Looking For Earlier Integration: An Application Example

Abstract

A "creative" approach to reservoir characterization is not always the best choice while integration should be the appropriate methodology, if properly planned and developed. This paper describes the integrated sedimentology-petrophysics-geomechanics methodology used to characterize the reservoir and cap-rock that will be interested by gas storage activity at overpressure conditions. The determined data are then used in the modelling phase aiming at evaluating the safe injection/storage maximum operating pressure.The analyzed sequence is located in Central Italy and is represented by sand-shale intervals. The available data are: conventional and high last technology logs, mini-frac tests, laboratory core analysis, sedimentological and fracture description on cores.The advantage of the approach relies in the use, during the different project tasks, of each provisional result to drive the work group for finding the solution which better honours the response of different disciplines, looking therefore for an 'integration on the job'.The two shales, bounding the reservoir, had similar geomechanical properties but different petrophysical ones (different sedimentological process). The overburden ("cap-rock") is mostly massive with maximum horizontal stress direction 155 N while acoustic logs showed also anisotropy surfaces. The underburden shales ("argille basali") show different sedimentological features and diffuse slumping surfaces. The stress direction is similar for both shales, therefore an unique stress profile was needed throughout the layers and the mini-frac/stress tests were used to constraint the minimum horizontal stress. The geomechanical data allowed to derive reliable mechanical and failure parameters. The sand reservoir shows laminations with few fractures. From a geomechanical standpoint, these results allowed a statistical analysis of the main parameters, for the use in the subsequent modelling activities.An earlier integration approach was the key for the quality of a reservoir/sealing sequence characterization for the appropriate and safe storage operation. Scope of workThe option of delta-pressuring, exceeding the discovery pressure in a depleted gas storage field, is one of the most costeffective ways used by Stogit to increase working gas capacity and deliverability. The feasibility study of the "P>Pi Projects" needs to collect new and detailed information about geological and structural features of the field (Bruno et al., 1998).A geognostic well was recently drilled by Stogit in a gas storage field located in Central Italy, expressly targeted to acquire geological information, both in the reservoir and in the cap-rock units. The well will be besides equipped with downhole permanent microseismic and geodetic monitoring network, aimed to check the cap-rock strain and integrity, in order to minimize the risk of gas leakage through the weakest parts of the cap-rock.An integrated petrophysical and geomechanical study has been finally achieved, which contributed, together with the new interpretation ...