致密砂岩气藏裂隙-孔隙型弹性岩石物理模板研究:以川西坳陷A区为例

相对于常规砂岩,致密砂岩在岩石物理性质、力学性质等方面具有明显差异,并呈现出很强的非均质性.岩石物理模型能将储层参数与地震特性信息联系起来,因此可以作为致密砂岩储层参数与地震特性信息转换的桥梁.常规的岩石物理模型通常只考虑单一因素(例如非均匀性,单一孔隙,单一尺度等),建立的岩石物理模板并不适用于致密砂岩.本文针对高饱和气、微裂隙发育、非均质性强的致密砂岩储层,利用Voigt-Reuss-Hill模型计算混合矿物的弹性模量,采用微分等效介质(DEM)模型描述含裂隙、孔隙岩石的骨架弹性模量,基于Biot-Rayleigh波动方程构建了岩石物理弹性模板,给出了致密砂岩储层弹性参数与物性的关系.基于测井数据和实验数据对岩石物理弹性模板进行校正,并将校正后的岩石物理弹性模板结合叠前地震资料应用于川西地区储层孔隙度与裂隙含量预测.结果显示,反演裂隙含量、孔隙度与储层试气报告、测井孔隙度基本吻合,表明该模板能够较合理地应用于致密砂岩储层孔隙度及裂隙含量解释中.

Study on fracture-pore elastic rock physics template of tight sandstone gas reservoirs:a case study of area A in West Sichuan depression

Compared with conventional sandstone reservoirs,tight sandstone has obviously different rock physics and mechanical properties,and exhibits strong heterogeneity.Rock physics model can link reservoir parameters with seismic characteristic information,which can be used as a bridge between reservoir parameters and seismic characteristic information of tight sandstone reservoirs.Conventional rock physics models are built based on the simplified assumptions(for instance,heterogeneity,single-porosity,singlescale,etc.).Hence the established rock physics template by such rock physics models is not suitable for complex tight sandstone reservoirs.For the tight sandstone reservoirs with high gassaturation,developed micro-fractures and heterogeneity,the Voigt-Reuss-Hill model is used to calculate the elastic modulus of mixed minerals.The Differential Effective Medium(DEM)model is used to describe the elastic modulus of the rock skeleton containing fractures and pores.Based on the Biot-Rayleigh equation,the rock physical elastic template is constructed.The template presents the relationship between elastic parameters and physical properties of tight sandstone reservoirs.The rock physics elastic template is corrected based on the well logging data and experimental data,and the corrected rock physics elastic template is applied to reservoir prediction in Western Sichuan basin.The results show that the predicted fracture content and porosity are consistent with the production reports and log curves,which indicates that the template can be reasonably applied to the interpretation of porosity and fracture content in tight sandstone reservoirs.