Low-permeability Layers Research Articles

Evaluation and Application of Fractal-Based Hydraulic Constitutive Model for Unsaturated Flow in Heterogeneous Soils

The physical-based hydraulic constitutive model developed by fractal theory has received much attention, however, its performance in two-phase flows has not been fully evaluated. This study evaluates the ability of fractal-based hydraulic constitutive models to describe the two-phase flow combining mass and momentum conservation equations. After that, we investigate the injection and displacement characteristics of the amendment at NAPL (non-aqueous phase liquids)-contaminated low-permeability sites based on this fractal model. Points of interest are the effect of the location of hydraulic fracturing in layered soils on amendment injection and distribution and the corresponding key parameters. Comparison with experimental results reveals that the fractal model describes the two-phase flow behavior very well. Fractal dimension and intrinsic permeability of soils have significant effects on the two-phase flow. For layered soils, the lower part of the low-permeability layer is preferably recommended as the main fracturing and injection zone to obtain the optimal injection efficiency. Besides, due to the lower flow resistance, hydraulic fractures across layers can be treated as fractures in highly permeable layers. This work provides new insights into the application of fractal theory in describing two-phase flows.

Improved oil recovery in sandstone reservoirs with deep profile control technology: A comparative study between modified starch gel and polymer gel

Deep profile control technology was implemented to alleviate the issue of oil recovery in sandstone reservoirs caused by varying permeability. Rheological tests, injection and plugging capacity experiments, core flooding experiments combined with Computed Tomography (CT) analysis were performed to study the mechanisms of profile control, oil displacement, rheology, and plugging properties of modified starch gel and polymer gel. Moreover, a comparison was made regarding the oil recovery, sweep efficiency, and displacement efficiency for both the starch gel and polymer gel. The results show that the ease of injection and plugging properties of the modified starch gel are superior to those of the viscoelastic polymer gel. The visual and quantitative distribution profiles and migration characteristics of water, oil, and gels are characterized. During the gel flooding stage, the modified starch gel maintained a rigid shape compared to the lax behavior observed with polymer gel. During the subsequent water flooding stage, the modified starch gel became immobile. It plugged the high permeability layer of the core plug, increasing the sweep efficiency of the low permeability layer by 60.00%. The sweep efficiency of the low permeability layer increased by 37.26% as the polymer gel continued to flow through the core plug. In addition, the high permeability layer is easily swept clean, so enhancing the displacement efficiency is the key to maximizing recovery. The displacement and relatively easy sweep efficiencies must be improved simultaneously to maximize the recovery in the low permeability layer. The study's findings shed light on the significance of modified starch gel in enhancing oil recovery in sandstone reservoirs with varying permeability.

Optimization of Gel Flooding during the High Water Cut Stage in a Conglomerate Reservoir of the Xinjiang A Oilfield.

Influenced by water injection, a dominant flow channel is easily formed in the high water cut stage of a conglomerate reservoir, resulting in the inefficient or ineffective circulation of the injected water. With gel flooding as one of the effective development methods to solve the above problems, its parameter optimization determines its final development effect, which still faces great challenges. A new optimization method for gel flooding is proposed in this paper. Firstly, the gel flooding parameters were obtained through physical experiments; then, an experimental model of gel flooding was established according to the target reservoir, and parameter sensitivity analysis was carried out. Next, a history matching of the gel flooding experiment was carried out. Finally, history matching of the target reservoir was also carried out, and a gel flooding scheme was designed and optimized to determine the best parameters. The experimental results showed that the gelation time was 4 h and the gel viscosity was 6332 mPa·s; the breakthrough pressure, resistance factor (RF), and residual resistance factor (RRF) all decreased with the increase in permeability. The gel had a good profile control ability and improved oil recovery by 16.40%. The numerical simulation results illustrated that the porosity of the high permeability layer (HPL) had the greatest impact on the cumulative oil production (COP) of the HPL, and the maximum polymer adsorption value of the HPL had the largest influence on the COP of the low permeability layer (LPL) and the water cut of both layers. Benefiting from parameter sensitivity analysis, history matching of the gel flooding experiment and a conglomerate reservoir in the Xinjiang A Oilfield with less time consumed and good quality was obtained. The optimization results of gel flooding during the high water cut stage in a conglomerate reservoir of the Xinjiang A Oilfield were as follows: the gel injection volume, injection rate, and polymer concentration were 2000 m3, 50 m3/d, and 2500 mg/L, respectively. It was predicted that the water cut would decrease by 6.90% and the oil recovery would increase by 2.44% in two years. This paper not only provides a more scientific and efficient optimization method for gel flooding in conglomerate reservoirs but also has important significance for improving the oil recovery of conglomerate reservoirs.

Preparation and Performance Evaluation of a Temperature and Salt Resistant Hydrophobic Associative Weak Polymer Gel System.

We targeted high-temperature and highly saline old oil fields, whose environmental conditions could be attributed to the significantly high heterogeneity cause by long-term water flooding. The Huabei Oilfield was chosen as the research object. We developed a hydrophobic functional monomer-polymer with temperature and salt resistance by introducing the temperature-resistant and salt-resistant monomer NVP and a hydrophobic functional monomer into the main chain for copolymerization. We used a crosslinking agent with phenolic resin to prepare a weak gel system that showed temperature and salt resistance and investigated its temperature and salt resistance, infective property, plugging performance, liquid flow ability, micropore throat migration, and plugging characteristics. The results obtained using the infrared spectroscopy technique revealed the successful preparation of the phenolic resin crosslinker. The weak gel exhibited good temperature and salt resistance when the polymer concentration was 2000 mg/L, the cohesion ratio was 1:1.5, the additive concentration was 2000 mg/L, the reservoir temperature was 120 °C, and the injected water salinity was 40,300.86 mg/L. The average viscosity retention rate of the 90-day weak gel reached more than 80% and its microstructure was examined. The coreflow experiment results revealed that the weak gel system was characterized by good infectivity. After plugging the weak gel, the effect on the direction of the liquid flow was evident and the flow rate of the low permeability layer increased to a maximum of 48.63% under conditions of varying permeability levels. A significant improvement in the water absorption profile was achieved. The plugging was carried out through a sand-filling pipe under varying permeability conditions and the pressure measuring points in the sand-filling pipe were sucessfully pressurized. The migration ability of the weak gel was good and the blocking rate was >85%.

Study on the Oil Displacement Mechanism of Different SP Binary Flooding Schemes for a Conglomerate Reservoir Based on a Microfluidic Model

The objective of this study is to elucidate the oil displacement mechanism of different surfactant- polymer (SP) binary flooding systems in conglomerate reservoirs and to determine the optimal scheme. On the basis of water flooding, the microfluidic model is used to reveal the oil–water flow law of different SP binary flooding systems and then determine the oil displacement mechanism. The experimental results show that the SP binary flooding solution can enhance oil recovery by enhancing the sweep volume; the oil displacement efficiency of the echelon viscosity reducing (EVR) scheme is better than that of the echelon viscosity increasing (EVI) scheme and the single constant viscosity (SCV) scheme. For the EVR scheme, the oil displacement system with a high molecular weight and high concentration preferentially enters the large-scale pore-throat of the reservoir. After a period of time, a high resistance area can be formed in the large-scale pore-throat along the main flow direction of water flooding so as to reduce the mobility of the displacement solution in the dominant seepage channel and decrease the frequency of water channeling and then improve the oil displacement efficiency in the large-scale pore-throat to enhance the oil recovery. When the molecular weight and viscosity of the SP binary solution are both reduced, the oil displacement solution with a low molecular weight and low concentration mainly produces low-permeability layers by adjusting the displacement path to enhance the sweep volume in the small-scale pore-throat. Through the reconstruction of a pressure field and the redistribution of seepage paths of chemical micelles with different sizes, the displacement mechanism of crude oil in pores and throats shows a changing trend from large-scale pore-throats to small-scale pore-throats. After the viscosity reduction of the SP solution, the lower production limit of the pore-throat radius is reduced to 1 μm and the sweep volume of the small-scale pore-throat is enhanced. The stepwise production of crude oil in pores and throats with different radii is realized so as to enhance the oil recovery of the conglomerate reservoir. Finally, a new model of SP binary flooding suitable for “echelon injection and stepwise production” of a conglomerate reservoir is established innovatively.

Effect of low-permeability layers on vadose well recharge rates

Recharge in unconfined aquifers during Managed Aquifer Recharge (MAR) is influenced by the lithologic characteristics of the vadose zone. The capacity of vadose wells to achieve recharge rates above those possible with recharge basins is studied in heterogeneous unsaturated porous media. Although near-surface low permeability layers can be bypassed with vadose wells, subsequent low permeability layers below or adjacent to the well screen influence recharge rates by forming perched conditions. The numerical model VS2DTI was used to evaluate the effect of heterogeneous lithology on vadose well recharge. A sand aquifer was modeled using hydrogeologic characteristics from the Hueco-Bolson aquifer in Texas. Modeled recharge was studied for a 33 m deep vadose well with a 10 m high water column evaluated under conditions of both a homogenous aquifer and an aquifer with heterogeneity formed by a thin, low permeability clay layer. These low permeability layers were modeled at various depths alongside and below the well to study the impact of heterogeneity on MAR processes. Results contrast vadose wells a) without clay layers to recharge 200.6 m3/d, considered the well's maximum (100%) efficiency, and b) inclusion of clay layers creating perched conditions which are shown to reduce recharge. Specifically, recharge rates greater than 180 m3/d (90% efficiency) occur if the clay layer was aligned at or above the upper half of the well screen. Simulating the low permeability clay layer along the bottom half of the well caused recharge rates reduction to a minimum of 30 m3/d (15% efficiency). Rates above 100 m3/d (50% efficiency) occurred when the clay layer was 10 m below the base of the well. These results characterize the impact of low permeability layer distance adjacent to and below a vadose well. A low permeability horizon at a fixed depth relative to vadose wells at variable depths was also studied to demonstrate that recharge rate increases corresponding to deeper vadose wells due to additional screen length and greater pressure head. Results quantify the impact of vadose well placement relative to low permeability layer depth, and promote understanding to achieve design recharge rates using the fewest and shallowest wells possible.

Water Invasion Into Multi-Layer and Multi-Pressure Carbonate Reservoir: A Pore-Scale Simulation

AbstractCarbonate reservoirs contribute the highest proportion of natural gas production around the world, and commingled production is frequently used to increase production for the multi-layer reservoirs. However, the complex pore structure including pore, fracture, and cavity, and the presence of edge/bottom water increase the difficulties in evaluating its commingled-production performances. In this work, three comingled patterns of digital rocks are reconstructed based on the computerized tomography scanning images, and the lattice Boltzmann method is used to investigate the commingled production with water invasion. The results show that the fracture and cavity commingled production pattern has the largest interlayer heterogeneity, and the production ratio between the two layers can reach 6.7. Commingled production for the system with different interlayer pressure may lead to backflow phenomenon, which is not only dependent on the initial pressure, but also related to the heterogeneity between the producing layers. Especially, if the interlayer heterogeneity is large and the initial pressure of the low-permeability layer is lower, the backflow volume would be very large. The water invasion during commingled production can influence the flow capacity of the other gas layers even there is no pressure interference. In addition, if the water layer has larger pressure, the produced water will continuously flow back to the gas layer until the pressure of the two layers becomes balanced. The coupled effects of pressure interference and water invasion significantly damage the commingled-production performance. This work can help for better understanding of the gas-water two-phase flow behaviors during commingled production, which provides fundamental support for the scientific development of multi-layer carbonated reservoirs.

Study on Micro-Displacement Mechanism and Reservoir Compatibility of Soft Dispersed Microgel.

Polymer flooding is a key technology for improving reservoir heterogeneity around the world, and it has made great progress. However, the traditional polymer has many shortcomings in the theory and application, which causes the efficiency of polymer flooding to gradually decrease and secondary reservoir damage after a long period of polymer flooding. In this work, a novel polymer particle (soft dispersed microgel, SMG) is used as the research object to further investigate the displacement mechanism and reservoir compatibility of SMG. The visualization experiments of the micro-model prove that SMG has excellent flexibility and can be highly deformable to realize deep migration through the pore throat smaller than SMG itself. The visualization displacement experiments of the plane model further show that SMG has a plugging effect, which makes the displacing fluid flow into the middle and low permeability layers, improving the recovery of these layers. The compatibility tests show that the optimal permeability of the reservoir for SMG-μm is 250-2000 mD, and the corresponding matching coefficient range is 0.65-1.40. For SMG-mm-, its corresponding optimal permeabilities of reservoir and matching coefficient are 500-2500 mD and 1.17-2.07, respectively. The comprehensive analysis demonstrates that the SMG has excellent ability of the water-flooding swept control and compatibility with reservoirs, having the potential to solve the problem of traditional polymer flooding.

Long- and short-term dynamic stability of submarine slopes undergoing hydrate dissociation

Natural gas hydrates (NGHs) have recently been recognized as a promising source of relatively clean alternative energy and a significant factor in triggering marine geohazards. This paper presents a numerical method for calculating the transient excess pore pressure associated with hydrate dissociation in submarine sediments with THC (Thermo-Hydro-Chemical) coupling. Then, the dynamic stability of submarine slopes experiencing gas hydrate dissociation is evaluated based on limit equilibrium analysis considering the real evolution of excess pore pressure. Finally, this work is applied to investigate the dynamic responses of typical hydrate slopes in the Shenhu Sea area, South China Sea (SCS), under two different timescales: 1) Case I: gradual temperature increases at the seafloor due to climate warming and 2) Case II: sharp temperature increases in the interior of the hydrate deposit due to hydrate extraction. In Case Ⅰ, the timescale of hydrate dissociation is millennial. Due to the long-term temperature rise, the hydrate will dissociate slowly, which allows the generated free gas to migrate upwards and gradually accumulate at the transition zone between a porous layer and an overlying low-permeability layer. Eventually, the slow accumulation of free gas may lead to disc-shaped failure of the hydrate-bearing slope. In contrast, in Case Ⅱ, the temperature rises sharply over a short period of time, which leads to the drastic dissociation of the hydrate. The timescale of hydrate dissociation is decadal. As a result, the excess pore pressure accumulates rapidly. Under the influence of excess pore pressure, the sediment will deform dramatically, which may cause a penetration failure of the hydrate-bearing slope. These findings are relevant to the long-term (millennial) safety of human beings and short-term (decadal) utilization of energy resources.

Geology and vegetation control landsliding on forest-managed slopes in scarplands

Abstract. Landslides are important agents of sediment transport, cause hazards and are key agents for the evolution of scarplands. Scarplands are characterized by high-strength layers overlying low-inclined landslide-susceptible layers that precondition and prepare landsliding on geological timescales. These landslides can be reactivated, and their role in past hillslope evolution affected geomorphometry and material properties that set the framework for present-day shallow landslide activity. To manage present-day landslide hazards in scarplands, a combined assessment of deep-seated and shallow landsliding is required to quantify the interaction between geological conditions and vegetation that controls landslide activity. For this purpose, we investigated three hillslopes affected by landsliding in the Franconian scarplands. We used geomorphic mapping to identify landforms indicating landslide activity, electrical resistivity to identify shear plane location and a mechanical stability model to assess the stability of deep-seated landslides. Furthermore, we mapped tree distribution and quantified root area ratio and root tensile strength to assess the influence of vegetation on shallow landsliding. Our results show that deep-seated landslides incorporate rotational and translational movement and suggest that sliding occurs along a geologic boundary between permeable Rhätolias sandstone and impermeable Feuerletten clays. Despite low hillslope angles, landslides could be reactivated when high pore pressures develop along low-permeability layers. In contrast, shallow landsliding is controlled by vegetation. Our results show that rooted area is more important than species-dependent root tensile strength and basal root cohesion is limited to the upper 0.5 m of the surface due to geologically controlled unfavourable soil conditions. Due to low slope inclination, root cohesion can stabilize landslide toes or slopes undercut by forest roads, independent of potential soil cohesion, when tree density is sufficient dense to provide lateral root cohesion. In summary, geology preconditions and prepares deep-seated landslides in scarplands, which sets the framework of vegetation-controlled shallow landslide activity.

Visualized Study on a New Preformed Particle Gels (PPG) + Polymer System to Enhance Oil Recovery by Oil Saturation Monitoring Online Flooding Experiment

After tertiary recovery from the oilfields, improving the production of the remaining hydrocarbon is always challenging. To significantly improve oil recovery, a heterogeneous composite flooding system has been developed with preformed particle gels (PPG) and polymers according to the technical approach of plugging and flooding combination. In addition, an oil saturation monitoring device and a large-scale 3D physical model were designed to better evaluate the performance of the technique. The evaluation results show that the viscosity, stability, and elasticity of the heterogeneous composite flooding system are better than the single polymer system. In addition, both systems exhibit pseudoplastic fluid characteristics and follow the principle of shear thinning. The results of seepage experiments showed that PPG migrates alternately in porous media in the manner of "piling plugging-pressure increasing-deformation migration". The heterogeneous composite system can migrate to the depths of the oil layer, which improves the injection profile. In the visualization experiment, the heterogeneous composite system preferentially flowed into the high-permeability layer, which increased the seepage resistance and forced the subsequent fluid to flow into the medium and low permeability layers. The average saturation of the high, medium, and low permeability layers decreased by 4.74%, 9.51%, and 17.12%, respectively, and the recovery factor was further improved by 13.56% after the polymer flooding.

Estimating drainable gas reserves by the method of material balance

The algorithm of estimating the reserves of gas deposits by the material balance method is described. The advantages of this method are the use of rather precise field technological information for calculations and the possibility of regular checks for compliance with the actual nature of field development. However, there are problems of practical application of this method. One of them is the determination of average weighted pressure for the whole gas-saturated volume, especially for low permeable reservoirs with deep depression craters around wells. The process of correct determination of weighted average pressure by means of isobar map and map of effective gassaturated thicknesses of gas reservoirs is proposed and described. Another problem is the long time interval between measurements of reservoir pressure during the field development. We offer the method that allows increasing frequency of isobar mapping by interpolation of reservoir pressure values by calculating this value through the productivity of wells in order to perform operational analysis of the field development. The input data for the calculation are the dynamics of gas flow rate and wellhead pressure dynamics. This approach allows us to estimate formation pressure around each well outside the de-resistivity funnel at any time. The article presents the results of testing the proposed method under field conditions at one of the Yamal fields. The results of the analysis show the difference in the volume of drained reserves with the geological model for a low permeable layer. The difference in the reserves volume estimation by the material balance method using the isobar map was 18 % of the initial geological reserves. The analysis of the reasons of divergence of the drilled reserves was carried out and the fact of differently sorted excavation along the section and the presence of uninvolved reserves was revealed.

Phreatic seepage around a rectilinear cutoff wall: The Zhukovsky-Vedernikov-Polubarinova-Kochina dispute revisited

The problem of steady 2-D potential Darcian flow from a flat-bottomed reservoir of a coffer or other type of dam, separated from an empty tailwater by an impermeable vertical sheet piling, is one of the pillars in groundwater hydrology and soil mechanics. Analytical solutions to this problem are presented in the books by Forchheimer, Zhukovsky, Vedernikov, Polubarinova-Kochina, Harr, among others. For the case of seepage with a phreatic line, descending from the downstream face of the cutoff, the formulae presented in classical textbooks - despite the simplicity of conformal mappings of the complex potential quarter-plane onto the Zhukovsky half-strip - have lacunae and flaws. We discuss and clean the mismatch in the abovementioned formulae. The classical analytical solutions in the textbooks deal with the regime of no backwater, for which the magnitude of the specific discharge vector at infinity coincides with hydraulic conductivity of the soil. We obtain a general solution for most general flows with backwater, for which the specific discharge at infinity is zero and the free surface has an inflection point in the physical plane. The capillary fringe in the hodograph domain is imaged by a circular cut. The pressure head infinitely deep under the cutoff-wall is infinite. A circular tetragon in the hodograph domain is conformally mapped onto the quadrant in the complex potential plane via a reference plane. In the case with backwater, one extra condition is needed to fix a mathematical solution. For this purpose, the location of a point on the free surface is fixed. Mathematically, two affixes in the reference plane are found by solving a system of two nonlinear equations (in the no backwater case, only one affix is found and one equation is solved). We also examine flow with a phreatic line in a low-permeable layer (e.g. concrete apron of a dam) with an Λ-shaped topology of streamlines, bounded from the left by a cutoff. Seepage from a dam reservoir through a subjacent highly-permeable alluvium induces the pore water motion in the upper layer. A Hilbert boundary-value problem is solved for the complex potential in this cell. In the Kirkham-Brock type boundary condition along the interface between the two layers, the horizontal component of the specific discharge is constant. Phreatic surfaces rising on the downstream face of the cutoff caps Λ−shaped streamlines, which turn around a hinge point on the interface between two layers of contrasting permeability.

Combined Well Multi-Parameter Logs and Low-Flow Purging Data for Soil Permeability Assessment and Related Effects on Groundwater Sampling

Cost-effective remediation is increasingly dependent on high-resolution site characterization (HRSC), which is supposed to be necessary prior to interventions. This paper aims to evaluate the use of low-flow purging and sampling water level data in estimating the horizontal hydraulic conductivity of soils. In a new quali-quantitative view, this procedure can provide much more information and knowledge about the site, reducing time and costs. In case of high heterogeneity along the well screen, the whole procedure, as well as the estimation method, could be less effective and rigorous, with related issues in the purging time. The result showed significant permeability weighted sampling, which could provide different results as the pump position changes along the well screen. The proposed study confirms this phenomenon with field data, demonstrating that the use of multiparameter well logs might be helpful in detecting the behaviour of low-permeability layers and their effects on purging and sampling. A lower correlation between low-flow permeability estimations and LeFranc test results was associated with high heterogeneity along the screen, with a longer purging time. In wells P43, MW08 and MW36, due to the presence of clay layers, results obtained differ for almost one order of magnitude and the purging time increases (by more than 16 min). However, with some precautions prior to the field work, the low-flow purging and sampling procedure could become more representative in a shorter time and provide important hydrogeological parameters such as hydraulic conductivity with many tests and high-resolution related results.

Numerical Simulation of Vacuum Preloading for Chemically Conditioned Municipal Sludge

Municipal sludge is a sedimentation waste produced during the wastewater process in sewage treatment plants. Among recent studies, pilot and field tests showed that chemical conditioning combined with vacuum preloading can effectively treat municipal sludge. To further understand the drainage and consolidation characteristics of the conditioning sludge during vacuum preloading, a large deformation nonlinear numerical simulation model based on the equal strain condition was developed to simulate and analyze the pilot and field tests, whereas the simulation results were not satisfactory. The results of the numerical analysis of the pilot test showed that the predicted consolidation degree was greater than that measured by the field tests, which is attributed to the relatively low permeability layer formed during the preloading process of the prefabricated vertical drain. To better reflect the consolidation process of the conditioned sludge, a simplified analysis method considering the low permeability layer around the prefabricated vertical drain was proposed. The initial permeability coefficient of the low permeability layer is determined via numerical simulations using finite difference method. The predicted settlement curve was in good agreement with the measured results, which indicated that the numerical simulation based on the equal strain condition considering the relatively low permeability layer can better analyze the consolidation process of ferric chloride-conditioning sludge with vacuum preloading.

Field Testing of Geomorphic Landform Design Features in Central Appalachia

Reclamation Highlights: We assessed construction methods for the application of geomorphic landforming and the use of paper mill sludge as a soil amendment for coarse coal refuse. The cap and cover system included a growth layer and low-permeability layer over coarse refuse. Coarse coal refuse and paper mill sludge blend can sustain vegetation.

Residual oil start-up mechanism of polymer/surface dual flooding after polymer flooding in medium-high permeability reservoir

The remaining oil distribution and displacement mechanism of poly/surface dual flooding stage in medium and high permeability reservoir are not clear. In this paper, the reservoir conditions in Gangxi Area 3 of Dagang Oilfield were taken as the research object. Based on nuclear magnetic resonance and large model physical simulation experiment, the characterization of micro and macro residual oil start-up mechanism and enhanced oil recovery experiment were carried out respectively after polymer flooding poly/surface binary flooding. The experimental results suggest that polymer-surfactant flooding could increase the oil displacement efficiency by 12-29% after polymer flooding, and the contribution of porous to recovery degree is in the order of medium pore, large pore, and small pore. When the surfactant concentration is higher than 0.25%, the increase of oil displacement efficiency tends to be stable, and further enhancing oil recovery requires the expansion of sweep volume. Physical model experiments results show that medium permeability layer has the highest contribution to the recovery degree in the chemical flooding stage, and the displacement mechanism is mainly based on the synergistic effect of expanding sweep volume and improving displacement efficiency. The contribution of low permeability layer to recovery degree is next, and the displacement mechanism is mainly to expand sweep volume. The high permeability layer has the lowest contribution to the recovery degree, and the oil displacement mechanism is mainly to improve the oil displacement efficiency.

A PRODUCTION SPLITTING MODEL OF HETEROGENEOUS MULTI-LAYERED RESERVOIRS WITH COMMINGLED PRODUCTION

Production splitting is the basis for a proper understanding of the development effect of reservoirs when multiple layers are commingled to produce, and it is a difficult part of the development evaluation of this type of reservoir. Reservoirs with multiple layers are usually developed through commingled production. However, due to interlayer interference, the total output of commingled production is lower than the sum of individual production of each subordinate layer. It's significant to clarify the interlayer interference mechanism during layers with commingled production, establish an accurate splitting model of the production from subordinate layers, split the commingled production into each subordinate layer, and effectively understand the production level and remaining potential of the subordinate layers during commingled production. It is expected to develop a theoretical basis for the rational and effective development of multi-layered commingled production reservoirs. In this paper, a combination of multi-tube parallel displacement experiments and numerical simulations of a multi-layered reservoir with commingled production is used to analyze the influence of factors such as permeability ratio, production pressure difference, and crude oil viscosity on the interlayer interference mechanism. According to the research results, the interference coefficient is firstly introduced on the basis of the theoretical production formula of seepage flow. The change rate of the oil production splitting coefficient at the stage when the water cut is more than 80% is also proposed, and the production splitting model of subordinate layers in heterogeneous reservoirs is established, considering multiple factors. Taking multi-layered Reservoir A with commingled production as an example, this model is used to split the production of commingled wells. Results show that interlayer interference can be reduced by decreasing the permeability ratio and high permeability laminar fluidity, and increasing the production pressure difference. When the water content is greater than 80%, the oil production segmentation coefficient of the layers with high permeability decreases sharply with the increase of the water content. For the low-permeable layer, the situation is just the opposite. At the same time, based on the study of the interlayer interference mechanism coupled with the oil well radial flow production formula, the interference coefficient and the oil production segmentation coefficient change ratio are introduced. The findings of this study can help develop a more accurate model for production of subordinate layers in heterogeneous multi-layered reservoirs. The established splitting model is carried out using the data from two wells and four subordinate layers in Reservoir A, indicating that the accuracy of the proposed model is close to 90%.

Controlling metal ion migration in contaminated groundwater with Iraqi clay barriers for water resource protection.

This study investigates the effectiveness of using Iraqi clay as a low-permeability layer to prevent the migration of lead and nickel ions in groundwater-aquifers. Tests of batch operation have been conducted to determine the optimal conditions for removing Pb2+ ions, which were found to be 120 minutes of contact time, a pH of 5, 0.12 g of clay per 100 mL of solution, and an agitation of 250 rpm. These conditions resulted in a 90% removal efficiency for a 50 mg L-1 initial concentration of lead ions. To remove nickel ions with an efficiency of 80%, the optimal conditions were 60 minutes of contact time, a pH of 6, 12 g of clay per 100 mL of solution, and an agitation of 250 rpm. Several sorption models were evaluated, and the Langmuir formula was found to be the most effective. The highest sorption capacities were 1.75 and 137 mg g-1 for nickel and lead ions, respectively. The spread of metal ions was simulated using finite element analysis in the COMSOL multiphysics simulation software, taking into account the presence of a clay barrier. The results showed that the barrier creates low-discharge zones along the down-gradient of the barrier, reducing the rate of pollutant migration to protect the water sources.

Foam placement for soil remediation: scaling foam flow models in heterogeneous porous media for a better improvement of sweep efficiency

If injected with a large gas fraction, foam reduces mobility more in high-permeability layers and diverts flow to low-permeability layers. Here is a qualitative statement that has been claimed many times in many works related to environmental remediation and oil recovery. It is so true and relevant for foam flow in porous media and yet so little quantified and even less exploited in Darcy-scale numerical simulation. After briefly reviewing opportunities and challenges related to the use of foams in porous media and its Darcy-scale implicit-texture and population-balance modelling, we make a detour out of the strict framework of mathematical models by revisiting with a fresh eye the physics of foams on the large scale of heterogeneous natural porous media in terms of scaling laws. Specifically, it has been recently shown experimentally and theoretically that foam mobility reduction scales approximately as the square root of rock permeability within the framework of Darcy-type implicit-texture foam flow models [Douarche et al. (2020) Scaling foam flow models in heterogeneous reservoirs for a better improvement of sweep efficiency (Paper ThB04), in:17th European Conference of the Mathematics of Oil Recovery (ECMOR), Edinburgh, Scotland, 14–17 September; Gassara et al. (2020) Trans. Porous Media 131, 1, 193–221]. This also appears to hold for population-balance models under the local steady state assumption. This quantitative scaling law for the effect of permeability on foam properties was inferred from an analogy between foam flow in porous media and foam flow in capillary tubes and was found consistent with the modelling of available experimental data. We demonstrate by varying the permeability contrast and anisotropy of a stack of porous layers how foam regulates the flow and leads to flow diversion from high- to low-permeability layers. The threshold in permeability heterogeneity for which such a foam-driven diversion becomes effective is quantified through a sensitivity study accounting for foam injection type, permeability heterogeneity and anisotropy, heterogeneity structure, and scaling procedure. The simulations carried out clearly indicate that ignoring mobility reduction dependence on permeability in the foam process assessment of heterogeneous formations leads to an underestimation of mobility reduction benefits to improve flow conformance. The question of cores selection, as this rock-typing strategy in relation to the porous medium characterization may guide a smart and optimal design of pre-feasibility laboratory campaign for foam evaluation, and the generalization of the findings to multi-facies geological formations are also discussed. As such, the use of physical foam mobility reduction scaling law is highly recommended for foam process evaluation.