Expandable liner hanger deployed after CDD

Kevin Bourassa, Tove Husby and Rick Watts, ConocoPhillips;  Chris Nussbaum* and Peter Wood, READ Well Services

When ConocoPhillips decided to conduct Casing Directional Drilling (CDD) operations from a platform in the Norwegian North Sea, the well design required that the drilled-in 7¾-in. production casing string be converted into a liner before completion. A liner hanger system was required that would be suitable for CDD operations, that did not require a running tool, would maintain a full ID for running and retrieving BHAs and would act as a barrier against gas migration over the life of the well.

Expandable technology was identified as a potential solution. After identifying a service provider, establishing a basis of design and testing, the team successfully deployed a 7¾-in. liner hanger that was drilled in from surface; successfully expanded into 10¾-in. casing; and had a load capability of over 440,000 lb and a 5,000-psi gas-tight seal qualified to ISO 14310:V0.

INTRODUCTION

ConocoPhillips wanted to CDD a long string of 7¾-in. casing to the top of the reservoir, cement the casing shoe, then convert the long string into a liner and retrieve the upper section of 7¾-in. casing. This conversion was required for the completion and stimulation design; for future sidetrack operations; to address concerns regarding Equivalent Circulating Density (ECD) while drilling the 6½-in. reservoir section; and to address space constraints within the wellhead system.

BHAs would have to be run on wireline through the liner hanger, which would be picked up at surface and needed to be drilled in and set at about 4,800 ft. Therefore, a conventional liner hanger assembly was not a viable solution.

Under these circumstances, it was desirable to use a liner hanger that had the same (or similar) OD and ID as the casing string and did not require a running tool, specifications that favored expandable technology. The liner hanger had to bear bidirectional axial loads and provide a gas-tight seal once set. However, before it was set inside the 10¾-in. parent casing string, the liner hanger had to reliably interface with the CDD equipment—primarily BHAs—and withstand expected drilling loads (i.e., pump pressure, torque and drag). READ Well Services’ liner hanger and the Hydraulically Expandable Tubular System (HETS) technology appeared fully compliant with this scenario. During well planning, it was decided to run two of the 7¾-in. liner hangers in the well separated by a joint of 7¾-in. casing. The second liner hanger would remain dormant and be used as a backup in case the first liner hanger did not set or test. A mechanical release tool was installed above the top liner hanger only. During the operation, only one hanger, the lower one, was used.

Before expansion and setting, the liner hanger was to form an integral part of a CDD string. It needed the strength and durability to withstand the rigors of a drilling environment and, therefore, required a burst pressure rating before expansion of 4,200 psi, a maximum axial load rating of 662,000 lb and a maximum torque rating of 45,000 ft-lb.

The liner hanger’s load-bearing capability was to be achieved by creating a metal-to-metal “interference” fit between the hanger and the parent casing. The capability to form very strong mechanical connections between expanded concentric tubulars is a principal quality of HETS. This expansion principle was applied to the liner hanger, so that the liner hanger’s OD was plastically deformed along its entire length of 8 ft to reach the parent casing string’s 10¾-in. ID.

The well design required that the liner hanger have a load rating of 440,000 lb in both compression and tension, throughout its service lifetime. The liner hanger device was also required to achieve a gas-tight seal against both internal and external pressure. The desired differential pressure rating was 5,000 psi, applied under all load conditions. This degree of seal was achieved by a combination of metal-to-metal and elastomer seal elements on the outer surface of the liner hanger.

The hanger was rated to 60°F–240°F to reflect expected well conditions.

DESIGN CONSIDERATIONS

The liner hanger would require sufficient strength to meet the mechanical requirements placed upon it both before and after expansion, while exhibiting enough ductility to allow it to fully expand and contact the parent casing.

For the liner hanger body, 316L stainless steel with a 36,000-psi minimum yield was chosen, as this was sufficiently strong to withstand the deployment and service loads and offered good ductility. It was not strong enough to achieve the required specification of the connection thread, so a higher-strength material (AISI 8630, with an 80,000-psi minimum yield) was butt-welded to the 316L.

The hanger is a tube of near-constant OD along its entire length, with wall thickness greater near the ends, and some internal thinning of the walls to achieve the correct mechanical behavior under expansion. The seals sit in the thicker wall section at each end, and the thinner-walled center section expands first. The hanger seals come into contact with the outer casing toward the end of the expansion process. Expansion from the center toward the ends ensures that no fluid is trapped between the seals, thus avoiding a hydraulic lock that might prevent full expansion. The design process used Finite Element (FE) modeling to define how expansion would progress. During the testing program, the design was refined—mostly related to metallurgy and to the placement and shape of the HETS seals—but the basic premise did not change.

Design of the seal assembly underwent modification during the live-test phase of the hanger development. The initial design did envisage a combination of metal-to-metal and elastomer elements, but the final (and successful) seal arrangement was the result of exhaustive testing. The seals, which are multiple and independent to provide redundancy, occupy a short length on the outer surface of the hanger at each end. Critical to their performance is the residual interfacial pressure between the liner hanger and the parent casing after expansion. FE modeling indicates that the contact pressure on the metal-to-metal seals can be as high as 150,000 psi.

TESTING AND QUALIFICATION

The design of the liner hanger for this application was entirely new, and the success of its first field deployment would be critical to the well completion. An extensive test program was devised and implemented starting in December 2006. Five full-size hangers were expanded, pressure tested and load tested, with expansion performed under the expected downhole load and temperature. One of the five hangers was deployed and set during a full-scale onshore trial in a test well. The sixth hanger was subjected to testing to simulate the drilling environment.

The post-expansion testing was carried out in accordance with the V0 specification of ISO Standard 14310. The testing scope included:

• Tension cycling between the test limits of ±440,000 lb

• Thermal cycling between the test limits 60°F and 240°F

• Application of external and internal pressure to 5,500 psi with nitrogen gas, and verification of a V0 (zero bubble) leak rate

• Application of external and internal pressure to 5,500 psi with water, and verification of a V3 specification leak rate

• Cyclic bend testing under pressure to simulate the drilling environment.

As testing progressed, some shortcomings in the initial design came to light. Of particular note was the development of the seal configuration to achieve a V0 rating in accordance with the ISO 14310 standard. After the first trial on a hanger with an A333-6 carbon steel body proved unsatisfactory, the subsequent design combination of 316L with AISI 8630 end pieces proved adequate.

Notable among qualification test results are the following:

Hanger 3, which was a trial of a different material (A333-6), suffered catastrophic failure, and the test was abandoned.

Hanger 5 was subjected to cyclic bend loading. A total of 962,316 cycles at 4.72°/100-ft bend with 2,000-psi internal pressure were applied to the hanger. Internal pressure tests to 5,500 psi were performed before and after the cycle test to check for integrity; no leaks were observed. Dye penetration tests were performed on the hanger to check for cracks that might have formed due to the cyclic loading; none were found.

Hanger 6 was expanded and set in an onshore test well. The resulting test piece was not suitable for hydraulic testing, but was tested to the maximum safe load limit. In compression, a 3-mm movement was detected at 816,000 lb.

BHA FOR THE EXPANSION TOOL

Once the liner hanger, which is part of the casing-while-drilling string, reached the planned setting depth and was cemented, the HETS assembly was run on drill pipe and located within the hanger. The HETS components, from the bottom up, are the depth latch, the expansion tool, the Downhole Hydraulics Module (DHM) and the hydraulic fluid reservoir.

The depth latch system was developed specifically to locate the HETS tool accurately inside the liner hanger while not conflicting with running and retrieving drilling BHAs. A unique double (female) profile is located within the 7¾-in. casing below the hanger. The male latch assembly, mounted at the bottom of the expansion tool, has five sprung dogs that precisely match the profile in the latch sub. The latch is designed to descend through the sub, generating 3,000 lb of resistance. When it is pulled upward and engages in the sub, 20,000 lb of over-pull upward is required to release it. Pulling up to 10,000 lb therefore confirms engagement and indicates that the BHA is correctly located within the hanger.

The expansion tool is a high-pressure, hydraulically activated, dual-packer expansion device with elastomeric seal rated up to 29,000 psi. After the two seals are activated, high-pressure fluid is pumped between them, and the pressure is increased to first elastically, and then plastically, expand the hanger. Activation of the seals is controlled to ensure seal is maintained until full contact with the parent casing is achieved, Fig. 1. As the pressure continues to increase, the outer casing is elastically strained, until the pre-set final expansion pressure is achieved. The applied pressure is then bled off, and the seals are retracted via a 1,500-psi retract cycle. The seal design incorporates a polymer-sealing element, together with anti-extrusion backup steel fingers.

Fig. 1. The HETS expansion process of an expansion tool inside two concentric tubulars, along with the stress/strain curve of the process.

The downhole hydraulics module can be run with coiled tubing or drill pipe, and is comprised of filters, hydraulic control valves, a pressure intensifier, a mechanical shear release and a pressure data-recording module. The pressure intensifier—a piston type with a 7:1 compression ratio—is used to achieve the final expansion pressure (about 23,000 psi). For any given inlet pressure, the intensifier provides a low-volume, intensified outlet pressure up to 30,000 psi. The inlet to the intensifier is protected via two banks of fluid filters.

The control valve system enables the automatic sequencing of the downhole seal activation and pressurization. The downhole data module is a conventional memory gauge adapted for use in this application.

The hydraulic fluid reservoir was developed to store a supply of clean fluid (usually water, HW443 or HW540) for use in the DHM. The reservoir is typically a few joints of tubing crossed over to the drillpipe above and the DHM below. Once the reservoir joints are made up, they are filled with clean fluid. A wiper dart is installed on top of the clean fluid, and the assembly is tripped into the well on drill pipe. Once the HETS tool is latched into the depth profile, pumping from surface can begin with the wiper dart displacing clean fluid through the DHM.

FIELD DEPLOYMENT

After qualification testing, operations were conducted to set the HETS solid expandable liner hanger in the Eldfisk B-16A well in January 2007. In the end, three runs in hole were made, with modifications to the running procedure and to the expansion tools required to successfully set the hanger. The hangers were picked up when the bit was at 7,615 ft of MD. Drilling then proceeded to a 12,100-ft MD over the next 21 days. Once the BHA was retrieved, the casing was reamed to bottom and cemented in place. Operations to expand and set the liner hanger began.

First run. The HETS BHA was run on drill pipe and then engaged in the latch sub at 4,711 ft of MD. Surface pumps were started, and the pressure began to rise steadily. However, the pressure monitored at surface was not as expected; a constant increase in pressure to 6,200 psi was observed. The expected switching of the tool from retract to set mode did not occur. The most likely explanation was thought to be a blockage either at the DHM or at the reservoir. Once the fluid supply in the reservoir was exhausted, the BHA was recovered to surface and the DHM was function checked; there was no indication that the DHM was working.

Investigation revealed that a pressure differential of about 1,500 psi between the well and the drill pipe (14.3-ppg mud in the well, water in the drill pipe) had caused mud to enter the DHM and reservoir. The mud had contaminated the hydraulics and the pressure had damaged the wiper plug, which had been forced upward against the top crossover. This was due to an exhaust port that experienced a check valve failure.

For the next run, it was decided to replace the water above the reservoir with 14.8-ppg mud to compensate for the hydrostatic differential between the hydraulic fluid in the reservoir and the mud in the well. The plugged HETS tool could not be stripped down and cleaned in the field, so the backup HETS BHA was run.

Second run. With the HETS BHA located in the latch sub, the surface pump was started. The surface pump was a high-pressure/low-volume system with output of about 4 L/min. Pressure rose steadily to 2,200 psi, at which point indication was seen that the tool had switched to set mode, as expected. From there, pressure buildup was as expected, although the actual pressures achieved were somewhat low. The change in pressure gradient normally seen once the hanger comes into contact with the casing was not observed. With 1,000 L pumped (1,200-L reservoir capacity), the operation was halted and the BHA retrieved.

The BHA was function tested at surface and found to be fully operational. Analysis of both the downhole and the surface pressure data identified a possible mechanism for a hydrostatic imbalance within the HETS tool, which would result in the well pressure preventing the tool seals from being activated. Modifications of the HETS tool to ensure pressure balance were devised and carried out offshore.

Third run. With the modified HETS BHA located on depth, the surface pumps were started. After pumping for some time, the surface pressure data gave the expected sign of the downhole tool switching at 2,200 psi, then began to climb in the normal manner. After some time, the surface pressure peaked at 4,900 psi and began to drop off after about 105 min. of pumping, indicating that the downhole relief valve had operated. The system was bled off and the tools pulled out of hole. The liner hanger was then pressure tested to 3,700 psi with mud (equivalent to 5,000 psi with water).

The intended maximum expansion pressure was 23,000 psi above hydrostatic. The downhole data showed that after three cycles of pressurization, the tool had functioned as expected, generating 21,000 psi on the seal line (recorded data minus 3,100 psi hydrostatic), Fig. 2. FE analysis of the hanger at this expansion pressure confirmed that the hanger had been fully expanded and that the 5,000-psi (V0 rated) seal elements were fully engaged. The FE model predicted a hanger load capacity of over 573,000 lb.

Fig. 2. Surface and downhole pressure data during expansion operations (third run).

NEW DEVELOPMENTS

In parallel with this work, an electric line-deployed HETS tool is under development and is scheduled for deployment. This should allow a more efficient operation by eliminating the need to run the HETS tool on the drillstring. Additionally, a variety of other sizes of liner hangers/casing packers are being qualified with expandable technology.