西南石油大学学报(自然科学版)

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Research on Saturation Index n of Tight Sandstone Reservoir

Luo Shaocheng1, Cheng Zhigang1, Zhou Jinyu2, Xi Hui1, Wang Changsheng2   

  1. 1. Reservoirs Evaluation Center,China Petroleum Logging Co. Ltd.,Xi′ an,Shaanxi 710077,China
    2. Exploration and Development Institute of PetroChina Changqing Oilfield Company,Xi′ an,Shaanxi 710018,China
  • Online:2014-08-01 Published:2014-08-01

Abstract:

The traditional statistical analysis method of computing the saturation index n in Archie equation is of low precision, because tight sandstone reservoir has complex pore structure,poor connectivity and inhomogeneity of pore fluid distribution. For this kind of reservoir,the computed oil saturation is often somewhat low. Based on lab data of petrophysical-electric property,we find the relationship between the resistivity increscent I and water saturation S w is dispersed in double logarithmic coordinate system and there exists an obvious inflection point when S w= 90%,and the saturation index n is not fixed in this kind of reservoir. On the basis of previous research results,combined with NMR,this study analyzes the influence factors of saturation index. The pore structure of reservoir rock is the major influence factor of saturation index n. The more complex pore structure,the greater the saturation index n. According to the major influence factor,and by using the multivariate regression analysis method,we established statistical model of saturation index with NMR T2 spectrum. In this way,the calculation result is approximately the same with the real value of the saturation index n which makes sure that the Archie equation applies to oil saturation calculation of reservoir with high accuracy.

Key words: tight sandstone reservoir, saturation index, pore structure, porosity, NMR logging