Abstract

Drilling complication and/or in economizing the cost of a development well often forces E & P companies to lower casing without wire-line services. In such situation, C/O ratio method is relied upon in finding prospective zones and to evaluate them. The principle is based on Induced neutron gamma ray spectroscopy and induced capture gamma die-away responses against formations. By off-setting and adjusting parameters emanating from these responses against shale and water bearing zones, the potential layers are highlighted as well as their saturations quantified.

In the absence of this vital supplementary information, a greater challenge is imposed upon analyst for rational interpretation. A challenge of this nature was faced in one well of Gujarat State in India where the data was recorded in   4 1/2″ casing using 2.125″ OD RMT** (Reservoir Monitoring Tool) without any input from open-hole log response. The problem has been addressed by modeling C/O ratio curves in association with Ratio of Near/Far Inelastic values (RIN) and Ratio of Near/Far Capture values (RNF).