Unique Real and Relevant Time Formation Evaluation: A Case Study from the Gulf of Mexico with Innovative Advances in Logging While Drilling

Abstract

Abstract This case study presents a success story of a development well in the Gulf of Mexicodrilled with oil-based mud, with latest high-definition borehole image and comprehensive formation evaluation-while-drilling suite. Historical data from multiple offset wells suggested that the standardresolution petrophysical logs were insufficient to accurately evaluate this low-resistivity, low-contrastreservoir. The presence of salt intrusions compromises the surface seismic interpretation and poseadditional geological challenges, adding uncertainty to the oil water contact—which, if incorrectlyidentified, would cause early water production and compromise the success of the well. Deploying a unique, high-resolution dual-physics imaging-while-drilling system and the advanced petrophysical LWD logging suite for the first time in this field was critical toachieving the optimal reservoir characterization and making subsequent operational decisions. Real-timecapture-spectroscopy and sigma measurements were essential to evaluate the mineralogical compositionand saturation estimation. Water saturation computed from sigma gives an estimate of free- and bound fluid volume, independent of the resistivity measurement, which showed little contrast betweenhydrocarbon- and water-filled formations. The real-time transmission of apparent resistivity images enabled the identification and interpretation of the low-resistivity low-contrast reservoir, which appeared to be comprised of cross-bedded, sand-silt laminated facies. High-definition borehole images detected features such as fine lamination and fractures, which were not possible to be identified with the standard-resolution logging suite previously deployed in this field. This information provided an insight into the reservoir architecture and possible extent of the depositional facies vertically and laterally. The ultrasonic high- and low-frequency borehole images further helped refine the understanding of reservoir architecture in relevant time to aid in completion design. Additionally, the apparent resistivity derived from the high-definition resistivity provided a proxy to ultra-shallow resistivity that was able to identify the movable fluid in the reservoir when compared to standard resistivity measurements in singular drilling pass and confirmed the oil-water contact which were a critical information for well completion design This case study demonstrates the integration of petrophysics and geological interpretation of comprehensive LWD logging which has been fundamental to resolve the reservoir characterization uncertainties and optimizing the completion strategy in a challenging low resistivity reservoir in one drilling run with real-time transmission of high-quality data.