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Pore Networks to Characterize Formation Damage Due to Fines at Varied Confinement and Sand Shape
Abstract
Carbon sequestration in geological formations is in demand for many applications, especially energy production from hydrates. During gas production in a sandy hydrate reservoir, two phase flow and changes in confinement takes place. Nine fully saturated sand systems were scanned three times; before, during and after CO2 gas injection. The confinement pressure was altered, by placing a vertical spring that presses against the upper port of the sediment cylinder. 3D images were analyzed by direct visualization, followed by quantification and pore network analysis. Outcomes demonstrated that shape of sand particles affects how the unconsolidated media will impact the flow, in angular sediments with high confinement pressure, there is more friction between the grains, this results in no dislocations of sand, the fines clog the throats, and more formation damage is noted. In rounded grains with lower confinement pressure, sand grains dislocated; opening large pathways for gas flow; this resulted in lower formation damage. Measures done using pore networks, showed that because of micro-fractures, permeability of the system can increase during hydrate production. This is in contrast to the other systems, where throat sizes shrunk, decreasing the permeability; because of fines migration toward the throats and the small sand grains dislocations.
... The experiment employed a widefield macroscope with microfluidic chips that resemble the pore morphology of sandstone rock samples. To study, the mechanisms of hydrophobic colloids retention and subsequent clogging (Hannun et al., 2019). The microfluidic flow experiments were captured using 5 MP images at a spatial resolution of 1µm/pixel. ...
Water recharge wells can provide a solution for 3.5 billion people, living in regions suffering from water scarcity. Due to fines migration, freshwater wells that are used to recharge aquifers, often experience expedited deterioration. Colloidal clay fine particles can be mobilized from within aquifers due to hydrodynamic forces or the sweeping of gas-water interface (GWI). The released colloids concentration increases then starts to retain and clog at the pores within the aquifer formation. Although fines migration is responsible for decommissioning many recharge wells, yet there is a lack of pore scale observations that uncover clogging mechanisms within porous media. Thus, this study utilizes wide-field optical macroscopy and microfluidic models with pore morphology of sandstone, to investigate the clogging mechanisms of hydrophobic colloids. The aim is to discover how interfacial surfaces within porous media retain colloids. Hence imbibition and drainage of colloidal suspension were carried to vary water saturation. Flow experiments were imaged at a resolution of 1µm/pixel, while colloids diameter was 5 µm. Images were segmented into solid, water, gas and colloids. Then the amount of colloids retained on each interface was quantified. Findings revealed that hydrophobic colloids retained mainly on the GWI. For colloids suspension in deionized water, affinity of colloids to GWI was high enough to cause bubble stabilization. In both hydrophobic and hydrophilic porous media, colloids disconnected the gas phase to create larger GWI surface. More than 90% of hydrophobic colloids were cleaned from the media after drainage, uncovering an efficient remediation technique for water aquifer.
Fine particles within porous media may migrate with the flowing fluid and cause bridging or clogging in the pore space. Bridging and clogging reduce the flow permeability of porous media, which has a significant influence on petroleum engineering applications such as water and oil extraction, sand production, and gas production from hydrate-bearing sediments. Although the migration of fine particles and its impact on bridging and clogging have been investigated for a single-phase flow, it has not been understood clearly for a multi-phase flow. This work reports an approach using microfluidic pore models to study the migration of fine particles and the bridging/clogging behavior in a structure mimicking porous media. Results from the microfluidic model show that: (1) fine particles accumulated along the water and gas (CO2) interface; (2) fine particle concentrations in pores locally increased due to the accumulated particles at the interface, and (3) consequently bridging and clogging occurred in the pore throat. Findings from this work provide a starting point in understanding complex phenomena including a reduced flow permeability of porous media on a fluid containing fine particles for a variety of petroleum engineering applications.
Production of methane from hydrate-bearing sediments requires hydrate dissociation for releasing mobile methane gas in sediments prior to gas production operations. Fines may migrate through or clog the pore space of sandy sediments depending on the geometry and topology of the pore space. Multiphase flow experiments were conducted on brine saturated uniform silica sand mixed with different percentages of kaolinite. Fines concentrations were correlated to computed tomography (CT) numbers in their host brine phase. Representative element volume (REV) procedure was used to study local porosity and local fines concentration. A cubical REV with a side length of 850 was selected. For low fines content (less than 6%), gas percolated through the specimens with no major particle translation or porosity change. For 6% kaolinite specimen, fractures were initiated, and propagated by densifying surrounding sediments. Local fines concentration study showed that fines migrated through the pores for specimens with fines content less than 6%. For the 6% kaolinite specimen, fines concentrated near fractures due to clogging. Clogging induced an increase in the capillary pressure at the pore throats and caused the capillary pressure to overcome the effective stress between sand particle, and fractures to be initiated. Sand particles experienced up to 200 translation and 15° rotation due to gas driven fracture in the 6% kaolinite specimen.
