Once a well is drilled and the casing is run and cemented, an efficient and immaculate wellbore cleanup operation is paramount as it can make a huge economic difference to the success of the production and completion phases. Within this cleanup process, liner tops and casing shoes are tested to confirm well integrity.
Coretrax, an independent wellbore cleanup and abandonment specialist, has created a robust wellbore cleanup product line that includes applications for HP/HT, extended-reach drilling and multilateral projects. Along with nonrotating scrapers, brushes, magnets and circulating tools, the company deploys its Liner Top Test Tool (CX-LTTT) to provide assurance of well construction before a completion is run.
With pressure in the formation and the removal of what is essentially a barrier of heavy fluid, this intentionally creates a weak point, often at the liner top. Therefore, it is necessary to test integrity through simulation with a packer.
The CX-LTTT is designed to perform isolated negative inflow tests on liner tops and casing shoes. When teamed with various other wellbore cleanup tools, it can be used as part of a single trip wellbore cleanup and displacement run. It works by setting down weight to compress and extrude the elements. The large bypass facilitates quick running speeds when running to depth. Capable of combining the cleanup, displacement and inflow test operations in the same run, the device is a proven and reliable inflow test packer.
Enhanced wellbore cleanup
Drilling through multiple types of materials like cement, shoe tracks and plug sets have traditionally been carried out over multiple trips in the hole. Due to the high volumes of debris created over each run, this can potentially have a detrimental effect to the liner top packer.
On the request of a major operator in the Middle East to design a heavy-duty tool that can deliver further rig time savings, Coretrax developed the CX-LTTT (HD), a cement drill-out device. This enhanced version of the LTTT was designed for all inflow test applications to include situations where there is a need for drilling through cement, plug sets, float collars and partial shoe tracks. This determines the integrity of the liner top before the next section is drilled.
Wellbore cleanup has traditionally been an operation where the environment needs to be devoid of large pieces of debris that can damage the string. With additional debris generated through the drillout of cement and various types of metal, there was an increased need for a heavy-duty packer to use in these applications. Following extensive research, analysis and testing over three months, the Coretrax in-house engineering and design team added a robust, purpose-built packer to the wellbore cleanup assembly to allow inflow testing to be performed concurrently in this harsh environment.
Several technical and safety challenges were apparent, including long drilling hours of about 30 hours, circulating large pieces of debris past the packer element in a high flow-rate environment and working across different metallurgies in the shoe track.
The tool is designed with a large concentric bypass that allows quick running speeds and a generous flow area passed the tool to achieve high flow rates, essential for recovering the debris out of the hole and minimizing the risk of damage to the packer.
Over two years, the CX-LTTT (HD) has achieved a substantial run history for operations in the Middle East and has delivered excellent results for the operator. In early 2017, the CX-LTTT (HD) device was used for cement drill-out operations and inflow testing of a 7-in. 32# liner. The cement was tagged at 3,629 m (11,905 ft) measured depth and drilled out along with the landing collar and float collar to a depth of 3,746 m (12,291 ft) measured depth. Over a period of 12 hours, 118 m (386 ft) were drilled.
The hole was circulated clean before landing the tool on top of the 7-in. liner at 3,502 m (11,490 ft) and setting down 35,200 lb to shear and function the tool. Over 10 minutes, a backside pressure test of 1,000 psi was completed confirming the integrity of the device.
The packer was then unset and freshwater was pumped to achieve a final drawdown pressure of 4,400 psi. When set down with 30,000 lb, the pressure was then bled off in stages of 500 psi to perform the inflow test, which was plotted on a Horner graph per the client’s procedures. Once the test was confirmed as successful, the drillstring was pressured to 4,400 psi and the device unset and pulled out of the hole.
This one-trip hybrid tool string now saves the operator about 30 hours of rig time per job and has been utilized in challenging conditions, including being successfully set at 5,334 m (17,500 ft) with a well inclination of about 74 degrees.
In the initial three-month period of bringing the LTTT-HD to the market, Coretrax has successfully performed eight inflow tests. Of these, seven were cement drillouts and one was a conventional wellbore cleanup and inflow test. By combining the inflow test with a cement drill-out run, the CX-LTTT (HD) saved about 480 hours (20 days), which equates to a further financial saving of $1.2 million. To date, the company has successfully reached more than 100 well runs, saving the operator more than 3,500 hours of rig time and about $9.2 million in costs.