Reservoir Samples Research Articles

Soil Erosion and Deposition Rate Inside an Artificial Reservoir in Central Italy: Bathymetry versus RUSLE and Morphometry

This study, using different direct and indirect methodologies, evaluated the sedimentation rate in an artificial reservoir in central Italy. This reservoir is regionally representative and was built in the 1960s for hydroelectric purposes; it has experienced a strong decrease in trap efficiency and a loss of over 70% of the stored water volume. Direct measurements of the lake bottom bathymetry, carried out in 2006 and 2015, and 3D reconstructions performed in a GIS environment, made it possible to calculate the volume of filling material and to verify an increasing trend in the sedimentation rate since 2006. The sample reservoir denudation rate was compared with that obtained using the Revised Universal Soil Loss Equation method to calibrate the fundamental and critical factors of the method itself, and verify the contribution of a hydrological “direct” (through new channels or gullies) or “diffuse” (overland flow) connectivity. Furthermore, the comparison with the results obtained from past studies on ten other artificial regional reservoirs, performed with morphometric analysis, demonstrated a good relationship between soil erosion rate, stream frequency, and contributing area size. The study highlighted how a correct estimate of soil erosion and/or solid transport rates within a hydrographic basin is fundamental for the assessment of the trap efficiency of a reservoir, in a period in which the availability of water resources is becoming more and more vital.

Abrolhos Magmatic Province petrogenesis and its link with the Vitória-Trindade Ridge, Southeast Brazilian Margin, South Atlantic Ocean

The Abrolhos Magmatic Province (AMP) is an example of an igneous province with about 63,000 km2 located at the Continent-Ocean Boundary (COB), into the Southeast Brazilian Margin. The AMP emerges as five small islands (Santa Bárbara, Redonda, Siriba, Sueste, and Guarita) which integrate the Abrolhos Archipelago located about 55 km offshore Brazil. The studied rocks belong to a transitional basalt series of alkaline affinity, with evolved rocks with high TiO2 contents. This work presents new detailed fieldwork mapping, petrographic, and whole-rock chemistry data, besides Sr–Nd isotopic compositions from AMP rocks. Mapped magmatic rocks in the Abrolhos Islands have been described as extrusive rocks, but we point out that they are shallow intrusions, mostly sills, and should be grouped into diabase units based on fieldwork and textural features. The AMP lithogeochemical and isotopic data suggest the operation of differentiation processes more complex than simple fractional crystallization or AFC. Our model mixing calculations based on new and compiled Sr-Nd-Pb isotopic data suggest a mixture with a prevailing depleted asthenosphere mantle source (represented by DMM; ca. 80%) metasomatized by an enriched mantle I (EMI) component (≤ 10%) and a possible HIMU-type constituent (up to 10%) in the AMP genesis. The assimilation of subducted slabs of the oceanic crust associated with the HIMU signatures is possibly linked to the Brasiliano Event due to the range of the AMP Nd TDM model ages, from 407 to 767 Ma. A viable mechanism for the EMI end-member contribution could either be a physical detachment of the South American subcontinental lithospheric mantle during the breakup of the Gondwana or lithospheric delamination of the South American plate caused by an edge-driven convection mechanism. The AMP and the Vitória-Trindade Ridge (VTR) show an eastward decreasing age pattern from the older ca. 60 Ma Abrolhos Province to the younger Martin Vaz and Trindade Islands (ca. 4 – 0.1 Ma), located ca. 1200 km away from the Brazilian coastline. The volcanic alignment between the VTR and AMP, along with the overlap of geochemical and isotopic data of their different igneous rocks, cannot be a random feature but instead represent the sampling of similar shallow mantle reservoirs, thus suggesting a cogenetic relationship. Finally, a possible petrogenetic link between the AMP and VTR magmatism is discussed.

Bioconversion of carbon dioxide to succinate by Citrobacter

Carbon dioxide as a feedstock for synthesizing chemicals and fuels attracts numerous efforts via biological or chemical approaches. A newly Citrobacter BD11 was detected with distribution of 71.31 % in reservoir samples by metagenomic sequencing, and can convert CO2 to succinic acid with hydrogen production under anaerobic condition. The pathway of hydrogen production and the succinic acid synthesis was explored by whole-genome sequencing and real-time quantitative polymerase chain reaction. The results showed the positive influences of pH, hydrogen pressure and magnesium ions on succinic acid production. The stage transition of hydrogen production and utilization was detected, and the nonlinear relationship between succinic acid production and exogenous carbon dioxide was proved. Under optimized conditions, the carbon fixation rate of 1.77 g/L*d and the succinate production rate of 7.51 g/L*d were finally achieved at pH = 7.0 with 50 KPa of hydrogen pressure and 4.0 g/L of MgCl2. This study demonstrated that this Citrobacter could be a promising platform for hydrogen production and convert CO2 to diverse acids.

Numerical modelling of reservoir at pore scale: A comprehensive review

Pore scale reservoir modelling is carried out to digitally build the inner structure of the reservoir samples using proper mathematical algorithms based on certain priors extracted from training image(s) or laboratory measured data. Although various imaging devices can provide the inner structure of the rock sample directly, numerical modelling methods still has its irreplaceable advantages. Firstly, due to some intrinsic limitations, no imaging device so far can provide a 3D porous structure satisfying both resolution and field of view except for a very few of homogeneous reservoir samples with relatively large pore-throat size, while numerical modelling is an effective approach to improve the resolution of the machine produced images. Secondly, in some cases, where only 2D images (such as the images of drill cuttings) are available, numerical modelling is the only option to reconstruct a 3D porous structure. Thirdly, numerical modelling is a convenient and low-cost technique that makes it widely applicable. This paper presents a comprehensive review of the pore scale reservoir modelling. Pore structure's modelling can be treated as a supervised prediction process with two steps: 1) extraction of descriptors (prior knowledge) from the training image(s) or laboratory measured data; and 2) numerical reconstruction under the supervision of the extracted descriptors. In terms of extraction of descriptors, using multiple-point statistics (MPS) instead of random function models is a great step that made the empirical multivariate distributions inferred from training images can be directly used to reconstruct porous structure. Another great progress is the application of multiple-resolution training images where the image degradation mechanism contained in these different resolution images can be used to supervise the reconstruction. In terms of supervised reconstruction, some mathematical strategies such as Gaussian Random field, simulated annealing are applied to reproduce these descriptors in the reconstructed images. Along with the flourish of deep learning, a convolutional neural networks model is introduced into reconstruction process with an impressive performance.

Accuracy, Precision, and Optimal Sampling Duration of Low‐Frequency Electrofishing for Sampling Reservoir Flathead Catfish Populations

AbstractFlathead Catfish Pylodictis olivaris are popular among anglers; however, information about their sampling is limited. Low‐frequency electrofishing (LFE) is the most used method for sampling Flathead Catfish, but LFE data quality (precision and accuracy) has not been previously studied. Therefore, we evaluated accuracy, precision, and optimal sampling duration for maximizing precision of LFE sampling for Flathead Catfish. To quantify accuracy, we created known populations by tagging Flathead Catfish in Lake Carl Blackwell, Lake McMurtry, and Boomer Lake, Oklahoma, with numbered modified Carlin dangler tags and calculated their capture probabilities from recapture data with a Cormack–Jolly–Seber model, with water temperature as an environmental covariate and fish size as an individual covariate. Capture probability was negatively correlated with increases in fish length for Lake Carl Blackwell and Lake McMurtry but was positively correlated with increases in fish length for Boomer Lake. Capture probability was highest at warmer temperatures at Lake Carl Blackwell and Lake McMurtry but was highest at lower water temperatures at Boomer Lake. Therefore, catch rate and size bias varied by system, but size bias was still relatively consistent at all temperatures within lakes (i.e., lake‐specific differences in slopes were subtle even though significantly different), indicating that LFE could be used to detect relative changes in size structure if temperatures were standardized. Catch rates were highest and most consistent from June to September when water temperatures were ≥24°C. The number of 5‐min LFE efforts needed to achieve a relative standard error ≤25% was lowest when water temperature was ≥20°C from months between May and September. Catch rates and size structure did not differ between LFE efforts (5, 10, or 15 min), suggesting that any LFE effort would produce similar relative abundance estimates.

The impact of hydrothermal alteration on the physiochemical characteristics of reservoir rocks: the case of the Los Humeros geothermal field (Mexico)

Hydrothermal alteration is a common process in active geothermal systems and can significantly change the physiochemical properties of rocks. To improve reservoir assessment and modeling of high-temperature geothermal resources linked to active volcanic settings, a detailed understanding of the reservoir is needed. The Los Humeros Volcanic Complex, hosting the third largest exploited geothermal field in Mexico, represents a natural laboratory to investigate the impact of hydrothermal processes on the rock properties through andesitic reservoir cores and outcropping analogs. Complementary petrographic and chemical analyses were used to characterize the intensities and facies of hydrothermal alteration. The alteration varies from argillic and propylitic facies characterized by no significant changes of the REE budget indicating an inert behavior to silicic facies and skarn instead showing highly variable REE contents. Unaltered outcrop samples predominantly feature low matrix permeabilities (< 10–17 m2) as well as low to intermediate matrix porosities (< 5–15%), thermal conductivities (0.89–1.49 W m−1 K−1), thermal diffusivities (~ 0.83 10–6 m2 s−1), and sonic wave velocities (VP: ~ 2800–4100 m s−1, VS: ~ 1600–2400 m s−1). Average magnetic susceptibility and specific heat capacity range between 2.4–7.0 10–3 SI and 752–772 J kg−1 K−1, respectively. In contrast, the hydrothermally altered reservoir samples show enhanced porosities (~ 7–23%), permeabilities (10–17–10–14 m2), and thermal properties (> 1.67 W m−1 K−1; > 0.91 10–6 m2 s−1), but a significant loss of magnetic susceptibility (10–3–10–6 SI). In particular, this latter characteristic appears to be a suitable indicator during geophysical survey for the identification of hydrothermalized domains and possible pathways for fluids. The lack of clear trends between alteration facies, alteration intensity, and chemical indices in the studied samples is interpreted as the response to multiple and/or repeated hydrothermal events. Finally, the proposed integrated field-based approach shows the capability to unravel the complexity of geothermal reservoir rocks in active volcanic settings.

Estimation of the Bubble Point Pressure of Multicomponent Reservoir Hydrocarbon Fluids

This study developed a novel C-sharp (C#) programming language for the estimation of bubble point pressure (BPP) of various hydrocarbon mixtures at equilibrium state. The methodology was based on vapor–liquid equilibrium calculation using Peng Robinson equation of state implementation, thermodynamic equilibrium calculation and Newton-Raphson’s method for the successive substitution of the unknown variables. The equal fugacity constraint can be satisfied by obtaining the equilibrium which serves as a criterion for two or more phases to exist at equilibrium. The problem was resolved by searching for a pressure that will satisfy the two constraints. Complex calculation was performed by successively substituting the pressure value estimated by Newton–Raphson’s method at reservoir temperature until the two constraints were satisfied. The BPP values for the eight reservoir sample fluids were within the range of 29.32–308.00 atm with an absolute error deviation ranging from 0.00–4.27 and average percentage error of 0.54%. BPP values were obtained were within the reservoir temperature range of 328.15–398.71 K. This procedure is a potential approach for the estimation of BPP for hydrocarbon mixtures with defined fluid composition irrespective of their composition.

Parallel Weighted Random Sampling

Data structures for efficient sampling from a set of weighted items are an important building block of many applications. However, few parallel solutions are known. We close many of these gaps. We give efficient, fast, and practicable parallel and distributed algorithms for building data structures that support sampling single items (alias tables, compressed data structures). This also yields a simplified and more space-efficient sequential algorithm for alias table construction. Our approaches to sampling k out of n items with/without replacement and to subset (Poisson) sampling are output-sensitive , i.e., the sampling algorithms use work linear in the number of different samples. This is also interesting in the sequential case. Weighted random permutation can be done by sorting appropriate random deviates. We show that this is possible with linear work. Finally, we give a communication-efficient, highly scalable approach to (weighted and unweighted) reservoir sampling. This algorithm is based on a fully distributed model of streaming algorithms that might be of independent interest. Experiments for alias tables and sampling with replacement show near linear speedups using up to 158 threads of shared-memory machines. An experimental evaluation of distributed weighted reservoir sampling on up to 5,120 cores also shows good speedups.

Characterizing the Microscopic Anisotropic Permeabilities of Tight Oil Reservoirs Impacted by Heterogeneous Minerals

This study aimed to reveal the anisotropic permeabilities of tight oil reservoirs impacted by heterogeneous minerals. SEM imaging, image processing, fractal calculation, microscopic reservoir modeling, and visual flow simulation were carried out to investigate the above problems. Results show that the variation coefficient of two-dimensional permeability for the studied tight reservoir samples ranges from 0.09 to 0.95, with an average value of 0.68. The penetration coefficient ranges from 1.16 to 2.64, with an average value of 2.13. The ratio of maximum to minimum permeability is between 1.25 and 7.67, with an average value of 5.62. The fluid flow in tight reservoirs has significant anisotropy comprising dominant flow through conductive channels. Flow in tight oil reservoirs tends to involve minor hydraulic fracturing with no proppant.

Microfluidic paper-based analytical device for determination of sucrose in sugarcane juice using Benedict's reagent.

This work presents a microfluidic paper-based analytical device (μPAD) for the determination of sucrose using the Benedict's test. An asymmetric dumbbell-shaped hydrophobic barrier was produced by rubber stamping the barrier pattern onto a laboratory filter paper. Hydrochloric acid and solution containing sucrose were successively deposited onto the sample reservoir of the μPAD attached to a glass slide. The device was placed in a plastic bag and dipped into boiling water for accelerating the hydrolysis of sucrose into the reducing sugars. Then the Benedict's reagent was added at the narrow straight channel connecting the two circular zones of the μPAD, which was replaced in the plastic bag and heated again for reduction of Cu(II) by the reducing sugars. Precipitate of brick-red copper(I) oxide was formed. The image of the μPAD was recorded by a smartphone. The ratio of the red to blue intensities gave linear correlation with the concentration of sucrose in the range of 0.5-10% w/v. The relative standard deviation of the measurement was less than 5% for 2 and 4% w/v sucrose (n = 10), with limit of determination, calculated using standard deviation of regression divided by slope of calibration, of 0.26% w/v sucrose. The method was successfully validated using the dinitrosalicylic acid method for sucrose measurement. Percent recoveries of sucrose were evaluated using ten sugarcane samples. The recoveries were in the range of 89 to 101%, demonstrating that there were no significant sample matrix effects on the quantification.

Enhanced oil recovery in carbonate rocks using seawater spiked with copper chloride: Imbibition experiments

It is widely accepted that oil recovery during waterflooding can be improved by modifying the composition of the injected brine, typically by depleting the total salinity or altering potential determining ions (PDI) such as: Ca2+, Mg2+, and SO42− concentration. Numerous laboratory experiments and field tests have demonstrated this effect in both clastic and carbonate rock Samples and reservoirs. However, some authors have found alternative ions, such as phosphate (PO42−) and borate (B(OH)4-) which, in some cases, presented additional recovery and have thus opened the discussion for potential alternative ions to enhanced oil recovery. With this in mind, copper ion's potential for enhanced oil recovery (EOR) was studied, combining different conditions usually employed on smart water experiments, such as depleting the total salinity and removing the PDI to highlight the real effect of copper on additional oil recovery. The investigation was carried out with Brazilian pre-salt reservoir Samples in imbibition experiments using Amott cells at ambient pressure and 63 °C. The evaluation of the copper effect on oil recovery for coreflooding was proved in a previous paper by Bernadinelli et al. (2021), however the analysis with imbibition experiments in this study aim to clarify the effect of copper on the capillary pressure, by analyzing the eventual additional oil production. These Samples were prepared and aged, and the oil production was monitored during the experimental time. The experiments were carried in four sequences to evaluate the effect of copper on oil recovery, consisting first of salinity reduction from 0% of sodium chloride to 100% of the original amount in the seawater (SW), followed by the removal of PDI salts, the study of the production mode (secondary or tertiary), and the analysis of the copper chloride concentration on the final recovery. The results using copper at the secondary recovery showed remarkable increases (from 6.3% to 10.0%) of the original oil in place (OOIP) compared to the oil recovered from the formation water (FW). In tertiary mode, the best recoveries occurred at salinities between 8 and 18 kppm and copper chloride (1 g/L), and presented increasing recoveries 3.9%, 5.8%, and 9.3% of OOIP. This work presents an initial investigation on the use of copper as an active ion for the smart water effect and sheds light on its effect on both secondary and tertiary modes for strategies of recovery that use soaking methods and also for fractured reservoirs.

Corroborative insights into genetically related kerogen, asphaltenes and hydrocarbons using free and bound biomarkers

Unlike the free biomarkers, which can be routinely recovered via solvent extraction, the bound biomarkers are covalently linked to the kerogen or asphaltene macrostructures and are more resistant to secondary alteration processes. Although similarities have been identified between these two types of biomarkers using different techniques, it remains unclear how the kerogen- and asphaltene-bound biomarkers are complicatedly corelated with their free counterparts, thus limiting the applications of bound biomarkers in geoscience research. In this study, the characteristics of free biomarkers recovered from shale samples, from 10 sedimentary basin around the world, and petroleum samples, from the North Sea, have been systematically compared with their kerogen- and asphaltene-bound biomarkers, which were released by the newly developed Microscale Sealed Vessel Catalytic Hydrogenation (MSSV-Hy) method. Although the kerogen-bound biomarkers are characterized by the absence of rearranged biomarkers (e.g., Ts and diasteranes) and elevated C29/C30 hopane ratios, many key source-related parameters show strong positive correlations between free and bound fractions, including the steranes/hopane, C27/C29 sterane, C30/C29 sterane, C29/C30 hopane (αβ + βα), C35/C34 homohopanes and C24 tetracyclic terpane/C26 tricyclic terpane ratios. These results suggest that bound biomarkers can reveal critical information about deposits and organic matter precursors of source rocks. Thermal maturity indicators, such as C29 sterane ββ/(αα + ββ), C29 sterane S/(S + R), C31 hopane S/R, and Tβ/Tm ratios, also display excellent correlations between the free and bound counterparts in the source rocks. Although the correlations are not 1:1, empirical formulae, which are based on the correlations between free and bound biomarkers, can be used to calibrate bound biomarkers into values that can be directly compared to routine free biomarkers. Importantly, asphaltene-bound biomarkers of North Sea samples exhibit similar characteristics to kerogen-bound biomarkers, and the conversion between free and bound biomarkers of the source rock and reservoir samples is the same. In summary, the bound biomarkers are found highly effective in determining the organic facies, lithology, and thermal maturity of the parent kerogen and/or asphaltene, and, thus, have a great potential to be widely used in geoscience research when information from free biomarkers is hampered by oil mixing, contamination or biodegradation.

On the Water-Oil Relative Permeabilities of Southern Algerian Sandstone Rock Samples

The water–oil relative permeability behavior of different plugs from the Hassi Messaoud reservoir in south Algeria has been investigated to understand the fundamental processes of two-phase flow taking place within the macro-structure of rock samples. The experiments were conducted on cylindrical reservoir samples (plugs) using the unsteady-state method to measure the oil–water relative permeabilities due to operational simplicity. The impact of factors such as wettability, overburden pressure and rock characteristics based on the relative permeability curves have been carefully assessed. During this test, temperature was kept in the range of 95 to 100 °C and pressure was maintained at 100 bar. Large variations in relative permeability curve trends have been experimentally observed for different rock samples under investigation, which can be explained by the heterogeneous nature of the studied reservoir. Results showed an intermediate alteration of wettability and for all studied samples, and the intersection point of the relative permeability values for oil and water is less than 50%, showing that these samples exhibit oil-wet behavior. Our results also show that displacement pressure increases from 0.13 to 2 psi, promoting a gradual displacement of oil relative permeability (Kro) toward higher saturations in water (45% to 60%). The results show that the oil recovery rate at breakthrough is approximately 16% to 28% of the initial oil in place (IOP), with an average of 23%. The final oil recovery rate, obtained by moving at constant pressure, ranges from 43% to 55% of the initial oil in place (IOP), with an average value of around 49%. The forced displacement at the end of the performed tests increased the average recovery rate by about 4%. These rates vary from 46% to 61% of the initial oil in place (IOP). The residual oil saturation (Sor) varies from 33.7% to 47.8% relative to pore volume (Vp); the average is about 42%. The residual oil saturation (Sor) is about 30% to 45% Vp after forced displacement at the end of the test, the average is about 38.5%, and the relative permeabilities Krw and Kro are equal to the water saturations of 33% to 50%; the average value is about 41%.

Gas Condensate Wells: Challenges of Sampling, Testing and Production Optimization

The main problem of fluid sampling during well testing of reservoirs with near-critical fluids (gas condensate and volatile oil) is due to the fact that even a small pressure drawdown usually leads to the formation of a two-phase mixture in the bottom hole area, and it is almost impossible to take representative samples with downhole samplers or a formation tester. Sampling via test-separator and the current non-separation methods are also imperfect. An alternative method—MIKS (Multiphase IsoKinetic Sampling)—of gas condensate well testing was proposed, which is based on emulsifying a multiphase flow to particles of about 1–10 μm. Thereby MIKS would eliminate the problem of particle slippage in a homogeneous flow and enables high-quality sampling directly from the flowmeter line. The initial formation fluid is characterized by the maximum value of the condensate-gas ratio (CGR). Therefore, first, the well effluent would be adjusted to the mode with the maximum CGR using a choke manifold and a multiphase flow meter. Then the flow mixture is transferred to a by-pass line with an emulsifier to achieve an isokinetic flow. Thereafter, pressure samples can be taken into pressurized sampling bottles, in which thermodynamic conditions are preset according to the flow line. The efficiency of sampling and recombining procedures allows for conducting a study of reservoir samples in the field laboratory directly on the rig and obtaining a complete PVT report even before the completion of drilling and abandonment of the well. An additional economic effect is achieved by reducing the costs of transporting and samples storage. Well test equipment setup becomes much more compact and less weight; the costs of drilling time are reduced, which is viably important for well testing on the Arctic conditions. Another major problem in the development of gas condensate reservoirs is avoiding the condensate banking around producing wells. Optimization of condensate production can be achieved by maintaining the well operation mode at maximum CGR level by means of multiphase flowmeters. The formed condensate bank can be destroyed by a combination of methods—hydraulic fracturing, followed by cycling process—purging the formation with dried gas and/or injection of methanol into the formation. Methanol can be obtained from synthesis gas as a by-product in the utilization of associated gas also at the field. The specified set of measures will allow to revive the GC wells that are losing productivity, as well as to extend the period of high productivity of new wells.

3D Printable Reservoirs for Potentiometric Analysis of Solid Samples

Potentiometric sensing has shown to be highly effective for diagnostic testing of many important ionic biomarkers. Outside of biological analytes, ion-selective electrodes (ISEs) have been utilized for environmental and forensic analytes due to their high specificity and sensitivity. Unfortunately, many samples to be analyzed (especially in the case of forensics) are solids (e.g., powders, soils, etc.) which require sample preparation steps prior to analysis. In this work, we further expand on the utility of fabricating ISEs through 3D printing protocols by developing a sampling reservoir and placing it in contact with the sensing element of potentiometric sensors (i.e., the ion-selective membrane (ISM). This reservoir works as a sampling well, dissolving solid samples and allowing the ions to diffuse to the ISM for quantification.

Unbiased inverse volume rendering with differential trackers

Volumetric representations are popular in inverse rendering because they have a simple parameterization, are smoothly varying, and transparently handle topology changes. However, incorporating the full volumetric transport of light is costly and challenging, often leading practitioners to implement simplified models, such as purely emissive and absorbing volumes with "baked" lighting. One such challenge is the efficient estimation of the gradients of the volume's appearance with respect to its scattering and absorption parameters. We show that the straightforward approach---differentiating a volumetric free-flight sampler---can lead to biased and high-variance gradients, hindering optimization. Instead, we propose using a new sampling strategy: differential ratio tracking , which is unbiased, yields low-variance gradients, and runs in linear time. Differential ratio tracking combines ratio tracking and reservoir sampling to estimate gradients by sampling distances proportional to the unweighted transmittance rather than the usual extinction-weighted transmittance. In addition, we observe local minima when optimizing scattering parameters to reproduce dense volumes or surfaces. We show that these local minima can be overcome by bootstrapping the optimization from nonphysical emissive volumes that are easily optimized.

Single‐pass stratified importance resampling

AbstractResampling is the process of selecting from a set of candidate samples to achieve a distribution (approximately) proportional to a desired target. Recent work has revisited its application to Monte Carlo integration, yielding powerful and practical importance sampling methods. One drawback of existing resampling methods is that they cannot generate stratified samples. We propose two complementary techniques to achieve efficient stratified resampling. We first introduce bidirectional CDF sampling which yields the same result as conventional inverse CDF sampling but in a single pass over the candidates, without needing to store them, similarly to reservoir sampling. We then order the candidates along a space‐filling curve to ensure that stratified CDF sampling of candidate indices yields stratified samples in the integration domain. We showcase our method on various resampling‐based rendering problems.

Effect of thermal shock on the permeability and seismic wave velocity of the caprock and reservoir during CO2 injection

The injection of relatively cold CO2 into warmer reservoirs causes rapid cooling of the host reservoir and the overlying caprock in the near wellbore region. This rapid cooling may cause thermal fracturing, which may potentially lead to escape of the CO2. We have here investigated the effect of thermal fracturing, due to rapid quenching, on the permeability and P-and S-wave velocities of caprock and reservoir samples from the In Salah CO2 storage site, Krechba field, Algeria. Injection of CO2 may have cooled the caprock and reservoir by up to 65°C. Laboratory experiments were conducted where caprock and reservoir samples were heated to various temperatures (50, 150, 250, 350 and 500°C) and rapidly quenched to room temperature (20°C). Permeability and P- and S-wave velocities were measured pre- and post-thermal treatment at effective pressures up to 60 MPa. Backscattered scanning electron microscopy analysis revealed that most of the fracturing is mainly within siderite (Fe carbonate). X-ray diffraction analysis showed that the minerals chlorite (Fe-clay) and siderite were destroyed in specimens heated to 500°C. Specimens that were rapidly quenched by 230°C experienced less than half an order of magnitude increase in permeability and very small to negligible changes in the P- and S-wave velocities. We conclude that the effect of thermal shock fracturing in the Krechba field due to CO2 injection is negligible because the change in the permeability and velocities are insignificant for the predicted maximum degree of cooling (approximately 65°C) of the formation due to CO2 injection. The conclusion of the lack of thermal quenching effects due to CO2 injection at In Salah may be applicable to all global Carbon Capture and Storage prospects.

Development of an NMR workflow for determining nano-petrophysical properties of marine and lacustrine mudrocks

Nuclear Magnetic Resonance (NMR) is a powerful method of pore structure and fluids characterization for a wide range of porous media due to its fast and non-destructive capabilities, but its utilities of nano-petrophysics (the properties of rocks and fluids, as well as their interactions, in the presence of predominantly nm-sized pores) for tight oil formations warrant more studies. In this work, a total of four cylindrically-shaped tight reservoir samples at 2.54 cm in diameter with four different lithologies in USA and China were selected for systematic NMR analyses with T2 relaxation time, T1-T2 mapping, NMR cryoporometry (NMRc), and magnetic resonance imaging (MRI) techniques, along with other supplemental tests of X-ray diffraction (XRD), mercury intrusion porosimetry (MIP) and vacuum-assisted water immersion porosimetry (WIP), to characterize their petrophysical properties. The results show that the effective porosity obtained from NMR was highly consistent with WIP. Three samples characterized by MRI showed that T2 spectra had a good response to the fluid distribution in the samples. In this study, T2 time was converted into the pore size by combining corrected NMR T2 spectrum and MIP pore-throat size distribution. Finally, The Katz-Thompson model was applied for NMR data to calculate the permeability at different inflection points (connected pore networks) to quantitatively evaluate their individual permeabilities and porosities. Furthermore, except for sample N9 (carbonate-rich Wolfcamp A mudrock), a satisfactory agreement was achieved between the results of K2C (cut-off time at the second inflection point) and helium method for permeability analyses.

Continual Refoircement Learning Using Real-World Data for Intelligent Prediction of SOC Consumption in Electric Vehicles

The accelerated migration towards electric vehicles (EV) presents several problems to solve. The main aspect is the management and prediction of the state of charge (SOC) in real long-range routes of different variations in altitude for a more efficient energy consumption and vehicle recharge plan. This paper presents the implementation of a new algorithm for SOC estimation based on continuous learning and meta-experience replay (MER) with reservoir sample. It combines the reptile meta-learning algorithm with the experience replay technique for stabilizing the reinforcement learning. The proposed algorithm considers several important factors for the prediction of the SOC in EV such as: speed, travel time, route altimetry, consumed battery capacity, regenerated battery capacity. A modified principal components analysis is used to reduce the dimensionality of the route altimetry data. The experimental results show an efficient estimation of the SOC values and a convergent increase in knowledge while the vehicle travels the routes.