Low-ECD Inverted Emulsion Fluid Shows Superior Performance
Authors: Carpenter Chris 
Published: November 2023

_
This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 211539, “New Low-ECD Organophilic Clay-Free Inverted Emulsion Fluid Weighted With Manganese Tetroxide Showed Superior Performance in Different Fields: Success Story of Drilling With OCIEF in High-Overbalance Environment Without Downhole Problems, Stuck-Pipe Events, and Nonproductive Time,” by Vikrant Wagle, SPE, Abdullah Yami, SPE, and Abdullah Al Moajil, SPE, Saudi Aramco, et al. The paper has not been peer reviewed.

_
The complete paper describes the success of using a new low-equivalent-circulating-density (ECD) organophilic clay-free inverted emulsion fluid (OCIEF) in gas reservoirs at elevated temperatures and with differential pressures up to 4,500 psi. The objective of the paper is to highlight the superior performance of OCIEF over barite-based conventional invert-emulsion drilling fluids and formate-based, water-based drilling fluids in the study. The fluid overcame challenges in such an environment without compromising performance.

Introduction
The new low-ECD OCIEF, using manganese tetroxide as the weighting agent, was developed with an aim to offer improved drilling performance in maturing fields. Its nondamaging nature, the result of the presence of the acid-soluble and micronized manganese tetroxide, would help to complete the well with an openhole design.
In an OCIEF, the organophilic clay and organophilic lignite are replaced by a polymeric viscosifier and a polymeric filtration-control agent, respectively. A unique gel structure is provided by the use of the polymeric viscosifier in the oil-based drilling fluid. Also, it not only increases cuttings-carrying capacity but also helps to increase barite sag resistance in the fluid. In the absence of low-gravity solids in terms of organoclay and organolignite, an OCIEF shows low plastic viscosity and a higher rate of penetration compared with conventional organoclay-based oil-based muds.
In the OCIEF described in the paper, the solids content has been further reduced by replacing the barite (4.2 SG) with manganese tetroxide (4.8 SG). The acid solubility of manganese tetroxide would make the drilling fluid nondamaging, especially for reservoir zones.
Formulation of Low-ECD OCIEF.
The OCIEF was designed for long lateral sections where low rates of penetration (ROPs) can be observed in a slimhole drilling environment with a bottomhole temperature (BHT) of approximately 300°F. The OCIEF was tested for drilling in high-static overbalance conditions (3,000–4,500 psi) and had to be resistant to potential contaminants. The OCIEF was formulated with the acid-soluble manganese tetroxide with a water-phase salinity of 200,000–250,000 ppm.
Two 95-lbm/ft3 OCIEFs were formulated. The 95-lbm/ft3 OCIEF 1 was developed with an engineered bridging package of variously sized ground marbles. This formulation was specifically for short laterals and lower differential pressures. The acid solubility of the ground-marble-based package was an additional benefit of the OCIEF 1 fluid formulation.
An alternate, OCIEF 2, was developed for longer intervals with higher overbalance conditions. OCIEF 2 was formulated with a bridging package that included sized resilient graphite, fibers, and sized ground marble. The bridging package was designed for longer laterals because it was expected that the bridging solids would undergo increased mechanical attrition. A single polymeric filtration-control additive was used in both formulations.