Operating in a challenging underbalanced coiled tubing drilling (UBCTD) environment, with temperatures exceeding 150 degC for 50% of the time and surpassing 125 degC for 90% of the time, the customer used a novel propagation resistivity technology to effectively geosteer the lateral sections of onshore wells, enabling a thorough analysis of reservoir properties and informed decisions during drilling operations.

The customer had reservoirs with low mobilities. To address the challenges of formation damage caused by overbalanced drilling and enhance productivity, UBCTD is a proven solution. However, one of the limitations of UBCTD has been the need for logging-while-drilling (LWD) technology to effectively geosteer the well within the pay zone for optimal reservoir rock placement. Without the appropriate technology to geosteer accurately, the customer relied on data from offset wells or cuttings analysis, which are not always the most reliable methods for precise geosteering. As a result, an ultraslim LWD array resistivity technology with a built-in geosteering workflow was designed.

The customer turned to CTDirect Ultraslim LWD Array Resistivity™ coiled tubing logging‐while‐drilling service, a new slimhole resistivity propagation measurement for geosteering with model-compare-update techniques. In this solution, four resistivity measurements and gamma ray (GR) data were combined in a model‐compare‐update process to steer the lateral section efficiently. The detected inverse correlation between attenuation and phase shift in field tests was precisely modeled and explained as a synergistic effect of a high-angle well path and complexities in high‑resistivity formations.  

Using slimhole LWD technology, precise propagation resistivity measurements, including phase shift and attenuation at dual frequencies, were obtained. This technology is specifically designed to be reliable under harsh coiled tubing drilling (CTD) environments in underbalanced or overbalanced conditions and is complemented by GR, annular pressure, and annular temperature readings. The resistivity data collected from the initial well were compared with data from offset wells in the same geographical area, allowing for a comprehensive analysis of the reservoir properties and facilitating informed decision making during drilling operations.