IAS Meeting of Sedimentology - Sedimentary environments of Mediterranean Island(s) edition:27 location:Alghero date:20-23 September 2009
A multidisciplinary approach in the study of karst effects on carbonate reservoirs is applied by Eni E&P on different outcrops. The study of the relationships between the sedimentary framework, tectonic evolution and subaerial exposure characteristics in three-dimensional outcrops in Apulia is a key to interpret and forecast the petrophysical properties distribution in Southern Italy’s carbonate reservoirs.
During the Upper Cretaceous several phases of exhumation of the Apulia carbonate platform caused karstification and creation of vugs and caverns in different shapes and sizes. Apart from the duration of exposure and sea-level fall, the distribution as well as the organisation of the karst cavities are influenced by several factors. The aim of this study is to define the dominant factors for the observed karst types.
Sedimentological (deposition environment, bedding texture) and diagenetic (small scale dissolution, stylolites, cementation, fracturing) aspects have been studied in the field, hand samples and thin sections. Mechanical stratigraphic analyses has been performed on different structural datasets (fracture orientation, length, opening) obtained by field measurements, high resolution photography and LIDAR acquisition. Karstification phenomena have been described based on field characteristics and the relations with influencing parameters were explored. Cement phases and (paleo-)speleothems were sampled and their stable isotope composition was determined. To refine the relative stratigraphic setting of the outcrops studied chemostratigraphic and biostratigraphic analyses have been carried out.
Based on the results different concepts controlling karst development are proposed and their effects have been listed from small to large scale. Within one depositional layer the sedimentological influence is shown by the karsthole outline. Slight compositional changes are reflected in the horizontal extents of the karst cavity. For example algal horizons stick out into the karst cavity while a pelletal wackestone fabric dissolves more easily, and thus here the cavity is broader. The contact between depositional layers of different thickness also reflects different mechanical stratigraphy/fracture spacing and therefore the fluid flow is distributed over less (or more) fractures in function of the mechanical characteristics of the layers. This causes more (or less) dissolution than in adjacent layers. These contacts play an important role in redistributing the fluids. Fractures through impermeable horizons (e.g. paleosol) focus the flow of fluid through fractures along which important dissolution occurs. Larger scale normal faults are a good conduit for penetration of fluids. From the faults’ surface fluids infiltrate into the footwall along smaller fractures and cause karstification.