Organophilic-Clay-Free Invert-Emulsion Fluid Helps Drill Record-Length Well in the UAE
Authors: Wilson Adam 
Published: May 2018

This article, written by Special Publications Editor Adam Wilson, contains highlights of paper SPE 186917, “Breaking Records Using an Innovative Organophilic-Clay-Free Invert-Emulsion Fluid To Drill the Longest Well to Date in the United Arab Emirates,” by Mena Nasrallah and Matteo Vinci, SPE, Halliburton, prepared for the 2017 SPE/IATMI Asia Pacific Oil and Gas Conference and Exhibition, Bali, Indonesia, 17–19 October. The paper has not been peer reviewed.

This paper discusses the successful design, laboratory testing, and performance of an innovative, low-solids, organophilic-clay-free invert-emulsion fluid (OCF-IEF) used to drill the reservoir section of an extended-reach-drilling (ERD) well. This specially designed drill-in fluid helped maintain the key ERD factors within the specifications necessary and set new limits for drilling performance, thus maximizing the horizontal-section displacement and reservoir drainage and production output.

Introduction

ERD is an operative practice for drilling high-angle wellbores with long horizontal displacement. Typically, a well design is classified as ERD when the horizontal displacement is at least two times the vertical-displacement true vertical depth (TVD). The longest well drilled in the UAE had a measured depth of 35,800 ft, with 18,800 ft of horizontal displacement and a 7,894-ft TVD (Fig.  1). This technique is considered one of the more technically challenging in the industry. However, because of in-creased reservoir contact, it is generally preferred to conventional well designs.

Proper fluid selection is fundamental during the ERD-well-planning phase. Software support is necessary to predict the well conditions and simulate the fluid behavior to maintain the equivalent circulating density (ECD) lower than the fracture gradient, maximize hole cleaning, provide wellbore stability throughout the well execution, and prevent losses. The different drilling parameters used to drill the horizontal section should also be considered during the planning phase to help enable correct simulations and optimize the execution accordingly.

Fluid Properties

During drill-in-fluid design, formation damage and production rates should be considered while maintaining the optimal mud properties for drilling and rate-of-penetration (ROP) enhancement. A comprehensive testing and validation process was compiled using a systematic approach to customize this specific well design. Clay-free invert-emulsion fluids (CF-IEFs) are designed to provide a much stronger gel structure than traditional IEFs. However, with the application of force, these gels break easily, thus reducing the wellbore stresses and pressure spikes. Progressive yet fragile gel strengths are important elements of a CF-IEF system that allow the cuttings to be suspended while maintaining low ECD and minimal circulation pressures compared with a clay-laden system. The organophilic clays and organophilic lignites are replaced with various organic polymers to achieve different fluid behaviors. Acid solubility to minimize formation damage was another important system-design criterion. This helped minimize formation damage and maintain proper bridging by use of ground marble with the correct particle-size distribution (PSD), determined by specialized software.