Challenges, Lessons Learned, and Successful Implementations of Multilateral Completion Technology Offshore Abu Dhabi
Challenges, Lessons Learned, and Successful Implementations of Multilateral Completion Technology Offshore Abu Dhabi
Challenges, Lessons Learned, and Successful Implementations of Multilateral Completion Technology Offshore Abu Dhabi
Summary Introduction
Zakum Development Company (ZADCO), with the support from The Upper Zakum Field in offshore Abu Dhabi consists of three
shareholders and the cooperation of Abu Dhabi Marine Operating main reservoirs, namely Reservoirs A, B, and C, as shown in
Company (ADMA-OPCO), successfully completed the final Fig. 1. Reservoirs A and B were developed simultaneously imple-
design of the multilateral completion (MLC) system for Reser- menting five spot water injection patterns and horizontal drilling
voirs A and B through the Multilateral Tie Back System technology. This was done in conjunction with a dual-completion
(MLTBS) project. Well T-2 in the Upper Zakum field was recom- system applied for both producers and water injectors.
pleted as dual lateral/dual producer using a re-entry drilling sys- Water breakthrough initially occurred from Reservoir A in the
tem (RDS) Version 2 and a dual bore deflector (DBD) oriented middle of 1991. Since then, the number of water-cut string has
and set on a latch coupling in the 7-in. liner hanger assembly. increased. A high-permeability layer at the bottom of Reservoir A
According to Technology Advancement Multilateral (TAML) caused premature water breakthrough. It was then recognized that
level specification, the final MLC is categorized as TAML Level- along with an optimized junction placement, a new dual-completion
4 E-2-PN-D/4-TR-SEP (Level-4, existing well application, two system that provides upper lateral access, could be introduced to
junction, producer with natural lift, dual completion, tubing re- improve the well’s performance. This system does not only allow
entry, separated flow). The multilateral liner hanger (MLLH) sys- the monitoring of the upper lateral’s productivity and amount of
tem (i.e., accommodating a latch coupling in 7-in. liner hanger water breakthrough, but also ultimately provides several options to
assembly to have a certain access to the upper lateral) was the first reduce or delay water production from Reservoir A.
successful application of that kind in the world. TAML Level-1 and Level-2 multilateral junctions, with dual-
The teamwork and integrated approach for the trial planning completion systems, were applied in producers of Reservoir C,
and implementation, as well as lessons learned from a predesign which is divided into several subreservoir units.
trial (TAML Level-4 E-2-PN-D-TR-SEP using straddle assembly) One of the producers of this category, completed with the short
for Well T-1 completed in 2000, have led to reaching the final string in the upper three laterals (subreservoir units-1, 2, and 3)
goal of the MLC in Well T-2, which provides ZADCO with the and the long string into subreservoir unit-4, showed unexpected
following reservoir benefits: flow behaviors during the cleanup operation of the short string. In
- Independent coiled tubing access to the upper (Reservoir A) this well, a huge loss (3,300 bbls) was encountered during the
and lower laterals (Reservoir B) through a dual completion to drilling phase, and a significant amount of 15% hydrochloric acid
perform effective stimulation and reservoir monitoring. (2,000 bbls) was bullheaded through the short string into the top
- Full bore access to each lateral immediately after pulling out three laterals during the stimulation. Any spent acid and water
the completion, which is an additional feature to the predesign of could not be recovered at surface, and dry oil production was
an MLC for Well T-1. immediately observed during the cleanup operation.
- Allow selective water shutoff to cope with water break- It was considered that the phenomena occurred because of the
through into the upper-cased lateral. majority of water loss and acid having converged into the lateral
- Possibility of extending well life by drilling a secondary of subreservoir unit-1, which is more permeable and subject to
lateral through a window joint installed in the upper-cased lateral. much lower reservoir pressure compared with subreservoir units-2
Moreover, another MLC trial, installed in the quadrant multi- and 3. During the cleanup operation, this may lead to no-flow
lateral well RL-2 in 2005, has been successfully implemented by contribution from the lateral of subreservoir unit-1 and dry oil
using mechanically selective through tubing re-entry equipment. production from the laterals of subreservoir units-2 and -3.
This success was largely because of the lessons learned from a This situation meant that effective stimulation and clean up, as
similar MLC design implemented in well RL-1 in 2001. well as a full-flow contribution from each lateral aided by its
These successful trial implementations proved the MLC independent flow-testing and reservoir-monitoring capability,
system is applicable for any new/re-entry wells in ZADCO reser- then became essential for the multilateral well of Reservoir C.
voirs, which provides new methods of reservoir management, and These reservoir situations, briefly described, have highlighted
creates new completion strategies for ZADCO field development. the limitations of conventional dual completions, (no independent
This paper covers the MLC strategies, lessons learned through lateral access); and emphasized the importance and advantages
the successes and failures and the additional challenges planned of the MLC systems, which allow re-entering any service tool,
for the future of the MLTBS project. including a drilling assembly through the junction and coiled
tubing (C/T) access through the completion as well—which is
what defines an MLC.
Oil, Gas, and Metals National Corporation (JOGMEC), ZADCO, 2. DBD, designed to: deflect the short string of a dual comple-
ADMA-OPCO, and Halliburton-Sperry Sun. Initially, the focus tion into the upper lateral of Reservoir A, while connecting the
was given to developing the most suitable MLC system for Reser- long string to access the lower lateral of Reservoir B, all in a
voirs A and B. single trip.
The strategy for developing MLC for the Upper Zakum reser- The development of the new systems as well as utilization of
voirs was designed to: 1) enhance the production and injection field-proven technologies (e.g., a precut window joint, mechani-
potential, 2) achieve effective reservoir management, 3) advance cally selective through tubing re-entry equipment, etc.) made the
MLC technology, 4) develop possible applications for other fields, MLC design realistic.
and 5) generally improve overall well quality. The specific goals Three years were necessary for the R&D, which included the
are as follows: engineering of designs, prototype laboratory and field testing
• Because of the limited availability of open slots for drilling detailed completion designing, and the planning and execution of
new wells on offshore platforms, the application of an MLC is not the first field trial.
only for new horizontal wells but also for existing wells, with
horizontal recompletion being the target. MLC Trial in Well T-1 (MLTBS Phase-1). TAML Level-4 E-2-
• Acquire C/T access to each lateral through both single- and PN-D/4-TR-SEP (Level-4, existing well application, two junc-
dual-completion systems to perform effective stimulation and tions, producer with natural lift, dual completion, tubing re-entry,
reservoir monitoring. and separated flow), using straddle assembly, was designed for the
• Introduce cased and perforated completion for the Reservoir A. first trial of the MLC (MLTBS Phase-1) for Reservoirs A and B.
• Provide options for selective water shutoff. The additional features of MLTBS Phase-1 compared to con-
• Extend well life cycle by drilling secondary laterals. ventional dual completions were (Fig. 2):
• Assure consistent and reliable lateral access, zone isolation, • Introduction of cased and perforated liner completion for the
and integrities for the lateral junctions (i.e., mechanical connec- upper lateral of Reservoir A.
tion to the parent casing and hydraulic isolation at each junction). • Using a straddle assembly to install an orientation device,
• Create a technical basis for the final goal of MLC systems, with the aid of a latch coupling as the reference point for the
multireservoir contact (MRC) with full access functions. window milling in parent casing and an approach to the upper-
With the objective of achieving the MLC strategy, comprehen- cased lateral.
sive completion designs, associated research and development
(R&D) works, extensive prejob planning, and the executions of
four MLC trial wells, namely, T-1 (1999, Re-entry well) , RL-1
(2001, Re-entry well), T-2 (2004, Re-entry well), and RL-2 (2005,
New well) were accomplished as part of the MLTBS project.
Fig. 5—Mill and open pilot window for upper-lateral using RDS
milling tool (Version 2).
addition, the RDS milling tool (Ver. 1), using the triple latch
assembly and “J-slot” indexing mechanism, was not operationally
feasible for several reasons; specifically, the latch key position
was difficult to identify because of a pipe stretch of 4 to 5 feet,
which was three times longer than the distance between latchkeys,
and the difficulty of torque transmission to the “J” slot when
indexing.
Considering the previously discussed failure and lessons
learned during the second pass cut of Well T-1, the three-latch
system became obsolete, and the new RDS milling system
Fig. 6—Window enlargement by single trip dressing tool. Fig. 7—Failure of RDS milling tool (Version 1).
observation of no cement indication in the recovered remnant, a upper-cased lateral during completion phase to establish hydraulic
7-in. composite bridge plug is to be set above the window joint, isolation across the junction (TAML Level-5 completion).
and a dry test (drillstem test in the closed system) is performed by The washover operation, which recovers the transition joint
applying a 1,000 psi drawdown against the junction. If any flow is and the drilling whipstock, was considered as one of the most
noticed from the dry testing, a 7-in. lateral packer is installed in the critical tasks during the trials for Wells T-1 and T-2. However,
the operations proceeded with no difficulty and was completed in
approximately only 1 day. Good cement bonding and accurate
positioning of the transition joint helped to cut the transition joint
smoothly and symmetrically, resulting in easy re-entry to the
upper-cased lateral (Fig. 12). A latch-cleaning tool is run to
Fig. 10—Washover transition joint and whipstock. Fig. 11—Establishment of Level-4 junction.
Fig. 15—Running and landing dual completion. Fig. 16—Well durations of MRC trials for Reservoirs A and B.
establish zonal isolation, hole cleaning, and a difficulty to set the any new or re-entry wells in Reservoirs A, B, and C. These
tubing whipstock, which resulted in a modification of the latch- systems provide new methods of reservoir management
keys, were the primary causes. The time breakdown analysis by enabling lateral re-entry to effectively stimulate each lat-
suggested that 65% of the NPT was not directly related to the eral, selectively monitor each reservoir’s performance, as
MLC trial. well as providing options for selective shutoff and future
remedial work.
Future Challenges for MLC 3. Junction integrity and zone isolation are one of the major con-
The following are planned/potential applications and challenges cerns for MRC applications. There was no compromise of well
for MLC technology in offshore ZADCO fields: integrity during the MLC trials. Intensive testing and the assur-
• An MLC application (TAML Level-4 E 2-PN-D-TR-SEP) is ance of hydraulic isolation at the junction as well as remedial
scheduled in the fourth quarter of 2007. The candidate well is a actions to establish zone isolation led to delivering quality
producer, and the MLC applied is for dual-opposed laterals drilled wells.
in the same reservoir. 4. The best practices and procedures for the MLC (TAML Level-
• Water breakthrough has been observed in the upper-cased 4 E-2-PN-D-TR-SEP) for Reservoirs A and B have been estab-
lateral of Well T-1. Several water shut-off technologies are applic- lished through the lessons learned from the four trials. It is our
able, such as: chemical treatments, a cement squeeze off against the challenge to deliver an MLC in Reservoirs A and B within 65
perforations, running solid expandable casing inside the 7-in. liner, days, without compromising well integrity. The best practices
or even drilling a secondary 6-in. lateral, which would exit out the learned from the MLC trials, further performance improvement
preset window joint installed in the 7-in. upper-cased lateral. in the predrilling phase, and minimizing conventional NPT,
• Existing technologies, such as a surface-splitter system and lead to attaining this performance target.
extend-reach/horizontal drilling, along with MLC technology
developed and tested through the MLTBS project assists in
achieving the MRC concept with full access to each lateral on
demand through the final completion string. The combined tech-
nology (Fig. 18) provides several options for field development in
a cost-effective manner.
Conclusions
1. MLC technology is continuing to mature to provide several
methods for reservoir management and enhance field produc-
tion and injection potential. An integrated approach for the
system design, R&D, and prejob planning are essential to the
development and optimization of an MLC system. The key
issues for the successful implementation of the technology is
reliability, supported by thorough risk analysis, contingency
planning, and optimization of operational procedures through
previous lessons learned.
2. Four MLC trials for the wells T-1, RL-1, T-2, and RL-2 were
implemented as part of the MLTBS project. Three out of four
trials were successfully installed while following the MLC
strategy for the project. The successful implementation of
the MLC designs proved the systems are applicable to Fig. 18—MRC through combined technologies.