Horizontal wells drilling using open hole completions is a common approach to maximize formation fluids production through the exposure of a bigger surface area of the reservoir. This approach is dependent on the combination of economic and technical aspects that are intrinsically connected. Within the technical considerations, pressure and temperature of the reservoir do play a critical role in the design of both reservoir drilling fluids (RDF) and filter cake remover to be used in operation. While the 200 degF temperature threshold is not an issue for most reservoir drilling fluids, this is a challenge to obtain adequate delay time for normal filter cake breaker technologies.

The RDF are designed with the first premise assuring formation pressure is kept under control as it is the first barrier for well control. Such control is obtained through the definition of the mud weight required to prevent the uncontrolled influx of the reservoir fluids and act to mechanically stabilize the drilled formations. The RDF is also designed to prevent formation damage being fully compatible with the completion method and filter cake removal technology to be used while assuring it is stable at the reservoir temperature for the duration required by all operations. The filter cake remover design criteria must consider: the completion operation steps, required delay times to avoid early removal of the filter cake with loss to the formation, stability under reservoir temperature condition, and density to assure well is maintained under control and mechanically stable.

The field reservoirs, which can reach temperatures higher than 280 deg F with drilling fluid density requirements of up 11.1 ppg for proper well control and mechanical stability have been historically drilled using barite-based drilling fluids followed by a casing and perforating method of completion. This approach had demonstrated various levels of success but presented some setbacks, such as sand production and average financial performance due to normal productivity. This approach was challenged, seeking improvement in the production of the reservoir and sand production control efficiency while still delivering flawless drilling and completion operations. This paper describes the design and optimization of a barite-free RDF, a filter cake remover suitable for 285 deg F, and a displacement method for spotting in the filter cake remover in the open hole annular between the stand-alone screens and reservoir face. All the simulation work and the laboratory data, including return permeability, are discussed, showing the steps required to obtain the best holistic approach for the operation. This solution enabled an average productivity increment of 40% in each of the four wells where it was executed while delivering a stable wellbore and executing all drilling and completion operations.

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