Tatneft’s Expandable Systems Isolate Cavernous, Lost Circulation Intervals While Drilling

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Such problems often result in numerous isolation jobs, sometimes require shutoff of problem intervals with intermediate casing strings and liners with the resulting loss of wellbore diameter, more complicated wellbore designs, increased consumption of tubulars and cement, added capital investment and time.

Unknown or incorrect depth information of incompatible formations can bring errors in casing string length or set point and create similar problems. Sometimes separate casing strings are used to isolate formations, which are incompatible under drilling conditions, even if the zones are thin or a short distance apart.

Tatar Oil Research and Design Institute (TatNIPIneft) has developed a unique technology, allowing for local isolation of formations, using steel casing run in the trouble zone, without cementing and without loss of wellbore diameter.

This unconventional technology, which has got the name of expandable profile liner, or local well casing with expandable pipes, employs steel casing made from a proprietary alloy with the diameter exceeding the hole size. The expandable profile liner is profiled through its length to allow for free run in the trouble zone. The wellbore in the problem-zone interval is enlarged by expandable underreamers to the external diameter of the initial nonprofiled casing string. After that the expandable profile liner is run into place across the problem formation interval with a designed for purpose bottomhole assembly and drill pipes. Once the expandable profile liner is in place, drilling mud is injected, thus creating pressure to straighten and to inflate the profile liner to the full working diameter of the wellbore. After the profile liner has been tightly pressed against the underreamed formation face, a specially designed expander is run through for final sizing of the system. The profile liner uses packer elements to establish a seal with the casing above and at the end sections.

Expandable profile liners have been installed in more than 1,000 wells as an alternative to running intermediate casing strings and successfully solving lost circulation and wellbore stability problems, regardless of severity or the size of wellbore washouts. However, sometimes lost circulation is complicated by drag and sticking of the drillstring bottomhole assembly. To solve such issues TatNIPIneft has advanced the technology of local well casing to extend casing strings with expandable profile liners from bottom.

The operating company Samaraneftegaz had pioneered application of the expandable profile liner technology to case off a difficult lost-circulation zone, with accompanied BHA sticking problems, in Garaevskaya area Well No. 202. Difficult lost-circulation problems occurred at 353-366.5 m, when the 215.9-mm (8 1/2 in.) hole section was drilled. Sloughing of the wellbore accompanied the lost circulation, causing the drillstring and BHA to drag and get stuck.

Drilling the well deeper was impossible. Operations to regain circulation conventionally with lost-circulation material continued for 34 days but failed and the operator decided to use expandable profile liners to attempt shutting off the problem zones.

Fig. 1 shows the sequence of operations. First, an expandable underreamer, referred to as RRM 216/234, was run to ream the interval 341-370 m, opening the hole to 234 mm per one trip. Then the 16-meter long section of expandable profile liner was run and set it in the interval 345-361 m (Fig. 1a). After that pressure was applied through the drillstring to straighten the liner to its final cylindrical shape. This operation had pressed the expandable profile liner walls tightly against the wall of the reamed section of the wellbore above the washout, which was checked by pulling on the drillstring. Rotating the drill pipe to the right the liner-setting tools were disconnected from the profile liner that had been set and the rig tripped the drillstring out of the well. After that expanders, referred to as RSh-196, RSh-208, and RSh-218, expanded the profile liner fully to its final 218-mm ID. The next operation provided for enlargement of the lower 1 m of the profile liner to 232 mm using an expanding tool. Then a three cone, 215.9-mm drillbit cleaned out a cement plug and continued drilling to the bottomhole.

Using the same technology a lower section 8.5-m long (one joint of pipe) profile liner was run. This profile liner was set in the interval 360-368.5 m, overlapping the lower end of the first profile liner by a length of 1 m (Fig. 1b). Thus, the profile liner setting operations took only 60 hr.

This job was the first interval isolation of a sloughing, lost-circulation zone using two expandable profile liners connected tightly between each other in the well without cementing and without loss of working wellbore diameter. Upon isolation of the problem zone the well was drilled to its final total depth of 2,670 m without further problems. The drilling operations were completed in 836.7 hr and 19 bit trips.

Building on the experience of extending casing strings by adding expandable profile liners at the bottom, Tatneft applied the technology to Vietnam White Tiger oil field Well No. 818WT, which had extremely difficult lost-circulation and wellbore stability issues.

Lost-circulation zones in the Lower Miocene, which included intense sloughing intervals, had complicated drilling operations. The well was suspended and shut-in for three years because of the continuous problem of the drillstring getting stuck.

Through arrangement between Tatneft and VietSovPetro JV, the companies agreed to run a 210-m expandable profile liner that would case off all of the lost-circulation Lower Miocene zones and resolve the drillstring sticking issues.

In the process of conditioning the borehole prior to running the expandable profile liner in the interval 3,287-3,496 m, however, the operator faced the following operational problems:
– Continuous drag and jamming of the drilling tools occurred, when conditioning the wellbore or circulating mud in the interval 3,287-3,564 m. Violent sloughing and hole caving led to drillstring got stuck, and it had to be pulled using jars.
– The drillstring and BHA could only be run freely to 3,350 m and further running was possible only with flushing and conditioning of the borehole. To pull the drillstring through the interval 3,550-3,369 m, every other joint pulled from the wellbore had to be circulated.

In light of these problems, it was decided to isolate the entire interval by setting expandable profile liners in two stages:
– The first stage profile liner isolated the most severe lost-circulation and washed out intervals from 3,287 m to 3,405.5 m (118.5 m). The profile liner isolated three severe washouts or caverns that were 80 m, 8 m, and 21 m thick, individually (109 m total), Fig. 2a.

Fig. 2 shows the well caliper log and details of the two profile liners.
– The second stage profile liner isolated five smaller washouts from 3,405.5 m to 3,496 m, which individually were 14 m, 8 m, 13 m, 11 m, and 10 m, thick (56 m total) in the interval 3,405.5-3,496 m, Fig. 2b.

For the first profile liner operations began by milling the inside wall of the lower end of the 9 5/8-in. casing from 223 mm to 234 mm, in the interval 3,282-3,287 m.

Then RRM 216/234 expandable underreamers reamed the openhole interval 3,287-3,415 m, performing the job in two trips to replace worn cutters. Intense sloughing required simultaneous mud circulation and hole conditioning during the reaming operations.

After the wellbore had been conditioned t o 3,415 m with a BHA that included a one-blade spiral gauger, the profile liner was assembled and ran to 3,405.5 m leaving a 3.5-m overlap with the 9 5/8-in. casing. A cementing unit applied up to 10 MPa pressure to the drillstring, straightening out the profile liner. Turning the drillstring to the right the drillstring assembly was detached from the profile liner, leaving it in place. RSh-196 expander, which was run on the drillstring, successfully expanded the profile liner. Subsequent runs with the one-roller (RSh-216) expander and the three-roller (RR-170/218) expander further extended the profile liner’s diameter.

For the second profile liner operations began with reaming and conditioning the openhole interval 3,405.5-3,511 m. Expandable underreamer reamed and prepared the bottom 1 m of the first profile liner in the interval from 3,404.5 m to 3,405.5 m, opening the section to 232 mm ID.

No problems were encountered while running in the second 91.5-m long profile liner. The liner was set successfully with 10 MPa expansion pressure. The liner’s stability was checked, the running tool detached and pulled out of the hole.

The second profile liner was expanded in the interval 3,405.5-3,496 m using RSh-196 and RSh-216 single-roller expanders and the RR 170/218 three-roller expanders. The top 1 m of the second profile liner was tightly connected to the bottom expanded end of the first profile liner.

Casing off the Lower Miocene formations with the two profile liners, tightly joined with each other and to the 245 mm casing string allowed drilling operations to raise the mud weight to 1.64 t/cu. m (13.7 ppg). This created a pressure differential on the profile liners of 19 MPa.

The operator continued drilling the 215.9 mm hole section of the well to 4,010 m, entering the Upper Oligocene. The 194-mm liner was run and cemented in the interval 3,210-4,010 m with no problems. Since 2001 this well has been on stream.

Expandable profile liner technology, or local well casing technology, has been successfully used for shutoff of lost-circulation zones, control of drilling-tool sticking problems, as well as for interval isolation of washed out or cavernous zones by extending the bottom of casing strings and expandable profile liners without cementing and without loss of wellbore diameter.

The following paper addresses Tatneft’s experience of application of expandable systems for isolation of sloughing shales accompanied by difficult lost circulation in the Iranian Kupal field and in three Chinese wells.
 

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