawak, Malaysia. 2 Petroleum Engineering Department, University of Tripoli, Libya. 3 Libyan Academy, Janzour, Libya. a https://orcid.org/0000-0002-8231-9730 Abstract Stability of drilling fluid property is very crucial for smooth and less troublesome drilling because contamination of drilling fluid during drilling operations is usually unavoidable. This work presents an investigation of the effects of various contaminants on laboratory prepared water based drilling mud at ambient conditions. Three mud samples each has a different concentrations of Sodium Carbonate (Na2CO3) and Sodium Bicarbonate (NaHCO3) contaminants were mixed with Water Based Mud (WBM) fluid and formulated to investigate their effect on drilling fluid rheological properties. The measured properties were pH, fluid loss, mud thickness, plastic viscosity and yield point. The results indicate that the mud thickness increased with the increase of different cement contaminations. Mud pH increased as sodium carbonate concentration increased but decreased as bicarbonate concentration increased. Plastic viscosity decreased with the increase of concentrations of both cement contamination and the treating agent while yield point increased with the increase of cement contamination concentration. Furthermore, fluid loss was found to proportionally increase with the increase of contaminants concentration. Most of the results obtained from this work are consistent with previously published results; however, the developed mud rheological properties should be further studied at elevated temperature and pressure conditions encountered while drilling an oil or gas well. Keywords: WBM, Contaminants (Sodium Carbonate, Sodium Bicarbonate), Treating agents (calcium sulphate, Sodium Hydroxide), Rheological properties, Ambient condition INTRODUCTION Circulating mud while drilling an oil or gas well is the main task of the circulating system. Therefore, the drilling mud properties, especially the rheological properties, should be given extensive attention as they describe the mud characteristics at various flow conditions. Various flow conditions occur during drilling because of shear rate, shear stress and the type of mud contaminants. However, contaminants, such as acid gaseous, encountered during drilling are usually unavoidable and may significantly affect the rheological properties of the drilling mud that must be maintained throughout the drilling operation. Thus, any rheological properties alterations are a sign that the mud has become contaminated. If mud contamination is not instantly treated, low rate in penetration, abnormal pressure and pipe sticking are among the complications that could occur during the drilling operation. Adding additives into the mud while mud is being re-fed through the drill stem usually treats the contaminated mud. It is not achievable, however, that the mud is fully restored but the additives can minimize contaminants’ concentrations and thereof their negative effects. Mud additives are chemicals added into the drilling mud to enhance its performance by altering its compositions and properties in order to eliminate or minimize the effects of contaminants. Once, the rheological properties of the mud and the ideal composition has been established, several crucial functions are performed by the mud that include lubricating and cooling the drill bit, equalizing wellbore pressure, transporting drill cuttings to the surface, maintain wellbore stability and suspending particles when the drilling operation stops. Cost, type of well, environmental impact and performance are important factors that dictate the type of drilling mud that must be used as mud can be of gas, gas/liquid mixture or liquid nature. The liquid, which is most commonly used, can be oil- based muds, OBM, or water-based muds, WBM, indicating that the continuous phase of the mud system is either oil or water, respectively. However, among many factors such as maintaining the original wettability status of the target formation(s), WBM are predominantly used in the petroleum industry. Air also has been used as a drilling mud but because of air’s density and compressibility, it may not always prevent the wellbore from collapsing. Contaminants are material or substances that change mud properties in an undesirable manner. While drilling an oil or gas well, drill cuttings and solid rock particles that result from the drilling operation is the most encountered drilling mud contaminant that cause significant decrease in the rate of drilling penetration. Chemical contents of penetrated formations are also contaminants that may destroy the rheological properties of the designed mud when both the chemicals and mud come in contact with each other. Salt contamination in drilling mud is considered as naturally occurring contaminant that maybe initiated from various sources including salty water content in drilling mud and