Effects of Material Parameters on Stress Distribution in Casing-cement-formation(CCF)Multilayer Composite System

This work focus on the stress distribution of the casing-cement-formation(CCF)multilayer composite system,which is a borehole system with multiple casings and cement sheathes.Mostof the previous relevant studies are based on the traditional CCF system with the single casing and cement sheath,but these results are not adaptive to the CCF system multiple composite system.In this paper,the FEM numerical model of CCF multilayer composite system was constructed.Numerical simulations were calculated and compared with the system which consists of the single casing and cement sheath.Results show that the multilayer composite system possesses better performance.On this basis,the sensitivity analysis of main influence mechanical parameters such as in-situ stress,the elastic of cement sheathes and the elastic of formation are conducted.The cement sheath on the inside,namely cement sheath-1,is sensitive to its elastic modulus;meanwhile,the cement sheath on the outside,namely cement sheath-2,is not so sensitive to the elastic modulus of cement sheath-1.Cement sheath-1 and cement sheath-2 are all sensitive to the elastic modulus of cement sheath-2,and the mises stress of them has opposite trend to the elastic modulus of cement sheath-2.The proper values of elastic modulus of cement sheath-1 and cement sheath-2 are 5GPa and 5GPa to 30GPa,respectively.Under the in-situ stress ratio σh/σH=0.7,the maximum mises stress of cementsheath-1 and cement sheath-2 increase as the increase of σh,and they are nearly equal when σh=15GPa.This research can be helpful for the design and analysis of CCF multilayer composite system.

Research on the Damage of Porosityand Permeabilitydue to Perforation on Sandstone in the Compaction Zone

A perforating hole is a channel through which the oil and gas in a reservoir pass into the production well bore.During the process of perforating due to explosion,the surrounding sandstone will be damaged to a certain extent,which will increase the well bore skin and lead to the decrease of production consequently.In this work a mechanical model of perforating damage is developed to describe the influences of perforating due to explosion on the porosity and permeability of the surrounding sandstone near the compaction zone.Based on this developed model,the important data related to the damage of sandstone,such as matrix effective stress,plastic deformation,volumetric strain,and so on,can be numerically simulated.Especially the behaviors of plasticity kinematic hardening at high strain rate due to impact loads,which are the important characteristics in the sandstone,is taken into account in this developed model.Both numerical and testing results show that the damage due to perforation in the sandstone can be accurately predicted by the developed model together with the porosity and permeability evolving model of perforation in a compaction zone.As a practical application,a methodology for the analysis of damage of porosity and permeability around a perforation tunnel is supposed based on the developed model and the core flow efficiency test of interparticle pore spaced sandstone target in China Shengli Oilfield and the computed tomography test.