Title: Investigations of water saturation and fractal characteristics in tight sandstone gas reservoirs using centrifugation and NMR experiments

Authors: Aifen Li; Weibing Tian; Xiaoxia Ren; Shuaishi Fu; Dongdi Cui; Qi Fang; Min Ma; Yapcheptoyek Josephine

Addresses: School of Petroleum Engineering, China University of Petroleum – East China, Qingdao 266555, China ' State Key Laboratory of Petroleum Resources and Prospecting, China University of Petroleum – Beijing, Beijing 102249, China ' School of Science, Qingdao University of Technology, Qingdao 266525, China ' School of Petroleum Engineering, China University of Petroleum – East China, Qingdao 266555, China ' School of Petroleum Engineering, China University of Petroleum – East China, Qingdao 266555, China ' School of Petroleum Engineering, China University of Petroleum – East China, Qingdao 266555, China ' School of Petroleum Engineering, China University of Petroleum – East China, Qingdao 266555, China ' School of Petroleum Engineering, China University of Petroleum – East China, Qingdao 266555, China

Abstract: In this paper, the petrophysical properties were analysed by X-ray diffraction (XRD), scanning electron microscope (SEM) and nuclear magnetic resonance (NMR) experiments and the centrifugation and NMR experiments were conducted to investigate the water saturation and fractal characteristic in tight sandstone gas reservoirs. Experimental results showed that connate water saturation increases with decrease in permeability. Average connate water saturation, connate water saturation at the paraxial end and NMR connate water saturation are 58.4%~80.6%, 37.3%~60.7% and 64.6%~84.6%, respectively. The optimum centrifugal force is 1.70 MPa~2.40 MPa. A formula for calculating average water saturation was derived for different permeability cores. In addition, three models for calculating connate water saturation were presented. Finally, the fractal characteristics of pore throat using the improved NMR method were analysed. Results showed that the structure and surface of pore throat are irregular and heterogeneous, and the distribution of connate water becomes more complex and irregular after the centrifugation, compared with the saturated state. [Received: February 1, 2019; Accepted: January 20, 2020]

Keywords: water saturation; connate water; tight sandstone gas; nuclear magnetic resonance; NMR; centrifugation; pore throat; fractal.

DOI: 10.1504/IJOGCT.2021.114069

International Journal of Oil, Gas and Coal Technology, 2021 Vol.26 No.4, pp.405 - 421

Received: 01 Feb 2019
Accepted: 20 Jan 2020
Published online: 08 Apr 2021 *

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