Case Histories and Applications of a New Slimhole MWD Multiple-Depth-of-Investigation Resistivitiy Sensor

Abstract

Summary The use of measurement while drilling (MWD) resistivity tools in boreholes 8½ in. and greater in diameter has evolved over the past 10 years from a little-used, qualitative service to a routinely used quantitative service in directional, horizontal, and extended-reach wells. Today's applications include reconnaissance logging, geo-steering, pore pressure evaluation, wireline replacement, and enhanced formation evaluation. Over the last several years, there has been an increasing trend worldwide toward drilling smaller boreholes to optimize the costs of tubulars and gain greater drilling efficiencies. Until recently, there have been no MWD resistivity tools available for logging 6-in. diameter boreholes. A new multiple-depth-of-investigation MWD resistivity sensor housed in a nominal 4$34-in. diameter drill collar has been developed for use in slimhole drilling operations. This new MWD resistivity sensor provides eight different depths of investigation in any mud type and allows for derivation of the flushed zone resistivity, true resistivity, and the diameter of invasion across a wide range of formation resistivities. The tool is designed for boreholes larger than 5⅞ in. in diameter and can be used in medium-radius drilling applications. Extensive operations in the North Sea, Gulf of Mexico, south Texas, Middle East, Alaska, and Australia have demonstrated a variety of applications. Slimhole MWD resistivity has been shown to have use in geosteering horizontal wells to maintain and optimize wellbore placement. Additionally, it allows determination of true formation resistivity and diameter of invasion for formations with invasion effects and provides for application of advanced modeling techniques to enhance formation evaluation and log interpretation.