United States Bureau Of Mines Research Articles

Time-dependent variations in desorbed gas composition: methodological analysis of asphaltite vein investigation results

In this study, a phenomenon that can have significant technical and economic impacts in the mining and unconventional gas production of hydrocarbon resources is discussed, change of gas composition during desorption period. The change is analyzed, related findings are obtained and engineering tools are forged. In this scope, a member of the Southeastern Turkey asphaltite’s gas content and composition character was examined. 12+1 samples were collected at equal intervals from an inclined drillhole that cut through the asphaltite vein. The United States Bureau of Mines (USBM) direct method was employed to determine the gas content. Gas composition analysis was performed on gas samples, which were collected four times throughout the desorption period. Residual gas composition is determined as well. During desorption period, methane and hydrogen ratios exhibited decreasing trends, while others have increasing trends. In evaluating of the collected data, the desorption order between gas compounds are revealed. Logarithmic trend functions are generated to estimate the concentrations of gas compounds at specific time points. With these functions and gas content measurement data, weighted average concentrations for gas compounds are determined. These concentration functions and the weighted average results are used to create engineering tools showing unit energy content of desorbed gas through desorption period both instantaneous and cumulative. Similarly, change in lower explosive limit and auto-ignition temperature during desoption period is shown. The weighted average gas concentrations obtained are used to interpret geological insights as they are the actual gas composition of the samples. In the study, gas content characteristic properties of Üçkardeşler asphaltite vein is comprehensively presented. Accordingly, the mean gas content, excluding one sample with a value of 2.78 m3/t at a location near a fault intersection, was found to be 1.66 m3/t. The average volumetric concentrations of methane, ethane, propane, and acetylene in the desorbed gas were determined as 61.6%, 24.5%, 10.7%, and 2.3%, respectively. The remaining part primarily consisted of heavier hydrocarbons, with low amounts of carbon dioxide and hydrogen.

An Integrated Overview of Blasting Damage Criteria for Engineering Structures

Blasting applications are frequently used during the construction of engineering structures. In our country, damage assessment criteria created by reference to the Report of Investigations RI 8507 prepared by the United States Bureau of Mines (USBM) are used to control the impact of blast vibrations on existing structures or structures under construction. In this study, the structures in the database of that report of investigation and the points on which the damage criteria are based are examined. Moreover, in the light of the other studies carried out by different researchers about the blast damage criteria in engineering structures, the requirement of reevaluation of USBM damage criteria for reinforced concrete buildings, tunnels, pipelines and other engineering structures has been revealed.

Predicting different components of blast-induced ground vibration using earthworm optimisation-based adaptive neuro-fuzzy inference system

ABSTRACT This study focuses on addressing the complexity inherent in various amplitude components of blast-induced ground vibration (BIGV), encompassing vertical, radial, transversal, and the vectoral sum of PPVs of particle velocity. It takes into account their nonlinearity across diverse quarry environments, and aims to present an enhanced nonlinear intelligent system for accurate prediction of these components. Multiple artificial intelligence models were explored and developed for this purpose, including a support vector machine (SVM), an adaptive neural network based on the fuzzy inference system (ANFIS), and a novel hybrid model that combines earthworm optimisation (EO) and ANFIS (EO-ANFIS). The study also leverages the empirical model offered by the United States Bureau of Mines. The outcomes highlighted that the predictions of the three individual components prove to be more accurate compared to the vectoral sum of PPVs of particle velocity. However, the latter remains a valuable metric for evaluating the magnitude of BIGV in open-pit mines. Notably, the hybrid EO-ANFIS model emerges as the most accurate, achieving an impressive ~ 75% accuracy across 10 quarries characterised by distinct geological conditions.

Computation of Surface Wave Parameters and Peak Particle Velocity

In recent times, the rise in terrorist activities has underscored the critical need for designing structures with blast resistance capabilities. However, many Indian codes currently in place do not adequately address the issue of blast loads. This knowledge gap poses a significant challenge to engineers who must ensure the safety and security of structures against such threats. In light of this, the objective of this study is to provide an educational resource to bridge this gap by exploring various methods for calculating blast loads on structures. This paper delves into the subject matter, discussing different methodologies and approaches for estimating blast loads on structures, with a specific focus on the Unified Facilities Criteria (UFC) guidelines. To illustrate the practical application, a numerical example is presented, demonstrating the computation of blast loads on structures using the UFC guidelines. Notably, the results reveal that the surface blast load exhibits an exponential variation along the front wall of the structure. Furthermore, the study introduces the concept of peak particle velocity (PPV) as a parameter for identifying the threshold vibration level that would cause no structural damage. The methodology suggested by the United States Bureau of Mines (USBM) is adopted to calculate the PPV and the corresponding results are presented. By providing insights into blast load computation and the determination of safe vibration levels, this study contributes to enhancing the understanding and preparedness of engineers when it comes to designing structures that can withstand and mitigate the destructive effects of blasts.

A data-driven approach for the prediction of coal seam gas content using machine learning techniques

A new data-driven approach to interpreting the nonlinear problem of total desorbed gas content analysis of coal seams is presented in this study. The study focuses on a low-rank coal reserve located in the Kınık coalfield, which was investigated using the United States Bureau of Mines (USBM) direct desorption method to anticipate the total desorbed gas content of coal seams for underground mining operations. The core samples collected during the reserve and gas content analysis were used to feed machine learning models, which were trained using coal properties data such as depth, moisture, ash, volatile matter, and calorific value, in relation to total desorbed gas content. Multiple linear regression, support vector machine, and artificial neural network were employed to predict the total desorbed gas content of coal seams in the Kınık coalfield. The machine learning models were optimized using hyperparameter tuning, and the most successful model was selected based on its regression and computational cost performance. Sensitivity analysis was conducted to investigate the performance of the coal properties on total desorbed gas content. The selected model was then utilized for predicting the total desorbed gas content of coal seams at a single point in the coalfield. The findings of this study provide insights and guidelines for unconventional reservoir analysis and petrophysical system prediction using machine learning methods. Overall, this study demonstrates the potential of machine learning in addressing nonlinear problems in the field of geology and provides a promising approach for future research in this area.

Comparison and Verification of Gas-Bearing Parameter Evaluation Methods for Deep Shale Based on the Pressure Coring Technique

Gas-bearing properties, such as gas-in-place (GIP) content and adsorbed gas ratio (AGR), have drawn considerable attention because they are essential for shale gas resource evaluation and sweet spot forecasting. The above-mentioned metrics have been determined using a variety of approaches, but they lack systematic comparison and accuracy verification, particularly for deep shale gas, where conventional methods frequently fall short. A total of 30 shales were taken for the investigation utilizing pressure and conventional coring methods from Wufeng and Longmaxi Formations in the Sichuan Basin, China. For pressure coring samples, we developed the experimental protocols and a GIP content classification scheme that categorizes the GIP content into four categories: lost gas (estimated using the temperature-corrected pressure-holding ratio), extracted gas from depressurization, degassed gas, and residual gas. The four pressure coring samples from well Y206 with measured GIP content range from 2.84 to 5.58 m3/tonne, with an average of 4.72 m3/tonne. In contrast to the calculated GIP content of the pressure coring samples, the validity of the current GIP content evaluation methodologies has been confirmed. The comparison results demonstrate that the GIP content assessed using the United States Bureau of Mines (USBM) method is frequently underestimated for samples from conventional coring and notably overstated for samples from pressure coring. The polynomial fitting method dramatically overestimated the GIP content. With its accurate time-dependent boundary conditions and strict theoretical foundation, the simplified carbon isotope fractionation (s-CIF) model exhibits the highest level of accuracy in determining GIP content. Additionally, the s-CIF model can find yet another crucial parameter of AGR. Shale samples from well Y206 had an average AGR of 20.4% but a range from 12.2 to 33.2%. The examination of the influencing factors demonstrates that the lost gas ratio, AGR, and diffusion coefficient are responsible for controlling the calculation error of the USBM method. The lost gas ratio prior to core retrieval increases with decreasing AGR (or increasing diffusion coefficient), which increases the computation error of the USBM method.

Interpretation Method for Lost Gas in Deep Coalbed and Its Application

The gas loss time during the deep coalbed coring process is long. The measured desorption curve does not meet the application conditions for the classical United States Bureau of Mines (USBM) method. However, the industry still lacks a reliable interpretation method, which affects identifying deep coalbed methane reserves and optimizing sweet spots. (Method) The classical double-porosity and double-permeability theoretical model was adopted, and the influence of reservoir permeability, water saturation, and temperature on gas output in the coalbed desorption process was considered. Based on the measured field desorption data of the P1 sample of the No. 8 coal in the Benxi Formation on the eastern margin of Ordos, the entire process for the deep coalbed gas content test was numerically simulated. (Results) The simulation results show that the lost gas in the P1 sample accounts for 24.7% of the total gas, reaching 8.64 m3/t, including 18.81% of loss in wellbore lifting and 5.88% of loss during surface exposure. The total gas content of the sample is 35.34 m3/t. The P1 sample contains free gas, with a content of 9.71 m3/t, and the ratio between adsorbed and free gas is close to 7:3. Matrix permeability, initial gas saturation, and lifting time are the key factors that determine the amount of lost gas. The results of deep coalbed gas loss calculated by the USBM method were excessively large, approximately twice that calculated using the new method. The total gas content calculated based on multiple parameters is consistent with the interpretation results of the new method, with an average error of approximately 7%. (Conclusion) The interpretation method of gas loss in deep coalbeds has acceptable reliability and can be applied in shale gas content testing.

Analysis of the application of methane-bearing capacity test methods in the conditions of Polish mining

The methane hazard is one of the natural hazards occurring in hard coal mining. The content of natural methane in hard coal seams, the so-called methane-bearing capacity, is one of the key parameters that allow for proper assessment of the methane hazard and the state of the threat of gas and rock outbursts. For safety purposes, there is a constant need to improve the methods for the determination of this parameter. In the conditions of Polish mining, the method used for methane-bearing capacity determination is the direct drill cuttings method. This paper contains a comparative study presenting three different methods of methane-bearing capacity determination. Tests were conducted using two direct methods (the drill cuttings method and the United States Bureau of Mines (USBM) method), and the indirect method based on the desorption intensity index. On the basis of the obtained test results, it was found that the results obtained with the USBM method were slightly higher than those obtained with the direct drill cuttings method. Gas losses, an important element affecting the final value of the assay, were also analysed. This comparative study will evaluate the validity and applicability of the above methods under specific conditions in hard coal mining.

Prediction of Peak Particle Velocity of Blast-induced Ground Vibrations using Boosted Regression Trees Authored

Loosening of rockmass during its excavation in an infrastructure project is carried by rock blasting. The blast-induced ground vibrations pose a major challenge to the blasting engineers, whose main objective is to control their potential to cause any damage to the buildings in the vicinity. The research reported in this paper explains how the error in the prediction of the Peak Particle Velocity (PPV) by the United States Bureau of Mines (USBM)-based approach can be minimised using machine learning techniques. The complex correlation between the blast parameter and the PPV value has been modelled using the least square boosted decision tree approach after the selection of the best suitable feature has been selected based on the correlation matrix. The proposed model automatically maps the input blast feature (SD) with the target PPV values by aggregating the decision of various weak learners. The generalization of the proposed model has been validated through a 5-fold cross-validation approach using a dataset comprising of two hundred blast records generated by monitoring the blasts at International airport site, Navi Mumbai, India. The assessment of the prognostic ability of the proposed model demonstrates that it has outperformed the USBM-based approach for PPV prediction. The results establish that the predictions by the proposed model are closer to the measured values than the other regression models.

Estimating Lost Gas Content for Shales Considering Real Boundary Conditions during the Core Recovery Process.

Shale gas has become an important natural gas resource in recent years as the conventional oil and gas resources are depleting. Shale gas content is one of the most important parameters for reserve calculation and sweet-spot prediction. The traditional core recovery method is widely used to determine gas content. However, the estimation of lost gas content is the main factor of error and difficulty. Large errors and uncertainties occur when using the widely used methods, such as the United States Bureau of Mines (USBM) method. Hence, a more accurate method is required. In this work, a full-process model is developed in COMSOL Multiphysics to describe the lost gas with time during the core recovery process as well as the desorption stage after the core is covered. In this method, by setting the initial gas pressure and flow parameters and matching the desorbed gas volume and considering variable diffusivity with respect to temperature, the initial gas content and the gas lost with respect to time are calculated. Overall, 10 field data are tested using this full-process model, and the USBM method is also applied to compare the results. It is found that if the ratio of lost gas volume estimated using the USBM method to the desorbed gas volume of the field data is lower than 2.0, the USBM method underestimates the lost gas compared to the full-process method; if the ratio is about 2.0, the results from the USBM and the full-process methods are comparable; and if the ratio is close to 3.0, the USBM method tends to overestimate the lost gas. The modeling results indicate that this proposed full-process method is more theoretically sound than the USBM method, which has high uncertainties depending on the number of desorbed gas data points used. Nevertheless, this proposed method requires a large number of parameters, leading to the difficulty in finding true parameters. Therefore, an optimization algorithm is required. In summary, this study provides theoretical support and a mathematical model for the inversion calculation of lost gas during shale core recovery. It is helpful to evaluate the resource potential and development economics of shale gas more accurately.

The Effect of Blast-Hole Arrangement, Delay Time, and Decoupling Charge on Rock Damage and Vibration Attenuation in Multihole Blasting

Rock damage and vibration attenuation are the basis of blasting design, which will affect rock breaking results and the safety of structures (buildings). In this paper, the effect of blast-hole arrangement, delay time, and decoupling charge on the rock damage and the vibration attenuation in multihole blasting were numerically investigated. Through dynamic analysis software ANSYS/LS-DYNA, the JOHNSON_HOLMQUIST_CONCRETE (JHC) rock model and fluid-solid coupling method were used to establish single-hole and multihole rock blasting models. Based on the analysis of single-hole rock damage and vibration, firstly, the effect of the above three factors on the rock damage characteristics of multihole blasting was analyzed. Then, the extracted peak particle velocity (PPV) data of multihole blasting were fitted to the United States Bureau of Mines (USBM) equation to obtain the blasting vibration attenuation parameters (the site constant K and α). It is found that the blast-hole arrangement, delay time, and decoupling charge have a much smaller effect on α than K. At the same time, a delay-time-dependent model of PPV correction coefficient was proposed, and its rationality was verified by field data. The results obtained in this paper have reference significance for optimizing the blasting design and improving the blasting effect.

A Lasso and Elastic-Net Regularized Generalized Linear Model for Predicting Blast-Induced Air Over-pressure in Open-Pit Mines

Air overpressure (AOp) is one of the products of blastingoperations in open-pit mines which have a great impact on the environmentand public health. It can be dangerous for the lungs, brain, hearing and theother human senses. In addition, the impact on the surroundingenvironment such as the vibration of buildings, break the glass doorsystems are also dangerous agents caused by AOp. Therefore, it should beproperly controlled and forecasted to minimize the impacts on theenvironment and public health. In this paper, a Lasso and Elastic-NetRegularized Generalized Linear Model (GLMNET) was developed forpredicting blast-induced AOp. The United States Bureau of Mines(USBM) empirical technique was also applied to estimate blast-inducedAOp and compare with the developed GLMNET model. Nui Beo open-pitcoal mine, Vietnam was selected as a case study. The performance indicesare used to evaluate the performance of the models, including Root MeanSquare Error (RMSE), Determination Coefficient (R2), and Mean AbsoluteError (MAE). For this aim, 108 blasting events were investigated with theMaximum of explosive charge capacity, monitoring distance, powderfactor, burden, and the length of stemming were considered as inputvariables for predicting AOp. As a result, a robust GLMNET model wasfound for predicting blast-induced AOp with an RMSE of 1.663, R2 of0.975, and MAE of 1.413 on testing datasets. Whereas, the USBMempirical method only reached an RMSE of 2.982, R2 of 0.838, and MAEof 2.162 on testing datasets.

Characteristics of Viscoelastic-Surfactant-Induced Wettability Alteration in Porous Media

Wettability alteration is one of the most important mechanisms of surfactant flooding. In this work, the combined Amott/USBM (United States Bureau of Mines) method was applied to study the average wettability alteration of initially neutral cores after viscoelastic-surfactant (VES) filtration. The effects of static aging, dynamic aging, VES concentration, filtration flow rate, and pore radius on the alteration of a core’s average wettability were studied. The wettability-alteration trends measured by Amott and USBM were consistent, demonstrating that the overall hydrophilicity of the core was enhanced after VES filtration. The wettability alterations of the core brought about by dynamic aging were more significant than by static aging. The viscoelastic properties of the VES played an important role in altering the wettability. In addition, the ability of the VES to affect the core’s wettability was significantly enhanced when the VES concentration was increased, which was beneficial in increasing VES adsorption on the pore-wall surface, thus altering the overall wettability of the core. Increasing filtration flow rates can destroy those high-viscosity VES aggregates via the higher shear rate. A higher retention of VES makes the core more hydrophilic. The difference in the wettability of cores with different pore radius after VES filtration was not significant. The alteration of average wettability caused by VES in porous media provides a new vision for studying the EOR mechanism of VES.

Numerical Simulation Based on the Canister Test for Shale Gas Content Calculation

The accurate determination of the gas in place in shale reservoirs is a basic but challenging issue for shale gas evaluation. Conventional canister gas desorption tests on retrieved core samples and subsequent data analyses (via linear or polynomial regression)—originally developed for coalbed methane, where gases are mainly stored in the adsorbed phase—is unadvisable for shale gas, which is stored as an appreciable amount of free gas in shale reservoirs. In the present study, a mathematical model that simultaneously takes into account gas expansion, adsorption/desorption, and the gas flow in shale is proposed to simulate gas release from a core sample retrieved from the Lower Silurian Longmaxi Formation of the Fuling shale gas field, Sichuan Basin. The results indicate that, compared with the value of 2.11 m3/t rock estimated with the traditional United States Bureau of Mines (USBM) method, the total gas in place within the studied Longmaxi Shale estimated with our mathematical model under reservoir pressure conditions is up to 5.88 m3/t rock, which is more consistent with the result from the new volumetric approach based on Ambrose et al. According to our mathematical model, the content of free gas is 4.11 m3/t rock at true “time zero”, which accounts for 69.9% of the total gas. On the other hand, the lost gas portion is determined to be up to 4.88 m3/t rock (~85% of the total gas). These results suggest that the majority of the free shale gas is actually trapped within the pore space of the shale formation.

CO2 – brine – sandstone wettability evaluation at reservoir conditions via Nuclear Magnetic Resonance measurements

CO2-rock wettability is a key parameter which governs CO2 trapping capacities and containment security in the context of CO2 geo-sequestration schemes. However, significant uncertainties still exist in terms of predicting CO2 rock wettability at true reservoir conditions. This study thus reports on wettability measurements via independent Nuclear Magnetic Resonance (NMR) experiments on sandstone (CO2–brine systems) to quantify Wettability Indices (WI) using the United States Bureau of Mines (USBM) scale. The results show that CO2 (either molecularly dissolved or as a separate supercritical phase) significantly reduced the hydrophilicity of the sandstone from strongly water-wet (WI ≈ 1) to weakly water-wet (WI = 0.26), and associated with that the water-wetness of the rock for the two-phase systems. This was caused by additional protonation of surface silanol groups on the quartz, induced by carbonic acid. Capillary pressure and relative permeability curves and residual CO2 saturation were also measured; these results were compared with literature data, and general consistency was found. NMR T2 distribution measurements also demonstrated preferential water displacement in large pores (r > 1 µm) following scCO2 flooding, while no change was observed for smaller pores (r < 1 µm). These insights add confidence to the assessments of CO2-rock wettability and therefore reduce project risk. This work thus aids in the implementation of large-scale CO2 sequestration.

A novel model to determine gas content in naturally fractured shale

A shale reservoir’s gas content is an indispensable, crucial parameter used in exploration, formation evaluation, block selection and exploitation. Canister gas desorption measurements are used to quantify lost gas volumes that are key to determine the gas content of the reservoir Usually, a lost gas volume is evaluated using the United States Bureau of Mines (USBM) direct method and/or a polynomial curve-fitting method. These methods extrapolate desorption data to time zero in the curve of a cumulative desorption volume versus the square root of time. Lost gas time is the time spent lifting the core out of a hole, handling and placing it inside a canister for evaluation., For cores with densely developed natural fractures, neither the USBM method nor the polynomial curve-fitting method can accurately estimate the lost gas volume if the lifting, handling and canister storage takes a long time. The lost gas period is a non-isothermal gas desorption process; the surrounding temperature keeps declining. Experiments were conducted to determine the methane desorption volumes of a Duvernay shale sample under various pressures and temperatures. Using Boyle’s law and the multilayer adsorption model, a novel mathematical model was built to calculate lost gas volume, including free gas and desorption gas. Because gas desorption is an endothermic procedure, equations for the inhaled energy were developed to overcome the van der Waals force between the molecules, deorbit the vibration equilibrium and the migration of molecules into the air. Finally, a shale sample with dense natural fractures from the Duvernay formation of Alberta, Canada, was used to validate the mathematical model. For comparison, the results from the USBM method, polynomial curve-fitting method and model’s calculations are illustrated in tables and figures. The outcomes exposed the results from the USBM method and polynomial curve-fitting method as deviating from the real gas content in the Duvernay formation without the consideration of the free gas loss. The model is reliable for performing gas content evaluations because it considers dual-pore structure, PVT behaviour and free gas escape simultaneously.

Application of SEM Imaging and MLA Mapping Method as a Tool for Wettability Restoration in Reservoir Core Samples for SCAL Experiments

In reservoir engineering, special core analysis experiments (SCAL) are performed in the lab to evaluate the production capabilities of an oil reservoir. A critical component of SCAL experiments is core wettability restoration to its original wettability, i.e., oil wet condition. Typically, aging is performed by saturating the core with oil and aging at reservoir temperature where time is the variable in question dictating whether the resulting restored core is strongly or weakly oil-wet. In the lab, core wettability is often experimentally validated using contact angle measurements or USBM (United States Bureau of Mines) wettability tests, which are often time consuming, expensive and prone to error. In this study we developed a novel method by using Scanning Electron Microscope (SEM) and mineral liberation analysis (MLA) imaging (at low vacuum conditions) to determine the wettability of rocks saturated with reservoir fluids such as oil and brine. For this work a systematic approach was applied with comparing the SEM-MLA method against conventional methods to quantify the degree of uncertainty linked to a) wettability estimation and b) the aging time. We have used a comprehensive suite of core samples such as Berea, Silurian Dolomite and Chalk to represent the bulk of oil reservoirs in the world.

A Method for Evaluating the Methane Content of the Nanoscale Pores in Deep Coalbeds.

Since the sampling depth is large in deep coalbed methane wells, during the lifting process of coalbed cores, the core surface pressure drops nonlinearly with time, which is contradictory to the premise of the conventional United States Bureau of Mines (USBM) method and the Smith-Williams method. In this paper, a desorption-diffusion model was established to quantitatively characterize the actual escape process of methane gas from nanoscale pores in coal cores in both the wellbore and desorption tank by considering the nonlinear relationship between the core surface pressure and time. Based on the optimization method, the measured volume of the desorbed gas in the desorption tank was fitted, and then, the amount of lost gas in the wellbore was inferred. The calculation result of the USBM method was smaller than that of the method used in this paper. In the calculation model of lost gas volume proposed in this paper, the lost gas time was corrected, and the non-uniform decreasing characteristics of the core surface pressure were considered. Therefore, the lost gas obtained by this model was more accurate than that obtained by the conventional method.

Shale adhesion force measurements via atomic force microscopy

Wettability of sedimentary rock surface is an essential parameter that defines oil recovery and production rates of a reservoir. The discovery of wettability alteration in reservoirs, as well as complications that occur in analysis of heterogeneous sample, such as shale, for instance, have prompted scientists to look for the methods of wettability assessment at nanoscale. At the same time, bulk techniques, which are commonly applied, such as USBM (United States Bureau of Mines) or Amott tests, are not sensitive enough in cases with mixed wettability of rocks as they provide average wettability values of a core plug. Atomic Force Microscopy (AFM) has been identified as one of the methods that allow for measurement of adhesion forces between cantilever and sample surface in an exact location at nanoscale. These adhesion forces can be used to estimate wettability locally. Current research, however, shows that the correlation is not trivial. Moreover, adhesion force measurement via AFM has not been used extensively in studies with geological samples yet. In this study, the adhesion force values of the cantilever tip interaction with quartz inclusion on the shale sample surface, have been measured using the AFM technique. The adhesion force measured in this particular case was equal to the capillary force of water meniscus, formed between the sample surface and the cantilever tip. Experiments were conducted with a SiconG cantilever with (tip radius of 5 nm). The adhesion forces between quartz grain and cantilever tip were equal to 56.5 ± 5 nN. Assuming the surface of interaction to be half spherical, the adhesion force per area was 0.36 ± 0.03 nN/nm2. These measurements and results acquired at nano-scale will thus create a path towards much higher accuracy-wettability measurements and consequently better reservoir-scale predictions and improved underground operations.

Linking continuum-scale state of wetting to pore-scale contact angles in porous media

HypothesisWetting phenomena play a key role in flows through porous media. Relative permeability and capillary pressure-saturation functions show a high sensitivity to wettability, which has different definitions at the continuum- and pore-scale. We hypothesize that the wetting state of a porous medium can be described in terms of topological arguments that constrain the morphological state of immiscible fluids, which provides a direct link between the continuum-scale metrics of wettability and pore-scale contact angles. ExperimentsWe perform primary drainage and imbibition experiments on Bentheimer sandstone using air and brine. Topological properties, such as Euler characteristic and interfacial curvature are measured utilizing X-ray micro-computed tomography at irreducible air saturation. We also present measurements for the United States Bureau of Mines (USBM) index, capillary pressure and pore-scale contact angles. Additional studies are performed using two-phase Lattice Boltzmann simulations to test a wider range of wetting conditions. FindingsWe demonstrate that contact angle distributions for a porous multiphase system can be predicted within a few percent difference of directly measured pore-scale contact angles using the presented method. This provides a general framework on how continuum-scale data can be used to describe the geometrical state of fluids within porous media.