Congratulations to ELSA – leading subsea landing string technology for 25 years

11th March 2020

This year we’re celebrating the silver anniversary of our ELSA (Expro landing string assemblies) landing string subsea safety system, which provides a safe and environmentally secure operating system for the commissioning of subsea wells through the complete well lifecycle timeline.


It’s no exaggeration to say the history of ELSA is essentially the history of large bore subsea test tree technology and landing string development in the industry as a whole.


We’ve been looking over some key milestones in ELSA’s evolution during the past quarter century; from how it was established as a stand alone product, to changes in focus from a mono-bore and dual bore safety system, to being a high debris (HD) solution through to increasing pressure capabilities and advanced electro hydraulic (EH) and direct hydraulic (DH) subsea controls.


The story of Expro’s landing string development actually starts in 1983 with our first subsea test tree project. However, the first ELSA branded project was in 1995. It was the successful support of the first horizontal Christmas tree system for horizontal well stimulation on the Åsgard field in the Norwegian Sea, where we were commissioned to deliver a 10K psi 7-3/8” diameter subsea safety system that would provide an inline barrier to the well, disconnect capability and allow hydrocarbon clean up to the rig.


An absolute game changer later on in this project was the introduction of Expo’s ELSA-HD technology involving the high integrity ball valve, which prevents solids ingress from the well or from well stimulation into the valve mechanism. This enabled operations on Åsgard to be carried out in debris concentrations up to 15% solids - way in excess even of today’s API 17G performance standard requirement of 2.5%. Furthermore, this first ELSA-HD system gave the operator the capability to run the completion, frack/stimulate and then clean the well to the MODU (Mobile Offshore Drilling Unit) in one trip - setting the benchmark for high quality safety integrity systems, which is recognised throughout all ELSA products today.


From this first project, it was clear that a technology traditionally associated with exploration and appraisal (E&A) had much wider capabilities as a completion and intervention product for use with vertical and horizontal wells in deeper waters where exposure to greater pressures and temperatures was seen.


Successful vertical tree projects on the original Fionaven and Schiehallion fields followed, allowing us to introduce our first ‘true’ dual bore (5”x2” and 6-3/8”x2”) operating safety systems. Then in 1998 we designed our first electro hydraulic control operating system – EXpress - for use offshore Angola in deep-water E&A wells from a dynamically positioned drilling rig. We are now on the fourth generation of our control technologies, providing a true ‘point to point’ fully SIL2 compliant control logic in line with the newly released API 17G standard.


When the horizontal tree subsea completion market made its first move into deeper water, higher pressure (HP) reservoirs in 2007, we launched our first ELSA-HP 15K electro hydraulic deep-water safety control package, for use in the Gulf of Mexico. These systems, which allow large-bore subsea completion and interventions to be conducted safely in HP operations, are still being used today.


In 2012 we launched the Expro 15K psi ELSA-EA exploration and appraisal tool incorporating a hybrid, high debris, trunnion-mounted and latch mechanism that has become established as the standard E&A product today. It includes a smaller version of the original HD valve and has been designed to comply with modern industry and qualification requirements.


Three years later we developed our first 6 1/8” 15K ‘fast response’ electro hydraulic control/HD valve hybrid system, for use in high rate gas operations in Azerbaijan and bespoke to a specific client. Well isolation/closure speed was essential, so we created a system that allowed the operator to isolate the well at the mud line within two seconds.


Currently, we’re extremely excited about the application of our landing string valve and controls technology in our new Light Weight Intervention (LWI) and Riserless Well Intervention Systems.


Our latest next generation landing string 7-3/8” ELSA-HD valve, design launched in 2018, is the latest development in our subsea test tree assembly product portfolio. It includes the new HD functionality fully aligned with the new and recently issued API 17G standard and sits alongside the most recent versions of those products that have become the industry byword for landing string technology.


At Expro, we’ve always led the market in the landing string sector and, as future technical challenges arise, we’re confident that with our customer bespoke solution philosophy we’ll continue to be one step ahead of our competition. Learn more about how we can help you -

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