Case History: Clay-Free Invert Fluid in Norwegian High-Temperature Well Provides Consistent Low ECD Profile

摘要

Historically, invert emulsion drilling fluids (IEFs) require organophilic clays to provide viscosity and suspension characteristics. Whilst effective, these chemicals are prone to stratification in certain conditions, slow chemical reaction times, high pressure spikes, and high equivalent circulating densities (ECDs) attributed to the solids contribution and inherent chemistry of the fluid. To help reduce such adverse effects, clay-based chemicals used in IEFs can be replaced with highly sophisticated polymer viscosifiers, filtration agents, and emulsifiers, which provide a strong, stable emulsion, even with low-oil/water ratio (OWR) IEFs. Legislation governing the energy industry’s use of chemicals in Norway prohibits use of certain products that are otherwise globally used in drilling fluids. To address such restrictions, extensive research and development has resulted in availability of environmentally acceptable chemicals that produce the unique rheological and suspension characteristics inherent to clay-free IEF systems. This paper describes the first application of clay-free IEFs in the Norwegian continental shelf (NCS) with an emphasis on an impressively low ECD contribution far more consistent than previously recorded in comparable wells. Further, a treatment was developed to allow the IEFs to be used to drill into a section exhibiting temperatures greater than 160°C. Chemical consumption was substantially lower compared to previous wells using traditional IEF systems, thus reducing shipping requirements. Before planning the subject well, the environmentally acceptable chemicals intended for use were approved by governing bodies. Consequently, a vertical exploration prospect was selected as the initial well to be drilled using a clay-free IEF. This well was comparable to a previously drilled high-pressure/high-temperature HP/HT well, allowing direct comparison of several of the metrics.