Deep saline aquifers are promising locations for carbon
sequestration,
but the impact of the CO2 injection on rock properties
requires careful investigation. This study will examine the effects
of CO2-saturated brine injection on limestone, specifically
analyzing how pore pressure influences wormhole formation and subsequent
changes in the petrophysical and geomechanical properties. Four Indiana
limestone samples, each with dimensions of 1.5 in. in diameter and
3 in. in length, were utilized. These samples exhibited an average
porosity of 15.7% and an average permeability of 2.6 mD. During the
experiments, the samples were subjected to one of selected pore pressure
values (4000, 3000, 2000, and 1500 psi) and a temperature of 60 °C,
with a brine concentration of 120,000 ppm mixed with CO2 at a ratio of 70:30. Notice that the pressure was kept in the accumulator
at 1200 psi initially before compressing it to the desired pressure
to maintain the same mass of CO2 in all experiments. An
injection rate of 1 cm3/min was employed for the coreflooding
experiments. Before and after coreflooding, Young’s modulus
(YM) and Poisson’s ratio of the samples were measured at various
confining pressures. Additionally, the porosity, permeability, and
surface hardness of the treated samples were assessed. A micro-CT
scan was employed to visualize the generated wormholes and quantify
their volumes. Our study demonstrated that among the four tested injection
pressures, 2000 psi yielded the lowest pore volume to breakthrough
(PVBT). No clear trend was observed between PVBT and pore pressure.
However, a strong correlation emerged between the mechanical properties
of the treated samples and pore pressure values. The investigation
established that increasing injection pressure results in greater
damage to the core, as evidenced by reductions in both surface hardness
and dynamic YM.