Intelligent Completion Installations Instrumental in Brazilian Presalt Development
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Presalt heterogeneous carbonate reservoirs typically present long net pays, high production and injection rates, and flow-assurance risks. The complete paper presents a discussion of the use of intelligent well completion (IWC) in Santos Basin Presalt Cluster (SBPSC) wells. With the use of this technique and the introduction of several improvements, well-completion time was reduced to less than 50% of that seen in initial wells.
The SBPSC is in ultradeep water—between 1900 and 2400 m—approximately 290 km offshore Rio de Janeiro. From the opening phases of SBPSC development, IWC has been crucial, not only to improve reservoir management but also to provide better capability to deal with reservoir uncertainty. Extensive use of IWC has presented challenges for well-engineering teams because of the complexity associated with this completion design. Minimizing well-construction costs and risks is essential for any project, but, in ultradeep water, it is even more critical.
Intelligent Completion Systems
Internal risk assessments were conducted to determine optimal solutions for the first production-development project. Direct hydraulic systems were chosen to actuate interval control valves (ICVs) remotely in two- and three-zone wells. This field-proven system was considered the simplest and most reliable for long-term use. However, because the wet tree (WT) designed for SBPSC projects comprises multiplex control systems, addressing these additional integration issues during the planning phase demands exceptional efforts. An extensive integration process had to be conducted to assure that every interface would perform correctly during the production phase.
Most projects consider the use of a 9⅝- or 9⅞-in. production casing set and cemented in front of the reservoir, allowing the use of wider completion equipment, including IWC components. The use of larger-diameter accessories provides the production string the capability to deal with higher mechanical loads, a feature important in the absence of an expansion joint.
The full completion string, installed in a single run, has no separated lower completion system. This integral completion design avoids the use of downhole connections and allows control lines to be run continuously during deployment and the equipment functionality to be tested fully during installation.
Dedicated pressure and temperature sensors are located on each interval and inside the completion string. For two-zone production wells, three chemical-injection points are available. Two of them are upstream of the ICVs to prevent scaling formation in the valves by injecting scale inhibitors in the annulus. These chemical-injection points are especially important when producing the well with any of the ICVs in choked positions, leading to higher-pressure drops across the valves. A third chemical-injection system, injecting into the production string, is above the upper packer and may be used for a second chemical injection or as a backup for the main chemical-injection systems.
A major concern in carbonate reservoirs such as those found in SBPSC fields is achieving effective zonal coverage on acid-stimulation operations. To minimize the chance of poor distribution during acidizing operations, the engineers added a mechanical sliding-sleeve valve in the bottom of the upper and intermediate zones and considered mechanical access to the lower part of the lower perforations. These additional accesses allow spotting a small volume of acid in the lower part of each zone, creating a thief zone on the base of each interval.
Usually, in the lower zone, a coiled-tubing run was performed to jet acid in the lower part of the perforations, intended not only to help in treatment diversion but also in creating enough injectivity to displace the next stages of the acid job to the bottom of the well by injecting the brine into the formation.
The construction of several wells during the initial campaigns allowed stimulation experts to evaluate several emerging solutions for improving and simplifying acid stimulations. Some wells submitted to well testing with drillstem tests were especially important because, in these, a production-logging tool usually was run and helped evaluate the diversion of the treatment.
The use of coiled tubing and slickline operations added complexity, risk, and cost to operations. Consequently, performing through-tubing operations after installing the WT had a significant effect on well duration and cost. Initially, the operator was not using a subsea intervention tree (SSIT) in its tubing-hanger-deployment system. But, when an SSIT became available for SBPSC wells, the engineers were free to explore different stimulation strategies. Besides allowing coiled-tubing runs without the WT installed, this system made it possible to circulate fluid to the bottomhole with return on the drilling riser.
Once this solution was tested and applied successfully, the next wells completed with the use of the SSIT dismissed the use of coiled tubing, allowing the WT to be installed with a dedicated vessel. This well-construction sequence was known as anticipated stimulation.
As an additional step in well-construction optimization, the completion team was challenged to perform the same kind of operation without the use of an SSIT system because its availability was limited and its cost was significantly high. With the implementation of an optimized sequence, provided in the complete paper, for performing the acid job using the anticipated-stimulation method without an SSIT, the WT of almost every well since has been installed by a dedicated vessel, reducing rig time used for completion by approximately 10 days per well. At the time of writing, this sequence has been applied in 50 wells, with a savings of approximately 500 days of rig time. The anticipated-stimulation technique represents the innovation in completions for SBPSC wells that has had the most significant effect on well-construction budgets.
IWC Use in Production Phase
Among the more than 100 wells equipped with IWC in the SBPSC, more than 70% are already in the production phase. The IWC systems have been used in both proactive and reactive reservoir management.
During the production phase of these fields, some anomalies and failures have already been detected in IWC systems. These commonly are related to undesired and spurious movements on ICVs or difficulties in cycling some valves. Such events are related frequently to supposed malfunctions of hydraulic incremental-opening modules used in the systems of one of the service providers. To minimize this kind of failure, the use of multiple-position ICVs has been reduced, prioritizing the use of simpler designs when downhole choking capability is not mandatory. The risk of scale occurrence in the producer wells of some fields also has been taken into consideration when deciding to choose ICVs.
The operations team has also faced a few cases of stuck or leaking ICVs and one confirmed case of control-line failure. Finally, in two gas-injector wells, gas has migrated through control lines to reach the subsea control module on the WT, causing control-line blockage. To avoid this complication elsewhere, injector wells were operated while maintaining positive pressure in the control lines to prevent hydrocarbon migration.
Petrobras has achieved significant and consistent performance during the completion phase of wells equipped with intelligent completions in the SBPSC. Fig. 1 shows the number of wells completed per year and the normalized average duration per year, considering the duration average of the two initial wells as 100%. When compared with the eight wells completed until 2013, a reduction of more than 50% is observed, with significant effect on development projects in the SBPSC. In initial projects, the well-construction cost was responsible for almost 50% of the project budget, but this has changed dramatically because of well-construction-cost reduction in both drilling and completion phases.
Intelligent Completion Installations Instrumental in Brazilian Presalt Development
01 May 2020
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