Delineation of hydrocarbon and non-hydrocarbon zones using fractal analysis of well-log data from Bhogpara oil field, NE India

Abstract

Hydrocarbon (HC) and non-hydrocarbon (NHC) zones have been characterized using fractal analysis of wireline log data. Well-log responses such as spontaneous potential (SP), gamma ray (GR), resistivity (LLD, LLS, MSFL), neutron porosity (NPHI), bulk density (RHOB) log have been analyzed from five boreholes of Bhogpara oil field using rescaled range (R/S) and power spectrum density (PSD) techniques. Primarily, both the techniques were applied on the log responses associated with the traditionally identified potential and non-potential zones of 100 m thickness. The Hurst exponent (HPSD) obtained using PSD analysis for GR, NPHI and RHOB log, shows higher values for HC zones as compared to the NHC zones. Furthermore, to understand the scaling pattern more explicitly for main potential sector of the reservoir. Both of the techniques were applied to the wireline log data that are associated with traditionally defined HC and NHC zones of different thickness. The Hurst exponent (HR/S) obtained using R/S analysis was found to be of relatively higher values for HC zones as compared to the NHC zones for all wireline log response. Again opposite trend was also observed for HPSD values that obtained from GR, MSFL, NPHI and RHOB log responses only. Hence, the HC and NHC zones can be delineated from fractal analysis of wireline logs and also overcome the chance of misinterpretation, which is quite possible in the case of hydrocarbon zone detection in traditional reservoir characterization.