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Based on a genetic algorithm and field production data, this paper reasonably optimizes the fracture parameters of multistage fractured horizontal wells (MFHWs). First, a mathematical model of MFHWs in shale gas reservoir is proposed under the conditions of variable production and variable pressure. Then, the main factors affecting well production are determined by sensitive analysis. Finally, the production prediction model based on a genetic algorithm (GA) is used to optimize the fracture parameters of the Fuling shale gas reservoir. The results show that in the study area, the number of fractures in typical wells is 10, and the fracture half-length is 90m, and the fracture conductivity is 15.24mD.m. The effective fracture half-length is the main parameter affecting production, so the effective fracture half-length and effective fracture number should be increased reasonably, and the support concentration should be increased properly. What's more, the optimal solution of fracture half-length is 160m, and the optimal solution of fracture number is 8, and the optimal solution of fracture conductivity is 20 mD·m. This paper provides a new idea based a genetic algorithm for optimizing fracture parameters of shale gas wells in the Fuling area.

Warning and controlling the water invasion in water-driving gas reservoirs is significant because water invasion will seriously hamper well productivity and gas recovery. Unfortunately, there are few comprehensive methodologies to control water invasion. In this paper, firstly, a water invasion model of reservoir scale is established and verified. Then a new workflow for Warning and controlling the water invasion is developed by the numerical simulation method in this paper. This paper takes the water-gas ratio corresponding to the turning point of the water invasion rate as the water invasion identification signal. Then, the method of water control after water invasion is studied by turning off the perforation of the primary water production. Finally, the optimal water control scheme is obtained by comparing water and gas production. The results show that the reserve accuracy of the established water invasion model is 99%, and the model has a good pressure-fitting result. After studying the warning method of water invasion, it is found that the water-gas ratio of about 10-2 m3/104m3 is the signal of water breakthrough under the well produced at fixed production. The water-gas ratio in the range of 10-3 to 10-2 m3/104m3 signals water breakthrough in the well producing at a fixed pressure. The water-gas ratio as a signal of water breakthrough will increase with the increase of gas production rate and decrease with the fixed bottom hole pressure increase. The water-gas ratio chart of the early warning under the different producing models is drawn in this paper for applications in the field. A study of the water control method found that there will be a success in controlling the water cut after closing the perforation of the primary water production. Water production has been reduced by 90.9%, and gas production has been reduced by only 9.7% after using the technique in the field.

Replacing oil from small pores of tight oil-wet rocks relies on altering the rock wettability with the injected fracturing fluid. Among different types of wettability-alteration surfactants, the liquid nanofluid has less adsorption loss during transport in the porous media, and can efficiently alter the rock wettability; meanwhile, it can also maintain a certain oil-water interfacial tension driving the water imbibition. In the previous study, the main properties of a Nonionic nanofluid-diluted microemulsion (DME) were evaluated, and the dispersion coefficient and adsorption rate of DME in tight rock under different conditions were quantified. In this study, to more intuitively show the change of wettability of DME to oil-wet rocks in the process of core flooding experiments and the changes of the water invasion front, CT is used to carry out on-line core flooding experiments, scan and calculate the water saturation in time, and compare it with the pressure drop in this process. Besides, the heterogeneity of rock samples is quantified in this paper. The results show that when the DME is used as the fracturing fluid additive, fingering of the water phase is observed at the beginning of the invasion; compared with brine, the fracturing fluid with DME has deeper invasion depth at the same time; the water invasion front gradually becomes uniform when the DME alters the rock wettability and triggers the imbibition; for tight rocks, DME can enter deeper pores and replace more oil because of its dominance. Finally, the selected nanofluids of DME were tested in two horizontal wells in the field, and their flowback fluids were collected and analyzed. The results show that the average droplet size of the flowback fluids in the wells using DME decreases with production time, and the altered wetting ability gradually returns to the level of the injected fracturing fluid. It can be confirmed that DME can migrate within the tight rock, make the rock surface more water-wet and enhance the imbibition capacity of the fracturing fluid, to reduce the reservoir pressure decline rate and increase production.

Semiconductor–graphene composites have been widely reported as photocatalysts for hydrogen generation. The structure of the semiconductor, intimate interfacial contact between the components, and high electrical conductivity of the catalyst support can affect the performance of semiconductor–graphene composite photocatalysts. We successfully synthesized size-controlled ZnGa2O4 nanospheres by adjusting the amount of surfactant trisodium citrate, and assembled size-controlled ZnGa2O4 nanospheres on the two-dimensional platform of an N-doped reduced graphene oxide (N-rGO) sheet through the conventional and efficient hydrothermal method, during which the intimate interfacial contact between ZnGa2O4 nanospheres and the N-rGO sheet are achieved. The obtained photocatalysts were characterized by X-ray powder diffraction, Raman spectroscopy, transmission electron microscopy, X-ray photoelectron spectroscopy, and ultraviolet visible diffuse reflectance spectroscopy. The photocatalytic activity of the prepared samples for H2 evolution was tested using sodium sulfite as the sacrificial agent. The effects of the crystallinity, morphology, and specific surface area of the ZnGa2O4 samples on the rate of photocatalytic hydrogen production were studied. Considering the above three factors, the rate of H2 production was highest when the diameter of the ZnGa2O4 spheres reached 230 nm. The rate of H2 evolution of the ZnGa2O4/rGO and ZnGa2O4/N-rGO composites dramatically improved when compared with that of pure ZnGa2O4. ZnGa2O4/N-rGO had higher photocatalytic activity than ZnGa2O4/rGO because the nitrogen atoms in N-rGO could anchor the metal nanoparticles to form an intimate interfacial contact between N-rGO and ZnGa2O4, and N-rGO had higher electrical conductivity than rGO, resulting in more effective charge separation and transfer in the ZnGa2O4/N-rGO composites. This study offers a promising method to design more efficient graphene-based nanocomposite photocatalysts for enhancing photocatalytic activity.

Tight oil reservoirs typically have an estimated ultimate recovery of less than 10% after hydraulic fracturing, where enhanced oil recovery (EOR) technique is needed. Comparing to the gas-EOR, the surfactant-EOR neither alters the current fracturing procedure nor requires special injection facilities, and thus can be economically-viable under the current environment of low oil prices. However, tight rocks have small pores and large specific surface areas, which can make the adsorption rate of surfactants significant and thus limit the penetration depth of surfactants and its enhancement on oil recovery. In the published studies on the surfactant-EOR for shales and other tight reservoirs, this key parameter is only measured with the crushed rock samples, which can be underestimated comparing to that in the intact rock. Moreover, the dispersion coefficient that determines the penetration speed of a surfactant has never been directly measured in the tight rock, and the potential interaction between the surfactant and the friction reducer has neither been studied. In this study, a new form of surfactants is introduced, in which the wettability-alteration surfactants are firstly synthesized into oil-in-water microemulsions and then diluted to a designed concentration in the fracturing fluid. The thermodynamically-stable structure of microemulsion can minimize the adsorption rate of surfactants when transporting in the tight rock. Using coreflood experiments with UV–vis spectroscopy, the adsorption rate and dispersion coefficient of this form of surfactants are directly measured in tight rocks with a range of permeabilities, which are key parameters to modeling the EOR process and further scaling up laboratory findings for designing a field operation. To ensure the success of the surfactant-EOR technique in the field, the chosen surfactant needs to pass the preliminary screening including the aqueous stability test, the emulsion tendency test, the oil-water IFT measurement, and the shearing test; besides, it is also crucial to examine the compatibility between the slickwater and the wettability-alteration surfactant with different electric charges, which is seldom reported yet. In the end, the chosen surfactant is tested in two pairs of horizontal wells on one pad site, whose flowback water is collected and analyzed for better understanding the behavior of this surfactant.

The adsorption and nucleation behavior of Run (n = 1–4) clusters deposited on absolutely dehydrated and hydroxyl-modified γ-Al2O3 (100) and (110) surfaces were studied using density functional theory slab calculations. The results indicated that the adsorption process was strongly sensitive to cluster size and surface structure, with deformation and metal–support interactions apparently related. A single Ru atom preferred to adsorb on the (100) surface with small deformation energies, while small interaction energies led to the adsorption of Ru4 clusters on the (110) surface. When the surface was dehydrated, the adsorption of Run (n = 2–4) clusters on the (110) surface was substantially more stable than that on the (100) surface. The stronger acceptor and almost equal donor sites present on the dehydrated (110) surface increased the bidirectional electron transfer between the clusters and surface sites, resulting in lower adsorption and interaction energies. When the surface was hydrated, the introduction of hydroxyl groups lowered the Run (n = 2–4) clusters' adsorption ability on the hydrated (110) surface by decreasing the surface acidity and basicity, thereby weakening the driving force underlying electron transfer. However, for single Ru atoms, the opposite behavior was observed. In this case, the surface hydroxyl groups increased the stability of the adsorption of the Run (n = 1–4) clusters on the hydrated (100) surface as surface H acted as an adsorption site, receiving an electron from the Ru atom because of its strong Lewis acidity. Further, the support can stabilize the Run (n = 2–4) clusters by decreasing the binding energies of supported configurations lower than the corresponding gas phase. And the nucleation of Run clusters on all surfaces is thermodynamically favourable. The hydration of the (110) surface facilitates agglomeration of Ru4 clusters, while it is suppressed on the (100) surface. These results are relevant to understanding the interaction between surfaces and clusters.

In this paper, we demonstrate an effective method for the performance improvement of organic thin film transistors (OTFTs), in which the SiO2 dielectric layer was dually modified with polystyrene (PS) and hexamethyldisilazane (HMDS) self-assembled monolayer. The relationship between interfacial modification and device performance of OTFTs was systematically investigated. With the dual HMDS/PS modification, the SiO2 dielectric film turns from intrinsically hydrophilic surface to hydrophobic one. Moreover, the dual HMDS/PS modification induces the ordered growth of pentacene layer with large grains up to about 1.5 μm. As a result, the performance of OTFTs is remarkably enhanced, such as the increase in charge carrier mobility from 0.56 to 1.05 cm2/Vs and the increase in on/off current ratio from 105–106 to 106–107. These results indicate that the dual interfacial modification of dielectrics is a simple and effective approach for the OTFT performance improvement.

Solution-processed high-k dielectrics for organic thin film transistors (OTFTs) have been widely studied with the objective of achieving high-performance and low cost OTFTs for next-generation electronics. In this study, we introduce a universal solution fabrication of high-k amorphous oxide dielectrics for high-performance OTFTs. The amorphous oxide films by solution processes feature a smooth surface, uniform composition and excellent dielectric properties. With ZrTiOx as a typical example, a k value and capacitance as high as 53 and 467 nF cm−2 could be achieved. The polystyrene (PS) modification of ZrTiOx dielectric films results in a leakage current as low as 4 × 10−8 A cm−2. Based on their implementation as a gate insulator, the solution-processed high-k ZrTiOx dielectric films realize high and stable performance OTFTs during operation at a low-voltage. A carrier mobility of 0.58 cm2 V−1 s−1, an on/off current ratio of 104, and a low operating voltage of 6 V were achieved through simple control of the annealing temperature. Our results show the possibility of the solution-processed high-k amorphous oxide dielectric layer as a gate insulator for OTFTs. We believe that these high-k amorphous oxide dielectric films offer great potential for next-generation high-performance organic electronics, especially low-voltage electronics.

Nanocrystalline Y3Al5O12:Eu 3+ phosphors with particle size about 20-40 nm have been synthesized by a facile solution com- bustion method. XRD and TEM studies show that Y3Al5O12 nanocrystals can directly form at a low temperature of 825 � and highly crystalline at 850 �. With the increase of annealing temperature, the charge transfer band shows a blue shift due to the dielectric con- finement effect. The color purity of Y3Al5O12:Eu 3+ phosphors can be improved by decreasing the grain size of nanocrystals. Furthermore, the high concentration doping of Eu 3+ can be realized in Y3Al5O12 nanocrystals, which will enhance the luminescent intensity. This work demonstrated that solution combustion is a feasible method to synthesize europium rare earth doped Y3Al5O12 nanocrystals with en- hanced optical properties.

In this paper, nanostructured ZrO2 films were prepared by electron beam evaporation with the glancing angle deposition (GLAD) technique. Columnar films with voids in between formed owing to the self-shadowing effect and the limited diffusion of deposited atoms. The microstructure evolves from slanted columnar structure to helical and pillar structures as the substrate rotational speed increases. The diameter of the columns is in the range of 30–50 nm. A higher rotational speed favors a larger nodule size and a greater surface roughness. Due to the porous structure, the refractive index n of GLAD ZrO2 films varies from 1.75 to 1.80, lower than that of bulk material. A maximum value of birefringence (Δn=0.03) is obtained in a slanted columnar structure, and the relationship between birefringence and microstructure orientation is discussed. Our results demonstrate that glancing angle deposition is a feasible approach for designing the nanostructure and optical properties of thin films.

In this paper, the organic pentacene-based thin film transistors with SiO 2 /PMMA bilayer dielectric were fabricated and the device performance improvement with the varying PMMA concentration was investigated. When the PMMA concentration decreases from 60mg/ml to 20 mg/ml, the device mobility increases from 0.06 to 0.1 cm2/Vs, and the on/off current ratio increases from 103 to 104. Top-contact OTFT devices with double PMMA layer were also fabricated. The results showed that the second PMMA layer can modify the dielectric/semiconductor interface and therefore improve the device performance.

A gold nanoparticle enhanced organic transistor non-volatile memory (ONVM) operated at ultralow voltages of up to −1 V has been achieved by facile room-temperature solution-processed hybrid nanolayer dielectrics. The amorphous ZrTiOx nanolayer dielectrics exhibit a high-k value of 18.9 and a high capacitance of 705 nF cm−2. With the modification of the octadecylphosphonic acid (ODPA) monolayer, the a-ZrTiOx/ODPA hybrid nanolayer dielectrics exhibit a high capacitance of 514 nF cm−2 and a very low leakage current density of 2 × 10−7 A cm−2. The pentacene transistor-based ONVMs with the a-ZrTiOx/ODPA hybrid nanolayer dielectrics could be operated in operating voltages as low as −1 V. With ultralow operating voltages, ONVMs show high performances, such as high hole mobility (0.3 cm2 V−1 s−1), large memory window (1.5 V), and long charge retention time (4 × 104 s) directly in ambient air. Our results suggest the great potential of low-temperature solution-processed hybrid nanolayer dielectrics for the realization of low-power and high-performance organic electronic devices.

In this paper, the controlled performance of a novel organic pentacene transistor memory device with an ultrathin LiF blocking layer was investigated. Our results demonstrate the introduction of an ultrathin LiF layer has a significant influence on the transistor memory performance. As the LiF thickness increased from 0 to 3 nm, the charge carrier mobility showed a three-fold increase from 0.15 to 0.43 cm2 V−1 s−1 due to hole injection enhancement. Moreover, the on/off current ratio increased from 5 to 50 at long measurement times. This significant enhancement of charge retention behavior (∼10 times improvement) was ascribed to the LiF blocking effect when the trapped charge was released from silver nanoparticle induced trap centers. However, the memory window showed a slight decrease from 60 to 37 V, which is due to the decreased penetration depth of silver nanoparticles into the pentacene layer. The physical origin of the memory effect with the LiF ultrathin layer was also discussed. Our introduction of an ultrathin LiF layer offers a simple and feasible way to control the different memory performances of this novel transistor memory device.