Formation evaluation using wireline log data of Bakhrabad gas field

Abstract

Formation evaluation can be performed in several stages such as during drilling, after logging as detailed log interpretation, and core analysis in the laboratory, etc. This study shows the formation evaluation using wireline log data of Bakhrabad Gas Field (BK#9). Lithology has been identified from Spectral and Natural Gamma Ray logs where hydrocarbon bearing zones are detected by resistivity and lithology logs including cross checking of porosity logs. The shale volume is estimated from Gamma Ray and True resistivity methods, respectively. Porosity has been estimated from single log methods as well as from Neutron-Density combination formula. Formation water resistivity is estimated from Inverse Archie’s, Rwa analysis. The Archie’s, Indonesia and Simandoux models have been used for water saturation estimation. According to log data analysis, there are six sands present in this well where small mud cake is present within gas bearing sand zones depth interval. Lithology is laminated shale. The average gamma ray value and resistivity ranges are 96-111 API and 13-23 ohm-m of reservoir sands. The shale volume is about 11 and 18 percent from Natural Gamma Ray and True resistivity methods of thick sand with 18 meter reservoir thickness. Average formation water resistivity for virgin zone is 0.10 ohm meter. These gas bearing reservoir sands porosity and permeability quality is good. The average water saturation is 14-40 percent using aforementioned models, which is close to estimation by Interkomp Kanata Management Limited, 1991 and RPS Energy, 2009. This water saturation is more reliable for estimating reserve estimation and future reservoir analysis of this formation.