Reduction In Capillary Forces Research Articles

Heavy oil recovery in blind-ends during chemical flooding: Pore scale study using microfluidic experiments

The blind-end is a typical tiny structure widely distributed in reservoir rock. In this work, we used the microfluidics to observe the fluid flow phenomenon in blind-ends at pore scale. A microfluidic chip that contains four blind-ends with different widths was designed. The microfluidic chip is initially saturated with light oil or heavy oil. Then, deionized water, sodium oleate solution, or hydrolytic polyacrylamide solution is selected to inject into the microfluidic chip to displace the oil in blind-ends. We recorded the blind-end snapshots at different experiment conditions and then analyzed the variation of oil saturation quantitatively. Moreover, we explained the oil displacement mechanism in blind-ends with the perspective of micro force. The results demonstrated that the oil in wide blind-end is more easily displaced than the narrow blind-end due to higher shear force and lower capillary force. Heavy oil in blind-end is more difficult to displace from the blind-end due to higher viscous force and elastic force. Polymer flooding is more effective to light oil due to the extrusion swell effect. The reduction of capillary force caused by surfactant is beneficial to recover more oil from the blind-end. This work presents detailed oil displacement mechanism of blind-ends and can be a method to screen more effective chemicals for blind-end oil.

Experimental investigation of water sensitivity effects on microscale mechanical behavior of shale

Drilling and multi-stage hydraulic fracturing bring a large amount of water into clay-bearing shale reservoirs, which may lead to attenuation of fracturing effects and wellbore instability. However, a thorough understanding of changes in shale micromechanics and corresponding mechanisms when exposed to water remains unclear. In this work, samples were selected based on clay enrichment. Subsequently, the contact resonance (CR) technique based on atomic force microscopy (AFM) was performed to characterize the micromechanics of shales after exposure to water. Visual phenomena provided by environmental scanning electron microscopy (ESEM) assisted to explain the underlying mechanisms. It was found that the hydration effect lowered both the storage modulus and stiffness of samples, but with different contributions from brittle minerals and clay, as well as variations depending on bedding plane orientation. Due to the difference in composition, the investigated terrestrial shale material exhibited stronger water sensitivity and anisotropy, with a general decrease of 15%–25% in storage modulus, compared with variations of -5%–15% in modulus of marine shale samples. Moreover, microscopic observation experiments revealed that the reduction of capillary force and the interlaminar swelling of clay particles might have been active after water adsorption, which led to the decreases of modulus and stiffness values. However, the swelling-caused confining effect or void space closure during the water imbibition process might have offset this weakening effect and even increased storage modulus. At mesoscale , excessive shrinkage caused the growth of micro-cracks, which in turn significantly attenuated overall mechanical properties. • Comparison of clay composition between terrestrial and marine shale based on clay enrichment. • AFM contact resonance method to characterize the micromechanical properties of shale before and after water adsorption. • Investigation of mechanisms of microscale mechanical changes in hydration and dehydration processes.

The role of polar organic components in dynamic crude oil adsorption on sandstones and carbonates

An appropriated wettability characterization is crucial for the successful implementation of waterflooding operations. Understanding how crude oil adsorption takes place on different mineral surfaces and how these processes impact reservoir wettability are essential aspects that can help unlock and produce large underground oil reserves.
 Polar organic components (POC) present in crude oil are surface-active molecules with high affinity towards mineral surfaces. POCs are quantified by the acid and base numbers (AN and BN) with units of mgKOH/g. The POC adsorption behavior is highly influenced by the type of minerals and brines present in the reservoir system.
 This study aims to shed light onto the most important features of oil adsorption on carbonates and sandstones mineral surfaces; particular attention is given to the role of acidic components. Therefore, outcrop sandstone and carbonate materials were used. The sandstone material contains various silicates, including quartz, Illite clay, and feldspars. The carbonate outcrop material came from the Stevns Klint quarry in Denmark and is considered a very pure calcium carbonate with minimum silicate impurities.
 Dynamic adsorption tests were performed at 50°C by injecting low asphaltene crude oils into core plugs, and AN and BN values of the effluent oil samples were measured and compared with the influent oil values. Furthermore, spontaneous imbibition (SI) tests were performed to assess the wettability impact of crude oil injection in oil flooded cores.
 The results showed that after crude oil injection, the cores became mix-wet. Confirmation of a reduction in capillary forces and a shift towards a less water-wet state was reported for both mineralogies, i.e., sandstones and carbonates. The acidic polar components had a substantial impact on carbonates wettability, while on sandstones, the experiments suggested that acidic polar components had a lower impact on wettability than that observed in the basic polar components.

Collapse Mechanisms of Low Cohesion Compacted Soils

Despite the knowledge of collapse phenomena, there have been many documented cases presented in the literature of compacted fills, earth dams, and road embankments which failed at least partially as a result of wetting-induced collapse. Two aspects of wetting-induced collapse not fully explored for compacted silty-sands are the magnitude of collapse and the fabric alteration after wetting. This paper presents the results of two studies of collapse potential of such soils using Double-Oedometer Tests and Scanning Electron Micrographs (SEM's). In one study, silty-sand soils compacted dry of (less than) optimum water content at 90 percent of Modified Proctor maximum dry density showed appreciable magnitude of collapse upon wetting. In the second study, similarly prepared soils with a lower clay content indicate little to no collapse. The sand component of each soil is similar; however, different sources of silt were used in each study. SEM's showed that the silt of appreciably collapsible soils is more angular. Also, clay binds silt grains together leading to a more open structure. The clay quantity triggers the collapse of these soils more than the removal or reduction of capillary force.