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.