Abstract

The significance of exploring deep and ultra-deep wells is increasing rapidly to meet the escalating global demands on oil and gas. Drilling at such depth introduces a wide range of difficult challenges. One of these challenges is the negative impact on the drilling fluids rheological properties when exposed to high pressure high temperature (HPHT) conditions and/or becoming contaminated with salts, which are common in deep drilling or in offshore operations.

The drilling engineer must have a good estimate for the values of rheological characteristics of a drilling fluid, such as viscosity, yield point and gel strength, and that is extremely important for a successful drilling operation. In this research work, experiments were conducted on water-based muds with different salinity content, from ambient conditions up to very elevated pressures and temperatures.

In these experiments, water based drilling fluids containing different types of salt (NaCl and KCl) at different concentrations were tested by a state-of-the-art high pressure high temperature viscometer. In this paper, the effect of different electrolysis (NaCl and KCl) at elevated pressures (up to 35,000 psi) and elevated temperatures (up to 450 ºF) on the viscosity of water based mud has been investigated.

Conducting this study led to the conclusion NaCl contaminated samples had higher shear stress-shear rate curves than water based mud; whereas, KCl contaminated samples had lower shear stress-shear rate curves than water based mud. Also, the study showed that Hershel-Bulkely model provides a good fit for the experimental data and well predicts the observed muds behavior.

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