Print this pageAnalysis on Geophysical Responses Characteristics of High Quality Shale in Southeast of Chongqing
Yu Zhu1,2, Jun Cheng1,2, Zhenguo Zhou2, Chaogang Chen1,2, Heng Yu2, Kexiong Song1,2, Ting Wang1,2, Yonghua Zheng1,2, and Weizhi Fan1,2
1Chongqing Institute of Geology and Mineral Resources, Chongqing, China
2Schlumberger Zhongyu Shale Gas Technical Services (Chongqing) Co., Ltd., Chongqing, China
In China, several suits of Paleozoic marine shales developed in Yangzi platform. Most part of Chongqing is in the northwest of the platform, mainly locating in prolific shale gas accumulating zone in the southeast and east of Sichuan Basin and well developed Upper Ordovician Wufeng-Lower Silurian Longmaxi shales. In the exploration and development of shale gas, the identification and evaluation of high quality shale will provide an important guidance for sweet spots and final well completion, so it is highly significant to develop a technique to effectively distinguish high quality shale reservoirs from non-reservoirs. Based on AI&GR crossplots, we can identify shale reservoirs, but can’t identify correctly high quality shale reservoirs. So it is very important to optimize the geophysical methods of predicting high quality shales. The high quality shale reservoir is normally of features of high gamma ray, low sonic velocity, low acoustic impedance and high resistivity, etc., by which the reservoir can be identified. But using the single geophysical parameters, we can not correctly identify the high quality shales. Using the log data and seismic inversion technique for inversion processing, we obtained the geophysical parameters: AI, Vp/Vs, RHOB. And then according to the correlation of AI, GR, Vp/Vs and RHOB, we can map out several crossplots based on the different combinations of elastic parameters for the whole intervals and the target intervals. Based on these crossplots, sandy shale, tight shale, high quality shale and carbonate show good separation. Through using the crossplots analysis color coded by Vcl, PHIE and Sw, it is found that the high quality shales around the target zone is of geophysical characteristics of low density, low Vp/Vs and low P-wave impedance. Meanwhile through the fitting of log data, it is shown that the density and TOC of the shale are fit for the common formula called Schmoker. Therefore, conclusion shows that correctly using the geophysical characteristics, it not only plays an important role for shale gas exploration and development, but also has a great realistic significance.
AAPG Datapages/Search and Discovery Article #90180©AAPG/SEPM/China University of Petroleum/PetroChina-RIPED Joint Research Conference, Beijing, China, September 23-28, 2013