The challenge of drilling through depleted zones, particularly in mature areas, continues to increase in importance as they are a frequent and familiar scenario for many fields. Pressure overbalances have been reported as high as 13,000 psi, although they more typically range in the hundreds to thousands psi. Wellbore stability problems associated with these zones can be linked to both drilling-induced and pre-existing fractures resulting in subsequent fluid losses. It is generally acknowledged that the solution to these problems is a combination of drilling fluid optimization and good drilling practices. Currently, the fluid solution is to incorporate large particulates in the form of a pill to seal such fractures, which consequently increases the drilling window. While the advantages of using a pill are known, large particulates also carry disadvantages, for example the retroactive nature of acting as a remedy rather than a prevention for lost circulation as well as leading to non-productive.

Formulations with various synergistic additives were examined through standard tests, including rheological profiles, high-pressure/ high-temperature fluid loss, and permeability plugging, some of which were performed on various porous disk media, including sandstone formation samples. Unique equipment was also developed and used to simulate a growing fracture mouth, or aperture, along with a proprietary mathematical model for the mechanism and geometry of fracture growth. The laboratory data supported a clear fracture mechanism and subsequent sealing, which was ultimately proven by yard test to confirm the laboratory and model predictions of performance.

Compared to commonly used particle packing/stress caging, the novel technology developed and testing performed demonstrates a new approach. The solution employs a continuous self-healing filtercake, rather than a large-sized lost circulation material pill application, to increase the drilling window and decrease risks of formation damage. The authors will present selected laboratory test methods and results, including a large scale fracture test and the associated mathematical modeling. This work shows a potential improvement in the drilling window while meeting environmental regulatory requirements in the Gulf of Mexico.

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