The Cambrian-silurian Black Shale Reservoir Characteristics And Reservoir-forming Condition In Xiuwu Basin, Jiangxi Province

Xiuwu basin is located in the juncture of middle-lower Yangtze. The previous research showed that the organic-rich shales developped well with abundant shale gas resources in this basin. But the previous study was only about regional geological survey or metal and cement resources. While it was relatively lacking of systematical research about oil-gas geology and reservoir forming of shale gas. Based on the scientific achievements, focussing on the domestic and international research hottopic, according to modern sedimentary geology, reservoir geology and petroleum geology, combined with field investigation and drilling core observation analysis data, this paper has carried out systematically and comprehensive research about the black shale reservoir characteristics and reservoir forming condition of Cambrian – Silurian in Xiuwu Basin. And the following results had been produced in this article.The petrological characteristics of the black shale of Cambrian – Silurian in Xiuwu Basin had been studied. The main lithology composition of Lower Cambrian Wangyinpu –Guanyintang Formation includes grey-black carbonaceous shale, siliceous shale, marl, stone coal and phosphorite nodule. The main lithology omposition of Upper Ordovician Xinkailin – Lower Silurian Lishuwo Formation includes black carbonaceous shale, siliceous shale and silty shale. The aboved mentioned black shales were mainly developed in continental shelf which could be divided into deep shelf and shallow shelf facies according to the water depth and lithologic association.The black shale reservoir characteristics had been deeply studied. Results showed that the black shales had a high content of brittle minerals, mainly including quartz, feldspar, pyrite(nodule) and so on. The main typies of reservoir pores including intragranular pore, intergranular pore, organic matter hole were recognized with the range from 0.5um to 10 um. Physical statistics showed that porosity mainly distributed in the 2-4%(shale) and 10-15%(containing sandy) interval, with average value 5.16%; permeability mainly distributed in the(0.001-0.01)×10-3μm2, with average value 0.07×10-3μm2. Relative high values of permeability occurred in the area of fracture well developed. And the porosity showed a low correlation with permeability.The black shale of Cambrian and Silurian in Xiuwu basin and the domestic and foreign typical shale stratum had been compared comprehensively. The similar performance included the sedimentary environment, lithology, brittle mineral content, organic matter abundance and so on. While the performance of differences included burial depth, shale maturity of organic matter, shale thickness and total resources quantity. And then through the research of tectonic and sedimentary conditions, gas source condition, reservoir condition, accumulation conditions, temperature and pressure conditions, preservation conditions and reservoir forming conditions, self-generating and self storage reservoir model of the shale gas had been established for the first time, with the characteristics of “widely covered type of hydrocarbon generation and expulsion, crack / micro fissure conduction, large area to collect”.In view of comprehensive analysis of differences of shale gas geological characteristics at home and abroad, the main controlling factors of reservoir forming of Xiuwu basin had been produced and the shale gas assessment parameters of research area had also been established. According to the shale gas evaluation criterion, three favorable targets of Xiuwu basin were evaluated as a whole, with estimated quantity of resource 1014.66 × 108m3.