Formation Evaluation Through Stuck Heavy Weight Drill Pipe for Drilling Optimization: A Case Study

Abstract

Abstract Formation evaluation plays an important role in the planning and design of a well. Understanding subsurface reservoir and fluid properties are critical in the efficient management of subsurface resources. During drilling, several challenges including failure of Logging While Drilling sensors could limit the gathering of formation evaluation data, particularly well logs. In this paper, a detailed case study is discussed showcasing an unconventional application of pulsed neutron logging for drilling optimization. A multidetector pulsed neutron tool was logged through stuck heavy weight drill pipe (HWDP) in an unknown environment with limited data. Significant focus was placed on real time data monitoring to ensure high amount of neutron interaction could be generated for measurement. Pulsed neutron data was acquired in both inelastic and capture modes. Due to the wellbore environment, customized environmental fan charts were modeled to specifically correct for the impact of the heavy mud and HWDP to assess the response from the formation behind the pipe. The pulsed neutron data was acquired along with gamma ray across the newly drilled formations through the HWDP. The natural gamma ray data was highly attenuated and thus, could not be used for lithology identification. Sigma data along with pulsed neutron porosity indicators were used for lithology identification, shale volume estimation and porosity calculations. Slow capture data from the third detector of the pulsed neutron tool combined with inelastic count rate was used for gas saturation analysis while carbon-oxygen data was used to evaluate the presence of oil. Proper environmental corrections were applied during data analysis using pre-modeled fan charts for the specific wellbore environment. The results of the interpreted pulsed neutron data confirmed the presence of light hydrocarbons within the encountered reservoir along with the associated pay thickness, saturation and formation properties. Consequently, invaluable data was gathered in the untested fault block within the field despite the attendant challenges. Furthermore, drilling operations and recovery plans were optimized based on the pulsed neutron interpretation, thereby avoiding unnecessary well costs associated with making wrong decisions. This paper demonstrates the application of pulsed neutron logging for formation evaluation through heavy mud and stuck heavy weight drill pipe in order to make efficient corporate management and drilling decisions. The impact of the wellbore drilling environment was assessed real-time to ensure logging parameters were optimized. The value of pulsed neutron logging in this unconventional application was successfully illustrated in this case study despite the limited data and unfavorable logging conditions.