Click here to read the rest of this article, part of what promises to be an interesting series, on Crain's website.Local construction companies are perfectly capable of building much of the cement infrastructure at the surface of an oil and gas drilling rig.They could possibly do the big, critical cement jobs around casing that encapsulates the well bore as well — but their equipment would have to be highly advanced and specialized and they would need to stock a different class of cement for this purpose. They would need laboratories in which to design special cement slurries, and they would need specialized training far beyond that necessary for surface construction activities.
Conventional construction cement trucks carry the familiar big cone-shaped cylinders that rotate and keep the cement workable even as it rolls down the highway. The cement inside is a heavy, thick mass that can be dumped on site. It is far too thick to be pumped through pipes.
On surface work, the cement is held in place with wood or other forms and can be worked by hand to provide a smooth surface. It gradually “sets” and gets stronger over several weeks before loads such as vehicles are allowed on top. It is made stronger with rebar or steel-reinforcing mesh, inside the cement mass, in many cases.
But an oil/gas well casing cement job requires total replacement of the drilling fluid with cement around the well's steel casing, after the casing is assembled and run into the well. This is accomplished by pumping liquid cement slurry down through the inside of the casing, through a valve near the bottom, and then up and around the casing to the desired depth. This desired depth is at the surface on the first layer of casing, because this casing is run and cemented through the fresh water strata before any more hole is drilled.
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