Abstract

For decades, non-aqueous drilling fluids (NADF's) have been the fluid of choice to drill challenging wells. This is because they possesses high robustness, high rate of penetration (ROP) and high thermal stability. However, there is a growing interest in developing alternative fluids to replace non-aqueous drilling fluids, because they are expensive to dispose of, environmentally unfriendly, and may cause formation damage. Alternative fluids should have a better HSE profile and have an equivalent, or even better performance compared to the non-aqueous fluid. In addition, due to the increase of drilling costs, a substitute for expensive brines such as Cs formate for completion fluids is sought.

Recently the use of potassium formate brine (KFo), weighted with manganese tetraoxide (Mn3O4) as a drilling & completion fluid, has grown rapidly, particularly for sensitive formations such as shale and other clay-containing formations. In addition, being environmentally friendly, the KFo / Mn3O4 fluid has excellent performance for shale stability, high thermal stability and has less potential for formation damage compared to non-aqueous fluids. This fluid is very stable and is usable over a long period.

This paper will discuss the development of a novel, stable slurry of Mn3O4 in KFo with a high density of 2.3-2.5sg. The properties of the slurry were optimized to ensure easy flow and long-term storage stability. The stability of this slurry was monitored for a period of 6 months. The use of such slurry in preparing drilling fluids will be illustrated. The new liquid weight material simplifies the fluid mixing significantly. It can be used on its own or diluted back with water or KFo brine and the addition of other additives, such as fluid-loss agent, dispersant, viscosifier, etc., to convert it into a drilling or completion fluid. As a liquid additive, it is easy & safe to handle. The use of liquid chemicals eliminates any dust issues which may be encountered with powder handling.

In addition, the paper will show the design of a new high-density fluid 2.62sg (22ppg) and testing at temperatures of 200°C for ultra HPHT drilling. The new fluid has a low plastic viscosity of 48cp, and low fluid loss of <15 ml on 5µm ceramic disc at 150°C. It has a low dynamic sag of 0.16lb/100ft2.

This is the first time to develop such a high-density aqueous weight material (2.5sg) for drilling & completion fluids. It is also the first time to design environmentally friendly & high-density fluids (2.6sg) for ultra HPHT drilling.

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