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Tatneft Expandable Technology: Track Record and Range of Expandable Products
Continued from Part 1 published in OGE #4, 2007
In 1988, we started to use the expandable technology to case off caving formations penetrated by slanted wells and to control caving and well stability issues when drilling horizontal wells through the Kynovian formation targeting the Pashiyan deposits.
The first experience was horizontal well No. 39454 targeting the Pashiyan formation, where incompetent rocks within the Shugurian and Kynovian horizons were cased off with the 144.5-m long profile liner (Fig. 3a).
Well No. 1623 "G" of Bastrykskoye oil field presents another example. Caving problems occurred after the horizontal wellbore had already been drilled. Attempts to isolate caving by cementing failed. Finally, the problem was solved after 32 hours with a 17.6 m long expandable profile liner. The well is still producing 10.3 tons of oil per day (Fig. 3b).
Influx from low permeability overpressured zones saturated with high-salinity water may cause serious troubles, such as an increase of drilling mud salinity, mud coagulation and increased water loss of the drilling mud resulting in filter cake buildup, which in turn is the cause of drillstring jamming and sticking issues. In such cases mud has to be replaced, which means added capital investment and time.
In 1990, we successfully applied the technology of water producing intervals shutoff. Expandable profile liners had cased off zones responsible for high-salinity water influx from low-permeability overpressured zones of the Aleksinsky horizon in four inclined wells in Tatarstan's Bavlinskaya area without loss of working wellbore diameter.
Another expandable product is a screen hanger, developed in 1991-1992. It was first applied in Tatarstan's two horizontal sidetracks. Commercially available screen hangers are rather complicated in design, not always reliable, and much more expensive compared to profiled hangers (Fig. 3c).
Drilling operators often face the problem of lost circulation complicated by intense sloughing which causes drag and sticking of the drillstring and bottomhole assembly (BHA). Caving and sloughing in the process of deepening often make it impossible to drill through the lost circulation zone, since drill pipes get stuck as soon as the mud pump is stopped. Fighting such problems calls for immense effort and time, which not infrequently come to nothing.
Our technology of extending expandable profile liners from bottom, developed in 1993, successfully solves such problems. For the first time in international practice the technology was applied in the Garaevskaya area Well No. 202 operated by Samaraneftegaz. The operator encountered a difficult lost-circulation zone with accompanied BHA sticking problems. Drilling deeper was impossible.
Two expandable profile liners installed in a row and connected tightly between each other in the well successfully isolated sloughing in the lost-circulation zone without loss of working wellbore diameter. Upon isolation of the problem zone, the operating company drilled another 2,000 m to the well final TD without further problems.
Wells in many oil and gas fields pass through permeable zones, many of which have commercial hydrocarbon volumes that must be preserved for future production. However, primary consideration is the main pay. When drilling and completing producing formations, various techniques, such as balanced and underbalanced drilling can be applied. Certain regulatory requirements and environmental policies may also govern specific well completion activities.
For example, in the Republic of Tatarstan when drilling into the Devonian formations the well often intersect the Middle and Lower Carboniferous commercial beds. Water-based drilling fluids, containing heavy clays, circulate past the zones exposing them to potential invasion and formation damage.
Proper well cementing requires cement circulation to surface. The resulting hydraulic loading, however, often cause partial or complete formation fracturing and subsequent irrevocable permeability loss in the affected zone.
The only way to preserve reservoir properties of producing zones penetrated by a well is pressure-balanced drilling of the zone and isolation of the interval with a tight sheath.
Since 1994 two expandable profile liner-based technologies have been commercially available to protect producing zones against formation damage caused by invasion of cement slurry (Fig. 4a, b). Productivity in such wells increased by 1.5-2 times, on the average, compared to neighbours drilled using conventional technology.
Over the past few decades horizontal drilling has become a routine commercial process for efficient field development. There is a clear trend toward increasing horizontal producing well stock. However, logging, well testing, completion and, particularly, water shutoff jobs in horizontal wells is still a weak link.
In 1996-1997 Tatneft suggested using expandable casing to shut off water producing intervals in open horizontal wells. Well No.11251G of the Onbiyskoye oil field, Tatarstan, was the testing site. From 1993 to 1996 the well was shut in because of 100 percent watering. After two water producing intervals had been shut off with expandable profile liners, the well was put onstream with a production rate of 20 water-free oil per day (Fig. 5).
Maturing major oil fields result in an increase in the share of hard-to-recover reserves, a considerable drop in oil production rates and a decrease in the current and final oil recovery factors. A large number of producing wells come to the break-even-point, while the pay-back period of new wells put onstream increases markedly. One of the most promising methods to make brownfields economically attractive is re-entry and sidetracking horizontal wells out of vertical and inclined wells. Sidetracking techniques require the use of whipstocks, which may differ in design. However, a variety of commercially available whipstocks have one drawback in common: increased weight of the construction because of expandable slips and packer elements. Not infrequently this is the cause of poor fixing of a whipstock in a well. In addition, the cost of such devices is rather high.
In 2001-2002 Tatneft developed a novel sidetracking device (whipstock) which employs an expandable profiled pipe as an anchor unit which differs from commonly used whipstocks by increased reliability and simplified design. Production of whipstocks has been commercialized by Bugulma Mechanical Plant (Tatarstan, Russia).
To conclude our overview we may safely say that Tatneft expandable technologies successfully cope with the most notorious and arduous drilling troubles: lost-circulation, water shutoff, and wellbore stability issues. Expandable profile liners have been installed in more than 1,000 wells in very different environments in Lithuania, Western Siberia, the Far North and Kazakhstan, and have shown one hundred per cent efficiency.
Conventional Methods of Well
Casing and the Future of Expandable Technology
Present day well construction implies increasing drilling depths and telescoping casing design (Fig. 6a).
Analysis of typical well designs shows that 26-77 percent of casing pipes and oil well cement is spent on isolating trouble zones with intermediate casing strings. Separate casing strings with a length of 300-4,000 m are run to isolate formations, which are incompatible under drilling conditions, even if the zones are 20-100 m thick or a short distance apart.
Conventional telescopic casing design leads to a dramatic decrease in wellbore diameter, and in troublesome geologic setting proves inefficient at depths of around 4,000-5,000 m, since the ratio of the hole diameter on the well head and toe may be as large as ten to one (10:1). Not infrequently the final wellbore diameter drops to 104 mm, thus creating numerous problems both at the stage of well construction and casing, and during the production phase.
One of the common methods to simplify well design is to increase the drilling interval below the shoe of the previous casing by controlling mud parameters. However, serious complications are associated with this method, including water production, drilling shows, loss of returns, caving, BHA and drillstring sticking, and not infrequently, loss of hole. On top of it, cementing quality is impaired resulting in behind-the-casing flows fraught with far-reaching consequences during the production phase (inevitable loss of commercial beds, salinization of fresh waters, formation pressure issues, etc.).
Tatneft experience of well construction proves that the common technique of casing with telescoping placement of strings (Fig, 6a) can be put away for good, and expandable casing strings can efficiently isolate incompatible formations in the process of drilling without cementing without compromising the wellbore diameter (Fig. 6b). However, for this technique to become a generally accepted oil and gas industry practice, expandable profile liners must be able to withstand high pressure in downhole conditions.
In 1999 Tatneft started new research. Today we can offer expandable equipment for local casing of trouble zones to be used in HTHP conditions.
In 2002-2003, we developed a new threaded connection for profiled pipes. When expanded by 22% from its original diameter it may withstand a 25.0 MPa pressure drop. This equipment was installed in complex geologic environments in Iran and China where lost circulation was complicated by sloughing (when drilling through shales), washouts, and in some cases tight holes.
In the Iranian Kupal field Well No. 41 KL an expandable profile liner with a length 434.5 m was installed in one trip. To date this is the longest expandable product in international drilling practice that was installed in open hole without cementing and without wellbore diameter loss. The above expandable profile liner had 15 threaded and 40 welded connections.
In 2001, building on the experience of extending casing strings by adding expandable profile liners at the bottom, we successfully applied the technology to Vietnam's White Tiger oil field Well No. 818WT, which had extremely difficult drilling problems. Lost-circulation zones in the Lower Miocene, which included violent sloughing intervals, had complicated drilling operations. The well was suspended and shut-in for 3 years because of the continuous problem of the drillstring getting stuck. All trouble zones in the well were isolated in two stages with two expandable profile liners tightly joined with each other and to the 245 mm casing string. The subsequent drilling of the 215.9 mm hole section of the well to 4,010 m with increased-weight mud (1.64 ton/cu. m) and running and cementing the 194-mm liner at an interval of 3,210-4,010 m went smoothly without any problems. The well has been on stream since 2001 (See photo).
The above example shows that Tatneft has come near to a slim monobore well to be constructed without intermediate casing strings when surface casing is extended from the bottom with expandable casing string as trouble zones are drilled through and which acts as a production casing (Fig. 6c).
It is commonly known that time is a critical factor when drilling through sloughing rocks. The latest Tatneft development (2005) is an expandable system set in a well in one trip, allowing for time saving when isolating trouble zones. The technology was tested in three Tatarstan wells. Total time including wellbore reaming, logging, and expandable profile liners installation was 27 hours for the first well where an expandable profile liner with a length of 49 m was installed, and 40 hours for the subsequent wells (lengths of expandable profile liners were 67 m and 66 m). For comparison, conventional isolation jobs in these wells would require 7 to 10 days.
Beginning in 1994, Tatneft gave numerous technical presentations of the expandable technology to petroleum companies from the USA, Egypt, Iran, China, Vietnam, Saudi Arabia, and Oman, as well as for Russian drilling services providers. Tatneft's expandable technologies have been recognized by drilling experts of the leading international companies as truly transformative techniques that can radically change the present-day well construction approach.
Back in 1990 Tatneft patented its invention in many foreign countries. In the USA (Patent 4,976,322 as of Dec. 11, 1990) "Method of construction of multiple-string wells", claimed that "...drilling of the rock after the casing-in of the well with the conductor casing and the surface casing string is performed with a bit of one and the same diameter, with the troublesome zones being reamed to a diameter equaling the outer diameter of the reamed profile pipes, which are successively set in all the troublesome zones of the well as they are exposed by the drilling". By that time Tatneft had already had a long expandable profile liner track record in Russia with over 570 installations, when expandable casing was installed as an alternative to intermediate casing strings and liner strings. Again, expandable technology was first applied in Tatarstan.
Wherever Tatneft's expandable products are presented, whether it be a national or an international conference, symposium, or a specialized show, they are sure to arouse interest and attention of drilling experts. This fact by itself testifies to the highest level of Tatneft expandable technology.