The Effect of Fluid Saturation on the Geo-Mechanical Properties of Reservoir Rock

Abstract The knowledge of how saturation affects rock geo-mechanical properties can be crucial for planning fluid injection strategies, minimizing environmental impacts, enhancing recovery efficiency and safe drilling operations. Formation fluid and injected fluids, which usually are in contact with the rock can react with the rock and affect the rock geo-mechanical properties. This study investigated the effect of 100% water saturation and 100% crude oil saturation on the geo-mechanical properties of unconsolidated reservoir rocks. Unconfined compressive strength (UCS) test was conducted on nine (9) core samples (three dry samples, three fully saturated with oil, and three fully saturated with water). The geo-mechanical properties of the reservoir core samples were obtained by generating the stress-strain relation from the UCS test conducted by using the load and deflection readings obtained from the test to calculate the stress and strain. The young modulus was calculated from the slope of the stress-strain diagram. The young modulus of the dry sample had an average value of 8666.67psi, which is higher than that of the Oil saturated (6333.33psi) and water (2788.89psi). The UCS values across the samples indicated that dry samples with average UCS of 7304.22 psi demonstrate greater resistance to deformation than oil-saturated samples with an average UCS of 5620.10 psi and water-saturated samples with an average UCS of 4330.88 psi. The average values of the elastic limit and the yield points of the dry, oil saturated and water saturated are 3881.5psi, 2883.37psi, 1364.3psi and 4066.67psi, 3200psi, 1966.69psi respectively. The compressive strength values obtained for oil and water saturated samples highlights the impact of fluid on the geo-mechanical behavior of reservoir rocks, as the introduction of fluids diminishes the material's strength, thereby lowering the elastic limits and young modulus and affirming that the presence of fluid adversely affects rock integrity. Statistical analysis shows that there are statistically significant relationships between obtained UCS values from the dry core samples and the fluid saturated core samples since confidence levels higher than 95 % were obtained (average R-square = 0.99).