Drilling with liner goes deep

Steve Rosenberg and Ming Zo Tan

September 1, 2015

Weatherford’s Steve Rosenberg and Ming Zo Tan demonstrate how drilling-with-liner technology isolated a depleted sand section in deepwater Gulf of Mexico well in one trip.

The Weatherford Defyer casing bit seen here was drilled out in 19 minutes with no damage to the drill out bit. Images from Weatherford.

Working in an area that leaves no room for error, an operator sought to mitigate risks when drilling and isolating a 6.5ppg depleted-sand formation.

The well, in the deepwater Mississippi Canyon section of the Gulf of Mexico at 5743ft water depth, featured a 60ft shale interval with a high risk of catastrophic fluid loss during drilling and cementing. A Weatherford drilling team collaborated with the operator in the early development stages and planned a drilling-with-liner (DwL) operation.

The team would drill below existing 13 5/8in, 88.20lb/ft x 14in 113lb/ft casing and execute a 9 7/8in, 62.80lb/ft Q-125 DwL operation from a measured depth (MD) of approximately 13,000-13,400ft at a deviation of 38°.

The operational objective was to isolate the depleted sand formation, drill a sufficient interval of shale, accomplish the operator’s cementing objectives, and obtain an acceptable formation integrity test (FIT).

Mitigating risks with one-trip

Weatherford drilling-with-casing (DwC) technology increases drilling efficiency and reduces risk exposure by removing the need to trip pipe and bottomhole-assembly (BHA) components while constructing leaner wellbores.

Because of the early collaboration between Weatherford and the operator, the team was able to select a technology that not only met the drilling objectives, but did so in one trip. The single-trip focus would help to mitigate risks associated with fluid loss and wellbore exposure.

Drilling through depleted sands is among the hazardous conditions in which the stakes increase with every trip. Conventional drilling—running pipe, setting liners, and then cementing them in place can damage the borehole before the first joint of liner goes in the hole. Tripping in and out of the hole, wiper trips, and extra circulation can often create other problems in addition to the trouble zones.

The DwL technology simultaneously runs liner during drilling and allows for immediate cementing, which seals off the trouble zones and eliminates the need for wiper trips. The technology also allows for the use of a reduced mud weight and reduces the likelihood of well integrity failure as a result of poor cementing.

Planning for error-free drilling

Weatherford and the operator collaborated for a comprehensive planning stage. This included torque, drag, and hydraulics modeling of the liner running and drilling operation; connection cyclic fatigue analysis, bottomhole assembly (BHA) and directional tendency modeling; cementation and centralization; and plastering effect evaluation.

Combing operator data, case histories, modeling, and simulations, the team identified a number of risks. Among the potential issues were induced losses resulting from surge effects; lost circulation below the 14in casing shoe; inability to re-establish circulation after drilling, which could necessitate cementing the liner higher than desired; cement failing to circulate to the top of the liner, which would require a remedial top-of-liner squeeze; differential sticking caused by the 3500 psi pressure differential between the mud and formation pressures; and helical buckling during liner-top packer setting.

Setting drilling procedures

Seeking to mitigate the risks identified during the assessment phase, the team set drilling procedures and recommendations. The team would use a flow rate of 100-300gpm to ream below the existing 13 5/8in x 14in casing shoe. Once drilling commenced, the operation would maintain a flow rate of 300l/min, which would provide a 70.6% cuttings-transport ratio. The differential pressure across the liner top would be 135 psi. Calculations show the standpipe pressure will not exceed 500 psi at 300gpm, with 11.8ppg mud and a 50ft/hr rate of penetration (ROP).

The minimum allowable flow rate to evacuate cuttings is 190gpm in the riser and 90gpm in the 13 5/8in x 14in casing. In the event that flow rate needs to be lowered to between 90-190gpm, the riser booster can raise the flow rate to 190gpm.

According to calculations, doubling the rate of penetration (ROP) from 40 to 80ft/hr would increase equivalent circulating density (ECD) by 0.16ppg. However, the team could double the revolutions per minute (RPM) from 50 to 100rpm and show a negligible ECD effect of <0.003ppg. At this high RPM, the standpipe pressure is also not expected to exceed 500 psi at 300gpm, with 11.8ppg mud and 50ft/hr ROP.

Drilling through the depleted sand

Operational execution began after setting the 13 5/8in x 14in casing. The drilling team picked up the 649ft liner BHA string, torqued to 36,000ft-lb, and ran to a depth of 12,900ft. The team periodically stopped running the liner to function test the blowout preventer (BOP) and diverter and to verify that the well remained static.

As planned, circulation started at 100gpm and background rotary torque readings were established at 12,900ft, just above the 13-5/8in x 14in casing shoe. The team added LCM consisting of 12ppb calcium carbonate and 3ppb graphite to the mud system. The rat hole was cleaned out to 12,950ft with lost circulation.

Drilling commenced with a 170-300gpm pump rate, 300 psi surface pressure, 10,000-20,000lb weight-on-bit (WOB), 70-90 rpm, and 15,000-20,000ft-lb of torque. Although the team experienced total fluid losses, the annulus remained full during connections while pumping 300gpm with the riser booster pump.

The team reached a total depth of 13,256ft in 20 hours with a controlled on-bottom ROP of 16.7ft/hr while incurring total fluid losses during the entire DwL operation. Measured fluid losses during the DwL operation were 5850 bbl, and the Defyer casing bit was drilled out in 19 min.

Cementing through the depleted sand

The team shut down the pumps and rigged up the cement head. They pumped a 2 1/8in liner-setting ball downhole to the mechanical ball seat, but several attempts to pressure up and set the hanger were unsuccessful. The hanger was sliding downhole as the slips were trying to bite into the casing wall, probably because of the large amount of LCM in the system. The team slacked off and set the liner on bottom at 13,256ft.

The team picked up the string to neutral weight, freely rotated at 8000-10,000 ft/lb of torque, and released from the hanger with 585,000-lb pick-up weight. They pressured the string to shear the ball seat at 3684 psi and then circulated 3 bbl of mud at 225 psi to ensure that the string was not plugged.

They performed the liner cement job by pumping 100 bbl of 12.5ppg spacer and 3 bbl of 13.7ppg cement along with the bottom dart. Then they pumped another 54 bbl of cement along with the top dart and 20 bbl of spacer. This was displaced with 11.6ppg oil-base mud (OBM) until the bottom dart latched into the bottom plug, which required 295 bbl.

The team then launched the bottom plug with 1150 psi of pressure and continued pumping until it landed on the float collar, which required 326 bbl. The rupture disc was blown at 1030 psi, and the top dart latched into the top plug at 351 bbl. The plug was bumped with 1300 psi of pressure, held for 3 minutes, and then bled off to check that the floats were holding.

Next, the team performed a liner-top cement job by bullheading 50 bbl of spacer, 75 bbl of 13.7ppg cement, and a further 20 bbl of spacer. They displaced with 359 bbl OBM at a maximum pressure of 710 psi. Total mud losses during both cement jobs was 1139 bbl.

Finally, the team applied 130,000lb of set-down weight to set the liner top packer and successfully tested the liner-top packer to 1135 psi for 5min.

Conclusion

Weatherford DwL technology isolated the depleted-sand formation and avoided potential contingency liners, sticking, and other delays that would have occurred if conventional drilling means had been deployed. The operation mitigated the expected catastrophic fluid losses and enabled the client to meet its well construction objectives. The DwL operation, was completed in 21 hours and ahead of schedule.

Steve Rosenberg is the global drilling reliability manager for Weatherford’s Well Engineering and Project Management Team with over 30 years’ experience in the oil and gas industry. He has previously worked with Diamond Offshore and Conoco. He holds BS degrees in petroleum engineering from Mississippi State University and biology from St. Lawrence University.

Ming Zo Tan is the global product champion for Weatherford Drilling with Casing Product Line. He joined Weatherford 12 years ago as a DwC Product Line Manager and held the position of Global Application Engineering Manager prior to current position. Prior to Weatherford, Tan held various positions within Halliburton. He holds a BS degree in petroleum engineering.