Plugging Characteristics and Evaluation Predicting Models by Controllable Self-Aggregation Nanoparticles in Pore Throat Microcapillaries.

Injecting nanoparticle profile agents into low-permeability heterogeneous reservoirs to plugging water breakthrough channels is a widely used technical method to enhance oil recovery. However, insufficient research on the plugging characteristics and prediction models of nanoparticle profile agents in the pore throat has led to a poor profile control effect, short profile control action time, and poor injection performance in the actual reservoir. This study uses controllable self-aggregation nanoparticles with a diameter of 500 nm and different concentrations as profile control agents. Microcapillaries of different diameter sizes were used to simulate the pore throat structure and flow space of oil reservoirs. Based on a large number of cross-physical simulation experimental data, the plugging characteristics of controllable self-aggregation nanoparticles in the pore throat were analyzed. Gray correlation analysis (GRA) and gene expression programming algorithm (GEP) analysis were used to determine the key factors affecting the resistance coefficient and plugging rate of profile control agents. With the help of GeneXproTools, the evolutionary algebra 3000 was selected to obtain the calculation formula and prediction model of the resistance coefficient and plugging rate of the injected nanoparticles in the pore throat. The experimental results show that the controllable self-aggregation nanoparticles will achieve effective plugging when the pressure gradient is greater than 100 MPa/m in the pore throat, and when the injection pressure gradient is 20-100 MPa/m, the nanoparticle solution will be in the aggregation to breakthrough state in the pore throat. The main factors affecting the injectability of nanoparticles, from strong to weak, are as follows: injection speed > pore length > concentration > pore diameter. The main factors affecting the plugging rate of nanoparticles, from strong to weak, are as follows: pore length > injection speed > concentration > pore diameter. The prediction model can effectively predict the injection performance and plugging performance of controllable self-aggregating nanoparticles in the pore throat. The prediction accuracy of the injection resistance coefficient is 0.91, and the accuracy of the plugging rate is 0.93 in the prediction model.

A Form of Non-Volatile Solid-like Hexadecane Found in Micron-Scale Silica Microtubule.

Anomalous solid-like liquids at the solid-liquid interface have been recently reported. The mechanistic factors contributing to these anomalous liquids and whether they can stably exist at high vacuum are interesting, yet unexplored, questions. In this paper, thin slices of silica tubes soaked in hexadecane were observed under a transmission electron microscope at room temperature. The H-spectrum of hexadecane in the microtubules was measured by nuclear magnetic resonance. On the interior surface of these silica tubes, 0.2-30 µm in inside diameter (ID), a layer (12-400 nm) of a type of non-volatile hexadecane was found with thickness inversely correlated with the tube ID. A sample of this anomalous hexadecane in microtubules 0.4 µm in ID was found to be formable by an ion beam. Compared with the nuclear magnetic resonance H-spectroscopy of conventional hexadecane, the characteristic peaks of this abnormal hexadecane were shifted to the high field with a broader characteristic peak, nuclear magnetic resonance hydrogen spectroscopy spectral features typical of that of solids. The surface density of these abnormal hexadecanes was found to be positively correlated with the silanol groups found on the interior silica microtubular surface. This positive correlation indicates that the high-density aggregation of silanol is an essential factor for forming the abnormal hexadecane reported in this paper.

Field Validation of a Non-logging Alternative Method for the Prediction of the Location of Water-Cresting in Horizontal Wells for Water-Drive Reservoirs.

A previously reported method for a non-logging alternative method for the prediction of the location of water-cresting in horizontal wells for water-drive reservoirs is validated in a field test for the first time in this study. Using this method, the wellbore trajectory, variation in the reservoir permeability, and the pressure gradient data were used to calculate what is called the breakthrough coefficient for the different segments along the length of a set horizontal well with the largest calculated breakthrough coefficient corresponding to the most likely location of the actual water-cresting occurrence. This method was field-validated and found to be in good agreement with log testing for a group of seven wells in an oilfield in Northern China. Another calculated parameter derived from the breakthrough coefficient which is called the variation of the breakthrough coefficients that characterize the effect of the variation of water production along the length of the horizontal well due to the effect of the variation of the wellbore trajectory, permeability, and pressure gradient on the oil production is also introduced. This field validation found variation of the breakthrough coefficients to be weakly and inversely correlated to the oil production in application to a group of 27 wells in the same field.

Core-Shell Co2VO4/Carbon Composite Anode for Highly Stable and Fast-Charging Sodium-Ion Batteries.

Sodium-ion batteries (SIBs) are promising candidates for large-scale energy storage systems due to the abundance and wide distribution of sodium resources. Various solutions have been successfully applied to revolve the large-ion-size-induced battery issues at the mid-to-low current density range. However, the fast-charging properties of SIBs are still in high demand to accommodate the increasing energy needs at large to grid scales. Herein, a core-shell Co2VO4/carbon composite anode is designed to tackle the fast-charging problem of SIBs. The synergetic effect from the stable spinel structure of Co2VO4, the size of the nanospheres, and the carbon shell provide enhanced Na+ ion diffusion and electron transfer rates and outstanding electrochemical performance. With an ultrahigh current density of 5 A g-1, the Co2VO4@C anode achieved a capacity of 135.1 mAh g-1 and a >98% capacity retention after 2000 cycles through a pseudocapacitive dominant process. This study provides insights for SIB fast-charging material design and other battery systems such as lithium-ion batteries.

Method of Predicting the Location of Water Cresting for Horizontal Wells in a Water-Drive Reservoir for Early Prevention.

A method of prediction of location of water cresting and characterizing its intensity in a horizontal well in a water-drive reservoir is introduced for the first time. A mechanistic model for water cresting derived from Darcy's equation incorporating the main parameters reported in the literature affecting water cresting-viscosity, well distance to the aquifer, wellbore pressure gradient, and reservoir heterogeneity-is introduced with two new characterizing parameters. First is a model-derived parameter, called the breakthrough coefficient, which is defined as the ratio of the average time of breakthrough to the time of breakthrough for a segment of the well, with the model-predicted location of water cresting corresponding to the well segment with the largest breakthrough coefficient. The second is the Cresting index, which is the ratio of the maximum breakthrough coefficient to the minimum breakthrough coefficient as a characterizing parameter, with a well with a higher cresting index corresponding to a faster breakthrough in a group of similar wells. This methodology was validated through a series of sophisticated experimental corefloods and found to predict 78% of the location of the water cresting accurately. The cresting index is found to be weakly correlated with the speed of breakthrough among similar wells.

Interplay between Rock Permeability and the Performance of Huff-n-Puff CO2 Injection.

The CO2 huff-n-puff experiments are often conducted on a rock sample with a given permeability. However, there is a need for understanding the production performance of CO2 huff-n-puff over a range of rock permeability values. In this study, CO2 huff-n-puff corefloods were conducted by using 30 cm long artificial cores over a permeability range between 0.7 and 240 mD. After that, the cores and produced oil were analyzed by NMT tests and gas chromatography tests. The effects of rock permeability on primary parameters, such as ultimate oil recovery, gas and oil ratio (GOR), pressures, residual oil distribution, and produced oil composition, were studied in detail. The experimental results indicate that the overall CO2 huff-n-puff efficiency increases with permeability, while the production dynamics also changes with permeability. The oil production is greater and realized faster in high permeability core samples than low-permeability rocks; hence, maintaining the same production efficiency for low-permeability samples needs more production cycles and a longer production time. Fortunately, the GOR of CO2 huff-n-puff in low-permeability samples is lower, which is favorable in long-term production. In contrast, a larger produced GOR is realized in high-permeability core samples, especially beyond the optimal cycle. Moreover, although the CO2 front occurs at a shorter distance from the inlet as rock permeability decreases, CO2 huff-n-puff can simultaneously produce oil from different pore sizes of different permeability core samples. The permeability of core samples also has a significant influence on the composition of the produced oil. The CO2 extraction capability is stronger in samples with a lower permeability.

Experimental study on factors affecting the end effect in gas viscosity measurement using capillary-tube viscometer.

Because of its simple principle and high adaptability to severe operational conditions, the capillary-tube viscometer has been widely used for viscosity measurement. However, difficulties in accurately correcting the end effect induced measurement deviation will result in great uncertainty for measurement results. In order to solve this problem, in this work, we studied factors affecting the end effect by conducting the high pressure nitrogen viscosity measurement at low flow velocity with an improved capillary-tube viscometer. The experimental results indicated that the influence of the end effect became less significant with the decrease in flow velocity (v) and tube inner diameter (d) and varied inversely with the length of tube (L). We defined the ratio of measured viscosity to standard viscosity obtained from the NIST database as the viscosity deviation coefficient (Ce). From the Ce vs v, Ce vs d, and Ce vs L curves, we have observed that there existed a threshold velocity (vthreshold), a threshold diameter (dthreshold), and a threshold length (Lthreshold) at which Ce got closer to 1.0. It suggested that under certain experimental conditions, the influence of the end effect on gas viscosity measurement became negligible. Based on that, we established end effect free capillary-tube viscometry and compared the nitrogen viscosity results measured by this method with the data provided by the NIST database. The results presented a good match with error within 1.2%. These insights will contribute to improving the accuracy of a capillary-tube viscometer especially under high pressure.