Shale Gas Basic Characteristics of the Lower Cambrian Niutitang Formation for Jinye 1 Well in the Upper Yangtze Platform

Chao Luo¹, Shugen Liu^1,3, Wei Sun², Bo Ran^2,3, Di Yang¹, Jiawen Qiu¹, and Zhiqiang Bai^1
1College of Energy Resources, Chengdu University of Technology, Chengdu, Sichuan, China
²School of Geosciences, Chengdu University of Technology, Chengdu, Sichuan, China
³State key laboratory of Oil and Gas reservoir geology and exploitation (CDUT), Chengdu, Sichuan, China

It is characterized with a sequence of black shale with Early Cambrian age in Jinye l well located at the north margin of Qianzhong uplift that southeastern of Yangtze platform. The black shale is 119.7 m thick, In the lower part it is composed by mudstone deposited in deep-water while in the upper part it is calcareous mudstone with silty laminations or streaks deposited in shallow-water shelf environment. The geochemical elements value of the black shale are: V/Cr, V/Sc, Ni/Co, V/(Ni + V) ,U/Th and δU are 6.09, 147.62, 15.36, 0.81, 7.00 and 1.66, respectively. They indicate that the black shale was deposited in an anoxic environment. The higher values of U/Th (>1) together with negative anomalies in Ce, positive anomalies in Eu and Y, suggest hydrothermal input on sedimentation. The black shale is characterized by occurrence of type-I kerogen. The sapropelinite accounts for 87.8%. The TOC values range from 0.10%to11.83%, with average value of 2.79% (from 166 samples). The thickness of black shale with TOC>2% is 62.62m, and have the Ro values ranging from0.79% to 5.28%, with an average value of 3.11% (from 18 samples.) The mineral composition of black shale is predominantly clay minerals (e.g. illite, chlorite and little smectite), quartz, feldspar, barite, and gypsum. Quartz content is relatively high with an average of 34.55%, and it is positive correlation with TOC values as well as decreased upwards in the section. Clay content is also relatively high, however, it is increased upwards with an average of 47.18% but was negatively correlated with TOC values which as opposed to the quartz’s. There is a few carbonate minerals at the upper part of the well. The porosity of black shale and siliceous rocks in the lower section ranges from 0.52% to 6.92% with an average of 2.70%, with density from0.56g/cm³ to 3.72g/cm³, in average of 2.12 g/cm³, respectively. Four types of pores are present in the shale, such as interparticle pores, intraparticle pores, fracture pores and organic-matter pores. The first two are more common in minerals. In general, there is increasing pore size but decreasing porosity upwards in the Jinye 1 well. The adsorption isotherm experiments suggest that adsorbed gas in black shale is 1.80m³/t~ 3.10m³/t with an average of 2.45m³/t, which indicate a strong adsorption capacity. The adsorption ability of black shale and TOC show positive correlation, TOC content is also positively correlated with nanopore distribution frequency. The study shows that , TOC content, quartz content, and nanopore distribution play leading roles in influencing the adsorption capacity of gas in black shale of the Jinye 1 well.

AAPG Datapages/Search and Discovery Article #90180©AAPG/SEPM/China University of Petroleum/PetroChina-RIPED Joint Research Conference, Beijing, China, September 23-28, 2013