The Influence Of Rock Anisotropy On Differential Strain Analysis

Relevant researches about in-situ stress in geomechanics,have shown their status in oil and gas explorations and developments.According to the isotropy hypotheses,the differential strain analysis(DSA)has been applied to measure the stress ratio and the directions of in-situ stress.In fact,most of the strata rocks have some anisotropy,which may lead to inaccurate results.Few experts focus on this issue in the mainland.The thesis is to analyse the influence of anisotropy on differential strain analysis.Firstly,hypotheses and limitations on DSA are investigated and concluded.Secondly,a modified DSA method and an in-situ stress formula for anisotropic rocks are put forward.The new method allows the measurements of sandstones,conglomerates and shales.The outcomes with the new formula show the inherent anisotropy and the stress history of rocks.Thirdly,the relation is detected among the effective rock compressibility,the elastic modulus and the aspect ratio of microcracks,unveiling the mechanisms of such influences.Brief conclusions are listed below.(1)Results are different among sandstones,shales and conglomerates.(2)The stress differences are enlarged by the formula of anistropic rocks for in-situ stress ratio.(3)The stress-induced anisotropy should be considered.(4)The effective compressibility of rock changes and the cracks close with hydrostatic loads.