Calculation of fracture parameters and their effect on porosity and permeability using image logs and petrophysical data in carbonate Asmari reservoir, SW Iran

Abstract

Evaluation of fractures and their parameters, such as aperture and density, is necessary in the optimization of oil production and field development. The purpose of this study is the calculation of fracture parameters in the Asmari reservoir using two electrical image logs (FMI, EMI), and the determination of fracture parameters’ effect on the porosity and permeability using thin sections and velocity deviation log (VDL). The results indicate that production in the Asmari reservoir is a combination of fractures and rock matrix. Fracture aperture (VAH) and fracture porosity (VPA) are only measurable with core and image logs directly. However, regarding core limitations, the image log has been recognized as the best method for fracture parameter determination due to their high resolution (2.5 mm). In this study, VDL log and thin sections have been used as auxiliary methods which may be available in all wells. The VDL log provides a tool to obtain downhole information about the predominant pore type in carbonates. Results indicate that between fracture parameters, VAH is considered as the most important parameter for determining permeability. For well No. 3, VAH ranges from minimum 51 × 10−5 mm to maximum 0. 047 mm and VPA changes from min 10−5% to maximum 0.02056%. For well No. 6, VAH varies from 5 × 10−4 to 0.0695 mm and VPA varies from 10−5 to 0.015%. Therefore, due to high fracture density and fracture aperture, it seems that most of effective porosity originates from fractures especially in well No. 3. However, VDL for well No. 6 indicates that intercrystalline and vuggy porosity are the dominant porosity. This result may be an indication for fracture set diversity in the two studied wells. While in well No. 3, they related to the folding and active faults, in well No. 6 they are only of folding type. Furthermore, results indicate the high capability for both of EMI and FMI image logs for calculation of fracture and vug parameters in the carbonate reservoirs.