Documentation of 45% CO2 reduction by replacing a conventional conductor with a CAN-ductor
The two Lundin exploration wells Bask and Polmak, drilled with the West Bolstad rig in the same area in the Barents Sea in 2020, were compared against each other. The Polmark well had been established with conventional drilling and a cemented conductor whilst the Bask well utilised a pre-installed CAN-ductor. The total environmental impact for each well was assessed and compared by one of Norway’s leading environmental consulting firms Asplan Viak. The study documented a total reduction equivalent of 420 tonnes CO2 with the use of a CAN-ductor, a reduction of 45%.
1. Methodology The environmental impact of both wells was measured using life cycle assessment (LCA). LCA is a systematic method which aims to evaluate the environmental impact of a product or service through its life cycle; from extraction of virgin material, production, transport, use phase and waste management. According to the European commission it is the best available framework to assess the environmental burden of a product (Hellweg and Milà i Canals, 2014). An LCA study may consider several environmental impact categories, such as climate change, human toxicity, particulate matter formation, terrestrial acidification, freshwater eutrophication and marine eutrophication.
LCA consists of four phases: 1 – goal and scope, 2 – inventory analysis, 3— Impact assessment and 4 – interpretation, which are illustrated in Figure 1 and described below.
Figure 1 - The four phases of a Life Cycle Assessment
The inventory analysis modelling and impact calculation (see figure 1) in this study was conducted with SimaPro software 2. SimaPro is the most used software for LCA worldwide and allows for continuous and subsequent revisions and investigations. In an LCA study, it is typical to distinguish between foreground and background data. The foreground data is collected for a specific study and describes the system in question, while the background data is generic data from a database. The foreground data in this study was based on information provided by Lundin Energy Norway (LENO) and Neodrill, while the background data was based on inputs from the ecoinvent database, and a pre-existing database of offshore oil and gas operations developed by Asplan Viak. The ecoinvent database was developed and is maintained by the Swiss Centre for Life Cycle Inventories. The database is constantly expanding and is to date the World’s most extensive database for conducting LCAs, containing nearly 15 000 datasets in areas such as energy supply, transport and fuels, chemicals, construction materials, wood, and waste treatment. The study is based on well geometry data and descriptions for the well sections as provided by LENO and Neodrill. The model includes inputs for scenarios describing the conventional conductor and the CAN-ductor technology. As the CAN-ductor affects the requirements related to the subsequent 26" well section, the study examines this well section to some degree. The input for the analysis is based on delta values, meaning that the environmental impacts do not cover the total impacts of the drilling operations for the wells. The data inputs include the offshore drilling unit, supply vessels, energy, casing materials, and the production, installation, removal, and maintenance operations of the CAN-ductor unit. Figure 2 illustrates the considered wells architecture and input data tables for conventional and CAN-ductor technologies. The rig time for the conventional conductor is higher due to the top-hole drilling activities and conductor cutting and removal activities. With the CAN-ductor there is a high diesel fuel consumption related to transport and mobilization of the CAN. The Bask well has rig time related to an increase in 26" hole section drilling activities.
Figure 2 - Well architecture with input data from conventional conductor and CAN-ductor 2. Conventional drilling verses CAN-ductor technology For the conventional conductor on the Polmak well, spudding consisted of drilling the 42" x 36" hole section and installing a 67 m 36" x 30" conductor. The 50 tonnes of casing was transported from Hammerfest to the Polmak well by LNG supply ship and is accounted for in the life cycle model. Installation of the conductor amounted to 66 hours of operation on the West Bolstad rig. The process involved seawater and water-based mud being pumped into the well to transport cuttings out of the well, cool and lubricate the drill bit, stabilize the formation, and maintain down-hole pressure. Cuttings and drilling fluid are deposited to the seabed. Thereafter, the annulus between the open hole and the conductor are filled with cement. Some of the cement is discarded on the seabed. Before the well is abandoned, the conductor will be cut and partially removed, which requires a rig time of 16,7 hours.
Figure 3 provides an overview of the system processes related to the modelling of the Polmak well. Drilling time (West Bolstad) includes all activities related to activities when installing a conventional conductor. The well casing profile includes all activities and impacts from the casing itself, and offshore discharge includes all impacts from discharges of cuttings, drilling fluids and cement.
Figure 3 - Overview of system processes in the LCA model of Polmak
The CAN-ductor is a pre-installed and re-usable well foundation that is installed by suction anchor, prior to the arrival of the drilling rig. The CAN is lowered to the seabed using its own weight to plant itself on the sea floor. An ROV creates an under pressure in the CAN by sucking water out of it, making the CAN penetrate deeper into the seabed.
Figure 4 - CAN lowered to the sea floor by support vessel and penetrates the seabed by ROV
The CAN-ductor removes the need for top hole drilling, conductor installation, and the use of drilling fluid, thereby avoiding disposal of cuttings, subsequent leaching of heavy metals, and discharge of drilling fluids on the seabed.
The weight of the CAN-ductor unit installed on the Bask exploration well is 116 tonnes - 106 tonnes of steel and 10 tonnes of concrete.
The manufacturing and maintenance processes of the CAN-ductor are included in the life cycle model. The CAN unit was transported to the offshore location by the marine diesel fueled installation vessel, Island Victory. In order to keep the assumptions for conventional conductor casing and CAN on the same level, the transport from Stavanger to Hammerfest have been disregarded in this study, as the detailed transportation of conventional casing is not available and the differences in environmental impact are negligible.
It is assumed in the study that the CAN unit is used on one well before being transported back to shore for maintenance. Maintenance of CAN-ductors takes place in Stavanger and includes equipment washing after every use, repainting every second use, and targeted welding after being used on five uses. The expected lifetime of a CAN-ductor is ten wells. The Bask well was ascribed 10 % of the impacts associated with production and maintenance of the CAN-ductor unit.
The first hole section drilled on the Bask CAN-ductor well was the 26"section. As this section on the well required more work compared to the Polmak well, 3 hours of rigtime was added to its life cycle modelling. There was also an added volume of cuttings with residue of water-based mud, based on the 53 meters of additional drilling length on the 26"section. Although CAN facilitated riser-less mud recovery systems (RMR), there remained a slight mud residue on the cuttings discharged to the sea floor. It is assumed that the 26"well section had a disposal rate of 0,34 m3/m (theoretical factor) resulting in 20 m3 added cuttings. The CAN-ductor eliminates the need of cement in the top hole, however 15 m3 of additional cement was required as the CAN-ductor was 53 m shorter than the conventional conductor.
Figure 5 provides an overall overview of the system processes relating to the modelling of the Bask well. West Bollsta represents all extra drilling activities connected to the 26"hole section on Bask. The CAN manufacture, maintenance, and installation processes include all activities related to the CAN itself. All discharges to sea occur due to the increased activity on the 26" hole section and are represented under offshore discharge processes.
Figure 5 - Overview of system processes in the LCA model of Bask
3. Impact Assessment Result
The compared environmental impacts of the conventional conductor
(Polmak) and the CAN-ductor (Bask) well are presented in Table 1.
Table 1 - Compared environmental impacts for the Polmak and Bask wells
Figure 6 - Contribution analysis for delta values of conventional VS. CAN-ductor well impacts
The CAN-ductor well has lower impacts associated with drilling time and the well casing compared to the conventional well. While the CAN- ductor well had additional impacts associated with production, installation and removal and maintenance, the re-usability resulted in lower impacts compared to the conventionally drilled well.
For the conventional conductor technology, drilling time and well casing were responsible for around 90 % of the impact in several categories, including climate change, while discharges to sea were responsible for the remainder.
The goal of this LCA study was to quantify the difference in environmental impacts associated with the conventional conductor technology used on the Polmak well and the CAN-ductor technology used on the Bask well. The CAN-ductor drilling well had lower environmental impacts compared to the conventional conductor, especially for the climate change category. The reduced environmental impacts can be mainly attributed to lower rig time and fewer well casing materials. The reduction in CO2-equivalents amounted to 420 tonnes.
The CAN-ductor required transport and handling by a diesel driven vessel, as opposed to the conventional equipment which is transported by an LNG carrier. Replacing this diesel driven vessel with an LNG carrier in the model, substantially reduce the emissions of SOx,NOx and greenhouse gases.
In addition to the quantified benefits in the LCA analysis, the CAN-ductor offers further environmental benefits and advantages. This includes cuttings reductions which subsequently reduce the disturbance of benthic ecosystems that are sensitive to the turbulence by cutting disposal to the seabed. Furthermore, the CAN-ductor well drilling technology offers advantages with respect to cost, use of tool and special equipment, cement service crew, logistics, transport, and HSE aspects.
In conclusion, the use of the CAN-ductor technology offers several environmental benefits and advantages compared to the conventional conductor technology.
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Asplan Viak Rapport 630444-01-Comperative LCA of the Neodrill CAN-ductor technology