Middle East companies improve multilateral junction completions

MULILATERAL TECHNOLOGY-Conclusion

Robert W. Taylor, Richard Russell
Halliburton Energy Services
Dubai

Completion technologies in the Middle East have become increasingly effective in providing mechanical connectivity, lateral isolation, and reaccessibility for mulitlateral wells and junctions.

This conclusion of a two-part series, which began in OGJ Mar. 16, 1998, details an effective method for constructing an isolated junction within a multilateral well.

With the introduction of the retrievable whipstock system, techniques for creating multilateral junctions and well bores from a cased parent bore have been developed into standard procedures. However, once the whipstock is retrieved, the ability to easily relocate the milled window and re-enter the lateral well bore is lost.

While not impossible, re-entering the lateral junctions can be difficult and is not considered practical without a rig on location. A breakthrough in this difficult operation has been reported in Oman where selective re-entry success has been achieved with the use of a diverter whipstock and radioactive tagging in multiple drain-hole cased wells.¹

In the Middle East, operators in Abu Dhabi have become industry leaders in drilling open-hole lateral well bores. Case histories in Abu Dhabi describe up to six different lateral well bores drilled from open hole sections.² Attempts to re-enter these laterals using coiled tubing have been made, but in all cases, the uncertainty of which particular lateral was entered deterred effective reservoir management techniques.

The need to selectively stimulate laterals has helped propel the need for sophisticated selective re-entry completion systems in the Middle East. Scenarios for mechanically isolating and selectively re-entering lateral well bores, for the purpose of water or gas production, have become of primary importance to many Middle Eastern operators.

In Qatar and Saudi Arabia (Khafji), effective selective re-entry completion systems have been successfully installed as part of the overall completion configuration.

This article describes one system that has been successfully installed in the Middle East, with the aim of providing connection, isolation, and selective re-entry capability for post-rig, through-tubing operations, performed with coiled tubing or wire line. The sequence of completion steps, discussed below, is shown in Figs. 1-7.

Junction construction

The procedure for constructing an isolated junction assumes the junction points for the laterals are located in 95/8-in. casing. This casing may have been set and cemented after drilling a 121/4-in. open hole in a new well scenario, or may have been set in an existing well.

If the well is a recompletion, the condition of the casing and the cement behind it must be taken into account. The steps are as follows:

Step 1. Run multilateral packer with solid whipstock on starter mill (Fig. 1 [67,765 bytes]).

Step 2. Once on depth, orient packer to 15° left of high side (ideal orientation). Pressure up on drill pipe and set packer. Shear starter mill and start milling window. Pull out of hole with starter mill. If required, the packer has an orienting nipple made up below it so a diverter can be set. This allows access to the lateral with service tools. The nipple also allows a window bushing to be set across the packer, which in turn, allows the setting of a diverter for through-tubing access to the lateral (Fig. 6, Step 16).

Step 3. Run in hole with window mill and watermelon mills and open window to full size. Pull out of hole. Run in hole with second watermelon mill assembly and dress window. Pull out of hole.

Step 4. Drill 81/2-in. lateral to total depth (Fig. 2 [62,267 bytes]).

Step 5. Run in hole with retrieving tool and pull solid whipstock. Pull out of hole.

Step 6. Run in hole with hollow, filled whipstock on running tool. Set same in packer (it will orient automatically and latch into top of packer). Pull out of hole with running tool.

Step 7. Run in hole with 7-in. liner and following bottom hole assembly (Fig. 3 [51,250 bytes]):

Float shoe
Shoe track
Float collar
Baffle adapter
Liner
ES stage cementer
Liner
Densely centralized liner joints set across the whipstock and window. Note that Spiroliser-type centralizers spaced approximately 8.2 ft apart should be used on these joints.
Liner hanger assembly.

Step 8. When liner is on bottom, perform first stage cement job using standard Class G cement. Bump plugs and allow first stage cement to set up.

Step 9. Pressure up and open ES stage cementer. Allow second stage to set up between 24 and 48 hr, depending on hole parameters. Test liner lap in accordance with local procedures.

Step 10. Run in hole and clean up 7-in. liner. Pull out of hole (Fig. 4 [69,931 bytes]). Drill 6-in. hole and cement 41/2-in. liner, if planned.

Step 11. Run in hole with mill anchor, mill guide, and skirted mill assembly to junction area. Orient mill anchor and circulate to set mill anchor. Shear out skirted mill and commence to time mill 7-in. liner. Once skirted mill has penetrated required distance, pull out of hole.

Step 12. Run in hole with pilot mill assembly to open a pilot hole through the liner and hollow whipstock. Pull out of hole with pilot mill and mill anchor. The pilot mill bottom hole assembly includes a collet-retrieving tool that serves to release the mill anchor when pulling the pilot mill back.

Step 13. Run in hole with mill to open up hollow whipstock and packer to full ID of about 6 in. Pull out of hole (Fig. 5 [51,777 bytes]).

Step 14. Run in hole with packer plug mill and mill packer plug to finally re-establish main well bore. Clean up hollow whipstock and packer ID with watermelon mills, which are made up in the packer plug mill BHA.

Step 15. If the well is to be completed with 51/2 in. or smaller tubing, run and set window bushing in the orientation nipple below the packer so the window bushing straddles the lateral junction (Fig. 6 [67,288 bytes]). The window bushing will reduce the ID through the packer and hollow whipstock, allowing a through-tubing deflector to be run.

Step 16. The window bushing contains an orientation nipple that allows a diverter to be set through the production tubing, allowing access to the lateral using wire line or coiled tubing.

If more than one junction is to be constructed, repeat Steps 1 through 15 as necessary.

More recent innovations have made it possible to mill the window in parent casing using the hollow whipstock. This eliminates Steps 5 and 6 and removes the associated risks and rig time involved in performing these steps.

If the junction is to be constructed in an existing well, it is imperative that the casing be in good condition and that there is good cement behind it. Depending on the cement bond log evaluation, it may be necessary to perform a cement squeeze to ensure good cementation at the junction.³

The junction construction and completion techniques are geared toward permitting selective lateral access for post rig operations. Primary management objectives are lateral flow control and reservoir management capability for stimulation of selected producing zones. A number of successful post-completion, selective re-entry cases have been demonstrated in the Middle East with coiled tubing and slick line.

Important completion aspects

The importance of the completion aspect for multilateral wells cannot be understated. Failure to consider the impacts of completion and interference can lead to wildly optimistic production estimates.¹

Applying the right solution to the right opportunity should be the responsibility of an interdisciplinary team that has been set up to design, plan, and execute the multilateral well. Multilateral techniques provide the advantages of horizontal well bores, but have proven to be more cost-effective than individual horizontal wells.

The importance of maximizing the distance between the endpoints of all multilateral branches for the same drilled lengths is discussed.⁴ Likewise, the placing of the exit points in the casing is a critical consideration in the completion of any multilateral horizontal well.

In addition to the mechanical considerations of the exit point, such as the circumstance surrounding completion, consideration must be given to proper assessment of the possible interference effects of one multilateral branch upon the other, resulting from the commingling of fluids up the well bore.

Thus, a proper nodal analysis must be performed.⁴ Analytical solutions also indicate that the branch orientation is a critical factor affecting well performance because it controls completion and interference effects between different branches in multilaterals.⁵

Acknowledgments

The authors wish to thank the management of Halliburton Energy Services for recognizing the value that multilateral technology offers, providing the support to develop the technology, and the encouragement to publish this article.

References

1. Odell, A.C., Payne, M.L., and Cocking. D.A., "Application of a highly Variable Gauge Stabiliser at Wytch Farm to Extend the ERD Envelope," SPE paper 30462 presented at the SPE Annual Technical Conference and Exhibition, Dallas, Oct. 22-25, 1995.
2. Ismail, Gamal, and El-Khatib, H., "Multi-lateral Horizontal Drilling Problems and Solutions Experienced Offshore Abu Dhabi," SPE paper 36252 presented at the SPE/ADIPEC Exhibition and Conference, Abu Dhabi, Oct. 13-16, 1996.
3. Hovda, S., Haugland, T., Waddell, K., and Leknes, R., "World's First Application of a Multilateral System Combining a Cased and Cemented Junction with Full Bore Access to Both Laterals," SPE paper 36488 presented at the 71st Annual Technical Conference, Denver.
4. Salas, J.R., Clifford, P.J., and Jenkins,D.P., "Multilateral Well Performance Prediction," SPE paper 35711 presented at the Western Regional SPE meeting, Anchorage, May 22-24, 1996.
5. Akinmoladun, O.J., Rothenhoefer, J.S., and Wevers, A., "Innovative Drilling of Fork Type Dual Lateral Horizontal Well's in PDO's Saih Rawl Field," SPE paper 36252 presented at the SPE/ADIPEC Exhibition and Conference, Abu Dhabi, Oct. 13-16, 1996.

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