Abstract：The Oilfield LF13-2 is located in the Hui-lu lower uplift of Pearl River Mouth Basin. In this oilfield, the Enping and Zhuhal formations of Pleo-gene at the well LF13-2-1 was interpreted as oil-water bearing layers using the conventional well logging data. However, the sidewall core data indicate that these formations are oil-bearing reservoir. It is challenging to determine whether these formations are oil-water bearing or oil bearing with low resistivity due to the sparsity of the wells and the lack of the necessary test on the core data, which makes it difficuit to accurately discriminate the reservoir type and evaluate the reservoir in the oilfield. In this paper, the test on the core samples from the zones oi interest in this oilfield and adjacent one are sorted and analyzed as well as the dia-genetic geology. Afterwards, using the histogram and scatter plot of the thorium and kalium from the gamma ray spectrometry logs, the clay mineral type with high adsorbing water, mass fraction and the low-resistivity mechanism caused by the conductive water-film net of the clay mineral are studied. Based on our study, the following new conclusion has been drawn on the formations at well LF13-2-1：the zone in depth from 2879. 5 meters to 2885 meters that was considered as oil-water formations is actually the oil layers with rich bound water and low resistivity. This conclusion has been indirectly verified by the scanning electron microscope and X-ray data of the core samples from the east of Huizhou depression in the adjacent oilfield.
