Log interpretation and evaluation of tight sandstone reservoir in Chang 8 Member of Longdong West area, Ordos Basin, China, are facing great challenges due to the co-development of normal oil pay and resistivity low-contrast oil pay. To better guide the exploration and development of oil resources in this area, the reservoir characteristics and control mechanism of resistivity low-contrast oil pay were studied. Firstly, the reservoirs were divided into resistivity low-contrast oil pay (RLP) and normal oil pay (NP) based on the relative value of the apparent resistivity increase rate. Then, the difference of reservoir characteristics between RLP and NP is analyzed by comparing a series of experimental data and real logging data in those two reservoir types. Finally, the control mechanism of RLP was studied from reservoir micro-factors and regional macro-factors, respectively. It is found that the chlorite and illite are the most abundant clay minerals in RLP and NP, respectively. Compared with NP reservoir, the average porosity of RLP is better, but the pore space is mainly composed of micropores, which lead to smaller average pore throat radius and poor pore structure. The high irreducible water saturation and high formation water salinity reduced the reservoir resistivity from micro-aspect. Besides, the difference of hydrocarbon expulsion capacity of source rock and the regional difference of formation water salinity controlled the distribution of RLP and NP. Comprehensive consideration of the reservoir micro-factors and regional macro-factors is important to carry out effective logging interpretation and evaluation.

鄂尔多斯盆地龙东西长8段致密砂岩储层解释评价正面临着正常油层和电阻率低对比度油层共同开发的巨大挑战。为更好地指导该区石油资源勘探开发，研究了电阻率低对比度油层的储层特征及控制机制。首先根据视电阻率增加率的相对值将储层分为电阻率低对比度油层（RLP）和正常油层（NP）。然后，通过比较这两种油藏类型的一系列实验数据和实际测井数据，分析了RLP和NP油藏特征的差异。最后，分别从储层微观因素和区域宏观因素研究了RLP的控制机制。发现绿泥石和伊利石分别是RLP和NP中含量最多的粘土矿物。与NP储层相比，RLP的平均孔隙度较好，但孔隙空间以微孔为主，导致平均孔喉半径较小，孔隙结构较差。高束缚水饱和度和高地层水矿化度从微观方面降低了储层电阻率。此外，烃源岩排烃能力的差异和地层水矿化度的区域差异控制了RLP和NP的分布。