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Over the last decade, economic and environmental factors have led to low salinity water injection (LSWI) becoming one of the most important improved oil recovery methods. Although many results have been obtained from laboratory tests, only a few papers have been published regarding the modeling and simulating LSWI in carbonate reservoirs compared to sandstone reservoirs. This paper investigated the most affecting parameters on oil recovery during LSWI at the core and field scale. The published work focused more on the effective parameters related to ultimate oil recovery using LSWI. However, important parameters affecting the oil recovery rate were not investigated. We compared how important parameters affected the ultimate oil recovery factor and ultimate oil recovery rate. According to the results of this study, the salinity of injected water and curvature of oil relative permeability were the most important factors on the ultimate oil recovery factor. By reducing both of these parameters, more increment oil was recovered. By increasing the injection rate of water, the curvature of the water relative permeability, wettability, and the endpoint of oil relative permeability, the oil recovery rate also increased. Furthermore, threshold capillary pressure and the endpoint of relative permeability of water had inverse effects on oil recovery. Injecting low salinity water into the reservoir will change its wettability. As a result, it will change the properties of the reservoir and increase the production from the reservoir, resulting in more oil being produced. LSWI resulted in an increase of oil recovery factor of 5% and 11% respectively after 25 and 58 years in this case. [ABSTRACT FROM AUTHOR]

The impact of the land use landscape pattern on river hydrochemistry has significant scale effects. It is the premise and foundation of landscape optimization and the conservation of water resources to accurately identify the core scale of the landscape pattern impacting on river hydrochemistry. Taking Binggou River Basin in the source region of Shiyang River Basin as the study area, this paper selected the three spatial scales of catchment area, buffer zone, and riparian zone, and the relationships between land use types and landscape indices and river hydrochemical characteristics were analyzed at different spatio-temporal scales using redundancy analysis. The results showed that the hydrochemistry characteristics of Binggou River Basin had strong temporal variability, and the rainy season was the key period when the land use landscape pattern affected the river hydrochemistry. The sub-watershed and riparian scales were the core scales of influence of the landscape pattern on river hydrochemistry in Binggou River Basin. In particular, the landscape pattern index contributed the most to the river hydrochemistry at the sub-watershed scale on the whole, which was the core scale affecting river hydrochemistry. The “source” or “sink” functions of the same land use type also changed as the scale changed. Forest land showed weak “source” effect at the sub-watered scale, but a strong interception effect on the soil erosion process at the riparian scale, which is a typical “sink” landscape.

Wettability is an essential property of reservoirs that is of great importance for enhancing oil recovery (EOR) and oil migration. The wettability of reservoirs is generally believed to be strongly affected by mineral compositions but it is not always the case. An integrated study of petrography and wettability was carried out to determine the impact of chlorite minerals on the wettability of the sandstone reservoirs in the Upper Triassic Yanchang Formation. Chlorites are found to be commonly present in the reservoir sandstones as detrital grains, rim-shaped cements, and biotite-chloritized forms with the pore peripheries being largely coated by chlorite, which is the main mineral in direct contact with pores. At pore scale, the wetting state of chlorites can either be oil-wet or water-wet in the tight sandstone reservoirs depending on wettability alteration by oil charge. Chlorites in contact with pores occupy a large of proportions of oil-wet pore walls and are crucial for the formation of oil-wetting state of reservoir sandstones. At core scale, the contents of chlorites in direct contact with pores do not correlate well with the Amott-Harvey index due to other factors such as heterogeneity, oil-bearing degrees of samples. [ABSTRACT FROM AUTHOR]

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We have experimentally investigated the impact of heterogeneity on the dissolution of two limestones, characterised by distinct degrees of flow heterogeneity at both the pore and core scales. The two rocks were reacted with reservoir-condition CO 2 -saturated brine at both scales and scanned dynamically during dissolution. First, 1 cm long 4 mm diameter cores were scanned during reactive flow with a 4 μm voxel size between 10 and 71 times using 4D X-ray micro-tomography (μ-CT) over the course of 90 min. Second, 3.8 cm diameter, 8 cm long cores were reacted at the same conditions inside a reservoir-condition flow apparatus and imaged using a medical-grade X-ray computed tomography scanner (XCT). Each sample was imaged ~13 times over the course of 90 min at a 250 × 250 × 500 μm resolution. These larger cores were then scanned inside a μ-CT at a 27 μm voxel size to assess the alteration pore-space heterogeneity after reaction. Both rock types exhibited channel widening at the mm scale and progressive high porosity pathway dissolution at the cm scale. In the more heterogeneous rock, dissolution was more focussed and progressed along the direction of flow. Additionally, the dissolution pathways contained a distinct microstructure captured with the μ-CT that was not visible at the resolution of the XCT, where the reactive fluid had not completely dissolved the internal pore-structure. This microstructure was further analyzed by performing a direct simulation of the flow field and streamline tracing on the image voxels. We found that at the larger scales the interplay between flow and reaction significantly affects flow in the unreacted regions of the core. When flow is focussed in large reacted channels, this focusing is carried through to the unreacted parts of the rock where flow continues to be confined to preferential pathways after passing the reaction front. This focussing effect is greater with increasing pore space heterogeneity indicating that the representative elementary volume (REV) for dissolution is far greater than the dissolution front itself. This study of scale dependence using in situ 4D tomography provides insight into the mechanisms that control local reaction rates at the mm and cm scales. Furthermore, this work suggests that under these conditions at larger scales it is likely to be structural heterogeneity that dominates the pattern of dissolution and therefore the evolution of high permeability pathways. [ABSTRACT FROM AUTHOR]

• The rainy season was the key period when land use landscape pattern affected the river water chemistry. • The sub-watershed scale was the core scale that affects river water chemistry as a whole. • The "source-sink" functions of the same land use type changes with the change of scale. • Forestland and grassland have obvious interception effect on soil erosion at riparian scale. The impact of the land use landscape pattern on river hydrochemistry has significant scale effects. It is the premise and foundation of landscape optimization and the conservation of water resources to accurately identify the core scale of the landscape pattern impacting on river hydrochemistry. Taking Binggou River Basin in the source region of Shiyang River Basin as the study area, this paper selected the three spatial scales of catchment area, buffer zone, and riparian zone, and the relationships between land use types and landscape indices and river hydrochemical characteristics were analyzed at different spatio-temporal scales using redundancy analysis. The results showed that the hydrochemistry characteristics of Binggou River Basin had strong temporal variability, and the rainy season was the key period when the land use landscape pattern affected the river hydrochemistry. The sub-watershed and riparian scales were the core scales of influence of the landscape pattern on river hydrochemistry in Binggou River Basin. In particular, the landscape pattern index contributed the most to the river hydrochemistry at the sub-watershed scale on the whole, which was the core scale affecting river hydrochemistry. The "source" or "sink" functions of the same land use type also changed as the scale changed. Forest land showed weak "source" effect at the sub-watered scale, but a strong interception effect on the soil erosion process at the riparian scale, which is a typical "sink" landscape. [ABSTRACT FROM AUTHOR]