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Home / Issue Archive / 2006 / September #9 / Application of Tatneft’s Expandable Profile Liners in Complex Geologic Environment

№ 9 (September 2006)

Application of Tatneft’s Expandable Profile Liners in Complex Geologic Environment

Since early 1980s, expandable casing strings developed by Tatneft engineers have been extensively used for isolation of trouble zones.

By Shafagat Takhautdinov, Gabdrashit Abdrakhmanov, Khamit Kaveev, Nigmatyan Khamityanov, Nail Vildanov

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Different expandable systems known as expandable profile liners, have been developed and tested, and since the very first application, the work on their improvement has never ceased. The designer addressed a number of issues: applicability and enhanced reliability of expandable profile liners subjected to high pressure differential and high temperature; increased length of expandable profile liners for isolation of lengthy trouble zones in incompetent rocks (e.g., sloughing shales); reduction of time required for the system installation.

Currently expandable profile liner system, referred to as OLKS-216 (Russian acronym which means “equipment for local well casing” with the diameter 215.9 mm), and used for isolation of trouble zones without cementing and without wellbore diameter loss shows the best characteristics: it withstands pressure differential up to 20 MPa and temperature up to 150 C.

The uniqueness of the Tatneft’s expandable systems lies in specific design of expandable pipes: two-channel (or multi-beam) profile along the entire length, while the ends are cylindrical, with the diameter the same as the diameter of the circumscribed circle of the profiled portion. Cylindrical ends are provided with threads to connect pipes with each other and with the drillstring, which runs the expandable profile liner downhole.

The method of expanding the string radically differs from other methods known in the industry, and consists of the following two stages:

1. Simultaneous expansion of the profiled portion of the string (95-97 percent) through 12-14 MPa hydraulic pressure, which is created by injection of drilling mud inside the string. The major benefits of the system are application of profiled pipes and simultaneous expansion of string in the downhole conditions by drilling mud pressure. These are necessary prerequisites for a reliable placement of the expandable profile liner in the project interval of the wellbore, and any displacement of the profile liner in either axial or radial direction once the profile liner has been set in place and expanded by hydraulic pressure, is next to impossible.

2. Mechanical expansion of the cylindrical threaded ends (3-5 percent of the total length), once the expandable profiled string has been straightened and tightly pressed to the formation face, through either radial expansion with roller and cutter expanders, or through top-down pulling of special mandrels, or expansion cones.

The above features ensure one hundred percent passability of drilling tools once the expandable profiled string has been set in place.

However, troublesome geology and complexity of in-situ conditions, as well as inappropriate mechanical expansion tools, may bring about certain wellbore problems, and fighting those emerging challenges would require additional time and money. Such situations are not infrequent in sloughing shales.

Our experience of lost circulation isolation in incompetent rocks – Well No. 41-KL in the Iranian Kupal oil field – may serve a good example and warn operators against possible mis-steps.

Fig. 1a shows typical well design in the Kupal field. After casing of the abnormally high-pressure Gacharan formation with 9 5/8-inch string, the underlying Asmari formation is typically drilled-in with 8 3/8-inch bit (212.7 mm) with 63 psf (1.02 t/cu. m) drilling mud, and isolated with 7-inch liner (177.8 mm). 6 1/8-inch bit (155.6 mm) is used for exposing Pabdeh and Gurpi formations. Pabdeh is drilled with 81.5 psf mud (1.3 t/cu. m), while for drilling the Gurpi formation operator has to raise the mud weight to 97-104 psf (1.56-1.67 t/cu. m) and add LCM. 5-inch liner (127 mm) is run through these two formations. The Bangestan reservoir – final target – is drilled with 4 1/8-inch bit (104.8 mm) with 82.5 psf mud (1.32 t/cu. m), and completed openhole.

Drilling with 4 1/8-inch bit involves a lot of problems, both during drilling and production phases, as well as future well intervention operations. The task set before the expandable profile liner technology – to substitute 4 1/8-inch bit (104.8 mm) for 6 1/8-inch (155.6 mm) – was successfully accomplished. Expandable profile liner with the length 434.5 m was set in Well No. 41-KL (Fig. 1b), however, the services provider, Tatneft, has spent twice as much time as planned. The reason for this was unexpected complications attributed to complex geological environment. The exposed rocks were, generally, shales, and drilling was accompanied by sloughing, cavern washouts, and, in some cases, tight hole. To allow for all these contingencies the services provider and the operator had to revise the project several times.

Fig. 2a and 2b present the original and the actual projects. According to the project suggested by Tatneft, the Asmari formation had to be isolated with two expandable profile liners: 120.5 m-long section had to be set in the expected gas show zone, and the 331-m long section, connected with the first expandable profile liner, run to the Asmari bottom.

The original project provided for installation of the 1.5-m long box-type pup joint with 232-mm ID in the lower portion of the 9 5/8-inch casing string, to which the upper section of the first expandable profile liner had to be connected.

However, in the process of 9 5/8-inch string drilling the operator faced with troubles that would have made free running of the string and setting of the thin-wall box-type pup joint rather problematic. It was decided to run the 9 5/8-inch string without the pup joint and without connecting the expandable profile liner to the string. Caverns that would be formed in the process of drilling with 8 3/8-inch bit (212.7-mm) had to be cemented.

The original project also provided for drilling with 8 3/8-inch bit (212.7-mm) with simultaneous reaming of the wellbore, which had to be attained through the use of near-bit-expandable underreamer. In this case expansion job would have been excluded, and the operator would have had enough time to set an expandable profile liner before the shales started to slough.

But since the operator had no experience of drilling with simultaneous underreaming in Asmari, it declined the idea. It was decided first to drill the interval with 8 3/8-inch bit (212.7-mm), and then ream it with the expandable underreamer.

Once the Asmari formation had been penetrated, the well was logged, and according to log analysis interpretation, gas show zone has not been recorded. This made us alter the project once again and run the expandable underreamer through the whole exposed interval with the following setting of 434.5-m long expandable profile liner per one trip.

All these deviations from the Tatneft’s original project led to significant loss of time and gave rise to future problems.

Fig. 3 and 4 present caliper logs before and after reaming; after cementing below the 9 5/8 string shoe; after drilling out of cement plug; and before repeated reaming of tight hole sections.

Caliper logs showed that delay in operations had an adverse effect on the wellbore status: caverns enlarged in diameter and tight spots appeared in the already reamed wellbore interval. This was another evidence in support of our assertion that time plays a pivotal role when we are dealing with sloughing rocks.

After repeated reaming of the tight sections, setting the profile liner in place and inflating it with mud pressure, it was expanded with 211-mm rigid mandrel. Still, restriction of the borehole and squeezing of the profile liner, at that time not expanded up to 216 mm, continued. Assembly for repeated expansion of the profi le liner included the same 211-mm rigid mandrel, this time used as a centralizer, and 216-mm expandable cone. At a depth of 3,497 m the rigid mandrel stuck. The rig pulled out the collapsible 216-mm cone, and as for the stuck mandrel, it was recovered by reciprocation and rotation of the drillstring under different loads (up to 200 tons).

Release of the stuck tool was complicated by falling out of cement from the cemented caverns below the 9 5/8 string shoe. This is evident from the caverns’ sizes in Fig. 3 and caverns’ sizes above the profile liner in Fig. 6. Besides, the pulled out tools were blocked with cement.

Once the mandrels have been pulled out of hole, the profile liner’s ID was sized with the 213.5-mm single-roller expander.

Fig. 5 presents caliper log of the interval of mandrel sticking after the expandable profile liner has been installed in place. One can see how the profile liner was indented into the cavern, which happened while releasing the stuck tool. However, because of good bond between the profile liner and the wellbore walls created by expansion with hydraulic pressure, the profile liner was able to withstand loads associated with reciprocating and rotating the drillstring, and future drilling with 212.7-mm bit was made possible.

To prevent leakage, that would have taken place during pulling out of the stuck tool, it was decided to inject cement slurry in the expandable profile liner setting interval. Cement slurry was squeezed under 20 MPa pressure. The top 250 m of the expandable profile liner were cemented. Cement plug inside the profile liner was drilled out with 212.7-mm hard-alloy button rolling-cutter bit.

Notwithstanding all unexpected complications, the expandable profile liner was successfully set in the 3,341-3,775.5-m interval (Fig. 2b); Pabdeh and Gurpi formations were drilled through with 8 3/8-inch bit (212.7-mm) with flushing with weighted drilling mud according to the project, and cased off with 7-inch liner (178-mm). The well was drilled to the projected depth with 6 1/8-inch bit (155.6 mm) without further problems (Fig. 1b).

Similar jobs were performed by Tatneft in three more wells in China. Expandable profile liner with the length 62.6-m was installed in the 2,452-2,414.6 m interval in Well No. L7-71, operated by Tuha Company, and two jobs were performed for Shengli Petroleum Group Corporation: trouble interval (1,452-1,486 m) was isolated with expandable profile liner in Well No. 3-8-N/N-216, and in Well No. 2-5-238 expandable profile liner shut off water producing zone in the 1,772-1,822 m interval.

For mechanical reaming and sizing of the expandable profile liner in all the above wells single-cutter and roller expanders were used.

A new task set before the team of Tatneft scientists and engineers was to cut time spent on casing off of trouble zones. The solution is seen in expandable systems set in hole per one trip. Such expandable systems have been developed and currently they are being tested in Tatarstan oil wells. To date one-trip expandable profile liner has been set in three wells. In the first application all operations including wellbore reaming, well logging, running of 49-m long section of expandable profile liner in the preset interval and expanding it with pressure, were completed in 27 hr. In two other wells operations took 40 hr, and the lengths of expandable profile liner sections were 67 m and 66 m, respectively.

Tatneft has gained an invaluable experience of expandable systems usage in complex geologic setting. Our experience shows that:

1. Cementing of washouts before setting an expandable profile liner is not a viable option. Eventually it results in additional problems. In case the project provides for trouble interval isolation immediately below the 9 5/8 string shoe, running of a box-type pup joint and extension of the casing string from bottom is a must. For such special applications thick-wall custom-made pup joints are available, whose strength properties are compatible with those of 9 5/8 string.

2. When isolating trouble zones in sloughing shales, drilling with simultaneous reaming of the wellbore with expandable underreamer is the best solution. This excludes additional reaming operation, thus saving time, which is the most critical factor in incompetent rocks.

3. Rigid mandrels are not fit for mechanical reaming and sizing of the inside diameter of the expandable profile liner. For this purpose expandable cones or roller/cutter expanders shall be used.

4. Thief zones in incompetent rocks, such as sloughing shales, shall be isolated with expandable systems set in place per one trip, immediately after exposing of the trouble interval.
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