COMPLETION TECHNOLOGY World's first through-tubing multilateral intervention system installed

Steve Button
Pressure Control Engineering

The reasons for drilling multilateral wells are now well established with the resultant cost benefits and increased recovery. Drilling practice can side-track from horizontal sections in wells to increase formation exposure and to reach pockets of reserves which would not be economic for recovery from a dedicated well.

Accepting the above, there is still a considerable investment in time and money to drill and complete these multilateral wells. Therefore, to protect and service this investment there must be a requirement to manage the reservoir and ensure that its potential is realized.

Doing so involves gaining access at will to the well branches to:

monitor performance in all parts of the well.
perform stimulation work to assist production.
control production by means of isolation.

PCE's multilateral re-entry system provides a means of:

gaining access to any lateral bore at will.
enabling coil tubing to perform any of the functions above without the use of a drilling rig.
to do this through the restrictions of an upper completion at any time during the production phase.
hydraulic isolation of lateral bores.

Basic system requirements

Four main criteria needed to be addressed when designing the system.

1. All equipment for post completion re-entry would have to pass through the upper completion.

2. A means of diverting the coiled tubing into the lateral branch.

3. Somewhere for these through tubing tools to locate as most laterals branch out of the larger diameter lower liner section.

4. Whatever was used could not be permanent as access into the well with the rig at a later date might be required.

The solution was to provide a "sleeve" that would be run into the well after drilling and before the completion that would sit across the "window".

This sleeve, or MLR nipple, would have an outside diameter to suit the liner and an inside diameter the same as the upper completion. Setting this sleeve in a known position in relationship to the lateral bore exit point or window, both for depth and orientation, would allow deployment and location of tools with coiled tubing at the window.

The MLR nipple needs to be positioned for depth and orientation so that the diverter will accurately deploy the lateral access tools cleanly into the lateral bore. Tolerance for depth needs to be within parts of an inch, and orientation within a few degrees. The best and most accurate way is to use the device employed to drill the lateral bore.

A latch collar as used by the directional drilling contractor is part of its casing-deployed lateral drilling equipment, and comprises two main components: a machined profile in a casing collar to give a depth and orientation correlation with a pre-machined casing window above. This window is then wrapped with GRP for easy drilling out.

One of the drilling contractor's systems also includes a mechanical tieback to the lateral liner by means of a gate mechanism. This is a fork type sleeve in the backbone that when closed will lock around a liner hanger giving a mechanical tie.

When the casing assembly is run as part of the liner, the MWD technique is used to orient the window so that exit is in the correct orientation on the high side of the hole. PCE uses this existing latch collar to locate and orient the MLR nipple across the lateral. In this way we have complete alignment and orientation with the lateral bore, allowing re-entry operations on coiled tubing to take place. PCE's multilateral selective re-entry system allows for selective entry into any lateral bore to carry out well intervention procedures at any time. This system also allows for the isolation of any lateral bore or any part of the horizontal backbone to give full control over the production from the reservoir.

The system is also flexible enough to allow for more laterals to be drilled from the back bone liner by using workover techniques, as it does not require permanent structures to be built into the well.

Also, if more than one lateral is drilled from the backbone liner, we can selectively set the diverter or whipstock when up to as many as five or six laterals are drilled. This can be done without reducing the bore through the MLR nipples, i.e. by stepping down the ID to locate.

Case history

PCE entered into discussions with a North Sea operator last August as to how to complete a dual multilateral well which the operator was planning to drill late 1995. An important factor to the customer was simplicity of the design and system installation, and the use of tried and tested equipment.

A proposal was submitted and in September, PCE was awarded a contract to supply a through-tubing multilateral completion system with a delivery date of late 1995.

PCE's extensive experience in the supply of wireline, coiled tubing, pressure control and completion equipment and its reputation for innovative technology were key factors in winning this work, and its fast-track approach was important as the lead time from system design to delivery was very short.

The completion consisted of a 9 5/8-in. casing shoe set at 1,262 meters at a deviation of 40 degrees. 7-in. backbone liner was set from 1,207 meters to 2,400 meters. The lateral was drilled 4 3/4-in. OD at 1,800 meters for some 528 meters at 14 degrees left of high side.

Within this lateral was set a 3 1/2-in. slotted tubing mechanically tied back to the main bore. Into this lateral was located a PCE nipple profile at approximately 1,843 meters into which we could locate a PCE coiled tubing-conveyed plug to isolate the lateral.

The PCE multilateral re-entry system was successfully installed this February and in so doing became the world's first successful installation of a through tubing multilateral well intervention system.