Mitigating drilling hazards with solid expandable profile liners (Jul-2009)

Expandable systems have been used in the FSU for lost circulation since 1978.  

Shafagat F. Takhautdinov and Nail G. Ibragimov, Tatneft; Ravil R. Ibatullin, Gabdrashit S. Abdrakhmanov, Farit F. Akhmadishin and Nigmatyan G. Khamityanov, TatNIPIneft 

Tatneft has been successfully using its Expandable Profile Liner (EPL) technology since the late 1970s. The technology has eliminated drilling hazards not only in Tatarstan––the primary area of the company’s activity––but also in other Former Soviet Union (FSU) countries and abroad.

DRILLING DEEP WELLS

Nowadays, total well depths tend to increase, and the number of intermediate casing strings in the conventional telescopic well design also increases. The deeper the well, the greater the number of formations it passes through. Each formation is characterized by particular strength, in-situ pressure (may be abnormally low or high), fluid content, etc., which are translated into certain drilling hazards––such as differential pipe sticking, sloughing and caving, lost circulation, unwanted water and gas flow.

Incompatible formations have to be isolated with intermediate casing strings, with each casing string adding 30–40% to total well cost. World well construction practice shows that when drilling wells with total depth of 4,000–5,000 m (13,000–16,500 ft) in a complex geologic environment, five to seven telescopic casing strings are run. The cost of such wells is an order of magnitude higher compared to wells with 2,000–2,500-m (6,500–8,200-ft) TD and a regular well design. Besides, excessive use of intermediate strings drastically downsizes the final diameter, resulting in challenging completion and production.

NEW SOLUTION

The company’s first research program dealing with the problem of effective zonal isolation dates back to 1975. In 1978, it successfully attempted a new approach to zonal isolation with expandable (enlarged in the cross-section) casing pipes.^1,2 The prime objective was to find a way to place the same diameter protective casings successively without cementing and with no loss of hole size. Expandable systems made it possible to decrease completion complexity and to improve bed isolation, thus solving two of the most acute well problems.

In the following two decades, solid expandable systems were installed in more than 600 wells. The technology of well drilling with one size of bit and successive isolation of trouble zones with expandable protective casing has been given the name Expandable Profile Liner (EPL) and has been patented in Russia and 13 other countries.³ To date, Tatneft’s expandable technologies have obtained more than 40 Russian and 57 foreign patents.

Since the early 1990s, the company has been presenting its expandable technology in specialized international conferences and oil and gas shows, and has published a number of papers in foreign journals. In 1999, the largest companies involved in the oil business started research in this area, and in a very short period of time it became evident that expandable tubulars represented a revolutionary change for standard oilfield practice. Shell, Baker Hughes, Halliburton, Weatherford and other leading companies patented and started early commercialization of their expandable products. By this time, Tatneft had solved one of the most arduous drilling troubles––lost circulation––and the effectiveness of the expandable technology was proved by numerous successful field applications in the FSU. In a large number of wells, two and three expandable systems have been installed without reduction in wellbore size.

Broad hands-on experience gained by the company while solving lost-circulation problems facilitated further research. It revealed the huge potential of this method and concentrated efforts to find how it could be used to provide effective remedies for other well problems.

EPL BOTTOM EXTENSION

The situation is seriously aggravated when the casing cannot be landed to the project depth. Attempts to run casing strings to the required depth during well construction sometimes fail because of filtercake buildup, or sludging, rock sloughing and wellbore stability issues. Such problems often result in numerous isolation jobs, and sometimes require the shutoff of problem intervals with intermediate casing strings and liners. This results in loss of wellbore diameter, more complicated wellbore designs, increased consumption of tubulars and cement, plus added capital investment and time.

In 1984–1985, a method of casing string extension from bottom without ID loss using EPL was developed. In 1985, the operating company extended the casing string length by 29 m (95 ft) in the West Siberia Verkhne-Katangskaya area Well 160 to solve a difficult lost-circulation problem, saving a wellbore considered for abandonment. EPL was installed from the bottom of the 219-mm (8.62-in.) intermediate casing string and run to 2,634 m (8,642 ft), retaining the same borehole diameter. This was the first casing expansion in the world.⁴ In the following years, numerous applications testified to the high effectiveness of this technology. Apart from its primary objective––isolation of lost circulation zones––it was used to solve common drilling problems, including gas flow, well stability issues and casing off of branching intervals, Fig. 1.

Fig. 1. In October 2004, an EPL cased off the branching interval in Well 221A.

REPAIR WHILE DRILLING

Another application involves casing string integrity restoration, which allows drilling ahead with the same size bit. In 1985 in Lithuania, Well Genchai-2 used a 41-m (134.5-ft) EPL with wall thickness of 8 mm (0.32 in.) to case off damaged 219-mm (8.62-in.) casing in the interval 214–236 m (702–774 ft). The well was drilled to TD with the same size bit, 190.5 mm (7½ in.).⁵

In 1987, Well 51 for a Pechora oil and gas enterprise had the integrity of 245-mm (9.64-in.) casing string restored with 42.5 m (139 ft) of EPL. In 1989, Yamalneftegasgeologia’s Well 35 used 14 m (46 ft) of EPL to restore the integrity of a leaking 219-mm (8.6-in.) casing string.⁵ In 2004, Nadymgasprom’s Well  50 used two expandable systems to restore two damaged intervals of 245-mm (9.64-in.) casing: 2,435.9–2,459.4 m (7,992–8,069 ft) and 1,564.5–1,587.5 m (5,133–5,208 ft). After the EPL was installed, the casing string was successfully pressure tested with 35 MPa.

WELLBORE STABILITY

Lack of wellbore stability produces many mechanical and log interpretation problems and adversely affects the overall well economics. In 1989, Tatneft started a project aimed at a mechanical solution for wellbore stability problems in inclined and horizontal wells using expandable systems. An EPL, installed in the Pavlovskaya inclined Well 28852, successfully solved violent sloughing and caving issues. Caving was also controlled when drilling through the shales of the Kynovian horizon. In 1995, an EPL with 144.5-m (474-ft) total length, installed in horizontal Well 39454, successfully cased off incompetent rocks.

Producing horizontal Well 1623 of Bastrykskoye Field presents another example. Production was impossible because of sloughing shales. The operator’s attempts to solve the problem by cementing failed. The trouble zone was isolated with 17.6 m (57.7 ft) of EPL in just 32 hr, and the well continues producing oil at 10.3 tons/day, Fig. 2.

Fig. 2. Sloughing shales were isolated in Well 1623G during 2005.

EXPANDABLE LINER HANGERS

In 1991–1992, the company developed expandable liner hangers for horizontal sidetracks, which were installed in two wells.⁵ In contrast to commercially available hangers, expandable counterparts have a simplified design, are more reliable and are less expensive.

MINIMIZING FORMATION DAMAGE

In 1994, two new expandable technologies were added. The company began using EPL to protect overlying potential producing formations as soon as they were drilled, minimizing formation damage from drilling fluid invasion and cement slurries, Fig. 3. Wells completed with EPL are producing at rates 1.4–2 times the rate from wells completed with conventional cemented liners.

Fig. 3. a) The Bashkirian and Tournaisian producing intervals were sealed with EPL in Well 3484. b) A non-cementable EPL completion was used in Well 2586.

HIGH-PRESSURE WATER FLOW

In 1996, the company developed technology and relevant expandable equipment for water influx shutoff within the horizontal wellbore sections. In 1997, the technology was successfully field tested in Tatarstan Well 11251. The well had been suspended for two years because it produced water. After remediation jobs using expandable systems, the well was put on production. It still produces oil at 18–20 tons/day.⁶

EMERGENCY SITUATIONS

Application of any novel technology that has not yet become a routine industry practice is fraught with either errors, emergency situations from in-situ conditions or both. Such emergencies call for relevant response. New methods and equipment to solve the emerging problems thus need to be developed, leading to maturation of technology.

EPL FROM THE TOP

It may happen that because of incorrect setting in a well, interpretation or other errors, the upper portion of a trouble zone remains uncased. If this happens, the EPL has to be expanded from the top to case off the problem interval.

As far back as 1978 in the Abdrakhmanovskaya area, Well 14124 had an EPL set in the 908.4–956.6-m (2,980–3,138-ft) interval. The internal well diameter was partially reduced and the well was drilled to TD with a 190.5-mm (7½-in.) bit. However, the size of the production string remained the same, 146 mm (5.74 in.). The well tests after remediation showed the same lost-circulation rate, though the cavernous interval had been isolated, Fig. 4a. The operator wasted 24 days on futile isolation jobs using conventional methods, and after well logging decided to run a 16.8-m (55-ft) section of EPL and connect it to the first one. After successful installation, the well was drilled to the projected total depth of 1,731 m (5,679 ft) with a 190.5-mm (7½-in.) bit without any complications. It took just seven days to install two jointed sections of EPL.¹ 

Fig. 4. Emergency situations can be overcome with EPL. a) Extension of EPL from top in Well 14124; caliper logs before and after installation of two EPLs. b) Repair of EPL in Well 2601. c) Dealing with multiple emergency situations in one well.

REPAIRING DAMAGED EPL

In Zaikinskaya Field, Orenburgneft’s Well 2601 had two cavernous zones with difficult lost circulation at 3,268–3,288 m (10,722–10,787 ft) and 3,326–3,351 m (10,912–10,994 ft). During 15 months, the operator fought the problem using conventional lost-circulation materials, but failed to control the trouble zone. The well with 3,383-m (11,099-ft) MD was considered for abandonment. Tatneft suggested saving the wellbore with EPL. Engineers decided to install two sections, beginning from the lowermost trouble interval. However, the first section could not be run to the required depth because of sticking in the upper lost-circulation interval caused by sludging.

The EPL stuck in the 3,265–3,321-m (10,712–10,896-ft) interval was straightened by fluid pressure, and the expander pressed it tightly to the wellbore walls, Fig. 4b. Well tests showed that the upper trouble interval was effectively isolated. To isolate the lowermost trouble interval, EPL was installed from 3,323 to 3,354 m (10,902–11,004 ft). Trouble-free drilling continued with a 190.5-mm (7½-in.) bit. The well was deepened for an additional 949 m (3,114 ft), and after 840 hr of on-bottom time, lost circulation resumed.

Downhole survey and well logging showed EPL breakdown at 3,293 m (10,804 ft). To restore the seal with zero wellbore diameter loss, the upper EPL was drilled out with single-cutter bits to 3,295 m (10,810 ft) and a new 42-m (138-ft) EPL was added. After setting the liner, the well was drilled with a 190.5-mm (7½-in.) bit for another 306 m (1,004 ft) to 4,638 m (15,217 ft) of TD. Total cost of all operations, including preparation of three EPL sections and drilling out 30 m (98.4 ft) of pipe, was 10 times less compared to the cost of “trial” isolation.

The most valuable features of using EPL extension from the top are that the ID of the liner is not lost and that the jointed ends fit together and are effectively sealed.

REMEDIATING LOST CIRCULATION AND SLOUGHING

Difficult lost circulation, accompanied by formation sloughing, drag and sticking of drilling tools, is one of the most serious drilling hazards. Caving problems prevent drilling-in the lost-circulation interval, since when the mud pump is stopped to make a connection, the last pipe gets stuck. Solving such problems involves much time, heavy expenses and, not infrequently, all efforts go unrewarded.

Tatneft developed a method to extend the EPL from the bottom in 1993, and the technology was first applied in the Garaevskaya area Well 202. This well had difficult lost circulation accompanied by severe formation sloughing that caused caving and BHA sticking. EPL solved the problems without sacrificing any wellbore diameter. After two sections were installed, more than 2,000 m (6,560 ft) were drilled without any problems.⁴

COMBINATION TROUBLES

Operating companies occasionally face multiple emergency situations, which have to be promptly handled to save the wellbore. This was the case with Samaraneftegas’ Well 95 in the Zapadno-Kommunarskaya area. The well penetrated a severe lost-circulation zone accompanied by sloughing rocks, which caused BHA drag and sticking. The vugular interval 2,556–2,620.4 m (8,386–8,597 ft) was shut off with a 64.4-m (211.2-ft) EPL with no loss of ID.

The hole was deepened for 100 m (328 ft), first with partial, and then with total circulation loss. The second EPL, with length of 109 m (357.6 ft), was installed by extending the first one. An overexpanded shoe at the bottom of the first EPL was provided for that purpose. The two liners were tightly joined, creating a single-diameter junction. The trouble interval 2,619–2,728 m (8,593–8,950 ft) was successfully shut off, and, again, the wellbore diameter was not reduced, Fig. 4c.

When deepening the hole, difficult lost circulation resumed. The second EPL installed did not provide for a bell bottom section, and the third EPL, with length of 74.5 m (244.4 ft), partially reduced the wellbore ID. A subsequent 190.5-mm (7½-in.) bit was used to deepen the hole.

In the process of further drilling, there again was loss of returns. A downhole survey showed that the thread connections of the first liner were damaged, causing leaks. The whole length of the first EPL and the overlying cavernous interval were shut off by a fourth liner with length of 95 m (311.6 ft), Fig. 4c. The well was drilled to project TD with no further problems. Even though four EPL were installed, the well was completed with a 146-mm (5.74-in.) production casing string––the original project size.

Well 818 WT in Vietnam, which had extremely difficult drilling problems,⁴ Well 41 in the Iranian Kupal Field,⁷ and Alimovskaya area Well 35 operated by Tatneft-Samara ZAO (Fig. 5) present perhaps the most prominent examples of high-efficiency expandable technology in complicated in situ conditions.

ALIMOVSKAYA AREA WELL 35

When the BHA reached the measured depth of 1,961–1,964 m (6,434–6,444 ft) it began to get stuck and partial loss of returns started, and at a depth of 1,969 m (6,460 ft) complete loss of circulation occurred. Drilling mud was displaced with water; however, this led to strong water inflow with the rate of 60 m³/hr. The operator attempted cementing to control the thief zone. In the first cementing job, 15 tons of cement was pumped, then another 18 tons in three more jobs was added. After drilling out, drilling was continued with 10–40% returns. At 2,079-m (6,820.8-ft) MD, the BHA got stuck.

In the process of remediation operations, drill pipe broke away. At 1,985-m (6,512.4-ft) MD, the unrecovered pipes were sidetracked, and the new wellbore was deepened to 2,188 m (7,178.4 ft) with 80% returns. At 2,207-m (7,240.8-ft) MD, drilling fluid returns to surface stopped. The operator tried to regain circulation by cementing and drilling with aerated fluid. Drillers succeeded in deepening the hole to 2,259 m (7,411.4 ft) with 20–40% returns. Two thief zones were shut off with EPL without reducing wellbore diameter.

The first liner successfully shut off the 2,156–2,223-m (7,073–7,293-ft) interval. While under-reaming to install the second EPL, the bit with the under-reamer got into a cavern, which led to the loss of the wellbore. At 2,041 m (6,696 ft) the BHA spontaneously sidetracked the third wellbore. At 2,107-m (6,912.7-ft) MD the second EPL was installed to case off the 1,925–2,074.3-m (6,315.6–6,805.4-ft) trouble zone. At 2,149-m (7,050.5-ft) MD, the third EPL was installed from 2,077 to 2,126 m (6,814.3–6,975 ft).

However, when expanding the threaded connections of the third liner with the fit-for-purpose expander, the latter got stuck at 2,105 m (6,906 ft). Fishing operations were a failure—the expander broke and a roller cutter was left inside the liner. To save the well, the operator decided to sidetrack a new hole (the fourth) from the shoe of the second EPL. A whipstock of TatNIPIneft design, which uses an expandable, shaped pipe as an anchor, was used to mill a window through the EPL from 2,060 to 2,064 m (6,759–6,772 ft).

While further deepening the hole, another lost-circulation zone was penetrated. At 2,093 m (6,866.8 ft) returns to surface stopped. Voids in rocks occurred from 2,093 m to 2,095 m (6,866.8–6,873.3 ft) and from 2,097 m to 2,098 m (6,879.9–6,883.2 ft). At 2,156-m (7,073.4-ft) MD, circulation was regained by casing off the lost-circulation zone by the fourth EPL installed in the interval 2,074–2,121.8 m (6,804.4–6,961.2 ft). In the process of further deepening the hole, returns dropped to 70%, and at 2,192 m (7,191.6 ft), there again were no returns. Circulation was restored by the fifth liner set in the interval 2,143–2,211.6 m (7,030.8–7,255.9) at 2,262-m (7,421.2-ft) MD. The well encountered several more trouble zones—lost circulation, BHA drag and getting stuck––all of which were shut off by two more EPLs. The sixth liner was installed at 2,282-m (7,486.8-ft) MD from 2,213 to 2,274 m (7,260.5–7,460.6 ft) and at 2,372-m (7,782-ft) MD it was extended from the bottom, forming the seventh EPL. The well was drilled to the project total depth, Fig. 5.

Fig. 5. Seven EPL were used on Well 35 to solve multiple drilling hazards.

Never before in the international drilling practice have so many expandable systems been installed in one wellbore. Multiple drilling hazards were eliminated with zero loss in the wellbore ID.

Our experience proves that telescopic sequences of liners and casing strings can soon become history, inasmuch as EPL technology is working toward a well with the same diameter casing from surface to bottom—a single-diameter well. This technology has become a standard Tatneft tool to solve drilling problems.  

LITERATURE CITED

¹  Abdrakhmanov, G. S. and A. G. Zainullin, “Lost circulation control by use of steel profile liners,” Neftyanoye Khozyaistvo, No. 7, 1981, pp. 19–23.

²  Abdrakhmanov, G. S., Safonov, Y. A. and A. G. Zainullin, “Isolation of lost circulation zones with steel pipes without wellbore diameter loss,” Neftyanoe Khozyaistvo, No. 4, 1982, pp. 26–28.

³  Abdrakhmanov G. S. et.al., “Method of construction of multiple-string wells,” US Patent No. 4,976,322, Dec. 11, 1990.

⁴  Takhautdinov, S. F., Abdrakhmanov, G. S., Kaveev, K. Z. and N. K. Khamityanov, “Liners extend casing length without wellbore diameter loss,” Oil and Gas Journal, Aug. 12, 2002, pp. 41–43.

⁵  Takhautdinov, S. F. et. al., “Tatneft expandable technology: Track record and range of expandable products,” Oil & Gas EURASIA, No. 4, 2007, pp. 50–55; No. 5, 2007, pp. 32–39.

⁶  Takhautdinov S. F. et. al., “Expandable liners isolate water influx from directional, horizontal wells,” Oil and Gas Journal, Aug. 19, 2002, pp. 53–56.

⁷  Abdrakhmanov, G. S., Khamityanov, N. K. and N. N. Vildanov, “New expandable-profile liners used in Iran, China, Tatarstan,” Oil and Gas Journal, April 3, 2006, pp. 45–50.
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