A new jet assembly harnesses the turbulent force of a tornado to clean sand and cuttings out of horizontal wells.

The petroleum industry has long been aware of the need for effective computer modeling to predict multiphase flow conditions, pressure losses and tubing forces within the well bore and coiled tubing. Several service companies have developed software programs to meet this need and optimize job performance.

BJ Services Co. engineers have collected and compiled extensive job data for more than 20 years, resulting in the creation of a coiled-tubing software platform known as CIRCA. The coiled-tubing job modeling software includes a module for analyzing solids transportation and deposition called Tornado Pro. The software is based on data from numerous flow tests conducted during a 6-year period using a full-scale flow simulator at the company's Calgary research lab.

BJ recently introduced the Tornado Tool, a new specialized jetting assembly that enhances the coiled tubing clean-out process. The tool is designed for use in conjunction with the company's coiled tubing job modeling software.

The computer software simulator accurately models the sand-washing process for various hole geometries and angles, pumping rates and fluid types. Based on understanding fluid properties and solids transport mechanisms, engineers and scientists have developed a new method for clearing particulate solids from deviated and horizontal well bores.

The solids-removal software models the sand-washing process as the coiled tubing moves down into the well bore. It predicts the amount of sand entrained in the fluid and subsequently deposited as a sand bed on the low side of the hole and predicts the balance, if any, of sand transported out of the well bore.
Once the coiled tubing reaches the bottom of the well, the model further predicts the time required to reach an equilibrium condition where an "equilibrium sand bed" is formed that simply stays in place and is not altered by further circulation at existing pump rates.

Improved wiper trip efficiency

To complement the software, BJ engineers developed a specialized jetting assembly, which combines switchable forward- and rearward-facing jetting nozzles as a new element in the clean-out process specifically aimed at exploiting the concept of the wiper trip.

Once the circulation clean-out process has established an acceptable re-distribution of sand in the well, the crew switches the jetting assembly from the forward-facing nozzles (Figure 1) to the rearward-facing nozzles (Figure 2). This creates a localized turbulent flow stream to the rear. As the coiled tubing is pulled out of the hole, the rearward jetting action entrains the front of the sand bed, allowing it to be carried out of the hole in the flow stream above the equilibrium bed.

Coiled tubing operators maintain the pull-out-of-hole speed and flow rate that the computer model predicts will keep the sand above the jetting assembly and avoid bridging on the way out of the hole.

Success in GOM and North Sea

To date, the combined use of the software and tool has been extremely successful. "We have used the process and jetting assembly in numerous wells in the Gulf of Mexico and have recently introduced the technology to our land operations in Texas, where a handful of horizontal clean outs have been successfully completed. Our latest success was a sand clean out from a floater in the Norwegian sector of the North Sea," said John Misselbrook, director of Global Coiled Tubing Services for BJ Services. "The software modeled well conditions and job parameters accurately, and all jobs resulted in effectively removing the offending solid materials. In view of this impressive performance, we are confident that the Tornado system will soon become the industry standard for clearing sand and other particulate solids from deviated and horizontal wellbores," he said.

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