An innovative experimental apparatus for the analysis of natural gas hydrate cavitation erosion process using laser-induced cavitation.

Natural gas hydrates (NGHs) are an emerging source of clean energy distributed in the pores of soil sediments in deep seabed and permafrost zones with abundant reserves. Cavitation contains enormous energy, thus allowing radial cavitation jets to improve drilling and production rates of NGHs. This paper presents an experimental apparatus that was developed to synthesize NGHs and generate cavitation bubbles by laser for the analysis of the erosion rules of NGHs by cavitation in a reservoir environment. The apparatus consists of a working fluid injection and pressure control system, a temperature control and circulation system, a laser-induced cavitation system, a visual reaction vessel, and a data acquisition and measurement system. The laser-induced cavitation erosion on NGHs and multi-bubble interaction experiments can be conducted over temperatures and pressures in the range of 0-20 °C and 0-12 MPa, respectively, in a visualized reaction vessel. Hydrophones and high-speed photography were utilized for monitoring and analyzing the erosion process within the visualized reaction vessel. In addition, bubble groups of different components in various environments can also be tested in this apparatus to obtain the interaction characteristics under different conditions. This paper discusses the basic structure and principle of the apparatus and conducts a series of experiments to verify the effect of cavitation erosion on hydrate and the feasibility of using cavitation to increase production in hydrate exploitation.

A Comprehensive Evaluation Framework of Water-Energy-Food System Coupling Coordination in the Yellow River Basin, China.

For mankind's survival and development, water, energy, and food (WEF) are essential material guarantees. In China, however, the spatial distribution of WEF is seriously unbalanced and mismatched. Here, a collaborative governance mechanism that aims at nexus security needs to be urgently established. In this paper, the Yellow River Basin in China with a representative WEF system, was selected as a case. Firstly, a comprehensive framework for WEF coupling coordination was constructed, and the relationship and mechanism between them were analyzed theoretically. Then, we investigated the spatiotemporal characteristics and driving mechanisms of the coupling coordination degree (CCD) with a composite evaluation method, coupling coordination degree model, spatial statistical analysis, and multiscale geographic weighted regression. Finally, policy implications were discussed to promote the coordinated development of the WEF system. The results showed that: 1) WEF subsystems showed a significant imbalance of spatial pattern and diversity in temporal changes; 2) the CCD for the WEF system varied little and remained at moderate coordination. Areas with moderate coordination have increased, while areas with superior coordination and mild disorder have decreased. In addition, the spatial clustering phenomenon of the CCD was significant and showed obvious characteristics of polarization; and 3) the action of each factor is self-differentiated and regionally variable. For different factors, GDP per capita was of particular importance, which contributed most to the regional development's coupling coordination. For different regions, GDP per capita, average yearly precipitation, population density, and urbanization rate exhibited differences in geographical gradients in an east-west direction. The conclusion can provide references for regional resource allocation and sustainable development by enhancing WEF system utilization efficiency.

Study on Cutting Chip in Milling GH4169 with Indexable Disc Cutter.

The study and control for chip have a significant impact on machining quality and productivity. In this paper, GH4169 was cut with an indexable disc milling cutter. The chips corresponding to each group of cutting parameters were collected, and the chip parameters (chip curl radius, chip thickness deformation coefficient, and chip width deformation coefficient) were measured. The qualitative relationship between the chip parameters and cutting parameters was studied. The quadratic polynomial models between chip parameters and cutting parameters were established and verified. The results showed that the chip parameters (chip curl radius, chip thickness deformation coefficient and chip width deformation coefficient) were negatively correlated with spindle speed; chip parameters were positively correlated with feed speed; chip parameters were positively correlated with cutting depth. The maximum deviation rate between measured values and predicted values for chip curl radius was 9.37%; the maximum deviation rate for cutting thickness deformation coefficient was 13.8%, and the maximum deviation rate of cutting width deformation coefficient was 7.86%. It can be seen that the established models are accurate. The models have guiding significance for chip control.

[Research progress on compliant characteristics of lower extremity exoskeleton robots].

The lower extremity exoskeleton robot is a wearable device designed to help people suffering from a walking disorder to regain the power of the legs and joints to achieve standing and walking functions. Compared with traditional robots that include rigid mechanisms, lower extremity exoskeleton robots with compliant characteristics can store and release energy in passive elastic elements while minimizing the reaction force due to impact, so it can improve the safety of human-robot interaction. This paper reviews the compliant characteristics of lower extremity exoskeleton robots from the aspects of compliant drive and compliant joint, and introduces the augmentation, assistive, rehabilitation lower extremity exoskeleton robots. It also prospect the future development trend of lower extremity exoskeleton robots.

Nanoscale Surface Properties of Organic Matter and Clay Minerals in Shale.

Surface properties of shale play an essential role in adsorption, transport, and production of hydrocarbons from shale reservoirs. Nanoscale surface properties of kerogen and minerals of shale were examined by a series of techniques including X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIRS), and atomic force microscopy (AFM). The results show that aluminosilicate is the main component of inorganic matter, while kerogen chiefly consists of carbon. FTIRS and XPS analysis indicate that the chemical bonds of the kerogen surface are O-H, C-C, C-O, pyrrolic, and so on. In contrast to kerogen, illite's bonds are mainly Si-O and Al-O. AFM results indicate that the adhesion force of kerogen is higher than that of illite in shale. In addition, at a preloading force of 2500 nN, the adhesion force of kerogen increases from 40.8 to 118.2 nN when retraction velocity increases from 500 to 2500 nm/s. The adhesion forces of montmorillonite, calcite, and muscovite are 33.7 ± 6.28, 23.8 ± 11.8, and 105.1 ± 9.1 nN, respectively. The chemical composition and bonds have a profound effect on the adhesion force of shale, which further reveals the transport and adsorption mechanism of methane in kerogen.

Single-component multiphase lattice Boltzmann simulation of free bubble and crevice heterogeneous cavitation nucleation.

This work serves as an important extension of previous work on cavitation simulation [Sukop and Or, Phys. Rev. E 71, 046703 (2005)10.1103/PhysRevE.71.046703]. A modified Shan-Chen single-component multiphase lattice Boltzmann method is used to simulate two different heterogeneous cavitation nucleation mechanisms, the free gas bubble model and the crevice nucleation model. Improvements include the use of a real-gas equation of state, a redefined effective mass function, and the exact difference method forcing scheme. As a result, much larger density ratios, better thermodynamic consistency, and improved numerical accuracy are achieved. In addition, the crevice nucleation model is numerically investigated using the lattice Boltzmann method. The simulations show excellent qualitative and quantitative agreement with the heterogeneous nucleation theories.

A Comprehensive Model for Real Gas Transport in Shale Formations with Complex Non-planar Fracture Networks.

A complex fracture network is generally generated during the hydraulic fracturing treatment in shale gas reservoirs. Numerous efforts have been made to model the flow behavior of such fracture networks. However, it is still challenging to predict the impacts of various gas transport mechanisms on well performance with arbitrary fracture geometry in a computationally efficient manner. We develop a robust and comprehensive model for real gas transport in shales with complex non-planar fracture network. Contributions of gas transport mechanisms and fracture complexity to well productivity and rate transient behavior are systematically analyzed. The major findings are: simple planar fracture can overestimate gas production than non-planar fracture due to less fracture interference. A "hump" that occurs in the transition period and formation linear flow with a slope less than 1/2 can infer the appearance of natural fractures. The sharpness of the "hump" can indicate the complexity and irregularity of the fracture networks. Gas flow mechanisms can extend the transition flow period. The gas desorption could make the "hump" more profound. The Knudsen diffusion and slippage effect play a dominant role in the later production time. Maximizing the fracture complexity through generating large connected networks is an effective way to increase shale gas production.

Optimization of Operation Parameters for Helical Flow Cleanout with Supercritical CO2 in Horizontal Wells Using Back-Propagation Artificial Neural Network.

Sand production and blockage are common during the drilling and production of horizontal oil and gas wells as a result of formation breakdown. The use of high-pressure rotating jets and annular helical flow is an effective way to enhance horizontal wellbore cleanout. In this paper, we propose the idea of using supercritical CO2 (SC-CO2) as washing fluid in water-sensitive formation. SC-CO2 is manifested to be effective in preventing formation damage and enhancing production rate as drilling fluid, which justifies tis potential in wellbore cleanout. In order to investigate the effectiveness of SC-CO2 helical flow cleanout, we perform the numerical study on the annular flow field, which significantly affects sand cleanout efficiency, of SC-CO2 jets in horizontal wellbore. Based on the field data, the geometry model and mathematical models were built. Then a numerical simulation of the annular helical flow field by SC-CO2 jets was accomplished. The influences of several key parameters were investigated, and SC-CO2 jets were compared to conventional water jets. The results show that flow rate, ambient temperature, jet temperature, and nozzle assemblies play the most important roles on wellbore flow field. Once the difference between ambient temperatures and jet temperatures is kept constant, the wellbore velocity distributions will not change. With increasing lateral nozzle size or decreasing rear/forward nozzle size, suspending ability of SC-CO2 flow improves obviously. A back-propagation artificial neural network (BP-ANN) was successfully employed to match the operation parameters and SC-CO2 flow velocities. A comprehensive model was achieved to optimize the operation parameters according to two strategies: cost-saving strategy and local optimal strategy. This paper can help to understand the distinct characteristics of SC-CO2 flow. And it is the first time that the BP-ANN is introduced to analyze the flow field during wellbore cleanout in horizontal wells.

Design of experimental setup for supercritical CO2 jet under high ambient pressure conditions.

With the commercial extraction of hydrocarbons in shale and tight reservoirs, efficient methods are needed to accelerate developing process. Supercritical CO2 (SC-CO2) jet has been considered as a potential way due to its unique fluid properties. In this article, a new setup is designed for laboratory experiment to research the SC-CO2 jet's characteristics in different jet temperatures, pressures, standoff distances, ambient pressures, etc. The setup is composed of five modules, including SC-CO2 generation system, pure SC-CO2 jet system, abrasive SC-CO2 jet system, CO2 recovery system, and data acquisition system. Now, a series of rock perforating (or case cutting) experiments have been successfully conducted using the setup about pure and abrasive SC-CO2 jet, and the results have proven the great perforating efficiency of SC-CO2 jet and the applications of this setup.

Study and application of a high-pressure water jet multi-functional flow test system.

As the exploration and development of oil and gas focus more and more on deeper formation, hydraulic issues such as high-pressure water jet rock breaking, wellbore multiphase flow law, cuttings carrying efficiency, and hydraulic fracturing technique during the drilling and completion process have become the key points. To accomplish related researches, a high-pressure water jet multi-functional flow test system was designed. The following novel researches are carried out: study of high-pressure water jet characteristics under confining pressure, wellbore multiphase flow regime, hydraulic pressure properties of down hole tools during jet fracturing and pulsed cavitation jet drilling, and deflector's friction in radial jet drilling. The validity and feasibility of the experimental results provided by the system with various test modules have proved its importance in the research of the high-pressure water jet and well completion technology.