基于横向各向同性模型的致密砂岩地应力测井评价方法

Geostress logging evaluation method of tight sandstone based on transversely isotropic model

中国致密砂岩储层属陆相成因,在成岩过程中不但存在组成矿物定向引起的内在各向异性,也存在板状层理、交错层理或成分层等引起的各向异性。常规基于各向同性模型的地应力计算方法已不适用,需要建立适用于致密砂岩性质的新模型。通过对松辽盆地全直径致密砂岩进行不同方向取心,测量了不同岩心不同方向的纵、横波速度,实验结果表明,致密砂岩具有横向各向同性性质,进一步建立了基于横向各向同性特征的弹性系数表征方法。将岩心应力应变实验与声波实验相结合,建立了适用于目标区的动、静态模量转换模型,并将其应用于基于横向各向同性模型的致密砂岩地应力测井评价中。应用结果表明该模型与压裂结果一致,能更好地反映实际地层情况。

The tight sandstone reservoirs in China present a terrestrial genesis. In the diagenetic process, there is not only the inherentanisotropy caused by mineral orientation, but also the anisotropy induced by tabuIar bedding, cross bedding or compositional iaye-ring. The conventional geostress calculation methods based on isotropic models are not applicable, and thus it is required to establish a new model for tight sandstone. Through the whole-diameter coring in different directions of tight sandstones in Songliao Basin, the P- and S- wave velocities of different cores in various directions were measured. The experimental results show that tight sandstones have the transverse isotropy, based on which the characterization method of elastic coefficients was established. Through combina- tion of core stress-strain experiments with acoustic experiments, dynamic and static modulus conversion model was built for target zone, and applied to the geostress logging evaluation of tight sandstone based on transverse isotropie model. The application results indicate that this model is consistent with the fracturing results, and able to better reflect the actual formation.