致密砂岩储层孔隙度预测方法研究

Novel porosity prediction method for tight sandstone reservoirs:a case study of member of He8,Ordos Basin,Northern China

鄂尔多斯盆地临兴地区盒8段致密气储量大,然而现阶段大部分井在该层段测试产量并不乐观.近期通过测试三口井获得高产,压后产量超过10000 m^(3)/d,揭示了盒8段具有可开发的潜力.根据已钻井分析,孔隙度是影响产能的关键因素,寻找高孔储层对于提高盒8段产能意义重大.岩石物理分析表明,本区纵横波速度比能够区分砂泥岩,基于此,本次研究通过叠前反演预测临兴地区A区块盒8段砂岩分布.在此基础上,利用致密砂岩储层分类型孔隙度预测技术,针对低阻抗区,采用分斜率线性拟合预测厚储层孔隙度;针对高阻抗区,采用贝叶斯判别分析和协模拟预测薄储层孔隙度;将厚储层孔隙度和薄储层孔隙度的预测结果进行融合,得到储层整体的孔隙度预测结果.结果表明,该方法能够有效预测I类厚储层和II类厚储层的孔隙度分布,兼顾刻画I类和II类薄储层的孔隙度分布.通过分类型预测的方式,使储层孔隙度的刻画更加准确,为致密砂岩储层高效开发提供有效成果.

The tight gas reserves of He8 member in Linxing area of Ordos Basin are large.However,the testing production of most wells in this member is low at the present stage.Recently,three wells have been tested,and the production yield after fracturing is more than 10000 m^(3)/day,which reveals that the He8 member is of potential for development.According to the analysis of drilled wells,porosity is the key factor affecting productivity.Therefore,searching for high porosity reservoirs is of great significance for improving productivity of He8 Member.The rock physics analysis shows that Vp/Vs ratio in this area can distinguish sandstone from mudstone.According to the rock physics analysis result,this study predicts the distribution of sandstone in He8 member of Block A in Linxing area through pre-stack inversion.On the basis of pre-stack inversion result,the porosity prediction technology of tight sandstone reservoir is used to predict the porosity of thick reservoir by linear fitting for different reservoirs seperately for data in low P-impedance area.For the high impedance area,Bayesian discriminant analysis and co-simulation are used to predict the porosity of thin reservoirs.The porosity prediction results of thick reservoir and thin reservoir are combined to obtain the overall porosity prediction results of the reservoir.The results show that this method can effectively predict the porosity distribution of ClassⅠthick reservoirs and ClassⅡthick reservoirs,and simultaneously depict the porosity distribution of ClassⅠand ClassⅡthin reservoirs.By means of using different prediction method for different types of reservoirs,the description of reservoir porosity is more accurate,providing effective results for efficient development of tight sandstone reservoirs.