Agip using live wells for deepwater production, subsea equipment tests

Engineering R&D Group Agip Agip's subsea boosting and monitoring equipment sled is lowered to the seafloor for an endurance trial. Agip's research and development efforts in advanced offshore engineering technologies have steadily increased, mainly concentrated towards deep water systems. Agip has a long tradition and experience in offshore operations and since the early 1970s has been involved in the deep water challenge.

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Engineering R&D Group
Agip
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Agip's subsea boosting and monitoring equipment sled is lowered to the seafloor for an endurance trial.


Agip's research and development efforts in advanced offshore engineering technologies have steadily increased, mainly concentrated towards deep water systems. Agip has a long tradition and experience in offshore operations and since the early 1970s has been involved in the deep water challenge.

Today, the company can count on a valuable technological asset, the result of multi-year offshore drilling and production activity and an R & D effort in advanced offshore technologies.

Multiphase technology

Agip started R&D in the mid-1980s recognizing the high potentialities of this technology in reducing offshore costs, especially those relevant to marginal or satellite field development. In 1994, Agip installed offshore Sicily the first subsea multiphase boosting system electrically driven.

Several alternatives have been proposed for the safe and economical exploitation of deep water fields. For many applications, multiphase can represent the answer to the problems related to such developments by moving to the sea bottom the overall production plant.

SBS project

In 1985, Agip, in cooperation with Snamprogetti and Nuovo Pignone, started a research project aimed at developing a subsea boosting system ( SBS ). The SBS would be suitable for installation in water depths up to 1,000 meters and capable of transferring over distances up to 100 km the untreated well fluids of a 30,000 b/d field.

After a preliminary theoretical and experimental screening of the various multiphase pumping concepts, four systems were selected for further development and prototype construction, namely: centrifugal pump, twin-screw pump, diaphragm pump, and hydrobooster system.

The pump prototypes were tested at full operating conditions on a special loop designed and built at Nuovo Pignone facilities in Florence and suitable to handle a two-phase

hydrocarbon mixtures. Afterwards, a more severe qualification program was successfully completed for the screw pump and diaphragm pump utilizing a test facility built at Villafortuna Trecate (Agip's oil field in Italy) for the specific purpose of endurance tests in real condition.

The installation and successful start-up of the subsea boosting unit occurred in the summer of 1994 at Prezioso Field (offshore Sicily). It is the first electrically driven multiphase booster ever installed and in operation subsea. The experience gathered from the field operation will contribute substantially in expanding multiphase boosting technology.

Simulation, metering

Agip also supported, through in house and sponsored projects, the development of other fundamental items as the multiphase flow meters and multiphase simulation tools, in order to develop the technology.

The development of three multiphase flow meters (MIEM, SWTS, and BRIS) were successfully supported. In addition, Agip built, with the EEC support, a multiphase test loop (Trecate test loop) in order to test in real conditions (live oil) for the developed multiphase flow meters.

In the future, Agip will support, through JIP projects, mainly those activities addressing field qualification of developed multiphase meters.

In order to design a complete multiphase transportation system, it is considered essential to have a precise transient multiphase computer code able to perform the steady state and transient analysis. In 1990, Agip joined Norwegian firms to improve computer codes for multiphase flow. In parallel, and in cooperation with Elf, Total, and various research institutes, a project for code verification with qualified field data was started.

Floating production

Since the late 1970's, Agip promoted studies and research, in view of identifying safe and economic solutions for deep water fields exploitation. Special attention was given the tension leg platform (TLP).

Unlike the general approach at that time, tendons were proposed to be steel tubulars to be welded on the platform at the installation site. To ensure that this was feasible and economic, prototype testing and trials were considered fundamental. The concept has been developed for a reference oil field located in the Mediterranean Sea, in a water depth of 830 meters.

When Agip decided to undertake a research project on TLPs, two major objectives to be achieved were set:

  1. Develop a reliable and economic concept suited for deep water and low-to-medium payload.
  2. Develop a more general engineering knowledge to support the concept development.

The key areas for this development were: fast and reliable welding techniques, accurate NDE techniques, and efficient and proven handling of tendons during installation.

The tendon system is composed of 16 pipes, all with 20-in. diameter, 1-in. thickness, and made of X65 steel grade steel.

Tendons are deployed from the platform by welding them in segments 16.5 meters long. Eight welding units are used to deploy the sixteen tendons at the same time, each welding unit being alternately working on two adjacent tendons.

The entire operation lasts 200 hours, including downtime allowance. Platform and hanging tendons are able to survive the design storm for the installation condition.

TLP tendons

The aim of this research was to carry out sea tests on instrumented risers, in conditions as similar as possible to that experienced by actual TLP risers, or tendons, under operating

conditions.

The primary objective of the present research was the acquisition and analysis of experimental data on the dynamic behavior of operating risers suitable for verifying the capability of the available theoretical calculation procedures.

A suitable designed and constructed test system was installed on the Barbara-F platform in the Adriatic Sea. A major novelty of the project was the use of a fixed structure to support the test equipment. The test rig was designed so that it can impose both harmonic and non-harmonic top motions in any given direction on the top of the riser.

The tests results were compared with an in-house riser dynamic analysis. A package was also developed to predict and assess vortex induced oscillation of risers under various loading conditions using state of the art techniques. An analysis of the tests demonstrated the reliability and precision of the system in executing all the tests:

  • The in-house computer package is to be considered a reliable and precise calculation tool to evaluate loads on vertical risers of floating platforms under the combination of all the possible environmental conditions.
  • The values of hydrodynamic coefficient deduced by experimental campaign are in line with available literature data used for design and dynamic analysis purposes.

Production, offloading

The development of floating production technologies for deep water applications has always been an Agip objective, considering the significant number of marginal fields located in deep water. In addition to the tension leg platform, various alternatives of floating production systems (FPS) have been investigated with the objective of obtaining more cost-efficient and versatile solutions for the development of marginal fields.

The interest of Agip in floating production systems began in 1984, when in collaboration with Tecnomare, Fincantieri, Saipem, and Snamprogetti a project started for the design of various alternatives of floating production systems.

The turret floating production system (TFPS) project started in 1986 from the result of the first screening phase mentioned above. The project was aimed at developing a low-cost concept with integrated storage that can be relocated to various fields in order to reduce the incidence of investment costs on single marginal fields.

The TFPS concept is based on a monohull with an internal turret mooring system which has been designed and verified in various operative scenarios.

two similar vessel configurations have been obtained, mainly different on the storage and treatment plant capacity and on the size of the mooring line.

The hull form has been designed in consideration of such aspects as: reduction of construction costs, the dynamic behavior of the vessel, and storage and safety requirements.

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Multiphase screw and diaphragm pumps are endurance tested onshore on live wells at Agip's Villafortuna Trecate facility before installation offshore.


Subsea systems

Agip's experience in subsea well completions dates back to the early 1970s, with the installation of several subsea christmas trees by its affiliate Iminoco in the Iranian offshore. In the following years, Agip continued to utilize this technology for bringing in production satellite wells and marginal fields in Italy, Tunisia, Congo, Angola, and the North Sea.

In 1985, Agip started, with the financial support of the EEC, a project, named SAF, with the purpose of developing a new generation of subsea systems suitable for producing marginal fields in very deep waters. The scope of the project, carried out with a joint venture embracing Snamprogetti , Kvaerner Engin-eering, and Tecnomare as main contractor, was the design, construction and testing of a diverless and guidelineless subsea production system and its service ROV for use in water depths up to 1,000 meters.

The SAF basic design philosophy and operating choices were outlined as follows:

  • Modular approach.
  • Diverless and guidelineless technology.
  • Remote control.
  • Automatic intervention procedures.
  • Dynamic positioning capabilities.
  • ROV-assisted backup visual inspection, light tasks, and emergency procedures.
  • Power/data transmission based on electrical/optic umbilical.
  • Load lifting by wire rope.

The modularity of the system allows an arrangement of the various components depending on the type of operation required, namely: first installation, normal maintenance, repair activity, workover activity, and disassembling and recovery.

Moreover, such a modularity also allows as much as possible the best performance in underwater operations without mobilizing an expensive spread such as a drilling vessel.

The maintenance system, that may be deployed via an adequate handling system installed on a DP vessel, enables the operator to perform a great number of operations on the subsea production system.

The SAF project, in terms of construction of all the module and tests qualification, was completed in 1993. Its installation on Luna's 40 live gas well in 170 meters water depth is ongoing. The SAF technology then will be applied in the development of the Aquila Field at a depth of 830 meters in the Adriatic Sea.

Control systems

So far, the control system used for the subsea production of hydrocarbons has the surface units always connected to the subsea control modules by means of one or more umbilicals.

This approach, however, has some economic and technical constraints. The umbilicals are very expensive and require costly marine operations for laying an disconnection.

Agip, with the aim of eliminating the umbilicals in many future subsea applications, put resources on development activities and projects needed to control autonomous systems.

  1. SWACS project: A research and development project named subsea wells acoustic control system (SWACS), was carried out with Tecnomare and Kongsberg as main contractors. The system can control and monitor up to 15 wells in water depths up to 1000 meters. No umbilicals to the surface are required, either for electric lines or for hydraulic ones.

    The system relies on an autonomous energy source for power supply and on acoustic link for signal transmission. Following extensive dry tests of all the components and of the assembled prototype, a successful installation of the system's first prototype took place in the summer of 1987 on an Agip live well, the Luna 27, in the Ionian Sea. The well was located in 176 meters water depth, and 3,700 meters away from the Luna A platform.

    The SWACS project demonstrated that a control system without umbilical connection from the surface facilities to the subsea control modules is feasible within the capabilities of the present technology.

  2. SACOS project: In order to improve and upgrade the knowledge developed during the SWACS project, Agip is now committed with Statoil in developing a novel autonomous system based on seawater batteries as an alternative to the lithium ones. The main objective of the project is the installation of the batteries on Agip's Luna 27 subsea well for a period of two years.

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