Investigation of mechanisms of supercritical CO2 trapping in deep saline reservoirs using surrogate fluids at ambient laboratory conditions

Abstract

Geological storage of carbon dioxide relies on the effectiveness of immobilizing CO 2 in the pore space of deep geological formations through a number of trapping mechanisms that include capillary, dissolution, and mineral trapping. Improved fundamental understanding of these processes is expected to contribute towards better conceptual models, improved numerical models, more accurate assessment of storage capacities, and optimized placement strategies. However, studying these processes at a fundamental level is not feasible in field settings because fully characterizing the geologic variability at all relevant scales and making observations on the spatial and temporal distribution of the migration and trapping of supercritical CO 2 (scCO 2) is not practical. The specific goal of this study is to develop and implement an experimental method in intermediate scale test tanks under ambient laboratory conditions to make observations and generate data to improve the understanding of capillary trapping affected by fluid and formation properties. Since it is challenging to visualize multiphase flow processes occurring at high pressure conditions at the meter scale, a testing method was developed based on the use of surrogate test fluids to replace the scCO 2 and formation saline water. To set a foundation for extrapolating experimental results to the field, we chose a set of dimensionless groups that define the relative contributions of buoyancy, viscous, and capillary forces to the displacement behavior of immiscible fluids. The experiments were designed with the goal of understanding and accurately quantifying the immobilization of the scCO 2 analog in a homogeneous formation confined by a slightly dipping structural barrier. A set of three displacement experiments through unconsolidated sands with variable permeability was conducted in a quasi-two-dimensional flow cell to gain insight into the influence of buoyancy forces on the propagation of the displacing phase. This work takes advantage of laboratory 3 experiments at the intermediate scale to investigate gravitational and hysteresis effects on entrapment of scCO 2 currents in brine-saturated reservoirs. Understanding these phenomena at a fundamental level represents a critical step to improve injection strategies and to enhance capillary trapping mechanisms.

Experimental Investigation of Supercritical CO2 Trapping Mechanisms at the Intermediate Laboratory Scale in Well-defined Heterogeneous Porous Media

“…Following the research presented in a previous paper [5], where we conducted immiscible displacement experiments through homogenous sandpacks with variable permeabilities, here we compare two experiments with the goal of understanding the effects of heterogeneity and the influence of capillary barriers on migration and entrapment of a scCO 2 plume through a brine-saturated reservoir. The experimental apparatus used to carry out the displacement experiments is illustrated in Fig.1a, and consists of a rectangular flow cell with internal dimensions (L x W x H) of 91.4 x 5.6 x 61 cm 3 .…”

“…The experimental apparatus used to carry out the displacement experiments is illustrated in Fig.1a, and consists of a rectangular flow cell with internal dimensions (L x W x H) of 91.4 x 5.6 x 61 cm 3 . The details of the procedure to prepare the synthetic reservoir and constrain the boundary conditions, as well as the x-ray attenuation method, which was used to non-destructively measure the spatial and temporal variations of NWP saturation, are described in Trevisan et al [5]. Each experiment consisted of a 5.5-hour injection of NWP, followed by a fluid redistribution period characterized by spontaneous imbibition at the trailing edge of the plume and slow drainage at the front edge facilitated by the 2° inclination of the reservoir.…”

“…In this investigation we develop two-dimensional experiments conducted in intermediate-scale (centimeter to meter) flow cells aimed to represent a suitable intermediary for mimicking flow processes occurring between one-dimensional column tests and field-scale [4] and to study the effect of flow dimensionality on the distribution of residual saturation in controlled laboratory settings [5]. Eventually, these experiments will provide data sets to test the applicability of numerical multiphase flow models for prediction of long-term CO 2 migration and trapping under field conditions [6].…”

Evaluation of relative permeability functions as inputs to multiphase flow models simulating supercritical CO2 behavior in deep geologic formations

“…Additionally, maintaining CO 2 in a supercritical state can be experimentally challenging in many laboratory settings under ambient temperature and pressure conditions. To overcome this difficulty, the use of surrogates for brine and scCO 2 under ambient laboratory test conditions has been proposed (Trevisan et al, 2014;Mori et al, 2015). In a companion paper, Mori et al (2015) showed that these surrogate fluids were able to replicate the scCO 2 and brine P c -S w relationships by comparing the results with actual scCO 2 and brine capillary pressure measurements for quartz sand presented by Tokunaga et al (2013).…”

“…To experimentally mimic flow and capillary trapping of scCO 2 in saline aquifers, Soltrol 220 (hereafter referred to as Soltrol) and an 80% by weight solution of glycerol in water (hereafter referred to as 80% glycerol) were used as surrogates for scCO 2 and brine, respectively. These fluids were chosen as to be within the range of dimensionless groups such as capillary num- Table 2 Density ( ) and viscosity ( ) of 80% and 50% by weight solutions of glycerol in water (Cheng, 2008 ber, bond number, viscosity ratio, and density ratio, relevant to that of scCO 2 and brine (Cinar et al, 2009;Pentland et al, 2010;Aminzadeh-goharrizi et al, 2012;Trevisan et al, 2014;Mori et al, 2015). These dimensionless numbers are defined in Mori et al (2015).…”