Optimizing winograd-based convolution with DCU’s matrix cores

Volcanic gas reservoir in Xushen gas field has complex microscopic pore throat structure and dense physical property, which is quite different from that of conventional high-permeability sandstone gas reservoir. It is of great significance to know its seepage mechanism for scientific and efficient development technology countermeasures. Through the parallel and series experiments of volcanic fracture cores and matrix cores, the gas flow changes of fractures and matrix cores with different permeability levels under different pressure gradients were measured, and the percolation mechanism of volcanic gas reservoirs with different pressure gradients was revealed when fractures and matrix cores were in parallel or series. The experimental results show that the fracture is the dominant channel relative to the matrix, and the supply and exhaust capacity of the fracture is much larger than that of the matrix, and the permeability of the matrix determines the supply and exhaust capacity of the series system composed of fracture and matrix

A novel gastro-floating multiparticulate system for dipyridamole (DIP) based on a porous and low-density matrix core: In vitro and in vivo evaluation

Stress-sensitive permeability (SSP) influences gas well productivity and is a crucial element influencing gas reservoir development. SSP for high-pressure fractured gas reservoirs with an initial reservoir pressure of more than 20 MPa has never been comprehensively evaluated to the best of our knowledge. SSP experiments with special procedures were designed by adopting the variable confining pressure (VCP) and variable internal pressure (VIP) methods. VCP is a test method in which the confining pressure is altered and a constant internal pressure is maintained for the experimental core holder. VIP is a test method in which the internal pressure is changed and a constant confining pressure is maintained. A four-stage curve analysis method was developed to perform regressions on semilogarithmic curves and exponential curves of experimental data. A method to evaluate the SSP was developed using stress sensitivity coefficients obtained via regressions. A calculation approach for determining the degrees of permeability damage and permeability recovery also was evaluated. In total, six matrix cores and six cores with artificial fractures from a high-pressure fractured sandstone gas reservoir were tested using the two methods. The SSP curves for high-pressure reservoirs were characterized by four-stage variation trends, which show differentiation with low-pressure reservoirs with an initial reservoir pressure less than 20 MPa. The stress sensitivity of the VCP method was stronger than that of the VIP method. The core samples mainly showed a “medium”/“medium-strong” stress sensitivity under low/high effective stress conditions. Compared with matrix cores, fractured cores showed stronger stress sensitivity owing to strong plasticity and weak elasticity. The maximum permeability damage degree reached 99.67%, and the minimum permeability recovery was only 6.9%. Our method of experimental design, four-stage curve analysis, stress sensitivity evaluation, and our overall findings can provide references for future studies on SSP in high-pressure fractured sandstone gas reservoirs.

Context: This article discusses the downstream processing of nanosuspensions into oral solid dosage forms.Objective: Various factors influencing the release kinetics of various pellet formulations containing drug nanocrystals have been evaluated. The effects of binder types, drug content and pellet type on the in-vitro dissolution profiles were investigated.Materials and methods: Hydrocortisone acetate (HCA) was nanosized by using a piston gap homogenizer Micron Lab 40. The nanosuspension was admixed to various binder solutions based on chitosan chloride, polyvinyl alcohol, hydroxypropyl methylcellulose or polyvinylpyrrolidone (PVP) and sprayed on sugar beads using fluidized bed coating. For comparison, matrix cores have also been prepared using the extrusion-spheronization process. An enteric top coating was applied onto both pellet types. All pellet formulations have been tested In in-vitro dissolution studies.Results and discussion: HCA nanosuspensions were compatible with all binders tested except for PVP. Various suspensions could be successfully transferred into spray coated pellets as well as matrix cores including a top coating. The different binder types have influenced the stability of the nanosuspensions, the zeta potential of the drug nanocrystals as well as the dissolution profiles of the final solid dosage forms.Conclusion: Nanosuspensions can be easily processed into various pellet formulations. Spray coating with water-soluble binders is recommended for high dose drugs. This technology is also more variable with respect to the drug load In the final dosage form. Matrix cores can be beneficial for highly water-insoluble formulations, especially when only relatively low doses are needed.

Enhanced oil recovery by air-foam flooding system in tight oil reservoirs: Study on the profile-controlling mechanisms

Understanding mechanisms and performance of formation sensitivity damage in naturally fractured carbonate reservoirs is crucial for avoiding productivity attenuation at any development stage. In this paper, based on the investigation of reservoir microscopic feature, a series of experiments were conducted to systematically evaluate formation sensitivity damage through a multistep coreflood platform. Firstly, the influence of flow velocity on core permeability was studied. Then, coreflood experiments under the condition of beneath the threshold velocity were performed to research the influence of the salinity and PH value for the injected water on core permeability. Finally, four types of cores from Ordos Basin—matrix cores, non-packed cores, semi-packed cores, and fully-packed cores—were used to conduct stress sensitivity damage experiments. Permeability is measured in the process of increasing confining pressure with a constant pore pressure. The experiment results show that the velocity sensitivity of the reservoir is medium to strong and the threshold velocity is 0.28 m/d. The water sensitivity is weak and the average water sensitivity index is 22.62%. There is no alkali sensitivity. The stress sensibilities of these four types of cores ranking from strong to weak are non-packed cores, semi-packed cores, packed cores, and matrix cores. With the decrease in packing degree of core fractures, the stress sensitivity of core permeability increases and the recovery degree of permeability decreases. The influence factors of sensitivity damage are systematically studied and it provides the suggestions for stimulation design and development of naturally fractured carbonate reservoirs in Ordos Basin.

Ultra-low permeability rocks have plenty of microfractures. The stress-dependent permeability has a significant impact on the seepage. Previous studies are mainly on the permeability variation with stress in low permeability reservoir. But few are involved in ultralow permeability cores. In this paper, the experiment of stress sensitive ultralow permeability cores which are fabricated (both matrix cores and microfracture cores) is conducted. The experimental results shows that the permeability of microfracture low permeability cores which are fabricated increases greatly while the porosity of low permeability cores is little affected. This indicates that the fabricated microfracture cores are in line with that of the real situations of fracture media reservoir. By comparison, the permeability stress sensitive hysteresis degree of microfracture cores is not apparent and the permeability recovery degree is high in the unloading cycle. This study is of great benefit to reveals the stress sensitivity features of ultralow permeability reservoir

Stress sensitive experiments for abnormal overpressure carbonate reservoirs: A case from the Kenkiyak fractured-porous oil field in the littoral Caspian Basin

Experimental study on EOR potential of P(AM/NVP) based gel in ultra-high temperature reservoirs

An experimental investigation was undertaken to modify the permeability profile of high permeability fluid zones (producing and injection) using gelling (cross linking) polymers. The first phase of this study included characterization of "super-K" zones. Computerized Tomography (CT), Scanning Electron Microscopy (SEM), X-ray Diffraction (XRD) and an Apparatus for Pore Examination (APEX) system were used to determine the mineralogy and pore geometry of carbonate core plugs obtained from the matrix and super-K zones. In the second phase of the study, various gelling solutions were injected into reservoir core samples to evaluate the ability of the gel to resist extrusion and determine the robustness of the treatment chemical under downhole conditions. Core plugs used in this study were obtained from an oil producer in a carbonate reservoir in Saudi Arabia. The results of the first phase indicated that the super-K streaks have a tortuous path. There are significant differences between the lithology and pore size distribution of the super-K zones and the normal matrix. In addition, there is convincing evidence that the super-K intervals may be fractured as well diagenetically induced. The use of thin section petrology has highlighted potential problems in using the gel in formations that are vugular or have large diameter natural fractures. The data has demonstrated that the gel will not fully fill pore voids greater than 400 microns, and would not invade pores smaller than 70 microns. Coreflood tests indicated that the gelling solution could be injected into either the matrix super-K or the fractured super-K. Reservoir condition aging improved the stability of the gels that were placed in matrix cores, but gave in less promising results in fractured intervals.

The application of miscible CO2 flooding for enhanced oil recovery in a vuggy/fractured carbonate formation has found commercial success in the Weyburn reservoir (Saskatchewan). The Weyburn waterflood performance indicated that flow could be classified as matrix flow, with certain sections of the reservoir dominated by fracture flow. The physical mechanisms that lead to improved miscible flood recovery in fracture-dominated flow are only partially understood. To highlight the different recovery mechanisms, coreflood tests in homogeneous, matrix cores and artificially fractured limestone cores were conducted. For some of these miscible CO2 displacement tests, the in situ oil saturations were continuously monitored using a magnetic resonance imaging (MRI) technique. Image analysis demonstrated how channeling, gravity segregation, and partial displacement led to contrasting recoveries in matrix and fractured cores. Additional improvement in oil recovery was obtained by implementing conformance control methods such as foams, gels, and gel-foams. Injecting blocking and diverting gels into the fractured cores proved to be the most effective means of conformance control, providing improved sweep efficiency and resulting in accelerated oil production during subsequent CO2 injection. Introduction In the Weyburn, Midale reservoir, two oil-bearing intervals, the Vuggy and the Marly, have different fracture characteristics, extents of water invasion and degrees of heterogeneity1,2. Since this reservoir is characterized by trending fractures and alternating layers of high and low permeability, conformance control of the injected CO2 is crucial in optimizing the oil recovery and enhancing the storage capacity of the CO2. Once miscibility has been achieved, in situ, between the injected CO2 and the displaced oil then conformance control is the key factor in conducting an economic miscible displacement flood. Two forms of conformance control have already been implemented in the Weyburn reservoir. Injecting the CO2 in water alternating gas (WAG3,4) mode controls the mobility of the gas between more viscous slugs of water. A mechanical form of conformance control has been achieved by placing the horizontal injection and production wells such that the overall fluid flow is in the off-trend fracture direction. But even in the off-trend direction, fractures with generally smaller apertures can be found. Thus CO2 channeling between injector and producer could occur. Additional conformance control measures for the CO2 injection project need to be implemented in order to achieve maximum oil recovery efficiency. The overall scope of this study was to evaluate the performance of commercially available conformance control technologies and move the technology from laboratory tests to field application. These technologies were all based on chemical formulations, which can be categorized into mobility control agents (foams5,6,7), blocking and diverting agents (gel8,9,10), and hybrids thereof (gel-foams11,12,13). The first objective in this research project was to screen and optimize conformance control formulations for the three chemical conformance technologies. The impact of the optimized formulations for CO2 conformance control was then tested in coreflood experiments. Homogeneous carbonate packs were used as the porous medium to conduct early coreflood studies. More rigorous testing of the conformance products was conducted in artificia

Compared to values inferred from laboratory tests on matrix cores, many field tracer tests in fractured rock have shown enhanced matrix diffusion coefficient values (obtained using a single-process matrix-diffusion model with a homogeneous matrix diffusion coefficient). To investigate this phenomenon, a conceptual model of multi-process matrix diffusion in a single-fracture system was developed. In this model, three matrix diffusion processes of different diffusion rates were assumed to coexist: (1) diffusion into stagnant water and infilling materials within fractures, (2) diffusion into a degraded matrix zone, and (3) further diffusion into an intact matrix zone. The validity of the conceptual model was then demonstrated by analyzing a unique tracer test conducted using a long-time constant-concentration injection. The tracer-test analysis was conducted using a numerical model capable of tracking the multiple matrix-diffusion processes. The analysis showed that in the degraded zone, a diffusion process with an enhanced diffusion rate controlled the steep rising limb and decay-like falling limb in the observed breakthrough curve, whereas in the intact matrix zone, a process involving a lower diffusion rate affected the long-term middle platform of slowly increasing tracer concentration. The different matrix-diffusion-coefficient values revealed from the field tracer test are consistent with the variability of matrix diffusion coefficient measured for rock cores with different degrees of fracture coating at the same site. By comparing to the matrix diffusion coefficient calibrated using single-process matrix diffusion, we demonstrated that this multi-process matrix diffusion may contribute to the enhanced matrix-diffusion-coefficient values for single-fracture systems at the field scale.

The rates of release of Al by M NH4NO3 (pH 3) from minerals saturated with Al ions at pH 3 suggest that Al ions migrated from the surface layers and the matrix cores of kaolinite, montmorillonite, illite, and biotite, but only from the matrix core of muscovite mica. From the 0.25–0.5 μm kaolinite and montmorillonite, part of the ‘surface’ Al is released ‘instantaneously’ and the rest by first order kinetics, but the coarse 1.5–2.5 μm kaolinite has only the former component. From illite and biotite, ‘surface’ Al is released by ‘bulk diffusion’ kinetics suggesting the existence of disturbed peripheral layers of finite thickness. The diffusion coefficients, Dm, for the matrix core follow the trend: mica ≃ biotite > illite > montmorillonite > kaolinite.Based on models proposed in previous work, the ionic composition of the ‘surface’ Al is calculated. This shows that (1) this composition varies according to the mineral from 3 to 100% Al3+, the remainder being in the hydrolyzed form, and (2) the apparent hydrolysis constants are different for each mineral and significantly different from those of Al ions in solution.

Empodisma minus and Sporadanthus ferrugineus (both Restionaceae) coexist in New Zealand raised bogs, yet Sporadanthus have significantly more depleted 15N natural abundance signatures than coexisting Empodisma. Their root systems are spatially separated with Empodisma having a thick surface layer of about 50 mm of cluster roots overlying the deeper Sporadanthus roots. We hypothesized this root displacement allows Empodisma to preferentially access the primary N input from rainfall, thus establishing niche separation, and tested this using tracer stable isotopes. We aerially applied 1.6 mmol m−2 of 15N as (NH4)2SO4 chased by deionized water to simulate a rainfall event of 34 L m−2. Root/peat matrix cores were harvested after 5 h and analysed for 15N uptake. Approximately 80% of the tracer applied was recovered in the cores, with 90% of this recovered in the upper Empodisma cluster root layer. Seven weeks after application, young shoots of Empodisma were significantly enriched (mean δ15N = +7.21‰; reference = −0.42‰), whereas those of coexisting Sporadanthus were not (mean δ15N = −2.76‰; reference = −4.24‰). However, we were unable to quantify the 15N uptake because of the dilution effect of the large biomass. We calculated the contribution of biological nitrogen fixation as a possible alternative source of N in achieving niche separation. The acetylene reduction assay showed minor amounts of nitrogenase activity are associated with Empodisma and Sporadanthus roots (equivalent to 0.045 ± 0.019 and 0.104 ± 0.017 kg N ha−1 year−1 respectively). Our results suggest that the species acquire nutrients from different rooting zones, with Empodisma accessing nutrients at the surface from rainfall and Sporadanthus accessing nutrients from mineralization in deeper peat layers. Such niche differentiation probably facilitates species coexistence and may provide a mechanism for slowing the rate of competitive displacement during long‐term succession.

Physical simulation of the nonlinear transient flow behavior in closed high-pressure gas reservoirs. Part I: Pressure-depleted flow experiments on matrix cores