Abstract

It is important to predict the economical feasibility of geological sequestration of CO2. This paper applies reservoir simulation to model the characteristics of CO2 injection in the specific injection site location.It could provide input to the economic evaluations by defining Bottom Hole Pressure and injection relationships. Selecting an appropriate grid system was particularly discussed in this study. The flexible corner point grid system and grid refinement technology were proven to be suitable for the simulation of CO2 geological sequestration. By this approach, we finally obtained the ultimate capacity of reservoir to store CO2, and further produced data about different possible injection scenarios needed for economic modeling. It was concluded that the geological structure and direction of CO2 migration were two important factors in the selection of the optimum well pattern. The results showed that using one well can satisfy the injection requirement, and also CO2 geological sequestration in the Barrow Sub-basin is feasible.

Introduction

Climate change is a global issue and reducing greenhouse emissions in the face of growing energy demand is attracting more and more people's attentions.(J.A. Jimenez 2002,A. Kumar 2004). A major mitigation strategy for reducing intensity and amount of CO2 emission is geological sequestration (D.N.Nguyen 2002, J.Ennis-King 2002).A pilot study site for a hypothetical CO2 geological sequestration project was selected in the Barrow Sub-basin, offshore West Australia. The target horizon chosen for the injection was a regionally extensive saline water-saturated sandstone formation, sealed by a thick shale sequence. The economic target of the project is to sequester CO2 at a rate of 7.56 MMscm/day (267 MMscf/day) for at least twenty years. This reservoir simulation study aims to determine whether this target is feasible, and further produces data about different possible injection scenarios needed for economic modelling. This project neglects the long-term evolution of the CO2 injected and the effects on the reservoir and the environment. It will support following technical data for economic and risk analysis.

  • Ultimate capacity of reservoir to store CO2 in a maximum sustainable rate within 20 years

  • Required Injection pressure under different well numbers, well pattern, and well spacing for the injection target

Modelling Reservoir with Corner Point Grid

Selection of Model grid Before modelling reservoir, defining an appropriate grid system is very important. The following limitation is put forward in this study:

  • CO2 migration is expected to trend upwards towards Barrow Island

  • Aquifer is laterally unbounded, and analytical aquifer is not appropriate to this study and the Additional large grids are needed to model aquifer's effect

  • Multi injection wells are possibly needed for injection

  • The grid in which the injection well is located should be small up to 50m

By trial and error, tilted cartesian grid can't get ideal simulation result, and the flexible corner point grid system is regarded to be suitable for this simulation (shown in Figure 1 and Figure 2), it can be used to model real and accurate reservoir. The reservoir was modelled by 13*11*8 grid system, In order to get the accurate BHP, we apply the grid refinement technology.

The grid in which the well was located was refined to 33m.At the same time, the large grid size is adopted to model aquifer's effect.

Reservoir Modelling A suitable reservoir property model is crucial to this study. Since Wonnich-1 is the closest well to the injection site and CO2 won't migrate far in injection phase, the information of this well will be used to model reservoir property. The properties are described in Table 1.

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