Optimized Nuclear Logging for Fast Drilling

Abstract

TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractSlow data acquisition rates have generally not been a problem for LWD due to moderate logging speeds while drilling. With the recent advances in drilling technology, high logging speeds impact the log quality and, in particular, the nuclear logs. When a detector passes a longer interval of rock for each acquisition period, its vertical resolution is degraded. For azimuthally sectored data, this is even more of an issue, as bedding features within a sample period get blurred.The objective of the study is to develop a methodology to optimize LWD data acquisition, enabling the E&P company to drill faster and meet its data acquisition objectives. This paper describes analytical simulations and field tests performed to optimize data acquisition for fast drilling in the Norwegian North Sea. Optimization of data acquisition is described as addressing the trade-off between low data density with accurate measurements versus high data density with less accurate measurements.Based on nuclear logs acquired in adjacent wells, bed contrasts were defined for zones of interest. Modeling was done to define the minimum acquisition time needed to detect the defined contrasts. Telemetry was designed with adequate resolution for geo-steering, thus saving bandwidth. The impact on memory data accuracy caused by faster acquisition rates was modeled to check feasibility. Field tests were performed to validate the modeling results.Real-time telemetry accuracy proved adequate and the improved data density provided better definition of bedding features versus standard setup. Memory data contained better vertical resolution, further enhancing bedding features, while maintaining the required accuracy. Understanding all end users' specific data quality requirements is key to an acceptable compromise.Applying this methodology in the planning phase for other wells ensures all stake holders' needs are considered, and aids the overall understanding of LWD acquisition limitations and highlights the possibilities.