Cryogenic liquid nitrogen treatment for enhancing gas production in Sui main limestone carbonates, Central Indus Basin, Pakistan

The Early Eocene Sui Main Limestone (SML) reservoirs in the Qadirpur area are significant hydrocarbon-producing formations but suffer from low permeability and poor reservoir characteristics that lead to well abandonment. Although commonly used, conventional stimulation techniques such as hydraulic fracturing and acidizing pose environmental risks, high costs, and sensitivity to fluctuations in crude oil prices. Meanwhile, cryogenic liquid nitrogen (LN₂) treatment has emerged as an innovative, eco-friendly alternative due to its thermal shock effects, which enhance rock permeability and porosity. Herein, SML core samples are treated with LN₂ for 30, 60, and 90 min to obtain samples designated as SML_30, SML_60, and SML_90, respectively. These are examined using X-ray diffraction (XRD), atomic force microscopy (AFM), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), nanoindentation, and petrophysical measurements to evaluate the changes in their petrophysical, morphological, and micromechanical properties. The post-treatment analysis reveals that LN₂ cooling effectively induces micro-cracks, with fracture widths of up to 40 µm, along with a substantial increase in surface roughness from 350 to 942 nm. Additionally, micromechanical analysis indicates notable changes in the indentation modulus due to stress-induced alterations in the rock matrix. At optimal LN₂ exposure (90 min), the porosity and permeability of the SML sample is more than doubled. These findings provide valuable insights into LN₂-induced reservoir enhancements, thereby contributing to a better understanding of fluid flow behavior and hydrocarbon recovery in tight gas reservoirs. Thus, LN₂ treatment presents a promising, cost-effective, and environmentally sustainable alternative to conventional stimulation methods.