Progress of Development and Application of Drag Reduction Agents for Slick-Water Fracturing

Fracturing technology is the key technology of shale oil and gas exploitation in the United States. The key of hydraulic fracturing lies in the formulation of fracturing fluid, which can improve the permeability of shale gas layer, reduce pumping resistance, optimize production conditions, reduce strata damage and other purposes. Slick-water is widely used in water-based fracturing for unconventional oil and gas exploitation, which can reduce the friction resistance. As the core of the slickwater fracturing fluid, the friction reducer determine the fluid’s performances. Combining with the related literature at home and abroad, this paper analyzes the mechanism of friction reducer, introduces the research and application progress of natural polysaccharide, surfactant and polyacrylamide. It is considered that both the instant powder polymer and W/W dispersion polymer have great application potential. The friction reducer with high-efficiency sand-carrying and salt resistance is the focus of future research.

Drop impact on superheated surfaces: short-time dynamics and transition to contact

When a volatile drop impacts on a superheated solid, air drainage and vapour generation conspire to create an intermediate gas layer that delays or even prevents contact between the liquid and the solid. In this article, we use high-speed synchronized reflection interference and total internal reflection imaging to measure the short-time dynamics of the intermediate gas film and to probe the transition between levitation and contact. We observe that the substrate temperature strongly affects the vertical position of the liquid–gas interface and that the dynamic Leidenfrost transition is influenced by both air and vapour drainage (i.e. gas drainage), and evaporation, the latter giving rise to hitherto unreported vertical oscillations of the gas film that can trigger liquid–solid contact. We first derive scaling relations for the height of the gas film trapped under the drop's centreline, called the dimple height, and the minimum film thickness at short times. The former is set by a competition between gas drainage and liquid inertia, similarly as for isothermal impacts, while the latter strongly depends on the vapour production. The gas pressure, at the location where the minimum thickness is reached, is determined by liquid inertia and vapour production and ultimately balanced by the increasing interfacial curvature, determining the minimum thickness. We show that, in the low impact velocity limit, the transient stability of the draining gas film remarkably makes dynamic levitation less demanding than static levitation. We characterize the vertical gas film oscillations by measuring their frequency and monitoring their occurrence in the parameter space spanned by surface temperature and impact velocity. Finally, we model the occurrence of these oscillations and account for their frequency through a hydrodynamic mechanism.

MODELING THE INTERACTION OF A FILM OF A NONLINEAR VISCOUS LIQUID WITH A GAS FLOW

The problem of the interaction of a two-layer film of a nonlinear viscous liquid flowing down a flat surface with a gas flow directed vertically up or down is considered. To simplify the initial system of differential equations, the method of a small parameter is used, for which the relative thicknesses of the films and the gas layer were chosen. Analytical expressions are obtained for the profiles of the velocities and thicknesses of liquid films.

Cases of Generalized Low-frequency Shadows of Tight Gas Reservoirs

The phenomenon that frequency decreases and amplitude increases near the bottom of a gas layer on a seismic profile is called a low-frequency shadow, but this phenomenon may not occur in all gas reservoirs. When the tight gas reservoir is thick enough, spectral decomposition data after Fourier transform will show the characteristics similar to those of low-frequency shadows. We call it a generalized low-frequency shadows. Compared with dominant frequency of non-gas-bearing zone spectral, the dominant frequency of a gas zone moves toward the low end of the frequency range and the low-frequency amplitude increases accordingly. By analyzing known gas reservoirs such as the Sulige and Yanchang tight sandstones in the Ordos Basin and tight carbonate rocks in the Tarim Basin, we can see that, with the visual dominant seismic frequency close to 30 Hz, the peak frequency of the gas-bearing tight sandstones and tight dolomite reservoirs will move from about 30 Hz to about 10–15 Hz. There is a certain correlation between the drop of the dominant frequency of a tight gas reservoir, the attenuation energy difference, and the thickness and productivity of the gas layer. Several cases show that nearly all tight gas layers thicker than 15 m exhibit attenuation characteristics of the generalized low-frequency shadows.

Possibility of using gas lubricant in the cylinders of internal combustion engines of transport vehicles

The prospects of using the gas-static suspension of the internal combustion engine piston in transport vehicles and power plants are considered. The diagram of the piston and the method for calculating the stiffness and bearing capacity of the gas layer surrounding the piston are presented, as well as the results of experiments that showed the relevance of this method. The possibility of gas and static centering of the engine piston is confirmed. Keywords: internal combustion engine, piston, gasstatic suspension, stiffness, bearing capacity, gas medium. [email protected]

Using diving waves for detecting shallow overburden gas layers

We propose to use simple time shift analysis of diving waves to analyze shallow gas layers in a sedimentary overburden. By using simple equations for how the traveltime will change if a thin sand layer is charged by gas in a localized and constrained region, we show that such variations can be used to map and quantify the thickness of the gas layer. We use conventional 3D seismic data acquired close to a well where an unintended underground gas flow occurred in 1989. Raw seismic data are used as input and timeshifts are estimated for constant offsets for events that are interpreted as being predominantly diving waves. By assuming that the very shallow subsurface has a constant velocity gradient of 0.5 s-1, we find diving wave time shifts that fits an average thickness of the gas layer of approximately 3-4 m. This is the minimum gas thickness since it is assumed that the time shift analysis captures both the diving wave hitting the top and the base of the gas layer (sufficient dense offset sampling is important to achieve this). The outline and circumference of the close to circular gas anomaly around the well obtained by the diving wave analysis is confirmed by the 3D reflection mapping of the same anomaly.

Enhanced laser-driven proton acceleration with gas–foil targets

We study numerically the mechanisms of proton acceleration in gas–foil targets driven by an ultraintense femtosecond laser pulse. The target consists of a near-critical-density hydrogen gas layer of a few tens of microns attached to a $2\ \mathrm {\mu }$ m-thick solid carbon foil with a contaminant thin proton layer at its back side. Two-dimensional particle-in-cell simulations show that, at optimal gas density, the maximum energy of the contaminant protons is increased by a factor of $\sim$ 4 compared with a single foil target. This improvement originates from the near-complete laser absorption into relativistic electrons in the gas. Several energetic electron populations are identified, and their respective effect on the proton acceleration is quantified by computing the electrostatic fields that they generate at the protons’ positions. While each of those electron groups is found to contribute substantially to the overall accelerating field, the dominant one is the relativistic thermal bulk that results from the nonlinear wakefield excited in the gas, as analysed recently by Debayle et al. (New J. Phys., vol. 19, 2017, 123013). Our analysis also reveals the important role of the neighbouring ions in the acceleration of the fastest protons, and the onset of multidimensional effects caused by the time-increasing curvature of the proton layer.