Experiment and analysis for the influence of saturating method on saturation exponent n

Abstract

Reservoir evaluation of tight sandstone involves the determination of reservoir properties from samples and logs. In the calculation of water saturation, Archie formula is an important fundamental and connection between log evaluation and petrophysics. Highly accurate parameters of Archie formula are the key to the log evaluation of gas-bearing tight sandstone. At present, there are two methods of the rock-electric experiment to measure parameters of Archie formula: water increment (imbibition) and water decrement (centrifugation). In this paper the experimental measurement of a group of tight sandstone has been designed and the results of the two experimental ways are quite different. In the experiment, the distribution of brine is a main factor affecting the electrical properties of rocks. Fluid distribution model during imbibition and drainage is used to explain the results of rock electrical experiments, and the results are verified by nuclear magnetic resonance measurement. In the end, the Pickett chart method of actual data is used to compute the ranges of the saturation exponent n approximately, then to verify the correctness of the theoretical analysis. The results demonstrate that the centrifugal method is more applicable. In the log evaluation of tight sandstone, the appropriate choice of the method which can get accurate rock electrical parameters is important. Reliable evaluation will provide support for future development of gas-bearing tight sandstone.