Multi-point resistivity measurement system for full-diameter long cores during fluid displacement.

Abstract

Water injection is often used to improve oil and gas recovery in the late stage of oil and gas reservoir development. Studies show that this process leads to complex changes in reservoir resistivity and affects the evaluation of remaining oil and gas saturation in the reservoir. In this study, a multi-point resistivity measurement experimental system suitable for full-diameter rock samples during fluid displacement was designed to simulate and explore the distribution and variation of resistivity in the reservoir flooding process. In this regard, two columnar electrodes were installed on the end face of the core sample to serve as fluid injection and outflow channels. Moreover, five groups of nail-shaped electrodes arranged at equal intervals were embedded on the rubber sleeve of the core holder. The electrical bridge metering combined with seven electrodes was used to measure the resistivity and variation of six parts of the core sample during fluid displacement. A confining pressure was applied to the core sample to simulate the underground high-pressure environment and force the nail-shaped electrodes to cling to the sample to improve the accuracy of resistivity measurement. The simulated water flooding experiment was carried out with a sandstone sample from Tarim Oilfield in western China, and the distribution and variation of the sample's resistivity were recorded. The experimental results conform to the laws of rock physics and confirm the reliability of the experimental system. The experimental system provides a guideline for determining the resistivity variation and evaluating the remaining oil and gas saturation of water-flooded reservoirs.