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Progressive multilateral reentry system clears technical hurdle, overtakes completion obstacles.

Development of a lateral selective reentry system that provides reliable access to all levels of multilateral wells and offers new options for cost-effective treatment of Level 1 and 2 laterals is overtaking traditional completion and reentry techniques. The Schlumberger Discovery MLT* system is successfully replacing trial-and-error access methods (referred to within the industry as "poke and hope"efforts), offering an economical and operationally simple solution for maximizing performance in multilaterals-independent of their complexity level. The new technique also enables real-time production data acquisition for use in optimizing the subsequent stimulation treatment.

While the number of multilateral wells drilled mushroomed as a result of rapid advances in drilling methods, comparable advances in multilateral reentry equipment and designs has not kept pace, even though today more than 60 percent of all multilaterals are sidetracked out of openhole or cased hole and then left openhole.

The potential or anticipated requirement for wellbore cleanouts, formation damage removal, acid stimulations, nitrogen lifts or wellbore logs has traditionally forced operators to incorporate means to selectively reenter branches of multilateral wells. Access to a specific lateral, or branch, to conduct acidizing, cementing, logging or fishing operations can be achieved by inserting sophisticated completion equipment near the junction where a lateral splits away from the main wellbore. But completion equipment is expensive, and it must be installed at the time of drilling.

The decision to install sophisticated completion hardware had to be made prior to confirming that production data warranted the investment. While adding complexity to wellbore construction and completion phases, investments for these installations have been added to overall wellbore costs. Reentering a specific lateral to conduct any workover operation becomes problematic at best, and is often fruitless using hit-or-miss techniques.

Selective reentry of all levels can now be economically performed using the Discovery MLT system on coiled tubing. Matrix acidizing has been the primary application since the tool.s introduction last year. Additionally, the Discovery MLT approach has proved ideal for cleaning out laterals--particularly horizontal ones--that have become clogged with debris.

Use of this new technique using coiled tubing conveyance for operations such as openhole formation washes, selective matrix stimulation, production logs and nitrogen kickoff operations promotes real-time treatment in live, flowing multilateral wells. Add-on assemblies enable wired, real-time coiled tubing logging operations-without shutting in a well.

Revisiting reentry methods

The patented device has a controllable bent sub that connects to the end of the bottomhole assembly (BHA). The 2.125-in. tool has two primary functions: to detect the window where the lateral deviates away from the main wellbore and to steer the coiled tubing into the lateral. The technique does not require a wired coiled tubing string; the corrosion-resistant reentry tool is operated solely on flow and is conveyed with standard coiled tubing equipment.

The system includes a rotational device, or orienting tool, above the bent sub that rotates the unit to change its orientation and align the BHA with a lateral's window. The angle of the pivot arm of the bent sub is a function of the pump rate. No flow rate, or a low rate, keeps the arm straight. A high flow rate causes the arm to bend to its maximum. Between a straight orientation and fully bent one, the sub finds the window and slips into the lateral. Once the lateral is entered, a multinozzle, hydraulically actuated circulating sub is used to pump the treatment fluid at a high rate.

The ability to adjust the sub orientation, or bend, from surface and the real-time feedback to surface of window identification saves a substantial amount of time by increasing the chance of successful reentry on the first attempt. Only one run to the bottom of the lateral is required for confirmation.

The orientation of the bent sub relative to the lateral window is changed with the orienting tool, indexing 12 times to cover 360 deg. Even if the tool cannot be oriented (perhaps because the bent sub is locked in a washout), the upward movement of the wand allows the tool to flip in the desired orientation after the first few inches of movement.

To locate a lateral window, the approximate depth of the window must be known. Once the tool is at this target depth, the area is profiled using specially developed software to locate the window. A pressure signal is used as feedback to the software when a multilateral window is located. Once the window has been located, the software also keeps track of the toolface orientation.

Having accomplished operator objectives on more than 20 projects in Canada, the Middle East, Africa, South America and North America, other applications are becoming apparent and are being addressed.

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