Abstract
Investigation into geological storage of CO2 is underway at Hontomín (Spain). The storage reservoir is a deep saline aquifer formed by naturally fractured carbonates with low matrix permeability. Understanding the processes that are involved in CO2 migration within these formations is key to ensure safe operation and reliable plume prediction. A geological model encompassing the whole storage complex was established based upon newly-drilled and legacy wells. The matrix characteristics were mainly obtained from the newly drilled wells with a complete suite of log acquisitions, laboratory works and hydraulic tests. The model major improvement is the integration of the natural fractures. Following a methodology that was developed for naturally fractured hydrocarbon reservoirs, the advanced characterization workflow identified the main sets of fractures and their main characteristics, such as apertures, orientations, and dips. Two main sets of fracture are identified based upon their mean orientation: North-South and East-West with different fracture density for each the facies. The flow capacity of the fracture sets are calibrated on interpreted injection tests by matching their permeability and aperture at the Discrete Fracture Network scale and are subsequently upscaled to the geological model scale. A key new feature of the model is estimated permeability anisotropy induced by the fracture sets.
Highlights
CO2 geological storage has reached industrial scale in sites, such as Sleipner (Norway), In-Salah (Algeria), and Decatur (IL, USA)
As the approaches to elaborate and calibrate the Discrete Fracture Network (DFN) are statistically based, the results presented in this paper shall only be considered as initial and it will serve as the basis to the future full-field history matching of the CO2 and brine injection tests which will be performed within the ENOS project [33]
A geological model encompassing the whole storage complex was established based upon newly-drilled wells, legacy wells and 3-D seismic interpretation of the Hontomìn site
Summary
CO2 geological storage has reached industrial scale in sites, such as Sleipner (Norway), In-Salah (Algeria), and Decatur (IL, USA). The characterization workflow applied to fractured sandstone formations at In-Salah [8] is transposed to naturally fractured carbonate. These reservoirs are challenging to handle because of their high level of heterogeneity that conditions the reservoir behaviour during the injection. This work integrates the characterization (size, conductivities) of the natural fracture networks by its modeling in the drainage volume of the wells [10]. As part of the European project “Enabling Onshore CO2 Storage in Europe” (ENOS) [11], the site geological model is updated by integration of the recently acquired data, such as the image log interpretations from injection and observation newly-drilled wells. The DFN characteristics were upscaled and propagated to the full-field reservoir simulation model as three-dimensional (3-D) fracture properties (fracture porosity, fracture permeability, and equivalent block size)
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