1 Introduction
This case study presents field development work performed for Hasselmus project using SFACE based on publicly available data and deduced data. The objective of the study is to identify the SURF and SPS CAPEX of the project. This follows a bottoms-up approach, where all the system calculations are performed, equipment configured and costs calculated based on detailed MTO & offshore operations sequence.
This complete exercise after data collection took less than 1 hour of effort in SFACE.
2 Facts about Hasselmus project
The Hasselmus gas discovery is located on the western edge of the Trøndelag platform in the Norwegian Sea, 7 km northwest of the Draugen platform, in production license 093. The development concept is a single subsea well with direct tie-back to the Draugen platform. Production start-up is planned in Q4 2023 with plateau gas production of more than 4,400 barrels of oil equivalents per day gross [1].
| No of production trees | 1 |
| Flowline length | 9km |
| Flowline type | Pipe in Pipe |
| Water depth | 250 m |
| Production type | Gas |
| Production rate | 4400 boe/d = 0.7 Msm3/d=24.7 MMSCFD |
| Bottom hole temperature | 70 °C [4] |
| Bottom hole pressure | 240 bara [4] |
| SURF+SPS capex | 50 – 150 MUSD [3] |
Field layout, credit OKEA [2]
2.1 Assumed data
| Flowing wellhead pressure | 180 bara |
| Shut-in wellhead pressure | 200 bara |
| Flowing wellhead temperature | 50 °C |
| Sand rate | 0.02 lb/MMSCF |
| Topside arrival pressure | 100 bara |
| Pipeline size |
8” ND, 190mm ID, Uvalue 1.0, CS pipeline + NA625 cladding |
| Umbilical length | 7km |
3 SFACE model
The model consists of process system only, controls & chemical distribution is not covered.
3.1 Flow assurance calculations
The first set of simulations were performed with low arrival pressure (~ 20 bara), which resulted in freezing conditions downstream the subsea production choke. From there it was identified that early life arrival pressure has to be ~100 bara, requiring additional choking topside.
3.2 Preliminary flowline design
The cross section and other relevant details for the flowline is presented in the table below. It was identified that 8” ND with SCH60 for flowline inner pipe and 12” ND with SCH60 for outer pipe is required.
| Flowline Name | Gas Flowline | Riser |
| Length [m] | 9000 | 300 |
| Water Depth [m] | 250 | 250 |
| ND [inch] | 8 | 8 |
| OD [mm] | 219.1 | 219.1 |
| SCH | 60 | 80 |
| Selected_WT [mm] | 10.3 | 12.7 |
| Req_WT [mm] | 8.9 | 11.2 |
| Req_WT_internalPressure [mm] | 8.4 | 10.7 |
| Req_WT_externalCollapse [mm] | 4.2 | 4.2 |
| Req_WT_propBuckling [mm] | 8 | 8 |
| Reeling_WT [mm] | 6.6 | 6.6 |
| Material | X65 | X65 |
| Clad_Thickness [mm] | 3 | 3 |
| Clad Material | SS316L | SS316L |
| Coating_Thickness [mm] | 3 | 3 |
| Pipeline Coating | 3LFBE_PP | 3LFBE_PP |
| insulationReq | Yes | Yes |
| insulationType | Pipe in Pipe | Pipe in Pipe |
| Insulation thk [mm] | 13 | 14 |
| CarrierPipe_ND [inch] | 12 | 12 |
| CarrierPipe_OD [mm] | 323.8 | 323.8 |
| CarrierPipe_SCH | 60 | 60 |
| CarrierPipe_Material | X65 | X65 |
| CarrierPipe_Selected_WT [mm] | 14.3 | 14.3 |
| CarrierPipe_Req_WT_externalCollapse [mm] | 6.2 | 6.2 |
| CarrierPipe_Req_WT_propBuckling [mm] | 11.8 | 11.8 |
| CarrierPipe_Reeling_WT [mm] | 11.8 | 11.8 |
| Achieved UValue [W/m2-K] | 0.72 | 0.74 |
| Required UValue [W/m2-K] | 1 | 1 |
3.3 PLET results
Main results for PLET piping are shown in below table.
| Pipe_name | mainHeader |
| ND [inch] | 6 |
| OD [mm] | 168.3 |
| SCH | Std |
| Selected_WT [mm] | 7.1 |
| Req_WT [mm] | 6.4 |
| Material | SDSS-S32750 |
| Sand Mass Rate [kg/s] | 2.6E-06 |
| Sand Mean Size [micron] | 50 |
| Inlet_Pressure [bara] | 122.6 |
| Inlet_Temperature [°C] | 36.7 |
| Pipe erosion rate [mm/yr] | 4.7E-08 |
| Bend erosion rate (GF2.0) [mm/yr] | 4.8E-06 |
| Bend erosion rate (GF4.0) [mm/yr] | 9.5E-06 |
| Tee erosion rate (GF2.0) [mm/yr] | 9.4E-07 |
| Tee erosion rate (GF4.0) [mm/yr] | 1.9E-06 |
3.4 Subsea Xmas Tree (XT) schematic
Automatically generated by SFACE in native CAD format.
3.5 Capex results
Assumptions:
- 35% margin on equipment cost to arrive at equipment prices
- Standard project management and engineering
- All equipment pre-qualified
Exclusions:
- Umbilical and subsea controls distribution systems (equipment and installation)
- Topside controls equipment
- Capital spares
Estimated SURF + SPS capex of 70.1 MUSD.
3.6 Concluding remarks
The estimated capex of 70.1 MUSD presented above is without the umbilical and controls distribution equipment. The cost for typical production umbilical & controls distribution would be approx. 10-15 MUSD, which will bring the total capex to 85 MUSD. All this estimate also assumes standard project management and engineering.
The capex estimated by SAFCE is within the capex bracket available in public domain. Also, it should be noted that all the results presented here were obtained with less than 1hour work. This demonstrates the effectiveness of SFACE.
4 References
- https://www.okea.no/okea-has-awarded-contracts-for-the-hasselmus-project-to-subsea-integration-alliance-and-aker-solutions/
- https://www.okea.no/decision-to-develop-the-hasselmus-gas-discovery/
- https://www.offshore-technology.com/news/subsea-7-okeas-hasselmus-project/
- https://factpages.npd.no/en/wellbore/pageview/exploration/all/1990
