Abstract
Assessment of reservoir and fracture parameters is necessary to optimize oil production, especially in heterogeneous reservoirs. Core and image logs are regarded as two of the best methods for this aim. However, due to core limitations, using image log is considered as the best method. This study aims to use electrical image logs in the carbonate Asmari Formation reservoir in Zagros Basin, SW Iran, in order to evaluate natural fractures, porosity system, permeability profile and heterogeneity index and accordingly compare the results with core and well data. The results indicated that the electrical image logs are reliable for evaluating fracture and reservoir parameters, when there is no core available for a well. Based on the results from formation micro-imager (FMI) and electrical micro-imager (EMI), Asmari was recognized as a completely fractured reservoir in studied field and the reservoir parameters are mainly controlled by fractures. Furthermore, core and image logs indicated that the secondary porosity varies from 0% to 10%. The permeability indicator indicates that zones 3 and 5 have higher permeability index. Image log permeability index shows a very reasonable permeability profile after scaling against core and modular dynamics tester mobility, mud loss and production index which vary between 1 and 1000 md. In addition, no relationship was observed between core porosity and permeability, while the permeability relied heavily on fracture aperture. Therefore, fracture aperture was considered as the most important parameter for the determination of permeability. Sudden changes were also observed at zones 1-1 and 5 in the permeability trend, due to the high fracture aperture. It can be concluded that the electrical image logs (FMI and EMI) are usable for evaluating both reservoir and fracture parameters in wells with no core data in the Zagros Basin, SW Iran.
Highlights
Direct and indirect methods are available to detect fractures in reservoirs (Thompson 2000)
Core and image logs are the most common and direct methods for the evaluation of fracture and reservoir parameters, core sampling can suffer from important limitations such as high coring cost, low recovery factor and Edited by Jie Hao and Xiu-Qiu Peng
By building on previous studies, the present study aims to determine fracture-controlled reservoir properties from formation micro-imager (FMI) and electrical micro-imager (EMI) logs, which can be implemented in wells without core data
Summary
Direct and indirect methods are available to detect fractures in reservoirs (Thompson 2000). Core and image logs are the most common and direct methods for the evaluation of fracture and reservoir parameters (porosity and permeability), core sampling can suffer from important limitations such as high coring cost, low recovery factor and Edited by Jie Hao and Xiu-Qiu Peng. Image logs have become recognized as the most important borehole logging technique for fractured reservoir evaluation, and they have developed rapidly due to their excellent performance in characterizing borehole features such as fractures and bedding (Serra and Serra 2004a, b; Tingay et al 2008). The use of image logs has decreased overall costs by reducing coring intervals and by accurately determining the perforation zones (Aghli et al 2017).
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