A two-component multilateral junction enhances collapse resistance, excludes sand and enables a wide variety of completion options.

In many instances, multilateral junctions have experienced connectivity problems due to unstable formations, which induce high mechanical loads that sometimes severely affect the integrity of the junction. In sand-producing reservoir environments, sand production at the junction can be a common problem.
A high-strength multilateral junction completion system has been developed to support mechanical loads created by formation instability and to resist migration of sand solids. A high-strength junction evolved based on the field-proven multilateral completion technology of the RapidConnect system. This enhanced version exhibits collapse strength that exceeds 2,500 psi, and excludes solids particles equal or greater than 40 micron grain size. As a reference, most junctions other than TAML Level 5 or 6 would likely exhibit a collapse resistance in the 10 to 100 psi range and would have a junction gap of an inch or more.
Two components provide such mechanical properties: a template located and secured in the parent bore, and a connector tightly interlocking in the template (Figure 1).
Installation process
After exiting casing with a conventional milling system and drilling the lateral branch with full-size capability, the appropriate completion is installed in the lateral branch, terminated at the top with a polished bore receptacle (PBR) placed off the main bore. The main bore is cleaned after retrieval of the whipstock (Figure 2-A). The junction template is set adjacent to the casing exit. A selective landing and orienting casing profile, initially used to set the whipstock, locates the template at a desired depth. The template running tool uses work string pressure to latch into the template assembly (Figure 2-B). A service tool carrying the connector is lowered in the parent hole. When approaching the top of the template, the lower end of the lateral connector stabs in the lateral liner PBR. At this point, a positive hydraulic feedback is received at surface. The service tool is activated and reciprocated to insert the connector into the junction template (Figure 2-C). Another positive hydraulic feedback at the surface indicates full junction connectivity is accomplished.
The connector engages into the template via a tongue-and-groove interlock as illustrated on the cross-sectional view (Figure 1). Exhaustive computer modeling was required to design this interlocking feature. Finite element analysis shows this particular type of interlock acts as a single, strong mechanical structure. The junction was subjected to positive and negative pressure tests in order to qualify the design.
System components
The RapidExclude ML junction system includes:
• junction with template and connector;
• lateral and upper main bore PBR;
• indexing casing coupling (ICC) and compatible landing tools;
• selective through-tubing access; and
• service tools.
The core of the system is shown in Figure 1, which illustrates the fully engaged junction. The equipment can be run in 9 5/8-in. casing (40-53.5 lb/ft). The junction enables full-size lateral drilling. The lateral maximum completion ID is 3.81 in. and the parent bore maximum completion ID is 4.75 in. A 6-in. PBR placed on top of the junction allows for large bore production tubing sufficient to carry significant production flow from commingled zones, thereby increasing well productivity.
Field qualification
The 95/8-in junction system was qualified in June 2002 at the Gas Technology Institute's Catoosa, Okla., facility in Well Nelda 8. The well had been completed with 95/8-in., 43-lb/ft casing and an ICC. The depth of the junction was 970 ft (296 m); inclination at the kickoff point was 32 degrees. The casing exit was milled at 242 degrees azimuth in a shaly sand.
A conventional two-trip milling system was run with a debris barrier about 70 ft (21 m) above a construction selective landing tool (CSLT) and landed in the ICC. A window was milled 30 degrees left of the high side in two trips in about 6 hours of total milling time utilizing the top drive at 120 rpm and sweeping with viscous bentonite gel for cleaning purposes.
The whipstock was retrieved and replaced with a construction rentry deflection tool (CRDT) to drill the lateral. The lateral was drilled to 230 ft and a slotted liner with PBR on top was placed in the hole using a scab liner and a Quantum packer set in the main bore. Once the liner was at bottom, a liner disconnect tool was successfully operated to release the liner from the running tool. The CRDT/CSLT combination was retrieved as per plan, leaving the hole ready for the junction installation as illustrated in Figure 2-A.
The template assembly was set adjacent to the window and latched in the ICC as illustrated in Figure 2-B. In a consecutive trip, the connector was run, stabbed in the lateral PBR and engaged in the junction template. There was a clear mechanical signal that the connector radial alignment was correct before initiating rail engagement. After a positive feedback indicating the connector assembly was completely engaged in the template, the running tool was released. The junction installation was complete.
Reversibility
The installation of the system is reversible. The reversal was tested during the qualification field test. The connector assembly was retrieved with a conventional spear by applying 50,000 lb straight pull. In the next step the template assembly was successfully retrieved by applying 100,000 lb straight pull. Both components were in good condition and fully functional.
The intervention tools, selective re-entry deflector and isolation sleeve were successfully run and retrieved with slick-line to complete the system qualification.
The system performed as expected and is qualified and ready for commercial installation.
Applications
The high strength of this new type of junction is specially suited for reservoirs that require collapse resistance, sand exclusion or both. It can be applied in layered, compartmentalized or faulted reservoirs, in which either a single junction with dual laterals or multiple junctions with multiple laterals are desired. In the event multiple junctions are installed, a "fish-bone" architecture would be created, from which flow would be commingled to the surface, either naturally or artificially lifted. The exceptional combination of strength, sand exclusion and large parent tubing size especially benefits multiple laterals where friction losses may be critical. Heavy oil or sub-economic reservoirs may greatly benefit from these combined features. Maximizing the minimum diameter of the parent bore, while providing high strength also offers more effective well intervention options over the life of the well.
The junction can be used for new or re-entry wells, wells with different pressure regimes that require inflow control or infill well drilling in mature assets. The junctions can be located above the reservoir or in the pay zone itself.
As an alternative to setting the liner off the window and stabbing the connector in a PBR, the connector and lateral completion can be run together in a single run. In this case, the lateral liner or screen O.D. is limited to 4.75 in.
The junction allows a wide array of completion options, including single commingled flow, remote flow measurement and control (RMC) at the junction, and reservoirs requiring sand management, as illustrated in Figure 3. The combination of RMC with artificial lift methods such as electrical submersible pumps or gas lift is also possible. Various flow control options can be installed in the laterals and the parent bore to control production over the life of the reservoir.

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