In March 2019, TOTAL planned and executed the first of its kind Large Scale Exercise (LSE) in Nigeria. Before this operator led LSE, capping equipment had not been deployed in Africa. Since this was the first exercise of the sort to be undertaken in Nigeria, there were several objectives defined at the outset of the exercise:
test the entire response chain (logistics, preparation, execution and communication);
demonstrate to the Nigerian authorities that a comprehensive and efficient response could be executed in a timely manner; and
document, record lessons learned and then feed them back to the local affiliate and others to improve future response operations
For this exercise, TOTAL deployed its Subsea Emergency Response System (SERS) which was commissioned for construction at the beginning of 2012. Two systems were developed for drilling and production hydrocarbon blowout scenarios. The LSE's focus was to deploy the capping system while also taking the opportunity to simulate pumping dispersant. TOTAL has two SERS's that are stored in Pointe Noire, Congo and Luanda, Angola. Due to the readiness of the system in Congo (recently tested and the appropriate connector installed), it was chosen to be used for the LSE.
An abandoned appraisal well was chosen for the exercise due to it being free from subsea infrastructure. The detailed work scope for the LSE was as follows:
○ Controls Distribution Unit (CDU) deployment
○ Flying Lead Deployment Frame (FLDF) deployment
○ Diverter Spool Assembly (DSA) deployment
○ Connection of the Hydraulic Flying Leads (HFL's) and Electric Flying Leads (EFL's)
○ Landing the DSA and locking the connector by Remote Operated Vehicle (ROV)
○ Performing an Acoustic Communication System (ACS) test
Subsea Dispersant Injection (SSDI)
○ Deploying the Hose Deployment Frame (HDF)
○ Deploying the routing manifold on Coiled Tubing (CT)
○ Connecting all hoses with the ROV
○ Simulating pumping dispersant over the well
All equipment was successfully deployed and tested with all objectives achieved. The highlights of the operations were as follows:
○ 20 days from Congo SERS equipment loadout until the end of operations
○ Approximately 27 hours from OneSubsea (OSS) arrival on the vessel until the DSA was locked on the wellhead
○ DSA connector lock and unlock between 4 to 5 minutes
○ 52.1 bbls of simulated dispersant pumped within a one hour timeframe
The LSE involved deploying TOTAL's SERS on an abandoned well and simulating pumping subsea dispersant for an hour. These successful results are the culmination of lessons learned after Macondo and TOTAL's stance to increase its response capacity. Figure 1 shows TOTAL's response readiness evolution over time up to the completion of the LSE in Nigeria which includes the availability of Oil Spill Response Limited (The Subsea Well Response Project, 2018) and Wild Well Control capping stacks (Wild Well Control, 2020).
This paper shares the lessons learned from the deployment of emergency equipment in the Gulf of Guinea (GoG) which could influence response time and the Response Time Model (RTM).
The SERS consists of three main packages with multiple pieces of equipment that can be used to intervene on a well, whether in drilling or production modes. A description of each piece of equipment shown in Figure 2 is set out below (OneSubsea, 2014a):
DSA – an assembly of valves, connectors, instruments and a choke that can shut in a well that is rated to 10,000 psi.
Subsea Accumulator System (SAS) – provides the hydraulic and electrical power in order to function the DSA. The SAS consists of the Subsea Accumulator Unit (SAU), CDU and the FLDF which is spooled with HFL's and two EFL's.
Multiple Application Reinjection System (MARS) shown in Figure 3 consists of the Dynamic Kill Package (DKP) and Flexible Hose Assembly (FHA) which allows well killing through an injection or production Christmas Tree (XT) at the choke by utilizing the choke kill insert included in this package.
The SERS allows well shut-in in three different scenarios. The scenario determines which equipment will be needed and are as follows (OneSubsea, 2014b):
Scenario 1: Through the wellhead and tubing hanger
○ Well shut-in is achieved by using the DSA with the correct connector installed to connect to the high pressure 18–3/4” subsea wellhead. In this case, the XT and Blowout Preventer (BOP) should not be installed.
Scenario 2: Through the BOP
○ Well shut-in is achieved by using the DSA attached to the top BOP mandrel.
Scenario 3: Through the XT
This method allows for two entry points on the XT:
○ Through the re-entry spool production/injection bore (after removal of the XT cap) through the top of the XT using the DSA, the projects existing Interventions Workover Control Systems (IWOCS) and landing string, or Light Well Intervention Vessel (LWIV) and landing string.
○ Through the production/injection XT choke body (which requires removal of the original choke insert) utilizing the DKP. This scenario and entry point is the only one which utilizes the MARS.
Due to the versatility of the SERS, it can be deployed for various scenarios in environments that have similar conditions to the GoG. The main specifications of the system are shown in Table 1 (OneSubsea, 2014a):
The SERS can be deployed with different vessels and can function in a variety of manners due to the weight of the DSA (< 50 mt). The options to function the DSA are as follows:
○ All SAS components can be run with the SAU which is utilized to provide the necessary pressure to the CDU to perform the connector lock/unlock and valve functions on the DSA.
○ An ROV can be used to directly connect to the CDU with a hot stab and perform all the connector and valve functions.
○ The DSA can be deployed from a LWIV and controlled by the LWIV control system. In this case, the SAS does not need to be deployed.
During the initial planning phase of the LSE, the DSA was to be functioned with the SAU: instead at the time a decision was made to utilize an ROV to perform all functions subsea to test the operability of the system with the backup option. Utilizing the ROV provided the opportunity to test its performance as a surface test had been performed with the SAU during the System Integration Test.
The objective of the LSE was not only to show that TOTAL could deploy a capping system but also that it could deploy dispersant. Typically, if an operator wants to deploy dispersant, they can access the subsea equipment from a third party but needs to source all other surface equipment, including the crossover, from the subsea manifold to the downline. In order to prepare for this phase of the exercise, TOTAL sourced coiled tubing in country as it was readily available, surface pumps for displacement and fresh water and dye to be used to simulate dispersant. In addition to sourcing equipment, TOTAL needed to pre-fabricate a coiled tubing frame, shown in Figure 4, so that the dispersant equipment could be deployed through the moonpool. The frame was specifically fabricated for the LSE and took one week of fabrication with another week to install and sea fasten to the African Vision (AV).
DSA and SAS
Two complete systems are stored in Luanda, Angola and Pointe-Noire, Congo to facilitate a robust and timely response in the GoG. After the delivery of both systems, surface testing was performed but the equipment was not deployed subsurface. Therefore, in collaboration with the Nigerian affiliate, the LSE was planned to be conducted in March 2019.
The SERS in Congo was identified and chosen to be utilized for the LSE due to planned maintenance scheduled for February 2019. In order to prepare the equipment for the LSE, all the valves on the DSA were functioned, the connector was stroked, and inventory was taken to ensure that all necessary equipment needed was identified and packed as per the export manifest.
All planned maintenance and equipment testing was completed as per procedure and the equipment sailed away from Congo on March 12, 2019. Figure 5 shows a timeline of the work performed in Congo.
The equipment arrived in Onne, Nigeria on March 16, 2019 and final deployment preparations began to ready the equipment for load out and sail away following customs clearance. Once the equipment arrived in Nigeria, the following work scope was conducted in six days with a day and night crew:
○ installation of the Tree Running Tool on the DSA;
○ CDU preparation for ROV operations;
○ inspection of the DSA for damage and prepare it for deployment; and
○ inspection of the FLDF for damage and prepare it for deployment.
The AV, a planned charter, which can be seen in Figure 6 was chosen to perform the deployment as it had the necessary equipment and crane capacity to safely deploy and retrieve all the equipment.
The main specifications of the equipment located on the AV are in Table 2 (Marine Platforms, undated).
All the equipment that was shipped from Congo to Nigeria was loaded on the AV, except for the Hydraulic Power Unit, SAU and the buoyancy container. Figure 7 shows a picture of the equipment loaded on the vessel. For actual deployment, it was decided to function the system with the ROV as the primary means to ensure that the backup option could successfully perform as intended.
The AV sailed away on March 25, 2019 and arrived on site that evening. TOTAL personnel departed the base and arrived on location after the vessel reached its destination. Deployment personnel arrived on the vessel on the morning of March 26, 2019 and they immediately began making final preparations to the equipment to ready it for deployment. All equipment was successfully deployed and landed on the seabed without incident. The deployment sequence was as follows:
CDU – Pressure Relief Valve change out occurred on the vessel due to it coming off seat at 2600 psi but then was deployed first.
FLDF – deployed second with minimal problems except for after passing through the splash zone, the HFL became detached from the frame.
DSA – deployed last and was successfully landed on the wellhead and the connector was locked without incident with the ROV.
Details of the equipment deployment can be seen in Figure 8.
Once the DSA landed on the well, the H4 connector was locked in 31 minutes and 39 seconds. Following this operation, functioning of all the valves on the DSA was performed. Table 3 contains the results showing the decrease of valve and connector function times from the longest to the shortest of some valve functions (see Subsea Operations, Lessons Learned, for details).
As operations were carried out, trials were conducted in order to optimize and improve the times of each function. These trials resulted in a significant decrease in time, of which some can be seen in Table 3. In total, two complete cycles of opening and closing all valves were performed subsea.
Simulated Subsea Dispersant Injection
A dispersant simulation was conducted to display the ability to deploy all necessary equipment and to show that the appropriate amount of simulated dispersant could be pumped in case of an emergency. In order to perform these operations, several pieces of equipment had to be sourced from different places. The subsea equipment was sourced from Wild Well Control (WWC) while the top side equipment (pumps and coiled tubing unit) were sourced separately from Schlumberger and Halliburton. Everything was planned and shipped as per plan. To utilize the coiled tubing unit, prior preparation was completed to install a coiled tubing frame on the vessel. The coiled tubing unit was sea fastened prior to the mobilization of the vessel from Onne en route to the well. After locking the DSA, deployment of the subsea dispersant equipment commenced with the HDF and routing manifold which are shown in Figure 9.
The HDF was run to the seabed and all the necessary hoses were connected to the routing manifold. The routing manifold was connected to the surface equipment by coiled tubing and ran through the moonpool before being suspended above the well for the displacement operations. In order to simulate dispersant, fresh water and red dye were mixed together and pumped, as shown in Figure 10.
During the dispersant pumping simulation, a total of 52.1 bbls were pumped in an hour at a maximum rate of 1.2 bpm.
Overall, operations concluded as planned and without incident. All equipment was tested, deployed and functioned as designed. All operations were conducted within the planned operations timeline estimation as seen in Figure 11.
Due to a delay in receiving the ACS, the AV performed surveillance work on another well for two days (March 30th – 31st). Once the ACS arrived, the vessel returned to location to perform the ACS deployment and conclude the LSE.
As the LSE in Nigeria was the first deployment of the SERS, there were lessons learned that will have a positive effect on operations in case of an actual deployment. The lessons learned were partitioned into different categories and some are discussed below.
1. As the LSE was a planned event which included planned vessel charters, planned dispersant kit mobilization and coiled tubing frame fabrication, it is believed that these planned events would have a minimal impact on the RTM.
○ Planned vessel charter – in and around the GoG, there are a multitude of vessels that meet or exceed the requirements to deploy the SERS as the DSA weighs less than 50 mT. Due to this, acquiring a vessel on the spot market would have been feasible.
○ Planned dispersant kit mobilization – the dispersant package is stored in a condition that is ready to be airfreighted in a Boeing 747. Boeing 747's are typically available, thus the planned mobilization of this kit had minimal impact on the response time.
○ Coiled tubing deployment frame fabrication – pre-engineering and fabrication of the frame was completed in advance to deploy the downline. This pre-work ensured that the frame would not be on the critical path, thus not impacting the response time. If pre-work is not conducted, the dispersant deployment time could be affected. Utilizing the RTM tool accompanying IOGP 592 (IOGP Wells Expert Committee, 2019b) can help identify elements that can affect the response time.
2. The focus of the LSE was to deploy the capping system while taking advantage of the opportunity to perform a dispersant simulation trial. The steps of the LSE were not executed as they would be in a typical emergency response as the capping system was deployed first and then the dispersant. Although the events of the LSE weren't performed as they would be in an emergency, there were no impediments identified that would indicate that a response time of 10 days or less (IOGP Wells Expert Committee, 2019a) would not have been achieved if the exercise focused primarily on subsea dispersant.
3. When the DSA landed on the wellhead, it took 31 minutes and 39 seconds to lock the connector which was significantly longer than what was expected. After inspecting the complete system, there was a restriction between the ROV hose and the line going to it which caused a decrease in the allowable flowrate. After removing the restriction, the ROV was able to produce the appropriate flowrate which decreased the locking time to 4 minutes and 45 seconds. Before operations begin, all equipment and lines should be examined to make sure that there are no restrictions in order to minimize locking/unlocking times.
4. The operations procedure states that the equipment functions at 3000 psi. The same reading should be displayed on the pressure gauge in order to verify that the proper amount of pressure has been supplied. While running the CDU, ± 1800 psi was registered on the gauge (hydrostatic pressure) which is shown in Figure 12. Verify that procedures account for the possibility of hydrostatic pressure showing on gauges and account for it when functioning equipment.
5. Planning an exercise of this magnitude required resources from Paris Headquarters, Nigeria, Congo and Angola along with dedicated personnel from the participating contractors. Several countries were involved in the planning in order to manage the export and import customs clearance between Congo and Nigeria, vessel sourcing, SERS equipment preparation and operational execution. Furthermore, contractor involvement was needed for their equipment preparation and personnel mobilization (visas, medical clearance, etc.). These different interfaces required weekly meetings over the course of a year to ensure that everyone was on the same page and no details had been overlooked or forgotten leading up to the exercise. Dedicating the necessary resources to an exercise such as this is extremely important as it could command a great deal of time depending on the breadth of the exercise.
The objective of the LSE was to show that the SERS could be deployed subsea and fully function as it was designed. In addition, it was planned to demonstrate that the affiliate could respond to an emergency in line with the guidance from the IOGP 594 (IOGP Wells Expert Committee, 2019a). As shown in Figure 13, these objectives were met (additional time for preparation and loadout in Onne would be excluded in an actual scenario).
As a first of its kind deployment in Nigeria and Africa, TOTAL demonstrated the capability to safely, efficiently and quickly respond in the GoG with the ability to pump subsea dispersant and cap a well. In order to achieve this level of response, collaboration and execution are needed between various contractors working together to achieve a common goal. In addition, this exercise demonstrated that mobilizing a capping system/equipment, which is not in country, can be performed within industry recommended timing. The SERS deployment and SSDI simulation validated that TOTAL and the Nigerian affiliate are ready to respond in an emergency and have the means in place to do so.