Mitigating Surge and Swab by Changing Tripping from a Batch to a Continuous Process

A significant portion of the time required to drill an oilwell is spent moving the drillpipe in or out of the wellbore, called "Tripping". The drill crew must trip pipe for numerous reasons. These include changing the bit as it wears out, inserting new casing strings, cleaning and treating the drillpipe and/or wellbore to allow more efficient drilling, and to run in various tools that perform specific jobs required at certain times in the oilwell construction plan. The traditional tripping process (TTP) inherently creates pressure transients developed from stopping and starting the vertical motion of the drillpipe during connections. These pressure transients called, "Swapping" and "Surging", contribute to borehole instability, restrict tripping speed, and increase non-productive time (NPT). This paper focuses on the benefits that can be gained from a bottom hole pressure (BHP) surge/swab perspective. Specifically, how these undesirable pressure transients can be dramatically reduced by modifying the TTP from a start/stop (batch) process to a continuous tripping process (CTP), where drillpipe tripping speed is kept constant throughout the entire tripping sequence and thereby significantly reducing the numerous starts and stops associated with traditional tripping. In this paper both the TTP and CTP systems were kinematically modeled using a custom simulator coded in C#. It is important to note that all the equipment used in the modified CTP exists and has only been reconfigured to facilitate a continuous process. This is inclusive of real-life limits for such items as derrick height, traveling block (TB) height as well as velocity, acceleration and inertia limits for TB, crown blocks, drawworks, their associated reeving configurations as well as racking system arms, grippers, and latches. The simulation results indicates that for a continuous tripping system we can achieve a ~73% slower average pipe speed that has an overall tripping speed approximately 4 times faster than traditional tripping. CTP decreased BHP deviation significantly. The continuous tripping process was awarded a patent by USTPO in 2016, US 9,441.247 B2.