Mechanical property design method of cement sheath in a horizontal shale oil well under fracturing conditions

Based on the elastoplastic model of cement sheath considering the influence of three-dimensional principal stress and the stress field model of interface crack,a mechanical performance design method of cement sheath is established to meet the wellbore sealing requirements during fracturing.This method takes the failure types of the cement sheath,such as tensile failure,plastic yield,interface crack propagation along interface and zigzag propagation into account.Meanwhile,the elasticity modulus and Poisson's ratio quantitative design charts of cement sheath are constructed based on this method,and the safety and risk areas of wellbores are defined,which quantify the yield strength and tensile strength indexes of cement sheath.The results show that decreasing elasticity modulus,increasing yield strength and Poisson's ratio of cement sheath can avoid plastic deformation of cement sheath;increasing the tensile strength of cement sheath can prevent its tensile failure;increasing elasticity modulus and Poisson's ratio of cement sheath is good for shortening the length of the interface crack,but will increase the risk of interface cracks zigzagging into cement sheath.The model calculation and case verification has proved that the method in this paper can give accurate calculation results and is convenient for field application.

Seawater temperature and salinity sensing based on in-fiber Michelson-Fabry-Perrot hybrid interferometer employing frequency domain decomposition method

We propose an in-fiber Michelson-Fabry-Perrot(M-FP)hybrid interferometer for the simultaneous measurement of seawater temperature and salinity.The sensor head consists of two parallel hetero Fabry-Perot(FP)cavities fabricated on the end face of the twin core fiber(TCF).A fiber fusion taper is used to split and recouple the light in the two cores.In this case,the Vernier effect can be obtained which can greatly enhance the sensitivity and solve the problem of temperature cross-sensitivity.Different from the traditional demodulation method based on envelop detection,we employed frequency domain decomposition method(FDDM)to demodulate the sensing signal.The simulation results indicate that the proposed sensor has high sensitivity to salinity and temperature.Thanks to the merits of high sensitivity,ease of fabrication and small footprint,the proposed seawater temperature and salinity sensor would have potential applications in marine science,food industry and ocean ranching.

Reconstruction performance for image transmission through multimode fibers

Due to the applications in the fields of optical communication,neuronal imaging,and medical endoscopic imaging,the study of multimode fiber(MMF)wavefront transmission is crucial for image reconstruction and wavefront generation in user terminals.State of art studies in this area focus on high-quality image reconstruction and wavefront shaping.Besides the way of imaging reconstruction,the performances of image reconstruction and wavefront shaping are also dependent on system and environment parameters.This paper numerically analyzes the influence of key factors,such as the numerical aperture(NA)of the near-end objective lens of the MMF imaging system,the charge coupled device(CCD)noise of the acquired image,and the ambient temperature at close distances.This work would help to the optimization of the MMF-based imaging system and provide a theoretical basis for potential applications in optical communication systems,neuron imaging and endoscopic diagnosis.

Research of line-of-sight angle on aero-optic imaging deviation for vehicles flying at 40—60 km

Aero-optical imaging deviation is a kind of optical effect,aiming at a conical aircraft.This paper analyzes the influence of the aircraft on the imaging deviation with the change of altitude and line-of-sight angle.In this paper,the relationships between imaging deviation and altitude as well as line-of-sight angle are analyzed,and the coupling relationship between altitude and line-of-sight angle is studied.We give the imaging deviation results of 5°—75°line-of-sight angle.The analysis shows that when the line-of-sight angle is in the range of 5°—35°,the imaging deviation is more sensitive,while the line-of-sight angle is in the range of 35°—75°,the imaging deviation is relatively flat,and the imaging deviation does not gradually decrease with the increase of line-of-sight angle,but there is a turning point in the middle of 5°—75°.The imaging deviation decreases first and then increases,and the turning point of line-of-sight angle is closely related to height.