Detection of Low Contrast, Low Resistivity Pay (lclr) Challenge in Shaly Sand Gas Reservoir Through Acoustic Data in the on Shore Nile Delta, Egypt

Abstract In the onshore Nile Delta gas fields, the Upper Miocene Abu Madi clastic reservoir show significant challenges for effective gas production, development, and exploration. The Abu Madi Formation contain unconventional reservoirs, including thin-bedded intervals and low resistivity zones, which are usually overlooked by normal petrophysical evaluation techniques and conventional logging tool analyses. These challenges are mostly clear in areas with significant facies changes, typical of the complex depositional environment of the Nile Delta, or in exploratory wells. Detecting these hidden Abu Madi reservoirs is difficult due to their high shale content, which complicates formation evaluation. The maximum deep resistivity reading in these wet sand reservoirs can reach up to 1.6 ohm.m., while pay intervals exhibit low resistivity readings of less than 2.58 ohm.m. due to high water content. This narrow resistivity range often leads to misinterpretations and affects the pay calculations, reducing the reserve estimation for the whole field. The volume, distribution, and type of clay minerals present in the shale significantly affect the readings which come from conventional logging tools, especially resistivity reading. The conductive nature of clay can mask high resistivity values indicative of gas-bearing intervals, especially when these intervals are thinner than the vertical resolution of the conventional resistivity tools. This study explains that combining conventional logging data (such as gamma ray, resistivity, density, and neutron data) with acoustic data (such as shear and compressional sonic data) can effectively detect these hidden pay reservoirs. This integrated approach depends on the theory that says, while the compressional sonic waves are influenced by reservoir fluids, the shear waves are not affected by it. This methodology helps to mitigate the masking effects of shale conductivity and establishes a strong framework for detecting these hidden reservoirs. Identifying and analyzing these hidden pay zones can significantly increase commercial reserves and production, which is necessary for maintaining low water cut values and ensuring the long-term production of these gas fields. This integrated assessment ensures that valuable resources within low resistivity and thin-bedded intervals are not overlooked, thereby enhancing the identification and understanding of various unconventional reservoirs, including tight formations and shaly sand.