Production Enhancement Through Subsea Wells Reactivation Via Topside Technology: Offshore Libya Gas Field
Authors: Alawar N. , Raniolo S. , Esposito C. , Guzzo F. , Polzone N. , Mazzocchitti K. , Allegro N. , Trovato E. , Vergani M. , Ong E. , McCudden T. 
Published: October 2023

This paper discusses a real case study application of a topside technology that allowed an operator to re-establish the raw gas production without any subsea campaign in offshore Libya. The approach consists of enhancing the subsea cable insulation by the transmission of a passivation signal to produce an electrokinetic/electrochemical effect that increases the Insulation Resistance (IR) thus enabling electrical power to be re-applied and leading to subsea well reactivation.

Long term operation and exposure to harsh subsea environment conditions can lead to insulation degradation in cables, umbilicals, and electrical equipment over time, which is most often caused by moisture intrusion into the majority of commonly used insulation materials. Such effects result in decreasing the dielectric strength, increasing electrical current leakage and in a continual degradation leading to eventual subsea system failure. As a matter of fact, the impact of subsea electrical failure is significant both in terms of time/costs and revenues. Indeed, historically the replacement of cables, equipment or even umbilicals has been the only solution to this problem.

In such a framework, the application of topside technology represents the optimum solution to solve the subsea electrical problem maximizing efficiency. The real case study application in offshore Libya consisted of a dynamic process that offers an active "healing" solution for low IR. The technology is installed topside within the Subsea Output Module (SOM) and it is part of the Line Insulation Monitoring (LIM) panel. It consists of a passivation signal which is applied between the system electrical power conductors and Earth to produce a continuous, dynamic, non-conducting precipitate through an electrokinetic/electrochemical effect that increases the IR.

The topside technology application had the target to re-establish the raw gas production in the Mid-Line Manifold consisting of a total of 6 subsea wells. In September 2022, the IR reduction led to a partial failure with only 2 gas wells remaining active. In November 2022, the entire MLM system was put offline due to low IR with consequent total gas production losses. In December 2022, the full MLM production was restored via the topside solution. The preinstallation IR of ~173 kOhms was immediately increased after the topside signal activation allowing the full wells recovery within a few hours.

This paper demonstrates the added value of this approach through a real case study application in offshore Libya. The production impact exceeded 80 MMscfd raw gas allowing to re-establish the plateau in only a few months from the first IR problem without resorting to any subsea campaign with an estimated cost saving ~20 M$. Finally, the full gas production recovery led to an improved reservoir management strategy via a full raw gas production coverage exploitation and consequent water management.