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Numerical simulation of borehole Stoneley wave refection by a fracture based on variable grid spacing method

100%

Ou W. , Wang Z. , Ning Q. , Xu F. , Yu Y.

Acta Geophysica

2019

tom Vol. 67, no. 4

1119--1129

In this paper, the finite difference method is used to model the Stoneley wave refection by a horizontal fracture in a borehole. The fracture shape is described by some finite difference grids. Therefore, the fracture aperture can be varied in the radial direction, thus extending previous researches on the assumption that the fracture aperture is constant throughout the fracture. Finite difference grids can also be used to describe a fracture which extends a finite distance in the radial direction. In addition, the finite difference algorithm can deal with the problem of inhomogeneous formation. Therefore, it allows the variation of formation elasticity in the model. Fine grids are needed to describe the small fracture aperture, and variable grid spacing is employed by finite difference method to improve computational efficiency. The Stoneley wave propagation is simulated by the variable grid spacing finite difference method in several models with variable fracture aperture, finite extension fracture and models with heterogeneous formation. The variable grid spacing finite difference method is validated through a comparison with real axis integration method and the analytical method. We get some conclusions by simulating and investigating effects of the variation of fracture aperture, the fracture of finite extension and inhomogeneity of formation on the Stoneley wave refection. Although the fracture aperture changes along the fracture extension direction, the refection coefficient of Stoneley wave is mainly controlled by the fracture aperture near the borehole. The Stoneley wave in the fracture is reflected back into the borehole, by the tip of finite extension fracture, which results in some notches in the refection coefficient curve. If the Stoneley wave propagates from the formation with small elastic modulus to the formation with large elastic modulus, the refection coefficient of Stoneley wave will be larger than that of homogeneous model with small elastic modulus. And if Stoneley wave propagates from the formation with large elastic modulus to the formation with small elastic modulus, the refection coefficient of Stoneley wave will be smaller that of homogeneous model with large elastic modulus. These results provide some basis for the use of Stoneley wave to detect the fracture properties in formation.

Simultaneous determination of carbofuran and 3-hydroxycarbofuran in duck liver by an UPLCMS/MS

86%

Chen S. , Yu Y. , Ma J. , Wen C. , Wang X. , Zhou Q.

Acta Chromatographica

2021

tom Vol. 33, no. 4

354--360

Carbofuran is a carbamate pesticide, a broad-spectrum, high-efficiency, low-residue, and highly toxic insecticide, acaricide, and nematicide, widely used in agriculture. Carbofuran is most harmful to birds, and birds or insects killed by furan poisoning can be killed by secondary poisoning after being foraged by raptors, small mammals, or reptiles. In this paper, an UPLC-MS/MS method was developed for the determination of carbofuran and its metabolite, 3-hydroxycarbofuran, in duck liver. Liver tissue was first ground into a homogenate and then passed through ethyl acetate liquid-liquid extraction processing samples. Multiple reaction monitoring (MRM) mode was used for quantitative analysis, m/z 222.1 → 165.1 for carbofuran, m/z 238.1 → 180.9 for 3-hydroxycarbofuran and m/z 290.2 → 198.2 for an internal standard. The standard curves of carbofuran and 3-hydroxycarbofuran in duck liver were within a range of 2–2000 ng/g, where the linearity was good, the lower limit of quantification was 2 ng/ g. The intra-day precision of carbofuran and 3-hydroxycarbofuran was <14%, and the inter-day precision was <13%, the accuracy range was between 91.8 and 108.9%, the average extraction efficiency was higher than 75.1% with a matrix effect between 93.4 and 107.7%. The developed method was applied to a situation of suspected duck poisoning at a local farm.