Estimation of Permeability using Simple Multi Criteria Decision Analysis in Gumuskoy, Aydin, Turkey

Abstract

The aim of this study was to develop a methodology to estimate geological formation permeability in a geothermal system. Permeability is an important parameter for geothermal exploration since it defines the flow capacity of reservoir rocks. However, most of the time it is either not possible to calculate hard rock permeability or it requires time consuming tests and analysis. Thus, a more practical solution was needed to estimate permeability for the exploration studies. In this scope, a Multi Criteria Decision Analysis (MCDA) method was utilized. The case study area was selected as the Gümü?köy geothermal area, which is located in the Western end of Büyük Menderes Graben (BMG). The methodology was constructed similar to Weights of Evidence (WoE) method, which belongs to a group of multi-criteria decision making methods. MCDA was used to determine favorability of permeable areas by means of giving scores and weights to the input parameters and evidences. Weights were estimated from the measured parameters and the values on well logs were used as predictors. For this purpose, 3 deep wells were utilized with spacing up to 800 meters. The parameters used for permeability estimation included, Lithology, Spinner Log, Caliper Log, Water Loss Test Results, Resistivity Log, Temperature Log, Formation Micro-Imager (FMI) Log, Drilling Parameters; Rate of Penetration (ROP), Weight on Bit (WOB), Mud Temperature, and Rock Quality Designation (RQD). A permeability log is evaluated for all possible well locations using the given weights producing favorable zones in one dimension and then extrapolated into a 3D Permeability Model using kriging interpolation. Consequently, permeable zones were modeled from favorability logs generated with MCDA method in 3D and the model was mostly in line with the estimated reservoir depth and thickness.