Home Institution: University of Malta
Host Institution: Ruden AS, Oslo
Duration of stay(days): 9
Objectives: The aim of the visit is to implement a robust quantitative use of geophysical logs from deep Oil&Gas wells drilled in the southern offshore of Sicily (Italy), to estimate and/or extract groundwater salinity information as the base for a groundwater 3D salinity hydrogeological model. In particular, few key qualitative indications of fresh/brackish groundwater presence have been detected in the Oligo-Miocene ramp carbonate reservoir of the Ragusa Formation, based on a quick-look at composite logs, both in the onshore and in offshore of southern Sicily. The STSM objectives can be reached with the proposed visit to Ruden’s team, which has developed a specific and proven workflow on this topic (quantitative use of logs) and will be able to assist and support such a quantitative step.
Summary of the work: During the STSM in Oslo, c/o Ruden AS company, a workflow for the quantitative use of geophysical logs from deep Oil&Gas wells in southern Sicily (Italy) was implemented and carried out, with the final objective of estimating groundwater salinity information. The work was focused on the Oligo-Miocene interval of the Ragusa Formation, a medium-high porosity carbonate reservoir deposited in a ramp environment, outcropping over the Hyblean plateau in southern Sicily. The following steps were carried out: i) identification of 5 key wells in the area of interest (1 offshore and 4 onshore southern Sicily); ii) digitization of the full suite of logs required for the application of petrophysical workflow, such as SP (Spontaneous Potential), GR (Gamma Ray), DT (Sonic log) and Resistivity logs; iii) construction of a synthetic lithological log for each selected well, needed to characterize the lithological influence of electrical logs; iv) application of a customised petrophysical workflow for porosity and salinity estimation (concentration of salts in TDS), considering: lithotypes, BHT (borehole temperatures), porosity (derived to DT – sonic log), pore fluid resistivity; v) comparison of TDS results with salinity data from DST and composite logs; vi) well correlation and well salinity cross-section. All the five selected wells have been completed and fully analysed, in terms of logs digitalization and logs interpretation, for their whole drilled thickness.
The main outcome has been to quantitatively demonstrate, for the first time, the presence of fresh groundwater in the offshore of southern Sicily (Italy), within the Ragusa Fm. reservoir, through the use of digital logs and petrophysical concepts.
At the same time, the work done suggests that this deep aquifer appears likely connected with the onshore aquifer.
The work has also been a very good opportunity to exchange ideas, knowledge and reinforce the collaboration with colleagues from the host institution.