Water Imbibition Experiments Research Articles

Seed Dormancy Class and Germination Characteristics of Berberis amurensis var. latifolia Nakai, Native to Korea

Berberis amurensis var. latifolia Nakai is a plant native to the Ulleung Island in Korea. In this study, we aimed to identify seed dormancy-breaking and germination requirements of this species using water imbibition experiments, gibberellic acid (GA3) treatment (0, 10, 100, or 1000 mg/L), cold stratification (0, 2, 4, 8, or 12 weeks at 5 °C), move-along experiments, and phenological studies. In the water imbibition experiment, the seed weight increased by more than 120% after 24 h. Analysis of the internal morphological characteristics of the seeds revealed that the embryo in freshly matured seeds was fully grown and did not grow thereafter. The final germination percentages after 12 weeks of cold stratification at 5 °C were 49 ± 6.4% and 63 ± 3.4% under light and dark conditions, respectively. In move-along and phenological studies, a longer cold stratification treatment period resulted in a higher germination percentage; however, the warm stratification treatment did not affect germination significantly. The GA3 treatment had little effect on seed germination. Therefore, we concluded that B. amurensis var. latifolia seeds have intermediate physiological dormancy, and pre-treatment with cold stratification for 12 weeks and incubation in the dark are required for effective seed propagation.

Rapid assessment of water phase trapping on gas permeability reduction in typical tight gas reservoirs in China

Water phase trapping (WPT) is one of the primary formation damage issues which can cause a steep drop in tight gas production. This paper presented a rapid assessment of the damage potential of WPT in Daniudi, Nanpu 5th, and Keshen 9th tight gas reservoirs involving shallow to ultra-deep layers in China. Typical core samples of the three tight gas reservoirs were selected to perform water imbibition and drainage experiments to mimic the WPT occurrence. After that, the damage degree to core gas permeability induced by WPT was evaluated. Results showed that, for a 16-h vertical water imbibition experiment, the core samples of Daniudi gas reservoir experienced the fastest water imbibition process while the core samples of Keshen 9th gas reservoir established the highest water saturation. After water removal, the ranges of damage degree to core gas permeability induced by the incremental water saturation were 36.07%–78.13%, 36.06%–56.21%, and 61.00%–76.30% in Daniudi, Nanpu 5th, and Keshen 9th tight gas reservoirs, respectively. It found that with the increasing formation depth, tight gas reservoirs can suffer greater damage from WPT not only because of the decline in rock permeability but also the salting out of high salinity formation water. In general, it holds that strong water capillary imbibition phenomenon, low water removal capacity, and high gas permeability damage degree are found to be the striking features of WPT potential on these typical tight gas reservoirs in China.

Effects of Fracturing Fluids Imbibition on CBM Recovery: In Terms of Methane Desorption and Diffusion

Summary Hydraulic fracturing technology has been widely used to improve the productivity of the coalbed methane (CBM) reservoir, during which tons of fracturing fluids infiltrate the coal seam. However, the effects of fracturing fluids imbibition on CBM recovery are still unclear. In this study, spontaneous and forced water imbibition experiments in methane-bearing low-volatile bituminous (LVB) coal were conducted at various gas adsorption equilibrium pressures, following which methane desorption and diffusion experiments were performed. These experiments simulated the complete process of fracturing fluid imbibition during well shut-in and subsequent methane production upon reopening, which is helpful in understanding the impact of fracturing fluid imbibition on CBM production. The results show that water imbibition displaces adsorbed methane in the coal matrix, and with reservoir pressure increasing, the displaced effect decreases. Furthermore, the forced imbibition (FI) displaces less methane than the spontaneous imbibition (SI) due to water rapidly filling fractures and blocking methane migration out of the matrix in the FI. In the initial stages of gas production following spontaneous or forced water imbibition, the displaced methane diffuses out of the coal at a rapid rate and then slows down. Furthermore, in the case of FI, a significant amount of residual gas remains after desorption and diffusion due to the water blocking effect. However, the water blocking effect has a minimal impact on coal undergoing SI. In terms of desorption and diffusion, this study provides a comprehensive understanding of the effects of fracturing fluids imbibition on recovery of CBM, which is useful for practical shut-in operations following hydraulic fracturing in LVB coal seams.

Dynamic monitoring of dielectric properties during two phase immiscible displacements in sand packs using frequency domain electromagnetic sweeps

Electromagnetic heating is a promising soil remediation method especially in thin formations. The lack of a wide-spread adoption of this method stems from insufficient knowledge of how the complex dielectric properties, that govern propagation of the electromagnetic waves through porous media, change with changing frequency, water saturation, displacement types and flow regimes. To breach these gaps several sets of spontaneous deionized (DI) water imbibition experiments, followed by the primary drainage floods, that were followed by the secondary DI water imbibition floods in confined uniform sand packs were performed. The frequency domain relative dielectric constant and conductivities were extracted from the two-port complex S-parameter measurements taken with the vector network analyzer during these immiscible displacements at various water saturation levels at ambient conditions. A novel coaxial transmission line core holder was designed and commissioned, and a modified version of a plane-invariant dielectric extraction algorithm was developed for this purpose. Series, parallel and semi-disperse mixing models were applied to fit the water saturation dependent relative dielectric constant and conductivity values sampled at 500 MHz from the extracted frequency domain spectra. The Maxwell-Garnett parallel model was proved to be the most flexible because it could capture the sampled conductivity values in all secondary imbibition floods before and after the breakthroughs, where the inflection points were observed. These inflection points were attributed to silica production and a potential shear-stripping flow. This observation was further confirmed by conducting a single-phase Darcy's law analysis of two DI water imbibition floods.

Percolation transitions of spontaneous imbibition in fractional-wet porous media

Percolation transition is an important scientific question for characterizing complex two-phase flow phenomena in fractional-wet porous media composed of different wetting grains. Recent studies have shown significant transitions of fluid distribution and pressure system in fractional-wet porous media by changing wettability proportion. However, very few studies have systematically investigated controlling factors of percolation transition in spontaneous imbibition. Additionally, there is a lack of comprehensive knowledge and experimental observations about imbibition recovery and dynamic imbibition phenomena (including imbibition time, imbibition rate, and induction time) in fractional-wet porous media. In this study, these knowledge gaps are filled through a series of water imbibition experiments for fractional-wet artificial porous media with different water-wet proportions, three pore diameters, and two wettability heterogeneities. The results show that pore diameter and wettability heterogeneity are influential factors for percolation transition. Decreasing water-wet proportion results in the emergence of induction time, as well as the absences of transition and late imbibition stage, small pore radius enhances these negative impacts. Under strong wettability heterogeneity, relationship of water-wet proportion and imbibition recovery follows the classical percolation theory containing two percolation transitions. Small pore diameter retards percolation transitions, and weakens fluid displacements of the transition stage and late stage in the partial imbibition. Moreover, effects of water-wet proportion on dynamic imbibition phenomena exhibit exponential relationship resulted from transition of pathway type. Additionally, through decreasing wettability heterogeneity, three percolation transitions and an optimal imbibition ability are achieved, thus hydrophilization of hydrophobic pore is advantageous for water imbibition. These intriguing findings can broaden current knowledge about spontaneous imbibition in fractional-wet porous media.

Impacts of mineralogy and pore structure on spontaneous imbibition in tight glutenite reservoirs

Spontaneous imbibition plays a critical role in the two-phase flow in hydraulic fractures of tight reservoirs. Although massive contributions have been devoted to addressing this issue, very few studies focus on tight glutenite reservoirs, which is an important member of tight reservoirs. As a result, the imbibition mechanism and its influencing factors are still unclear, several key factors fail to be captured, and in-depth analyses are lacking in spontaneous imbibition for tight glutenite reservoirs. In light of the current knowledge gaps, this study conducted a series of water imbibition experiments, combined with X-ray diffraction tests, thin section and scanning electron microscopy observations, high-pressure mercury intrusion experiments, and corrected contact angle experiments to reveal the impacts of rock mineralogy and pore structure on spontaneous imbibition, and significance levels of main influential factors were determined by grey relation analysis. Results show that: 1) the hydrophilic mineral that exceeds 94% provides a strong driving force for water imbibition. Intergranular pore and gravel boost imbibition recovery through enhancing imbibition and drainage ability, respectively. However, intergranular dissolved pore is unfavorable for water imbibition due to extremely rough surface and small radius. Medium-size sand also has a negative impact because of incremental flow tortuosity and pore coordination number reduction; 2) A large percentage of micropore and macropore can significantly enhance imbibition rate and recovery. Three fractal characteristics in micropore, identified for the first time, complicates water imbibition process in tight glutenites. A critical total fractal dimension of micropore is observed, above which the negative influence magnitude of complex pore structure on spontaneous imbibition gradually decreases; 3) Water imbibition sequence and diversities of imbibition phenomena are significantly affected by the combination of multi-fractal dimensions and heterogeneous distributions of pore volume in different fractal regions. The superposition of smallest fractal dimension and the largest pore volume leads to the best imbibition recovery in the transition stage of imbibition, which is an extremely time-consuming process; 4) Upon grey relation analysis, oil drainage ability is the most critical factor for water imbibition in tight glutenites. These observations deepen our understanding of the distinctive imbibition mechanisms in tight glutenite reservoirs.

Effects of pH and aging on the texture and physicochemical properties of extruded pea protein isolate

Pea protein isolate (PPI) matrices were extruded at a water content of 50%w/w with the pH of the hydrated PPI adjusted to values between 5 and 9. The impact of the pH on the microstructure, mechanical and swelling of the extrudates was investigated by scanning electron microscopy (SEM), texture analysis and water imbibition experiments. We find that the hardness of the extruded PPI matrices as determined by texture profile analysis (TPA) decreases by ∼50% when the pH is increased from 5 to 9, while the water holding capacity (WHC) is observed to increase linearly from 126% ± 6% w/w on dry basis at pH = 5–442% ± 10% w/w on dry basis at pH = 9. The hardness of the extruded matrices at their WHC is observed to linearly decrease with the WHC. This is explained by a gradual loosening of the matrix as the balance of intermolecular forces shifts from hydrophobic to electrostatic with increasing pH. The extruded PPI matrices are swelling in an anisotropic manner when exposed to pH-adjusted water, with the longitudinal swelling strain being significantly larger than the transversal swelling strain, in particular towards lower values of the pH. Significant aging of the extruded matrices was observed for the first two days following extrusion. Owing to aging, the hardness of the matrices was observed to increase by between 18% (pH = 9) and 23% (pH = 7). Thus, the pH as well as aging are two novel parameters that can be exploited in optimizing the mechanical properties and water holding capacity of extruded PPI matrices, for instance for use in meat analogues.

Water imbibition and water sealing in water-driven gas reservoirs development

To improve the poor understanding of the mechanism of spontaneous water imbibition in water invasion in gas reservoirs and overcome the difficulty in quantifying imbibed water and its impact on reservoir development, a study is carried out based on development simulation experiments and theoretical analysis of fluid mechanics. Spontaneous water imbibition is an important mechanical mechanism for the formation of a water seal zone in a low-permeability matrix through water invasion in gas reservoirs. Water imbibition experiments into the reservoir were carried out to clarify the trends of the imbibed distance and imbibed fluid volume to establish the theoretical model of imbibition and to make experimental corrections. An application study was performed based on the understanding of water imbibition and water sealing mechanisms and the building of an imbibition model. The water seal zones formed by imbibition during exploitation are predicted, and the seal-breaking pressure and influx of imbibed water in the water seal zone are evaluated. The research findings fully revealed the large impact of water imbibition on the development of water-driven gas reservoirs, providing technical support for the assessment of water sealing and the establishment of water control measures in water-driven gas reservoirs.

Parameter Prediction of Water Imbibition in Unsaturated Shales Using the NMR Method

Although the hydraulic fracturing treatment can improve the conductivity of shale reservoirs, the low recovery rate of the fracturing fluid may cause potential environmental and production issues. For an accurate investigation of these issues, an appropriate model of the water imbibition in shales is required. However, the hydraulic parameters related to water imbibition in shales are hard to be measured due to their tiny pores. In this study, an effective method is proposed to estimate the water imbibition volume. The nuclear magnetic resonance method is applied to obtain the related parameters including the capillary curve, the intrinsic and relative permeability of the shale, which can significantly cut down the time and cost needed to get these data. This model is validated by water imbibition experiments. In addition, we compare two empirical equations used to calculate intrinsic permeability in the NMR method and calibrate the corresponding parameter a for shale, which is poorly investigated in literature. Finally, we suggest that the capillary force dominates the early stage of water imbibition process in unsaturated shales, and the late period may be influenced more by other mechanisms such as the osmosis and the surface hydration.

Evaluation of wettabilities and pores in tight oil reservoirs by a new experimental design

Understanding different types of pores and their wettability conditions in tight oil reservoirs is a crucial step in evaluating oil accumulation and migration process of these energy resources. Nuclear magnetic resonance (NMR) technique has been widely used in conventional reservoirs to study rock properties including porosity, permeability, pore structures, and wettability. However, the existence of high contents of organic matter and complicated NMR relaxation mechanisms pose considerable challenges on interpreting the NMR results of tight oil reservoirs. In this study, we performed NMR measurements on rock samples under different fluid saturation states and combined the results with imbibition methods as the novel experimental procedure to characterize wettability and pores of tight oil reservoirs. 1D and 2D NMR experiments were first conducted on core samples at four different fluid saturation states including water-saturated state, after-centrifuge state, 80 °C oven-dried state, and 140 °C oven-dried state. Then, we investigated the unmovable hydrogen-bearing matters by monitoring the loss of NMR signal in the four saturation states. In the next step, pores having different wettability conditions were investigated based on the NMR results of oil imbibition and water imbibition experiments. The results showed that while the transverse relaxation behavior of the tight oil rock samples were different from each other, hydrocarbon-wet pores, mix-wet pores and water-wet pores coexisted in these samples. NMR relaxation of oil in hydrocarbon-wet organic pores happened to be the fastest relaxation mechanism compared to other types of pores, and the peak transverse relaxation time was about 0.13 ms. In addition, our experimental results revealed the existence of intermolecular homonuclear dipolar coupling between organic matters and fluids.

Produced Flowback Salts vs. Induced-Fracture Interface: A Field and Laboratory Study

Summary The water recovered from hydraulic-fracturing operations (i.e., flowback water) is highly saline, and can be analyzed for reservoir characterization. Past studies measured ion-concentration data during imbibition experiments to explain the production of saline flowback water. However, the reported laboratory data of ion concentration are approximately three orders of magnitude lower than those reported in the field. It has been hypothesized that the significant surface area created by hydraulic-fracturing operations is one of the primary reasons for the highly saline flowback water. In this study, we investigate shale/water interactions by measuring the mass of total ion produced (TIP) during water-imbibition experiments. We conduct two sets of imbibition experiments at low-temperature/low-pressure (LT/LP) and high-temperature and high-pressure (HT/HP) conditions. We study the effects of rock surface area (As), temperature, and pressure on TIP during imbibition experiments. Laboratory results indicate that pressure does not have a significant effect on TIP, whereas increasing As and temperature both increase TIP. We use the flowback-chemical data and the laboratory data of ion concentration to estimate the fracture surface area (Af) for two wells completed in the Horn River Basin (HRB), Canada. For both wells, the estimated Af values from LT/LP and HT/HP test results have similar orders of magnitude (approximately 5.0×106 m2) compared with those calculated from production and flowback rate-transient analysis (RTA) (approximately 106 m2). The proposed scaleup procedure can be used as an alternative approach for a quick estimation of Af using early-flowback chemical data.

Reply to Comment by Y. Kovalyshen on “Ultrasonic Monitoring of Spontaneous Imbibition Experiments: Precursory Moisture Diffusion Effects Ahead of Water Front”

AbstractWe tested on a data set including 12 different rocks the assumption that, during water imbibition experiments, the interaction between direct P waves and reflected P waves on the imbibition front could explain the early P wave amplitude variation occurring before any velocity variation. Our calculations show that (i) the observed distance between the water front and the ultrasonic sensors is always larger than the estimated critical distance below which the first peak amplitude is impacted by the reflected P wave, (ii) the magnitude of the coefficients of reflection is generally very small, and (iii) using simulations of composite waveforms, an impact on the first peak amplitude is expected only in 25% of the tested samples. P wave interaction is definitively a mechanism which can lead to amplitude variations, but it is very likely that such a mechanism is not responsible for the early amplitude variation detected in most of the tested rocks. Moisture diffusion is still a very relevant mechanism to account for our observations on P wave amplitude variations during capillary rise.

Effects of Dissolved Oxygen on Water Imbibition in Gas Shales

Understanding the water uptake of gas shales is critical for designing and optimizing hydraulic fracturing operations during which a large volume of fracturing water containing dissolved oxygen is injected into tight reservoirs. Recent studies show that the dissolved oxygen may promote oxidation reactions which can affect salinity and pH value of flowback water; however, the effects of dissolved oxygen and oxidation reactions on water imbibition into the shale matrix and on the concentration of individual ions in flowback water are still poorly understood. In this study, we conduct water imbibition experiments under degassed and oxic conditions, and measure the imbibed water mass and concentrations of different ions in water. The results show that the initial rate and final amount of water imbibition are higher under degassed conditions compared with that under oxic conditions. These differences are mainly due to the enhanced dissolution of air in the shale pore network into the imbibing water under degas...

Water sorption behaviour of gas shales: I. Role of clays

In this study, we investigate the role of clays on water sorption (adsorption and desorption) behaviour of gas shale samples. First, we conduct conventional sorption experiments on downhole shale samples by placing them in a controlled relative-humidity (RH) chamber. The full sorption cycle is obtained by step-wise increasing of RH from 0 to 1 followed by decreasing RH from 1 to 0 for obtaining adsorption and desorption isotherms, respectively. The results reveal that the samples with higher clay content have (i) higher amount of water adsorption, (ii) faster initial adsorption rate, and (iii) more water retention at the end of the desorption process (i.e. more hysteresis). We propose a modified sorption technique to account for water adsorption of clays by adding an early sorption cycle to the conventional method. In the modified process, the sample first goes through a cycle of adsorption at RH≈0.215 followed by desorption at RH≈0 (early sorption cycle). Then, we place the samples in a controlled-RH chamber for a full sorption experiment; which is adsorption from RH≈0 to RH≈1, followed by desorption to RH≈0. The results of the early sorption cycle show similar trends to those we observed from the conventional sorption experiments. However, in the subsequent full sorption cycle (the modified adsorption and desorption isotherms), (i) the initial adsorption rate tends to be independent of clay content and (ii) the hysteresis is less significant for samples with higher clay content. These observations suggest that clays tend to remain saturated by water during the early sorption cycle in the modified technique. Moreover, we conduct spontaneous water imbibition experiments using deionized water to compare the total water uptake by imbibition and adsorption processes. The results indicate that for our samples, spontaneous water imbibition is always faster and yields higher water saturation compared to the water adsorption process. These observations suggest that water molecules probably cannot condense in all pores during water adsorption process. Additionally, the excess water saturation achieved by imbibition process increases by increasing the clay content. This observation suggests that water adsorption by clays (and the potential subsequent swelling and micro-fracture induction) is more prominent during imbibition process compared with that during adsorption process.

Initial water saturation and imbibition fluid affect spontaneous imbibition into Barnett shale samples

Spontaneous imbibition has been widely investigated due to its significant impact on gas/oil recovery from conventional sandstone and carbonate reservoirs. Unlike conventional reservoir rocks with relative high porosity and permeability, shale is characterized by its low porosity (<10%), ultra-low permeability (∼10−18–10−23 m2), complex wettability, and strong heterogeneity at multiple scales. This study is to understand the effects of initial water saturation and imbibing fluid on spontaneous imbibition of Barnett shale core samples taken from three different depths of Blakely #1 well in Wise County of Texas. Two partial, and yet uniform, water saturations of shale samples were achieved by equilibrating the samples inside closed containers at specific relative humidity controlled with over-saturated salts. The effect of imbibing fluids (water or oil-phase n-decane) on spontaneous imbibition behavior is evaluated by conducting replicate experiments. Our results show that the spontaneous imbibition behavior of shale samples could be affected by the initial water saturation conditions, and the effects are different for shale samples with different mineral compositions. The imbibition curves of shale samples with a high clay content show a poor reproducibility during water imbibition experiments due to the water sensitivity of clay minerals. In addition, n-decane could not be completely removed after its imbibition experiment. The interaction between remnant n-decane and shale matrix may change the sample wettability towards more oil-wet, which is indicated by a higher imbibition slope of second n-decane imbibition experiment on the same sample. Overall, this work helps understand the mechanism controlling fluid loss and ultimate gas/oil recovery in unconventional hydrocarbon exploration, which is significant for optimizing the selection of fracturing and treatment fluids to enhance recovery rate and minimize environmental risk.

Laboratory and field analysis of flowback water from gas shales

Flowback water is usually highly saline and the salt concentration varies by time and well location. Understanding the origin of the flowback salts is essential for evaluating fracturing and flowback processes. In this study, laboratory and field analyses are performed to investigate the origin of the flowback salts. The field data includes the total salt concentration (salinity), individual ion concentration, pH, and dissolved oxygen measured during the flowback process for three wells completed in the Horn River Basin. The rock mineralogy is determined using XRD. The cation exchange capacity (CEC) of shale samples are measured using ammonium acetate method. Water and oil imbibition experiments are conducted for shale samples of different surface-to-volume ratio. The individual ion concentration is measured during the water imbibition experiments using ICP–MS and IC. EDXS analysis is used to investigate the surface of natural fractures.Noticeable amount of barium found on the surface of natural fractures suggests that the barium in the flowback water primarily originates from the natural fractures. Furthermore, the samples with higher clay content have higher CEC. During the water imbibition process, these samples have higher and faster ion transfer from shale-to-water; suggesting the mobilization of the exchangeable ions from the clays. During the water imbibition experiment, the Na/Cl and K/Cl ratios are initially high and decrease at the later times. Leaching of the exchangeable sodium and potassium ions from the clay minerals is a possible reason for the initial high Na/Cl and K/Cl molar ratios. The dissolution of chloride-bearing components increases the chloride concentration, which decreases the Na/Cl and K/Cl molar ratios at later times. The measured pH is slightly above 8 for all of the flowback water samples. The presence of natural buffer systems such as calcite and dolomite may explain the neutral pH range of the flowback water.

Advanced Water Management in PEFCs: Diffusion Layers with Patterned Wettability II. Measurement of Capillary Pressure Characteristic with Neutron and Synchrotron Imaging

In this paper, we present an experimental study on the development of gas diffusion layer (GDL) materials for fuel cells with dedicated water removal pathways generated using radiation induced grafting of hydrophilic compounds onto the hydrophobic polymer coating. The impact of several material parameters was studied: the carbon substrate type, the coating load, the grafted chemical compound and the pattern design (width and separation of the hydrophilic pathways). The corresponding materials were characterized for their capillary pressure characteristic during water imbibition experiments, in which we also evidenced the differences between injection from a narrow distribution channel in the center of the material (and thus strongly relying on lateral transport) and homogeneous injection from one face of the material. All materials parameters were observed to have a significant influence on the water distribution. In particular, the type of substrate has a dramatic impact, with results ranging from a nearly perfect separation of water between hydrophilic and hydrophobic domains for substrates having a narrow pore size distribution to a fully random imbibition of the material for substrates having a broad pore size distribution.

Matrix Acidizing Characteristics in Shale Formations

Matrix acidizing is typically used to remove drilling and completion damage to reservoir conductivity around the wellbore and dissolve calcite in natural fractures. Despite being a common procedure, few studies have investigated the effect of matrix acidizing on the physical properties and oil recovery factors in shales. This paper describes the effect of HCl acid on porosity, spontaneous imbibition, mechanical properties, and crack distribution in samples from the Eagle Ford, Mancos, Barnett and Marcellus shale formations. Some of the samples were completely immersed in different HCl solutions (1-3 wt%) at 93°C. We measured the porosity in both the acid-treated and non-treated samples. The treated and non-treated samples were then exposed to spontaneous water imbibition experiments to measure the improvement in oil recovery in both parallel and perpendicular to bedding planes. The mechanical properties of the acid-treated and non-treated samples were also measured in both parallel and perpendicular to bedding planes using the same acid concentrations. The samples were 2.54 and 3.81 cm in diameter and 2.54 to 5.08 cm in length. The measured porosities were 1-3% for the non-treated samples and 1.3-10.5% for the treated samples. We observed that the oil recovery factors of the spontaneous imbibition for the samples treated with acid were 47% from Eagle Ford, 53% from Mancos, 28% from Barnett, and 38% from Marcellus. The recovery factors from the non-treated samples were 12% from Eagle Ford, 4% from Mancos, 13% from Barnett, and 3% from Marcellus. Furthermore, we observed that spontaneous imbibition parallel to bedding planes is higher than imbibition in perpendicular to bedding planes direction, especially for Marcellus samples where the recovery factors varied from 4% for the samples drilled parallel to bedding planes to 38% for the samples drilled in perpendicular to bedding planes. Eagle Ford and Mancos samples showed a reduction in confining compressive strength ranging from 50- 60% when exposed to 3 wt% HCl solutions with more reduction in the samples drilled parallel to bedding planes.

New Insight into Wettability Alteration to Gas Wetness: Core Experiment and Modeling

Many attentions have been paid on wettability alteration to gas wetness since it is widely concerned in 2000. Although many researchers tried to explain or realize such phenomenon, several problems have not been resolved now including possibility and mechanism of wettability alteration in water saturated cores. In this study, new insight is made into wettability alteration to gas wetness, both experimental and simulate. A serial of spontaneous water imbibition experiments are conducted to evaluate applicability of wattability alteration in different water saturated cores. SEM observation indicates microcosmic mechanism by compare of pore surface before and after chemical treatment. Numerical simulation in Eclipse gives theoretical evidence of wettability alteration phenomenon and also proves almost the same result with that in spontaneous water imbibition experiments.

A Study of Microscale Gas Trapping Using Etched Silicon Micromodels

Immobilization and trapping of carbon dioxide (CO2) enhances the security of geological storage. Trapping mechanisms have been characterized in four groups: structural, residual, dissolution, and mineralization. While structural trapping acts immediately when injection starts and is well investigated, the contribution of residual and dissolution trapping increases over storage time and these contributions need to be better understood for better predictions. This paper focuses on an experimental pore-scale investigation of residual and capillary trapping. CO2–water imbibition experiments were conducted in micromodels whose homogenous pore space is geometrically and topologically similar to Berea sandstone. Microvisual data, photographs and video footage, describes the trapping mechanism and, especially, the disconnection and shrinkage of the CO2 phase. Results show that depending on the flow rate of the imbibing water different trapping mechanisms are observed. Lower flow rates, comparable to the trailing edge of a CO2 plume, lead to more snap-off events and greater trapped residual saturation, whereas rates comparable to the near wellbore area during enhanced sequestration showed displacement of gas bubbles and greater dissolution that ultimately leads to very low or zero gas saturations. Furthermore, complete dissolution events showed that homogenous as well as heterogeneous dissolution occurs. Whereas the latter is subdivided into microbubble formation and dissolution on crevices or pore roughness, the former occurs without the influence of pore walls. Based on the observations we suggest that the type of rock and its roughness as well as the fines present at the CO2 brine interface are important factors determining the dissolution mechanism.