Drilling trouble zones has haunted drilling operations experts through the years. Conventional methods for mitigating formation problems encountered during the drilling phase of a well, such as unstable formations, overpressured formations, and loss zones, are often costly and ineffective. Age-old methods of simply setting a casing and drilling ahead with a different mud weight and a smaller hole size are becoming increasingly unacceptable as the industry strives to reach deeper reserves.

The use of cement, chemical "cocktails," and loss-circulation materials can significantly increase well costs. The use of conventional solid expandable drilling liners that have to be tied back to the previous casing can also be cost prohibitive and lead to non-standard equipment requirements for drilling and casing the following section of the well.

This paper explains how a non-cemented, solid expandable openhole clad (patch) can be installed remotely from a previous casing to isolate problem formations so that the target setting depth can be reached with conventional casing without sacrificing hole size.

Installation of a solid expandable openhole clad will result in mitigation of problem sections and allow drilling to continue with the same hole size. The problem formation is straddled with a short length of expandable casing or clad with a resultant drift ID equal to the diameter of the original hole or drill bit. With this full bore ID, further clads can be run through, and deployed lower, in the same hole section.

In addition to reducing operational risks associated with expansion of long lengths of conventional tied-back solid expandable openhole liners, this option significantly reduces well costs and results in higher and earlier production associated with the increased hole size in the reservoir section.

Although not widely known, the openhole patch system has been used extensively with excellent results in remote locations over the past 20 years and is currently poised for global commercialization.

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