复杂孔隙结构致密砂岩含油饱和度梯形孔隙模型

A tight sandstone trapezoidal pore oil saturation model

针对复杂孔隙结构致密砂岩储集层中大量存在的"非Archie(阿尔奇)"现象,提出一种新的考虑孔隙结构的梯形孔隙含油饱和度模型,即将致密砂岩孔隙结构划分为截面积不变的直孔隙和截面积变化的梯形孔隙,将岩石总的电阻视为两部分孔隙电阻的并联,综合考虑孔隙结构和导电体积对岩石电性的影响。基于梯形孔隙重构,在岩电实验的约束下,研究了梯形孔隙模型参数表征方法,并揭示了迂曲度、直孔隙比例和梯形因子等模型参数的变化规律。结合梯形孔隙重构模拟方法得到模型参数的表征方法,将该模型应用于多口致密砂岩井测井评价,结果表明,与变参数Archie模型相比,梯形孔隙饱和度模型从孔隙长度和截面积均质程度等角度考虑孔隙结构对岩石电性的影响,因此利用该模型计算的含油饱和度更加符合油藏实际和岩石物理特征,更接近地层真实含油情况。

＂Non-Archie＂ phenomena are common in tight sandstone reservoirs with complicated pore structure, bringing challenges to the logging evaluation of tight sandstone. Based on the characteristics of tight sandstone pore structure, a new trapezoidal pore saturation model considering the effect of pore structure on rock conductivity is presented, in which the pore in tight sand is divided into straight pore with constant cross-sectional area and trapezoidal pore with variable cross-sectional area, and the total rock resistance is taken as the parallel resistance of these two parts to compressively consider the influence of pore structure and conductive volume on rock conductivity. The model parameters are studied by reconstructing the trapezoidal pore structure. Based on the trapezoidal pore reconstruction, characterization methods of model parameters were studied under the constraint of rock electrical properties test, and the variation was revealed of tortuosity, straight pore proportion and trapezoidal factors. The model was used in logging evaluation of tight sandstone of several wells, the results show the oil saturation obtained from the new model considering the effect of pore structure on electrical properties from the aspects of pore length and pore cross-section is in good accordance with the real regularity and petrophysical characteristics of the reservoir, and much closer to the formation oil-bearing conditions than that from the Arehie model.