Low-permeability Zones Research Articles

Inverse modeling of saturated-unsaturated flow in site-scale fractured rocks using the continuum approach: A case study at Baihetan dam site, Southwest China

Modeling saturated-unsaturated flow in fractured rock formations remains a challenging issue due to the difficulties in properly calibrating the unsaturated flow properties for fractured rocks. On the basis of the continuum approach, this study uses inverse modeling to determine the unsaturated hydraulic parameters of fractured rocks, loose sediments, and geologic structures in a large-scale slope under difficult hydrogeologic conditions at the Baihetan dam site, Southwest China. The saturated hydraulic conductivities were determined a priori by packer tests. Field data, including time-series of groundwater level observations and available discharge measurements, is used. A combined procedure of orthogonal design, finite element forward analysis, artificial neural network, and genetic algorithm is adopted for the inverse analysis with high computational efficiency. The numerical results well reproduce the typical features of multiple water tables and wedge-shaped unsaturated zones controlled by gently-sloping tuff zones of low vertical permeability, showing 46–65% of groundwater flowing subhorizontally along each tuff zone and the remaining 35–54% infiltrating vertically and recharging deeper layers. The drastic drawdown of groundwater level after 10-year site characterization is also reproduced. The calculated discharge and water tables agree reasonably well with field observations, indicating that the estimated parameters are representative of the unsaturated hydraulic properties at the site. This work provides an efficient and effective methodology for seeking an optimal solution in large-scale inverse modeling of saturated-unsaturated flow, and further manifests the feasibility of the continuum approach in predicting unsaturated flow in site-scale fractured rock formations.

Experimental investigation on plugging and transport characteristics of Pore-Scale microspheres in heterogeneous porous media for enhanced oil recovery

To reduce water cut and improve sweep efficiency of water flooding, a novel pore-scale microsphere (NMPS) as profile control agent was firstly prepared through inverse emulsion polymerization technology. Then, its physical properties were investigated, including morphology, particle size distribution, elasticity, swelling property and long-term stability. Subsequently, the plugging and transport characteristics of NMPS were studied through dual parallel core displacement experiments. And then, oil displacement efficiency was evaluated through dual parallel core displacement experiments and nuclear magnetic resonance (NMR) experiment. Experimental results demonstrated NMPS possessed favorable elasticity, water swelling property, dispersibility and long-term stability with an initial average particle size of 7.58 μm. Also, NMPS could effectively plug high permeability channel and regulate heterogeneity. Moreover, NMPS effectively diverted subsequent injected water into low permeability zone and improve sweep efficiency. As a result, 10.83–31.6% of crude oil was produced during NMPS flooding and subsequent water flooding. It was believed that NMPS was a promising candidate for heterogeneity reduction and oil recovery enhancement.

Low permeability zone remediation of trichloroethene via coupling electrokinetic migration with in situ electrochemical hydrodechlorination

To address the challenge of trichloroethene (TCE) remediation in low permeability zone, an inexpensive Cu–Ni bimetallic cathode was proposed in electrokinetic (EK) remediation system to couple electrokinetic migration with in situ electrochemical hydrodechlorination. Aqueous phase TCE was originally added into the anolyte so that breakthrough curves through the low permeability porous soil compartment could be obtained to better understand TCE migration driven by electroosmosis flow using different cathodes. The Cu–Ni cathode resulted in more TCE migration of 7.64 mg compared to that of 5.99 mg with Ni and 4.22 mg with mixed metal oxide (MMO) cathode, suggesting that the Cu–Ni cathode was capable of driving more TCE flux out of the contaminated soil. With the Cu–Ni cathode, 98.4% of TCE flux that reached the cathode was electrochemically reduced on the cathode, which was much higher than that with MMO cathode (77.9%) or Ni cathode (59.6%). TCE mass that was transported by electroosmosis flow increased from 2.04 to 6.68 mg when the voltage gradient increased from 1 to 4 V cm−1, with the normalized energy consumption increasing from 0.06 to 0.16 kWh kg−1 per unit water movement, and from 0.54 to 2.55 kWh g−1 per unit TCE transport. For TCE that did reach the cathode compartment, > 98% degradation maintained at the Cu–Ni cathode with various voltage gradients. The coupled electrokinetic and electrochemical hydrodechlorination technology appears to be a promising strategy for the remediation of low permeability porous media.

Review of experimental and simulation studies of enhanced oil recovery using viscoelastic particles

The profile control that employs viscoelastic particles for enhancing oil recovery is a novel technology that has attracted widespread interest in recent years. Viscoelastic particles can selectively plug high-permeability zones and enlarge the sweep volume of low-permeability zones, which can better improve the effect of development. Based on the extensive investigation of existing literature, the research status of experiments and simulations of viscoelastic particles on profile control is introduced in this paper. First, the properties of viscoelastic particles are summarized. Thereafter, the injection ability, migration ability, profile control ability, and damage effects of viscoelastic particles are expounded. Moreover, the simulation methods for studying the profile control, including classical percolation theory, size exclusion theory, and lattice Boltzmann method–discrete element method, are generalized. The characteristics and applications of different simulation methods are discussed. Finally, the problems that hinder the implementation of experiments and simulations are identified, and suggestions for clarifying the focus and directions of future research are presented.

Controlling excess water production in fractured carbonate reservoirs: chemical zonal protection design

Fractured carbonate reservoirs are prone to premature water cut production at the early stage of recovery. Conventionally completed long horizontal wells, suffering from high water cut through fracture networks, need reliable and cost-effective treatment solutions to control water entry, without damaging oil-saturated segments. Protection of oil flow channels from polymer gel invasion could be a challenge in complex fractured reservoirs because of the enormity of the number of zones that may require damage protection. In this work, a chemical package system is developed, comprising three different chemical solutions. The first fluid is designed to protect the low-permeable oil-saturated zones by creating an impermeable barrier while keeping the water conductive fractures open, followed by a gelant, designed to invade, solidify, and seal off the water conductive fractures. The third treatment is designed for a complete dissolution of the protective barrier created by the first fluid. The effectiveness of this process is evaluated through a set of four core flood studies at reservoir conditions. It was observed that whereas the effective brine permeability could be reduced by 74–91%, oil effective permeability is reduced by 12–17% depending on the fracture aperture. The paper also discusses the key parameters to be addressed for successful field implementation of this technology.

Experimental Study on the Effect of Polymer Injection Timing on Oil Displacement in Porous Media

It has been proven that polymer injection at early times is beneficial to offshore heavy oil recovery. It is of significant importance to optimize the polymer injection timing and decide the residual oil distribution after polymer flooding. Aiming at a specific offshore heavy oil reservoir in Bohai, China, the optimum polymer injection timing is investigated through laboratory experiments. The influence of polymer injection timing on oil displacement and remaining oil distribution is analyzed by combining macroscopic and microscopic flooding experiments. The results reveal that the optimum polymer injection timing should be close to the water breakthrough, i.e., just before the waterflooding front reaches the outlet of the core. In addition, the waterflooding front position is analytically solved by using the Buckley–Leverett method and verified by experimental results, which supply an approach to predict the polymer injection timing. When polymer is injected before the waterflood front reaches the outlet of the core, the mobility control ability of polymer solution can reduce the fraction of bypassed volume of the reservoir by waterflooding. The early injected polymer mainly enters the high permeability zone, which works positively in two ways. Firstly, it improves the oil displacement efficiency of the high permeability zone. Secondly, the polymer establishes a flow resistance in the high permeable zones, thus improving the sweep efficiency in the low and medium permeability zones. However, our residual oil distribution experiments illustrate that there is still a large amount of oil remaining in the low and medium permeability zones. Therefore, it is necessary to explore additional EOR methods to recover the abundant residual oil.

Conformance control for production optimisation using polymer nanocomposite hydrogels

Conformance control is a major challenge in hydrocarbon recovery operations. One of the effective technologies for improving the conformance of a flood front and modifying the injected fluid profile is the application of polymer hydrogels. In this technique, polymer hydrogels are prepared as gel particles, which are injected into the reservoir to block-off preferential flow paths and thief zones, such as fractures and high permeability zones. Subsequently, the fluid injected as part of oil recovery operation would be directed and forced to pass through low permeable zones and sweep more hydrocarbon mass towards the production wells. Depending on the situation, this technology can result in a considerable incremental hydrocarbon recovery from a reservoir. In the present research, nanotechnology was combined with polymer engineering to develop a novel polymer nanocomposite hydrogel with supreme properties, as confirmed using advanced rheological characterisation. Subsequently, the performance of the newly developed nanocomposite hydrogel was tested using a specially designed core flooding setup and procedure. The core flooding results showed that the application of this novel hydrogel could increase the oil recovery by up to 16% under laboratory conditions.

The effect of porosity and permeability variations on convective stability of a two-layer system under longitudinal vibration in zero gravity

The effect of the porosity and permeability variations on the onset of average convection in a single-component fluid within an non-uniformly heated horizontal layer partially filled with a porous zone under zero gravity conditions is studied. The system of the fluid and porous layers oscillates as a whole with high frequency and small amplitude in the longitudinal direction. Permeability is uniform within the porous zone and related to porosity by the Carman–Kozeny formula. The method of constructing a fundamental system of solutions as well as the orthogonalization of vectors for partial solutions are applied to simulate a linear stability problem with respect to the fluid quasi-equilibrium state in the layers numerically. The instability threshold relative to the short-wave and long-wave convective rolls is found. An abrupt change in the type of instability from the short-wave to long-wave ones occurs with the growth of the porosity from 0.3 to 0.8. A similar variation also presents in the case of thermal gravitational convection in layered fluid systems with porous zones under Earth conditions. Convection in weightlessness distinguishes from that in the gravitational field by a non-monotonic behavior of the instability threshold with increasing porosity at different fixed frequencies of vibration. The onset of convection delays at low frequencies and, on the contrary, speeds up at high enough frequencies, if the porosity belongs to the interval from 0.3 to 0.8. In addition, one studies the effect of two types of boundary conditions for tangential velocities near the interface between the layers on the instability threshold in the system with a low permeable porous zone.

Fracturing and permeability enhancement with laser technology employing fuzzy logic

Increasing the rock permeability in low permeable zones of the hydrocarbon reservoirs by conventional methods will often cause formation damage and consequently will reduce the efficiency of recovery of the reservoirs in long term. The use of high energy laser technology as an alternative and innovative approach to mobilise heavy oil and improve permeability, as opposed to the conventional techniques, which have advert effects on the longterm reservoir productivity, was examined in this research. This paper will present study results of the employment of pulsed (Q-switched) Nd: YAG (Neodymium: Yttrium Aluminium Garnet) laser on impermeable heavy oil-bearing core samples which have been simulated in lab to be as close as possible to the real reservoir conditions.A unique technique was employed in this study where lasing experiment was conducted on samples followed by intervals of stopping lasing operation, known as relaxation intervals. The alternate lasing-relaxation intervals which were repeated for samples 3 times, yield positive and satisfactory results both for heavy oil mobilization as well as permeability improvement. Porosity increase was also observed due to fracture production. Specifications of applied laser pulses and their associated beam properties, samples characteristics and dimensions as well as the simulated experiment environment with that of the real reservoir conditions will be reported. Fuzzy logic was employed to normalize the varying and diverse parameters affecting the rock's thermal behaviour such as mineral content, fluid content and type and pressure.By employing the proposed technique on samples from heavy-oil-bearing low permeable zones of Burgan and Mauddud reservoirs of the Giant Burgan field in Kuwait, fractures were produced and permeability of the reservoir samples were improved to almost 3 times of their initial values in some of the samples. Upon the termination of the third lasing experiment, traces of oil could be observed on some of the core sample's surfaces, proving that the heavy oil was mobilised due to induced high temperatures generated in the samples during lasing.

Efficiency of foam flushing remediation in heterogeneous soil contaminated by nitrobenzene

Abstract The spatial distribution of nitrobenzene in a heterogeneous medium during the foam flushing remediation process was investigated through a two-dimensional simulation device. The remediation efficiency and the mechanisms of action of the surfactant foam remediation process in heterogeneous media were also studied. The experiments showed that during the contamination process, nitrobenzene preferentially enters the low-permeability zones of the medium and is intercepted as a free phase, bypassing the high-permeability zones. In the surfactant foam remediation process, a total removal rate of 95.7% was achieved, with the mobilization effect contributing 69.5%, and the solubilization and volatilization contributing 21.6% and 1.5%, respectively. Mobilization, solubilization, and volatilization are the main mechanisms by which nitrobenzene is eliminated from the soil during the surfactant foam remediation process. Finally, it has also been observed that this process showed a higher removal efficiency in high-permeability media than in low-permeability media due to interface effects.

Combination of nZVI and DC for the in-situ remediation of chlorinated ethenes: An environmental and economic case study.

Over the past two decades, the use of nanoscale zero-valent iron (nZVI) has emerged as a standard method of contaminated groundwater remediation. The effectiveness of this method depends on key intrinsic hydrogeological parameters, which can affect both reactivity of the nanoparticles and their migration in the aquifer. In the case of low hydraulic permeability, the migration of nanoparticles is limited, which negatively influences remediation. An application of nZVI reinforced with a DC electric field led to a significant increase in the efficiency of remediation, as demonstrated by long-term monitoring at a former industrial site in Horice (Czech Republic). For the method testing, a 12×9m polygon was defined around well IS4, where the original contamination was predominantly composed of DCE (7300μg/l), and with a total concentration of chlorinated ethenes of 8880μg/l. During the first stage of the activities, 49kg of nZVI was injected and monitored for two years. Subsequently, the electrodes were installed, and for three years, the synergistic action of nZVI within an applied DC field was monitored. Based on 32 monitoring campaigns performed over the six years, the combined method was compared with an application of the only nZVI in technical, environmental and economic terms. Technically, the method requires annual reinstallation of anodes as a result of their oxidative disintegration. Environmentally, the method provides significantly improved chlorinated ethane reduction, remediation of low permeable zones, and extended efficiency. Economically, the method is five times cheaper when compared to the nZVI used alone.

Acceleration and centralization of a back-diffusion process: Effects of EDTA-2Na on cadmium migration in high- and low-permeability systems

Pollutant accumulation in the low-permeability zones (LPZs) in groundwater systems is regarded as a secondary source, and its consequent back-diffusion can extend the timeframe of pump-and-treat remediation. However, the bioavailability and mobility of heavy metals and the medium characteristics can be changed during the process. This study investigated the accumulation and back-diffusion law of toxic metals and the effects of ethylenediaminetetraacetic acid disodium salt (EDTA-2Na) on them by implementing a series of tank experiments. In these experiments, a cadmium solution was injected first, and deionized water or EDTA-2Na constantly washed the system consisting of different medium layers. The experimental results showed that the cadmium breakthrough curves had some concentration gradient reverse points where the curves fluctuated with elution by deionized water, which did not exist when EDTA-2Na was the eluent. In these scenarios, the mass of accumulated cadmium in the media before elution was large, with a value of 931 mg (153 mg/kg), when the low-permeability medium was clay. However, when EDTA-2Na was injected together with cadmium, the value dropped to 319 mg (52.3 mg/kg), greatly reducing the cadmium accumulation. Additionally, the use of EDTA-2Na as an eluent resulted in the appearance of a secondary peak in the breakthrough curve, showing that EDTA-2Na accelerated and centralized the back-diffusion. Notably, the reduced cadmium accumulation in LPZs with the elution by EDTA-2Na was partly due to a reduced adsorption capacity of the clay minerals. The above results can advance the technology related to pump-and-treat remediation.

Experimental study and field demonstration of air-foam flooding for heavy oil EOR

Foam flooding is an effective oil displacement technique to improve fluid sweep efficiency and increase oil recovery. The objective of this study is to investigate the application of air-foam for heavy oil recovery under heterogeneous reservoir conditions. The paper first investigated the air-foam flow behavior in porous media and identified the effects of different factors such as gas-liquid ratio, injection rate, and crude oil saturation on air-foam resistance. Then, dual-tube sand-packs were used to evaluate the performance of air-foam for heavy oil recovery from heterogeneous reservoir conditions. The results indicated that the air-foam could divert the fluid from the high-permeability zone to the low-permeability zone, decrease the water cut and improve the oil recovery. Further studies revealed that there existed an optimal reservoir permeability contrast ratio in air-foam flooding for heavy oil recovery. The air foam performance for oil recovery would be reduced beyond or below this permeability contrast ratio. Finally, field tests on air-foam for heavy oil recover demonstrated that air foam flooding could increase heavy oil production rate and decrease the production water cut.

Optimization Design of Injection Strategy for Surfactant-Polymer Flooding Process in Heterogeneous Reservoir under Low Oil Prices

Surfactant–polymer (SP) flooding has significant potential to enhance oil recovery after water flooding in mature reservoirs. However, the economic benefit of the SP flooding process is unsatisfactory under low oil prices. Thus, it is necessary to reduce the chemical costs and improve SP flooding efficiency to make SP flooding more profitable. Our goal was to maximize the incremental oil recovery of the SP flooding process after water flooding by using the equal chemical consumption cost to ensure the economic viability of the SP flooding process. Thus, a systematic study was carried out to investigate the SP flooding process under different injection strategies by conducting parallel sand pack flooding experiments to optimize the SP flooding design. Then, the comparison of the remaining oil distribution after water flooding and SP flooding under different injection strategies was studied. The results demonstrate that the EOR efficiency of the SP flooding process under the alternating injection of polymer and surfactant–polymer (PASP) is higher than that of conventional simultaneous injection of surfactant and polymer. Moreover, as the alternating cycle increases, the incremental oil recovery increases. Based on the analysis of fractional flow, incremental oil recovery, and remaining oil distribution when compared with the conventional simultaneous injection of surfactant and polymer, the alternating injection of polymer and surfactant–polymer (PASP) showed better sweep efficiency improvement and recovered more remaining oil trapped in the low permeability zone. Thus, these findings could provide insights into designing the SP flooding process under low oil prices.

Patterns of recovery and injection wells in deposits of high-viscosity oil with reservoir decompression zones

The issue of patterns of injection and recovery wells in zones of non-uniform permeability reservoirs is discussed by many researchers. The researchers aim to identify the influence of well patterns in reservoir zones with different permeability on the efficiency of oil recovery. This issue is particularly acute for systems maintaining reservoir pressure. The location of injection wells in low-permeable zones, and recovery wells - in high-permeability zones helps increase the coverage of the impact. Moreover, even in the conditions of a partially developed reservoir, transformation of the existing development system has significant potencies for increasing the ORC. One more crucial problem is the study of the effect of extensive highly permeable inclusions (faults, zones of reservoir loosening) on the effectiveness of regular development systems.

Insights from stable isotopes of water and hydrochemistry to the evolutionary processes of groundwater in the Subei lake basin, Ordos energy base, Northwestern China

ABSTRACTChanges in groundwater evolutionary processes due to aquifer overexploitation show a world-wide increase and have been of growing concern in recent years. The study aimed to improve the knowledge of groundwater evolutionary processes by means of stable water isotopes and hydrochemistry in a representative lake basin, Ordos energy base. Groundwater, precipitation, and lake water collected during four campaigns were analysed by stable isotopes and chemical compositions. Results showed that temperature effect predominated the isotope fractionation in precipitation, while evaporation and inadequate groundwater recharge were the key factors explaining high salinity and isotopic enrichment in lake water. Additionally, the Kuisheng Lake was a preferential area of groundwater recharge, while the Subei Lake received less sources from underlying aquifer due to the combined effects of low permeable zone and upstream groundwater captured by the production wells. The homogeneous isotope signatures of groundwater may be ascribed to the closely vertical hydraulic connectivity between the unconfined and the confined aquifers. Isotopically enriched groundwater pumping from well field probably promoted isotopic depletion in groundwater depression cone. These findings not only provide the conceptual framework for the inland basin, but also have important implications for sustainable groundwater management in other groundwater discharge basins with arid climate.

Assessment of the Rheological Behavior of Polymer–Oxidant Mixtures and the Influence of the Groundwater Environment on Their Properties

Shear-thinning polymers have been introduced to contaminant remediation in the subsurface as a mobility control method applied to mitigate the inefficient delivery of remedial agents caused by geological heterogeneity. Laboratory experiments have been conducted to assess the compatibility of polymers (xanthan and hydrolyzed polyacrylamide (HPAM)) and oxidants (KMnO4 and Na2S2O8) through quantitative evaluation of the viscosity maintenance, shear-thinning performance, and oxidant consumption. The mechanism that causes viscosity loss and the influence of the groundwater environment on the mixture viscosity were also explored. The xanthan–KMnO4 mixture exhibited the best performance in both viscosity retention and shear-thinning behavior with retention rates higher than 75% and 73.5%, respectively. Furthermore, the results indicated that xanthan gum has a high resistance to MnO4− and that K+ plays a leading role in its viscosity reduction, while HPAM is much more sensitive to MnO4−. The viscosity responses of the two polymers to Na2S2O8 and NaCl were almost consistent with that of KMnO4; salt ions displayed an instantaneous effect on the solution’s viscosity, while the oxide ions could cause the solution’s viscosity to decrease continuously with time. Since xanthan exhibited acceptable oxidant consumption as well, xanthan–KMnO4 is considered to be the optimal combination. In addition, the results implied that the effects of salt ions and the water pH on the mixture solution could be acceptable. In the 2D tank test, it was found that when xanthan gum was introduced, the sweeping efficiency of the oxidant in the low-permeability zone was increased from 28.2% to 100%. These findings demonstrated the feasibility of using a xanthan–KMnO4 mixture for actual site remediation.

Study of Effects of Hard Thick Roof on Gas Migration and Field Experiment of Roof Artificially Guided Pre-splitting for Efficient Gas Control

Due to high gas content, high geo-stress and complex geological conditions, gas disasters occur frequently in deep coal mining. The hard thick roof (HTR) greatly increases the difficulty of coalbed gas control besides causing dynamic disasters. In this paper, the effects of HTR on gas migration were numerically analyzed based on a multi-field coupling model. Results indicated that the hanging arch leads to remarkable stress concentration and induces a “cap-shaped” low-permeable zone above the gob, which greatly prevents gas from migrating upwards. Meanwhile, HTR hinders the subsidence movements of the upper rock strata, contributing to very few roof fractures and bed-separated fractures. Without the formation of roof-fractured zone, coalbed gas completely loses the possibility of upward concentration and will accumulate in the gob, forming a major safety hazard. To overcome these problems, borehole artificially guided pre-splitting (BAGP) technology was proposed. Three different pre-splitting boreholes were constructed as a group to generate artificial fractures in advance in HTR via deep-hole blasting, promoting the evolution of roof fractures. With the effects of mining stress, a fracture network is eventually formed in HTR, which provides a preferential passage for the upward flow of coalbed gas. Moreover, the controllable breaking of HTR was achieved and the roof strata could deform and subside regularly, forming an “O-shaped” roof-fractured zone above the gob which greatly improves the gas extraction efficiency of roof high-level boreholes. In addition, after BAGP, several extraction measures can be applied in the gob-side entry to drain the gas in different concentrated areas. In the field experiment, the roof periodic breaking length was reduced by half, and the average gas extraction rate was increased by 4 times to 67.7%. The synergetic controls of HTR and coalbed gas were effectively realized. This study provides valuable insight into gas control in other deep coal mines with similar geological conditions.

Pore-scale study of counter-current imbibition in strongly water-wet fractured porous media using lattice Boltzmann method

Oil recovery from naturally fractured reservoirs with low permeability rock remains a challenge. To provide a better understanding of spontaneous imbibition, a key oil recovery mechanism in the fractured reservoir rocks, a pore-scale computational study of the water imbibition into an artificially generated dual-permeability porous matrix with a fracture attached on top is conducted using a recently improved lattice Boltzmann color-gradient model. Several factors affecting the dynamic countercurrent imbibition processes and the resulting oil recovery have been analyzed, including the water injection velocity, the geometry configuration of the dual permeability zones, interfacial tension, the viscosity ratio of water to oil phases, and fracture spacing if there are multiple fractures. Depending on the water injection velocity and interfacial tension, three different imbibition regimes have been identified: the squeezing regime, the jetting regime, and the dripping regime, each with a distinctively different expelled oil morphology in the fracture. The geometry configuration of the high and low permeability zones affects the amount of oil that can be recovered by the countercurrent imbibition in a fracture-matrix system through transition of the different regimes. In the squeezing regime, which occurs at low water injection velocity, the build-up squeezing pressure upstream in the fracture enables more water to imbibe into the permeability zone closer to the fracture inlet thus increasing the oil recovery factor. A larger interfacial tension or a lower water-to-oil viscosity ratio is favorable for enhancing oil recovery, and new insights into the effect of the viscosity ratio are provided. Introducing an extra parallel fracture can effectively increase the oil recovery factor, and there is an optimal fracture spacing between the two adjacent horizontal fractures to maximize the oil recovery. These findings can aid the optimal design of water-injecting oil extraction in fractured rocks in reservoirs such as oil shale.

Hydrogeochemical Model Supporting the Remediation Strategy of a Highly Contaminated Industrial Site

Delineation and understanding the geology and the hydrogeology of a contaminated site, considering its chemical and its biological aspects, are fundamental requirements for successful environmental remediation. The aim of this research is to provide some evidence about the effectiveness of a hydrogeochemical geodatabase to facilitate the integrated management, representation and analysis of heterogeneous data, enabling the appropriate selection, design and optimization of an effective remediation strategy. This study investigates a new technology for the remediation of a dense non-aqueous phase liquid aged source zone, with the aim of enhancing in situ bioremediation by coupling groundwater circulation wells with a continuous production system of electron donors. The technology was verified through a pilot test carried out at an industrial site highly contaminated by chlorinated aliphatic hydrocarbons. The multidisciplinary conceptual model confirmed a complex hydrogeological situation, with the occurrence of active residual sources in low permeability layers. The pilot test results clearly demonstrate a significant mobilization of contaminants from the low permeability zone, and the possibility of favoring the in situ natural attenuation mechanisms based upon biological reductive dechlorination. Different information related to the hydrogeochemical sphere must be integrated and taken into consideration when developing a reliable remediation strategy for contaminated sites.