Formation Evaluation and Uncertainty Analysis of the Ormen Lange Field, Norwegian Sea offshore Norway
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Formation evaluation is the process of analyzing and interpreting geophysical data performed as a function of wellbore depth, by describing the processes that determine the viability of a formation to produce hydrocarbons. According to the data availability, formation evaluation can be done using core data, well log and initial production data. The aim of this study was to do the formation evaluation using petrophysical parameters from wireline logs in order to determine lithology, porosity, permeability and fluid saturation and to understand the importance of the uncertainty analysis on reservoir permeability and predict gas recovery.In this work, Techlog software was used to perform a robust computation of petrophysical properties and then give summaries computed petrophysical properties. A formation evaluation module is a set of solutions for conventional log interpretation. In the summaries module the computed average of shale volume, porosity and water saturation are used to determine the reservoir interval pay zone. The permeability computation uncertainty analysis presented in this paper was done by using Monte-Carlo simulation that allowed understanding the relative weight of each variable by analyzing the sensitive case interpreting the tornado plot result. The gas recovery was predicted based on porosity, saturation and net productive thickness average of all the given wells. It is important to identify properly the lithology and the reservoir to allow an accurate petrophysical calculation of porosity, water saturation and permeability.The determination of lithology based on cross-plot neutron versus density log was important step to come up with the reservoir petrophysical properties. The quality of the reservoir as determined by permeability is good with permeability value around 45, 135 mD and by porosity was very good values between 24 to 30 percent. In general by plotting porosity values against permeability values showed strong linear relationship between the two variables of the reservoir indicating that Ormen Lange field reservoir are permeable. It should be noted that the presence of shale in the entire reservoir influenced negatively in the permeability values. The petrophysical properties of the reservoir in Ormen Lange field are enough to permit hydrocarbon production.