Data Driven Assessment of Rotary Sidewall Coring Performance

Abstract

Abstract This paper aims to review the quality of rotary sidewall coring service deliverables, performance of various tools and the main operational aspects from an operating company standpoint. Compilation of this document is based on 1650 selected core samples from a large dataset, acquired in a variety of borehole settings and formations using different tool types of three logging companies. The intention was to reduce bias toward certain instrumentation, and to provide mainly descriptive statistical information on core recovery and operational performance. Formation attributes based on wireline log data, borehole environment (mud type, properties, etc.), quality of the recovered cores and type of instrumentation used were tracked for each station. Core lengths and integrity were also considered. Coring and station times were assessed on every point. Wherever possible, the core location accuracy was revised based on the post coring image log runs. The distribution of depth discrepancies was evaluated. The assessment of rotary sidewall cores recovery based on formation, borehole properties and instrumentation types showed ranges and variability in core recovery. Correlation coefficients and principal components of borehole and formation models vary greatly depending on the input vectors. Despite the variability, having statistical records provides a valuable reference for cases of unusual performance. Recovery distribution was assessed for every tool type and compared to the specifications. When available, a real time recovery indicator usually provides fair estimate of expected recovery. Revised core traces on the post coring borehole images showed, that despite depth control procedures, the distribution of the assessed core depths indicated minor upward shift. This publication presents an informative reference for geoscientists and petroleum engineers, in terms of rotary sidewall coring service product quality. It reveals the range of operating environments for a large variety of formation and borehole properties, linked to core recovery. Derived conclusions are based on performance statistics from field coring jobs, including most of the current tool types offered by major logging providers.