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ABSTRACT:Using the classical pulse decay test to measure the permeability of tight rock such as serpentinized harzburgite can be time-consuming, often requiring hours or even days. This prolonged duration not only complicates experimental control but also introduces difficulties in maintaining stable environmental conditions. To address such challenges, a fast permeability measurement method has been developed based on an analytical solution that approximates the pressure distribution in the test specimen using parabolic arcs. This solution yields a simple linear regression formula, enabling rapid interpretation of rock permeability using data from only the initial stage of the pulse decay test. In this study, the proposed method is validated by numerical simulations using synthesized pulse decay test data. In addition, an experimental validation of this method using a serpentinized harzburgite is also presented. It is shown that the method is not only faster but also more accurate than the classical method, which ignores the storage of the rock specimen. 

ABSTRACT:Long-term deep sequestration of CO2-rich brine in deep formations of ultramafic rock (e.g. Oman serpentinized harzburgite) will be feasible only if a network of hydraulic cracks could be produced and made to grow for years and decades. Fraccing of gas- or oil-bearing shales has a similar objective. The following points are planned to be made in the presentation in Golden. 1) A branching of fracture can be analyzed only if the fracture is modeled by a band with triaxial tensorial damage, for which the new smooth Lagrangian crack band model is effective. 2) To achieve a progressive growth of the fracture network one will need to manipulate the osmotic pressure gradients by changing alkali metal ion concentration in pore fluid. 3) A standardized experimental framework to measure rock permeability at various ion concentrations and various osmotic pressure gradients is needed, and will be presented. 1 INTRODUCTIONCarbon dioxide (CO2) emissions by human activities is the largest contributor to global warming; therefore, effective carbon sequestration technologies attract great amount of interest. One emerging and promising technology for storing CO2 in the subsurface permanently is through carbon mineralization in mafic and ultramafic rock (Kelemen and Matter, 2008). Despite the abundance of these types of rock in the Earth's upper crust (Matter et al., 2016), the rate of this process in nature is too slow to reduce CO2 emissions effectively (Seifritz, 1990). One of the key challenges to achieve a sustainable and large-scale storage of CO2 by mineralization is to engineer a progressive growth of a fracture network conveying water with dissolved CO2 to reach a gradually increasing volume of the mafic rock formation. The CO2 rich water often cannot penetrate the tight matrix of silica-rich serpentinized harzburgites because under high concentrations of CO2, the wetting angle of CO2 -bearing water-rock-rock interface exceeds the critical value of 60 degrees. Therefore, the presence of a family of cracks is the only means by which CO2 -bearing fluids can interact with matrix of ultramafic rock (Bruce Watson and Brenan, 1987). Lateral fracture branching from a major fracture provides a sustainable fluid pathway and therefore is essential for continued rock-water geochemical reactions that lead to mineralization of carbonate minerals. Realistic computational modeling of hydraulic fractures in peridotite or basalt must involve lateral fracture branching and account for stress distribution changes between solid and fluid phases under constant tectonic stress, triggered by pore exposure to fluid pressure in hydraulic cracks.