Gravitational Differentiation Research Articles

Inter-layer interference for multi-layered tight gas reservoir in the absence and presence of movable water

Due to the dissimilarity among different producing layers, the influences of inter-layer interference on the production performance of a multi-layer gas reservoir are possible. However, systematic studies of inter-layer interference for tight gas reservoirs are really limited, especially for those reservoirs in the presence of water. In this work, five types of possible inter-layer interferences, including both absence and presence of water, are identified for commingled production of tight gas reservoirs. Subsequently, a series of reservoir-scale and pore-scale numerical simulations are conducted to quantify the degree of influence of each type of interference. Consistent field evidence from the Yan'an tight gas reservoir (Ordos Basin, China) is found to support the simulation results. Additionally, suggestions are proposed to mitigate the potential inter-layer interferences. The results indicate that, in the absence of water, commingled production is favorable in two situations: when there is a difference in physical properties and when there is a difference in the pressure system of each layer. For reservoirs with a multi-pressure system, the backflow phenomenon, which significantly influences the production performance, only occurs under extreme conditions (such as very low production rates or well shut-in periods). When water is introduced into the multi-layer system, inter-layer interference becomes nearly inevitable. Perforating both the gas-rich layer and water-rich layer for commingled production is not desirable, as it can trigger water invasion from the water-rich layer into the gas-rich layer. The gas-rich layer might also be interfered with by water from the neighboring unperforated water-rich layer, where the water might break the barrier (eg weak joint surface, cement in fractures) between the two layers and migrate into the gas-rich layer. Additionally, the gas-rich layer could possibly be interfered with by water that accumulates at the bottom of the wellbore due to gravitational differentiation during shut-in operations.

Differentiation of Lamproitic Magma: Case Study of Mesozoic High-K Dikes of the Ryabinovyi Massif (Central Aldan)

Abstract ––Studies of the mineral–petrographic and geochemical compositions of high-potassic lamprophyric dikes of the Tobuk complex, manifested at the Ryabinovyi plutonic massif (Central Aldan Mesozoic magmatic province, Russia), have shown that these dikes compose a single fractionation series formed from a high-Mg lamproitic parental melt in an intermediate chamber. The composition of the rocks ranges from olivine–diopside–phlogopite and diopside–phlogopite lamproites through minettes to microsyenites and syenite–porphyry. Early crystallization of high-Mg olivine and chromite in an intermediate chamber could produce cumulative dunites similar to those of the Inagli intrusion. Crystallization of olivine and chromite was followed by cotectic crystallization of olivine and clinopyroxene, then that of clinopyroxene and phlogopite, and, finally, eutectic crystallization of Na-rich clinopyroxene, phlogopite, and K-feldspar. Crystallization and gravitational differentiation of lamproitic melt was complicated by silicate–carbonate immiscibility, which is texturally manifested in minettes as carbonate–silicate globules and interstitial calcium and magnesium carbonates. Furthermore, compositional zoning of Sr in apatite and Ba in phlogopite and K-feldspar is considered to have resulted from the immiscibility. Separation of the carbonate–fluorite melt fraction might have led to formation of the carbonatite and fluorite–carbonatite schlieren and gangues which have been described in drill cores from the Ryabinovyi massif. In most of the geochemical and mineralogic features, the Ryabinovyi massif lamproites are similar to the low-Ti lamproites of the Mediterranean postcollisional belt and northern Vietnam and differ from typical high-Ti within-plate lamproites.

Paleovolcanism of the eastern Magnitogorsk megazone, Southern Urals: Petrology, geochemistry, and gold-bearing perspectives

The geological-petrographic and petrogeochemical features of volcanic rocks are considered of the Gumbeika zone in the Southern Urals, that is the frontal easternmost portion of the East Magnitogorsk paleo-island arc. The volcanites are united into the Gumbeika volcanic association. The association is shown to be represented by the basalt– andesite–dacite–rhyodacite “uninterrupted” homodrom igneous series. The compositional features of the volcanics allow confident assigning them to the island-arc calc-alkaline series, or more precisely, to formations of “developed” island arcs. It is concluded that the main process that determines the general appearance and composition of the unified petrogenetic series of rocks of the Gumbeika association was the fractional crystallization of the parental basaltic melts in deep-seated chambers and, then, in near-surface peripheral ones. The emplacement of some of the magmatic bodies was also accompanied by in situ gravitational differentiation. The general similarity of the volcanics-associated gold-silver deposits with the analogs within recent island arcs allows us to suggest a great perspectives for gold-silver mineralization throughout the Gumbeika zone. Two forecasted ore fields have been identified.

Experimental Study on the Sweep Law of CO2 Miscible Flooding in Heterogeneous Reservoir in Jilin

It is very important to effectively describe the sweep characteristics of CO2 miscible flooding based on physical models for actual reservoir development. In this study, based on the geological characteristics of the Jilin ultra-low permeability reservoir, which has significant vertical heterogeneity, a two-dimensional double-layer heterogeneous visualization model with a permeability contrast of 10 and thickness contrast of 2 was designed to perform experimental research on the sweep law of CO2 miscible flooding with an injection-production mode of “united injection and single production”. With the goal of determining the obvious differences in the gas absorption capacity and displacement power of the two layers, the CO2 dynamic miscible flooding characteristics were comprehensively analyzed, and the sweep law of CO2 miscible flooding, including the oil and gas flow trend, migration direction of the oil–gas interface, and distribution characteristics of the miscible zone, was further studied in combination with the oil displacement effect. In this experiment, the gas absorption capacity was the key factor affecting the sweep efficiency of the CO2 miscible flooding. Under the combined influence of the internal and external control factors of the reservoir thickness, permeability, and injection-production mode, the gas absorption capacity of the high-permeability layer was much greater than that of the low-permeability layer, resulting in the retention of a large amount of remaining oil in the low-permeability layer, which effectively displaced and swept the oil in the high-permeability layer. The gas absorption capacity of the reservoir, gravitational differentiation, and miscible mass transfer were key factors affecting the migration of the oil–gas interface and distribution of the miscible zone. The entire displacement process could be divided into three stages: ① The gas-free rapid oil production stage, which was dominated by the displacement; ② the low gas–oil ratio stable oil production stage, which was jointly affected by the displacement and miscible mass transfer; and ③ the high gas–oil ratio slow oil production stage, which was dominated by the effect of CO2 carrying.

Three-dimensional physical simulation of water huff-n-puff in a tight oil reservoir with stimulated reservoir volume

Water huff-n-puff has been considered as a cost-effective method to enhance oil recovery in tight reservoirs. However, the physical simulation method for water huff-n-puff is still lacking up to now, so that the production behaviors of actual tight reservoirs cannot be reproduced and the EOR potentials cannot be evaluated directly by scaled models in the laboratory. In this study, mathematical models for water huff-n-puff processes in tight oil reservoirs with stimulated reservoir volume (SRV) were established, then the corresponding scaling criteria were proposed and verified. Taking the tight reservoir ZMY in the Ordos Basin as a prototype, three groups of three-dimensional physical simulations of water huff-n-puff under different conditions (PSM-1, PSM-2 and PSM-3) were designed based on the scaled parameters respectively, then performed favorably and compared comprehensively. The experimental results show that oil recovery of PSM-1 can be increased by 20.16% within 8 cycles, which shows great EOR potentials for the tight reservoir ZMY. Compared with PSM-1, oil recovery of PSM-2 reduces by 8.23%, which indicates that forced imbibition is quite a helpful and promoting mechanism, and oil recovery enhancement will be greatly limited if no imbibition effect is given play between the matrix and fractures. Comparatively, oil recovery reduces by 3.39% for PSM-3, which can be inferred that if fracture density relatively increases and all fractures are well connected, the matrix imbibition effect can be further strengthened, the high pressure can propagate faster, the elastic energy can supplement into the matrix deeper, and the effect of gravitational differentiation can be better utilized as well. It is found that cumulative oil production of the three physical simulations in the first several cycles is always relatively high, which implies that sufficient oil supply in physical models can be maintained. As oil-water interface rises, less oil and more water will be produced and different dynamic characteristics of cumulative oil and water production are shown. It is also found that all three groups of water cut curves have the same upward trend and the Sigmoidal-Logistic model can be employed to accurately depict the dynamic characteristics of water cut at different cycles. This study aims to establish a physical simulation method for water huff-n-puff in tight oil reservoirs with SRV based on the three-dimensional scaled model, which will be greatly helpful to understand the EOR mechanisms and production characteristics of water huff-n-puff. • Scaling criteria of water huff-n-puff in tight oil reservoirs with SRV were proposed and verified. • Three-dimensional physical simulation method for water huff-n-puff was established. • Oil recovery of physical simulation model can be increased by 20.16% within 8 cycles for a case study. • Forced imbibition and large-scale fracture network can greatly enhance oil recovery during water huff-n-puff. • The Sigmoidal-Logistic model can depict the dynamic characteristics of water cut at different cycles.

Experimental Study on Dynamic Characteristics of Shut-In and Restart Process in Water Drive Strong Heterogeneous Oil Reservoir

The main purpose of this investigation is to study the dynamic characteristics of shut-in and restart process in reservoirs with high water cut and strong vertical heterogeneity. The physical model, which includes three layers with low, medium, and high-permeability from top to bottom, was made according to the similarity law. Water drive test, the first restart test, and the second restart test were conducted, respectively. Water cut, oil recovery, and saturation distribution of the remaining oil were obtained during the tests. On this basis, mechanisms of shut-in and restart process of the reservoir were analyzed. It is concluded that appropriate developing plan such as layering mining and cyclic waterflooding should be implemented for developing strong heterogeneity reservoirs. The shut-in and restart tests showed that closing the water-flooded layer is beneficial for enlarging the sweep volume. Besides, water cut of 98% does not mean the economic limits of waterflooding. Under the effect of capillary force and gravitational differentiation, oil and water will redistribute in the formation. The redistribution of the oil and water, the fluctuation of the pressure difference, and the rebuild of the flow path, which produce parts of the bypassed oil, are the main mechanisms of the recovery enhancement by shut-in and restart operation. It should be noted that the shut-in and restart process indeed prolongs the waterflooding development. However, simply replying on the oil and water distribution under static conditions cannot greatly enhance the oil recovery.

Chemical and Phase Reactions on the Contact between Refractory Materials and Slags, a Case from the 19th Century Zn-Pb Smelter in Ruda Śląska, Poland

Slags from the historic metallurgy of Zn-Pb ores are known for unique chemical and phase compositions. The oxides, silicates, aluminosilicates, and amorphous phases present therein often contain in the structure elements that are rare in natural conditions, such as Zn, Pb, As. The study focuses on processes occurring on the contact of the melted batch and the refractory materials that build the furnace, which lead to the formation of these phases. To describe them, chemical (X-ray fluorescence (XRF), inductively coupled plasma mass spectrometry (ICP-MS)) and petrological ((X-ray diffraction (XRD), electron probe micro-analyses (EPMA), Raman spectroscopy) analyses were performed on refractory material, slag, and contact of both. Two main types of reactions have been distinguished: gas/fluid- refractories and liquid- refractories. The first of them enrich the refractories with elements that migrate with the gas (Pb, K, Na, As, Zn) and transport the components building it (Fe, Mg, Ca) inward. Reactions between melted batch and refractory materials through gravitational differentiation and the melting of refractories lead to the formation of an aluminosilicate liquid with a high content of heavy elements. Cooling of this melt causes crystallization of minerals characteristic for slag, but with a modified composition, such as Fe-rich pyroxenes, Pb-rich K-feldspar, or PbO-As2O3-SiO2 glass.

Pyroclastic Density Current Facies in the Millennium Eruption of Tianchi Volcano, Northeast China: Insights From Topography, Stratigraphy, Granulometry, and Petrography

The 946 A.D. Millennium Eruption (ME) of Tianchi volcano produced masses of pyroclastic density current (PDC) deposits that cover an area that extends roughly 50 km from the crater. In order to understand PDC dynamic processes, this study examines the proximal to distal variations in the PDC facies by analysing the topography, stratigraphy, granulometry and petrography. Topography of Tianchi volcano has different slopes, including the cone (>6°), lava shield (2–5°) and lava plateau (20 km) are less than 10 m thick, with coarse-tail layers, ground surge layers, climbing layers, and carbonized woods in the plateau. The degree of PDC welding decreases with the distance from the crater. From the proximal to the distal strata, the emplacement temperature of the PDCs decreased from 740 °C to 280 °C. The medial layers indicate a gravitational differentiation effect and weakened transportation of the PDCs, which led to the formation of thick beds. The distal PDCs demonstrate fluidisation characteristics and a density far lower than those of the proximal and medial strata, which exhibit clear stratification. Grain size data (<64 mm) show that the median diameters decreases with increasing distance from the crater. Rhyolitic and trachytic pumice are found in the PDCs and are assumed to be associated with the composition of the magma chamber. Magmatic mixing structures were confirmed by microscope observations. The volume estimation of PDCs in China is 6.9806 km3. The PDCs exhibit characteristics of high temperatures, large volumes, flowing over long distances, and having the ability to climb hills. The PDCs were the most hazardous volcanic phenomena and can provide a reference for future potential PDC hazards around the Tianchi volcano.

Contrasting phase field method and pairwise force smoothed particle hydrodynamics method in simulating multiphase flow through fracture-vug medium

Strong heterogeneity and anisotropy result in complex flow and relatively low oil recovery in fractured-vuggy reservoirs. In this work, we assess the Cahn-Hilliard phase field method (PFM) and the pairwise force smoothed particle hydrodynamics (PF-SPH) method in modeling 2D multiphase flow through fracture-vug medium, in terms of different capillary numbers, mobility ratios, gravity, and wettability. Comparing the results of numerical simulations and physical experiments, the results of the PF-SPH method are closer to the physical experimental displacement process than those of the PFM, and the PF-SPH method is found to be computationally more efficient and accurate than the PFM. The experimental and numerical results reveal that when the injection velocity, represented via logarithm of the capillary number (LCN), is not greater than −4 (gas phase case) or −2.3 (water phase case) in the fracture-vug medium, the gravitative differentiation of the oil-gas or oil-water is significant, and the oil-gas or oil-water flow is a stable stratified flow. When the injection velocity LCN exceeds −3 (gas phase case) or −1.3 (water phase case) in the vertical section, the gravitative differentiation of the oil-gas or oil-water is not obvious, and the fluid flow pattern appears as an unstable jet flow.

Particle identification using semi-supervised learning in the PICO-60 dark matter detector

Astrophysical observations have demonstrated the existence of dark matter over the past decades. Experimental efforts in the search for dark matter are largely focused on the well-motivated weakly interacting massive particles (WIMPs) as a dark matter candidate. Current experiments in direct detection are producing increasingly competitive limits on the cross section of WIMP-nucleon scattering. The main experimental challenge for all direct detection experiments is the presence of background signals. These backgrounds need to be either eliminated by providing sufficient shielding or discriminated from WIMP signals. In this work, semi-supervised learning techniques are developed to discriminate alpha recoils from nuclear recoils induced by WIMPs in the PICO-60 detector. The two semi-supervised learning techniques, gravitational differentiation and iterative cluster nucleation, maximize the effect of the most confidently predicted data samples on subsequent training iterations. Classifications using both techniques can reproduce the traditional acoustic parameter with accuracies over 98%. The best model yields an accuracy of 99.2% and a class-wise standard deviation value of 0.11. These techniques can reliably serve as an intermediate verification tool before the acoustic parameter is constructed in future detectors.

Generalization of study experience of Ural ore deposits by method of tectonophysical analysis gravitational field

Gravity is important in the history of Earth 's formation and evolution. Gravitational accretion, gravitational differentiation of Earth matter by density. Gravitational accretion, gravity differentiation of the Earth 's substance in density, its movement and other processes deform the Earth 's crust, contribute to the formation in it of different scale, shape and metallogenical specialization of plicative and disjunctive structures, with which genetically and spatially related deposits of different minerals. The link between gravity and deformation of the geological medium is its density inhomogeneities. Their role is twofold: they are either formed by gravity stresses or are themselves sources of stress and strain. The method of studying the deformation of the geological medium by gravity is called tectonophysical analysis of the gravitational field. Its physical basis is two fundamental laws: the law of world gravity and the law on proportional dependence between stress and deformation. This method solves two problems.

Mineralogical and Geochemical Constraints of the REE Accumulation in the Almásfüzitő Red Mud Depository in Northwest Hungary

Detailed mineralogical and geochemical study of red mud samples from Hungary suggests geological and geochemical processes that determine the spatial distribution of certain elements inside the red mud pitfalls. The major processes are the following: (1) Heavy mineral grains (anatase, rutile, titanomagnetite, etc.) tend to subside due to gravitational differentiation and at present accumulate in the deepest horizons of the pitfalls. (2) Kaolinite reacts to cancrinite under hyperalkaline conditions. (3) Due to diagenetic processes, goethite-cancrinite aggregates form in situ. (4) Light mineral grains (e.g., cancrinite) move upward. (5) Cancrinite transforms to calcite at the shallowest horizons, due probably to the reaction with atmospheric CO2. All these processes have a significant role in accumulation tendencies of different groups of elements inside the pitfalls. The behaviour of chalcophile elements and the HFSE elements follow common geochemical rules and remind features of the host bauxite or even its precursor igneous or metamorphic lithologies. The REEs and Sc are possibly adsorbed on goethite and in the channels of cancrinite. Based on linear mixing model calculations, the major container of these elements is cancrinite. The proportion of the REEs and Sc in the Ti-phases, carbonates, phosphates, zircon, etc. is subordinate relative to the amount accumulated by goethite and cancrinite.

Gravitational differentiation in the regimes from stokes settling to Rayleigh–Raylor flows

The Earth’s core was formed under gravitational differentiation in the course of the separation of iron and silicates. Most of the iron has gone into the core as early as when the Earth was growing. However, iron continued to precipitate even during the subsequent partial solidification which developed from the bottom upwards. At the different stages and in the different layers of the mantle, iron was deposited in different regimes. In this paper, the mechanisms of the deposition of a cloud of heavy interacting particles (or drops) in a viscous fluid are considered. A new approach suitable for analytical and numerical tracing the changes in the structure of the flows in a two-component suspension under continuous transition from the Stokessettling (for the case of a cloud of large particles) to the Rayleigh–Taylor flows and heavy diapirs (for the case of a cloud of small particles) is suggested. It is numerically and analytically shown that the both regimes are the different limiting cases of the sedimentation convection in suspensions.

Gravitational Differentiation in the Regimes from Stokes Settling to Rayleigh–Taylor Flows

The Earth’s core was formed under gravitational differentiation in the course of the separation of iron and silicates. Most of the iron has gone into the core as early as when the Earth was growing. However, iron continued to precipitate even during the subsequent partial solidification which developed from the bottom upwards. At the different stages and in the different layers of the mantle, iron was deposited in different regimes. In this paper, the mechanisms of the deposition of a cloud of heavy interacting particles (or drops) in a viscous fluid are considered. A new approach suitable for analytical and numerical tracing the changes in the structure of the flows in a two-component suspension under continuous transition from the Stokes settling (for the case of a cloud of large particles) to the Rayleigh–Taylor flows and heavy diapirs (for the case of a cloud of small particles) is suggested. It is numerically and analytically shown that the both regimes are the different limiting cases of the sedimentation convection in suspensions.

Non-homogeneous Influence the Effect of CO2-N2 Compound Flooding in Ultra-low Permeability Reservoir

Affected by reservoir rhythmicity, permeability contrast and length-thickness ratio, using carbon dioxide-nitrogen compound flooding in ultra-low permeability non-homogeneous reservoir will influence the oil recovery. Based on the experimental core model, a series of targeted models are established by changing the correlation parameter by numerical simulations. The results shows that, the higher heterogeneity, the lower oil recovery in reservoir, the less carbon dioxide injection should be needed to achieve the maximum recovery; because of the gravitational differentiation and fluid exchange between the oil layers, using carbon dioxide-nitrogen compound flooding in non-interbedded positive rhythm reservoir will have a better recovery than positive rhythm of interbedded reservoir, negative rhythm of interbedded reservoir and negative rhythm reservoir without interbed; when the permeability contrast is a constant, the larger length-thickness ratio, the later the gas breakthrough and the higher oil recovery.

Experimental Modeling of the Formation of the Metallic Core of the Moon by the Method of High-Temperature Centrifuges

At early stages of the formation of planetary bodies, silicate, metallic, and sulfide phases, which have been formed in the course of the partial or complete fusion of the initial planetary substance, were subject to a gravitational differentiation. The latter is related to the separation of the crystalline and molten phases in density and composition. Althose in recent years a number of papers deal with the experimental and theoretical determination of the processes of the percalation of metallic melts through the crystalline silicate matrix and the physical properties of the metallic and sulfide melts. For the Moon, the problem of the existence of the metallic or sulfide core still remains unsolved. There is stil the nessity of further investigation in this direction. The possible origin of the Moon’s metallic core at the precipitation of iron-sulfide phases during the partial melting of ultramafic material under various redox conditions was experimentally modeled by partially melting the model system olivine (85 wt %)+ ferrobasalt (10 wt %)+ metallic phase Fe95S5 (5 wt %) in a high-temperature centrifuge at 1430-1450°C.

Analysis of Gas and Liquid Two-Phase Slug Flow Production Logging Interpretation Model in near Horizontal Shale Gas Wells

The development of shale gas reservoir is mainly based on horizontal well production. Slug flow of gas-liquid two-phase is invariably encountered in inclined wells and horizontal wells of a producing environment. Due to gravitational differentiation, oil-water two-phase flow pattern, the local velocity and local phase holdup along the radial direction of pipe in near horizontal wells will perform complicatedly. This paper presented the results of an experimental study and a theoretical analysis of two-phase gas/water flow in horizontal and highly inclined systems. Extensive experiments were conducted using a test loop made of 124 mm diameter acrylic pipe with inclination angles from the horizontal of 0°, 5°, 15°, 45°, -2°, -5° and -10°, and with the total flow rate ranging from 50 to 800 m3/day. Based on the research on the law of slug flow dynamics model for gas-water two-phase flow in near horizontal pipeline, the theoretical analysis and experimental researches were done to propose the expressions of stable and exact production logging interpretation model for two-phase flow in near horizontal pipeline. The performance of the proposed method for estimating water holdup and water superficial velocity is in good agreement with our measurements. As a result, the slug flow dynamics model of gas-water two-phase flow in near horizontal wellbore was developed. The application effect of production logging in near horizontal wells had been improved.

Study on the optimal development method for offshore buried hill fractured reservoirs

In order to understand the percolation mechanism and development regulation in offshore buried hill fractured reservoir, similarity criteria of physical simulation on water flooding in the fractured reservoirs were established by using similarity and flow theory. Based on the similarity theory and Warren–Root model, a large-scale (1 m × 1 m × 0.5 m) physical similarity model was built. By conducting the similar physical experiments, the behavior and mechanism of fluid flow in the reservoir in different development modes were studied, together with the optimal development program selected. The physical simulation results show that the stereoscopic staggered horizontal well pattern can give full play to the function of oil–water gravitational differentiation and reduce the rising rate of water cut. Flooding mechanisms vary from mode to mode: The sweep efficiency of cold water flooding is higher, whereas the oil displacement efficiency in the fracture and oil recovery in the matrix are lower in the affected area. The hot water flooding can improve the oil–water flow ratio of the mainstream line, reduce the seepage resistance, and improve the oil displacement efficiency in the fracture and the oil recovery of the matrix in the area. However, due to poor heat transfer efficiency, the difference of seepage resistance between the mainstream line and other regional increases results in decreased sweep efficiency. Surfactant flooding reduces oil–water interfacial tension and improves flooding efficiency in the area, yet degenerates oil recovery for the matrix.

Redox Evolution via Gravitational Differentiation on Low-mass Planets: Implications for Abiotic Oxygen, Water Loss, and Habitability

Abstract The oxidation of rocky planet surfaces and atmospheres, which arises from the twin forces of stellar nucleosynthesis and gravitational differentiation, is a universal process of key importance to habitability and exoplanet biosignature detection. Here we take a generalized approach to this phenomenon. Using a single parameter to describe the redox state, we model the evolution of terrestrial planets around nearby M stars and the Sun. Our model includes atmospheric photochemistry, diffusion and escape, line-by-line climate calculations, and interior thermodynamics and chemistry. In most cases, we find abiotic atmospheric buildup around M stars during the pre-main-sequence phase to be much less than calculated previously, because the planet’s magma ocean absorbs most oxygen liberated from photolysis. However, loss of noncondensing atmospheric gases after the mantle solidifies remains a significant potential route to abiotic atmospheric subsequently. In all cases, we predict that exoplanets that receive lower stellar fluxes, such as LHS1140b and TRAPPIST-1f and g, have the lowest probability of abiotic buildup and hence may be the most interesting targets for future searches for biogenic . Key remaining uncertainties can be minimized in future by comparing our predictions for the atmospheres of hot, sterile exoplanets such as GJ1132b and TRAPPIST-1b and c with observations.

Foam-EOR method in fractured-vuggy carbonate reservoirs: Mechanism analysis and injection parameter study

Fractured vuggy carbonate reservoirs in the Tahe Oilfield, China, have many diverse and unevenly distributed reservoir spaces. These spaces mainly consist of corrosion pores, high-density fractures, and large vugs. Reservoir development began with natural energy and pressure maintenance methods. However, a rapid rise of the water cut always led to poor oil production. Gas enhanced oil recovery (EOR) has shown notable improvement in the Tahe Oilfield; however, the recovery efficiency was limited by gas channeling. In this paper, a two-dimensional (2D) physical model was developed for a more detailed visual of the flow characteristics and the effect of the injection parameters (i.e., the injection rate, the injection slug size, the injection timing and the injection position) were evaluated. Water flooding can produce a certain amount of oil; however, the remaining oil types are the same as those found during the bottom water invasion period, that is, attic oil, bypass oil, and oil films. A better approach is N2 flooding, which can replace the attic oil at the top of the vug by gravitational differentiation. An even better method is N2 foam flooding. When the injection volume of N2 foam reached a certain level, foams accumulated in the flow channels, decreased fluid mobility, inhibited the gas channeling, and expanded sweep efficiency. Moreover, the N2 foam had excellent effects on oil film stripping, crude oil emulsification, and carrying oil droplets, thereby improving the microscopic displacement efficiency. In addition, the results of injection parameter effect can help researchers and reservoir engineers better understand and implement the foam-EOR method in the fractured vuggy carbonate reservoirs.