energies Article A New Insight into Shale-Gas Accumulation Conditions and Favorable Areas of the Xinkailing Formation in the Wuning Area, North-West Jiangxi, China Shangru Li 1,2, Li Zeng 1,2, Zhongpeng Wang 1,2,*, Jinchuan Zhang 3 and Dong Ma 4,* 1 Jiangxi Geo-Engineering (Group) Corporation, Nanchang 330001, China; [email protected] (S.L.); [email protected] (L.Z.) 2 GanZhongNan Institute of Geology and Mineral Exploration, Nanchang 330001, China 3 School of Energy Resources, China University of Geosciences, Beijing 100089, China; [email protected] 4 School of Petroleum Engineering, Yangtze Univeristy, Wuhan 430100, China * Correspondence: [email protected] (Z.W.); [email protected] (D.M.); Tel.: +86-157-2766-7223 (Z.W.) Received: 27 November 2017; Accepted: 19 December 2017; Published: 21 December 2017 Abstract: In north-west Jiangxi, China, most shale-gas exploration has been focused on the Lower Cambrian Hetang and Guanyintang formations, whereas the Upper Ordovician Xinkailing formation shale has been ignored for years due to heavy weathering. This study systematically analyzed gas source conditions, reservoir conditions and gas-bearing ability in order to reveal the shale-gas accumulation conditions of the Xinkailing formation. The results show that the Xinkailing formation is characterized by thick deposition of black shale (10–80 m), high organic content (with total organic carbon between 1.18% and 3.11%, on average greater than 2%), relatively moderate thermal evolution (with vitrinite reflectance between 2.83% and 3.21%), high brittle-mineral content (greater than 40%), abundant nanopores and micro-fractures, very good adsorption ability (adsorption content between 2.12 m3/t and 3.47 m3/t, on average about 2.50 m3/t), and strong sealing ability in the underlying and overlying layers, all of which favor the generation and accumulation of shale gas. The Wuning-Lixi and Jinkou-Zhelin areas of the Xinkailing formation were selected as the most realistic and favorable targets for shale-gas exploration and exploitation. In conclusion, the Wuning area has great potential and can provide a breakthrough in shale gas with further investigation. Keywords: north-west Jiangxi; Wuning area; Xinkailing formation shale; gas-generating conditions; reservoir conditions; gas-bearing potential; favorable area 1. Introduction Shale-gas exploration and development have seen enormous commercial success in the United States over the past 10 years [1–3], altering its status from an oil and gas importing country to an exporting one. Inspired by that, shale gas research has been conducted throughout marine, transitional and continental strata in China recently [4–7]. Significant progress has been made in shale gas exploration and exploitation in the Upper Yangtze Platform, most notably in the Upper Ordovician Wufeng formation–Lower Silurian Longmaxi formation [8,9]. With the growing demand for national energy production, several studies have been carried out concerning Lower Paleozoic black shale in the middle-upper Yangtze area [10–13]. Most of these studies have focused on the two high-quality formations [14–18]: the Upper Ordovician Wufeng formation/Lower Silurian Longmaxi formation (collectively known as the Longmaxi formation) and the Lower Cambrian Niutitang formation (including the Shuijingtuo formation or Qiongzhusi formation, collectively known as the Niutitang formation). It is worth noting that both formations Energies 2018, 11, 12; doi:10.3390/en11010012 www.mdpi.com/journal/energies Energies 2018, 11, 12 2 of 17 Energies 2018, 11, 12 2 of 17 formation, collectively known as the Niutitang formation). It is worth noting that both formations are are made up of high-quality source rock deposits. Due to the influence of its sedimentary age and made up of high-quality source rock deposits. Due to the influence of its sedimentary age and sub-surface depth, the Longmaxi formation was better developed than the Niutitang formation [19], sub-surface depth, the Longmaxi formation was better developed than the Niutitang formation [19], and commercial gas production has been achieved in the areas of Fuling, Weiyuan-Changning, and commercial gas production has been achieved in the areas of Fuling, Weiyuan-Changning, Zhaotong, and Pengshui [20]. The parameters, including thickness, TOC (total organic carbon), Zhaotong, and Pengshui [20]. The parameters, including thickness, TOC (total organic carbon), Ro R (referring to vitrinite reflectance), reservoir conditions and so on, have been testified to be the key (referringo to vitrinite reflectance), reservoir conditions and so on, have been testified to be the key factors of accumulation conditions and favorable areas of shale gas [17]. factors of accumulation conditions and favorable areas of shale gas [17]. Due to their similar tectonic dynamics [21], the lower Yangtze and middle-upper Yangtze areas also Due to their similar tectonic dynamics [21], the lower Yangtze and middle-upper Yangtze areas share similar sedimentary-tectonic evolution and shale-layer development. Previous studies concerning also share similar sedimentary-tectonic evolution and shale-layer development. Previous studies shale formation with rich organic matter in north-west Jiangxi focused on the shale development concerning shale formation with rich organic matter in north-west Jiangxi focused on the shale developmentcharacteristics characteristics of the Lower of Cambrian the Lower Hetang Cambrian formation Hetang and formation the Guanyintang and the formation Guanyintang [22,23 ]. formationHowever, [22,23]. there areHowever, few published there are accounts few publish thated describe accounts the that hydrocarbon describe the source-rockhydrocarbon potential source- of rockthe potential Upper Ordovician of the Upper Xinkailing Ordovician formation. Xinkailing Geochemical formation. Geochemical analysis data analysis of outcrop data samplesof outcrop from samplessection PM1from hassection shown PM1 that has the shown Xinkailing that the shale Xinkai is severelyling shale weathered is severely and weathered not suitable and fornot exploitation suitable for(as exploitation shown in Figure (as shown1A). Accordingly, in Figure 1A). it hasAccordingly, been ignored it has for been years. ignored for years. However,However, the the core core samples, samples, which which were were acquired acquired from from a water a water well well beside beside the the section section PM1, PM1, revealedrevealed excellent excellent shaleshale developmentdevelopment characteristics characteristics (as (as shown shown in Figurein Figure1B)and 1B)an and enormous an enormous potential potentialfor shale for gas shale resources gas resources in the Xinkailing in the Xinkailing formation. formation. Jiangxi Province Jiangxi Province is characterized is characterized by a continuous by a continuousdeficit in oil deficit and gas. in oil If and a breakthrough gas. If a breakthrough can be made can in be the made extraction in the ofextraction Xinkailing of shale,Xinkailing it may shale, change itthe may energy change structure the energy of the structure province. of the province. Figure 1. (A) The characteristics of an outcrop sample of Xinkailing-formation shale; (B) the characteristics Figure 1. (A) The characteristics of an outcrop sample of Xinkailing-formation shale; (B) the of a core sample of Xinkailing-formation shale. (The location of outcrop sample and core sample can characteristics of a core sample of Xinkailing-formation shale. (The location of outcrop sample and core be seen in Figure 2). sample can be seen in Figure2). ForFor this this study, study, the the thickness thickness of of Xinkailing Xinkailing shale shale in inthe the middle middle of ofthe the Xiuwu Xiuwu Basin Basin was was investigated investigated usingusing a ameasured measured profile. profile. Then, Then, features features such such as asorganic organic chemistry, chemistry, mineral mineral composition, composition, reservoir reservoir properties,properties, and and pore distributiondistribution and and structure structure were were analyzed analyzed using using laboratory laboratory testing testing of shale of shale samples samplesfrom the from water the well. water The well. primary The primary objectives objectives of this paper of this are paper to: (1) are characterize to: (1) characterize the hydrocarbon the hydrocarbon generation conditions of the Xinkailing shale; (2) determine whether the reservoir is generation conditions of the Xinkailing shale; (2) determine whether the reservoir is suitable for shale gas; suitable for shale gas; and (3) discuss the gas-bearing potential and favorable distribution areas and (3) discuss the gas-bearing potential and favorable distribution areas within the Xinkailing formation. within the Xinkailing formation. Energies 20182018,, 1111,, 12 12 3 of 17 2. Geological Setting 2. Geological Setting 2.1. Overview 2.1. Overview The study area is situated in the eastern Xiuwu Basin, Lower Yangtze Plate. The administrative regionsThe are study mainly area comprised is situated of in Wuning the eastern county, Xiuwu in the Basin, north-west Lower Yangtzearea of Jiangxi Plate. province The administrative (as shown inregions Figure are 2a). mainly The comprisedformation ofand Wuning evolution county, of inthe the area north-west can be broken area of Jiangxidown into province four (asmain shown stages in (asFigure shown2a). Thein Figure formation 2b): and (1) evolutionthe Mesoproterozoic-Silurian of the area can be broken (Pt2-S)