engleski

Porosity distribition models for numerical estimates of the regional CO2 storage potential in clastic sediments

Regional evaluation of the CO2 geological storage potential presumes estimates of various rock properties (depth, effective thickness, pressure, temperature and porosity). Modelling the spatial distribution of porosity is often burdened by scarce input data. The existing model for the Upper Miocene sandstone layers of the deep saline aquifer Poljana in the western part of Sava depression made by Iva Kolenkovid in her PhD Thesis is based on the quantitative interpretation of well logs in 20 wells, which is a relatively small number of input data for an extensive exploration area. To compensate for this and to increase reliability of a porosity model, two new maps were constructed. One of them based on the regional regression analysis of the dependance of porosity with mean depth of the regional saline aquifer, which rendered a good solution for simple evaluations in the lack of data. The flaw of this method is an assumption that porosity varies only with depth, i.e. with compaction, which led to overestimated values for shallow layers and underestimated values for the same sediments in deeper structural units. Considering that in the exploration area sandstones were deposited by turbidity currents, this assumption resulted in reduced values of specific CO2 storage capacity in central areas with thick layers of sandstone, and therefore the overall storage capacity in the deep saline aquifer Poljana was underestimated. The second map was constructed based on the regional regression analysis of the dependance of porosity on two parameters – mean depth and effective thickness. In the central, deeper areas, increased values of specific storage capacity were obtained in respect to the first model. In both cases, the porosity values were also estimated for wells without corresponding well logs, and the reliability of the calculation of specific and total CO2 storage capacity was increased. Tested models can be used for planning of detailed exploration in areas with larger potential, i.e. at the most prospective locations.

CO2 geological storage; Sava depression; Poljana sandstones; porosity; CO2 storage capacity

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