Enhanced Reservoir Understanding and Geomechanics With LWD High-Resolution Ultrasonic Imaging in an Unconventional Horizontal Well

Abstract

Abstract The Najmah carbonate-shale formation, an unconventional Jurassic kerogen layer in the North Kuwait region, has undergone testing, revealing its significant potential as a gas, condensate, and light oil reservoir in various well locations and as a prolific source rock. Given its exceptionally low porosity, the flow-control mechanism is heavily reliant on the presence of a natural fracture network. This layer, previously referred to as Najmah shale, serves as the source reservoir, characterized by its abundant organic-rich clay with both argillaceous and calcareous components. This is evident in the notably high total gamma ray values, which are accompanied by elevated uranium levels on spectral gamma ray logs. Matrix porosity averages between 2% and 6%, permeability is low, ranging from 0.01 to 1.5 mD, and the total organic content (TOC) falls within the range of 2% to 30%. The precise identification and interpretation of fractures, bed boundaries, and borehole breakout through high-resolution imagery play a vital role in the optimization of completion design. In the context of horizontal wells, utilizing wireline technology has been challenging, making the preference for logging-while-drilling (LWD) acquisition evident. The case in point pertains to a horizontal exploration well drilled in the Najmah formation of northern Kuwait, which employed a rotary steerable system combined with gamma ray and resistivity sensors. The drilling operation aimed to facilitate a multi-stage fracking completion. The comprehensive logging program also included measurements for density, neutron porosity, sonic, and high-resolution ultrasonic borehole imaging. To mitigate the risk of stuck events, the decision was made to utilize LWD acquisition. Traditionally, wells in the area were drilled in the minimum stress direction (SHmin) to intersect natural fractures perpendicularly for optimal fracking. Surprisingly, most of the natural fractures were found to be nearly parallel to SHmin. The data collected achieved a high level of quality, surpassing the expectations of the end data users. Within a measured-depth interval of 1,610 feet, a total of 96 natural fractures, 16 bed boundaries, and a few breakout intervals were interpreted. The newfound insights into fracture orientation will be considered in future well design planning. These results have also proven invaluable in enhancing the prospects for future field development and completion design optimization. Further analysis and studies in the field are on the horizon to validate the interpreted findings.