Search

Accurately predicting the propagation of hydraulic fracturing arising from the wellbore is essential in petroleum engineering, hydraulic engineering, etc. There are various factors influencing fracture propagation, such as the initial fracture orientation and in-situ stresses, while the limitation of appropriate methods and techniques hinders the further investigation on the propagating mechanism. In the study, a simulator based on High-order Generalized Finite Element Method (GFEM) is introduced to investigate the propagation behaviors of hydraulic fractures arising from the sidewall of wellbore. For better recognization of hydraulic fracturing, several numerical examples are performed based on the simulator. Different influencing factors are studied, including intersection angle between fracture and wellbore, in-situ stresses and fracture interactions. It is found that, regardless of in-situ stresses in the surrounding rock, pre-existing fractures approximately propagate straightforward along their initial directions and finally form planar fracture surfaces. Regarding in-situ stresses, with acute intersection angle between fracture and wellbore, fractures propagate toward the direction of the minimum principal stress. Besides, two parallel and opposite fractures individually arising from two parallel and non-coincidence wellbores always propagate towards each other after passing by each other. Moreover, the interactions between them become strengthened as the distance between them decreases. Finally, the propagating sequences of hydraulic fractures arising from a group of parallel wellbores are discussed. It is found that the sequence can influence the fracture geometry and previously propagated fractures can restrain the nearest fractures embedded in other wellbores propagating away from each other in subsequent stages.

In view of the importance and complexity of international crude oil price, this paper proposes a novel combination forecast approach that captures a variety of fluctuation features in crude oil data series, including change points, regime-switching, time-varying determinants, trend decomposition of high-frequency sequences, and the possible nonlinearity of model setting. First, product partition model-K-means (PPM-KM) model is used to detect change points in the oil price sequence. Next, we apply a time-varying transition probability Markov regime switching (TVTP-MRS) model to identify the regime-switching characteristic. Then, we use Bayesian model averaging (BMA) to filtrate main determinants at each regime. Finally, the time-varying parameter structure time series model (TVP-STSM) is used to decompose the oil sequence, capture the time-variation of coefficients in “volatile upward” regime, and forecast the crude oil price. Compared with some other competing models and benchmark model of ARIMA, the newly proposed method shows superior forecasting ability in four statistical tests. Besides, we make scenario prediction on WTI crude oil price to examine the implementation effect of OPEC cut-off agreement at the end of 2016. OPEC production and U.S. shale oil production are used as two scenario variables, and the WTI price is forecasted fluctuating around 50 dollar/barrel based on three scenario prediction. We conclude that WTI crude oil price would take a shock upstream tendency in the short-term but the rising scope would not be large.

As China’s high-speed railway featured by low-carbon quick prospers rapidly, railway transport has been regarded as a crucial means to replace the aviation transport. Selecting the data from 156 routes of China's 48 major cities from 2001 to 2014, the paper takes the aviation mileage as the threshold variable and the operation time as the control variable to build a panel threshold regression model. Firstly, under the consideration of the economic, demographic, environmental and railway indicators, the paper analyzes the influence of China’s railway on the aviation passenger volume and the flight number; secondly, under the condition that the railway speed is more than 250 km/h, the paper analyzes the shock effect of China’s high-speed railway on aviation transport. The conclusion shows that the higher the level of the economic development is, the more developed the aviation transport of the region will be. when the aviation mileage is below 1132 km, as the aviation mileage increases, the influence of China’s railway to the aviation transport fall into a decline; China’s high-speed railway has a positive shock effect on the aviation transport, and the shock effect reaches the maximum when the aviation mileage is from 650 to 755 km. This paper is of great practical significance to study the optimization of transportation structure.

VP60 capsid protein is the major structural and immunogenicity protein of RHDV (Rabbit hemorrhagic disease virus, RHDV), and has been implicated as a main protein antigen in RHDV diagnosis and vaccine design. In this report, egg yolk antibody (IgY) against N-terminal of VP60 was evaluated and developed as a new strategy for RHDV therapy. Briefly, N-terminal of VP60 (∼250aa) fragment was cloned and inserted into pET28a expression vector, and then the resultant plasmid, pET28a/VP60-N, was transformed into E. coli BL21(DE3) for recombinant VP60-N protein (rVP60-N) expression. Next, the rVP60-N was purified by Ni(+)-affinity purification chromatography and identified by Western blotting with RHDV antiserum. After immunizing the chickens with rVP60-N, the anti-rVP60-N IgY was isolated, and the activity and specificity of the IgY antibody were analyzed by ELISA and Western blotting. In our results, the rVP60-N could be expressed in E. coli as soluble fraction, and the isolated anti-rVP60-N IgY demonstrated a high specificity and titer (1:22,000) against rVP60-N antigen. For further evaluation of the IgY efficacy in vivo, rabbits were grouped randomly and challenged with RHDV, and the results showed that anti-rVP60-N IgY could significantly protect rabbits from virus infection and promote the host survival after a sustained treatment with anti-rVP60-N IgY for 5 days. Taken together, our study demonstrates evidence that production of IgY against VP60 could be as a novel strategy for the RHDV therapy.