Expro has invested in ELSA technology, including high-debris and high-pressure systems, which are used in conjunction with Express 7 electro-hydraulic controls to counteract the specific issues encountered in deepwater environments. (Images courtesy of Expro)

Ensuring safe operations becomes more challenging as deepwater (to 7,500 ft) and ultra deepwater (in excess of 7,500 ft) environments present harsher operating conditions in terms of pressure, temperature, equipment reliability, and potential debris ingress.

Safety is critical when carrying out the vital process of maintaining well control throughout well commissioning and intervention, and temporary subsea safety systems (landing strings) are deployed for this purpose. However, because some landing string systems are not designed to work safely and cost effectively at such depths, problems can arise.

To meet this demand, Expro has invested in Expro landing string assembly (ELSA) technology, including high-debris (HD) and high-pressure (HP) systems, both of which are used in conjunction with Express 7 electro-hydraulic (EH) controls to counteract the specific issues encountered in deepwater environments.

From past to present

The primary function of a landing string during completion operations is to provide full well control and, when required, a safe and reliable disconnect from the completion string while securing the well. When operations allow, the landing string carries out an efficient and reliable reconnect of the completion string. Disconnecting from the completion string can be required in the event of bad weather, vessel “drive off,” or for other operational reasons. Another key consideration during the disconnection, in addition to providing a controlled, emergency-well isolation, is the containment of hydrocarbons within the landing string riser.

Historically, landing string tooling has been certified to the API 14A specification for subsurface safety valve equipment standard. This specification was initially devised to provide the industry with a minimum acceptable standard for safety valves.

With the trend toward projects venturing into deeper waters and more hostile conditions, it became clear that landing string technology had to surpass these requirements.

Critical issues such as ball sealing reliability, unlatch/ relatch reliability, increased valve work frequency, debris control, improved washing profile, and remote maintainability needed to be addressed. To that end, Expro implemented a thorough design and testing process, which resulted in the creation of the ELSA HD technology.

The HD system has a robust double-ball valve design with a unique debris-tolerant, ball-seat sealing arrangement. The operating system automatically redirects the reaction load paths by allowing a very slight movement of the ball valve, while retaining a mechanism to allow the ball element to be unloaded off the valve seat during rotation. The system prevents debris ingress by remaining in contact with the ball and valve seat. The ball instantaneously reloads onto the valve seat upon closure. Automatic load redistribution occurs as a result of three differing levels of mechanical spring force, each interacting with one another at pre-determined intervals throughout the valve cycle.

The innovative design has a tested and field-proven tolerance to wellbore solids during such processes as high-rate well stimulation and frac/proppant flowback operations.

This design maximizes system reliability and service deployment times and minimizes maintenance, which eliminates operational downtime.

To enable use in deepwater and ensure the fastest possible reaction times, the Express 7 EH control system stores energy within the riser control module and deploys it subsea to the ball valves and/or the unlatch mechanism.

Unlatching is performed through the umbilical and a discrete and dual redundant control system within the surface electrical control panel (SECP). The SECP provides a fast and reliable emergency shutdown (ESD) and emergency quick disconnect (EQD) system. An EQD time of 15 seconds has been achieved, and this is critical for the safety of the rig while operating in deepwater locations, especially on a dynamically positioned (DP) vessel.

The EQD system protects the environment by retaining riser fluids prior to the disconnect. A passive latch orientation mechanism option can be incorporated to negate the need to rotate the string upon landing string reconnect. The system also provides well integrity assurance and the ability to kill or re-enter the well in a controlled manner.

As more DP vessels are being used for deepwater completion operations, the likelihood of shear ram activation during completions has increased.

A hydraulic latch retrieval tool has been developed for this event, allowing the latch assembly to be safely retrieved and enabling the system to be repaired and reinstalled so operations can continue.

Valves in the subsea test tree have been qualified under full hyperbaric conditions to 10,000 ft (3,048 m) water depth equivalent, ensuring valve failsafe closure with spring force only, while exposed to maximum external loads and pressures, this guarantees the safety features required to complete wells in harsh environments are present.

ELSA HD is rated to 10,000 psi, but projects in the Gulf of Mexico often exceed this pressure. The same design philosophy that went into the ELSA HD was used to develop the 15,000 psi ELSA HP landing string, which can withstand the high-pressure environment. The system is compatible with Expro’s EH controls system and has been developed with coiled tubing cutting capability. These assemblies also benefit from the HD design for trunnion mounted, high-integrity ball valves, which make the systems debris-tolerant, safe, reliable, and ideal for expensive deepwater subsea operations.

ELSA technology at work

Several years ago an operator in the North Sea requested that Expro provide two full landing string assemblies for a subsea project. Expro had been providing landing string technology for a number of years, but aggressive well stimulation and fracturing were taking place, which meant a significant injection and flowback of high viscous proppant were carried out during completion operations. After completing or stimulating each well, a cleanup flow period (generally lasting between one and two days) was performed. During this period, the well produced drilling fluids, formation sands, and perforating debris. The most aggressive conditions were encountered after hydraulic fracturing took place, with several tons of aggressive debris being produced.

This type of activity stretched beyond the limits and operational envelope of the original ball valve technologies, an indication that new technology would have to be developed. After two years of working closely with the customer to address specific needs, Expro developed and deployed the ELSA HD system. The new technology kept non-productive time to almost nil, and the system’s reliability significantly reduced capital expenditure.

Already in use in the North Sea, Africa and the US, Expro’s subsea safety systems are increasingly in demand in deepwater projects in the Gulf of Mexico, West Africa, Brazil, and Asia. As deepwater environments become more challenging, the company continues to invest in expanding its landing string technology to meet the changing demands of emerging markets.