Detection of low resistivity reservoirs using GR spectrometry logs: a case study
Xia Zhu1, Ling Yu1, Guo Jianming1, Zhang Sheng1, Xu Hai1, Zhang Tingting1, Zhao Shiquan1, Bie Jing1, and Li Kai1
The oilfield a – 13 - 2 is located in the C - low uplift of X Basin in south China. In this oilfield the Enping and Zhuhai Formations of Paleogene at the well L13 – 2 - 1 were 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 make accurately discriminate the reservoir type, evaluate the reservoir and enhance the oil recovery in the oilfield. In this paper, the core samples from the zones of interest in this oilfield and the adjacent one（the oilfield b-13-1and B-depression）were analyzed, and the diagenetic geology are studied. Afterwards, using the cross - plot and histogram of the TH and K 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 were studied. Based on our study, the following new conclusions have been drawn on the water-oil bearing formations at well L13 – 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.
AAPG Search and Discovery Article #90188 ©GEO-2014, 11th Middle East Geosciences Conference and Exhibition, 10-12 March 2014, Manama, Bahrain