鄂尔多斯盆地杭锦旗地区下石盒子组致密砂岩储层孔隙结构及可动流体特征

Pore structure and movable fluid characteristics of tight sandstone reservoirs in the Lower Shihezi Formation in the Hangjinqi area,Ordos Basin

核磁共振(NMR)及CT扫描技术对致密砂岩储层评价正发挥越来越重要的作用。以杭锦旗地区下石盒子组盒1段致密砂岩储层为例,基于NMR及CT扫描系统探讨了致密砂岩中不同类型孔隙的响应特征及流体识别能力。结果表明,测试样品的孔隙度主要分布在1.7%~10%,气测渗透率主要分布在0.1×10^(-3)~1.4×10^(-3)μm^(2),T_(2)弛豫时间截止值主要分布在1~14 ms,平均值为6.11 ms,属于典型的低孔、低渗型致密砂岩储层。根据离心前饱和分量T_(2)弛豫时间曲线,盒1段储层孔隙类型为双峰型(左峰为主,右峰不明显),包括3个亚类:微孔-小孔型、小孔-中孔型、微孔-小孔-中孔型,所对应的T_(2)弛豫时间区间分别为0.1~10,1~100,0.1~100 ms。三维CT扫描结果显示,小孔-中孔型储层的物性特征最好,其次为微孔-小孔-中孔型储层,而微孔-小孔型储层的物性相对较差。T_(2)截止值与样品可动流体含量负相关。盒1段可动流体孔隙度与渗透率具有良好的正相关性,反映可动流体含量受储层渗透率与喉道显著影响。盒1段致密砂岩储层中可动水饱和度主要分布在4%~9%,平均值为5.8%。开发实践显示,盒1段原始可动水饱和度较低,具有较大开发潜力,从侧面证实了NMP和CT扫描技术结果的准确性。

[Objective]In recent years,new discoveries have been made in the He 1 Member of the Hangjinqi Gas Field.And the initial gas production of some wells by fracturing can reach 10×104 m 3/d,which shows that the He 1 Member has great exploration potential.However,due to the strong heterogeneity of the He 1 Member,the gas production mechanism of the He 1 Member is not clear at present,which restricts its efficient development.To accurately and quantitatively characterize the microscopic pore structure and movable fluid characteristics of tight gas sandstone reservoirs.[Methods]In this paper,taking the tight sandstone reservoir in the He 1 Member of the Shangshihezi Formation in the Hangjinqi Gas Field as an example,NMR and CT tests were used to study the response characteristics and fluid identification ability of different types of pores in tight sandstone.[Results]The research shows that the porosity of the test samples is mainly distributed in 1.7%-10%,and the gas permeability is mainly distributed in 0.1×10^(-3)-1.4×10^(-3)μm^(2),which belongs to the typical low-porosity and low-permeability porous tight sandstone reservoir.According to the T_(2)relaxation time curve of the saturation component before centrifugation,the pore type of the reservoir in the He 1 Member is bimodal(mainly the left peak,the right peak is not obvious),including 3 subtypes:micropore-small pore type,small pore-mesopore type,micropore-small pore-mesopore type.The T_(2)relaxation time intervals corresponding to the above three subtypes of pore types are 0.1-10 ms,1-100 ms,and 0.1-100 ms,respectively.The results of 3D CT scans show that the micropore-mesopore reservoir has the best physical properties,followed by the micropore-small pore-mesopore type,and the micropore-small pore type reservoirs have relatively poor physical properties.The T_(2)cut-off values of the tested samples were mainly distributed between 1 and 14 ms,with an average value of 6.11 ms.There is a certain negative correlation between the T_(2)cut-off value and the movable fluid percentage of the rock samples.The movable fluid porosity and permeability have a very good positive correlation,reflecting that the amount of movable fluid is significantly affected by the reservoir permeability and the number of throats.The movable water saturation in the tight sandstone reservoirs of He 1 Member in the study area is mainly distributed at 4%-9%,with an average value of 5.8%.[Conclusion]Overall,the original movable water saturation of the He 1 Member is low and has great development potential.