基于线性和双曲型Drucker-Prager准则的水泥环完整性研究

Research of the cement sheath integrity based on the linear and hyperbolic Drucker-Prager criteria

水泥环在油井使用中起着至关重要的作用,它可防止层间错流,并为套管提供支撑。考虑到井下条件的复杂环境,数值模拟在水泥环完整性评价中起着重要作用,准确描述水泥环的力学性能变得越来越重要。本文对水泥石的破坏准则进行了研究。为了预测不同胶结石的强度特性,对胶结石进行了单轴拉伸和三轴压缩实验。根据实验结果,采用线性Drucker-Prager(D-P)准则和双曲型D-P准则对水泥石的破坏进行了预测。采用热-力耦合有限元模型对高温条件下水力压裂过程中水泥环的完整性进行了评价。实验结果表明,双曲型D-P准则在压缩剪切和拉伸破坏方面都比线性D-P准则具有更好的精度。

Cement sheath is of vital importance in well life,it prevents inter-zonal cross-flow and provides support for the casing.Considering the complicated environments under down hole condition,numerical simulation plays an important role in cement sheath integrity evaluation,accurate description of the mechanical behavior of cement sheath becomes increasingly important.This paper presents an investigation about the failure criteria of cement stone.In order to predict the strength characterization of different cement stones,a series of uniaxial tension and triaxial compression experiment were conducted for cement stone.Based on the experiment results,both linear Drucker-Prager(D-P)and hyperbolic D-P criteria were used to predict the failure of cement stone.A coupled thermo-mechanical finite element model is used to evaluate the cement sheath integrity during the hydraulic fracturing under high temperature condition.The experiment results indicate that hyperbolic D-P criteria show better precision than the linear D-P criteria for both compression shear and tensile failure.