The commercialization of Casing Drilling technology has spawned the development of specialized equipment and procedures aimed at efficiently handling casing on a drilling rig. These procedures and equipment have also proven to be effective for running casing on conventionally drilled wells. This technology provides a safer casing running operation, provides assurance that the casing can be run to the casing point on the first attempt, offers the potential to ream casing to bottom, and requires fewer additional people on the rig for casing running operations.
The new casing running technology uses the top drive and a portable Casing Drive System (CDS) as the primary components of the casing running system. The top drive provides the power for applying rotation and torque to the casing, while the CDS provides the ability to pick up joints of casing from the "V-door" with single joint elevators and then grip the top of the casing so that the top drive can be used to make up the connection. The CDS supports the full torsional and axial load for running the casing and provides the ability to circulate the well while running casing without picking up any other equipment. This system allows the casing to be washed and reamed to bottom any time tight hole or fill is encountered.
The new casing running system has been used on over 150 wells for thirty-one operators in seven countries torun more than one million feet of casing of various weights, grades, and connection types with sizes ranging from 4–1/2" to 13–3/8". Both coupled and flush joint casing strings have been run. These jobs encompass wells from vertical holes to high angle extended reach wells and include both onshore and offshore applications.
The conventional process for running casing uses large tonnage casing elevators to pick up and support the weight of the casing and casing tongs to rotate the top joint of casing while making up the connections. For most rigs, this process has changed little since slip-type casing elevators were introduced in 19241 and air and hydraulically powered casing tongs were introduced in the 1950's1. The casing is run on most rigs by a 'casing crew" which brings out the casing running tools, rigs them up, and runs casing as a specialized operation. While this process is efficient at screwing joints of casing together, it provides no capability to rotate the entire string of casing hanging in the well and only very limited and inefficient procedures for circulating the casing while it is being run.
This conventional casing running process offers opportunities for improvements related to safety, efficiency, and capability. First, let's consider safety. The floor becomes crowded for many rigs when the conventional casing running equipment is rigged up while drillpipe is racked in the derrick. The casing tongs are often operated from scaffolding set up on the floor as a work platform. A workman is positioned in the derrick to help align the casing joint in the elevators with the one in the slips (the stump) to prevent cross-threading as the two joints are screwed together.