This paper describes the development of a deepwater casing shoe which ensures subsea casing strings designed to land in a wellhead can be run to full wellbore depth with no rat hole. The problem with excess rat hole occurs when drilling and holecleaning operations enlarge a normally-gauged hole or the unsupported, uncemented portion of the wellbore collapses and leaves an over-gauged hole. Such hole conditions are conducive to compromised primary cementing operations, poor zonal isolation, and can lead to stuck logging or other downhole tools in the subsequent interval.This shoe allows the rat hole section to be completely covered with casing while simultaneously landing the subsea casing hanger in the wellhead. This technology represents a paradigm shift in primary cementing practice; allowing cement to be placed at wellbore TD without a rat hole. This is especially true in deviated and/or horizontal wellbores, where zonal isolation is critical to well-life expectancy and production.
This paper describes the development and deployment of a new method of determining the physical location of a top cementing plug in a subsea casing string. Typically, the position of the top plug is approximated based on the calculated volume of the string, which can often vary significantly from actual casing volume, especially in long, heavy subsea casing intervals.Such discrepancies can create major problems during primary cementing operations, including failure to bump the top plug or potential overdisplacement of cement. The former tends to increase subsequent drillout times; the latter may result in contaminated cement in the shoe track.After review of the problems, the operator in the region concluded that utilizing the described technology, the Plug Indicator System (PIS), was warranted. The PIS was expected to facilitate more effective primary cementing operations by mitigating these risks, thereby reducing nonproductive time (NPT) and associated costs and avoiding expensive remedial operations.This paper reviews and helps familiarize the reader with the problems associated with subsea casing primary cementing operations. A case history of the PIS and its successful conclusion is presented.
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