Opportunities for underground geological storage of CO2 in New Zealand : report CCS-08/8, Taranaki petroleum field simulations

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Archer, R.; Arnot, M.J.; Higgs, K.E.; Williams, B. 2009 Opportunities for underground geological storage of CO2 in New Zealand : report CCS-08/8, Taranaki petroleum field simulations. Lower Hutt, N.Z.: GNS Science. GNS Science report 2009/61 37 p.

Abstract: This report considers CO2 storage potential in depleted oil and gas fields in the Taranaki Basin via two case studies – the Cheal and Maui petroleum-producing fields. The Cheal Field was chosen as an example with enhanced oil recovery potential, while the Maui Field was chosen as an example of storage in a near depleted gas field. Cheal is an onshore field which produces waxy crude oil and is typical of many fields in the Taranaki area. The Cheal field is situated close to the Kapuni gas processing plant which is a point source emitting CO2. A reservoir simulation model was constructed to assess CO2 enhanced oil recovery (EOR) potential for this field. The field was difficult to history match because the well operating conditions have been quite variable over the life of the field. However, the match obtained is considered acceptable. The modelling results show that injection of CO2 into the field from two wells repressurises the field and boosts recovery of intermediate hydrocarbon components by 35% and heavy hydrocarbon components by 64 to 67%. During the enhanced oil recovery stage some CO2 cycling does occur, however, once the field is depleted the simulations show the field has the potential to store approximately 160,000 tonnes of CO2. The Maui Field is attractive because of its long history, large pore volume and relatively high permeabilities. Study of this field was rather limited due to a lack of public domain data about key production aspects of the field. The model presented in this report considers only one reservoir interval, namely the Mangahewa Formation or C sands. A static model of the C sands was constructed using open-file seismic and well data. The flow simulation model began by depleting the field by operating all the wells at a fixed (low) bottom hole pressure of 600 psi. Eight injection wells were then added to the simulation model. By injecting CO2 into these wells the field was effectively repressurised. The model predicted 222 million tonnes of CO2 could be stored in the Maui Field C Sands via the injection operation. Most (72%) of this was accommodated in the Maui B area. The injection of 222 million tonnes of CO2 corresponds to approximately 40 years of emissions from the Huntly power station. The storage capacity value should however be viewed as an upper bound on the capacity of the C sands since these sands were modelled in isolation from the D sands. The simulation model results could not therefore be calibrated against published information on the performance of the overall field. To improve confidence in these predictions, further study of both fields is recommended. At Cheal, the role of reservoir cooling and wax deposition needs to be further understood and modelled in greater deal. The data available at this stage were insufficient to fully include those effects in the current models. The Maui model should be extended to include the more heterogeneous Kaimiro Formation (Maui D sands). This will provide a greater understanding of the challenges that reservoir heterogeneity presents in CO2 storage projects. (auth)