OLGA is the main program to run the simulations and it has many settings and addition of components to build a proper model which must appear close to well 6608/10-D-2H of Norne oil filed. These settings are explained and the model that was designed in OLGA is shown in
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Figure 6.8. The upper figure illustrates the left end of the model where both in production tubing and wellbore the flow is zero. The near-well source extracts the information of reservoir from Rocx file attached to it. Then, there is valves in each section boundary from which the fluids enter into the wellbore. Similarly, leaks are the connectors of wellbore and production tubing whereas packers divide two different zones. For 8 zones the model has same component except at the end of the right end of the model is pressure node outlet. This pressure node creates the pressure difference between the production tubing and wellbore that makes the reservoir fluid to move towards the pressure node.
Figure 6.8: OLGA model of well 6608/10-D-2H of Norne oil field
6.2.1 Case definition
In case definition, a PVT file defining three phase system is used for developing OLGA model and an integration time is given for minimum time step of 0.01 s , maximum time step of 10000 s and the case is simulated for 200 days.
6.2.2 Composition
Three Black oil components for oil, water and gas must be defined in this setting since the simulation is being run for all three components and it should be the same values as defined in Rocx. Also, water drive and oil drive is defined same as done in Rocx.
6.2.3 Flow component
The flow component describes about the properties of components being used in production tubing and in wellbore. As shown in Figure 6.8, the OLGA model for well 6608/10-D-2H of
6 Development of model
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Norne oil field, to understand it better, a simplified diagram of how the models are designed with the components is shown in Figure 6.9.
Figure 6.9: Diagrammatic representation of a simple OLGA model with its basic components [9]
From the Figures 6.8 and 6.9, it is shown that there are two pipes, one for wellbore where various components are installed, and another is the production tubing from where the reservoir fluid flows. The information of each of this tubes along with the information of its properties is required in OLGA model. So, the diameter of production tubing is 0.1397 m which is 5.5 inches, and the tube is 992 m long while the diameter of wellbore is higher than that of production tubing which is 0.2286 m or 9 inches and has same length as production tubing.
The material of the pipe being used is same in both pipes therefore the value of surface roughness (𝜀) is same for both which is 0.00015 m.
As it is discussed earlier in subchapter 6.1.2 that length of the pipes are divided into 8 zones and these zones are the production zones shown in Figure 6.9 which are further divided to 16 sections, each zones subdivided into two hypothetical sections, making the length of each sections to be 62 m.
Each of the zones containing two sections in wellbore has four components. The first component is a packer, and it is a device that stops the fluid flow from one zone to another so, basically packer is used to separate zones. Then comes the nearwell source in first section of each zone that is plugged in with Rocx. The ICD valves are then installed in the imaginary boundary of the two sections from which reservoir fluids enters the wellbore and flows through leak in second section of each zones entering the production tubing. These fluids from all the zones collects the reservoir fluids from wellbore and moves towards the heel. The designation of each component is shown in Table 6.6.
Table 6.6: Description and specification of components of wellbore
Components OLGA module Description
Near-well source Near-well Linked with corresponding Rocx file ICD valve Valve Diameter = 0.09 m, CD = 0.84, connected to
wellbore from which reservoir fluids enter
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Leak Leak Diameter = 0.12 m, CD = 1, connected to production tubing
Packer Valve(closed) Diameter = 0.09m, opening = 0 (fully closed), connected to wellbore
After these zones are modelled for production, the boundary conditions must also be defined for the final step. There are four boundary conditions of the flow path that are given in Table 6.7. The boundaries of wellbore, both inlet and outlet, are closed node which also acts as packer for the first and the last section of wellbore however, the inlet boundary of production tubing is closed node, but the outlet acts as the pressure node because all the fluids collected from wellbore is driven towards the heel using this pressure outlet also called as pressure node. This is the same pressure node whose drawdown pressure was estimated as 12 bar in subchapter 5.6 and the temperature is assumed to be constant.
Table 6.7: Boundary conditions for wellbore and production tubing Flow path Boundary name Boundary type
Production Tubing
Inlet Closed node
Outlet Pressure node, Pressure = 265 bar, Temperature =115℃
Wellbore Inlet Closed node
Outlet Closed node