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The 3D geological models

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This report details the selection and building of three 3D geological models and their attribution carried out as part of the NERC funded Multiscale Whole Systems Modelling and Analysis Project led by Imperial College, London. The report describes the original purpose for the models in the wider Whole Systems project, their scope and limitations and references their use in CCS investigations so far. The report details how each was built, the data used and guidance on their attribution.

This is the first time that detailed 3D models of potential CO2 storage reservoirs have been constructed with the functional capability to represent the storage reservoir in different parts of the basin. They have direct relevance to the study of CO2 plume migration in the sub-surface and have the potential to contribute to future research in this area.

This work has developed the methodology and confirmed the approach to building complex 3D models from publically available information to further understand and measure CO2 injection and storage performance. These models, or those built using similar methods and data sources to those described in this report, may also have applicability in other fields of research where detailed earth models are required as a framework for flow modelling investigations. The papers published from application of these models (Korre et al., 2013<ref name="korre">KORRE, A, DURUCAN, S, SHI, J-Q, SYED, A, GOVINDAN, R, HANNIS, S, WILLIAMS, J, KIRBY, G, and QUINN, M. 2013. Development of key performance indicators for CO2 storage operability and efficiency assessment: Application to the Southern North Sea Rotliegend Group. ''Energy Procedia'', '''37''', pp.4894– 4901.
</ref>; Babaei et al., 2014a<ref name="babaei2014a">BABAEI, M, GOVINDAN, R, KORRE, A, SHI, J-Q, DURUCAN, S, QUINN, M, and MCCORMAC, M. 2014a CO2 storage potential at Forties oilfield and surrounding Paleocene sandstone aquifer accounting for leakage risk through abandoned wells. ''Energy Procedia, ''63, pp. 5164–5171.</ref>; Babaei et al., 2014b<ref name="babaei2014b">BABAEI, M, PAN, I, KORRE, A, SHI, J-Q, GOVINDAN, R, DURUCAN, S, and QUINN, M. 2014b. Evolutionary optimisationfor CO2 storage design using upscaled models: Application on a proximal area of the Forties Fan System in the UK Central North Sea. Energy Procedia, 63, pp. 5349–5356.</ref>; Babaei et al., 2016a<ref name="babaei2016a">BABAEI, M, PAN, I, KORRE, A, SHI, J-Q, GOVINDAN, R, DURUCAN, S, and QUINN, M. 2016a. CO2 storage well rate optimisation in the Forties sandstone of the Forties and Nelson reservoirs using evolutionary algorithms and upscaled geological models. International Journal of Greenhouse Gas Control, 50, pp. 1–13.</ref>; Babaei et al., 2016b<ref name="babaei2016b">BABAEI, M, GOVINDAN, R, KORRE, A, SHI, J-Q, DURUCAN, S, and QUINN, M. 2016b. Calculation of pressure- and migration-constrained dynamic CO2 storage capacity of the North Sea Forties and Nelson dome structures. International Journal of Greenhouse Gas Control, 53, pp. 127–140</ref>) demonstrate their use as tools to further understand the injection and behavior of CO2 in a geological reservoir.

The work described here illustrates what can be done with published maps and released well data. Since the work carried out for this project was completed, modelling software has become more and more sophisticated and BGS expertise in building 3D earth models has significantly increased. In particular, BGS can draw on its ability to access and gather data from an abundance of onshore analogues and apply our field geological and modelling expertise in realistic attribution of our geological models.

Finally, further reduction in uncertainty relating to these models could be facilitated by obtaining and interpreting seismic data over the model areas.

==The 3D geological models==
The three 3D geological models were built from defined areas within the depositional extents of three different sandstones that are proven hydrocarbon reservoirs but also exist as saline aquifers and therefore potentially significant CO2 stores. Reservoir characteristics will vary with location and one of the aims of the project was to assess the performance of the same sandstone reservoir in different parts of its depositional setting; thus the variation in reservoir petrophysics, thickness and depth was investigated and quantified. The delivered models are generic, but capable of being altered and attributed differently so that the reservoir could be assessed as a CO2 store in different parts of its depositional extents. The three generic 3D models are summarised in Table 15 below.

===The Rotliegend model===
The 3D model is representative of Leman Sandstone Formation with a simplified over- and underburden. The model explicitly includes faulting and reservoir sub-divisions. Through this work we have used knowledge of facies distributions and petrophysical properties (and controlling factors) to define five Area Types based on geological depth and thickness.

The basic Rotliegend model was utilized in Korre et al., 2013<ref name="korre"></ref> to develop performance indicators for the Leman Sandstone reservoir and a more detailed version of the model was built as part of an internal BGS project including further facies and property modelling (Hannis et al., 2011<ref name="hannis2011">HANNIS, S D, WILLIAMS, J D O, KIRBY, G A. 2011. 3D reservoir modelling of the Ravenspurn gas field, Southern North Sea. British Geological Survey, IR/11/005.</ref>).

===The Bunter Sandstone model===
The 3D model of part of the Bunter Sandstone Formation is located in what is considered to be a 'typical' setting in terms of closure sizes and shapes. It includes 3 main closures which could form topographic traps for CO2 storage. We interpreted the reservoir properties using available raw wireline logs and core data and correlated them across the model area using both the wells and regional geological understanding of the reservoir unit. The data was used to stochastically model reservoir properties (net to gross, porosity and permeability), honoring the well data to produce a simulation-ready model.

We presented the geological data to enable the model to be 'genericised' and highlighted the key geological uncertainties (which BGS continues to research). These could be sensitivity-tested to help understand the implications of selecting storage sites in different parts of the Bunter Sandstone Formation, in terms of potential differences in boundary conditions, heterogeneities and permeabilities that could be expected.

{| class="wikitable"
|+ Table 15 Summary of the three 3D generic models built in the Multiscale Whole Systems Analysis Project.

| style="background-color: #66CDAA;"| Potential storage reservoir
| style="background-color: #66CDAA;"| Specific location from which model was built
| style="background-color: #66CDAA;"| Depositional area in which generic model could be used
| style="background-color: #66CDAA;"| Geological environment of the reservoir
|-
| Cenozoic Forties Sandstone Member
| An area encompassing the Forties and Nelson hydrocarbon fields
| Depositional extents of the Forties submarine fan.
| Deep submarine fan sandstone.
|-
| Triassic Bunter Sandstone Formation
| An area encompassing two gas fields and two drilled, but water wet structural closures
| Depositional extents of the Bunter Sandstone in the Southern North Sea.
| Fluvial sandstones.
|-
| Permian Rotliegend Leman Sandstone Formation
| The Ravenspurn North and South gas fields
| Depositional extents of the Leman Sandstone Formation in the Southern North Sea.
| Aeolian and fluvial sandstones.
|}

===The Cenozoic model===
The 3D model of a deep submarine fan is based around the Cenozoic Forties Sandstone Member located in the UKCS Central North Sea. The variation in facies has been examined and attributed with petrophysical information. The attributed model has been used to model CO2 plume behaviour and, to date, results have been presented and published in four peer reviewed papers (Babaei et al., 2014a<ref name="babaei2014a"></ref>; Babaei et al., 2014b<ref name="babaei2014b"></ref>; Babaei et al., 2016a<ref name="babaei2016a"></ref>; Babaei et al., 2016b<ref name="babaei2016b"></ref>).

Three ‘Area Types’ have been defined in order to capture the variation in potential CO2 storage potential over the extents of the Cenozoic reservoir. The Area Types are defined on the basis of differences in thickness, number of reservoir zones and petrophysical values over the fan. This has enabled modeling and assessment of the CO2 storage performance of the reservoir at different locations in a deep submarine sandstone environment.

==References==
{{reflist}}

[[Category:OR/18/013 Multiscale Whole Systems Modelling and Analysis Project - A description of the selection, building and characterisation of a set of 3D generic CO2 storage models| 07]]

OR/18/013 Conclusions - Revision history

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