Triple-Zone Intelligent Completions Aid Extended Well Tests of Exploratory Wells
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This paper describes an extended-well-test campaign using intelligent completions in a presalt reservoir. To understand reservoir behavior during production better, several options were analyzed for the first extended well test. Drilling wells provides valuable rock and formation knowledge; however, this information is not sufficient to simulate formation-flow behavior during the field life cycle and reduce production uncertainties. A triple-zone intelligent completion was envisioned as the optimal solution to understand how each interval would behave under production or injection.
Presalt represents an important driver of the oil industry in Brazil because it is responsible for a large percentage of the total oil being produced in the country. In 2010, the discovery of a new and gigantic field (estimated at 8 billion bbl) increased the importance of the presalt polygon for the region, and it was considered a watershed in terms of the country’s economy, intensifying oil-industry activities at the time. The field, in the Santos Basin, is approximately 140 miles offshore Rio de Janeiro (Fig. 1 above).
According to Brazil’s National Agency of Petroleum, available field resources can vary from 8 billion to 12 billion bbl, while the production per day can reach up to 1.4 million bbl. With these significant numbers, field exploration and production became the focus of a main operator in Brazil.
Well Testing: An Important Step Before Production
Understanding the reservoir is fundamental to improving recovery and production performance. Poor decisions regarding this information can affect the final result directly. Some of the information necessary to understand a reservoir is obtained during the drilling and evaluation of wells. However, well testing escalates reservoir analysis to a higher level in terms of details. The more accurately data are acquired during the exploratory phase of the field, the better the reservoir models can be, resulting in optimal completion plans. During this particular project, the operator decided to perform extended well testing in three exploration wells, an injector and two producers.
This strategy was implemented successfully by the operator in previous deepwater reservoirs. Extended well testing provided key information for field development in those reservoirs, and it came to be considered essential for similar future projects. The primary difference between those extended well tests and the one discussed in this paper is the use of intelligent-completion equipment installed in each well. The equipment allows the operator to evaluate each zone with detailed data provided in real time.
Completion Design and Functionality
To help obtain detailed data in each zone of interest, a standard intelligent-completion design was defined for the wells with a minor change from producers to injectors.
For the injector-well design, the intelligent completion was composed of the following.
Feedthrough Packer. Sealing elements allow zones of interest to be isolated and actuated separately. Control lines and electric lines can feed through the packer elements and slips without losing functionality after the packer is set.
Pressure and Temperature Permanent Downhole Gauge. A resonating-quartz-crystal sensor installed in a mandrel (ported to the tubing or annulus) that communicates with the surface acquisition system will provide pressure and temperature information as long as it is powered up to the surface system.
Inflow-Control Valve With Choking Control. The debris-tolerant valve was designed for high-pressure, deepwater environments. Metal-to-metal seals provide proper isolation between annulus and string, and an incremental opening control system attached to the valve allows the well to be choked in the proper percentage to maintain bottomhole pressure or increase production rate.
For producers, a chemical-injection system was implemented in the lower end of the assembly and will allow scale and erosion prevention and other functionalities.
This design helps guarantee each zone will actuate and be analyzed independently, even when producing simultaneously. This can be a major advantage in terms of production statistics, where each well does not need to be a single point of analysis necessarily but each pay zone with its proper singularities and properties can be.
In the oilfield, well tests are performed to broaden knowledge of the reservoir and its hydrocarbon properties. Several tests gather data such as volumetric flow rate, temperature, and pressure, and these can be combined with other information, such as seismic data, to improve the reservoir modeling. Stated simply, the amount of information gathered and its precision are directly related to the quality of the reservoir model to be developed by the reservoir engineers. The use of intelligent completions combines zonal isolation, flow-control equipment, and permanent-monitoring functionalities that allow operators to manipulate tubing performance while analyzing pressure and temperature changes in real time at the producing intervals, providing precise zone-by-zone reservoir analysis. Performing well testing while injecting can enhance the reservoir-producing-zones evaluation because injection rates and performance will also be monitored by intelligent-completion equipment.
Variations in choke positions in flow-control valves will change bottomhole pressures, and, with the proper understanding of well data, formation and reservoir behavior can be understood better. Permanent downhole gauges play an important role in analysis, as does providing real-time data for each variation in the well.
For all the upper zones, the configuration in gauge mandrels allows the operator to obtain pressure and temperature from annulus and tubing, while, in other zones, only annulus data will be monitored. With this kind of information, the operator can estimate production curves and drawdown for the entire field on the basis of information from each well.
The inflow ports of flow-control valves installed with intelligent completions were designed to fit project purposes. Each exposed port allows a predetermined percentage of the total flow capacity of the inflow-control valve. This design was created considering reservoir parameters and expected production curves, where the inflow can be managed according to the operator’s perspective on performance.
Besides the benefits of data acquisition and reservoir understanding, the use of intelligent completion will also provide economic benefits during the extended-well-testing phase, and that can be attributed mainly to the capability to operate devices in the well remotely. To choke a valve in a determined zone, the operator can simply actuate hydraulic-power units at the surface by certain pressure and time and the valve will open or close as intended. With this benefit, no rig intervention will be necessary to change well parameters while well testing, allowing operators to simulate different scenarios with no increase in expenditures.
Presentation of Data and Results
The use of intelligent completions with extended well tests can lead to acquiring enough data to perform optimal and precise reservoir analysis, especially if combined with other geological data, resulting in an effective completion project for the field. To date, well-test results and how intelligent completions have contributed to well-test performance have not been published; however, considering permanent downhole reservoir-monitoring capabilities, evaluating various scenarios while producing, optimizing flow using intelligent flow control, and using acquired information for decisions throughout the field life, the asset value can be maximized. The results may have a substantial effect on future exploratory projects, not only in Brazil’s presalt but also in other major fields around the world.
Triple-Zone Intelligent Completions Aid Extended Well Tests of Exploratory Wells
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16 April 2018