Abstract

Extended Range Micro-Imager (XRMI) tool has been a great success in revealing subtle features along borehole circumference which could be discerned only through direct viewing of conventional cores. It has numerous applications in sedimentary environments and these are well documented in literature. Its primary function is to investigate strata stacking patterns & cyclicity of sedimentation in the context of sequence stratigraphy, in the finer scale of resolution.

This is an overlap and extended data source over core derived investigations which is a welcome feature to the E & P industry. Its significance is judged from the fact that wireline logs are continuous, free from data gaps & human interventions and could reveal even subtle features with distinction & clarity. As a result, trust could be laid on imagery to delineate— fractures, vugs, clasts, cleats, pebbles, cobbles, sedimentary structures; work out paleo environment and move towards digenetic & tectonic evaluation etc. with admirable detail. Geological episodes retain their imprints in the rock mass. Inferences to this effect are routinely being drawn involving core based observation & investigations done in the laboratory and till recently, this was the only source for such conclusions. Wireline derived information therefore becomes a befitting source for validation, integration and expanded co-viewing in a landscape. Imagery therefore is a viable data source that strengthens judgment on interpretation.

Imagery application is now being extended to characterize coal seams in terms of cleats, fractures, joints, dislocations and texture definitions. This study has been done in a borehole drilled in the eastern coal belts of West Bengal – Jharkhand area. The features noted in the imagery are found congruous to core photographs and in many ways validate core sample description. Important parameters of the coal beds have been quantified and Fracture porosity, Fracture permeability and Fracture intensity values have been estimated. Imagery vs. core comparison opens the possibility to extend visualization beyond the well bore; holding core vs. imagery disclosures and integration with other associated information as the key.