Water Front Movement Research Articles

Shale Matrix Petrophysical Evolution due to Spontaneous Water Imbibition.

Shale matrix alteration resulting from fracturing water-rock interactions has become a major concern. It significantly affects economic production from shale gas formation. Previous studies mostly failed to investigate the thickness of the water intrusion zone and quantified its effects on shale geophysical alteration. As a result, we present a one-dimensional countercurrent water imbibition model in which capillary pressure and chemical osmosis stress are included. This model is used to predict water front movement with respect to soaking durations. Based on the simulation results and theory derivations, the matrix porosity-permeability and mechanical alteration models are set up to reveal shale geophysical variables change due to shale-water interactions. Our results show that during the water imbibition process, capillary pressure plays a more crucial role than osmosis pressure. Furthermore, both core-scaled porosity and permeability are negatively associated with water saturation, the extent of which depends on different driving forces and penetration depth. Finally, water soaking is quantitatively demonstrated to induce an increase in compressive strength and stress sensitivity but a reduction in the elastic modulus. These findings will provide efficient insights into driving mechanisms involved in the water-rock interactions. The study is useful to be incorporated into production models for predicting hydrocarbon production from shale reservoirs.

Enhanced history matching process by incorporation of saturation logs as model selection criteria

This paper proposes a methodology for an alternative history matching process enhanced by the incorporation of a simplified binary interpretation of reservoir saturation logs (RST) as objective function. Incorporating fluids saturation logs during the history matching phase unlocks the possibility to adjust or select models that better represent the near wellbore waterfront movement, which is particularly important for uncertainty mitigation during future well interference assessments in water driven reservoirs. For the purposes of this study, a semi-synthetic open-source reservoir model was used as base case to evaluate the proposed methodology. The reservoir model represents a water driven, highly heterogenous sandstone reservoir from Namorado field in Brazil. To effectively compare the proposed methodology against the conventional methods, a commercial reservoir simulator was used in combination with a state-of-the-art benchmarking workflow based on the Big Loop™ approach. A well-known group of binary metrics were evaluated to be used as the objective function, and the Matthew correlation coefficient (MCC) has been proved to offer the best results when using binary data from water saturation logs. History matching results obtained with the proposed methodology allowed the selection of a more reliable group of reservoir models, especially for cases with high heterogeneity. The methodology also offers additional information and understanding of sweep behaviour behind the well casing at specific production zones, thus revealing full model potential to define new wells and reservoir development opportunities.

Water flow modeling in bounded gas-bearing fractured geological strata: A semi-analytical and experimental study

Underground water disposal is a technique for wastewater management, enhanced oil recovery (EOR), or artificial groundwater/aquifer recharge. Host layers might be naturally or even hydraulically fractured which can significantly increase the permeability of the medium where a linear flow geometry around the vertical fractures intersecting the wells is expected. In fact, each of flow from wellbore (injection point) to fracture as well as fracture-matrix flow may be linear in different conditions of fracture conductivity. When both are linear it is named “bilinear flow” in hydraulic fracture appications equivalent to “fully linear flow” in this study. In this paper, a semi-analytical solution is presented for transient saturation of injected water in naturally/hydraulically fractured gas-bearing rocks with linear flow in both wellbore-fracture and fracture-matrix spacings. The solution is general and can be used for either unsaturated soils or depleted reservoirs which are defined with no-flow boundaries. To do so, proposed semi-analytical model was validated with experimental results, based on waterflood testing apparatus in an artificially fractured core-plug which showed a very good matching. In addition to introducing new sets of type curves to delineate water saturation in both matrix and fracture in both constant terminal rate and saturation (CTR and CTS) inner boundary conditions, we defined the average water velocity ratio (AWVR), a conceptual criterion, to assess if CTS and CTR water storage can be logically compared. Results derived based on this concept are: 1) more speedy movement of water front along the last four-fifth of the fracture length by CTR and 2) higher matrix blocks storativity neighboring the first half of the straight fracture plane by CTS. Solutions from our model can directly simulate the unsteady behavior of saturation variations along the fracture and across the rock matrix versus time for an underground water injection problem. Ultimately, this can assist engineers to have an easy spatiotemporal estimation of water storage in the matrix of the host formation.

An Improved Embedded Discrete Fracture Model with Fracture Growth for Water-Induced Fracture Simulation in Low Permeability Reservoirs

Abstract Water injection is often used to supply formation energy in low permeability reservoirs. A lot of field data shows that fractures nearby the wellbores may extend hundreds of meters because of the poor injectability which is called water-induced fractures. The presence of these fractures significantly changes the flow of injected water thus affecting the development effects. However, few studies of reservoir numerical simulation methods have been presented to simulate the dynamic changes of fractures in the long-term waterflooding process. This study is based on the embedded discrete fracture model (EDFM) in which the fracture system has less dependence on the grid system. By improving the preprocessing algorithm, fracture growth can be considered in EDFM which is called the dynamic embedded discrete model (dEDFM). This new method provides an innovative idea for fracture propagation simulation by attaching new fracture elements to the original fractures once the failure criterion is satisfied. Meanwhile, there is no need to calculate the stress field once the in situ stress is provided, so the computational efficiency is greatly improved compared with the fluid-solid coupling method. Besides, dEDFM has a flexible way of handling fracture elements, so it is suitable for water-induced fracture simulation. Results show that fracture propagation speed is significantly influenced by matrix permeability, in situ stress, and injection intensity, and if the water-induced fractures propagate faster than the original waterfront movement velocity, changing law of the water content rate rising of production wells in different directions will be different. The contribution of this work lies in that it provides a suitable and efficient way for reservoir engineers to deal with water-induced fractures since the propagation of fractures can be considered when it comes to reservoir numerical simulation, and it is helpful for production data prediction and development adjustment in low permeability reservoirs.

Estimation of soil waterfront velocity and saturated hydraulic conductivity in a Hele-Shaw apparatus with an optical flow method

The estimation of saturated hydraulic conductivity is a key parameter for studying the water flow in the unsaturated zone of the soil. In this work, a combined modelling approach of the waterfront movement is elaborated, integrating a physical analogue type device with image analysis. A customized Hele-Shaw apparatus is designed for the wetting process visual inspection, while an optical flow algorithm is used for the numerical calculation of flow velocity and saturated hydraulic conductivity values at a pixel level of the image processing. Saturated hydraulic conductivity values estimated by the proposed method are in close agreement with values found in the literature under similar soil conditions. Also, the proposed method seems to be a useful tool for a comprehensive analysis of the waterfront movement in the vadose zone.

A physically-supported data-driven proxy modeling based on machine learning classification methods: Application to water front movement prediction

By defining an optimum injection/production strategy in the water flooding process, the water front movement is controlled and an early breakthrough is avoided, and as a result, the sweep efficiency is increased. The most important part of injection/production planning is determining the injection fluid front position. However, using a commercial reservoir simulator comes up with a considerable time and CPU effort, particularly in the case of large and complex reservoirs. Several proxy models, either physics-based or Data-Driven, have been developed to predict water front movement with low computational time and cost, each offering some advantages and shortcomings such as error accumulation and short-term predictions. In this paper, we use a hybrid view in developing a classification based smart proxy model at the grid-block level (CSPMG) for front prediction to benefit from the advantages of both physics-based and Data-Driven proxies. The idea is to formulate the problem by using the physical principles underlying the problem (physical-view) and then use machine learning classification models to capture the pattern between inputs and the target feature (Data-Driven view). Based on the Buckley-Leverett theory, which is a physics-based method for front advancement in porous media, water front prediction was formulated as a classification problem in which the grid-blocks behind and ahead of the front were considered as separate classes and a label was assigned to each class. Then, artificial neural networks (ANNs) were trained on a training database to predict the class label of each grid block. The water front was considered as the boundary between two adjacent classes. A binary and a ternary classification problem were formulated and two proxy models were developed. A blind test was carried out to compare their results with each other, with a Data-Driven regression model, and with those of a reservoir simulator. The results showed that the CSPMG matches the reservoir simulator results and outperforms the regression model and makes longer predictions.

Evaluation of Sorptivity and Water Captivation of Concrete with Partial Replacement of Cement by Hypo Sludge

Environs have important influences on the water captivation of concrete materials. This paper presents an investigational study on partial replacement of cement by hypo sludge (paper industry waste) influence of sorptivity and water captivation on the permanence of concrete materials. The sorptivity test measures the rate of movement of water front through the concrete under capillary suction. The waste product from paper industry i.e hypo sludge (HS) is causing serious pollution problem. In this paper the study of sorptivity and water absorption properties of hypo sludge concrete. The cement has been replaced by hypo sludge in the range of 0%, 10%, 20%, 30% and 40% by weight of cement for the M25 and M40 mix. Concrete mixtures were produced, tested and compared in terms of sorptivity and water absorption to the conventional concrete. The mix design was carried out for 1:1.50:3.36 (M25) and 1:0.80:2.29 (M40) proportions of cement concrete on the basis of IS: 10262-2009. The results show that the % water captivation and sorptivity of hypo sludge concrete shows higher % water captivation and sorptivity than conventional concrete.

Strain measurements during capillary water infiltration in porous limestones

Building stones are highly affected by environmental conditions. Differential stress/strain due to hydric dilation resulting from water front movements are suspected to be involved in the damage processes of surface decay, especially spalling. The present study investigated the strains that develop at different depths from the surface of limestones submitted to capillary water infiltration. Local strains were measured during water imbibition using strain gauge rosettes whereas global displacement of the sample was measured by a dial gauge. The results show differential strains between the surface and the core of the stone due to water ingress. They demonstrate the existence of a local contraction zone and expansion zone in each direction separately and show clearly the thickness of the surface which can be significantly stressed due to the progress of water in the stone during imbibition. Contraction at the height just above the water front can result in the development of significant tensile stress if the boundary conditions are restrained. This tensile stress, in the order of magnitude of tensile strength, could be the origin of a crack parallel to the surface exposed to rain. This contributes to assess the role of water movements in surface degradation processes.

New Fracture-Stimulation Designs and Completion Techniques Result in Better Performance of Shallow Chittim Ranch Wells

Summary The Sacatosa field in west Texas was discovered in 1956. Since then, more than 1,500 wells have been drilled and completed in the main reservoir section known as the San Miguel 1. The San Miguel 1 is primarily low-permeability sandstone, with several shale layers dispersed throughout. Economic development of the field requires effective well stimulation and an active waterflood program to provide pressure maintenance. Unfortunately, the available injection water is of poor quality and can rapidly plug up pore throats with solids, resulting in significant near-wellbore formation damage. When these factors are considered, hydraulic fracturing of both injector and producer wells is a viable option for improved long-term well performance. However, because of relatively shallow depths, traditional hydraulic-fracturing practices can lead to a multiplane fracture system with a mix of horizontal and vertical components. A significant presence of horizontal fractures can be detrimental to fractured-well performance because of the low conductivities of the fractures. In producer wells, this could impair production if the reservoir is laminated and has low vertical permeability. In injectors, water-front movement and sweep efficiency would be diminished greatly. This paper discusses the steps taken to plan and develop a strategy to place vertical fractures in shallow San Miguel 1 sands. These findings can easily be extended to similar shallow-depth reservoirs worldwide. Some major modifications in completion design included changes in perforation strategy, redesign of the pump schedule, and implementation of a staged stimulation. Fracturing treatments were pumped on a total of 26 injectors and eight producers through a variety of methods, including coiled-tubing fracturing. Post-fracture analysis suggests a strong vertical-fracture component, and analysis of injectivity tests shows fracture parameters in line with design objectives. All the producers that were fracture stimulated with this technique reported higher initial production when compared with wells stimulated through the use of legacy treatment schedules.

Numerical Study on the Influence of the Corner Curvature of Circular Micropillar on Microdroplet Size via a Dewetting Process

The influence of the corner curvature of circular micropillar on microdroplet formation by a dewetting process was numerically investigated. The diameter of the microdroplets is mainly determined by the capillary effect and viscous force contributed by the wetted surface i.e. on the top surface of micropillar magnifies, which slows down the movement of water front attached to the top surface of micropillar. The numerical simulations showed that the corner curvature of the micropillars play an important role in determining the flow pattern of the dewetting process, especially the evolution and movement of the meniscus across the micropillar before a microdroplet is formed. The water front on the top surface of micropillar with right-angle corner moves much slower than that on the micropillar with round corner. The numerical results also indicate that the curvature radius (r) on circular micropillar is one of the parameters governing the size of the microdroplets formed on the top surface of the micropillars after the dewetting process, while the microdroplet diameter decreases with the increase of the dimensionless of curvature corner.

Evaluation of Malaysian Ceiba pentandra (L.) Gaertn. for oily water filtration using factorial design

A packed-bed column was developed to study the performance of Ceiba pentandra (L). Gaertn. (kapok) for oily water filtration using a three-level, two-factor factorial design. This was based on the effects of packing density and flow rates on chemical oxygen demand (COD) and turbidity of the effluent. COD was significantly affected by the quadratic effects of flow rates. The optimum packing density and flow rate for minimum COD were predicted at 0.07 g/cm 3 and 1.09 L/h, which were within the range tested. About 99% of COD reductions were observed at all packing densities and flow rates. Similarly, more than 87% of turbidity reductions were achieved at all packing densities and flow rates. A deep-bed kapok filtration column constructed in this study had been successful in achieving oily water separation under different packing densities and flow rates. The oil and water front movements were shown to be influenced by the affinity of liquid to kapok fibers. This may suggest the excellent physicochemical property of Malaysian kapok for oil removal from water.

Characterization of Reservoir Heterogeneity Through Fluid Movement Monitoring With Deep Electromagnetic and Pressure Measurements

Summary This paper presents a novel technique to characterize detailed formation heterogeneity for a carbonate reservoir using measurements from electrode resistivity array (ERA), a wireline formation tester, and a permanent downhole pressure sensor. The ERA was installed on tubing in a barefoot well rather than permanently cemented outside the casing as in previous applications. This notable difference provided flexibility for device installation and operation but also introduced particular issues in the ERA data acquisition and interpretation. Furthermore, the ERA measurements were carried out in conjunction with low-salinity water injection and oil and water production in the same well. The primary finding presented in this paper is that the time-lapse ERA voltages near a source electrode showed unique characteristics that represented local formation heterogeneity. This localized sensitivity of ERA data allows detailed characterization of the formation heterogeneity within the length of the ERA string in the vertical direction and about 100 ft laterally around the wellbore. The scale size of the investigated formation heterogeneity is comparable to typical grid sizes used in current reservoir simulations. Models were developed to identify stratified permeability heterogeneities from the time-lapse ERA voltages. The stratified heterogeneity estimated from the ERA measurements was compared to and verified by openhole logs and core analyses data. The final heterogeneous reservoir model from the ERA was subsequently applied to a numerical simulation that integrated the dynamic fluid flow, salt transport, and electrode array responses for monitoring water-front movement and estimating multiphase formation properties. The history matching of the time-lapse ERA data confirmed the first pass estimates of the identified heterogeneities.

Using 4D Seismic Data to Understand Production-Related Changes in Enfield, NWS Australia

The Enfield oil field, located in the North West Shelf, Australia, began production in July 2006. In 2007 a 4D monitor survey was acquired to obtain a better understanding of injector pathways, stratigraphic and fault controlled reservoir connectivity, reservoir pressures and water front movement. A dedicated baseline survey was acquired in 2004 with good image quality. The monitor survey, acquired 7 months after production, is the first dedicated 4D monitor survey in Australia. Both base and monitor optimise 4D repeatability and they were processed in parallel to enhance production-related effects. A series of 4D modelling studies were conducted to decide the criteria for successful 4D interpretation. Pressure and saturation changes were modelled to determine the impact of production-related effects on the 4D. The competing effects of pressure and saturation on seismic amplitudes are complex, therefore an additional 3D swath was acquired over a water injector whilst injecting. This approach helped to calibrate pressure and saturation effects and identify preferential pathways within the main producing interval. The rock properties vary across the field with the eastern most area requiring AVO interpretation to determine fluid movement. In this paper we will present the initial 4D interpretation results using both conventional seismic and AVO volumes and describe how the results were integrated with production and geological data.

Analytical model of cold water front movement in a geothermal reservoir

Injection of cooled geothermal water back into the producing formation is a procedure that maintains reservoir pressure and increases energy extraction efficiency, but, because reinjected fluids tend to be much colder than the reservoir rock, injection can also cause cooling of the fluid produced from nearby wells. It is therefore essential to determine the cold front velocity in a geothermal reservoir. Constant thermal properties of both rock and fluid are generally assumed in order to solve this problem. In this paper, the rock density and heat capacity of the water–rock system as functions of temperature are assumed. Using the method of characteristics, an analytical solution is obtained. It is shown that the variable heat capacity of rock leads to a temperature-dependent speed of propagation of the thermal front. This results in a steepening of the front when cold water is injected into a hot zone, and eventually the formation of a discontinuous solution, or shock. A method is proposed for finding such discontinuous solutions and an equation for the velocity of the thermal front is presented. The difference between the front velocity obtained by means of the weak solution presented here and the classical model with constant thermal properties varies between about 1 and 14%.

Groundwater recharge and evapotranspiration for two natural ecosystems covered with oak and heather

The evapotranspiration and groundwater recharge from two natural areas with high (oak) and low (heath) vegetation were estimated by calibrating a semi-physical numerical soil water and heat model to fit 8 and 7 years of TDR-measurements of water content, respectively. The measurements were made between the surface and 7 m depth. For the oak stand, the estimated annual recharge for the years 1992–1999 is 390 mm, the evaporation from soil and interception is 205 mm, and the transpiration is 285 mm. For the heath area estimation was carried out for the years 1993–1999. However, the heath was struck by a heavy beetle attack in 1994, which strongly affected the vegetation and thus the water balance for the following 3 years. For years not affected, the estimated recharge is 733 mm (about 50% larger than for the oak stand for the same years), the evaporation is 316 mm, and the transpiration is 128 mm. The estimated recharge values compare fairly well to estimates obtained from bromide tracer experiments. However, the recharge estimates obtained from the tracer experiments are very uncertain. The uncertainty is mainly due to spatial heterogeneity making the three replicate samples taken here for each time and depth insufficient. The analyses of TDR-measurements and tracer data showed that water front movement depends on the antecedent soil water content. Some layers are bypassed, especially at low water contents, and at high soil water contents preferential flow was observed at the heath site.

Time-lapse seismic as a complementary tool for in-fill drilling

Time-lapse seismic data have improved the drainage understanding of the Gullfaks oil field and have resulted in several potential new in-fill drilling targets. The baseline survey was acquired in 1985, 1 year before production start-up. Since then, three more surveys have been acquired, one in 1995, one in 1996 and the last one so far in 1999. Key elements in the process of reducing the uncertainties are cross-disciplinary verifications and detailed geophysical analysis and modeling, where different saturation profiles are input to the model. Waterfront movements predicted by time-lapse seismic analysis have been confirmed by well observations. It is estimated that the recovery will most likely be increased by approximately 2% as a result of seismic monitoring, corresponding to a net value contribution of approximately US$100 million, assuming an oil price of US$15 per barrel.

The Gullfaks 4D seismic study

A time lapse analysis was performed on two 3D seismic datasets (4D seismic) acquired over the northern part of the Gullfaks oilfield in the North Sea. The first survey was acquired in 1985, prior to the production start in 1986, a second survey was acquired in 1995, followed by a third in 1996. The drainage interpretations carried out by means of the repeated seismic datasets are in reasonable agreement with similar interpretations performed the traditional way by reservoir engineers, and have locally resulted in an improved understanding of drainage. The time lapse seismic data are routinely used in well planning projects on Gullfaks. In 1997, two wells were drilled into segments that, based on repeated seismic data, were interpreted to be undrained. Both wells encountered oil-filled reservoirs. Although these wells were not based on time lapse seismic alone, the wells served as a good test of the reservoir management potential associated with the 4D technology. Furthermore, waterfront movements predicted on the basis of time lapse seismic data are confirmed by well observations.

Crystal dissolution-controlled release systems. II. Metronidazole release from semicrystalline poly(vinyl alcohol) systems.

Novel semicrystalline, poly(vinyl alcohol) (PVA)-based phase erosion systems were developed. The rate of drug release from these systems is controlled by the rate of crystal dissolution. PVA devices loaded with metronidazole were exposed to temperatures ranging from 90 to 120 C for times of 10-90 min to obtain samples with different degrees of crystallinity. Degrees of crystallinity were measured by differential scanning calorimetry and attenuated total reflectance Fourier transform infrared spectroscopy. In vitro release of metronidazole from such systems into deionized water at 37 degrees C was monitored. The influence of parameters such as polymer molecular weight, annealing time and temperature, and surface pretreatment on the crystal dissolution, and hence the drug release rate, were investigated. Measurements of water-front movements were carried out to study the effect of parameters such as drug solubility on the release rate. The drug release rate was found to be dependent on the crystallization conditions of the samples. Surface pretreatment was found to reduce the burst effect observed during the release.

Consideration of Drug Load on the Swelling Kinetics of Glassy Gelatin Matrices

The effect of drug load on water transport into glassy gelatin beads and on the dynamic swelling behavior of the hydrated gel was studied through microscopic measurements of moving boundaries. Isoniazid was found to alter the glassy structure of gelatin, resulting in an increase in water penetration rates with a lowering of the apparent activation energy for water front movement. Differential scanning calorimetry studies revealed a decrease in the glass transition temperature with drug load, further indicating plasticization of the gelatin glass. The presence of drug also accelerated the outer swelling gelatin front, but, in contrast to the water front, the apparent activation energy for matrix expansion rose substantially with higher drug loads for temperatures >20°C. This observation may be rationalized as an increasing osmotic stress on the matrix induced by greater loading with hydrophilic drug. The osmotic stress, in turn, forces the gelatin matrix to expand outward, resulting in a higher apparent activation energy (Eact). Furthermore, the enhanced expansion was especially pronounced at higher temperatures where physical bonds, which are associated with gel structure and needed to resist swelling, are presumably weaker and fewer in number.