Publications

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• Rubino JG, Barbosa ND, Hunziker J, Holliger K, Can we use seismic reflection data to infer the interconnectivity of fracture networks?While variations of seismic reflection amplitudes with incidence angle (AVA) and azimuth have been widely used to provide information on geometric characteristics of fractures, this attribute has, as of yet, not been linked to fracture interconnectivity, which tends to govern the hydraulic property of the affected formation. This is due to limitations of the forward models considered to represent the corresponding seismic responses. Based on a poroelastic upscaling procedure and a subsequent plane-wave analysis, we show for the first time that seismic reflection coefficients are highly sensitive to fracture interconnectivity. Moreover, our results suggest that crossplots of commonly employed AVA coefficients can be used to delineate regions of fractured formations with higher or lower fracture interconnectivity. This sensitivity is due to changes of the stiffening effect of the fluid contained within interconnected fractures in response to wave-induced fluid pressure diffusion (FPD), a physical process that has not been previously accounted for in seismic reflection analyses.
• He Y, Rubino JG, Solazzi SG, Barbosa ND, Favino M, Chen T, Gao J, Holliger K, Numerical Upscaling of Seismic Signatures of Poroelastic Rocks Containing Mesoscopic Fluid-Saturated VoidsSeismic waves are commonly employed to study porous and/or fractured geological formations in the Earth's upper crust. In the presence of relatively small heterogeneities, such as fluid-saturated fractures or vugs, seismic waves may exhibit velocity variation and amplitude decay due to fluid pressure diffusion processes, which are important characteristics of seismic waves. To date, it remains difficult to understand how complex and fluid-saturated voids impact these seismic characteristics. To address this problem, we propose a novel coupled fluid-poroelastic model and develop a corresponding numerical upscaling procedure to calculate seismic characteristics of porous media containing mesoscopic heterogeneities. Our results demonstrate that the proposed approach is more accurate and flexible than previous related models, which, in turn, opens new and interesting perspectives for the seismic exploration of corresponding geological environments.
• Barria, JC; Manzanal, D; Cerruti, P.; Pareira, JM, "Cement with bacterial nanocellulose cured at reservoir temperature: Mechanical performance in the context of CO2 geological storage"This work focuses on the microstructure and mechanical behavior of cement modified with bacterial nanocellulose (BNC) cured at 90 °C, simulating temperature at the reservoir level. The chemo-hydro-mechanical (CHM) coupled behavior of the cement–rock interface is also investigated through numerical analyses.
• Molinos Pérez, M.; Martin Stickle, M.; Navas Almodóvar, P.; Yagüe Hernán, Á.; Manzanal Milano, D.; Pastor Pérez, M., "Toward a local maximum-entropy material point method at finite strain within a B-free approach"The material point method can be regarded as a meshfree extension of the finite element method. This fact has two interesting consequences. On the one hand, this puts a vast literature at our disposal. On the other hand, many of this inheritance has been adopted without questioning it. A clear example of it is the use of the Voigt algebra, which introduces an artificial break point between the formulation of the continuum problem and its discretized counterpart. In the authors' opinion, the use of the Voigt rules leads to a cumbersome formulation where the physical sense of the operations is obscured since the well-known algebra rules are lost. And with them, the intuition about how stresses and strains are related. To illustrate it, we will describe gently and meticulously the whole process to solve the nonlinear governing equations for isothermal finite strain elastodynamics, concluding with a compact set of expressions ready to be implemented effortless. In addition, the classic Newmark-𝛽 algorithm has been accommodated to the local maximum-entropy material point method framework by means of an incremental formulation.
• Navas, P.; Molino, M.; Stickle Martin, M.; Manzanal, D.; Yagüe, A.; Pastor, M., "Explicit meshfree u−pw solution of the dynamic Biot formulation at large strain"In this paper, an efficient and robust methodology to simulate saturated soils subjected to low-medium frequency dynamic loadings under large deformation regime is presented. The coupling between solid and fluid phases is solved through the dynamic reduced formulation 𝑢−𝑝w (solid displacement – pore water pressure) of the Biot’s equations. The additional novelty lies in the employment of an explicit two-steps Newmark predictor-corrector time integration scheme that enables accurate solutions of related geomechanical problems at large strain without the usually high computational cost associated with the implicit counterparts. Shape functions based on the elegant Local Maximum Entropy approach, through the Optimal Transportation Meshfree framework, are considered to solve numerically different dynamic problems in fluid saturated porous media.
• C.M. Martín, N.B. Scarponi, Y.A. Villagrán, D.G. Manzanal, T.M. Piqué, "Pozzolanic activity quantification of hollow glass microspheres"Hollow glass microspheres (HGMS) have been widely used in the hydrocarbon industry for cementing wells with low-density slurries. These consist of amorphous siliceous hollow spheres filled with gas, providing a low-density material with high compressive strength. The present study aims to characterize the interaction between HGMS and the cement paste, focusing mainly on the development of the pozzolanic activity, given the nature of amorphous silica. Thus, two HGMS of different crush strength were studied. HGMS were used as a replacement of total cementitious binder at 10% by weight of cement. The pozzolanic activity was measured with the modified Chapelle test, the portlandite quantification with thermogravimetric analysis, and the strength activity index comparing the compressive strength of hardened cement paste samples. Additionally, isothermal calorimetry analysis, X-ray diffraction patterns and scanning electron microscopy images were obtained. Results demonstrated that HGMS interact with the cement paste initially as nucleation agents and later with a pozzolanic reaction, presenting an activity comparable to that of metakaolin or fly ash.
• Santiago G. Solazzi, Simón Lissa, J. Germán Rubino, Klaus Holliger, "Squirt flow in partially saturated cracks: a simple analytical model"Obtaining the seismic response of rocks containing cracks whose scales are much smaller than the prevailing wavelengths is a classic and important problem in rock physics. Seminal analytical models yield the seismic signatures of cracked rocks saturated with a single fluid phase. However, in a wide variety of practically relevant scenarios, cracks may be partially saturated with multiple immiscible fluids of contrasting compressibilities, such as gas and water. When a passing seismic wave deforms the medium, fluid pressure gradients arise within such partially saturated cracks, which, in turn, tend to relax through a process commonly known as squirt flow. The corresponding viscous dissipation may greatly affect the seismic amplitudes and velocities, as well as the anisotropic behaviour of the medium. To date, extensions of classical analytical models to include squirt flow occurring within isolated partially saturated cracks remain limited either in the saturation or in the frequency range. In this work, we present a simple analytical model to compute the seismic response of rocks containing partially saturated aligned cracks accounting for squirt flow effects. First, we solve the linearized Navier–Stokes equations within a partially saturated penny-shaped crack subjected to an oscillatory strain. Then, we obtain a closed analytical expression for a complex-valued frequency-dependent effective fluid bulk modulus which accounts for the stiffness variations of each crack due to squirt flow. Using classic effective medium models, together with such an effective saturating fluid, we retrieve the effective compliance matrix of the probed partially saturated cracked rock. The proposed analytical solution is validated by comparison with corresponding 3-D numerical simulations and existing analytical models.