致密砂岩气藏可动流体分布特征及其控制因素——以苏里格气田西区盒8段与山1段为例

Distribution characteristics and controlling factors of movable fluid in tight sandstone gas reservoir:a case study of the eighth member of Xiashihezi Formation and the first member of Shanxi Formation in western Sulige Gas Field

鄂尔多斯盆地致密砂岩气藏开发前景良好,但储层广泛发育的微纳米孔喉使得多孔喉介质空间内流体赋存、运移规律复杂,导致天然气开采难度较大。为明确储层可动流体分布特征及其控制因素,对苏里格气田西区主力产气层盒8段与山1段储层开展核磁共振、扫描电镜、物性测试及恒速压汞等实验研究。结果表明:①盒8段与山1段储层可动流体饱和度特征差异明显,前者(平均为48.75%)明显高于后者(平均为23.64%)。②盒8段可动流体分布特征受物性及孔喉结构控制明显,优势渗流通道的广泛发育及相对丰富的较大孔喉是储层较高可动流体饱和度的重要控制因素,复杂的孔喉配置关系导致山1段可动流体赋存特征影响因素复杂。③可动流体综合评价模型表明,强粒间孔-溶孔信号,高过渡半径及高过渡进汞饱和度均是较大可动流体饱和度的关键控制因素。该研究成果明确了不同段致密砂岩气藏可动流体控制因素,为致密砂岩气藏“甜点”预测提供了理论依据,对致密砂岩气藏开发具有指导作用。

The tight sandstone gas reservoir in Ordos Basin has great development potential. However,the existence of micro-nanopore structure increases the difficulty of fluid seepage and the development. The eighth member of Xiashihezi Formation(He 8)and the first member of Shanxi Formation(Shan 1)in the western of Sulige Gas Field were taken as an example to understand the distribution characteristics and controlling factors of movable fluid by using various experiments,including nuclear magnetic resonance(NMR),scanning electron microscopy( SEM),physical property tests and rate-controlled mercury intrusion(RCMI). The results show that:(1)The characteristics of the movable fluid distribution of He 8 and Shan 1 were different,and the average of the movable fluid saturation of the He 8 and Shan1 sandstones was 48.75% and 23.64%,respectively.(2)The distribution characteristics of movable fluids of He 8 sandstone were controlled by physical properties and porethroat structure,and abundant seepage pathways and pores with relatively large radius led to the high movable fluid saturation,while that of Shan 1 sandstone were hard to be found due to the complex pore-throat network.(3)According to the comprehensive evaluation model,strong signal of residual and dissolved pores derived from NMR,high transitional radius and mercury saturation were the key factors of high movable fluid saturations. The research results clarify the controlling factors of movable fluids in different sections of tight sandstone gas reservoirs,and could provide a theoretical basis for predicting“sweet point”of tight sandstone gas reservoirs and play a guiding role in gas reservoir development.