Advancing optimisation

Operators require cost effective flexibility in subsea architecture to provide increased well productivity throughout life of field. Ian Donald explains how ESI technology enhances production

Fifty-five years ago, the first subsea production tree was installed in the Gulf of Mexico. Today, almost 6000 trees have been installed on subsea wells worldwide.

As operators increasingly look to increase the productivity of subsea wells and increase their recoverable reserves, one of the biggest challenges they face is finding an adaptable cradle-to-grave solution applicable to any subsea infrastructure, which is independent of all major subsea hardware decisions.

How to tackle the challenge of multiple manufacturers, diverse engineering configurations, variable water depths and the desire for flexible production management throughout the life of an asset in one easy step was the conundrum which brought a team of experienced engineers together in 2011 to form Enpro Subsea.

Subsea wells typically produce 10-30 per cent less hydrocarbon than equivalent platform-based wells. The main reason for the difference in performance is the complexity and cost of monitoring, measurement and intervention on subsea wells. Typically, recovery without regular intervention is only 22 per cent of available reserves, although appropriate intervention could increase that figure to 50 per cent.

The challenge for operators is to find cost-effective methods that provide the flexibility required to enhance subsea production throughout the life of an asset. Conventional liquid intervention systems involving rig-based intervention, via the tree or a choke-replacement system, are constrained by the wide array of individual manufacturer specifications, varying interfaces, crossed license agreements, increased payloads, flow restrictions and limited workover access. An intimate knowledge of ‘as built’ and ‘as installed’ engineering is also required for each tree.

Decisions on subsea production systems are often based on limited information obtained from exploration wells. How production and water injection wells will behave over their lifecycle is, therefore, uncertain. Unlike a topside well, which can be accessed at any time, a subsea well requires co-ordination of significant hardware – rig, vessel, equipment and so on – to enable fluid intervention access.

To address these various issues, Enpro Subsea has developed the Enhanced Subsea Sampling & Injection (ESSI) system which is adaptable to any subsea tree or manifold for accessing hydrocarbon flow subsea for a range of applications, including well control, scale squeeze, acid stimulation, fluid sampling and multiphase metering. ESSI provides a universal interface that is deployed at multiple locations, including the jumper hub, pipeline end termination (PLET) or manifold.

The team behind the development were also responsible for the MARS (Multiple Application Reinjection System), acquired by Cameron in 2007.

The ESSI flow access hub is a safe access port for well or pipeline operations that is retrofitted into existing subsea hardware or seamlessly integrated into a new field development. ESSI is located ‘off the tree’ and comprises key subsea components that are standardised to enable fasttrack procurement, giving operators the ability to manage production efficiency as required across all phases of the project cycle.

The patented Flow Access Module (FAM) hub is supplied in a single or dual-port version either with new hardware or permanently retrofitted onto existing infrastructure. With the FAM hub in place, a range of interchangeable units are deployed allowing a range of optimisation solutions from the first day of production onwards. These enable multiple enhanced production solutions such as flow assurance, well control, scale squeeze, acid stimulation, hydrocarbon sampling, multiphase metering or multiphase pumping.

The ESSI Fluid Intervention System (FIS) is configured for single-vessel operations, significantly lowering the economics threshold of deepwater well control, scale squeeze and acid treatments. To reduce the risk and costs associated with fluid intervention, the FIS bypasses the traditional approach of squeezing wells via a MODU, LWI vessel or multiple vessel solutions using separate intervention and stimulation packages. Instead, this approach combines storage, pumping, delivery and deployment equipment onto a single optimised vessel deck. The ESSI Fluid Intervention System is interfaced to several well access points, such as the tree cap, a MARS enabled choke or ESSI FAM hub and service subsea well stock.

The ESSI head is a lightweight ROV-installed solution that minimises deployment loads onto the receiving structure and provides automated flow control and shut-off. These features further reduce the complexity and footprint of the deployment system, enabling greater storage for multi-well campaigns from a single vessel.

Potential ESSI Flow Access Modules operations include:

• Well fluid treatments and sampling
• Well flow rate, water cut, sand production monitoring for well performance and production system integrity
• Well pumping to increase well flow rates and recoverable reserves
• Well kill and control
• Production flowline integrity, providing flow access and system for flowline de-sanding and de-wax treatments

The ESSI system has a derivative application that allows operators with gravity base structures to fulfil decommissioning obligations in compliance with OSPAR convention guidelines. The ESSI decom system uses a patented anchor hub, which locks onto the cell top of gravity-based structures, enabling safe drilling, sampling and pumping operations via a safe and secure connection. Since Oct 2015, the ESSI decom system has been used in the North Sea to remove trapped fluid from a concrete gravity base structure during decommissioning.

ESSI systems are being manufactured for Gulf of Mexico, West Africa and the North Sea. In July 2016, a US operator took delivery of two ESSI Flow Access Modules (FAM) and associated intervention hubs in the Gulf of Mexico. These dual bore FAM hubs enable multiple applications including:

• Production Modules for retrievable well instrumentation including multiphase metering, water cut metering and acoustic sand detection
• Flow Assurance Module for mitigating hydrate remediation risk and providing retrievable chemical injection (methanol)
• Flow Intervention Module for well stimulation

The sustainability of the subsea sector relies on everyone playing their role. Standardisation and driving advances in production optimisation are a fundamental part of this evolution.

Enpro Subsea
Ian Donald is managing director and a founder of Enpro Subsea. Enpro Subsea is a global production optimisation specialist company focused on delivering enhanced hydrocarbon production for customers through their patented Enhanced Subsea Sampling and Injection System (ESSI) range of products and services.

For further information please visit: enpro-subsea.com