The valves can also be classified according to the flow control they provide – on-off, multi-position and infinitely variable. On-off valves provide selectivity simply by allowing or not allowing the flow. Multi-position valves provide several steps of choking and are designed according to the flow rate expected in the well. They can use an index system to restrict the course and supply choking or an external device that provides a very controlled volume of hydraulic fluid in each shifting. Infinitely variable valves are more complex, as they require sensors to give feedback on their position in order to adjust the choking. There are also several geometries for the valve orifices – the most common are circular and elliptical slots, which are used in on-off/multiposition and infinitely variable valves respectively. The main parameters for specifying intelligent completion valves are flow range, maximum pressure and maximum differential pressure.
When using hydraulically actuated valves, an hydraulical power unit (HPU) is needed. Basically, an HPU comprises a pump, which can be pneumatic or electrically actuated, and a manifold, which is manipulated according to a logic determined by the maker of the system. This logic can be placed in a programmable logic controller (PLC) that actuates solenoid valves on the manifold, making the entire procedure transparent to the operator, as well as providing the ability to operate the HPU remotely. To confirm shifting, intelligent completion HPUs usually have a small tank that verifies the volume of fluid returned after the pressures supplied to the valves have stabilised. Some HPUs also measure the flow rate of the returned fluid, but this process is much more complicated and significantly increases the cost without providing many benefits.
The cables used for monitoring and control have to be protected against chemically hostile environments, such as downhole conditions and mechanical shocks during intervention procedures. Generally, the conductor medium (electrical or optical) is encapsulated in a 1⁄4-inch metallic tubing – which offers mechanical resistance – and coated with a polymeric material – which protects against chemical attacks. Cable protectors (clamps) are used to hold the cable to the production tubing and to offer extra protection near the couplings, where the diameter of the tubing is increased. Dry-mate connectors are used to connect the cable to sensors or to another cable. Devices called ‘feed-throughs’ are used to pass the signal through the tubing hanger and wellhead and ensure that there is no pressure communication. In subsea trees or downhole, wet-mate connectors are used in seawater environments or in the presence of production fluids.
A range of electrical connectors – both dry- and wet-mate – and feed-throughs are already certified and used by Petrobras; optical dry-mate connectors and feed-throughs are currently passing through the certification process; while optical wet-mate connectors that match Petrobras specifications are still at the development stage.
The data gathered by the sensors need to be presented to the operators in realtime, which can be achieved using a supervisory. It is also very important that the connectivity of all equipment allows the integration of all data. The use of open standards and protocols reduces connectivity and integration issues.
Intelligent completion can be used together with other completion techniques such as sand control and artificial lift, but in these cases an interface project is crucial to ensure the reliability of the system. Specific completion tools or projects are used to integrate artificial lift systems with intelligent completion, allowing the intervention of the upper tubing – which contains the lift system – to be independent from the lower tubing – which contains the intelligent completion tools. These tools include a wet disconnect tool (WDT), which is the most practical solution for completions using electrical submersible pumps (ESPs). Electric-hydraulic and optical-hydraulic WDT tools are currently being developed by Petrobras in conjunction with service companies.
Value Chain
Several aspects regarding the use of intelligent wells need to be analysed. Permanent monitoring allows reservoir management to be optimised. The selectivity achieved by flow control allows formation and interference tests to be carried out more simply, and more precise data to be obtained with a view to updating reservoir models. The data obtained can also be used to minimise water production, reducing the need to process for re-injection and disposal and thus reducing the size of the plant. Distributed temperature monitoring can be used to optimise and evaluate steam injection and gas lift. Monitoring the pressure and temperature of the pump inflow allows automatic adjustment of pumping parameters. Surface or subsurface data can be used for early prediction of faults in processes and equipment through pattern recognition techniques such as neural networks and data mining. Realtime monitoring allows precise fault diagnostics, allowing better use of human and material resources.
As with any tool, an economic and value-added evaluation must be used to estimate all of the benefits. The operational impact of the equipment must also be evaluated due to its quantity and complexity. There are several endeavours both inside and outside Petrobras working to create analysis tools that support intelligent well projects, which will help operators to choose the most appropriate solution.
Applications in Petrobras Land Mature Fields
Petrobras chose the Carmopolis field, a land mature field, as its first intelligent field pilot project. As seen in Figure 3, the project encompassed seven wells equipped with intelligent completion, using different suppliers. The intention was to identify the suppliers that had solutions for moderated service conditions such as those found in Carmopolis.
An integrated intelligent well system was developed for the project. In this system, artificial lift automation was completely integrated with the intelligent completion system in order to satisfy the availability and reliability demands of the operators and to ensure that the benefits of the reservoir and production optimisation were effective.
The well completion consisted of three hydraulic packers, three flow control valves and four pressure and temperature optical fibre sensors. The equipment was developed to be low cost with moderate service condition specifications. The artificial lift method used in the project was a rod pump and the regular practices were to locate the pump below perforation and to use fixed pumps. A completely new automation system was used to integrate all systems using open standards and remote diagnostics ability.
Although the conventional well completion used in the Carmopolis field was very simple and had a low intervention cost, the large number of wells (more than 1,000) elevated the maintenance cost of the field. Also, being a land mature field, a large number of interventions were needed – mostly to change artificial lift equipment and to increase productivity – requiring a large number of rigs to maintain the field. The operation had a very limited budget due to its low productivity and a very limited number of rigs available to make the interventions.
The initial results from the Carmopolis project showed improved reliability, diagnostics and capital expenditure (CAPEX) when compared with similar implementations in Petrobras. The expectation from this point forwards is that operational expenditure (OPEX) will also be improved.
Conclusion
Drilling and completion operations in deep and ultra-deepwater require new technologies in order for final cost to be reduced. Petrobras faces this problem every day because its daily rig rates are expensive. When these technologies are not already available in the market, the only way to proceed is to develop them. The model Petrobras has used to develop most of these well technologies has been through partnership with other companies, universities and research centres. MPD and intelligent wells are two examples of new technologies that have been developed in partnership with the objective of improving the performance of wells. ;
|
Download PDF
