Petrophysical Evaluation of a Shaly Sand Reservoir- A Case study of exploration well 7220/8-1 from the Barents Sea, Norway
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This study is based on well data from the exploration well 7220/8-1 in the Barents Sea, Norway located at NS degrees 72° 29' 28.92'' N, EW degrees 20° 20' 2.25'' E, NS UTM [m] 8051910.71 and EW UTM [m] 678908.52 at UTM zone 33 (NPD, 2014).In petroleum industry the petrophysical properties derived from advanced petrophysical tools/logs are very useful to characterize and evaluation of the shaly sand laminated reservoir. In this study different parameters of shaly sand reservoirs including fluids, lithology, volume of shale, porosity, water/hydrocarbon were analysed with the help of core report and well log data. These data enabled to identify hydrocarbon potential intervals, fluid types and contacts, calculation of volume of shale, log derived and corrected porosity and resistivity. Water saturation was evaluated by considering three cases including; Case 1; for Clean sand assumption as a base case using Archie s equation and without considering shaliness volume, Case 2; for Shaly Sand taking into consideration the shaliness content based on the modified modified Simandoux equation and finally Case 3 for Laminated Shaly Sand (LSS) taking into consideration both shaliness (laminated and dispersed) and anisotropy/lamination based on modified Simandoux equation.The Porosity used in this study were derived from both log density and nuclear magnetic resonance (improved porosity) to form the so called the density magnetic resonance porosity (DMRP), formation resistivity from the High Resolution Laterolog Measurement (RT_HRLT) and volume of shale derived from the separation of neutron and density (Vclay_ND) which were used in Case 1 and Case 2. On the other hand the sand porosity (phi sand) resolved using the Thomas Stieber model along with sand resistivity derived from the Rv/Rh triaxial induction tool (Rsand) were employed in Case 3. This study comprised of approximately gas column of about 38m thick starting in the Stø formation below the thick shale possibly the caprock, (GOC at 1315 m), oil column of about 76m thick (OWC at 1399m) and water below the oil.The comparison of the three cases considered in this study showed that the laminated shaly sand (LSS) case was more accurate and reliable in laminated zones but inaccurate to cleaner and thicker zones compared to other cases.