EXPANDABLE-PROFILE LINERS IN WELL CONSTRUCTION-CONCLUSION:Expandable liners isolate water influx from directional, horizontal wells

Aug. 19, 2002
A concept that employs expandable-profile liners, developed to shutoff high-pressure water flows in drilling operations, has proven to be effective for isolating water influx from directional and horizontal well sections.

A concept that employs expandable-profile liners, developed to shutoff high-pressure water flows in drilling operations, has proven to be effective for isolating water influx from directional and horizontal well sections.

The operator OAO Tatneft pioneered the technology in Russia.

The company employed a viscous-hydrophobic emulsion and expandable-profile liners to isolate 30 m from the end and an 82-m section in the middle of the horizontal lateral of Onbiyskoye oil field well No. 11251-G.1 2

The job successfully isolated water entry allowing the well's production rate to increase from 2.0 tonnes/day at 95% water cut to stabilized water-free oil production of 18-20 tonnes/day.

Horizontal wells

Over the past few decades, horizontal drilling has become a routine commercial process-a tool for efficient field development.

Conventionally applied technologies for vertical wells such as zone stimulation treatments, hydraulic fracturing, and water shutoff jobs, however, are ineffective in horizontal wells. To a large extent such jobs complicate horizontal well operations.

Water shutoff jobs in horizontal wells involve two basic problems:

  1. Because water often fills the entire horizontal wellbore, attempts to identify the water-producing interval using geophysical means are not always accurate and successful.
  2. The process of shutting off the water-producing zone becomes complicated in actual practice.

Injection of quick-hardening agents, such as polymer compositions, resins, and cement, as performed conventionally in vertical wells may cause severe undesirable complications in a horizontal wellbore.

Excess or residual material left in the lateral will harden in the form of a whipstock, and attempts to drill out this artificial bridge often result in drillbit drift, side tracking, and subsequent loss of the horizontal wellbore.

Experience has also proven that injection of high-viscosity plugging agents, such as viscous oils or black oil compositions, cannot isolate intervals of water influx.

The formation's pore pressure, possibly supported by waterflood injection, will tend to force the plugging agent back into the horizontal wellbore within 10-30 days.

Investigations have proven that the combined approach of injecting a viscous-hydrophobic emulsion composition to form a rim around the horizontal lateral then securely screening it off with an expandable-profile liner would solve the problem.

Concept development

The concept of using a hydrophobic rim and expandable-profile liners to isolate water entry into horizontal wells stems from the use of profile liners to isolate high-pressure water bearing zones while drilling directional wells.

In the first example of such an application in Russia, expandable-profile liners had cased-off zones responsible for water influx during drilling operations in four wells in Tatarstan's Bavlinskaya area without loss of working wellbore diameter.

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These operations, however, did not employ injection of hydrophobic emulsions.

The wells penetrated the low permeability but abnormally high formation pressure Aleksinskiy horizon zones, which were saturated with highly mineralized water. Influx from the zones led to drilling mud's salinity increase and mud coagulation.

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Table 1 lists the details of water influx from the zones and liner isolation jobs. Fig. 1 shows the expandable-profile liner's installation details for the four wells.

Well logs had identified the saltwater contributing zone's top and bottom, as well as the drilling mud's salinity, while drillstem testing (DST) determined the formation pore pressure and average formation water inflow.

Field geologists determined the most permeable sections of the Aleksinskiy horizon that required the water shutoff or zone isolation jobs.

The jobs were successful in considerably reducing inflow of mineralized water in the first three wells, Nos. 2945, 2920, and 2588, and drilling operations continued to the target depths. Drilling mud salinity increased only partially.

The liner isolation job in well No. 2587 completely isolated the water-producing zone and eliminated mud salinity increase.

Hydrophobic emulsion

A number of factors account for the viscous-hydrophobic emulsion's effectiveness as a water-repelling agent. The hydrophobic or nonwetting nature of its composition and its specific rheological properties create a screening effect.

The composition is insoluble in reservoir fluids and resistant to being washed out of the reservoir by the formation water pressure. At the same time, the composition reduces effective rock permeability to water by affecting the wettability of the formation's pore channel walls.

The synergy of structural-strength properties of the composition's components in time, which is the thixotropic strengthening of emulsion structure, enhances its screening ability.

The emulsions' structural viscosity is at maximum, with low gel strength under reservoir conditions.

A profile liner, set in the water-producing interval, provides a mechanical barrier to maintain the viscous-hydrophobic emulsion's screening effectiveness with time. Thus, the essence of the technology results from two complementary operations:

  1. Injection of a structured, viscous-hydrophobic fluid in the water-production interval of a horizontal wellbore forces a frontal zone back into the reservoir by 20-25 m.
  2. TatNIPIneft engineers have designed an expandable steel profile liner for horizontal wellbores that isolates the screened-off zone and shuts off water entry.

Watered-zone isolation

In 1991, the operator drilled, completed, and began initial production of Onbiyskoye oil field well No. 11251-G, with an initial production rate of 4.5 tonnes/day at 2.5% water cut from the Tournaisian stage carbonates.

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The operator drilled into the pay zone with polymer drilling mud. Producing on artificial lift, in intermittent cycles, the well produced oil at low water cut prior to acidizing (Table 2).

With stimulation technology developed by TatNIPIneft, the operator acidized part of the horizontal lateral after 6 months of well operation. Table 2 highlights the productivity improvement. The water cut did not increase immediately following the acid stimulation.

The well produced 60-80 days at low water cut and at a rate of 12-14 tonnes/day, with a high flowing fluid level. From September 1992 to January 1993 the well produced a cumulative 2,500 tonnes of oil as the water cut increased gradually to 95%.

Geophysical surveys, based on radon injection and oxygen gamma-ray logging, showed that water flowed from the end of the lateral. Tatneft made the decision to plug a 30-m interval at the end of the horizontal wellbore.

Crews injected 26 cu m of inverted emulsion fluid with 0.5 tonnes of fluid-loss additive, called "Chek Loss," into the interval.

The rig then picked up one joint of expandable profile-pipe and ran it on drill pipe into the lateral to a measured depth of 1,430 m.

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A cementing pump unit applied 15.0 MPa (2,175 psi) of pressure to the drill pipe, expanding and straightening the profile liner into the tail section of the hole, isolating the interval (Fig. 2).

The action was unsuccessful in reducing the well's water cut, which remained at 90-95%. A 1996 induction log identified another water-contributing zone, 69 m long, in the interval 1,175-1,244 m (Fig. 2).

A 35-day production test, after isolating the interval by packer, confirmed the water-entry zone and had shown that the horizontal section (1,244-1,430 m) below the water entry would produce water-free oil.

The operator decided to perform the water shutoff job by isolating the water-producing interval 1,169-1,251 m.

Crews injected 55 cu m of viscous hydrophobic emulsion into the water-contributing zone. Using the same installation procedure as the profile liner set in the tail section of the horizontal wellbore, the rig expanded an 82-m profile liner across the interval.

Subsequent production history has proven the isolation job's effectiveness.

The effectiveness of the technology requires the following basic conditions:

  1. Precisely defining the horizontal wellbore's water-entry zone.
  2. Effectively injecting a high-grade hydrophobic plugging material into the water-producing interval.
  3. Precise assembly, running, and installation of the profile liner in the water-producing interval.

The combined technology of hydrodynamic plugging followed by mechanical shutoff using the profile-liner isolation of the horizontal lateral's water-producing zone proved highly effective in eliminating the water production.

Acknowledgments

The authors would like to thank Rustam K. Ibatullin, Albert G. Zainullin, Rafael G. Zagidullin, Vitaly P. Filippov for their contributions to this work.

References

  1. Takhautdinov, S.F., Khisamov, R.S., Suleimanov, E.I., Yusupov, I.G., Abdrakhmanov, G.S., Fazlyev, R.T., "Horizontal wells-development systems, technique and technology of drilling," Neft Tatarstana, No. 1, 1998.
  2. Orlov, G.A., Abdrakhmanov, G.S., Musabirov, M.K., Suleimanov, E.I., "Method of water production shutoff in oil producing well," Russia Patent No. 2114990, June 18, 1996.

The authors

Shafagat F. Takhautdinov is the director general of the joint stock company OAO Tatneft. He graduated, in 1971, as a mining engineer from the Moscow Petrochemical and Gas Institute, from which he also holds a PhD in technical science. His professional interests include various aspects of oilfield operations, oil production, gathering, transportation, and environmental protection.

Nail G. Ibragimov is the first deputy of director general of the joint stock company OAO Tatneft. He graduated from the Moscow Petrochemical and Gas Institute as a mining engineer and holds a PhD in technical science. He is one of the developers of the unique technology on recovery of hard recoverable reserves from old oilfields.

Gabdrashit S. Abdrakhmanov is a chief drilling expert in the External Economic Co. of the joint stock company OAO Tatneft. He graduated from the Moscow Petrochemical and Gas Institute and holds a Dr. degree in technical science. He is a professor and corresponding member of the Russian Academy of natural sciences. He has more than 20 years of experience in local casing of wells.

Izil G. Yusupov is a first deputy director on well construction and workover at Tatar Oil Research and Design Institute (TatNIPIneft) and is a professor. He graduated from the Ufa Petroleum Institute and holds a doctorate in technical science.

Grigory A. Orlov is a deputy head of well construction and workover department in Tatar Oil Research and Design Institute (TatNIPIneft). He graduated from the Moscow Petroleum Institute and holds a PhD degree in technical science. He has more than 30-years experience in well stimulation techniques.

Nigmatyan K. Khamityanov is a head of well construction and workover department in Tatar Oil Research and Design Institute (TatNIPIneft). He graduated from the Ufa Petroleum Institute and has 10 years of experience in local well casing using profile liners.

Munavir K. Musabirov is a head of well stimulation laboratory in Tatar Oil Research and Design Institute (TatNIPIneft). He graduated from the Kazan chemical institute and holds a PhD in technical science. His scientific interests include physicochemical processes in the bottomhole zone, enhancement of oil recovery.