针对致密砂岩气储层复杂孔隙结构的岩石物理模型及其应用

针对致密砂岩气储层复杂的微观孔隙结构进行岩石物理建模，在模型中比较了单一孔隙纵横比、双孔隙模型两种表征孔隙结构的表征方式。岩石物理正演分析表明，两种孔隙结构模型均可解释致密砂岩复杂的速度-孔隙度关系。岩石物理反演结果表明，双孔隙模型对测井横波速度的预测精度更高，说明该模型更适用于表征研究区致密砂岩的孔隙结构，反演的软孔比例参数能够反映地层中孔隙结构的非均匀分布。应用双孔隙模型计算致密砂岩地层岩石骨架的弹性模量，与Krief及Pride等传统经验公式相比，该方法考虑了岩石骨架模量与矿物基质、孔隙度和孔隙结构等微观物性因素的关系，理论上更具有严谨性。对致密砂岩骨架模量计算结果的分析表明，少量微裂隙的存在即能够显著影响致密砂岩骨架的弹性性质，同时孔隙空间中的球形孔隙是致密气的主要赋存空间。并且，通过致密砂岩骨架弹性模量，进一步计算了可用于地层评价的Biot系数等岩石物理参数。致密砂岩骨架模量的预测结果可为Gassmann流体替换理论、BISQ孔隙弹性介质理论等岩石物理方法提供关键参数。

Petrophysical Model for Complex Pore Structure and Its Applications in Tight Sand Gas Reservoirs

We conducted rock physical modeling to investigate the effect of complex pore space on elastic properties of tight gas sands. Two ways for the characterization of pore spaces were compared in the rock physical model. The modeling results show that the complex velocity-porosity relationships from well log data can be interpreted by both the two models. The rock physical inversion using well log data shows that compared to the single pore aspect ratio model, the dual-porosity model gives better prediction in shear wave velocity. It reveals that the dual-porosity model may be a more realistic representation of tight sands, and the obtained parameter of the proportion of soft pores can reflect heterogeneity of pore spaces. The proposed rock physical model is used to evaluate elastic modulus of the tight sand dry frame using logging data. Compared with the conventional empirical formulas such as Krief or Pride, this method considers mineralogy, porosity and complex microstructural pore structures,so it is more rigorous to determine the elastic properties of dry frame. The analysis on the obtained results indicates that a small amount of micro-cracks may play an important role in determining elastic behaviors of dry frame of tight sands, and round pores provide the main storage space for gas. The obtained dry frame modulus can be used to calculate many rock physical parameters for formation evaluation such as the Biot coefficient, and provide key parameters for the Gassmann fluids substitution theory and BISQ theory.