An Innovative Approach to Select Core Point in Challenging Environment Using the GWD&trade - (Gas While Drilling) Methodology

Core point selection plays vital role to ensure that cores are cut in best part of reservoir to fulfill objectives requested during well planning. Different methodologies are applied to select coring point. Depending on geological environment, these approaches reflect criticalities as rig time, offset of LWD tools, absence of markers etc. Here an innovative approach based on analysis of mud gas shows using GWD™ methodology is described. This methodology consists in computation of several ratios of hydrocarbon mixture (C1 to C5) continuously extracted from mud and monitored at rig site. A successful case history from a well recently drilled in Bhit field, Pakistan is presented. In this case, absence of drilling parameter changes and specific GR marker into thick shale sequence above reservoir does not allow proper identification of coring point. Gas data from two reference wells were analyzed and distinctive gas ratio trends between shale sequence and coring target were established, both qualitatively and quantitatively. After application of QC criteria, same trends were recognized in new well and coring point was selected even before scratching level of interest. Further confidence of quantitative aspects of methodology can lead to refine coring point selection, significantly saving rig time and costs.