In a corrosive downhole environment, the service life of a completion can be severely reduced if no precautions against corrosion are taken. Pipe made of corrosion resistant alloys (C.R.A.) is used to minimize corrosion. An analysis of various corrosion mechanisms shows that the surface integrity is an important factor for corrosion prevention .
Conventional spider and elevator inserts as well as conventional hydraulic power tong dies made of steel cause die marks that support corrosion. A gripping system named Micro-Grip distributes the required load equally onto a large number of small peaks, minimizing the indentation of each single peak [1–3]. This system is available for power tongs as well as accessories such as safety clamps.
In corrosive downhole environments, such as those that contain relevant quantities of CO2 and/or H2S at elevated temperature, C.R.A. materials with a high chromium content are often selected for the tubular and related accessories. In these environments using C.R.A., companies developed a "zero marking" policy especially for the makeup of the connections. In connection with higher torque values, this required a new gripping technology. A so-called Diamond-Grip gripping system was developed, together with a hydraulic gripping system for the power tong that delivers the required radial forces.
The paper describes this new gripping technology and a series of tests that were performed within pre-qualification processes for C.R.A. handling and running tenders in Qatar as well as in the Gulf of Mexico. The tests showed that there is no negative impact of Diamond-Grip and Micro-Grip in regards to corrosion under the severe influence of H2S and CO2.
The procedure of running pipe can be divided into handling tasks and tubular makeup
The task of handling the pipe includes
removing thread protectors
visual thread inspection
lift pipe to v-door
engage single joint elevator
lift pipe into derrick
Besides lifting and pipe handling equipment, equipment needs to be available that can carry the full weight of the string. So called slip-type spiders and slip-type elevators are used in combination with the spider transferring the string load onto the rotary table and the elevator transferring the load to the hook in the derrick.
The makeup procedures consists of:
apply thread compound
open power tong doors
move Power Tong towards string
install stabbing guide
stab-in the pin into the box
make-up the connection
check the JAM torque/turn graph
remove the power tong and bring it back to parking position (pinch point)
open the spider