Abstract
The Otakikpo marginal field was carved out of OML 11 and is situated in the southern part of the license. Green Energy International Limited, the operator, successfully implemented the first phase of the field development between 2015 and 2017. This was followed up with a 2nd phase in 2022. The field currently produces circa 11000 bopd.
Due to its proximity to the shoreline, an amphibious production and evacuation methodology was implemented. This consists of batch production into onshore tanks, a subsequent evacuation into offshore shuttle tanker via an installed 6", 6 Km offshore pipeline and final transportation to a 3rd party FSO facility. The end of the offshore leg is connected to a PLEM (Pipeline End Manifold) which acts as interface between marine pipeline and the submarine hose system. The mooring systems consists of 2 gravity anchors (5tons each ~ port and starboard); 200m steel anchor chains; 40m sling wire; 20m sling wire; and a 100m pick up rope.
However, the offshore environment experiences a significant adverse weather condition between March and December that peaks between June and November every year. Often, it could take professional divers up to 5 days to pick up rope from the seabed depending on weather condition. There were cases of incessant twisting, tension and curling as the hose is exposed to swinging by ocean swell and current leading to loss of operational integrity of the offshore system. Restoring the integrity of the system led to significant operational downtimes as high as 20 days per year; a situation that was not sustainable for a marginal field producer.
The GEIL engineering and operations team developed and implemented several vintages of design modifications over time to mitigate these concerns. The team realized that the most challenging part of resolving the hose swinging issue was finding a way to keep it fixed, in such a way that the hose end does not move under any weather condition(s). To achieve this, the team designed and installed a Crossbar + Buoy system. The Crossbar was installed on the seabed, while ensuring the height is above the water surface. A boat is used to unhook and hook up the cargo hose to the Crossbar before and after every shuttle loading respectively. This allows for a more efficient pick up and transfer of hose to tanker (10 mins) by professional divers while eliminating the challenges with hose twisting which usually results in hose curling around the PLEM and incessant shutdown from the EPF. Luckily for our operations, there was no spill recorded in these scenarios due the effective communication between EPF and the marine team, and timely shutdown of crude flow from the EPF.
This paper aims to highlight the seasonal integrity challenges faced by the Otakikpo offshore evacuation system, its effect on operational excellence and the various stages of the elegant solutions developed and implemented.
