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Report RSE 18002365

Numerical simulations of the industrial process of storage of natural gas in order to investigate the safety of a real depleted tank



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F. Colucci (RSE SpA), R. Guandalini (RSE SpA) , G. Agate (RSE SpA) , A. Amicarelli (RSE SpA)

ACCUMULO 2017 - Energy storage materials and technologies for the electric


The purpose of this research was to study, through numerical simulations, the industrial process of gasstoring and withdraw in deep reservoirs and subsequently to validate the increase in storage capacitieswith the exercise of overpressure reservoirs compared to the base reservoir at the time of the discoveryof the reservoir itself. These additional gas capacities would have a positive impact on the energysystem, in terms of ensuring the supply of raw materials and increasing flexibility.

In detail, the methodology developed for the characterization of a natural gas storage site has beenapplied to a real area called "Sergnano virtuale" located in Lombardy near the Sergnano StorageConcession.

The developed methodology involves the collection of information about the geological formationspresent on the site investigated, the creation of the static 3D geological model and the corresponding 3Dfluid dynamic model; these points have been done in the previous years of research.

The geological and seismological features have been thoroughly analyzed for the site being investigated.From the analyzes carried out, it emerges that in the area investigated the reservoir suitable for housinggas storage is located in the Sergnano gravel formation consisting of sand, gravel, conglomerates withsometimes thin clay interlacing while the caprock is identified in the above formation of the clay of the ‘Argille di Santerno’.

For the study area considered, the available data made possible to generate an accurate static 3Dgeological model; subsequently, integrating this geological model with information on well structures,and using the GeoSIAM Geometric Analysis Integrated System, the corresponding 3D Fluid DynamicModel was developed. Starting from this model the natural state of equilibrium and the cycles ofproduction/storage of natural gas have been reproduced, In the last year of research, these studies wererepeated, already carried out in previous years of research, in light of the updates made on both the preprocessingmodule of GeoSIAM (MethodRdS), solving problems that emerged as a result of theexperience gained in this type of applications, and on the gas module inserted into GeoSIAM(Tough2RdS-EOS7C). Thanks to the latest modifications of the code, it has been obtained a significantdecrease in terms of the calculation times, in addition to obtaining a higher degree of accuracy.

In general, the results obtained have fully demonstrated the validity of the methodology developed andthe reliability of the tools used to address the geological and fluid dynamics problems related to thestorage of natural gas.

Subsequently a simplified modelling approach is formulated to simulate geomechanical interactions.The present approach relies on the executable code of the FOSS (Free/Libre & Open-Source Software)tool PyLith v.2.2.1 ( [1], [2], [3]). The present approach is preliminarily applied to a simplified test case,which considered a 3D domain with a single injection well in the presence and absence of a fault and thepressure range was calculated analytically.

In order to carry out an application to a real site of the methodology developed to simulategeomechanical interactions, a procedure able to make a complete coupling between the fluid dynamicresults obtained with GeoSIAM and the PyLith code has been implemented in MethodRdS. Thecoupling was first verified by reproducing with MethodRdS the domain of the previous simplified case.Then the whole chain of analysis was applied to a case study related to the functional checks performedin the past for GeoSIAM, starting from the fluid-dynamic solution calculated with the Tough2RdS codeand coupling the results to the PyLith calculation module, obtaining the results in terms of displacementsvector fields.

Finally, using the fluid dynamic results obtained for the " Sergnano virtuale" reservoir, the displacementvector field was calculated with PyLith in order to verify the stress generated in the reservoir rock. Inthis case the scenario related to a thermal production / storage year was considered and it should benoted that in the geological domain considered there are no fault structures.

Of particular interest is the analysis of rock behavior under operating conditions with a 110%overpressure compared to the reservoir discovery pressure. This analysis makes it possible to evaluatethe stresses and deformations in the rock-reservoir and in the caprock, for example, in correspondencewith the monitoring wells according to the value of the minimum / maximum operating pressuresexpected.In particular, for the "Sergnano virtuale" case, even considering an overpressure up to an operatingvalue equal to 110% of the original value, the vertical deformation of the rock both on the ground leveland around the reservoir takes on very low values.

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