Top-Drive Casing-Running Process Improves Safety and Capability

Abstract

Summary The conventional casing-running process is personnel-intensive and requires considerable human contact with the casing. A new casing-running system facilitates mechanizing the casing-running process. This technology eliminates potential safety hazards, provides assurance that the casing can be run to the intended casing point, offers the ability to ream casing to bottom, reduces personnel requirements for running casing, and eliminates the need for a stabber in the derrick. A portable casing-drive tool is used to pick up joints of casing from the "V-door," position the casing over the stump in the rotary table, and grip the top of the casing without making a threaded connection. The drive tool supports the full torsional and axial load for running the casing and provides the ability to circulate the well at any time to wash and ream to bottom as tight hole or fill is encountered. The top drive provides the rotary power to make up and rotate the casing. The new portable casing-running system had been used on more than 430 jobs for more than 40 operators in nine countries (at the end of 2004) to run more than 3 million ft of casing of various weights, grades, and connection types, with sizes ranging from 4½ to 16 in. These jobs encompass wells from vertical holes to high-angle extended-reach wells and include both onshore and offshore applications. The system has been completely mechanized on one casing-drilling rig to allow the driller to routinely pick up casing from the pipe racks and make connections without human contact with the pipe. Introduction Multiple strings of casing are run on every oil and gas well. Some estimates (Tarr 1999) indicate that as much as 12 to 20% of the total rig time for a well is spent on casing installation. The casing-running process has changed little in many years, which provides an opportunity for process improvements that may impact the overall drilling economics. A "casing crew" rigs up casing-running tools and runs casing as a specialized operation on most rigs. Casing elevators are used to pick up individual joints of casing; casing tongs are used to rotate the top joint of casing while making up the connection; and then the weight of the casing string is supported with the casing elevators while the string is lowered into the wellbore. For most rigs, this process has changed little since slip-type casing elevators were introduced in 1924 (Brantley 1971) and air- and hydraulically powered casing tongs were introduced in the 1950s (Brantley 1971). 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, consider safety. The floor becomes crowded on 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 at the floor (the stump) to prevent cross-threading as the two joints are screwed together. The overall result is that there is an increased potential for falls from elevated work positions and for injuries from being caught between pieces of equipment as the casing is picked up, made up, and run.

Numerical Analysis of Pressure Gradient along Casing in Helical Turbulent Flow of Power Law Fluid in Eccentric Annulus

“…Defined average value of total pressure gradient around pipe circle as ()* and named it as average pressure gradient, which can be expressed as: In 1961, Burkhardt set up an empirical formula for surge pressure due to pipe axial movement. In his formula, surge pressure was function of average annular fluid velocityV + , which can be expressed as [1]:…”

“…Casing running tool (CRT) was a new kind of equipment for running casing into the well bore, and increased safety and efficiency of casing running process [1]. With the CRT, casing can be reciprocated, rotated at the same time [1]. And due to casing gravity, casing was assumed to be close to downside wall of inclined well [2].…”

Study on the Axial Tooth Shape of CRT Slips

“…The external clamping tool, grasping casing from exterior, is used to handle small size casings, whose outside diameter are smaller than 9 5/8″ for instance. The internal clamping tool is reverse to the external clamping tool [1,2,3]. Choosing appropriate slips tooth form is crucial in designing slips system to improve performance of contact interface.…”