Enhancing the Stability of Invert Emulsion Drilling Fluid for Drilling in High-Pressure High-Temperature Conditions

Salaheldin Elkatatny

doi:10.3390/en11092393

Abstract

Drilling in high-pressure high-temperature (HPHT) conditions is a challenging task. The drilling fluid should be designed to provide high density and stable rheological properties. Barite is the most common weighting material used to adjust the required fluid density. Barite settling, or sag, is a common issue in drilling HPHT wells. Barite sagging may cause many problems such as density variations, well-control problems, stuck pipe, downhole drilling fluid losses, or induced wellbore instability. This study assesses the effect of using a new copolymer (based on styrene and acrylic monomers) on the rheological properties and the stability of an invert emulsion drilling fluid, which can be used to drill HPHT wells. The main goal is to prevent the barite sagging issue, which is common in drilling HPHT wells. A sag test was performed under static (vertical and 45° incline) and dynamic conditions in order to evaluate the copolymer’s ability to enhance the suspension properties of the drilling fluid. In addition, the effect of this copolymer on the filtration properties was performed. The obtained results showed that adding the new copolymer with 1 lb/bbl concentration has no effect on the density and electrical stability. The sag issue was eliminated by adding 1 lb/bbl of the copolymer to the invert emulsion drilling fluid at a temperature >300 °F under static and dynamic conditions. Adding the copolymer enhanced the storage modulus by 290% and the gel strength by 50%, which demonstrated the power of the new copolymer to prevent the settling of the barite particles at a higher temperature. The 1 lb/bbl copolymer’s concentration reduced the filter cake thickness by 40% at 400 °F, which indicates the prevention of barite settling at high temperature.

Highlights

high-pressure high-temperature (HPHT) conditions may reach pressures greater than 10,000 psi and temperatures greater than 300 ◦ F [1]
Li et al [4] evaluate the effect of using cellulose nanoparticles (CNPs) as a modifier for rheological and filtration properties of bentonite water-based drilling fluid (BT-WBDF)
They concluded that adding cellulose nanocrystals (CNCs) to the BT-WBDF enhanced the rheological properties, especially at higher temperature, and reduced the fluid loss into the formation, and in addition, the formed filter cake was thin when compared with BT-WBDF

Summary

Introduction

HPHT conditions may reach pressures greater than 10,000 psi and temperatures greater than 300 ◦ F [1]. Drilling wells at HPHT conditions require a special design, especially for the drilling fluid properties. Polymers and nanoparticles play a vital role in providing stable rheological properties and reducing the filtration of the drilling fluid into the formation [3]. Li et al [4] evaluate the effect of using cellulose nanoparticles (CNPs) as a modifier for rheological and filtration properties of bentonite water-based drilling fluid (BT-WBDF). They concluded that adding cellulose nanocrystals (CNCs) to the BT-WBDF enhanced the rheological properties, especially at higher temperature, and reduced the fluid loss into the formation, and in addition, the formed filter cake was thin when compared with BT-WBDF. Rasool et al [5] developed a nanocomposite

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