Damage characteristics of high-temperature sandstone impacted by cetyltrimethylammonium bromide-enhanced jet

High-pressure water jet technology is an efficient and eco-friendly method with the potential to enhance rock-breaking efficiency in deep-earth high-temperature environments. This study introduces the use of the surfactant cetyltrimethylammonium bromide (CTAB) in water jets to improve thermal exchange between low-temperature jets and high-temperature rocks, aiming to optimize rock-breaking efficiency under high-temperature conditions in deep reservoirs. Experiments were conducted using jets with varying CTAB concentrations impacting rock at different temperatures to assess the feasibility and elucidate the underlying rock-breaking mechanisms. Computed Tomography (CT) combined with three-dimensional reconstruction was employed to establish the internal damage field of the rock, thereby analyzing the jet rock-breaking mechanisms. The findings indicate that the erosion pit formed in sandstone under the impact of a pure water jet has a regular inverted “Ω”-shape, while the pit formed under CTAB-enhanced jets resembles a “J”-shape. Furthermore, at elevated rock temperatures, the depth and volume of erosion pits created by jet impacts are greater than those at room temperature. At 100 °C, the rock-breaking volume increases by 16.81% with a pure water jet, whereas it increases by 75.46% with a jet containing 500 ppm CTAB. Optimal concentrations of CTAB additives range from 500 to 1000 ppm, substantially enhancing rock-breaking efficiency at high temperatures by bolstering heat exchange between the jet and rock and intensifying the water wedge effect. These findings provide a theoretical basis and novel approaches for hydraulic fracturing of deep, high-temperature hard rock.