Lin T.,China University of Geosciences |
Lin T.,Key Laboratory of Shale Gas Exploration & Evaluation |
Zhang J.,China University of Geosciences |
Zhang J.,Key Laboratory of Shale Gas Exploration & Evaluation |
And 10 more authors.
Shiyou Xuebao/Acta Petrolei Sinica | Year: 2014
This study evaluates shale gas accumulation conditions and gas-bearing properties of the Lower Cambrian Niutitang Formaion in northwestern Hunan, China. An optimal parameter well of shale gas in the Niutitang Formaion, Changye 1, was selected and drilled for the first time in Hunan Province. Collectively, it revealed the presence of dark shale series in the Niutitang Formation up to 674.5 m (true thickness), i.e., the thickest black shale series encountered during single-well drilling in China up to now. Core sampling and experimental analysis regarding organic geochemistry, rock mineralogy and reservoir properties show that the black shale of Niutitang Formation features high organic carbon content (average TOC content, 3.9%), moderate organic maturity (equivalent Ro, 2.6%), high brittle mineral content (quartz content, 50.1%), low clay mineral content (average clay content, 32.4%), poor porosity (1.7%) and permeability (1.32×10-3mD), and well-developed meso-/micropores and faults, which provide good conditions for shale gas accumulation in Well Changye 1. The well on-site desorption and isothermal adsorption tests show that the black shale of Niutitang Formation has good gas-bearing properties, with gas content generally increasing with depth. In Well Changye 1, the depth interval most favorable for shale gas accumulation is 1100-1250 m, as indicated by the average TOC content up to 10.1% and the gas contents of 0.5-2.1 (well on-site desorption) and 3.7-6.4 m3/t (isothermal adsorption). The Niutitang Formation in northwestern Hunan, as represented by Well Changye 1, has good prospect for shale gas exploration. Considering its huge sedimentary thickness, the black shale of Niutitang Formation in the middle-lower part should be given priority for exploration.