Custom fluid system stabilizes long interval in sensitive claystone

Overview

This case study explores challenges encountered when drilling for hydrocarbons in a carbonate formation of an offshore exploration well. This circumstance was the first of its kind for an operator in the country. The well design was near vertical, and the primary challenge was a long interval of reactive claystone in the intermediate section. In collaboration with the operator, Halliburton conducted dedicated sessions to identify the drilling challenges. The goal was to design a customized fluid that could tackle reactive claystone and adhere to stringent offshore environmental regulations with zero discharge.

Challenge

The limited offset well data revealed that shale in the block was reactive and sensitive to hydration caused by fluid invasion. X-ray diffraction (XRD) analysis showed the shale had high smectite and kaolinite clay content. These clays are reactive and to mitigate this risk, an inhibitive high-performance water-based drilling fluid (HPWBF) was deemed necessary. This system would stabilize the wellbore and provide a smooth environment for running and cementing casing.

While the operator initially favored the use of synthetic-based mud (SBM) for drilling the difficult section, the country’s environmental regulations made this option less attractive. SBM disposal involves additional costs for waste management and handling – an impact on the total cost of ownership. This prompted the need to explore water-based fluid options that could deliver similar performance to SBM.

Solution

The challenges were tackled with a custom approach to HPWBF design to close the gap on synthetic fluid performance for inhibition. BaraHib® Nano presented the benefit of tracking inhibitor concentration to increase the reliability of HPWBF with field execution. Adding BaraSeal™-957 to the fluid-enhanced sealing capability, complying with environmental regulations.

Result

The operator achieved its key performance indicators for the complex section. Halliburton delivered casing installation and successful cementation. The outcome convinced the operator to change its preference for SBM and to consider HPWBF for other projects. The operator’s next well campaign will use BaraHib® Nano.