Ika Field Case - An Integrated Approach to Ogip Evaluation

Ika Field is one of Croatian offshore gas fields. Gas reservoirs are discovered in Lower Pleistocene turbidites and in fractured Mesozoic carbonates. Modern logging tools provide recognition of highly laminated, gas bearing sand-shale sequences (“Thin Layers”) resulting in modifications of development scenario. Three different types of reservoirs were found. Although the Carbonate reservoir was the main target, the most of the work refers to the definition and description of three “Thin layers” sequences. Lateral continuity of these sequences was resolved utilising seismic reinterpretation and special attribute analysis. Supposing that thickness of lamina is bellow vertical resolution of logging data, the main criteria comprised gas shows during drilling, absence of free water and slight increase in resistivity associated with apparently low resistivity contrast between sand and shale sublayers. A specific approach was applied for petrophysical analyses in order to better describe “Thin Layers” internal geometry. Taking into considerations the uncertainty related with description and characterisation of these reservoirs, stochastic approach was adopted for OGIP estimation. <br><br>