Application of nuclear magnetic resonance logs for evaluating low-resistivity reservoirs: A case study from the Cambay basin, India

摘要

Low-resistivity pay sands have been identified in four wells, namely: AM-7, AM-8, TA-1 and TA-5, which penetrate the Eocene pay-IV(EP-IV) sand unit of the Kalol formation in the Cambay basin.These wells are located near the Dholka and Kanwara oilfields in the Cambay basin.The main objective of this paper is to evaluate nuclear magnetic resonance(NMR) logs of the low-resistivity reservoirs from these four wells and to determine the petrophysical properties more accurately than conventional logs have done.The thickness of low-resistivity sand varies from 5 to 17m in the wells under the study area.The formation has been characterized by a high surface area;thus irreducible water saturation(S _(wi)) is high.The resistivity of these pay zones varies from 1 to 8 m and the total NMR porosity ranges from 15% to 50%.The free fluid porosity ranges from 2% to 5% in wells TA-1 and TA-5 and 12-20% in wells AM-7 and AM-8.The Timur-Coates/SDR model derived that the permeability of the low-resistivity reservoir ranges from 0.8 to 1.5 md in wells TA-1 and TA-5 and 10-110 md in wells AM-7 and AM-8.