Most multilateral wells in the Middle East have been completed as non-access single-selective or limited-access, dual-selective wells. These configurations improved production by achieving increased reservoir exposure at reduced operating cost by hitting two or more targets from a single well. Previous applications had a disadvantage in that these configurations often limited the operator's ability to monitor and enhance well production or perform effective workover operations. Advances in multilateral (ML) completion technology for new or existing wellbores have now resolved some of these difficulties with unique completion systems. These have the capability to mechanically connect laterals to parent wellbores and allow segregated production and intervention at any time in the life of the well. Operators in Qatar, Saudi Arabia, and the United Arab Emirates have applied these innovative techniques, providing a greater variety of options to satisfy the completion, workover, and intervention requirements of dual producing wells.
This paper will discuss case histories in which dual-segregated completions with and without pressure-isolated junctions were developed and used. The completions were run in both new and existing wells and in both primary well construction and workover scenarios. In each case, the operator's requirements were satisfied. The success of these multilaterals has broadened the scope of applicability for dual-lateral completions and workovers.
The new ML concepts offer the following enhancements:
Since the completion configuration is dual segregated, it allows segregated production and segregated through tubing re-entry into two reservoirs.
New procedures for running the packers into the lateral have been developed. Construction of the pressure-isolated junction can commence during initial completion or during workover operations. This can reduce the cost of the initial completion and reduce some of the risk of debris problems.
Dual segregated completions can be installed as part of the initial completion or implemented later during a workover operation. If there are production problems with a conventional completion or a junction leak in a commingled completion, the dual segregated completion can be installed as a remedy that also supports production logging and any rigless interventions that may be required.
Early applications of ML technology did not provide laterals that were accessible by tubing after the drilling operation, serving only to add drainage paths from additional productive sections. In the last few years, however, many innovations in the construction of multilateral wells have taken place. The first innovations were noted during the drilling operations of the laterals.
The next generation of multilateral improvements focused on increasing junction integrity and the productivity of the lateral. These improvements included the development of drop liners, cemented liners and mechanically tied back liners. This generation of systems allowed the installation of many features, including packers in the main and lateral wellbores for isolation of the junction as well as flow-control features. However, the completions were mainly of the conventional type, allowing commingled production from the multilateral intervals.
Improvements then focused on accessibility. Casing junctions that could be selectively reentered were developed so that later re-entry with full drift assemblies for workover was possible. These completions initiated additional multilateral features, including flow control in commingled applications as well as lateral re-entry through tubing for the rigless well interventions.