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3. REAL APPLICATION IN THE NORTH SEA OFFSHORE OIL FIELD BY SIMOP
An analysis by using SIMOP was conducted in a real offshore oil field located in the North sea. The oil field has the following characteristic:
(1) Most of platforms are tower fixed type, because the North sea is shallow and is an oil field developed from 30 years ago.
(2) Transportation by the pipeline is the usual method. Pipeline is usual transport method from offshore platform to land facility.
(3) The ship is normally used for transport method of materials for platform and work persons.
(4) Gas is also transported to another land facility via pipeline.
Considering the above characteristic, SIMOP is modified as follows:
(1) The function of pipeline module is newly developed in SIMOP.
(2) The function of fixed/tower platform is added in the choice of platform type in SIMOP.
An example of the simulation screen of the modified SIMOP is shown in Fig.4. Also, analysis results of cumulative production oil amount(million barrel) and offshore facility/pipeline cost (million dollars)are shown in Fig.5.
The case in the North sea is not influenced by weather condition, because platform type is fixed/tower and oil transport is conducted by pipeline. The problem considered was unbalance of oil production speed and transport speed, but logistic design for keeping balance can be done by using SIMOP.
Fig.4 Screen of the SIMOP for real oil field application case
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Fig.5 |
Analysis results of cumulative production oil amount and offshore facility/pipeline cost |
4. EVALUATION OF INSTALLATION OF DPS BY SIMOP
When considering the installation of DPS for the FPSO, the installation cost of the DPS and the effect of improvement of operation rate by it should be compared and evaluated. The method shown in Fig.6 was developed to obtain a solution.
The effect of installation of DPS is evaluated by the present method as shown in Fig.6 with the help of DPMAP, SIMOP, and WIMFLOAT. SIMOP simulates the operation behavior of offshore production, storage, and offloading, while WIMELOAT analyzes shaking behavior of the floating structure.
The following effects result from the application of DPS.
(1) The direction of the floating structure can be kept with less shaking by means of DPS-based EPSO direction control.
(2) Mooring force can be reduced with the assistance of thrusters, and then the cost can be reduced by downgrading the mooring device.
(3) Mooring cost can be minimized using full DPS.
(4) Offshore offloading operating performance can be improved by controlling relative distance between the FPSO and shuttle tanker.
(5) Thruster installation effectiveness evaluation can be conducted by inputting initial cost, operating fuel cost, and maintenance cost data.
The influence of upper limit of significant wave height in offloading operation on the production amount, transportation amount, and downtime was studied by simulation using SIMOP. The limit of significant wave height in hawser connecting operation, that is different from the value for offloading operation limit, is set at 3.5m. The offloading work oy the DPS is continued to the limit significant wave height, and the work is interrupted for the wave height beyond it. Production facility downtime, weather recovery waiting time for ship mooring, thruster operating time in severe weather conditions, and the duration offloading operation interruptions are calculated and compared.
Simulation is conducted under the following conditions:
(1) Sea areas considered
The northern area of the North Sea, the area off Borneo, and the area off the Pearl River Basin
(2) Production facility conditions
Daily production of 30,000 barrels, continued for 10 years.
Offloading limited wave height of production system is 10m.
(3) Offloading facility condition
Platform tank volume of 800,000 barrels.
Limited significant wave height of 3.5m for offloading ship mooring operation.
Offloading limited wave heights of 3.5m, 4.5m, and 6.0m for operation continuation, only for the case of the northern area of the North Sea.
(4) Transportation facility condition
Two shuttle tankers.
Shuttle tanker volumes are 280,000 barrel for Case 1 and 250,000 barrels for Case 2. Navigation length is 4,500 km for one way and the same length for return. Shuffle tanker speed is 14 knots, and navigation time is 347 hours. Ship mooring operation time is 5 hours, and cutting-off operation time is 2 hours. Offloading capability is 10,000 barrels per hour, and offloading capability is 20,000 barrels per hour.
The authors compared simulation results of each sea area.
The total weather recovery waiting time for mooring shuttle tankers to FPSO and the offloading operation suspension time due to poor weather condition in each sea area are shown in Fig.7, 8, and 9.
The offloading operation suspension time in Case 1 is less than that in Case 2. Small differences in shuttle tanker volume have substantial influence on the offloading operation suspension time.
Also the time can be decreased when the offloading operation limit wave height increases from 3.5m to 4.5m. The operation performance rate can also be raised if the limit wave height for operation can be raised by equipping the FPSO with thrusters. The limit wave height would be more than 6m for smooth offloading in the actual case of the northern North Sea, because shuttle tankers with DPS are necessary in such severe environmental conditions, as demonstrated by the simulation results shown in Fig.9. The influence on operation performance rate of facility size and combination can be evaluated by means of SIMOP, and output necessary for cost evaluation can also be obtained.
Fig.6 Flow chart of application of DPS to the FPSO
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