First Application of LWD High-Resolution Ultrasonic Imaging in an Unconventional Horizontal Well in the Najmah Formation: Case Study from Kuwait

Abstract

Abstract The unconventional Jurassic Najmah carbonate-shale formation in northern Kuwait has been tested and found to be a prolific source rock as well as a producer of gas, condensate, and light oil in different wells. The flow-controlling system, given the very low porosity, is highly dependent on the presence of a natural fracture network. The Najmah kerogen member, formally known as the Najmah shale, is the source reservoir composed of highly organic-rich argillaceous and calcareous clay, represented by very high total gamma ray values associated with high uranium on spectral gamma ray logs. Average matrix porosity ranges from 2 to 6%, low permeability from 0.01 to 1.5 mD, and total organic content (TOC) from 7 to 12%. Identification and interpretation of fractures, bed boundaries, and borehole breakout from high-resolution images plays a crucial role in optimizing completion design. Using wireline has been a challenge in horizontal wells, making logging-while-drilling (LWD) acquisition preferable. The case study is from a horizontal exploration well drilled with a rotary steerable system combined with gamma ray and resistivity sensors in the Najmah formation of north Kuwait, where a multi-stage fracking completion was planned. The logging program also included density, neutron porosity, sonic, and high-resolution ultrasonic borehole imaging measurements. To minimize the risk of stuck events, it was decided to use LWD acquisition. Wells in the area are typically drilled in the minimum stress direction (SHmin) to cross natural fractures perpendicularly, to optimize fracking. However, surprisingly, most of the natural fractures were almost parallel to SHmin. Overall, high data quality was achieved, and the results exceeded the end data users’ expectations. In total 96 natural fractures, 16 bed boundaries, and a few breakout intervals were interpreted within a measured-depth interval of 1,610 feet. Some of the fractures could be identified with high confidence on a 1:200 scale log. The new information about fracture orientation will be considered for future well design planning. The results were also used to facilitate the optimization of future field development and completion design. Further field analysis and studies are planned to be performed to confirm the interpreted results.