Low-permeability Layers Research Articles

Research and Practice of Intelligent Separate Production Technology with Cable in Huabei Oilfield

In order to improve the separate production effect of sandstone reservoir in Huabei Oilfield and give full play to the production capacity of medium and low permeability layers, the intelligent separate production technology with cable is designed and developed. The technology uses cable packer to seal each layer in the well, and a set of intelligent separate production device is connected to the corresponding string position of each target layer. During the production process, the intelligent separate production device can send instructions according to the ground control center Open or close the oil layer to realize the exploitation of any layer and multi-layer co production of any layer. It can accurately measure the liquid production and properties of each section of the well, and calculate the formation permeability, skin factor and other parameters by sections, so as to realize the continuous testing and monitoring function.In the later stage, the switch opening can be adjusted by remote control to adjust the output of each layer in time to meet different production allocation requirements and achieve the purpose of increasing oil and reducing water, which is of great significance to realize the accurate development of the reservoir.

A Design and Optimization Method of Performing Layer Combinations in Separate-Layer CO2 Flooding to Improve Oil Recovery

Separate-layer CO2 flooding has increasingly been used to improve the overall development of multi-layer heterogeneous reservoirs. Due to their field technical limitations, layer combinations have to be carried out to reduce the number of layer-groups required for the separate injection of CO2. Currently there are few studies of the method of designing layer combinations. In field practice, the layer combinations are often made based on the permeability ratio of the layers to be developed, but it is not possible to accurately obtain the optimal scheme in many cases. Therefore, in this paper, a new design and optimization method based on the weighted standard deviation of permeability is proposed, which comprehensively considers the effects of multiple geological and fluid properties in different layers. The new method is applied to study the layer combination schemes in separate-layer CO2 flooding in H block, Daqingzijing Oilfield, Jilin, China. The prioritization of all of the schemes is obtained via the method, and a related numerical model is also established to perform verification and quantitative analysis. The results show that designing layer combinations using the new proposed method can achieve better development effect than using the conventional permeability ratio based method. It can achieve a more uniform interlayer CO2 displacement with an obvious improvement in the CO2 swept volume in low permeability layers and a higher overall oil recovery. According to the numerical simulation results, using the optimal layer combination scheme designed via the new proposed method, the ten-year swept volume of CO2 in the low permeability layer can be increased by 16.2%, and the ten-year overall oil recovery efficiency can be increased by 3.3%, with both measures showing a remarkable improvement. The work can provide a significant reference point for the field design of layer combinations in separate-layer CO2 flooding.

Combined method of impact on layered-heterogeneousn formation based on in-situ steam generation

This article discusses the combined method of influencing a layered-heterogeneous reservoir. In-situ steam generation (IPSG) is used as the main method, which in turn can be considered a combined technology of hot water injection and in-situ combustion. In order to improve the efficiency of the IPSG, it is proposed to inject a slug of an alkali solution (NaOH). The main mechanism in the application of IPSG is thermal interference between layers of different permeability. The use of alkali allows us to use its positive properties. The use of alkali allows us to use its positive properties. Such as lowering the surface tension at the boundary of the oil solution of alkali, the formation of an emulsion. The formation of an emulsion in a high-permeability layer contributed to an increase in the pressure drop in it and, accordingly, changed the direction of the fluid flow. Most of the injected water-air mixture began to flow into the low-permeability layer. Thus, the effectiveness of the impact on the formation was increased. The effect of alkali solution concentration on oil displacement from a layered-heterogeneous reservoir is estimated. The proposed technology made it possible to increase the coverage of the layered formation by the process and, accordingly, increase the oil recovery factor. Experiments were carried out for two oils with different viscosities: 86 mPa.s and 510 mPa.s.

Analytical model for CO2 geo-sequestration in deep saline aquifers considering the effect of heterogeneity and matrix-fracture interaction

Deep saline aquifers are considered to be the best storage option for long-term CO2 geo-sequestration because such geological formation has the largest identified storage potential that can securely trap CO2 under its low-permeability caprock layers. Many analytical models have been proposed to rapidly detect the CO2 leakage from the storage aquifers. However, the heterogeneity and matrix-fracture interaction of storage layers have not been taken into consideration in previous studies. In this paper, we develop an analytical model to determine the dimensionless leakage rate and pressure build-up due to CO2 leakage from the heterogeneous, dual-porosity and multi-layer bounded storage aquifer. Based on the model description and assumptions, the analytical solution is obtained by means of dimensionless transformation, Laplace transform and numerical inversion. Afterwards, our model is verified by comparing with existing analytical model. In order to determine the effect of heterogeneity and the matrix-fracture interaction on the dimensionless leakage rate and pressure change, we conducted sensitivity analysis taking account of the heterogeneous factors. Based on the obtained results, increasing layer number and layer thickness from the bottom layer to the upper layer will delay the CO2 leakage. Furthermore, each layer in storage aquifer with greater fluid mobility is not conductive to CO2 storage but the overall effect is not obvious. As for the matrix-fracture fluid transfer processes, when the ratio of the matrix permeability to the fracture permeability is small, the fast flow of CO2 through the fracture system without significant storage in the matrix. Obviously, the resistance along the leakage path is decreasing with the decrease of the caprock thickness, which leads to greater leakage between the two aquifers. The derived analytical solutions considering heterogeneity and dual media is practical and helpful for CO2 geo-sequestration site selection and storage risk assessment.

Modeling vadose zone hydrological processes in naturally occurring piezometric depressions: the Chari-Baguirmi region, southeastern of the Lake Chad Basin, Republic of Chad

The Chari-Baguirmi region, southeastern of the Lake Chad (Africa), has a wide naturally occurring piezometric depression with values deeper than the expected regional groundwater level. To date, the most widely accepted hypotheses to explain its origin and dynamics are based on lack of rainwater infiltration and exfiltration processes. The code HYDRUS-1D is applied to numerically simulate the hydrological flow processes along the unsaturated zone in two soil profiles located in the central part and on the boundary of this piezometric depression under bare and vegetated soil coverage. The simulated time period is 2004–2015 with 715 mm annual rainfall average. The computed recharge with respect to total precipitation accounts for 21% on the boundary and 12% in the central part, which is limited by thick silty low permeability layer on the top surface. Considering modelling uncertainty and limitations under the simulated climatic conditions, the rainfall effect is observed only at upper soil layers, which leads to low aquifer recharge, while the upward water flux causing water table evaporation is very low. Past climate conditions, capable of developing a drying front to reach the water table after thousands of years of drying and geological structural constraints, may explain the current depressed area.

The method of non-stationary flooding and the conditions for its effective use in the operation of an oil field

The article describes the essence of unsteady waterflooding, which is one of the most effective methods of increasing the oil recovery factor, used to change the direction of filtration flows, which makes it possible to engage in the development of undeveloped oil reserves and reduce the rate of watering of the deposit in productive reservoirs. A common technological method of unsteady water flooding is the use of cyclic modes of operation of injection wells. The essence of this method is that at an unsteady state in the oil deposit, there are conditions for the continuous manifestation of elastic forces of the reservoir system. In a heterogeneous reservoir between different zones, channels, and fluid flows there are gradients of hydrodynamic pressures, due to which there can be fluid flows from one layer to another, from fractures to blocks, as well as changes in flow directions. During unsteady flooding of heterogeneous formations, a part of oil reserves in low-permeability layers or zones remains uncovered by injected water. The waterflooded reservoir appears as an unsystematic alternation of watered and oil-saturated microflows. While creating in such reservoirs alternately changing in value and direction of pressure gradients, conditions for injection water penetration into stagnant oil-saturated low-permeable zones and channels appear in the oil reservoir and oil movement from them to active drainage zones. As a result of the analysis, the positive effect of the implementation of unsteady waterflooding technology was revealed, and recommendations for improving its application at other operational facilities of oil fields were given.

Performance Evaluation of Bacterial Consortia from Low-Permeability Reservoir in Ordos Basin

The combination of strains of different species and genera may enhance the effects of single bacteria, surpass the tolerance upper limit, and optimize the viscosity reduction and degradation. In this study, six strains were isolated in low permeability layers of the Ordos Basin and were combined to verify the effect of the consortium strains. The selected single strains have good emulsifying and viscosity-reducing effects, but their degradation components are different. SC4561 (Bacillus cereus), SC4551 (Bacillus sp.), and H-1 (Brevibacillus sp.) form consortium A, and SC4534 (2) (Bacillus sp.), SC4542 (Bacillus licheniformis), and A-3 (Bacillus licheniformis) form consortium B. The performance of the mixed strains was evaluated by the analysis of change in emulsification rate, crude oil composition, viscosity, and the tolerance (temperature, salinity, and pH) through GC-MS, rotational rheometer, and other methods. The results showed that the temperature tolerance of the consortium strains was improved by 5-7°C. Consortium B had higher emulsibility ( E 24 was higher than 40% in average) and viscosity degradation (above 35%), and the crude oil in consortium B has almost no wall adhesion. The components of crude oil that consortia use were still diverse, including both long- and short-chain hydrocarbons. However, the proportion of long-chain n-alkanes is further reduced compared with that of single bacteria, and the highest ratio was reduced by 23.81% (B-ALL). At the same time, they also had effects on aromatic hydrocarbons with complex structures (phenanthrene and phenanthrene). This research confirms the enhanced effect of consortium bacteria on single bacteria, facilitating the implementation of microbial enhanced oil recovery technology in the future.

Remediation of multilayer soils contaminated by heavy chlorinated solvents using biopolymer-surfactant mixtures: Two-dimensional flow experiments and simulations.

To assess the efficiency of remediating dense non-aqueous phase liquids (DNAPLs), here heavy chlorinated solvents, through injection of xanthan solutions with or without surfactant (sodium dodecylbenzenesulfonate: SDBS), we conducted a comprehensive investigation involving rheological measurements, column (1D) and two-dimensional (2D) sandbox experiments, as well as numerical simulations on two-layers sand packs. Sand packs with grain sizes of 0.2-0.3mm and 0.4-0.6mm, chosen to represent the low and high permeable soil layers respectively, were selected to be representative of real polluted field. The rheological analysis of xanthan solutions showed that the addition of SDBS to the solution reduced its viscosity due to repulsive electrostatic forces and hydrophobic interactions between the molecules while preserving its shear-thinning behavior. Results of two-phase flow experimentsdepicted that adding SDBS to the polymer solution led to a reduced differential pressure along the soil and improvements of the DNAPL recovery factor of approximately 0.15 and 0.07 in 1D homogeneous and 2D layered systems, respectively. 2D experiments revealed that the displacement of DNAPL in multilayer zones was affected by permeability difference and density contrast in a heterogeneous soil. Simulation of multiphase flow in a multilayered system was performed by incorporating non-Newtonian properties and coupling the continuity equation with generalized Darcy's law. The results of modeling and experiments are very consistent. Numerical simulations showed that for an unconfined soil, the recovery of DNAPL by injection of xanthan solution can be reduced for more than 50%. In a large 2D experimental system, the combination of injecting xanthan with blocking the contaminated zone led to a promising remediation of DNAPL-contaminated layered zones, with a recovery of 0.87.

Seismic Performance of Drained Piles in Layered Soils.

The provision of drains to geotechnical elements subjected to strong ground motion can reduce the magnitude of shaking-induced excess pore pressure and the corresponding loss of soil stiffness and strength. A series of shaking table tests were conducted within layered soil models to investigate the effectiveness of drained piles to reduce the liquefaction hazard in and near pile-improved ground. The effect of the number of drains per pile and the orientation of the drains relative to the direction of shaking were evaluated in consideration of the volume of porewater discharged, the magnitude of excess pore pressure generated, and the amount of de-amplification in the ground's motion. The following main conclusions can be drawn from this study. Single, isolated piles and a group of drained piles were tested in three series of shake table tests. Relative to conventional piles, the drained piles exhibited improved performance with regard to the generation and dissipation of excess pore pressure and stiffness of the surrounding soil, with increases in performance correlated with increases in the discharge capacity of the drained pile. The acceleration time histories observed within the pile-improved soil indicated a coupling of the rate and magnitude of porewater discharge, excess pore pressure generated, and de-amplification of strong ground motion. The amount of de-amplification reduced with increases in the number of drains per pile and corresponding reductions in excess pore pressure. The improved performance should prove helpful in the presence of sloping ground characterized with low-permeability soil layers that inhibit the dissipation of pore pressure and have demonstrated the significant potential for post-shaking slope deformation.

Experimental Study on Enhanced Oil Recovery of Adaptive System after Polymer Flooding.

After polymer flooding in Daqing Oilfield, the heterogeneity of the reservoir is enhanced, leading to the development of the dominant percolation channels, a significant issue with inefficient circulation, a substantial amount of displacement agents, and elevated cost. In order to further improve oil recovery, an adaptive oil displacement system (ASP-PPG) was proposed by combining preformed particle gel (PPG) with an alkali-surfactant-polymer system (ASP). This comprehensive study aims to assess the effectiveness of the adaptive oil displacement system (ASP-PPG) in improving the recovery efficiency of heterogeneous reservoirs after polymer flooding. The evaluation encompasses various critical aspects, including static performance tests, flow experiments, microscopic experiments, profile control experiments, and flooding experiments conducted on a four-layer heterogeneous physical model. The experimental results show that the adaptive system has robust stability, enhanced mobility, effective plugging capability, and profile improvement capability. Notably, the system demonstrates the remarkable ability to successfully pass through the core and effectively block the large pores, resulting in an 18.4% recovery incremental after polymer flooding. This improvement is reflected in the reduced oil saturation values in the ultra-high permeability, high permeability, medium, and low permeability layers, which are 5.09%, 7.01%, 13.81%, and 15.45%, respectively. The adaptive system effectively recovered the remaining oil in the low and medium permeability layers, providing a promising approach for improving the recovery factors under challenging reservoir conditions.

A New Tool for Mapping Water Yield in Cold Alpine Regions

Watershed management requires reliable information about hydrologic ecosystem services (HESs) to support decision-making. In cold alpine regions, the hydrology regime is largely affected by frozen ground and snow cover. However, existing special models of ecosystem services usually ignore cryosphere elements (such as frozen ground and snow cover) when mapping water yield, which limits their application and promotion in cold alpine regions. By considering the effects of frozen ground and snow cover on water yield, a new version of the Seasonal Water Yield model (SWY) in the Integrated Valuation of Ecosystem Services and Trade-offs (InVEST) was presented and applied in the Three-River Headwaters Region (TRHR) in southeastern Qinghai-Tibetan Plateau (QTP). Our study found that incorporating the effects of frozen ground and snow cover improved model performance. Frozen ground acts as a low permeable layer, reducing water infiltration, while snow cover affects water yield through processes of melting and sublimation. Both of these factors can significantly impact the distribution of spatial and temporal quickflow and baseflow. The annual average baseflow and water yield of the TRHR would be overestimated by 13 mm (47.58 × 108 m3/yr) and 14 mm (51.24 × 108 m3/yr), respectively, if the effect of snow cover on them is not considered. Furthermore, if the effect of frozen ground on water yield were not accounted for, there would be an average of 6 mm of quickflow misestimated as baseflow each year. Our study emphasizes that the effects of frozen ground and snow cover on water yield cannot be ignored, particularly over extended temporal horizons and in the context of climate change. It is crucial to consider their impacts on water resources in cold alpine regions when making water-related decisions. Our study widens the application of the SWY and contributes to water-related decision-making in cold alpine regions.

Experimental Investigation of Preformed Particle Gel and Alkali-Surfactant-Polymer Composite System for Enhanced Oil Recovery in Heterogeneous Reservoirs

Abstract Heterogeneity is a significant feature of the reservoirs after polymer flooding, resulting in challenges for further enhanced oil recovery (EOR) in heterogeneous reservoirs. In order to further improve oil recovery in the reservoirs after polymer flooding, a novel EOR system (ASP-PPG composite system) was developed using preformed particle gel (PPG) and alkali-surfactant-polymer system (ASP system). We designed an oil saturation monitoring device and a large-scale 3D heterogeneous physical model to evaluate the performance of the system. The performance of the system and the ASP system were tested. Based on the testing results, the fluid migration patterns and enhanced oil recovery mechanisms of the ASP-PPG system in an actual heterogeneous reservoir were investigated using the oil saturation monitoring device and the 3D physical model. Experimental results indicate that the ASP-PPG system has a higher viscosity and better profile control ability than the ASP system. Additionally, the interfacial tension can be maintained at a low level, around 10−3 mN/m. Flooding experiments using the three-dimensional heterogeneous physical model demonstrated the excellent elastic deformation ability of PPG, which can dynamically block the large pores that formed after the polymer flooding and effectively improve the heterogeneity of reservoirs. After injecting the ASP-PPG system, the recovery factor of the model increased by 15.8%. Specifically, the sweep coefficient of high, medium, and low permeability layers increased by 4.36%, 19.6%, and 37.55%, respectively. Moreover, the oil displacement efficiency increased by 7.4%, 14.4%, and 17.9%, respectively. These results highlight the synergistic effect of combining PPG and ASP systems, significantly enhancing heterogeneous reservoir recovery after polymer flooding.

Mitigation of Gravity Segregation by Foam to Enhance Sweep Efficiency

Foam-assisted gas injection exhibits promising potential for enhancing sweep efficiency through the amelioration of gravity segregation, particularly within reservoirs characterized by heterogeneity. In this work, the implicit-texture (IT) model featuring two flow regimes is employed to examine the impact of heterogeneity on gravity segregation. The validation of the numerical results for water–gas coinjection and pre-generated foam injection is accomplished through a comparative analysis with analytical solutions. A hypothetical two-layer model with varying permeabilities and thickness ratios is used to examine the impact of foam on gravity segregation. The numerical findings demonstrate satisfactory conformity with analytical solutions in homogeneous reservoirs. A high-permeability top layer in a layered model with a fixed injection rate results in sweep efficiency similar to that of a homogeneous reservoir with each individual permeability. A low-permeability top layer could increase the sweep efficiency, but with severe permeability contrast, the bottom high-permeability layer could impact the displacement process, even with a thin thickness. The sweep efficiency increases with the thickness of the high-permeability top layer and decreases with a thicker low-permeability top layer under fixed injection pressure. The predicted segregation length through a single-layer approximation cannot match the results of the layered models where the permeability contrast is too great or the thickness of two layers is comparable.

Nitrate Migration and Transformation in Low Permeability Sediments: Laboratory Experiments and Modeling

The excessive application of fertilizers and the uncontrolled discharge of untreated wastewater on land contribute to the nitrogen pollution of groundwater. Low permeability sediment plays an important role in slowing down the migration of nitrate in groundwater systems. This study focuses on the mechanisms that affect nitrate transport in the low permeability layer. A soil column experiment was conducted and an MT3D transport model (a modular three-dimensional multispecies transport model) of nitrate was proposed. The results show that a low permeation layer could act as a strong barrier to nitrate migration and transportation, as demonstrated by the column soil experiment. The denitrification rates were controlled by many other factors, including nitrate concentration, flow rate, pH values and sediment particle characteristics. This indicated that denitrification is the most important factor in the attenuation of nitrate in low permeability sediments. This study clarified the law of migration and transformation of nitrate in low permeability soils and the factors that influence these processes. The results not only provide a basis for large-scale nitrate simulations, but also provide a reference for nitrate treatment in low permeability layers.

New insights into pore fractal dimension from mercury injection capillary pressure in tight sandstone

Mercury injection capillary pressure (MICP) has been widely used for pore fractal dimension determination and thus leads to a variety of calculation models with different results. Here, taking the tight sandstone gas reservoir of Shaximiao Formation in Jinhua-Zhongtaishan area, central Sichuan Basin as the object, the theory, method and application of pore fractal dimension determination from MICP are explored. Based on Yu-Xia model and Washburn equation, rigorous analytical expressions on fractal dimension, capillary pressure and mercury saturation are deduced. After pre-processing including validation, consistency correction and shape-preserving interpolation, the fractal turning point is located with the local maximum of the front-back moving variance ratio of mercury saturation, and then the global, macropore and micropore fractal dimensions are determined respectively by nonlinear fitting. As suggested by the data processing results of the 39 MICP samples, there is no significant direct correlation between pore fractal dimensions and petrophysical properties represented by permeability. However, the combination of fractal model related parameters, especially global fractal dimension and entry pressure, can identify effectively reservoir quality ranks. Meanwhile, for gas layers with relatively high permeability, larger global fractal dimensions may imply roughly more favorable pore structure and better reservoir quality, while the total quality of the relatively low-permeability gas layers is poor and nearly independent of the fractal dimensions. The representative MICP-based pore fractal models, He-Hua and Shen-Li, are critically reviewed. The theoretical simplification and calculative approximate of these two models lead to some degree of error in pore fractal dimension determination, despite their slight correlation in the fitting results with those of the present model. This study may improve the understanding of the pore fractal dimension determined from MICP and provide reference for pore structure evaluation, reservoir quality classification and capillary pressure modeling.

N2 Foam Flooding Combined with Gel Plugging for Enhanced Oil Recovery in High-Temperature Reservoirs: Laboratory Experiments and Numerical Simulations.

The high-temperature reservoir (105 °C) in the Liubei block of Jidong Oilfield, with severe longitudinal heterogeneity, has entered a high water-cut stage. After a preliminary profile control, the water management of the oilfield still faces serious water channeling problems. To strengthen water management, N2 foam flooding combined with gel plugging for enhanced oil recovery was studied. In this work, considering a high-temperature reservoir of 105 °C, a composite foam system and starch graft gel system with high temperature resistance were screened out, and displacement experiments in one-dimensional heterogeneous cores were carried out. Through the three-dimensional experimental model and numerical model of a 5-spot well pattern, physical experiments and numerical simulations were carried out respectively to study water control and oil increase. The experimental results showed that the foam composite system had good temperature resistance up to 140 °C and oil resistance up to 50% oil saturation and was helpful to adjust the heterogeneous profile in a high temperature of 105 °C. The starch graft gel system had good injection performance, with a solution viscosity of 18.15 mPa·s, and its gel strength could effectively seal the high-permeability layer, with a gel viscosity of 34950.92 mPa·s. The displacement test results showed that after a preliminary implementation of N2 foam flooding, N2 foam flooding combined with gel plugging could still improve oil recovery by 5.26%. Compared with preliminary N2 foam flooding, gel plugging could control the water channeling in the high-permeability zone near the production wells. The combination of foam and gel made N2 foam flooding and subsequent waterflooding divert to flow mainly along the low-permeability layer, which was conducive to enhance water management and improve oil recovery. This method can be used as an effective technology to manage similar heterogeneous reservoirs.

Optimization of Soil-Sludge Mixtures by Compaction for Potential Use in Mine Site Reclamation

Studies have indicated the potential of mixtures of silty soil and sludge produced by active treatment of acid mine drainage for use in covers with capillary barrier effects for mine site reclamation. Very high water contents of sludge in the settling pond could negatively affect the required hydrogeotechnical properties of soil sludge mixtures with high sludge contents. The challenge is then to determine the optimum wet sludge content of soil-sludge mixtures with air entry values (AEV) and/or saturated hydraulic conductivity (ksat) required for use in mine site reclamation covers. This paper presents a method to determine the optimum wet sludge content βopt for obtaining the maximum dry density of compacted soil-sludge mixtures. Two types of soil (S1 and S2) and two types of sludge (A and W) were tested. It was observed that βopt can be determined when the initial water content of the soil used in the mixture is lower than the optimum water content determined from the Proctor curve of the soil alone (10 wt% and 6 wt% for soils S1 and S2, respectively) and that βopt does not change with increasing initial soil water content. Optimum wet sludge contents found were low (≈15 wt% and ≈7 wt% for mixtures containing soils S1 and S2, respectively) for the test conditions, indicting a limited quantity of reusable sludge in the mixtures. For all mixtures, the water content corresponding to βopt was close to the optimum water content of the soil alone. Results of soil water retention and saturated hydraulic conductivity (ksat) tests conducted on selected optimized mixtures indicated that the mixtures based on soils S1 and S2 have air entry values higher than 20 kPa and would be suitable for use in the moisture retention layer of covers with capillary barrier effects, while soil S2 and the derived mixtures exhibited ksat < 10−7 cm/s and would be potential materials for the low permeability layer in low saturated hydraulic conductivity covers.

Experimental Study on Enhanced Oil Recovery of PPG/ASP Heterogeneous System after Polymer Flooding

Following the application of polymer flooding in Daqing Oilfield, the heterogeneity between different layers has intensified, resulting in the formation of more favorable seepage channels and cross-flow of displacement fluids. Consequently, the circulation efficiency has decreased, necessitating the exploration of methods to enhance oil recovery. This paper focuses on experimental research utilizing a newly developed precrosslinked particle gel (PPG) combined with alkali surfactant polymer (ASP) to create a heterogeneous composite system. This study aims to improve the efficiency of heterogeneous system flooding after polymer flooding. The addition of PPG particles enhances the viscoelasticity of the ASP system, reduces the interfacial tension between the heterogeneous system and crude oil, and provides excellent stability. The heterogeneous system has high resistance and residual resistance coefficients during the migration process in a long core model, achieving an improvement rate of up to 90.1% under the permeability ratio of 9 between high and low permeability layers. Employing heterogeneous system flooding after polymer flooding can increase oil recovery by 14.6%. Furthermore, the oil recovery rate of low permeability layers can reach 28.6%. The experimental results confirm that the application of PPG/ASP heterogeneous flooding after polymer flooding can effectively plug high-flow seepage channels and improve oil washing efficiency. These findings hold significant implications for further reservoir development after polymer flooding.

Release of metal elements from clays during elution with EDTA: Insights into the side effects of washing contaminated sites

Ethylenediaminetetraacetic acid (EDTA) is frequently used to wash heavy metal contaminated fields, especially low-permeability zones which are rich in clays and have strong adsorption. However, the release kinetics of cations from clayey sediments during EDTA elution and the potential mechanisms controlling the cation release remain open questions. This study implemented heavy metal invasion and EDTA flushing experiments in a sandbox with clay-containing low-permeability layers, and batch kinetic experiments of cation release from clays in the presence of EDTA. Relatively small amounts of interlayer cations (i.e., Ca, Na, and K) and almost no structural cations (i.e., Al, Mg, Fe) were released due to ion exchange during the invasion of heavy metals. EDTA elution greatly enhanced the release of cations from clays; more interlayer cations were brought out via the complexation, and structural cations were released from clays because metal‑oxygen bonds in octahedral sheets were broken by EDTA. The first-order release rate constants of structural cations were around 0.008 min−1 and almost one order of magnitude smaller than those of interlayer cations (around 0.05 min−1), that is, mineral dissolution was slower. Additionally, when EDTA was injected into groundwater systems together with heavy metals from pollutant source zones, EDTA was mostly chelated with heavy metals and few cations were released from sediments. By adjusting the timing of EDTA injection, the complexation between EDTA and heavy metals became preferred, and little free EDTA remained and affected clays. This provides new insights into the side effects of washing heavy metal contaminated sites with chelating agents.

Magnetotelluric imaging of the magmatic and geothermal systems beneath Mount Meager, southwestern Canada

Magnetotelluric data were collected on and around the Mount Meager volcanic complex, an active volcanic complex with eruptions ∼2400 and ∼24 300 years ago. Three-dimensional inversion was used to create an electrical resistivity model to a depth of >20 km. The model is characterized by high resistivity (>100 Ωm) in the upper 6–7 km, implying relatively dry, unaltered rock. Within this resistive layer, localized conductors are observed in the upper 2 km beneath Pylon Peak and Fish Creek, corresponding to low-permeability, clay-rich layers, acting as caprocks to geothermal fluids below. Beneath the resistive upper crust, there is a large conductor at ∼5–15 km below sea level with an average resistivity of ∼3 Ωm. Laboratory experiments of melt resistivity and petrological data from erupted volcanic rocks were used to interpret the model. The magma body (deep conductor) is inferred to have a minimum volume of ∼2 × 1012 m3 comprising ∼18–32% dacitic-to-trachydacitic melt with ∼6–8 wt.% H2O at a temperature of ∼800–900 °C. This is below the melt fraction of an eruptible magma body. Resolution tests suggest it might be regional in extent, not localized beneath Mount Meager. There are fluid pathways from the northern part of the magma body, up toward Mount Meager and nearby fumaroles. This model is a significant advancement from its predecessors, created 20–40 years ago, providing the first deep 3D image of this volcanic system. Along with other geophysical and geological models of the Garibaldi Geothermal Energy Project, it will reduce the exploration risk associated with geothermal energy development.